Chapter 3 Water Based Mud

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G R O U P Agip KCO

WELL AREA OPERATIONSDRILLING SUPERVISOR TRAINING COURSE

WATER BASED MUDS

Cod.: RPWA2021A Date: 01/03/2005 Rev: 00 Page: 132



Agip KCO Code RPWA2021ADate: 01/03/2005

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Well Area Operations

INDEX

1.0 INTRODUCTION 8

2.0 NON INHIBITING FLUIDS 12

2.1 Service waters (clean waters) 12 2.2 Muds with formation shale (native muds) 13 2.3 Bentonite-water (spud mud) 16

2.4 Lignite/lignosulfonate mud 18

3.0 INTRODUCTION 25

4.0 FORMATION DAMAGE CONTROL 26

5.0 DRILLABILITY 26

6.0 COMPATIBILITY WITH COMPLETION PROCEDURES AND EQUIPMENT 27

7.0 FORMATION DAMAGE MECHANISMS 27

7.1 Plugging by solids 28 7.2 Hydration of formation shales (migration) 28 7.3 Emulsion blocking 29 7.4 Scaling 29

8.0 TYPES AND APPLICATIONS OF DRILL IN FLUIDS 30

8.1 Clear fluids without viscous cushions 30 8.2 Fluids with HEC 30 8.3 Calibrated salt systems (salt size) 30 8.4 Oil base systems 31 8.5 Synthetic base systems 32

9.0 INTRODUCTION 33

10.0 FLUID DENSITY (MUD WEIGHT) 33

10.1 Instruments 33 10.2 Mud balance 33

10.2.1 Description 33




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10.2.2 Calibration 34

10.2.3 Procedure 34

11.0 VISCOSITY 36

11.1 Instruments 36 11.2 Marsh funnel viscometer 36

11.2.1 Description 36 11.2.2 Calibration 36 11.2.3 Procedure 37

11.3 Rotational viscometer 37 11.3.1 Description 37

11.3.2

Specifications: Direct reading viscometers 38

11.3.3 Procedure to determine apparent viscosity, plastic viscosity and the yield point 39

11.3.4 Procedure to determine gel strengths (at 10” and 10’) 40 11.3.5 Taking care of the viscometer 41

12.0 FILTRATION 42

12.1 Description 42 12.2 Instruments 42 12.3 API fluid loss 43

12.3.1 Procedure 43

12.4 High temperature high pressure (HTHP) filtration - MB style (API #II) HTHP filterpress 44 12.4.3 Description 44 12.4.4 Procedure 45 12.4.5 API # I HTHP filter press 47 12.4.6 Description 47 12.4.7 Filter cake compressibility 50

13.0 SAND CONTENT 51

13.1 Instruments 51 13.2 Sand content testing kit 51

13.2.1 Description 51 13.2.2 Procedure 51

14.0 SOLID AND LIQUID CONTENT 52

14.1 Instruments 52 14.2 Description of the distiller 53

14.2.1 Procedure 53 14.2.2 Percentage from analysing the volume of solids, weight method (calculating the

difference in weight using a conventional distiller). 54 14.2.3 Equipment 54

14.2.4

Procedure 55




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14.3 Methylene blue capacity test 56 14.3.1 Equipment 56 14.3.2 Reagents 56 14.3.3 Procedure 57

14.4 Methylene blue capacity of clay 58 14.4.1 Methylene blue capacity (bentonite equivalent) 58 14.4.2 Cation exchange capacity of clays 58 14.4.3 Procedure 58

15.0 CONCENTRATION OF HYDROGEN IONS (PH) 59

15.1 Scope 59 15.2

Litmus (or pH) papers 59

15.2.1 Description 59 15.2.2 Procedure 59

15.3 pH meter 60 15.3.1 Description 60 15.3.2 Equipment 60 15.3.3 Procedure 60 15.3.4 Cleaning 6115.3.5 Principle of equivalent solutions 62

16.0 CHEMICAL ANALYSIS OF WATER IN MUDS 63

16.1 Alkalinity (Pf , Mf , Pm) and lime content 63 16.1.1 Equipment 63 16.1.2 Procedure to test filtrate alkalinity (Pf and Mf) 64 16.1.3 Procedure to test mud alkalinity (Pm) 65 16.1.4 Procedure to test calcium content (excess lime) 65 16.1.5 Filtrate alkalinity: P1 and P2 66 16.1.6 Equipment 66 16.1.7 Procedure 67

16.2 GARRETT GAS TRAIN (GGT) test for carbonates 68 16.2.1 Scope 68 16.2.2 Equipment 68 16.2.3 Procedure 69 16.2.4 Selecting the Dräger tube 72

16.3 Chlorides (Cl –) 73 16.3.1 Scope 73 16.3.2 Equipment 73 16.3.3 Light coloured filtrates 73 16.3.4 Procedure 73 16.3.5 Dark coloured filtrates 75 16.3.6 Procedure 75

16.4 Calcium – qualitative testing 77 16.4.1 Scope 77 16.4.2 Equipment 78




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16.4.3 Procedure 78

16.5 Total hardness 78 16.5.1 Calcium plus magnesium – Quantitative testing 79 16.5.2 Equipment 79 16.5.3 Procedure (total hardness) 80 16.5.4 Calcium and magnesium separately 82

16.6 Hardness in dark filtrates 83 16.6.1 Total hardness in dark filtrates – Quantitative testing 83 16.6.2 Scope 83 16.6.3 Equipment 84 16.6.4 Calcium and magnesium, separately 86

16.7 Sulphate 87 16.7.1 Qualitative testing 87 16.7.2 Scope 87 16.7.3 Equipment 87 16.7.4 Procedure 87 16.7.5 Availability of calcium sulphate 88 16.7.6 Scope 88 16.7.7 Equipment 88 16.7.8 Procedure 88

16.8 Potassium (K+) 90 16.8.1 Procedure I — Potassium <5,000 mg/l (STPB method) 90 16.8.2 Equipment 90 16.8.3 Procedure 90 16.8.4 Procedure II — Potassium ≥ 5,000 mg/l (sodium perchlorate method) 92 16.8.5 Equipment 92 16.8.6 Preparation 93 16.8.7 Procedure 95

16.9 Nitrate ion concentration 96 16.9.1 Scope 96 16.9.2 Equipment 97 16.9.3 Procedure 97 16.9.4. Dilution table 99

16.10 PHPA polymer concentration 101 16.10.1 Scope 101 16.10.2 Equipment 101 16.10.3 Procedure 102 16.10.4 Additional guidelines and trouble shooting 103

17.0 CHEMICAL ANALYSES FOR CORROSION 104

17.1 Zinc oxide (ZnO) and basic zinc carbonate (ZnCO3•Zn(OH)2) 104 17.1.1 Scope 104 17.1.2 Equipment 104 17.1.3 Procedure 105

17.2 Iron sulphide (qualitative testing) 106 17.2.1 Purpose 106




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17.2.2 Equipment 106

17.2.3 Procedure 107 17.3 Hydrogen sulphide (H2S) 107

17.3.1 Scope 107 17.3.2 Procedure 1: Hach test 107 17.3.3 Equipment 107 17.3.4 Procedure 108 17.3.5 Procedure 2: Garrett Gas Train (GGT) 109 17.3.6 Scope 109 17.3.7 Equipment 109 17.3.8 Procedure 109

17.4 Phosphate 115 17.4.1

Scope 115

17.4.2 Procedure 1 : Using a Hach Direct Reading Colorimeter 115 17.4.3 Equipment 115 17.4.4 Procedure 2 : Hach phosphate kit (PO-24) 118 17.4.5 Equipment 118

17.5 Oxygen scavenger: SO32- content 120

17.5.1 Scope 120 17.5.2 Equipment 120 17.5.3 Procedure 1: clear filtrates 121 17.5.4 Procedure 2: dark filtrates 122

18.0 RESISTIVITY 123

18.1 Equipment 123 18.2 Procedure 123

19.0 PROCEDURE FOR ANALYSING GLYCOL 124

19.1 Refractometer 124 19.1.1 Equipment 124 19.1.2 Reagents 124 19.1.3 Procedure 1 124

19.2 Dual-temperature retort analysis for glycol systems 125 19.2.1 Equipment 125 19.2.2 Procedure 2 125

19.3 Determining the amount of glycol (kilos) with a centrifuge 126 19.3.1 Procedure 126

20.0 PROCEDURE TO ANALYSE PLUGGED PERMEABILITY 127

20.1 Equipment 127 20.2 Procedure 127

21.0 COUPON RING FOR DRILL PIPE CORROSION 130




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21.1 Monitoring corrosion rings 130 21.2 Laboratory test 130 21.3 Calculating the degree of corrosion 131




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1.0 INTRODUCTION

Many types of water base drilling fluids (muds) are used in drilling operations. Basic drilling

fluids are usually modified in more complex systems, as the well depth increases - and

temperature and/or pressure consequently increase. Different drilling fluid systems are normally

used in each well. The choice of drilling fluid for a specific well is affected by a number of key

factors. Evaluating the cost-effectiveness of a drilling fluid for a given well or well section should

be based on the following criteria:

Field of application Water composition Driling rig/equipment

Surface interval Type of water (service or seawater) Well location

Intermediate interval Concentration of chloride Limited surface availability

Production interval Water hardness Mixing possibility

Completion method-type Mud Pumps

Type of production Equipment solid control

Geology Possible problems

Type of shale Shale problems

Type of sand

Bit/Bottom-Hole Assembly Permeability (BHA) balling

Other types of formation Drill string getting stuck

geological

Circulation losses

Depleted formation

Before reviewing different types of water base fluids, we shall discuss how muds are made up

and treated.




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Preparing and treating muds

The first information a fluid engineer needs, to prepare a fluid, is the quality and type of water

available.

Quality of water for preparing drilling fluids

The following factors need to be evaluated when preparing a mud programme and formula:

• Concentration of calcium and magnesium (water hardness)

• Concentration of chlorides (seawater, brackish water, etc.)

• pH

Mineral and organic colloids used in muds perform differently depending on the concentration of

these ions (Ca++, Mg++, Na+, Cl-). After determining these values, chemical treatment can be

planned, if necessary, to sweeten the water (reduce the calcium and magnesium or dilute it

because of the high chloride content), before making up the fluid. These treatments can include:

• Sodium carbonate (Na2 CO3)

• Sodium carbonate and caustic soda (NaOH)

• Treatments with combined products are more effective than using just one product.

• Hardness does not need to be totally eliminated.

• Obviously it is not possible to eliminate chlorides on an industrial scale (they can be

decreased by diluting with service water when there are problems relating to electric logs

for example).

Lastly, we should mention that when the hardness and salinity of water are excessive it may be

more cost-effective to use a different mud, which is better suited to the water in question, rather

than try and reduce the values in the original water. This scenario is common in offshore

operations where muds prepared with seawater are often used (if compatible with environmental

concerns or electric log recordings).




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Treatments in the (surface) mud circuit

The main characteristics to control and treat are:

• Density, solids content

• Rheology and thixotropy

• Filtration

• Appropriate chemical balance for the fluid

The most important quantitative treatments are to control the density and solids content (water,

barite, oil and/or new mud). Other characteristics are generally maintained with small-scale

treatments (CMC, HV/LV, lignosulfonates, FC, caustic soda, hydrated lime, etc.), apart from

major cases of contamination.

Treatments can be carried out with two techniques:

• Treatment with a solution (in a slug pit)

• Adding dry substances through a mixer funnel (hopper)

Treatment with a “solution”

A concentrated solution of chemical products for the entire mud volume in circulation is prepared

in a pit isolated from the mud circuit (a slug pit). This concentrated solution is added to the mud

at a constant rate, during one or more circulation stages.

Advantages:

• The concentrated solution can be prepared using the same circulation fluid.

• Additives are more effective when they are previously dissolved and hydrated.

• Dosing the solution at a regular and constant rate makes it possible to achieve uniform

characteristics for the entire volume circulating.




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Disadvantages:

• The pumpability/fluidity of the treatment solution must be guaranteed (for example, this method

is not suitable for adding bentonite).

Treatment with “dry” products

In this treatment, powder products (barite, bentonite, lignosulfonate, etc.) are added through a

mixer funnel, or supersaturated solution products are added.

Advantages:

• The treatment schedule can be changed, selecting an additive in relation to the

development of characteristics.

• The only solution for large-scale treatments (increasing rheological parameters or the

density).

Disadvantages:

• The method may not be constant and regular. As a result some volumes will be treated

more than others, when the rate of manually added products is not constant.

• The immediate efficiency of products is reduced, in relation to the amount of product in

the prepared mud.

• This treatment is not feasible when large quantities of several products have to be added

at the same time. The method cannot be used when switching from a simple mud to a

high density salt saturated system.




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2.0 NON INHIBITING FLUIDS

Non inhibiting fluids are simple and cheap. Their composition will vary depending on

requirements relating to the local lithology, water composition, borehole size and expected

contaminants. These muds have specific limitations which are evident when drilling

unconsolidated formations, encountering contaminants and high temperatures, or when the fluid

density increases. Each of these scenarios may require another type of fluid more suitable to

the new conditions.

Non inhibiting muds are divided into the following categories:

• Service waters

• Muds with formation shale (native muds)

• Bentonite muds (spud mud – to start drilling)

• Lignite/lignosulfonate muds (dispersed deflocculants).

2.1 Service waters (clean waters)

Service waters are practically ideal as drilling fluids; however when they include drill

cuttings, the cuttings are suspended and reduce drilling efficiency. Decanting is an

effective way to remove drill cuttings. The decantation area should be big enough to

ensure sufficient time for the suspended particles to deposit. Selective flocculants are

used to remove the drill cuttings; solid flakes form and deposit in the pits more quickly

than single particles. Treatments with lime or with polymers designed to flocculate drill

cuttings can be used to speed up the decantation process.

The removal of flocculated solids can also be improved using systems to control solids

and longer surface retention times, including settling pits, centrifuges, desilters and

superscreens.

Service water salinity varies from fresh water to saturated salt water. The choice of water

and salinity will depend on the composition of the water available or salinity required to

drill specific formations. Clean waters are Newtonian fluids, so they require high annular

velocities to guarantee borehole cleaning. Small viscous mud cushions are occasionally

circulated to clean the borehole, if necessary. They usually contain caustic soda and

lime to control corrosion risks.




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The following factors must be considered when drilling with service waters:

1. Initial treatment with selective flocculants should consider doses ranging from

one to two pounds per one hundred barrels of water.

2. Extra flocculants should be added while drilling using a chemical barrel (a 150-

200 litre barrel with agitator), placed downstream the shale shaker or in any

case downstream the desilter and the desander, if present.

3. The amount of flocculant to add should be evaluated in relation to the size of the

borehole, the penetration rate and amount of solids in the fluid.

4. Keep the pit channels as high up as possible.

5. Keep all lines between the pits closed, to prevent mud flowing from the pit

bottom to the next pit.

6. Empty or discharge mud from the pits at least once a day, to ensure the

maximum capacity for sedimentation (dispose of cuttings which have already

decanted).

7. Do not add water to the shale shaker, as it will dissolve and break up thecuttings, forcing them through the mesh.

8. Long sedimentation times are beneficial, so all practical approaches should be

taken to extend decantation times. Circulation in standby pits onshore or in

extra mud pits is recommended, to facilitate decantation.

9. Monitor the solid content in the flow line, channel and sump pit and adjust

flocculating treatments to minimise solids in the sump pit.

2.2 Muds with formation shale (native muds)

A drilled formation may contain shale or shaly rocks which turn into mud, in some zones.

When water is pumped into the well while drilling, it flows back up to the surface with

native dispersed solids. Equipment for removing solids is used to remove as many

formation solids as possible. Viscosity increases as drilling and circulation progress, until

a viscous mud forms. So the mud must be diluted to prevent an excessive increase in

viscosity. On the other hand, mud viscosity can be increased and filtration controlled by

adding small amounts of bentonite. In addition caustic soda or lime is normally added to

keep mud corrosion under control and stabilise rheology.




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This basic system mainly contains bentonite and is generally used as a spud mud, to

start a well. The benefits of this system include its low cost and a high ROP (rate of

penetration). The system often has a very low viscosity (borehole cleaning).

Contamination and treatments

Native muds are extremely sensitive to all contaminants. They behave like bentonite

muds but react very poorly to treatments. The treatment for these muds depends on the

size of the borehole, the rate of penetration and formation being drilled. Native muds

without thinning agents can be used for 500/1000 metres if contaminants are not present,

if enough water to prepare the mud is available and if solids control equipment is used

properly. When gel and viscosity strengths have to be lowered, light treatments with a

sulfomethylate tannin base should be used (DESCO by M.I. or New-Thin by BHI).

Sulfomethylate tannins do not require caustic soda and are ideal at lowering gel

strengths without dispersing mud. Lignosulfonates should not be used unless the mud

weight and/or properties make this necessary. Lignosulfonates need a pH from 10 to

10.5 and an alkalinity PF from 0.3 to 0.5. ml.

Controlling drilled solids is essential for using a low cost native mud. An accumulation of

drilling solids will increase maintenance costs and could cause other problems such as

the drill string getting stuck or circulation losses. Transport capacity should not be

achieved through drilling solids, but by adding bentonite and/or polymers instead. Adding

20 lbs/bbl of bentonite and 4 - 6 lbs/bbl of lignite is recommended to keep fluid losses

under control.

To convert a native mud to a non dispersed mud with a low solid content, only 10 – 14

pounds of bentonite should be added and a thinning agent specifically for bentonite

should also be used. Liquid filtrate losses can be controlled using polyanion cellulose

and/or carboxymethylcellulose sodium. Native muds with a high solid content are more

susceptible to contamination.

Common types of contamination are listed below:

Salt and salt water contamination – Mud contamination by salt or salt water is

indicated by an increase in the concentration of chlorides, high viscosity, an increase in

gel strength, more filtrate, a quick drop in pH values or the appearance of foams. This

type of contamination can be treated increasing the mud weight in the case of salt water

infiltration, and by increasing the caustic soda, sulfomethylate tannins, lignosulfonates




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and CMC to assist filtration control and integrate the bentonite solids diluted by the flow

of water.

Significant solids contamination - This type of contamination is indicated by a high

Marsh viscosity, high plastic viscosity, high methyl blue test (MBT) values, a slower

chemical treatment response time and a large amount of solids in the mud still. The

contaminated muds are treated by centrifugation and by eliminating low weight solids and

diluting with water, or by dilution alone (dilution may be the most expensive treatment).

Centrifugation should take place in the active system while water is added and the weight

in the pit is kept more or less constant. A small mesh shale shaker should be used and

combined moisture should be added downstream the shale shaker. The sieve size will

depend on the shale shaker available. Usually the smaller the mesh size (the more

meshes) the better the result.

Anhydrite (gypsum) contamination – This kind of contamination is indicated by high

viscosity, high gel strength and an increase in filtrate. Filtrate analysis will show an

increase in the concentration of both calcium and sulphates. In most cases, sulphates

are not tested at the drilling site as special reagents are needed. When drilling thin

layers of anhydrite, the mud can be treated with soda ash and in some cases with

sodium phosphates or carbonate. If a thick anhydrite layer is drilled, the mud can beconverted into a gypsum mud or high pH mud (with a low calcium solubility).

Cement contamination - Cement contamination is characterized by an increase in

viscosity, gel strength, a reduction in filtrate and in the filtrate calcium content. In these

cases the pH will increase dramatically because of the high content of hydroxyl groups in

the cement. This situation can be treated with phosphates, sulfomethylate tannins,

sodium bicarbonate or soda ash, depending on the pH value. The rheological properties

of mud can be restored using thinning agents. Pre-treatments with small amounts of

sodium bicarbonate, before drilling cement layers, will effectively reduce the effects ofcontamination.




