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Agip KCO Training Special Project SP 2Basic Oil and Gas in Exploration
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Drilling engineering
BO-019-GIA-001-E
Drilling Engineering
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Drilling engineering
Drilling Engineering
a)Objectives of drilling engineering
b)Evaluation of pressure gradients
c) The design of the drilling programme: selection
of bits, casings & muds
d)Monitoring & logging while drilling
e)Cutting disposal: problems and solutions
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Drilling engineering
Drilling Engineering
Drilling an oil well involves two main actions:
Overcoming the resistance of rock material
Transportation of rock material to the surface
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Drilling engineering
Objectives Of Drilling Engineering
a) To drill a well safely and economically
b) Drilling cost equations
c) Drilling fluid treatmentd) Pump operation
e) Bit selection
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Basic Oil and Gas in Exploration
and Production Activities
Drilling engineering
BO-019-GIA-005-E
Pressure Gradient
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Well Planning:
Casing Point Selection
Casing Design
Mud Density
Fracturing Gradient
Drilling Rig Selection
Importance of Formation Pressure Gradients
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Drilling engineering
While Drilling:
To use adequate mud density:
> to avoid kicks o blow-outs
> To avoid mud absorption and/or mud loss circulation
> to avoid sticking of drilling string for differential
pressure
> to avoid sticking of drilling string due to caving hole
> to reduce drilling times
To change, in case of need, the casing point depth while
drilling.
To reduce the drilling problems and reach the planned welldepth.
To cut drilling costs.
Importance Formation Pressure Gradients
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Drilling engineering
Hydrostatic pressure at a certain depth is defined as the pressure exerted by theweight of the fluid column with a given density.
P = hydrostatic pressure expressed in kg/cm2
H = examined depth expressed in meters
f
= fluid density expressed in kg/dm3, usually for water assumed to be equal to 1.03 kg/dm3
P
Hf=
10where
Hydrostatic Pressure
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Drilling engineering
where:
Ghyd = hydrostatic gradient expressed in kg/cm2/10m
P = pressure expressed in kg/cm2
H = examined depth in m
Pressure Gradient is defined as a ratio of pressure value and depth:
GP
Hhyd
= 10
Hydrostatic Pressure Gradient
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Drilling engineering
ABNORMAL Pore Pressure
The Formation Pressure can be :
OVERPRESSURE. Its value is > than the hydrostatic Pressure
UNDERPRESSURE. Its value is < than the hydrostatic Pressure
Formation Pressure (Ppore)
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Drilling engineering
Gradient > 1.03-1.07 kg/cm2/10m OVERPRESSURED:
UNDERPRESSURED: Gradient < 1.03-1.07 kg/cm2/10m
NORMALPore Gradient is considered normal when its value isbetween 1.03 and 1.07 kg/cm2/10m.
Pore Gradient is considered
abnormal when its value isdifferent from the ones mentioned above.
Hence there might be:
ABNORMAL
FORMATION GRADIENT
Formation Gradient
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Drilling engineering
OVERPRESSURESOVERPRESSURES
TectonicsTectonics
Sedimentation Speed
Reservoir GeometryReservoir Geometry
Artesian PressureArtesian Pressure
DiapirismDiapirism
OsmosisOsmosis
Clay DiagenesisClay Diagenesis
Sulfate DiagenesisSulfate Diagenesis
Reservoir RepressurizedReservoir Repressurized
Volcanic Ash DiagenesisVolcanic Ash Diagenesis
UNDERPRESSURESUNDERPRESSURES
Drop of Water TableDrop of Water Table
Depleted ReservoirsDepleted Reservoirs
Dilatation due toTectonic Phenomena
Dilatation due toTectonic Phenomena
ABNORMAL PRESSURESABNORMAL PRESSURES