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2.3 Bentonite-water (spud mud)

This basic system primarily consists of water and bentonite (5 % - 10 %). Bentonite

dispersed in service water produces a mud with a good drill cutting transport capacity, a

good rate of penetration and usually adequate filtration control (API ≅ 8-10). These

water-bentonite muds are normally used to drill during the initial surface stage (hence the

name spud mud) when there are no contaminants and the temperature and pressure are

not high. At times these muds are also used to drill deeper sections.

As drilling proceeds, the drilled solids are incorporated in the fluid and solids removal

equipment must be continually used to eliminate as many solids as possible.

The quality of the make up water is extremely important when formulating a water-

bentonite mud.

Chlorides (Cl ) and the hardness (Ca++e Mg++) of the make up water interfere with and

reduce bentonite hydration.

The concentration of calcium ions should not be above 150 mg/l (ppm). If this value is

higher, the water should be treated with soda ash (Na2CO3). Adding 0.1 pounds of soda

ash per barrel of water (160 l) will remove approximately 100 mg/l of calcium ions Ca

++

.

Hardness is caused by magnesium ions which are reduced by adding sodium hydroxide

(NaOH). The reaction between magnesium ions and hydroxyl groups at a pH of 9.7 is

complete when magnesium hydrate Mg (OH)2 precipitates.

Chlorides cannot be eliminated from make up water. A concentration below 5000 - mg/l

will not seriously affect commercial bentonite hydration. If the chloride concentration is

above 20,000 mg/l, bentonite hydration will be significantly affected and in this case fresh

water should be added to lower the concentration and allow for hydration.

Viscosity may increase in water-bentonite muds by adding more bentonite or a polymer

bentonite extension, lime or soda ash.

The pH is usually maintained within an 8.0 - 9.5 range by using caustic soda. This tends

to make hydrated bentonite flocculate but the effect can be minimised by slowly adding

caustic soda while vigorously agitating the mud.

The typical properties of bentonite muds are listed in table 1.




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Table 1

Typical properties ofwater-bentonite mud

Density Viscosity Yieldpoint Gels Filtrate

(sg relativedensity)

plastic(cPs) (lb/100 ft2)

10 sec/10min (lb/100ft2)

API (cm3 /30min)

1.03 – 1.05 15 - 60 10 5 25 12 – 25

Composition and preparation:

The composition will depend on the quality of the bentonite available. 50 - 100 Kg per m3

of water are needed for average bentonite, while only 30 – 50 kg per m3

are needed for

high performance bentonite. In the latter case, the amount of filtrate will be considerably

greater.

Low viscosity CMC can be added if a smaller amount of filtrate is required.

Preparation rate 25 m3 /hour

Conversion:

As this mud is very sensitive to contaminants, it must be quickly converted to a more

complex system. In fact conversion is not the right word and we should refer instead to a

quickish transition to a more complex system.

Maintenance

Maintenance is simple and involves keeping the solid and sand content within acceptable

limits.

-Keep the viscosity under control by adding water or bentonite or by adjusting the pH.

-Keep the filtrate under control by adding bentonite and/or CMC.




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2.4 Lignite/lignosulfontate muds

Table 2

Treating contaminants in bentonite muds

Contaminant Indicators Treatment strategies

Sand formation

Increase in plastic viscosity, solidcontent, gels, viscous bottomholecushions after trips

Dilute more. Improve solidsremoval. Centrifuge the mud.

Increase in the Pm, Pf , pH, yieldpoint,

Centrifugation.

Shales gels and Marsh viscosity. Possible

increase

Dilution.

in hardness. Polyphosphates (for thinning)

Cement

Apparent viscosity, yield point andgels, filtrate. Ca++ and pH Dilution – sodium bicarbonatePb, Pf, Mf

Gypsum/ Anhydrite

Density, apparent viscosity, yieldpoint and gels, filtrate, SO4 , andCa++, pH Pb and Pf. Change in thedrilling rate. Increase in the yieldpoint, in the Marsh viscosity andhardness. Decrease in the pH, Pm,and Pf .

Dilution, sodium carbonate,polyphosphates, CMC. Reduce theconcentration of calcium ions withbicarbonate or soda ash. Addlignosulfonate and/or convert togyp mud.

Salineformations

Density, apparent viscosity, yieldpoint and gels, filtrate, chlorides.Increase in chlorides, yield point,gels, Marsh viscosity and filtrate.Decrease in pH, Pm, and Pf.

Dilution, CMC. Dilute with cleanwater. If the chloride concentrationis above 35,000 mg/l, convert toseawater base mud. If a majorsaline formation has to be drilled,convert to salt saturated mud (ortreat as for a seawater flow).

Lignite-lignosulfonate base muds (deflocculated FW/SW-LS), can be used to drilldifferent kinds of formations. They may range in density from 10 - 19 lb/gal (2.16-2.28

Kg/l), when there is an appropriate level of low density solids (bentonite and drilling waste

including limestone, shale and sand). As the density increases (barite), the bentonite

content should be decreased.

The pH range for controlling lignite-lignosulfonate muds is from 9.5 to e 10.5. Magnesium

ions precipitate in this range. Moreover the concentration of calcium ions should be kept

below 200 mg/l.




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As for chlorides, a content below 10,000 mg/l should not damage fluid performance,

however the mud must be diluted with fresh water if values go above 25,000 mg/l.

Lignite-lignosulfonate muds are thermally stable up to a temperature of approximately

325°F (163°C). This limit is not exact as thermal stability also depends on the mud pH,

the type of lignosulfonate used (with or without chrome), the exposure time to high

temperatures as well as the solid content. Generally speaking lignosulfonate muds with

chrome ensure a better thermal stability than chrome-free lignosulfonate muds. When a

lignite/lignosulfonate mud deteriorates through heat, it produces carbon dioxide and ion

carbonates accumulate in the filtrate.

Main additives of lignite/lignosulfonate (deflocculated) muds

Lignite/lignosulfonate muds are fairly simple to prepare, convert and use. Table 3 lists the

additives, functions and concentrations of a typical lignite/lignosulfonate mud.

Table 3 Main additives of lignite/lignosulfonate muds

Additive Concentration, gr/l Function

Bentonite 30 - 70 Viscosity Filtrate control

Lignosulfonate 1 - 20 Deflocculant Filtrate control

Caustic soda/potassiumhydroxide For pH 9.5 - 10.5 Alkalinity control

Soda Ash 1 - 3 Calcium ion removal

Lignite 3 – 12 Filtrate control

Barite

Amount necessary for thedensity Weighting agent

Low viscosity PAC/CMC 1 – 3 Filtrate control

Gilsonite 5 - 20 Filtrate control

Bentonite – Bentonite is added to control viscosity and the filtrate. If fresh bentonite,

preferably as a prehydrated mud, is used, it should be added before other chemical

treatments. Overtreatment can cause rheological problems.




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Lignosulfonate – Lignosulfonates are used for controlling rheological properties (such

as the yield point) and the filtrate – by deflocculating bentonite. Clays deflocculate

because of the negatively charged lignosulfonate compound being absorbed on the edge

of the clay sheets This causes the clay particles to dissociate (deflocculation), which in

turn decreases viscosity at low rates and leads to a lower yield point and gel strength

(thixotropy). In addition filtering control is improved and a thick, compressible filter cake

forms.

Lignosulfonates degrade to CO2 and carbonate ions at temperatures above 325°F

(163°C). At even higher temperatures, usually above, 400°F (204°C), the lignosulfonates

can decompose and even release hydrogen sulphide (H2S) and sulphide ions. Chrome

lignosulfonates (CrL5) can be replaced with chrome-free lignosulfonates in

environmentally sensitive areas, but performance is affected (more products will be

needed).

Caustic soda or potassium hydroxide – Caustic soda (NaOH) or potassium hydroxide

(KOH) should be premixed in a chemical barrel and then slowly added to the circulating

system to correct the pH value. These alkalinity agents improve the performance of both

bentonite and lignosulfonate and also reduce corrosion phenomena.

Soda Ash - Soda ash (Na2CO3) is used to reduce the hardness of calcium ions and

improve the performance of lime bentonite.

Lignite – Lignite is used to control filtering and as a secondary flocculant. To make

lignite soluble, a highly alkaline solvent is required. Lignite acts as a filtrate reducer up to

temperatures of 400°F (200°C). When compared with lignosulfonate, lignite provides

better filtering control at high temperatures. It is normally added combined with

lignosulfonate, usually in a 4:1 ratio. This ratio may be decreased depending on the

quality of the lignite, the mud weight, type of formation drilled and borehole temperature.

Barite (BaSO4)- Barite is traditionally used to make mud heavier (specific weight ≅ 4.2 -

4.3). Barite should be periodically tested to make sure it meets API specifications and

does not contain any impurities which may constitute a source of alkaline-environment

soluble carbonate ions.

Typical properties of lignite/lignosulfonate (deflocculated) muds (FW/SW-LS)

The typical properties of lignite/lignosulfonate muds are listed in table 4. These muds are

characterised by low yield points and gel strengths, and have a low API filtrate.




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Table 4

Typical properties of lignite/lignosulfonate muds

Density(Kg/lt)

Plasticviscosity

(cPs)

Yield point(gr/100ft 2)

Gels 10 sec/10min(gr/100 cm2)

API filtrate(cm3 /30 min)

1.08 8 - 12 3 - 5 1 – 2 2 - 5 8 - 12

1.44 15 - 20 5 – 7 1 - 2 2 – 5 4 - 8

Conversion and maintenance

Conversion: Lignite/lignosulfonate (deflocculated) muds are quite flexible to prepare,

convert and maintain. Converting to a lignite/lignosulfonate mud should only be done

when borehole and mud conditions make it necessary.

Before converting mud to a lignite/lignosulfonate system, the volume of solids should be

decreased by diluting with water or mechanically removed beforehand.

The hardness of calcium ions should not be more than 200 mg/l. If higher, the mud

should be pre-treated with soda ash.

Any bentonite treatment should be carried out before adding lignosulfonate; otherwise

more bentonite will be needed to obtain the same filtering results and viscosity.

The pH should remain in a 9.5 - 10.5 range, while the Pf should be from 0.2 to 0.8 cm3

(H2SO4 N/50). The results of the pilot test carried out in the mud cabin/rigsite laboratory

will indicate the right treatment with caustic soda and potassium hydroxide. Treatments

with lignite, lignosulfonate and caustic soda should be carried out adding the substances

gradually and at the same time in one or two circulation stages, maintaining a pH from

9.5 to 10.5.

Maintenance: Pilot tests (at the rigsite mud cabin) are essential to achieve economic

and viable results. Small extra amounts of lignosulfonate are recommended when flow

properties become excessive.

Equipment to control solids (shale shakers, centrifuges, desilters, desanders, etc.) is

essential.




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The pH should stay between 9.5 and 10.5, with a Pf from 0.2 to 0.8 cm 3. Treatments with

PAC LC (low viscosity), CMC or starch (with anti-fermenting agent) can be used to

further control the filtrate.

Any borehole instability problems can be mitigated by additional treatments with

lignosulfonates or gilsonite, or by converting the mud to inhibiting systems such as

calcium or gypsum base, or even oil base muds (O.B.M.)

Advantages and disadvantages of lignite/lignosulfonate (deflocculated) muds

Lignite/lignosulfonate offer numerous advantages. They can easily be made heavier,

they guarantee good filtration control and are cheap to prepare and maintain. The most

significant disadvantage of this mud is that it tends to disperse drill cuttings, unless the

concentration of lignosulfonate is high, ranging from 35-45 Kg/m3

; in this case the yield

point and gel strengths may be very low. Table 5 lists the advantages and

disadvantages of these muds.




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Table 5 Advantages and disadvantages of lignite/lignosulfonate muds

Advantages Disadvantages

Can easily be weighted to 2.16 Kg/l whenthe content of low density solids is kept low

Disperses cuttings making it hard tomechanically remove them.

Good filtrate control with a thin, lowpermeability filter cake

A higher annular velocity is required toensure suitable borehole cleaning (low

rheology)

Simple to prepare and maintain. Borehole caving in shale sections.

Provides good protection from corrosion.

Waste disposal - BOD (biological oxygendemand) factors need to be considered.

Cheap to prepare and maintain up to 325°F(163°C).

Problems with disposal, if the muds containheavy metals or Cr +++ .

Effective with salinity from fresh water to

seawater.

Deteriorates at high temperatures (325°F -

163°C) forming carbonates and sulphideions.

an easily be converted to lime or gypsummud (inhibiting muds)

Problems with management and contamination

Lignite/lignosulfonate (deflocculated) muds are fairly resistant to contamination. Table 6

lists typical contaminants, contamination indicators, treatment strategies and

recommended practices for trouble shooting, to guarantee a quality product.




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Table 6 Treating contaminants for lignite/lignosulfonate muds

Contaminants Indicators Treatment strategy

High densitysolids

Increase in plastic viscosity, in thecontent of solids, gels. Viscousbottomhole cushions after trips.s.

Dilute more. Improve solidsremoval. Centrifuge the mud.

CementIncrease in Pm, Pf, and pH, in theyield point and Marsh viscosity.Possible increase in hardness.

Reduce the (Ca++) content in thecement with bicarbonate and/orSAPP and lignosulfonate. Diluteless. Increase the Pf to limit the

solubility of Ca++. Convert to limemud if necessary.

CarbonatesIncrease in gels, in the yield pointand MF. Viscous bottomholecushions after trips.

Use a GGT for accurate analysis.Increase the pH to 10.7 with NaOHor KOH. Treat with gypsum and/orlime to remove carbonates (avoidover treatments). Dilute less.

Poor productquality

Changes in the product make up.Increase in the number oftreatments. Mud properties cannotbe checked with standardtreatments.

Record the product history via thesupplier. Prepare for samples androutine analyses. Conduct pilottests on good quality materials.

Salt/salty waterWell flow, increase in the yieldpoint, in the Marsh viscosity, thehardness, the pH, , Pm, and Pf.

Increase the density if possible, toeliminate the flow. Dilute with freshwater. Increase the caustic soda,filtrate and chlorides. Decrease thelignosulfonate to control therheological properties, when theseare stable; add PAC to controlfiltering. If the chlorideconcentration is above 35,000 mg/l,convert to a salt base mud.

Temperaturefreezing

Increase in pumping pressure to

continue circulation, viscousbottomhole cushions after. trips.

Reduce low density solids andMBT. Use a thermally stable

deflocculant. Test the mud for anysign of carbonate contamination.

Gypsum/anhydrite

Change in the drilling rate.Increase in the yield point, in theMarsh viscosity and hardness.Decrease in the pH, Pm and Pf.

Reduce the Ca++ ion content withbicarbonate or soda ash. Addlignosulfonate and/or convert to agypsum mud.




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3.0 INTRODUCTION

Drill-in fluids, as non-damaging fluids, are particularly suitable for drilling hydrocarbon-bearing

zones (reservoirs). These fluids have been formulated to optimise drilling performance and

minimise reservoir damage, so a well’s production potential is maintained. Conventional muds

cannot normally be converted to drill-in fluids.

Conventional muds can cause serious reservoir damage. This impact may be minimized by

reducing the filtrate and keeping progressive gels under control (keeping drill cuttings

suspended).

This practice reduces filtrate invasion in the formation and helps to achieve better results in

production with casing cemented wells (isolating pay zones). In conventional completions, the

shots penetrate the casing and go beyond the borehole section invaded by mud and filtrate

(while drilling). Major pressure drops (during well clean-up) and larger diameter shots can help

to reduce the effects of damage induced by conventional muds.

In open hole completions, where cemented casings are not used, the fluid and cake must be

removed with acids or washing operations.

Drill-in fluids are specifically designed to reduce the damaging effects and obtain good cleaning

results during the clean-up stage. These fluids are very important when drilling horizontal wells,

where low drops in pressure make the borehole cleaning stage critical. Gravel packs and pre-

packed screens reduce the type and dimension of solids that may flow back up during the clean-

up stage, so drill-in fluids should always be planned when drilling horizontal sections to reach the

reservoir (avoiding the use of conventional muds).

Numerous fluids can be used for drill-in fluids (DIF) including water, mineral oil and synthetic

oils. Fluids are chosen depending on the type of formation, composition of the formation fluid,

damage mechanism and completion method. Many wells drilled with DIF are completed without

cemented casings in the pay zone.

The recommended practice for proper DIF planning includes the following stages:

1. Identify the formation and permeability.

2. Select the type of completion.

3. Select the DIF.




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4. Select the clean-up method (cleaning the mud and cake). Formation damage can be

quantified using a number of approaches. In the laboratory, measures on the permeability return,

cake solubility and lift-off pressure (clean-up) are used to compare fluid performance for a

specific well formation. The skin effects calculation and productivity index are used to measure

damage. A DIF should have the characteristics outlined below.

4.0 FORMATION DAMAGE CONTROL

A) The drill-in fluid must not contain clay or weighting material which is insoluble in acid (barite)

as this can penetrate the formation and obstruct porosities.

B) The fluid must be formulated with acid soluble or breakable viscosifiers, additives to control

filtrate and blocking agents with a controlled grain size (in relation to formation porosity values),

which can be removed from the well by clean-up jobs.

C) The filtrate must have chemical characteristics suitable for preventing formation shale

hydration and which damage the permeability.

D) The filtrate must not contain salts which cause insoluble elements (sulphates) to precipitate

when reacting with formation fluids.

E) The mud and filtrate must not change the formation’s wettability characteristics (from Water-

Wet to Oil-Wet and from Oil-Wet to Water-Wet.

F) The filtrate shall not produce emulsions with formation fluids or cause formation plugging.

5.0 DRILLABILITY

A) The DIF must ensure that cuttings are easily transported (borehole cleaning, lubrication and

inhibition of formation shales).

B) The fluid must minimise cavings and ensure borehole stability.




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6.0 COMPATIBILITY WITH COMPLETION PROCEDURES AND EQUIPMENT

A) The grain size of DIF additives must be suitable to form bridgings in the mud cake. The

additives must not fully penetrate the formation, but only small amounts should pass through

completion equipment (filters) during the production and formation cleaning stages.

B) The DIF must be formulated with materials that are acid soluble, water soluble, degradable

with oxygenation or soluble with solvents, but which do not produce precipitates and/or

emulsions.

C) Breakers (enzymes) must be compatible with the formation fluids and filtrate of the DIF.

Reactivity and damage vary a great deal and depend on the type of formation and well

conditions. Some formations can tolerate a wide range of DIFs (the composition) better than

others. When the well produces from fractured limestones, considerable amounts of insoluble

material may be tolerated, without causing a significant drop in productivity rates. Fluids that

invade this type of formation are usually recovered during the clean-up stage. Low permeability

sandstones and depleted or unconsolidated sandstones cannot tolerate the invasion of fluids

and solid particles, without causing extensive and significant damage. The following factors

should be considered in depth, to choose an appropriate DIF:

-Type of formation

-Permeability / porosity

-Formation pressure

-Mineralogy

-Formation fluid composition

7.0 FORMATION DAMAGE MECHANISMS

Mechanisms which damage productive pay may occur when drilling a well and these cause

lower productivity rates (daily production) and lower reservoir recovery rates. Some of these

harmful effects are listed below, with potential prevention techniques.




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7.1 Plugging by solids

Formation permeability and porosity can be plugged by mud solids, causing damage.

These solids may be materials used to make up the fluid, in the case of bentonite or

barite, or chemical additives or solids incorporated while drilling. Compressible,

deformable solids (plastics) such as hydrated clays, are the hardest (or impossible) to

remove. In addition, solids may block the completion string and reduce production rates.

To overcome this problem, solids used in DIFs should have a suitable, controlled grain

size) to bridge permeability openings at the borehole surface, without penetrating at

depth, and must also be acid soluble. The DIF cake traps fine solids which may cause

significant damage and prevents these solids depositing into the formation. If the solids

in the DIF are too fine to form bridging on the surface of the hydrocarbon bearing section,

and thus a thin, elastic cake, they will invade the reservoir matrix and may form a cake

inside the formation resulting in damage which is often irreversible. A surface panel can

be removed more easily that a panel in the formation. To reduce the likelihood of a

solids invasion, an “aggressive” solid control programme should be put in place, to

remove the solids during the first circulation stage. When drilled solids are re-circulated

and reground in several stages, they are reduced in size and dispersed in fluid, creating

an accumulation of fine solids. Minimising the overbalance (difference between thehydrostatic load and formation pressure) will help to reduce the depth of solids invasion,

consequently causing less damage.

7.2 Hydration of formation shales (migration)

Sandstone formations vary from clean formations (only containing sand) to very dirty

formations (containing significant amounts of shale). These interstitial shales can

hydrate, deform or migrate, causing damage to the producing formation when in contact

with the mud filtrate, cementing slurries or other fluids, such as acids or separator

cushions. This reduces the flow rate of hydrocarbons. Different inhibiting fluids (CaSO4,

NaCl, KCl, Ca(OH)2, K2CO3) can prevent re-swelling and migration of shale parts. These

include oil base or synthetic fluids, which are highly effective at preventing this problem.

Completion fluids include saturated or high salinity brines and water base fluids which

use potassium chloride or other chemical additives stabilising the shales.




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7.3 Emulsion blocking

Another factor damaging a well’s production capacity is caused by emulsions between

the DIF filtrate and formation fluid – emulsion blocking. This can be offset by fine solids

in the filtrate combined with asphaltenes in the oil, by surfactants or emulsifiers in the

mud which emulsify the formation fluids, or by exposing certain types of crude to a

chemical environment which react and form emulsions. Oil base or synthetic fluids can

alter wettability, releasing water which is then emulsified. In water base fluids, the

compatibility with the filtrate may be tested and corrected with alternative, non-

emulsifying formulations. Lowering the filtrate values in DIFs can help reduce the extent

of damage caused by emulsions.

7.4 Scaling

Incompatibility and chemical reactions between a DIF and formation or formation fluid

can cause precipitate to form which damages the formation. The most common problem

comes from reactions between calcium in the filtrate and sulphates and soluble

carbonates in the formation fluid, which produce insoluble calcium carbonate and/or

gypsum precipitates. Information on the chemical composition of the formation fluid

makes it possible to plan a compatible DIF and eliminate these reactions.




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8.0 TYPES AND APPLICATIONS OF DRILL IN FLUIDS

A wide range of DIF options exist. Selecting the most suitable fluid not only depends on the

mechanisms that may damage the producing formation, but also on the types of structure to drill

and planned completion method. The temperature, density and knowledge of drilling problems

are always taken into account. Some options and main applications are listed below.

8.1 Clear fluids without viscous cushions

Service water or brine can be used in mechanically suitable formations that have not

been damaged by the invasion of large volumes of formation fluid. These non-

viscosifying fluids are often used in dolomites and fractured limestones, and produce

good results in reef formations, fractured sandstones and low permeability clean

sandstones.

These fluids require a turbulent flow and high viscosity cushions to suitably clean the

borehole. High viscosity cushions do not contain clay and must consist of HEC or

xanthan gum. Flocculants can be used to precipitate drilled solids in the surface system

(pits) and keep the fluid clean. The wells, which are drilled - structural conditions

permitting – are usually completed in an open hole or with slotted casings.

8.2 Fluids with HEC

Hydroxyethylcellulose base fluids can be used in conditions similar to those above. HEC

can transport cuttings, but the gel structure to keep the cuttings suspended is very weak.

Low shear rate viscosities (LSRV) can be increased by adding xanthan gum and to keep

cuttings suspended. HEC makes many types of fluids viscous, from fresh water to salt

saturated fluids such as sodium chloride, potassium chloride, calcium chloride, sodium

bromide, calcium bromide and zinc bromide. HEC also provides limited filtration control.

Additional filtration control can be achieved using starch base additives.

Open hole completions or slotted casings are also used with these fluids. If necessary,

HEC, starches or Xanthan gum can be removed with acids or oxidising agents before

putting the well into production.

8.3 Calibrated salt systems (salt size)

Salt Size (NaCl) systems are used to drill unconsolidated sand formations. These

systems are based on salt saturated brine, with xanthan gum for viscosity and a

combination of starch and salt particles with a grain size specifically for controlling filtrate.




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These last two features ensure excellent filtration control. To ensure bridging, the fluid

must be supersaturated.

The density of these systems ranges from 1,20 - 1,44 Kg/l, providing an acceptable

borehole and temperature stability. The systems can be used for every type of

completion. Washing is carried out in two stages:

• Acid soap to destroy the polymers, followed by

• Low salinity water to dissolve the salt particles (which are in the cake with the

starch).

8.4 Oil base systems

These systems can be formulated with characteristics that will not have a damaging

effect, for drill-in applications. The fluids can be made up with diesel or mineral oil.

One important application of these fluids is in very dirty, shaly sands. Water blocking or

re-swelling of the shales will occur in these sands if water base mud is used, while this

problem does not happen with oil base systems. Oil base fluids significantly contribute to

shale stability, where hydrocarbon bearing levels comprise compact interbedding shaleand sand.

Oil base fluids produce thin, elastic cake with good inhibition and lubrication properties.

These features simplify many aspects of problems relating to horizontal wells. For

example, the improved lubrication of these DIFs makes it possible to operate with

complex hole geometries or extended horizontal intervals (these wells cannot be drilled

with water base muds).

The oil/water (O/W) ratio may vary from 100/0 - 50/50. Generally, calcium carbonate with

a specific grain size (acid soluble) is used as the weighting agent in prepacked screens.

A DIF with calcium carbonate can be weighted up to 1.50 Kg/l. Barite or hematite

(alternative weighting materials for special applications or formations) is needed for

greater densities and the well is usually completed so it can produce while draining this

material through a slotted liner or wire-wrapped screen.

Displacement with a clean completion fluid is critical for effectively removing the cake

produced by an oil base fluid. Surfactants and common solvents are often needed to




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invert cake wettability and acid can be used to dissolve it. In addition, an acid stimulation

programme should guarantee a uniform effect on the cake.

8.5 Synthetic base systems

These systems can also be formulated to prevent damage. The fluid’s rheological

properties can be modified to have gels with a low shear viscosity rate. Synthetic base

DIFs have the same advantages as oil base DIFs, but are far more expensive (3.4). The

use of these fluids enables the offshore disposal of cuttings, in many areas.

Synthetic base fluids are used in sensitive areas, particularly when production zones

comprise sandstones with a high shale content. The filtrate from synthetic base fluids

does not damage the interstitial shale. Moreover, synthetic base fluids guarantee better

shale stability in pay zones where shale formations are interbedding with production

intervals.

The synthetic material/water ratio for these fluids may vary from 100/0 to 50/50. Acid

soluble, calcium carbonate is normally used as a weighting agent, with a specific grain

size in wells completed with prepacked screens.

DIFs weighted with calcium carbonate can have a density of up to 1.50 Kg/l. Barite,

hematite or alternative materials (for special applications or formations) are needed for

greater densities and the well is usually completed so weighting materials can pass

through bottom hole equipment (slotted liners or wire-wrapped screens).

As in the case of oil base muds, displacement with a fully filtered completion fluid is vital

for effectively removing the cake produced by a synthetic base fluid. Surfactants and

common solvents are often needed to invert cake wettability, so that acid can be used to

dissolve it. In addition, an acid stimulation programme should be devised to ensure that

the cake is dissolved uniformly.



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Well Area Operation

9.0 INTRODUCTION

The American Petroleum Institute (API) recommends standard methods for conducting

laboratory and rigsite tests. These methods are published in its RECOMMENDED PRACTICES.

10.0 FLUID DENSITY (MUD WEIGHT)

10.1 Instruments

Density, which is often referred to as the “mud weight”, is measured using a mud

balance, with a 0.1 lb/gal (10 g/l) error of margin.

Density is defined as weight per unit volume. Mud weight can also be defined as the

hydrostatic pressure gradient, for example, 0.2 psi every 1000 ft (psi/1000 ft) or as the

density in lb/gal, lb/ft3 or Specific Weight or SG (Specific gravity) as shown in table 7.

litre

kgor

cm

gor

ft lbor

gallbSG

3

3

3.62

/

345.8

/=

Table 7: Density conversion table

10.2 Mud balance

10.2.1 Description

The mud balance (Figure 1) consists of a base with a graduated beam and mudcup on one end and a counterweight on the other, plus a slider weight to read

the mud density.




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Well Area Operation

Figure 1: Mud balance.

10.2.2 Calibration

1. Fill the cup with pure or distilled water.

2. Put the lid on and dry the cup with a cloth.

3. Put the graduated beam in the middle of the balance fulcrum.

4. The bubble should be in the centre, with the slider-weight indicating 1

g/cm3

(8.35 lb/gal). If a different value is indicated, calibrate the balance adjusting the

calibration screw at the end of the beam.

10.2.3 Procedure

1. Fill the cup with a sample of mud for measuring the density.

2. Put the lid back on, turn a few times to make sure there are no solids on

the inside. Make sure mud comes out of the middle hole.

3. Rinse and dry with a cloth.

4. Put the graduated beam in the middle of the balance fulcrum.

5. Move the slider-weight until the bubble is in the middle.




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Well Area Operation

6. Read the mud weight (or density) next to the slider-weight.

7. Note down the weight in lb/gal, lb/ft3, psi/1,000 ft of depth or specific

gravity (SG), depending on the unit of measurement required.

8. If the balance does not record the value using the required system,

consult the formula in Table 7. Mud gradient: psi/ft = 0.052 x lb/gal

= 0.4333 x SG

= 0.00695 x lb/ft3

kg/cm2

/m = SG / 10

SG at 60°F (15.6°C) = (141.5) / (131.5 + °API)

Where: °API = American Petroleum Institute gravity




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Well Area Operation

11.0 VISCOSITY

11.1 Instruments

Marsh funnel is used to measure viscosity at the rigsite, while a Fann V-G meter is used

when complete data on rheology (plastic viscosity, yield point and gels) is required.

11.2 Marsh funnel viscometer

Values measured with a Marsh funnel indicate the relative mud thickness (density).

11.2.1 Description

The Marsh funnel (Figure 2) is 6 inches wide at the top, 12 inches long, and has

a small bore tube 2 inches long and 3/16 inches wide at the bottom. The funnel

has a screen with a 1/16 inch wide mesh near the top (3.4 inches from the top).

Figure 2 : Marsh Funnel.

11.2.2 Calibration

Fill the funnel down to the screen (1,500 cm3) with fresh water at a temperature

of 70±5°F. The time for 1 quart (946 ml) to flow out should take 26 sec ±0.5 sec.




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Well Area Operation

11.2.3 Procedure

1. Keep the funnel in an upright position, covering the hole at the bottom

with your finger. Fill with mud which has just been sampled and filtered,

until the mud reaches the bottom of the screen (1,500 cm3).

2. Take your finger away from the bottom and measure the time it takes for

the mud to reach the notch of the first quart in the container (¼ American

gallon = 946 ml)

3. The result, which is rounded up or down to the nearest second, can be

noted as the Marsh Funnel viscosity. Record the temperature, in Celsius

or Fahrenheit, as well.

11.3 Rotational viscometer

Rotational viscometers can be used to measure the rate/shear stress of a drilling fluid,

and calculate the Bingham PV and YP parameters. Other rheological models can also

be used with the same data. Rotational viscometers are used to measure thixotropic

properties and gel strength as well.

Rheological data are normally used to provide information on the concentration of solids,

flocculation, deflocculation, suspension capacity and to calculate the hydraulic properties

of a mud.

11.3.1 Description

All rotational viscometers provide a direct readout and work electrically or are

manually charged. The mud sample is put in the annulus between two

concentric cylinders. The outer cylinder rotates at a constant number ofrevolutions. Rotation, via the fluid, exerts torsion on the inner cylinder, which is

connected to a spring balance and indicates movement.

Constants are calibrated so that plastic viscosity and the yield point are

calculated from readouts taken with the outer cylinder rotating at 600 and 300

RPM.




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Well Area Operation

11.3.2 Specifications: Direct reading viscometers

Rotor sleeve (outer cylinder)

- Inner diameter 1.450 in. (36.83 mm)

- Total length 3.425 in. (87.00 mm)

- Reference line 2.30 in. (58.4 mm) above the cylinder bottom.

-Two rows of 1.8-in. (3.18-mm) holes, placed at 120 degrees (2.09 radiants)

around the rotor, just below the reference line.

Balance (inner cylinder) - Diameter 1.358 in. (34.49 mm) – Cylinder length 1.496

in.

(38.00 mm) The balance is closed with a flat base which is contoured at the top.

Spring torsion constant - 386 dyne-cm/deflection degrees - High speed rotor:

600 RPM – Low speed rotor: 300 RPM

Figure 3 : Rotational viscometer.




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Well Area Operation

The following viscometers are normally used to test fluids:

1. Crank viscometer, with a speed of 300 and 600 RPM. A control on the

rotation point of the speed selection knob is used to determine gel

strength.

2. Electric motor (12-volt) viscometer, with a speed of 300 and 600 RPM. A

governor-release switch makes it possible to strongly agitate the mud

before measuring the viscosity. A manual hand wheel is then used to

determine the gel strength.

3. Electric motor (115-volt) viscometer (see figure 3), for two speeds

synchronised with a range based on an RPM of 600, 300, 200, 100, 6

and 3. A speed of 3 RPM is selected to determine gel strength.

4. Variable speed (115- or 240-volt with electric motor), with a RPM from

625 to 1. A speed of 3-RPM is selected to determine the gel strength.

11.3.3 Procedure to determine apparent viscosity, plastic viscosity and the yield

point

1. Pour the sample which has just been agitated into the thermic cell until

the level reaches the rotor line.

2. Adjust the temperature of the sample to 59°C (120°F). Slowly agitate

while calibrating the temperature.

3. Start the motor, turning the knob to high speed, with the gear lever facing

downwards. Wait for the readout to stabilise and then record at 600

RPM. Only change the ratio when the motor is working.




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Well Area Operation

Figure 4: Typical “Flow curve” of a drilling fluid.

4. Select a rotation speed of 300-RPM. When the value has stabilised,

record the readout at 300-RPM.

5. Plastic viscosity in centipoises = readout at 600 RPM minus the readout

at 300 RPM (figure 4).

6. Yield Point in lb/100 ft2 = readout at 300 RPM minus the plastic viscosity

in centipoises.

7. Apparent viscosity in centipoises = readout at 600 RPM divided by 2.

11.3.4 Procedure to determine gel strengths (at 10” and 10’)

1. Agitate the mud sample at 600 RPM for approximately 15 seconds and

put the gear lever in a neutral position.

2. Stop the motor and wait for 10” seconds.

3. Move the switch to low speed and record the unit of maximum deflection

in lb/100 ft2. If the instrument reading does not go back to zero, do not

reposition.



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4. Repeat steps 1 and 2, wait for 10’ minutes before putting the lever on low

speed and read the unit of maximum deflection. Record the measured

temperature.

11.3.5 Taking care of the viscometer

To clean the viscometer, put in water or solvent and rotate at a high speed.

Push the rotor slightly to release and remove. Carefully clean all parts with a

dry, clean cloth.

WARNING: The rotor must be cleaned after it has been disassembled, because

it is empty. Remove any traces of water with a specific solution. The rotor may

explode if put in mud with a very high temperature (>200°F).

NOTE: Never put the part with measurements in water.




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12.0 FILTRATION

12.1 Description

Filtration, or the capacity of a mud to produce filter cake, is determined by a filter press.

In this test, the rate at which a fluid is forced through a filter press is determined. The

test is carried out in specific time, temperature and pressure conditions.

The thickness of the solid panel which deposits is measured after the test. The filter

press must conform to API standards and should be used following API specifications.

The API fluid loss test is carried out at a pressure of 100 psi and fluid loss is recorded as

the quantity in millilitres lost in 30 minutes minus the filtering surface which equals 7.1

square inches.

12.2 Instruments

The instrument in figure 5 comprises a mud cell assembly, a pressure regulator and

pressure gauge assembled above the container. The cell is connected to the regulator

by an adaptor, with the cell simply fitted in the filter press receptacle, which is then

rotated 1.4 times clockwise.

Some cells may not have a device to secure them. In this case simply fit the cell in the

receptacle. Close the cell at the bottom with the lid containing a filter. Firmly push the

lid against the paper filter and turn to the right to tighten.

This will push the paper filter against the O-ring at the base of the cell. At this point, the

cell is pressurised by a carbon dioxide cylinder. A bleeder valve releases pressure

before disassembly. Do not use N2O (nitrogen oxide) for this step.




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Figure 5: A filter press.

12.3 API fluid loss

12.3.1 Procedure

1. Ensure a pressure of 100 psi (7 Kg/cm2) with gas or air.

2. Remove the lid from the bottom of the clean, dry cell. Fit the O-ring

making sure the seating is not damaged, then turn over. Any mechanical

flaw may affect the seal of the cell. Cover the hole with a finger.

3. Fill the cell with mud to 1.4” from the O-ring housing. Put the paper filter

(Whatman No. 50 or equivalent) above the O-ring. Put the lid on the

paper filter with the flanges between the flanges of the cell, then turn

clockwise and close. Turn the cell upside down and fit the male cell in

the female cell of the filter press and turn in both directions to close.

4. Put a graduated cylinder below the filtrate outlet to collect filtrate.

GraduatedCylinder

Carbone dioxide cartridges

Cell

Cell




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5. Open the valve to pressurise the cell. The needle on the pressure gauge

will immediately move, probably indicating higher pressures during

pressurisation. The needle will then stabilise at 100 psi.

6. API recommends a 30 minute test time. Close the valve after the test to

stop pressure at source. Bleeding will be automatic. Remove the cell.

7. Record the fluid loss in millilitres (unless otherwise requested).

8. Remove the cell, remove the mud and carefully remove the paper filter,

making sure the filter cake is not damaged. Wash the cake carefully to

eliminate excess mud. Measure the panel thickness in 32”.

12.4 High temperature high pressure (HTHP) filtration - MB style (API #II) HTHP filter

press

12.4.3 Description

The system in figure 6 comprises a heating jack with thermostat, cell assembly

and primary and final pressure sensor. The mud cell has a 160 ml capacity and

a filtering area of 3.5 square inches.

The filtrate receiver has a 15 cm3 capacity and the glass tube can withstand a

final pressure of up to 100 psi. If a higher pressure is necessary, stainless steel

rather than glass tubes will have to be used in routine tests with a temperature

of 300°F and differential pressure of 500 psi.

High temperature filtrate should be recorded as a dual value in relation to the

number of millilitres lost in 30 minutes. Filtering area = 3.5 square inches.




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Figure 6: HTHP Filter Press.

12.4.4 Procedure

1. Turn on the heating unit and wait for the system to reach the pre-heating

temperature. Put the thermometer in its housing and adjust the

thermostat to obtain a temperature which is 10 °F higher than the value

required.

2. Close the cell inlet valve and turn the cell upside down.

3. Collect mud from the flow line. Put it inside the container up to 0.2”

below the O-ring housing and wait for expansion.

4. Put a paper filter in the housing and the O-ring on top. Use a Whatman

no. 50 filter or equivalent.

5. Put the lid on top of the paper filter and secure.

6. Secure lids manually and close the blowdown valve.




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7. With the lid on the bottom of the cell, put the cell in the oven, making

sure all valves are closed. Put the thermometer in its housing.

8. Insert the CO2 cylinder in the primary pressure inlet, and tighten until it

opens. Make sure the regulator and bleeder valve are closed.

9. Raise the stop ring, put the primary pressure unit in the upper housing

and let the stop ring close.

10. Apply a pressure of 100 psi to the top valve, then open to pressurise the

unit. This pressure will minimise boiling when the sample is being

heated.

11. If the test temperature is equal to or above boiling point, always use a

bleeder collector to prevent the filtrate from vaporising. Fit and activate

the CO2 cylinder in the bleeder unit.

12. Put the bleeder unit in its housing.

13. Apply a pressure of 100 psi to the bottom unit, while the valve is still

closed.

14. After reaching the required temperature (300°F), (shown on the

thermometer), increase the pressure in the top cell regulator from 100 to

600 psi, keeping a pressure of 100 psi with the bottom regulator. Open

the valve (turn once) of the bottom cell and start the test.

15. Maintain a pressure of 100 psi on the receiver during the test. If

pressure increases, discharge a small amount of the filtrate and maintain

a differential pressure of 500 psi. Keep the temperature at ±5°F.

16. After 30 minutes of filtration, close the bottom cell valve and then the top

cell valve.

17. Loosen both T-screws in the regulator and release pressure from both

regulators.

18. Discharge the filtrate into the graduated cylinder and record the volume.

Remove the receiver.




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19. Disconnect the primary pressure unit; lift the stop ring and remove the

unit. WARNING: the cell is pressurized.

20. Keep the cell in an upright position and leave to cool at room

temperature, then release the pressure. Do not let mud come out from

the valve.

21. Turn the cell upside down, loosen the screws on the lid (use an Allen key

if necessary) and disassemble. Clean and dry the parts.

12.4.5 API # I HTHP filter press

The HTHP fluid loss test is carried out with a temperature of 300°F (148°C) and

differential pressure of 500 psi.

12.4.6 Description

1. Oven on a stand.

2. Cell for samples, to work at a pressure of 1000 psi. (filter surface area -

3.5 square inches).

3. Thermometer or electronic thermocouple (readings < 500°F [260°C]).

4. Top regulator suitable for adjusting pressure up to 1000 psi, starting from

any pressure source.

5. Filtrate receiver (recommended capacity - 100 cm3) tested to work at a

pressure of at least 500 psi.

6. Graduated cylinder to recover the sample (METAL)

NOTE: Take great care when carrying out an HTHP test. Make sure all

equipment is kept in safe conditions.




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Tests at temperatures equal to or below 300°F (149°C)

1. Connect the oven to the mains, make sure the voltage is appropriate.

Put the thermometer in its housing.

2. Heat the oven to 10°F higher than the test temperature and maintain at

this temperature, adjusting the thermometer if necessary. Check and

replace the O-rings if necessary.

3. Agitate the sample for 10 minutes and pour into the cell, making sure the

cell valve is closed. The cell should not be filled up more than 1.2 inches

from the edge.

4. Put a paper filter (Whatman no. 50 or equivalent) on the edge.

5. Put the lid on, align and tighten the Allen screws. Make sure the valves

are closed and put the cell in the oven. Screw the cell down on the

stand. NOTE: the cell is fitted on the stand with the end containing the

filter facing downwards.

6. Install the thermometer in its housing.

7. Put the pressure sensor in the top valve and secure.

8. Install the low pressure receiver in the bottom valve and secure (figure

7).

9. Apply 100 psi to both pressure units and open the top valve, turning it 90

degrees anticlockwise.

10. After the test temperature has been reached, increase the pressure in

the top unit to 600 psi, open the bottom valve 90° clockwise to start

filtration. Recover the filtrate in a graduated container for 30 minutes.

11. The temperature should be kept within ±5°F during the test. Discharge

the filtrate until external pressure is above 100 psi.




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12. After 30 minutes, close both valves and loosen the safety screws on the

regulator. Discharge the filtrate and release the pressure from the

bottom valve and remaining pressure from the top valve. Disassemble

the regulator and valve. Remove the cell from the oven and leave to cool

to room temperature, in an upright position. Be careful of residual

pressure inside the cell.

13. When cooling the cell, measure the amount of recovered filtrate and

record a value which is twofold the result. Record the filtrate in

millimetres, along with the test temperature and differential pressure.

14. After cooling the cell, carefully release the pressure from the top part, i.e.

the opposite part from the paper filter. Close the valve, then carefully

open the opposite part, to release the pressure. Make sure all pressure

has been released from the cell and sample before disassembly.

Note: Do not exceed the pressure, volume and temperature limits recommended

in the user’s manual.

Table 8: Steam pressure and water volume expansion between 212° and 450°F withrecommended external pressure

Test temperature Steam pressure

Water expansion volumecoefficient at saturation

pressure Recommendedexternal pressure

° F °C kPa Psi kPa psi

212 100 101 14.7 1.04 689 100

250 121 207 30 1.06 689 100

300 149 462 67 1.09 689 100

350 177 931 135 1.12 1104 160

400 205 1703 247 1.16 1898 275

450 232 2917 422 1.21 3105 450




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Figure 7: HTHP filter press with CO2 pressurization (sectioned)

Testing at temperatures from 300 - 400°F (149°C - 233°C)

The same procedures are used, apart from the following cases when a 500 ml

cell should be used, pressurising the manifold with nitrogen:

1. Heat the sample and pressurize both units to 450 psi. Start the test; the

upper pressure will increase to 950 psi, while the lower pressure will

remain at 450 psi.

2. A porous stainless steel disk (Dynalloy X5 or equivalent) should be used

instead of a paper filter when temperatures range from 350°F to 400°F

(see API RP 13B-1 and 13B-2).

3. The sample should not be heated for more than 1 hour. 12.4.3 Filter

cake compressibility

12.4.7 Filter cake compressibility

The same procedure for temperatures of 300°F (149°C) is used, but a pressure

of 200 psi is applied to the cell and of 100 psi to the bottom receiver. The

differential values for 100 and 500 psi are then compared.




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13.0 SAND CONTENT

13.1 Instruments

Sand content in mud is estimated using a sand sieve. The sieve test is widely used at

rigsites as it is simple.

13.2 Sand content testing kit

13.2.1 Description

The sand content testing kit (figure 8) has a 21.2 inch diameter opening, a 200mesh (74 micron) screen, a funnel below the screen and a graduated glass

container to measure mud volume, and consequently the percentage of sand on

the bottom of the container, which is graduated from 0 to 20%.

13.2.2 Procedure

1. Fill the glass container with mud up to the first mark. Add water to bring

the volume up to the second mark. Put your thumb over the container

opening and strongly agitate.

2. Pour the mixture onto the sieve. Pour more water into the container,

agitate and pour onto the sieve. Continue until the water is clean. Wash

the sand retained on the sieve.

3. Put the funnel above the opening. Insert the funnel end in the opening of

the glass container. Wash the sand from the sieve and let it run into the

container, with a little water. Leave the sand to decant. Read the sand

percentage from the graduation marks at the bottom of the container.




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Figure 8 : Sand content testing kit

14.0 SOLID AND LIQUID CONTENT

14.1 Instruments

Mud can be distilled by heating (see figure 9) in order to determine the amounts of liquids

and solids present (10-, 20- or 50- cm3 distillers). Distillers with an internal probe are not

recommended. Fill the container to the top with the mud sample, then put the lid on,

letting a little liquid leak out to ensure the volume is exact. Heat up until the liquid

components have vaporised. The vapours will be conveyed through the condenser to a

graduated cylinder, which usually indicates the percentage, so the volume of liquid – the

oil and water – is measured as a percentage. Suspended and dissolved solids are then

determined deducting 100% or recording the empty space at the top of the cylinder.

Elutiometer




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Figure 9 : Oil and mud distillation kitRetort Condenser

14.2 Description of the distiller

14.2.1 Procedure

1. Leave the mud to cool to room temperature.

2. Disassemble the distiller and lubricate the thread of the cup with grease

suitable for high temperatures. Fill the cup with mud nearly to the top.

Put the lid on, rotate strongly and let any excess fluid flow out, to obtain a

mud volume or 10, 20 or 50 cm3. Dry any traces of mud.

3. Fill the top expansion chamber with steel wool. The chamber will retain

the solids left after the mud has been boiled. Keep the assembly in an

upright position, to make sure the mud does not flow down the outlet.

4. Fit or tighten the outlet in the hole at the end of the condenser. Put the

graduated cylinder, which is calibrated to record the percentage, in the

condenser.

R

e t o r t A s s e m b l y




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5. Connect to the mains and keep on until distillation is finished. This might

take up to 25 minutes, depending on the characteristics of the oil, water

and solids.

6. Allow the distillate to cool to room temperature.

7. Read the % of water, oil and solids. A few drops of aerosol solution will

help to define the oil-water interface; read the percentage of solids.

8. Cool the distiller after the test, then clean and dry.

9. Carefully clean the condenser hole and outlet with a small pig. NOTE:

make sure the outlet is not obstructed in any way.

14.2.2 Percentage from analysing the volume of solids, weight method

(calculating the difference in weight using a conventional distiller).

14.2.3 Equipment

1. Conventional balance

2. Conventional 20 cm

3

distiller (with oven).

3. Analytical scales with a 0.01 g accuracy.

1. Record the following values:

A. Mud weight.

B. Distiller weight (including steel wool and cup)

C. Distiller weight with whole mud.

D. Distiller weight with mud solids.




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14.2.4 Procedure

1. Prepare the distiller with the steel wool and cup. Record the weight (in

grams). Value B.

2. Disassemble the distiller and fill the cup with mud. The volume or lid do

not have to be determined, as volumes are calculated with the weigh-

in/out procedure. Weigh and disassemble the distiller. Value C.

3. Use the distiller as normal (water and traces of oil).

4. Cool and weigh the distiller again. Value D.

Calculations

Calculate:

1. The mud density (g/cm3); SGMUD = mud density (lb/gal) x 0.11994.

2. Grams of mud in the distiller: g of mud = Value C – Value B.

3. Grams or cm3

of distilled water: Value C – Value D. Calculate the volume(%) of solids. The solids fraction = [(C – B) – SGMUD x (C – D)] / (C –

B) % solids = 100 x solids fraction volume

Example:

With four measurements from a rigsite mud:

A) 12.70 lb/gal

B) 317.45 g

C) 348.31 g

D) 332.69 g i.e. :

#1 = 12.70 lb/gal [0.1194gallb

cmg

/

/3

] = 1.523 g/cm3




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#2 = 348.31 – 317.45 = 30.86 g of mud

#3 = 348.31 – 332.69 = 15.62 g of water

The volume of the solids fraction = [30.86 – (1.52 x 15.62) ] / (30.86)

= 7.12 / 3086

= 0.2307

% solids = 100 x 0.2307 = 23.07%

14.3 Methylene blue capacity test

Rigsite procedure to determine cation exchange capacity.

14.3.1 Equipment

1. 3 cm3 syringe, 10 cm3 burette.

2. 0.5 cm3 micro pipette.

3. 250 cm3 graduated Erlenmeyer flask, with rubber cap.

4. 10 cm3 burette or pipette.

5. 50 cm3 graduated cylinder.

6. Mixing blade.

7. Hot plate

8. Whatman no. 1 or equivalent paper filter, 11 cm in diameter.

14.3.2 Reagents

1. Methylene blue solution: 1 cm3 = 0.01 milliequivalents 3.74 g of

methylene blue, USP grade (C16H18N3SCl•3H2O) per litre.

2. Hydrogen peroxide (3% solution).

3. 5 N sulphuric acid solution.




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14.3.3 Procedure

1. Add 2 cm3 of mud (or a suitable mud volume for 2 - 10 cm3 of reagent) to

10 cm3 of water in the Erlenmeyer flask. Add 15 cm3 of hydrogen

peroxide (3% solution), 0.5 cm3 of 5 N sulphuric acid solution and mix

with a blender before heating.

2. Boil on simmer for 10 minutes. Dilute with water to 50 cm3. NOTE:

besides bentonite, drillings fluids contain other substances which absorb

methylene blue. Using hydrogen peroxides allows the effect of organic

materials such as CMC, polyacrylates, lignosulfonates and lignins to be

neutralised.

3. Use a burette or pipette to add 0.5 cm3 of methylene blue solution at a

time.

4. After each dose, put the rubber cap on and agitate for approximately half

a minute.

5. Use a glass rod to collect a drop while the solids are still suspended

6. and place on the paper filter. Titration is finished when a greenish blue

streak appears around the solids deposited on the filter.

7. As soon as the greenish blue colour appears, shake the ampoule bottle

for another 2 minutes and repeat the test putting another drop on the

paper filter.

8. If the greenish blue streak is strong, the end point has been reached. If

the streak does not appear, continue until it develops.

9. Record the cm3 of methylene blue solution used.

10. Methylene blue capacity of mud; MBC imperial system (lb/bbl) = (of

methylene blue/cm3 of mud) x 5 MBC metric system (kg/m3) = (cm3 of

methylene blue/cm3 of mud) x 14 CEC (cation exchange capacity )= cm3

methylene blue / cm3 mud.




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14.4 Methylene blue capacity of clay

14.4.1 Methylene blue capacity (bentonite equivalent)

MBC imperial system (lb/bbl) = CEC x 5

MBC metric system (kg/m3) = CEC x 14

14.4.2 Cation exchange capacity of clays

Carefully weigh 1 g of dried, ground gypsum. Put in an Erlenmeyer flask and

add 50 cm

3

of deionised water. Boil on a low heat for 10 minutes with 0.5 cm

3

5N of sulphuric acid. Leave to cool and titrate, adding 0.5 cm3 at a time of 0.01 N

blue methylene solution.

CEC in milliequivalents/100 g of gypsum = (cm3 of methylene blue) / (g of

titrated gypsum)

FLOCCULATION EFFICIENCY TEST

14.4.3 Procedure

1. Measure 100 cm3 of service water, collected from the drilling rig flow line,

in a graduated cylinder.

2. Add 1 cm3 of 1%* flocculating solution to the graduated cylinder.

3. Slowly turn the cylinder upside down, 3 or 4 times, then rest on a flat

surface.

4. Record the time (seconds) it takes for flakes to form and leave to decant

to the 40 cm3

mark in the graduated cylinder.

5. Repeat for each flocculant. If flakes do not form, a flocculent is not

necessary. Repeat the test at least every two days.

6. The quickest acting flocculant should be used.




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15.0 CONCENTRATION OF HYDROGEN IONS (PH)

15.1 Scope

Recording and adjusting the pH of mud (or filtrate) is fundamental in controlling drilling

fluids. Interactions with clay, the solubility of various components and effectiveness of

additives depend on the pH; this also applies when acid and sulphate-induced corrosion.

Two methods are used to detect and measure the pH of filtrate in muds: litmus papers

and the potentiometric method, using a pH meter with glass electrode.

15.2 Litmus (or pH) papers

15.2.1 Description

Litmus papers (figure 10) are treated so that their colour changes depending on

the pH of the fluid soaking the papers. The kit includes a complete colour

palette for the entire pH range, for easier correlation.

15.2.2 Procedure

1. Put a litmus paper in the mud or filtrate, and wait for the colour tostabilise, which should take less than a minute. Rinse the paper with

distilled water but do not dry.

2. Compare the colour of the paper with the kit colour palette to estimate

the pH of the mud.

3. Record the pH of the mud, rounding the value up or down by 0.5.

Figure 10 : Litmus

paper.




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15.3 pH meter

15.3.1 Description

The recommended method for accurately measuring the pH of drilling fluids is to

use a pH meter with electronic electrode (figure 11). This is an precise and

reliable way to determine pH values, without interference. Readouts are easy,

quick and self-adjusting with temperature variations.

15.3.2 Equipment

The portable pH meter consists of a probe and digital read out. The probe has:

- a glass electrode

- a standard reference electrode

- a temperature sensor (optional)

15.3.3 Procedure

The following method is recommended for recording the pH:

(1) Calibrate the instrument,

(2) Determine the pH of a sample,

(3) Clean and store the probe.

Figure 11 : ph Meter.




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1. Remove the cap and rinse the probe with distilled water. Dry carefully.

2. Let the mud reach the temperature of the probe and buffers; this should

be around 75±5°F (24±3°C).

3. Measure the buffer temperature with a pH of 7. Put the probe in the

buffer solution with a pH of 7 and start the reader. Wait for the reading to

stabilise.

4. Adjust the knob to a temperature corresponding to a buffer solution pH of

7. Adjust the knob to calibrate the reader.

5. Rinse the electrode with distilled water and dry delicately.

6. Repeat steps 4 and 5 using a buffer with a pH of 4 and 10. Select the

buffer closest to the pH of the sample (usually for muds with a pH of 10).

If the pH reading is not correct, adjust the calibration knob accordingly.

Rinse the electrode with distilled water and dry carefully. Put the probe

back in the buffer solution with a pH of 7 and then retest the pH. If the

same pH is recorded, turn the calibration screw to adjust the pH reading

to the correct value. Repeat step 6 until values are correct.

7. Complete the calibration with the two buffers, rinse the probe and dry

carefully. Put the probe back in the sample and agitate carefully. Wait

for the value to stabilise.

8. Record the temperature of the sample in °F or °C. Record the pH of the

sample to the nearest decimal point.

9. Disconnect the equipment. Wash the probe with distilled water.

Saturate the cotton in the cap with a buffer that has a pH of 4. Put the

cap back on the probe.

10. Turn off the equipment and put in its case.

15.3.4 Cleaning

1. Electrodes must be cleaned regularly, and particularly when particles of

oil or gypsum have stuck on the surface of the glass electrode or on

porous electrode surfaces. Clean the electrodes with a soft brush and

mild detergent.




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2. Electrodes should be reconditioned if there is too much build up.

3. To recondition the electrodes, put in 0.1 molar HCl solution for 10

minutes, rinse thoroughly with water, put in 0.1 molar NaOH solution for

10 minutes and rinse with water.

4. Test the electrodes again, following the calibration procedure.

5. Only qualified personnel should carry out the next step. If no reaction

takes places, put the electrode in a solution with 10% NH4F HF for a

maximum of 2 minutes. (WARNING: this acid is extremely corrosive and

hazardous). Repeat the calibration steps.

6. If this procedure does not work, replace the electrode system and

recondition the electrodes.

15.3.5 Principle of equivalent solutions

1. A solution is defined as equivalent when one litre contains an amount of

salt (in grams) which is equal to the equivalent weight; for example

NaCl= 58.44 grams (molecular weight/valence).

2. The equivalent weight is given by: the molecular weight/valence, for

example AgNO3 = 169.89/2 g = 84.94 g

3. Equivalent solutions are “corresponding” i.e.: 1 litre of AgNO3 N/1

(containing 84.94 g), reacts in the exactly the same way as one litre of

NaCl n/1 (containing 58.44 g), according to the reaction

4. AgNO3+NaCL = NaNO3+AgCL (white precipitate)




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16.0 CHEMICAL ANALYSIS OF WATER IN MUDS

16.1 Alkalinity (Pf , Mf , Pm) and lime content

16.1.1 Equipment

The following materials and products are required to determine the alkalinity of

mud and its lime content:

1. Standard acid solution, 0.02 N (N/50); nitric or sulphuric acid

(NOTE: A 0.1N (N/10) acid solution can be used as an alternative, but should beconverted to the equivalent of ml 0.02 N multiplied by 5).

2. Phenolphthalein solution indicator.

3. Methyl orange/bromocresol green as an indicator. API recommends

methyl orange (from yellow to pink).

4. A 100 – 150 cm3 titration beaker, preferably white.

5. Graduated pipettes: from 1 cm3 - 10 cm3.

6. Stirring rod.

7. A 1 cm3 syringe.

8. A pH meter with glass electrode (optional, but recommended).




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16.1.2 Procedure to test filtrate alkalinity (Pf and Mf)

1. Measure 1 cm3 of filtrate in the titration beaker, then add 5 cm 3 of

deionised water.

2. Add 2 or more drops of phenolphthalein indicator. The solution will turn

pink.

3. Add N/50 acid, in drops, agitate until the pink has disappeared. If the

colour of the sample is so strong that it cannot be defined, the endpoint

should be recorded when the pH has dropped to below 8.3, recorded

using a pH meter with glass electrode (the sample can be diluted with

distilled water).

4. Record the alkalinity of the phenolphthalein of the filtrate, Pf, in cm3 of

0.02 N acid required for every cm3 of filtrate to reach the endpoint.

5. Add 3 to 4 drops of methyl orange/bromocresol green indicator to the

sample used to measure the Pf;

6. The reaction will produce a green colour.

7. Titrate with 0.02 N acid until the solution turns yellow (at a pH of 4.3).

8. The Mf is recorded as the amount in millilitres of acid used for the Pf in

addition to the last titration.

Example:

If you use 0.5 cm3 of acid to titrate the endpoint of phenolphthalein the Pf will be

0.5

Procedure BaCl2:

1. Measure 1 cm3 of filtrate in a titration beaker.

2. Add 2 drops of 10% barium chloride solution (NOTE: BaCl2 is poisonous;

do not aspirate with the pipette).

3. Repeat steps 2 to 4 to titrate the Pf.




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4. As a basic rule, carbonate contamination is present if the alkalinity of the

BaCl2 is one and a half times, or less, the previous titration of the Pf.

Example:

If you use 1 cm3 of acid to titrate the Pf, the Pf is equal to 1.0.

If you use 0.5 cm3 of acid to titrate the alkalinity endpoint with BaCl2, the value of

BaCl2 will be 0.5. So carbonate contamination is present, as the value of BaCl2

is less than half the Pf.

16.1.3 Procedure to test mud alkalinity (Pm)

1. Measure 1 cm3 of mud in the titration beaker, using a syringe. Dilute the

sample with 25 cm3 of distilled water. Add 5 drops of phenolphthalein

indicator, agitate and quickly titrate with 0.02 N or 0.1 N acid until the

pink colour has completely disappeared.

2. If the change cannot be determined because the colour is so strong,

record the endpoint when the pH has dropped below 8.3, as recorded

from the measurement taken with the glass electrode (ph meter).

3. Record the alkalinity of the phenolphthalein in the mud, Pm, as the cm3

of 0.02 N (N/50) acid required for every cm3

of mud. If 0.1 N acid is used,

Pm = 5 x cm3

of 0.1 N acid per cm3

of mud.

16.1.4 Procedure to test calcium content (excess lime)

Determine the Pf and Pm, as follows.

Determine the fraction of the water volume in mud, Fw (decimal fractions of

water), using the values recorded in the retort test (mud still). Record the lime

content in the mud in lb/bbl, calculated from the following formula:

Lime (lb/bbl) = 0.26 x (Pm -FwPf ). Or lime (Kg/mc)=0.742(Pm-FwxPf) AGIP

manual. 1996




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16.1.5 Filtrate alkalinity: P1 and P2

16.1.6 Equipment

1. Standardized solution of 0.02 N (N/50) sulphuric acid.

2. 0.1 N (N/10) sodium hydroxide solution.

3. 10% barium chloride solution.

4. Phenolphthalein indicator.

5. Deionized water.

6. Litmus papers or glass electrode indicator.

7. 100 to 150 cm3 titration beaker, preferably white.

8. Pipette: one 1- cm3, one 2-ml and one 10- cm3 pipette.

9. Graduated cylinder, one 25 cm3 and one 5 or 10 cm3 cylinder.

10. Stirring rod. Procedure: P1 - P2




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16.1.7 Procedure

1. Measure 1 cm3 of filtrate in the titration beaker and add 24 cm3 of

deionized water.

2. Add 2 cm3 of 0.1 N sodium hydroxide and agitate. Measure the pH with

a litmus paper or glass electrode pH meter. If the pH is the same as or

above 11.4 continue with the next step. If the pH is less than 11.4, add a

further 2 ml of 0.1 N sodium hydroxide.

3. Measure 2 cm3 of barium chloride using the graduated cylinder and add

to the titration beaker. Add 2 to 4 drops of phenolphthalein and agitate.

NOTE: Do not aspirate from the pipette; barium chloride is poisonous.

4. Titrate immediately with sulphuric acid, as soon as the purple colour

disappears (or when you record a pH of 8.3 using the pH meter). If the

colour reappears after a short time, continue with titration.

5. Record the alkalinity, P1, as the amount in cm3 of 0.02 sulphuric acid

required to titrate to the phenolphthalein endpoint.

Procedure P2

1. Put the filtrate on one side, or repeat the procedure for P1 using exactly

the same amounts of water and reagents. Titrate following the same

procedure used for P1.

2. Record the alkalinity, P2, in ml of 0.02 N sulphuric acid required to titrate

to the phenolphthalein endpoint.

Calculations

Within limits, ion alkalinities can be calculated as follows:

Where P1 > P2

OH– (mg/l) = 340 x (P1 – P2)

CO3

2–

(mg/l) = 1,200 x [Pf – (P1 – P2)]




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Where P1 < P2

–

HCO3 (mg/l) = 1,220 x (P2 – P1)

CO3

2–

(mg/l) = 1,200 x Pf

16.2 GARRETT GAS TRAIN (GGT) test for carbonates

16.2.1 Scope

The Garrett Gas Train test is used to analyse soluble carbonates in mud filtrate.

A CO2 Dräger tube reacts to the gas and turns purple. The length of the stain

indicates the concentration of CO2 as well as the rate and volume of gas passing

through the tube. However the gas must be captured in a 1 litre bag so the CO2

can mix uniformly with the gas. The CO2 Dräger tube may give incorrect

readings, if not used properly.

The filtrate must not contain solids and the first jet of filtrate must not be used as

it contains CaCO3; this could lead to excessively high values.

Apply 10 strokes of the Dräger hand pump to covey the contents of the bag

through the Dräger tube. This will make 1 litre of gas flow through the tube.

16.2.2 Equipment

1. Deionized water.

2. Octyl alcohol defoamer.

3. Approximately 5 N sulphuric acid.

4. Garrett Gas Train (figure 12).

5. Dräger tube for CO2 analysis, “CO2 100/a” marked from 100 to 3,000

ppm. Factor = 2.5 (make sure the factor does not change).

6. 1 litre #762425 Dräger bag.

7. Dräger hand pump for the multigas detector vacuum.

8. Two-way 8 mm graduated tube.




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9. Hypodermic syringes: one 10 cm3 syringe, with 21 needles suitable for

acid, one 5 cm3 syringe and one 2.5 cm3 syringe.

10. Cartridges for N2O recharging. Nitrogen or helium may also be used.

Figure 12 : Garrett Gas Train

16.2.3 Procedure

1. Make sure equipment is clean and resting on a flat surface.

2. Install the N2O cartridge and activate, with the regulator set to zero. Do

not use CO2 cartridges or compressed air.

3. Add 20 cm3 of deionized water to Chamber 1.

4. Add 5 drops of defoamer to Chamber 1.

5. Put the cover on the gas train and tighten uniformly to seal the O-rings.

6. Turn the regulator knob anti-clockwise to prevent pressurisation.

Connect the tubing to the dispersion tube in Chamber 1. Install and

activate the N2O cartridge.

7. Adjust the bleed line in chamber 1, so it is ¼” from the end.




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8. Refer to table 3, to the carbonate scale and Dräger tube, for the volume

required.

9. Turn the regulator knob clockwise for 1 minute, to release air from the

system and bleed the transport gas. Make sure there are no leaks.

Close the gas valve.

10. Connect to the gas bag and close the hand pump valve. Use a reject

Dräger tube for the connection and empty the bag.

11. Lift the hand pump entirely and compress again. The pump will stay

raised for several minutes when completely empty and if there are no

leaks. If there are leaks, intercept them, inspecting all connections, as

explained below. If there is a leak in the bag, replace.

Note: Insert a Dräger tube, closed at one end, in the pump and lower the

membrane to check the pump. If there are no leaks, the membrane will stay

lowered.

12. Make sure the bag is entirely compressed, then fit the rubber tubing from

the valve and from the bag to the outlet of chamber 3. Close the valve.

13. Use a hypodermic syringe with needle to inject the filtrate without solids

into chamber 1 via the rubber membrane. Measure the volume.

14. Use a hypodermic syringe with needle to slowly inject 10 cm3

of sulphuric

acid into chamber 1 via the rubber membrane. Gently shake the gas

receptacle to mix the acid with the sample in chamber 1.

15. Remove the tube from the outlet of chamber 3. Break off the ends

(make sure the arrow indicates the direction of the flow), then fit on the

side upstream the CO2 Dräger tube. Connect the Dräger hand pump to

the other end of the Dräger tube.

16. Open the bag valve. Slowly open the N2O cartridge to fill the bag, then

close and close the valve. Immediately go on to step 17.




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Figure 13 : Check losses into gas pocket.

Figure 14: GGT with gas bag for carbonate testing.

17. Remove the tube from the outlet of chamber 3. Break off the ends(make sure the arrow is in the direction of the flow), then fit on the side

upstream the CO2 Dräger tube. Connect the small pump to the opposite

end of the Dräger tube

18. Open the bag valve. Lower the pump lever, then let the gas flow out of

the bag via the Dräger tube. 10 pump strokes should be sufficient to

empty the gas bag.




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19. A pinkish deposit inside the tube indicates the presence of CO2. Record

the length, in line with the graduated scale, including the slight blue

shade.

16.2.4 Selecting the Dräger tube

Table 9: Volume of samples and type of tube to use to define carbonatescales

1 Carbonatescale (mg/l)

2 VolumeSample (cm3)

3 Selecting theDräger tube

4 Tube factor

25 - 750 10 CO2 100/a 2.5*

50 - 1,500 5 CO2 100/a 2.5*

100 - 3,000 2.5 CO2 100/a 2.5*

250 - 7,500 1 CO2 100/a 2.5*

*NOTE: The tube factor “2.5” refers to new CO2 100/a tubes (cat. no. 8101811)

with a 100 - 3,000 scale. Use a factor of 25,000 with a scale from 0.01 to 0.3%

for old tubes.

Calculations

Measure the sample volume, the length of the purple deposit in the Dräger tube

and tube factor of 2.5 (Table 9) to calculate the soluble carbonates in the filtrate

of the sample, with the following formula:

CO2–

(mg/l) = (length in the tube x 2.5) / cm3

of filtrate

NOTE: the gas train must be cleaned after use to prevent acid-induced

corrosion. Remove the tubing and top. Wash the chambers with lukewarm

water, a mild detergent and brush. Use a small pig to clean the ducts between

the chambers. Wash, rinse and jet air to eliminate residues. Do not use nitric

oxide for any other test, not even as a gas as it may cause explosions if used

incorrectly.




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16.3 Chlorides (Cl –)

16.3.1 Scope

Chloride testing is very important in zones where salt may contaminate the mud.

The chloride ion content is an excellent indicator when drilling, for example, salt

formations or salt water zones, and is also suitable for checking the quality of

service water.

Chloride ions (Cl-

) are analyzed by titrating the sample of filtrate, using silver

(Ag+

), to reach a red colour from the endpoint of silver chromate with potassium

chromate as an indicator.

16.3.2 Equipment

The following items are required to determine the concentration of chloride ions

in the filtrate.

1. Silver nitrate solution, 0.0282N or 0.282N (strong) AgNO3, stored in an

opaque bottle. A strength of 0.1N and 1N is used by ENI, Italy.

2. Potassium chromate indicator solution.

3. 0.02 sulphuric or nitric acid solution.

4. Distilled water.

5. Two graduated pipettes: one 1 cm3

and one 10 cm3

pipette.

6. A 100 - 150 cm3

titration beaker, preferably white.

7. Small glass spatula.

16.3.3 Light coloured filtrates

16.3.4 Procedure

1. Measure 1 cm3 of filtrate in the titration beaker.

2. Add 2-3 drops of phenolphthalein indicator.




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3. If the indicator turns pink, agitate with the glass spatula and add 0.02N

(N/50) sulphuric acid in drops until the colour disappears.

4. Add 50 cm3 of deionized water and 10 drops of potassium chromate.

5. Add silver nitrate solution (0.0282N for chlorides <10,000 mg/L and

0.282N for chlorides >10,000 mg/L.) and agitate until the yellow turns to

orange red and stays this colour for 30 seconds.

Record the cm3 of silver nitrate required to reach the endpoint. If the

concentration of chloride ions in the filtrate is < 10,000 mg/l, use 0.0282N silver

nitrate solution equivalent to 0.001 g Cl –

ions per cm3.

Record the concentration of chloride ions in the filtrate in mg/l, calculated as

follows:

Cl –

(mg/l) = cm3 of 0.0282 N silver nitrate x 1,000 / cm3 of filtrate for any normal

silver nitrate or 0.1N (frequently used by ENI):

Cl –

(mg/l) = (N x 35,000 x cm3 used) / (cm3 of filtrate of sample) CL(mg/l) =

(0.1Nx3500x cm3 used/( cm3 of filtrate of sample). As salinity is expressed as

NaCL (mg/l), the factors will be 58000 and 5800 rather than 35000 and 3500.




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Table 10 Chloride titration

Chlorides (Cl) – Light coloured filtratesChemical analysis

Column 1 Column 2

Sample 1 cm3 of filtrate 1 cm3 of filtrate

Deionized water No 25-50 cm3

Buffer No No

Colour indicator2-3 drops ofphenolphthalein

8-10 drops of potassiumchromate

Titrated with:(Titrator)

0.02 (N/50) H2SO4 (sulphuric acid)

0.028N AgNO3 or 0.282N AgNO3 * (silver nitrate)

Colour changeFiltrate, from pink tooriginal

From yellow to orange red

Record No

(cm3 of 0.0282 N AgNO3 x1,000) / cm3 of filtrate or(cm3 of 0.282 N AgNO3 x10,000 ) / cm3 of filtrate

Note: Go to col. 2

*Chlorides: 10,000 mg/l if <use: 0.0282 N AgNO3 if >

use: 0.282 N AgNO3

16.3.5 Dark coloured filtrates

16.3.6 Procedure

1. Measure 1 cm3 of filtrate in a titration beaker.

2. Add 2-3 drops pf phenolphthalein. If the solution is too dark, add 2 cm3

of 0.02N (N/50) sulphuric acid and agitate.

3. Add 1 g of calcium carbonate to this solution and agitate, adding 50 cm3

of deionized water and 10 drops of potassium chromate solution.

4. Continue to agitate. Add silver nitrate using a pipette (0.0282N for

chlorides <10,000 mg/l, and 0.282N for chlorides >10,000 mg/l) until the

yellow turns to orange red and stays this colour for approximately 30

seconds.

5. Record the cm3 of silver nitrate solution to reach the endpoint.

Calculations




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Record the concentration of chloride ions in the filtrate in mg/l. If the

concentration is <10,000 mg/l, use 0.0282N silver nitrate solution or equivalent

to 0.001 g Cl –

ions per 3cm. Cl –

(mg/l) = cm3 of 0.0282 N silver nitrate x 1,000 /

cm3 of filtrate. If the concentration is >10,000 mg/l, use 0.0282N silver nitrate

solution or equivalent to 0.001 g Cl –

ions per cm3.

Cl –

(mg/l) = (cm3 of 0.282 N silver nitrate x 10,000 ) / cm3 of filtrate




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Table 11 Chloride titration chart

Chlorides (Cl) – Dark coloured filtratesChemical analysis

Column 1 Column 2

Sample 1 cm3 of filtrate 1 cm3 of filtrate

Deionized water No 25-50 cm3

Buffer Non1 g CaCO3 (calcium carbonate)

Colour indicator2-3 drops ofphenolphthalein

5-10 drops of potassiumchromate

Titrated with: (Titrator)0.02 (N/50) H2SO4 (sulphuric acid)

0.028N AgNO3 o 0.282N AgNO3 *(silver nitrate)

Colour changeFrom yellow to theoriginal colour

From yellow to orange red

Record No

(cm3 of 0.0282 N AgNO3 x 1,000)/ cm3 of filtrate or (cm3 of 0.282 N AgNO3 x 10,000 ) / cm3 of filtrate

Note: Go to Col. 2

*Chlorides : 10,000 mg/l if < use:

0.0282 N AgNO3 if > use: 0.282N AgNO3

16.4 Calcium – qualitative testing

16.4.1 Scope

Hard water is water with a high mineral content, and particularly a high calcium

and magnesium content. The simplest example which shows that household

water is soft is when soap does not foam very much. Hard water is normally

present at rigsites. When drilling, clays are not very efficient if mixed with hard

water. The harder the water is, the more bentonite is required to obtain an

acceptable drilling mud. In more extreme cases, it is cheaper to treat water

chemically before making up mud, but this practice is not usually recommended

for purely economic reasons. If several types of water are available at the

rigsite, a test should be done to select the softest water.

Rigsite engineers are well aware of mud reactions when drilling through

anhydrite (calcium sulphate) or gypsum formations. Calcium can also




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contaminate cement, when running in cement plugs or drilling shale formations

with lime.

The main reason why calcium contaminates mud is a major increase in water

loss and the mud developing a high gel strength (increase in filtrate).

16.4.2 Equipment

The following items are required to effectively determine the presence of calcium

and/or magnesium.

1. Test tube

2. Dropper with saturated ammonium oxalate solution.

16.4.3 Procedure

Put 1 - 3 cm3 of filtrate in the test tube. Add a few drops of ammonium oxalate.

Record whether weak, medium or strong.

16.5 Total hardness

Water or mud filtrate hardness is mainly due to the presence of calcium (Ca++) and

magnesium (Mg++) ions. The harder the water is, the more difficult it will be for the

chemical products used to react and the efficiency of bentonite shales is affected in

particular. Moreover water hardness makes most polymer products less effective.

Hardness is analysed by titrating bivalent cations in the filtrate, using a standard

versenate reagent with an indicator that will change from a red wine to blue endpoint. In

dark coloured filtrates, there will be a greyish blue endpoint.




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16.5.1 Calcium plus magnesium – Quantitative testing

16.5.2 Equipment

1. Standard Versenate solution (EDTA) 0.01 M (1 ml = 400 mg Ca++ or

1,000 mg CaCO3).

2. Strong buffer solution (ammonium hydroxide/ammonium chloride).

3. Versenate solution as a hardness indicator (eriochrome black t)

4. 100 to 150 cm

3

titration plate, preferably white.

5. Three graduated pipettes: one, 1 cm3, one 5 cm3 and one 10 cm3pipette.


7. Distilled water.

8. Rod.

9. 8N NaOH or KOH solution.

10. Calcon or Calver II indicator.

11. Porcelain spatula.

12. Masking agent: 1:1:2 triethanolamine, tetraethylenepentamine: water

(API).

The total hardness of water or the filtrate can be determined following the

procedure described in 16.5.4, calculating the total hardness of calcium, in pm,

which is then recorded in the mud report.

Magnesium sometimes has to be tested as well, determined from the difference

between two titrations. Caustic soda, which is otherwise known as the buffer

solution, makes magnesium precipitate as a hydroxide, while the calcium is

titrated with a specific calcium indicator.




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16.5.3 Procedure (total hardness)

1. Add 50 cm3 of deionized water to the titration beaker; add 2 cm3 (20

drops) of versenate buffer solution (NH4OH base).

2. Add 10 drops of versenate hardness indicator solution (eriochrome black

t). If the deionized water contains calcium and/or magnesium, it will turn

wine red, otherwise it will stay blue.

3. While agitating the solution, titrate with standard versenate (EDTA) until

the colour changes from wine red to blue. DO NOT EXCEED THE

ENDPOINT.

Note: Steps 1-3 will eliminate the hardness of deionized water, if present.

4. Add 1 cm3 of filtrate to the deionized water. If the water contains calcium

and /or magnesium, it will turn wine red. While agitating the solution,

titrate with standard versenate (add in drops) until the colour changes

from wine red to blue.

5. Note the cm3 of versenate used (if the magnesium is measured following

the procedure in 16.5.4, record the value as “A” cm3) and calculate the

hardness in mg/l.

A = total hardness; B = hardness of calcium ; A-B = hardness of magnesium.

Calculations

Total hardness as Ca++

(mg/l) = (cm3 of versenate x 400) / (cm3 of sample)

CaCO3 (mg/l) = (cm3 of versenate x 1,000) / (cm3 of sample)

Occasionally, dark filtrates may not be easily visible at their endpoint, making it

hard to determine total hardness. The following method is recommended to

better define the endpoint. Calculations are the same.

1. Add 20 cm3 of distilled water to the titration beaker.

2. Add 1 cm3 of filtrate to the titration plate (up to 0.5 cm3,

measured

accurately; if necessary a sample >1 cm3 to reach the endpoint).




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3. Add 1 cm3 of masking agent.

4. Add 1 cm3 of strong buffer solution.

5. Add 6 drops of versenate indicator and agitate.

6. Use a pipette and titrate with a standard versenate solution until the

colour changes to blue/green. Record the ml needed for the

determination, as in the previous procedure.

Table 12 Total hardness – Titration chart

Total HardnessChemicalanalysis Column 1 Column 2

Sample No 1 cm3 of filtrate

Deionized water 50 cm3 No

Buffer

2 cm3 buffer, versenatehardness No

Colour indicator

10 drops versenatehardness indicator No

Titrate with: Standard versenate Standard versenate

Colour change

From wine red to blue. Donot exceed the endpoint

From wine red to blue

Record No(cm3 of versenate x 400)/(cm3 of sample)

Note: Go to column 2




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16.5.4 Calcium and magnesium separately

Calcium is obtained titrating the filtrate, using versenate as the reagent, then a

strong pH buffer so that the magnesium ions precipitate and only the calcium

ions are analysed.

1. Add 50 cm3

of deionized water to the titration beaker, then add 1 cm3

of

strong buffer solution for the calcium.

2. Add a small amount of indicator. If calcium is present, a wine red colour

will develop.

3. While agitating the solution, titrate with versenate (add in drops) until the

colour changes from wine red to blue. DO NOT EXCEED THE

ENDPOINT.

4. Add 1 cm3

of deionized water filtrate. If the water contains calcium, a

wine red colour will develop. While agitating the solution, titrate with

versenate (add in drops), until the colour changes from wine red to blue.

DO NOT EXCEED THE ENDPOINT.

5. Record the cm3

of versenate (note as “B” in cm3

) and calculate the

calcium in mg/l, as explained in 8.5.2.1:

A= total hardness; B= hardness of calcium; A - B = hardness of magnesium

Calculations

Calcium (mg/l) = (cm3

of versenate x 400) / (cm3

of sample) = (B x 400) / (cm3

of

sample)

The concentration of magnesium ions is determined from the difference of the

total hardness minus the calcium, multiplied by a factor of 0.6.

Magnesium in mg/L = [(Total hardness mg/L) – (Calcium mg/L)] (0.6)

or magnesium (mg/l) = (A – B) x 243) / (cm3

of sample)




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Table 13 Hardness ofcalcium/magnesium – Titration chart

Calcium Magnesium(Mg++)Chemical analysis

Column 1 Column 2

Sample No 1 cm3 of filtrate No

Deionized water 50 cm3 No No

Buffer 1 cm3 ofversenate bufferfor the hardness

of calciumNo

No

Colour indicator A small amount ofindicator

No

No

Titrated with: Versenate Versenate No

Colour change From wine red to

blue. Do notexceed theendpoint.

From wine red toblue

No

Record No (cm3 of EDTA x400)/ (cm3 ofsample)

Total Hardness –Calcium x 243

Note: Go to column 2 The calculation isbased on theresults of totalhardness and oncalcium tests.

16.6 Hardness in dark filtrates

16.6.1 Total hardness in dark filtrates – Quantitative testing

16.6.2 Scope

Problems may occur when titrating dark filtrates, due to the unpredictability of

the filtrate colour change when the endpoint is reached. The following method




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has therefore been developed and should only be used if the previous method is

not successful.

16.6.3 Equipment

1. Glacial acetic acid: (care should be taken).

2. Indicator (specific for Ca++).

3. Sodium hypochlorite 5.25%

4. Calmagite indicator

5. Sodium hydroxide; 8N NaOH.

6. Masking agent.

7. 0.01 molar versenate solution.

8. Strong buffer solution.

9. 100 cm3 beaker.

10. Two, 10 cm3 graduated cylinders. 10 cm3 graduated pipette.

11. Hot plate.

12. 1 cm3 volumetric pipette.

13. Porcelain spatula.

Method I (includes all metals titrated with versenate)

WARNING

: Make sure the area is well airy.

1. Use a 1 cm3 volumetric pipette to transfer 1 cm3 of filtrate into a 100 cm3

beaker.

2. Add 10 cm3 of chlorine (make sure it is fresh, and has not deteriorated).

Whisk to mix.




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3. Add 1 cm3 of acetic acid, whisk to mix.

4. Bring to the boil; boil at a high temperature for 5 minutes. Add deionised

water to top up the volume.

5. Remove the beaker from the hot plate and leave to cool at room

temperature. Carefully wash the outside of the beaker with deionised

water.

6. Add 1 cm3

of strong buffer solution; whisk to mix.

7. Add 6 drops of calmagite and mix. If the filtrate is hard, it will turn red.

8. Use a pipette to titrate with a versenate solution, while agitating, until the

sample has turned blue, without any traces of red. In the case of dark

filtrates, the colour will vary from purple to dark grey. Note the quantity in

ml of versenate solution used.

Calculations

Total hardness Ca++ (mg/l) = cm3 versenate x 400

Method II (includes calcium and magnesium, recorded as Ca++

)


beaker.

2. Add 10 cm3 of chlorine. Whisk to mix.

3. Add 1 cm3 of acetic acid and mix.





water.




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6. Add a strong buffer solution = 1 cm3 and whisk to mix.

7. Add 1 cm3 of masking agent and mix.

8. Add 6 cm3 of calmagite and mix. If calcium and/or magnesium are

present, the filtrate will turn wine red.

9. Use a pipette to titrate with a versenate solution, while agitating, until the

sample has turned blue, without any traces of red. Note the quantity in

ml of versenate solution used. This is value A.

Calculations

Total hardness Ca++

(mg/l) = A x 400

16.6.4 Calcium and magnesium, separately


beaker.

2. Add 10 cm3 of chlorine. Whisk to mix.

3. Add 1 cm3 of acetic acid and mix.





water.

6. Add 1 cm3 of sodium hydroxide (buffer) and mix (Mg2+ precipitate)

7. Add 1 cm3 of masking agent and mix.

8. Add 1.4 spoonfuls (0.2 g) of indicator and mix. If calcium is present, a

wine red colour will develop.

9. Titrate with versenate until the indicator develops a wine red to blue

colour, without any traces of red. Record the ml of versenate required.

This will be value B.




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Calculations

Calcium (mg/l) = B x 400

Magnesium (mg/l) = (A - B) x 243

16.7 Sulphate

16.7.1 Qualitative testing

16.7.2 Scope

Sulphate ions are present in a large number of natural waters because of the

dissolving action of water on minerals. Anhydrites (calcium sulphate) are slightly

soluble salts which can be encountered when drilling for a few hours. The

sulphate ion content in filtrate often needs to be checked. A concentration of

sulphate ions above 2,000 mg/l may cause viscosity and fluid loss problems.

16.7.3 Equipment

The following items are required to determine the calcium sulphate content:

1. Test tube

2. Decanter with 10% barium chloride solution. (WARNING: THIS

SOLUTION IS POISONOUS. Do not inhale).

3. Decanter with strong nitric acid.

16.7.4 Procedure

Pour 3 ml of filtrate in a test tube. Add a few drops of barium chloride solution.

The formation of white precipitate indicates that sulphates and/or carbonates are

present. Add a few drops of concentrated nitric acid. If the precipitate

dissolves, carbonate is present. If it does not dissolve, sulphate is present.

Note the amount of precipitate as slight, average or strong, after treatment with

acid.




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16.7.5 Availability of calcium sulphate

16.7.6 Scope

When gypsum muds are used, the excess amount of gypsum in the mud must

be assessed.

16.7.7 Equipment

1. Masking agent: 1:1:2 mixture of triethanolamine, tetraethylenepentamine

and water

2. Deionized water.

3. Calmagite indicator.

4. 0.01 molar versenate solution.

5. Strong buffer solution.

6. 400 cm3

beaker.

7. 250 cm3

calibrated beaker.

8. Electric hotplate.

9. 1 cm3, 2 cm3 and 10 cm

pipettes. 5 cm3 syringe.

10. 100 - 150 cm3 titration beaker, preferably white.

11. Mud still

16.7.8 Procedure

1. Add 5 cm3 of mud to the calibrated beaker, then add 245 cm3 of water to

top up to 250 cm3.

2. Heat to 160°F and agitate for 15 to 20 minutes. Heat while agitating if

possible. (If this is not possible, heat then agitate for 30 minutes).

3. Cool while agitating, top up with water to 250 cm3

4. Filter with a filter press; throw away the first cloudy part of the filtrate and

only keep the clear part.




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5. Add 10 cm3 of filtrate, 1 cm3 of strong buffer and 6 drops of Calmagite

indicator.

6. Titrate with versenate solution, agitate constantly until the sample turns

blue (or green if the filtrate is dark without any traces of red). Record the

amount of versenate used = Vt.

7. Clean the titration beaker and add approximately 20 cm3 of water.

8. Add 1 cm3 of filtrate from the mud.

9. Add 1 cm3 of strong buffer solution.


11. Add 6 drops of Calmagite and mix with a spatula.

12. Titrate with versenate solution, agitate constantly until the sample turns

blue (or green for dark filtrates) without any traces of red.

13. Record the ml of versenate solution used = Vf

Calculations

CaSO4 available (lb/bbl) = 2.38 x Vt – [0.2 x (Fw x Vf )]

Where:

Vt = Amount in cm3

of standard versenate solution used to titrate 10 cm3 of clear

filtrate in step 6.

Vf = Amount in cm3

of standard versenate solution used to titrate 1 cm3 of filtrate

in step 13.

Fw = fresh water should be fractioned with mud in static conditions. % water

/100 = Fw.




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16.8 Potassium (K+)

The purpose of potassium ions in mud is to stabilize water-sensitive clays, while

maintaining an appropriate potassium concentration to optimize the quality of potassium

base muds.

Either of the following procedures can be used to determine potassium ion concentration.

Procedure I can be used for any potassium ion concentration, while procedure II, which is

quick, can only be used for high concentrations.

16.8.1 Procedure I — Potassium <5,000 mg/l (STPB method)

16.8.2 Equipment

1. Standard sodium tetraphenylborate (STPB) solution.

2. Quaternary ammonium salt (QAS) solution, hexadecyltrimethylammonium

bromide.

3. 20% sodium hydroxide solution; 20 g/80 ml of deionised water.

4. Bromophenol blue indicator.

5. Graduated serological pipettes: one 2 cm3 pipette with 0.1 cm3 marking,

two 5 cm3 and two 10 cm3

pipettes.

6. Graduated cylinders: two 25 cm3 and two 100 cm3

cylinders.

7. 100 cm3 cylinder.

8. Paper filter.

9. Beakers: two 250 cm3 beakers and deionised water.

16.8.3 Procedure

1. Pour an appropriate amount of filtrate into a graduated 100 ml beaker,

referring to Table 14 for amounts. Use a pipette to measure the filtrate

and/or dissolved sample.




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2. Add 4 cm3 of NaOH using a 5 cm3 pipette; add 25 cm3 of sodium

tetraphenylborate solution measured using a graduated 25 cm3

test tube

and enough deionized water to top up to 100 cm3.

3. Mix and leave for 10 min.

4. Filter in a 100 cm3

graduated cylinder. Refilter the solution if the filtrate is

cloudy.

5. Transfer 25 cm3 of clear filtrate (measured using a 25 ml cylinder) into a

250 cm3 beaker.

6. Add 15 drops of bromophenol blue indicator.

7. Titrate with an appropriate solution until the purple blue colour turns to

light blue. Record the amount of solution used in cm3 Continue to titrate

to 25 cm3 making sure the endpoint is reached and that there are no

traces of purple blue.

Calculations

K+

(mg/l) = (25 cm3 of QAS) x 1,000 / (cm3 of filtrate). If a correction factor is

necessary: K+

(mg/l) = [25 – (cm3 of QAS x 4) / (rate from QAS to STPB)] x

1,000 cm3 of filtrate




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Table 14: Dimension of potassium samples

Estimate ppm K+ Sample preparation Filtrate (cm3)

> 100,000 Add 1 ml of filtrate to 9 cm3 of distilled

water. Mix and measure 1 cm3 of solution.

0.10

50,000 - 100,000 Add 1 ml of filtrate to 9 cm3 of distilled


0.20

20,000 - 50,000 Add 1 ml of filtrate to 9 cm3 of distilled


0.50

10,000 - 20,000 Collect 1 cm3 of undissolved filtrate. 1.00



250 - 2,000 Collect 10 cm3 of undissolved filtrate. 10.00

NOTE: The concentration of QAS should be checked against the concentrationof STPB at monthly intervals. To determine the QAS equivalent, dilute 2 cm

3

of

STPB solution in a titration beaker with 50 cm3

of distilled water. Add 1 ml of

sodium hydroxide solution and 10 – 20 drops of bromophenol blue indicator.

Titrate with the QAS solution until the colour changes from purple blue to light

blue.

16.8.4 Procedure II — Potassium ≥ 5,000 mg/l (sodium perchlorate method)

16.8.5 Equipment

1. Standard sodium perchlorate solution: 150.0 g of NaClO4 per 100 ml of

distilled water. NOTE: When in a dry state, sodium perchlorate can

explode if heated to high temperatures or if it comes in contact with

organic reducing reagents. Perchlorate is not hazardous if hydrated with

water and will break down harmlessly if disposed in water.

2. Standard potassium chloride solution, 14.0 g KCl mixed with 100 ml of

distilled water.




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- Turn the crank quickly for 5 seconds. If you turn the crank more than 10 times,

slow down a little and count the turns in 5 seconds again. Continue to adjust the

rotation speed.

2. Prepare a standard potassium chloride curve.

A standard calibration curve is required for each centrifuge. This can be

prepared as follows. You will need at least three points (3.5, 10.5, and 17.5

lb/bbl KCl) ( Figure 16).= Kg/mc 9.90 – 29.7 – 49 for an accurate diagram.

Table 15 Filtrate volumes for various concentrations ofKCl

Concentration scale Filtrate volume(cm3)

KCl (lb/bbl) K+ (mg/L)

3.5-18 5,250-27,000 7.0

18-35 27,000-52,500 3.5

35-70 52,500-105,000 2.0

> 70 > 105,000 1.0

a. Prepare a test to cover scales from 1 a 8% KCl adding an appropriate amount

(ml=) of standard potassium chloride solution (0.5 ml for every 3.5 lb/bbl) to the

centrifuge tube. Dilute with 7 ml of distilled water.

b. Add 3 ml of sodium perchlorate solution to each tube.

c. Centrifuge for 1 minute at 1,800 RPM and immediately record the amount of

precipitate (volume).

d. Wash the tube and dispose of the liquid.

e. Record the ml of precipitate versus the potassium chloride content (lb/bbl)

and plot a graph.




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Figure 16: Example of a concentration curve for KCI concentration

16.8.7 Procedure

1. Measure 7 ml of filtrate in a centrifuge tube. Add 3 ml of sodium

perchlorate solution (if potassium if present, precipitation will be sudden).

DO NOT AGITATE. Centrifuge at a constant speed of 1,800 RPM for 1

minute and immediately record the amount of precipitate (volume). Rinse

the precipitate thoroughly with water.

NOTE: Add 2 to 3 drops of sodium perchlorate to the centrifuge tube at the end

of the procedure, to make sure there are no more traces of potassium. If

precipitate has formed, the total amount of potassium ions is not measured and

the sample is diluted as explained in note 2.

2. Determine the potassium chloride concentration comparing the amount of

measured precipitate with the relative diagram. (see Figure 16).

3. Record the potassium concentration as lb/bbl KCl or kg/m3




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Calculations

The potassium concentration can also be recorded as the weight of KCI

(percentage).

KCl (wt %) = (lb/bbl) / 3.5

K+

(mg/l) = 1,500 x KCl (lb/bbl)

NOTE 2: These two calculations are based on filtrate with a specific weight of

1.00.

If the KCI concentration is above 21 lb/bbl, the precision can be improved using

a dilution which keeps the test result between 3.5 and 21 lb/bbl. The volume in

the tube must not exceed 7 ml with distilled water and should be agitated before

adding the sodium perchlorate solution.

If volumes of filtrate are not 7 ml, the KCI concentration should be calculated as

follows:

KCl (lb/bbl) = 7 / ml of filtrate

(values from a standard diagram)

This is a typical rigsite method and should be used as such. The purpose of the

procedure is to keep potassium ions in mud filtrate at a higher level. The best

results can be achieved when the potassium ion concentration is >5,000 mg/l

(KCl>9500 mg/l).

16.9 Nitrate ion concentration

16.9.1 Scope

Identifying filtrate and formation water from formation fluids sampled during a

DST can be problematic, and using nitrate ion in the filtrate as a tracer provides

for a better evaluation.




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16.9.2 Equipment

Nitrate testing kit (A.J. Chemicals), a spoon to measure lime.

16.9.3 Procedure

1. Measure a 5 ml sample of colourless or nearly colourless filtrate in a test

tube. If the filtrate is coloured, eliminate by dilution or treat with lime (see

Note 1 and Table 9).

2. Add an ampoule bottle of NO3 and agitate for 3 minutes.

3. Leave to decant in another test tube.

4. Add an ampoule bottle of NO3 . Leave to decant in another test tube.

5. Agitate then leave for 10 minutes until the colour has fully developed.

6. Pour the sample into a graduated 10 ml test tube and add deionised

water to make up to 10 ml. Agitate carefully.

7. Put the sample in the second test tube.

8. Prepare a test tube with a 5 ml sample that has been treated following

step 1; add 5 ml of deionised water to dilute as indicated in step 6.

9. Put the unknown sample in the right-hand hole of the comparison box.

10. Put the sample to test in the left-hand hole of the box.

11. Observe the samples through the holes, turn the colour wheel until the

right colour intensity has been reached. If the colour of the sample is

darker than the colour of the wheel marked no. 80 (note 2) estimate the

dilution required (Table 16) to reduce the concentration of nitrate ions to

the colour scale of the wheel and repeat the test.

12. Record the value.




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16.9.4 Calculations

Clear filtrates:

–

mg/l NO3 = (reading x dilution factor) / 10

Coloured filtrate requiring calcium treatment:

––

mg/l NO3 = [(reading x dilution factor / 10] – (6 x mg/1 NO3 in calcium*)

Coloured filtrate requiring two calcium treatments:

––

mg/l NO3 =[(reading x dilution factor) / 10] – 1 – (42 x mg/l NO3 in calcium*)

*Read this value on the calcium container.

NOTE 1: The 5 ml sample collected in step 1 does not necessarily have to be

colourless. A slight colouring is possible, provided that the container conforms

to the specifications in step 8. A very dark filtrate should however be

decoloured. To decolour the filtrate, dilute 5 mil of filtrate with deionised water,

add a spoon of calcium hydroxide, agitate as required and filter through a funnel,

for a dilution factor of 6. If the filtrate is too dark, take 1 ml and dilute to 5 ml with

deionized water to see whether the sample reacts as in point 1. If the sample

does not react, take 5 ml and repeat using the same dilution ratio and treatment,

then filter again, for a dilution factor of 36. Further discolouring should not be

necessary. However further discolouring with deionised water (Table 11) might

be required, and this can be verified after step 11.

NOTE 2: Readings >80 on the colour wheel are not accurate and should always

be rechecked.

[ Memo : 1 ml = 1 cc = 1 cm3 = 1/1000 litre]




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16.9.5. Dilution table

This table is a guide to choosing the right dilution ratio for the original filtrate

(except for calcium treatments) or further dilution after calcium, if the

approximate concentration of NO3 in mud filtrates is known.

The dilution factor column indicates the amount of filtrate used and final volume

which is diluted with deionized water.




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Treatment without lime

NO3 – (mg/l)

Dilution (ml) Dilution factor

0 – 8 None 1

8 – 20 2 – 5 2.5

20 – 40 1 – 5 5

40 – 80 1 – 10 10

80 – 200 1 – 25 1025

200 - 500 1 - 50 50

Treatment with calcium (1)

NO3 – (mg/l) Dilution (ml) Dilution factor

0 - 20 None 6

20 - 100 2 - 5 15

100 - 200 1 - 5 30

200 - 450 1 - 10 60

Treatment with calcium (2)

NO3 – (mg/l) Dilution (ml) Dilution factor

0 - 120 None 36

120 - 550 2 - 5 90

Table 16




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16.10 PHPA polymer concentration

16.10.1 Scope

PHPA polymers are added to mud to help stabilize clays in the borehole. The

following tests make it possible to determine free polymers and polymers that

can be absorbed by the well sidewalls.

16.10.2 Equipment

1. Electric hotplate/electric whisk with magnetic wires.

2. Two, 125 cm3 raduated Erlenmeyer flasks.

3. Distilled water.

4. Boric acid solution, 2% in weight.

5. Methyl orange indicator (methyl red).

6. 6 N sodium hydroxide solution.

7. 2 – 3 ft Tygon tubing, 0.25 in. ID.

8. 6 rubber stoppers with a 0.25 in hole.

9. 0.02 N sulphuric acid solution.

10. Polymer defoamer (such as Dow-Corning 84 AFC-78).

11. Small glass tube, 0.25-in. OD— (2 tubes, 3 – 4 in. long).




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16.10.3 Procedure

1. Connect the two small glass tubes to the two ends of the Tygon tubing.

Put one end inside the rubber stopper so it reaches the bottom of the

stopper.

2. Pour 25 cm3 of boric acid solution into an Erlenmeyer flask, add 6 drops

of methyl orange indicator. The original colour should be red/pink, but not

yellow.

3. Pour into another graduated flask (not into the reaction flask), add 50 ml

of distilled water, 2 cm3 of silicone defoamer and 10 cm3 of mud; if the

concentration of active polyacrylamide (PHPA with a high molecular

weight) is >1.5 lb/bbl, or if polyacrylamide (PHPA with a high molecular

weight) IS > 4.5 lb/bbl, use 5 cm3 of mud, then double the result.

4. Put the reaction flask with the mud on the electric hotplate and start

stirring. Add 3 ml of sodium hydroxide solution and immediately connect

the flask to the rubber stopper.

5. Put the other end of the tubing (Pasteur pipette) into the methyl orange

and 2% boric acid solution and bring to the boil. The condensation in the

flask (volume) should be approximately 25 cm3, with the colour varying

from pink to yellow.

6. Adjust to a medium heat so the fluid can be removed. Turn the plate to

“off”. As the solution cools, the boric acid can be sucked up from the

flask. After collecting 25 cm3, remove the stopper and empty the flask

entirely. Titrate the contents with 0.02 N H2SO4 until the colour returns to

the original red/pink and record the amount of acid used.

7. The concentration of Polyacrylamide – with high molecular weight PHPH -

can be determined using an accurate diagram. Double the result if a 5

cm3 sample has been used.




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16.10.4 Additional guidelines and trouble shooting

1. The glass tube must be washed when the bottom part is still inside the

rubber stopper. If the tube is sticking out of the stopper, the caustic

solution will collect around the lower part of the tube as it is distilled. As a

result it will be sucked up and dispersed in the boric acid solution.

2. Make sure methyl orange is used as the indicator. It will change from a

pale amber yellow to pink/dark red depending on the pH. Moreover, the

boric acid solution will change the colour to pink rather than yellow. If the

colour does not turn pink, use a fresh sample of boric acid. If this is not

possible, use 0.02 N sulphuric acid solution and add in drops until the

solution goes pink. Use this solution to collect the distillate.

By following this procedure, only the acid to titrate ammonia will be measured

during final titration. Any addition of acid to correct the boric acid is not

considered.

3. If the mud foams, increase the amount of defoamer and try to estimate

the active polymer scale of use, to determine amounts to use in actual

operating contexts.

4. The distillation temperature should be chosen so that the solution does

not boil for too long (as this would make the test result void). The solution

should be left to boil on a gentle heat, so that water distillation (or the

distillate) condensates at the top of the tube. As a result, the mud inside

the receiver ampoule bottle will not boil, but the distillate will thicken in the

tube, reaching the boric acid solution. NOTE: the temperature should be

adjusted to ensure the solution boils gently and consistently and to

prevent the ampoule bottle with the mud cooling due to the boric acid

being sucked up by the bottle.

5. Make sure the bottom end of the tube is below the level of the boric acid

solution. A Pasteur pipette should be used instead of the glass tube. As

it has a smaller opening, it is less likely that ammonia will leak.

6. When carrying out final titration, make sure you titrate to the original

colour of the boric acid solution. If a light pink colour develops, do not

continue titrating to try and obtain a darker pink.




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17.0 CHEMICAL ANALYSES FOR CORROSION

17.1 Zinc oxide (ZnO) and basic zinc carbonate (ZnCO3•Zn(OH)2)

17.1.1 Scope

Zinc oxide and zinc carbonate can be used to neutralise H 2S in drilling muds.

To determine the concentration of ZnO or ZnCO3 in mud, use the following:

17.1.2 Equipment

1. Glacial acetic acid.

2. 10% ammonium fluoride.

3. Concentrated ammonium hydroxide.

4. Masking agent.

5. Deionized water.

6. 4% formaldehyde solution.

7. Calmagite indicator solution.

8. Standard versenate solution.

9. 150 cm3 beaker.

10. One 10 cm3, one 25 cm3 and one 100 cm3 graduated cylinder.

11. Whisk with magnetic wires.

12. One 10 cm

3

and one 20 cm

3

syringe.

13. Plastic, 4 in. funnel.

14. Cone paper filters (S & S No. 588 - 18.5 cm).

15. Litmus papers.

16. One 10 cm3 and one 20 cm3 volumetric pipette.




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17.1.3 Procedure

1. Agitate the mud sample and measure 10 cm3 with a syringe.

2. Transfer into a 150 cm3 beaker.

3. Dilute to 40 cm3 with deionized water.

4. Add 10 cm3 of glacial acetic acid (WARNING: use protective

equipment).

5. Agitate for 10 minutes. This longer time is necessary, because thereaction is quite slow.

6. Add 15 cm3 of ammonium hydroxide (ATTENTION).

7. Check the pH. If it is >9, go on to the next step. If it is <9, add more

ammonium hydroxide with 5 cm3

increases until the pH is >9.


9. Add 10 cm3 of ammonium fluoride solution. NOTE: as ammonium

fluoride is poisonous, do not aspirate with the pipette and never mix with

an acid solution.

10. Transfer the solution to a 100 cm3 graduated cylinder and dilute with

deionised water up to 100 cm3.

11. Mix well and filter into a clean beaker.

12. Take 20 cm3 of filtrate and pour into a clean beaker.

13. Dilute with deionized water to approximately 40 cm3

.

14. Add 6 drops of calmagite indicator. If the solution is blue, go directly to

step 15. If the solution is red, slowly titrate with standard versenate to a

blue endpoint. The amount of versenate indicator does not have to be

recorded.

15. Add 5 cm3 of ammonium hydroxide.

16. Check the pH, which should be between 10 and 11. If the pH is <10,

add more ammonium hydroxide, 5 cm3 at a time, until the pH is 10.




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17. Add 5 cm3 of formaldehyde solution.

18. Leave for at least 2 minutes. The colour will turn from blue to wine red if

zinc is present.

19. Titrate with versenate indicator until the red wine colour turns to blue.

Calculations

ZnO (lb/bbl) = (28.5 x cm3 standard versenate) / (cm3 of sample x cm3 of filtrate)

ZnCO3 (lb/bbl) = (44 x cm3 standard versenate) / (cm3 of sample x cm3 of filtrate)

17.2 Iron sulphide (qualitative testing)

17.2.1 Purpose

A special reagent is needed if iron sulphide tests are carried out using steel

equipment. The presence of iron sulphide often indicates the presence of H2S

downhole, but is not an absolute indicator of H2S gas.

17.2.2 Equipment

Iron sulphide solution, containing 15% HCl, 1% sodium arsenite and 0.05%

detergent to use as a wetting agent.




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17.2.3 Procedure

Put a few drops of acid solution onto the equipment. If a straw-yellow arsenic

disulphide precipitate forms, the sample contains iron sulphide. The precipitate

will look like scrambled egg. As a minimum amount of iron is dissolved by acid,

producing a yellow-orange solution, this should not be mistaken for the yellow

precipitate formed by the sulphide. If the sample is effervescent, the carbonate

may have produced carbon dioxide.

WARNING: only carry out this test with steel equipment; do not use aluminium or

other materials, as the fumes produced by reactions are toxic.

17.3 Hydrogen sulphide (H2S)

17.3.1 Scope

It is highly likely that H2S will cause corrosion when it mixes with mud. This gas

has a lethal effect on all living things. There are two methods to detect the

presence of H2S in ppm (parts per million). The first is quick and simple,

however the results are less accurate and can only be used to determine

whether the gas is present. The second method accurately determines the ppm

of H2S in mud, analysing the filtrates.

17.3.2 Procedure 1: Hach test

17.3.3 Equipment

1. A bottle calibrated for the test, with punched top to bleed the gases.

2. Papers to test H2S (the papers must be able to fit in the top).

3. 1 10 cm3 hypodermic syringe.

4. Deionized water.

5. Alka-Seltzer tablets (not past their use-by date).

6. Colour comparison papers to determine H2S.

7. Octanol defoamer.

8. Approximately 6 N hydrochloric acid.




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17.3.4 Procedure

1. Use a syringe to transfer 8.3 cm3 of mud into the test bottle. Add 16.7

cm3 of deionized water and whisk. The total volume is now 25 cm3.

Add a drop of defoamer if foam is produced. Make sure the fluid does

not touch the paper.

2. Place an H2S testing paper inside the bottle top (the top has a hole for

this purpose).

3. Add the Alka-Seltzer to the sample and screw the top onto the bottle.

Slowly mix.

4. After 15 minutes, remove the paper and compare with the colour scale.

The ppm of H2S from the paper is multiplied by 3 to obtain the ppm of

H2S in the mud.

This test can also detect small concentrations of H2S. (for example 0.3 ppm).

The test is only valid when sulphide is mixed with the mud. Sulphides, such as

hydrogen sulphide, should be determined in an acid solution, so hydrogensulphide can be detected by adding 5 drops of HCI in step 3.

NOTE: If the concentration of H2S in mud is >15 ppm, the mud needs to be

diluted further. Use 1 ml of mud and 24 cm3 of deionized water for

concentrations ranging from 15 to 125 ppm and multiply the ppm of H2S

obtained from the paper by 25.

For concentrations from 125 to 1,250 ppm, mix 1 cm3 of mud in 9 cm3

of

deionized water in a small beaker. Take 1 cm3 of the mixture and add 24 cm3 of

deionized water for the test, multiply the ppm of H2S, obtained from the paper,

by 250.




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17.3.5 Procedure 2: Garrett Gas Train (GGT)

17.3.6 Scope

H2S is immediately ionized in alkaline mud, as it is neutralized and transformed

into sulphur (S) and bisulphite (HS) ions. When mud filtrate is put in a GGT and

acidified, the H2S reforms, is released and measured using the Dräger tube

inside the GGT.

17.3.7 Equipment

Section 1: Garrett Gas Train and accessories (figure 17).

Section 2. Dräger tubes for H2S analysis:

A) Low scale-H2S 100/a (labelled from 100 to 2,000) Factor = 0.12.

B) High scale H2S 0.2%/A (labelled from 0.2 to 7%) Factor = 1,500.

Section 3. Cartridges for CO2 (or other gases inert to H2S provided they do not

contain air or oxygen, such as nitrogen).

Section 4. Lead acetate paper strips (optional).

Section 5. Approximately 5 N sulphuric acid.

Section 6. Optanol defoamer.

Section 7. One, 10 cm3 hypodermic syringe with needle for acid (21 gauge),

one 40 cm3 and one 5 cm3 hypodermic syringe

17.3.8 Procedure

1. The gas train must be clean, dry and put on a flat surface. Tubing etc.

must not be obstructed, or damp as this would obstruct the flow and

invalidate results.

2. Fit a new CO2 cartridge.

3. Add 20 ml of deionized water to chamber 1

4. Add 5 drops of defoamer to chamber 1 (figure 18).




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5. Select the exact volume for the sample and the Dräger tube, with an

appropriate scale for sulphide, in line with table 17.

6. Break off both ends of the tube (figure 19).

Figure 17 : Garret Gas Train assemblied.




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Figure 18: Preparing the GGT for sulphide analysis.




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Figure 19: Breaking off the ends of the Dräger tube.

Broken ends

Receptacles

Figure 20 : Drager tube installed on the base of GGT.




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7. Wash the chambers with a mild detergent and soft brush. Use a small

pig. Put the tube with the arrow pointing downwards, in the receptacle

in the corner . After cleaning and drying the tube, install the flow meter

with the word “TOP” facing upwards, and ball in the channel at the side

facing downwards at the bottom. Make sure the O-rings seal the tubes.

8. Measure the samples in chamber 1. Chambers 2 and 3 will be empty

and are used as “traps” for the foam.

9. Put the O-rings in the grooves and assemble the top part of the gastrain. Tighten all screws uniformly.

10. Connect the dispersion tube to the Dräger tube.

11. Adjust the dispersion tube so it is 0.5 cm from the bottom.

12. Slowly inject CO2 for 15 minutes to remove air from the system.

Activate the gas flow gently to avoid the ball coming out of the flow

meter tube. Apply gentle pressure to the tube, to check air is being

eliminated and prevent the ball coming out.

13. Slowly inject 10 ml of sulphuric acid into chamber 1, through the rubber

top.

14. Restore the CO2 flow and adjust so that the ball is between the small

red lines (from 200 - 400 cm3

/min). A CO2 cartridge should guarantee a

15 to 20 minute flow at this rate.

15. Continue gas flow for 15 minutes. Record the maximum length of the

stain. Note: if sulphites appear in the top part of the Dräger tube, an

orange colour produced by the SO2 may form in front of the black part.

The orange part should be ignored. Only record the dark part. Note:

the length of the stain, which should cover more than half the length of

the tube, is the most accurate way to evaluate the Dräger tube.

16. The gas train must be thoroughly cleaned after use, as the acid could

cause damage. To clean the train, remove the flexible tube and upper

part of the GGT. Remove the flow meter and Dräger tube then cover




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the holes with stoppers to prevent damp getting in. Rinse with deionised

water and leave to drain.

Calculations

Referring to the sample volume, maximum length of the stain in the Dräger tube

and factor (table 17) calculate the sulphides in the sample:

Sulphides (mg/l) = (length of stain x tube factor) / (cm3 of sample volume).

Table 17: Selecting the Dräger tube and ranges. Volume of samples and tube factor touse for various sulphide ranges

Sulphide range(mg/l)

Sample volume(cm3)

Selecting theDräger tube

Tube factor

1.2 - 24 10.0

H2S 100/a (100 -2,000 range) 0.12*

2.4 - 48 5.0 H2S 100/a (100 -2,000 range) 0.12*

4.8 - 96 2.5

H2S 100/a (100 -2,000 range) 0.12*

30 - 1,050 10.0 H2S 0.2%/A 1,500**

60 - 2,100 5.0 H2S 0.2%/A 1,500**

120 - 4,200 2.5 H2S 0.2%/A 1,500**

* The tube factor of 0.12 is for new H2S 100/a tubes (Cat. No. CH-291-01), witha 100 - 2,000 range. Use a factor of 12.0 for old tubes with a 1 or 2 – 20 range.

** The tube factor of 1,500 is for new H2S 0.2%/A tubes (Cat. No. CH-281-01),

with a 0.2 - 7.0% range. Use a factor of 600 multiplied by a batch factor/0.40

ratio for old tubes with a 1 – 17 cm range.




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17.4 Phosphate

17.4.1 Scope

The active ingredient in inhibitors is an organic phosphate. However organic

phosphates may be found in drilling muds, so analysis must differentiate

between organic and inorganic phosphates.

17.4.2 Procedure 1 : Using a Hach Direct Reading Colorimeter

17.4.3 Equipment

1. Deionized water.


3. PhosVer III pillows.

4. Potassium persulphate pillows.

5. 8 N NaOH sodium hydroxide.

6. 5 N H2SO4 sulphuric acid.

7. 50 cm3 Erlenmeyer flask.


9. Hach direct reading colorimeter.


11. Pipettes: one 1 cm3, one 5 cm3 and one 10 cm3 pipette.

a) Inorganic phosphate

1. Use a pipette to transfer 5 - 10 cm3 of filtrate into a 50 cm3 flask. Add

deionized water up to the 20 cm3 mask.

2. Add 1 cm3 of sulphuric acid.




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3. Boil for 15 minutes, making sure the volume stays at approximately 20

cm3.

4. Cool.

5. Add a drop of phenolphthalein indicator.

6. Add sodium hydroxide in drops until the sample starts to turn pink. If

you add too much sodium hydroxide the pink colour will remain. Add

sulphuric acid in drops until the pink has disappeared.

7. Pour the sample into a 25 cm3 graduated cylinder and add deionised

water up to the 25 cm3 mark.

8. Pour into a square mixing bottle.

9. Add the contents of a PhosVer III pillow. AGITATE and leave for 1 to 2

minutes (do not leave for more than 2 minutes).

10. Put the deposit measuring device in the Hach colorimeter and use a

2407 colour filter.

11. Fill another square colorimeter bottle with filtrate that has not been

treated in the receptacle (blank). Make sure the concentration is the

same as the sample. If you used 5 cm3

for the sample volume, use 5

cm3 of filtrate diluted to 25 cm3 for the sample.

12. Put the blank in the colorimeter. Adjust the control light for a 0 mg/l or

100% reading (transmittance depending on which scale is being used).

13. Pour the sample into the colorimeter and read the PO43- (phosphate) in

mg/l or transmittance (%). If the value for PO43–

is >2.0 mg/l or if the

transmittance is <10%, repeat the procedure using less filtrate than step

1.

14. Record the mg/l of PO43- obtained from calculations. If you use the

transmittance table, refer to the transmittance vs. mg/lPO43-

graph.




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b) Total phosphate (organic plus inorganic)

1. Use a pipette to transfer 5 - 10 cm3 of filtrate into a 20 cm3 ampoule

bottle. Add deionised water up to the 20 cm3 mark.


3. Add one potassium persulphate pillow.

4. Boil for 30 minutes.

5. Boil down to 10 cm

3

(maximum). If necessary, add deionised water.

6. Continue with steps 4 – 11 from the previous section. NOTE: if the filter

discolours, because of potassium sulphate-induced oxidisation, do not

use a coloured filter for the blank in step 11. Use deionized water

instead.

7. Put the blank in the colorimeter. Adjust the control light for a 0 mg/l or

100% transmittance reading, depending on the table used.

8. Put the sample in the colorimeter and read the PO4

3-

(phosphate) in mg/lor transmittance (%). If the value for PO4

3- is >2.0 mg/l or if the

transmittance is <10%, repeat the procedure using less filtrate than step

15.

9. Record the mg/l of PO43- to use in calculations. If you use the

transmittance table, refer to the transmittance vs. mg/PO4 3-

graph.

Calculations

Inorganic phosphate (mg/l) = (mg/l of PO43- from the chart x 25) / (cm3 of filtrate)

Total phosphate (mg/l) = (mg/l of PO43- from the chart x 25) / (cm3 of filtrate)

Organic phosphate = (Total phosphate – Inorganic phosphate)




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17.4.4 Procedure 2 : Hach phosphate kit (PO-24)

17.4.5 Equipment

1. Deionized water.


3. PhosVer III pillows.

4. Sodium sulphate pillows.

5. 8 N NaOH sodium hydroxide.

6. 5 N H2SO4 sulphuric acid.

7. 50 cm3 graduated Erlenmeyer flask.

8. 25- cm3 graduated cylinder.

9. Hach PO-24 phosphate kit.


11. Pipettes: one 1 cm3, one 5 cm3 and one 10 cm3 pipette.

a) Inorganic phosphate

1. Use a pipette to transfer 5 - 10 cm3 of filtrate into a 50 cm3 Erlenmeyer

flask. Add deionised water up to the 20 cm3 mark.


3. Boil for 15 minutes, keep the volume at approximately 20 ml.

4. Cool.

5. Add a drop of phenolphthalein indicator. Add sodium hydroxide in drops

until the sample turns nearly pink. If you add too much sodium

hydroxide and the pink colour remains, add sulphuric acid in drops until

the pink disappears.

6. Pour the sample into a square bottle for mixing, then add water up to the

20 cm

3

mark.




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7. Add a PhosVer III pillow to the sample. Agitate then leave for 1 – 2

minutes.

8. Pour the sample into the tube to view the colour.

9. Put the tube in the colour comparator, in the opening closest to the

halfway point.

10. Put another tube in a blank. Make sure the concentration is the same as

that of the sample. If you used 5 cm3

for the sample, use 5 cm3 of filtrate

diluted to 20 cm3 for the blank.

11. Hold the comparator against the light and look through the two front

slots. Rotate the colour wheel to the corresponding colour. If the colour

is too dark, repeat the procedure, using less filtrate.

12. Record the readings and use them in the calculations.

b) Total phosphate (organic plus inorganic)

1. Use a pipette to transfer 5 - 10 cm3 of filtrate into a 50 cm3 Erlenmeyer

flask. Add deionized water up to the 20 cm3 mark.


3. Add a potassium persulphate pillow.

4. Boil for 30 minutes.

5. Boil at least 10 ml. If necessary, add deionized water.

6. Proceed as above, from point 4 – 10. NOTE: the sample colour does

not disappear because of potassium persulphate-induced oxidisation, do

not use the coloured filtrate for step 10. Use deionised water instead.

7. Hold the comparator against the light and look through the two front

slots.




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8. Record the readings and use them in the calculations.

Calculations

Inorganic phosphate (mg/l) = (reading step 12 x 2) / (cm3 of filtrate step 1a) Total

phosphate (mg/l) = (reading step 8 x 2) / (cm3 of filtrate step 13)=1b Organic

phosphate = (total phosphate – inorganic phosphate)

17.5 Oxygen scavenger: SO32- content

17.5.1 Scope

Oxygen scavengers containing sodium sulphite and ammonium bisulphite are

added to some muds to minimise oxygen content. The mud needs to have an

excess of sulphite (SO32-) in order to totally eliminate oxygen.

Two procedures are used in this case; the first for normal filtrates and the

second for dark filtrates. Procedure I should be used because it is more

accurate. However if the colour does not change, carry out procedure II. Do no

dilute the filtrate with hydrogen peroxide as this would dissolve the oxygen.

17.5.2 Equipment

1. Deionized water.

2. 6 N HCl hydrochloric acid.

3. Standard 0.008 N iodine solution (KI-KIO3).

4. Standard 0.008 N thiosulphate solution.

5. Starch indicator solution.

6. Test tube.

7. Two 125 cm3 Erlenmeyer flasks.

8. One 1 cm3 and one 2 cm3 pipette.

NOTE: If sulphides are present, titrate the sample. Determine the H2S with

another method and deduct the mg/l of H2S x 2.4 from the mg/l of SO32-

obtained. If the content tends to increase without adding sulphite, H2S should




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be checked. (If sulphide is present, a CI ion test could also indicate an increase,

as it will also react with the ions).

Sodium thiosulphate solution standardisation

Sodium thiosulphate deteriorates after it has been added to mud. It should be

checked every two weeks with a KI-KIO3 solution as described below. This is

important, because a weaker solution of sodium thiosulphate will have a lower

sulphite concentration, so a deterioration factor is necessary.

1. Use a pipette to transfer 2 cm3 of iodine solution into a 125 cm3 beaker.

2. Add 2 drops of HCl.

3. Dilute with 10 cm3 of deionized water.

4. Titrate with sodium thiosulphate until the yellow colour disappears

completely.

5. Add 5 drops of starch indicator.

6. Continue titration until the blue colour disappears.

7. Record the total ml of thiosulphate solution required to calculate the

deterioration factor.

8. Use the factor from the following formula to determine the mg/l of SO32–

only for coloured filtrates:

Factor = (cm3of KI-KIO3 solution) / (cm3

of sodium bisulphate)

17.5.3 Procedure 1: clear filtrates

Collect the sample for this analysis from above the shale shaker. The sample

should be immediately taken and analyzed straightaway because sulphite is

instable.

1. Use a pipette to transfer 5 cm3 of filtrate into a test tube. (If the volume is

reduced, use a 1 cm3 sample). NOTE: the sample is not diluted in this

test.




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2. Add 5 drops of starch indicator and 2 drops of HCl.

3. Titrate with iodine solution until a permanent blue colour develops.

Calculations

SO32- (mg/l) = (cm3 of iodine solution x 320) / (cm3 of filtrate)

17.5.4 Procedure 2: dark filtrates

If possible, follow the procedure used for clear filtrates as this is more simple

and accurate. However, if you see no colour change, do not dilute the sample,but use the procedure for dark filtrates. If the filtrate is not too dark, take a

sample of >1 cm3

1. Use a pipette to transfer 2 cm3 of iodine solution to each of the two 125

cm3

Erlenmeyer flasks.

2. Add 20 cm3 of deionized water to each flask.

3. Use a pipette to transfer 1 cm3 of filtrate to both flasks. Flask 1 is then

covered. Use a sheet of white paper as a background to see the colour

change better.

4. Add 4 drops of HCl to flask 2, and 5 drops of starch indicator solution.

The solution will develop a blackish blue colour.

5. Titrate the sodium thiosulphate drop by drop until the blackish blue

colour fades to the same shade as the solution in flask 1.

Calculations

SO32- (mg/l) = [cm3 of iodine solution – (factor x cm3 of thiosulphate solution)] x

320.2 / cm3 of filtrate




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18.0 RESISTIVITY

Mud, filtrate and filter cake resistivity is often fundamental for evaluating electric logs.

18.1 Equipment

1. Mud, filtrate and filter cake.

2. Resistivity meter for direct mud readings.

3. Calibrated resistivity cell.

4. 32 - 220°F thermometer.

18.2 Procedure

1. Fill the clean resistivity cell with filtrate and mud that has been recently agitated.

Try to eliminate the air bubbles. Fill the cell to the right volume, in line with the

recommended procedure.

2. Connect the cell to the gauger.

3. Measure the resistance in ohms-meter with direct readout. The value should becalibrated in ohms if this is not used.

4. Record the detected temperature.

5. Clean the cell, wash with deionized water and dry.

Calculations

1. Record the resistivity Rm or resistivity of the filtrate Rmf in ohm-meters, with the

value closest to 0.01.

2. Note the mud temperature in °F.

3. If the value is recorded in ohms, convert in ohm-meters as follows:

4. Resistivity (ohm-meters) = R (ohms) x K (cell constant, m2/m)




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19.0 PROCEDURE FOR ANALYSING GLYCOL

Rig site procedure to determine the glycol content in a mud

19.1 Refractometer

19.1.1 Equipment

1. Refractometer to determine the percentage of glycol per volume used in

mud systems. Different types of refractometer are available and the most widely

used measure glycol on a scale from 0 to 10%. Follow the manufacturer’s

directions if you need to measure values over this scale.

2. 10, 20 or 50 cm3 retort, clean steel wool, glassware.

19.1.2 Reagents

Glycol used in the mud.

Deionized water.

Graduated cylinders and receptacles for samples.

19.1.3 Procedure 1

1. Prepare a calibration diagram for water and glycol. This curve is

obtained adding the percentages of glycol in deionized water (usually

from 1% to 6% of the volume used). Put each mixture into the retort

and plot values on graph paper, which includes the corresponding BRIX

vs. the percentage of added glycol. BRIX is the refraction unit of

measurement to determine the glycol.

2. Distil the mud.

3. Record the fluid volume (percentage).

4. Agitate the liquid, so it flows from the graduated cylinder to the retort.

5. Put 2 to 4 drops of liquid from the retort onto the clean surface of the

refractometer prism. Make sure the entire surface of the prism is

covered by the liquid and close the lid.




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Observe through the refractometer window with the prism facing a light source

(figure 21).

6. Record the BRIX value, using the glycol calibration diagram, then convert

to the glycol volume in the mud (percentage).

7. Glycol percentage in the mud = percentage of glycol from the calibration

diagram x liquid fraction of the mud. The liquid fraction of the mud = Fw.

19.2 Dual-temperature retort analysis for glycol systems

Glycol is a primary inhibitor which neutralises in water systems with polyglycol as it is

absorbed by clays, so the concentration of glycol in mud has to be measured and

controlled. This procedure applies to all types of glycol. Although it is not an API

procedure, an API retort procedure is employed.

19.2.1 Equipment

API retort test kit (a 50 cm3

kit is recommended for accuracy). Make sure it has

a thermostat to heat up to 302°F (150°C) and 950°F (510°C).

19.2.2 Procedure 2

1. Measure a mud sample and put in the bottom beaker of the cell in the retort.

The air in the mud must be reduced to the minimum. Put fine, clean steel wool

in the top part of the cell. Lubricate the threads with grease suitable for high

temperatures when assembling the cells, to minimise leaks.

2. Adjust the thermostat to 302°F (150°C). Heat the retort until all the water has

been recovered (approximately 90 minute). Record as the value V1.

3. Adjust the thermostat to 950°F (510°C), and continue distillation of the

remaining liquid phase. Record the final volume as the value V2.

Volume of glycol (%) = (V2 – V1) x 100 / (Volume of mud sample)

NOTE: liquids with a high boiling point, such as lubricating oils, may alter the

results of this test.




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20.0 PROCEDURE TO ANALYSE PLUGGED PERMEABILITY

20.1 Equipment

1. Cylindrical cell, with a ¼” thick porous disk.

2. Resistance.

3. Thickness.

4. Caps for the ends (one with a filter for the hydraulic part).

5. Two rods: one rod with a quick fit attachment for the hydraulic line and the other with a

valve above the cell.

6. Pump with a quick fit attachment.

7. Hydraulic oil.

8. Piston with O-rings to keep the mud and hydraulic oil separate.

9. T-wrench to position the piston.

10. Cell for the bleeder valve.

11. Connection for the counter pressure regulator.

12. Two thermometers.

13. Two half cocks.

20.2 Procedure

1. Heat the resistance to the selected temperature. Open the cell and check the O-rings;replace if damaged. Cover the parts around the O-rings with a thin layer of silicone

lubricant. Tighten the floating piston on the T-wrench and put the piston at the bottom of

the cell. Reciprocate to check that the piston moves freely. NOTE: the bottom of the cell

is the part with the shorter recessed end. Put the piston at the bottom of the cell and

tighten the T-wrench. This is the access part.




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2. Before loosening the T-wrench, put the end of the piston close to the recessed part. Fit

the O-rings. Put in the hydraulic cell and bottom cap in the part accessing the cell. Apply

a thin layer of silicone to make installation easier. Insert the adjustment screws, check

alignment with the mark and tighten slightly. Use tempered stop screws and grease with

a high temperature lubricant to make it easier to tighten and loosen the screws. Use the

opposite end of the T-wrench to push the floating cap downwards and expel the air.

3. Fit the stem of the quick fit access valve. Fill the stem then open the pump bleeder

valve and use the opposite end of the T-wrench to push the floating cap downwards and

expel the air.

4. Put the cell in an upright position and fill with 300 cm3 of mud. Put an O-ring in the top

part of the cell. Insert the hydraulic tube in the hand pump, pump the mud to fill the

system and put the disk above the _ring, then disconnect the tube. NOTE: Put the disk

in fresh water for 5 to 10 minutes before using it to analyse the mud. If you analyse a

synthetic oil base mud, the disk should be put for 5 – 10 minutes in a fluid which is

compatible with the mud to be analysed. Never use disks more than once.

5. Fit the cap in the bottom. Put a thin layer of silicone grease on the O-ring to make

assembly easier. Make sure the adjustment screw housings are perfectly aligned withthe screws. Assemble the outlet valve, with bleeder valve, then assemble the parts and

put the cell in the heating unit until the cycle is completed. Turn the cell clockwise until it

stops in the locked position at the bottom of the heating unit.

6. Put a metal thermometer in the housing above the cell. Pour the filtrate in the

receptacle above the valve, check the O-ring then secure. Assemble the bleeder valve

and secure. Connect the hydraulic pump quick fit attachment to the valve inlet before

pressurisation. Pressurise the cell to 200 psi and close the valve. When the cell is

heated the pressure inside will increase as the hydraulic oil heats up. Activate the pumpvalve to release pressure and maintain a value of 200 psi.

7. Heat the cell to 150°F (temperature for these analyses). Record the time required to

reach the temperature. Close the bleeder valve on the pump and activate the pump to

pressurise to the required value. Operate the hydraulic pump to increase to an operating

pressure of 1500 psi. NOTE: Always wear safety goggles when working with a

pressurised cell at temperature. When the mud and/or filtrate are close to the test

temperature, slowly open the bleeder valve.




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8. After applying the required pressure, pressurise behind without exceeding 50 psi and

slowly open the bleeder valve. After 30 seconds slowly open the discharge valve and

recover the mud and/or filtrate which flows out in a small beaker, until the cell is entirely

empty.

9. Close the valve and maintain the required pressure in the cell using the hydraulic

pump. The pressure will decrease as the mud is filtered, so it needs to be kept stable.

Maintain pressure in the cell for 30 minutes, and discharge the liquid collected at regular

intervals. After 30 minutes note the total volume recovered (excluding any spurt losses).

Close the blowdown valve and open the pump bleeder valve. Keep the pressure behind

and open the bleeder valve. This will move the floating piston downwards so hydraulic oil

in the pump can be recovered. Turn off the resistance.

10. After recovering the oil, close the safety valve. Remove the hydraulic tube quick fit

attachment from the cell. Close the pressure inlet behind the receptacle and bleed. If

there is no residual pressure in the receptacle, remove the safety catch, remove the

device and pressurise behind the receptacle.

11. Leave the cell to cool when it is still inside the heater, or remove it carefully and cool

in water. After cooling, position so the safety valve is facing towards you. Carefully openand bleed the remaining pressure. Remove the top cover of the cell and turn the cell

upside down in a sink. Remove the cover from the hydraulic part (bottom) and uncover

the floating piston. Tighten the T-wrench and push downwards, to make the mud and

disk come out from the opposite end.

12. Recover the disk and filter cake and rinse with freshwater or a base oil if using an oil

base mud. Measure the thickness of the filter cake in 32”/inches. The total fluid is

calculated as follows:

Total fluid loss (cm3) = spurt losses (cm3) + 2 x (fluid recovered in 30 min. (cm3).




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21.0 COUPON RING FOR DRILL PIPE CORROSION

This system for determining drill pipe corrosion is important but hardly used nowadays, so we

shall give a brief overview. The rings, in bronze, are put between the threads of the drill pipes

before they are run into the well. The rings are then removed after some 100 hours. They are

carefully examined to determine the cause and rate of corrosion.

From this information, the type of inhibitors and products to use to prevent or minimise corrosion

can be selected.

21.1 Monitoring corrosion rings

1. The rings should stay in the drill string for at least 40 hours, as a shorter time

would give inaccurate data. The standard time is around 100 hours. The rings are

assembled in pairs; the first on the surface, in the Kelly Saver Sub, and the second in the

last drill pipe, above the drill collars.

2. The ring is put in a bag after it is removed from the drill string. The form on the

bag should be carefully filled in, with the name of the oil company, well name and

number, contacts, type of mud and products used in it, string metallurgy, depth, period of

use and removal date.

21.2 Laboratory test

1. Before evaluating corrosion, the ring needs to be washed with detergent and rinsed

and prior to this it should be weighed to compare the vale with the original weight on the

packaging. Use drops of reagent to check for any residual carbonates from dissolved

H2S, CO2 or other substances.

2. The ring should be washed with mild detergent and a hard bristle brush, then put in a

15% hydrochloric acid solution with an inhibitor, once or twice, to remove corrosion

products. The ring should be cleaned each time it has been put in the acid solution and

rinse with service water, followed by anhydride acetone or methyl alcohol to make sure it

is dry (always follow safety recommendations when using these chemical products).

3. Weigh the ring again (to the milligram) and calculate any weight loss (corrosion). Any

significant metal loss caused by mechanical damage should be recorded in the ring

report. The corrosion value is obtained multiplying the weight loss (g) by the K-factor,

divided by the total number of hours the sample was downhole.




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4. Visual inspection

Corrosion which is evident when the sample is removed from the drill string may be

caused by a general attack or pitting. The corrosion value is the weight loss of a general

attack. The pitting value cannot be determined from the weight loss of the ring.

Mechanical damage may consist of cuts on the metal, or metal which has been removed

from the surface. In some cases, the ring will have wear marks, which mean that the ring

and housing have moved considerably during drilling and manoeuvres. As the coupon

rings are exposed to mud circulation, the mud loss includes circulation corrosion and

erosion.

Inspection of the rings may reveal deep pitting with a fairly low weight loss. This

indicates a corrosion problem which goes beyond general surface corrosion.

The pH and Pf should be maintained at optimal levels for all water base muds. If these

values tend to increase, an organic inhibitor may be necessary. Bacteriological

problems also need to be considered as these may cause a number of problems for the

mud.

The corrosion values for freshwater and mud are usually 2 lb/ft2-y or less, without any

deviations. Values towards the top end of this scale should be further evaluated by

adding chemical treatments.

21.3 Calculating the degree of corrosion

Coupons for determining corrosion are available from service companies. These are

usually numbered, pre-weighed and packed in water-repellent paper. The coupon

number is on the packaging along with the K-factor calculation. The degree of corrosion

is obtained from the weight difference of a coupon before and after the test, multiplied by

the K factor and divided by the total number of hours.

For qualitative purposes, coupons should be weighted extremely carefully before and

after the test. The test should preferably be carried out at another laboratory.




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1. If the K factor is not available, the degree of corrosion can be calculated in lb/ft2 per

year (lb/ft2-y) using the following formula:

lb/ft2-y = (weight loss (mg) x 144 x 365) / (453,600 x *area (in2) x days of exposure **

or = (weight loss (mg) x 2,781) / (*area (in2) x hours of exposure**)

kg/m2-y = (weight loss (mg) x 10,000 x 365) / (1,000,000 x area (cm2) x days of

exposure**)

or = (weight loss (mg) x 87.60) / (*area (cm2) x hours of exposure**)

* The total surface area of the ring is used for this calculation.

** Time based on the total period of use of the string.

2. The conversion rates between various units for steel follow: mpy = 24.62 x lb/ft2-y mpy

= 5.03 x kg/m2-y lb/ft2-y = 0.04 x mpy lb/ft2-y = 0.20 x kg/m2-y kg/m2-y = 0.20 x mpy

kg/m2-y = 4.90 x lb/ft2-y

Chapter 3 Water Based Mud

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Transcript of Chapter 3 Water Based Mud