Abnormal Pressures
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Drilling engineering
GpGp >>
kg/cmkg/cm22/10/10mm
Overpressure Index
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Drilling engineering
Sedimentation Velocity
Tectonics
Reservoir Geometry
Artesian Pressures
Diapirism
Diagenesis
Osmosis
Sedimentation Velocity
Tectonics
Reservoir Geometry
Artesian Pressures
Diapirism
Diagenesis
Osmosis
Origin Of Overpressures
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Drilling engineering
A
BB
C
A - C = Normal PressureBB = OverpressureA - C = Normal PressureBB = Overpressure
Tectonics Uplift
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Drilling engineering
A - C = Normal PressureBB = Overpressure
A - C = Normal PressureBB =Overpressure
BB
C
A
Tectonics Uplift
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Drilling engineering
2000 m PPORE = (2000 * 1.03)/10 = 206 kg/cm2 ; GPORE = (206/2000) * 10 = 1.03 kg/cm
2/10 m
1500 m PPORE = 206 - (1.03 * 500/10) = 154.5 kg/cm2; GPORE = (154.5/1500) * 10 =1.03 kg/cm
2/10m
1000m PPORE =154.5 kg/cm2 -(0.7 * 500/10) = 119.5 kg/cm2 - GPORE = (119.5/1000) * 10 =
= 1.195 kg/cm2/10 m
1.195 > 1.031.195 > 1.031.195 > 1.031.195 > 1.03
OilOild = 0.7d = 0.7
Water d = 1.03Water d = 1.03
OverpressureOverpressure
1500
2000
1000
Reservoir Geometry
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Drilling engineering
2000 m PPORE = (2000 * 1.03)/10 = 206 kg/cm2 ; GPORE = (206/2000) * 10 = 1.03 kg/cm
2/10 m
1500 m PPORE = 206 - (1.03 * 500/10) = 154.5 kg/cm2; GPORE = (154.5/1500) * 10 =1.03 kg/cm
2/10m
1000m PPORE =154.5 kg/cm2 -(0.1 * 500/10) = 149.5 kg/cm2 - GPORE = (149.5/1000) * 10 =
= 1.495 kg/cm2/10 m
Water d = 1.03Water d = 1.03
OverpressureOverpressure
1500
2000
1000
Gasd. = 0.1
1.495 > 1.031.495 > 1.031.495 > 1.031.495 > 1.03
Reservoir Geometry
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Drilling engineering
+ 300 m
San
ds
San
ds
RKB 0 m
- 250 m
Piezometric Level
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Drilling engineering
221
3
Diapiritic Structures - Creation Of A Saline Dome
Di i i
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Drilling engineering
Overpressure
Salt
Diapirism
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BO-019-GIA-0022-E
Underpressures
U d I d
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Drilling engineering
kg/cmkg/cm22/ 10 m/ 10 m
(in depleted wells, for instance )(in depleted wells, for instance )
Gp
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Overpressure Analysis
O A l i
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Drilling engineering
Analysis methods are based on the following concepts:Sediment compaction grows with depth
(a higher sediment compaction corresponds to a higher depth.)
Overpressure analysis is performed taking
SHALES ONLY (possibly pure) into consideration.
Shales are overpressured when, not having been able to
expel their pore water, are more porous and therefore
NOT COMPLETELYCOMPACTED.
Overpressure Analysis
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BO-019-GIA-0026-E
Overpressure Analysis
While Drilling
Overpressure Analysis While Drilling
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Drilling engineering
THE EMPIRICAL METHODS OF OVERPRESSURE CONTROL WHILE DRILLING ARE:
dc Exponentdc Exponent
Sigma LogSigma Log (developed by AGIP)
FEATURES:
BOTH METHODS ARE INDICATORS OF SHALE FORMATIONS DRILLABILITY.
THEY ARE BASED ON THE CONCEPT THAT ROP (Rate of Penetration) DECREASES
FROM THE SURFACE DOWNWARD AS DEPTH INCREASES, ON ACCOUNT OF HIGHER
SEDIMENT COMPACTION.
WHEN OVERPRESSURED, FORMATIONS ARE ALSO UNDERCOMPACTED.
Overpressure Analysis While Drilling
Overpressure Analysis Well Indications
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Drilling engineering
GAS PRESENCE
Pipe connection gas
Trip gas
BOREHOLE SHRINKAGE
Torque while drilling
Overpulls while trippingBit reaming
Cavings
Borehole collapse
MUD PUMPING PRESSURE
Overpressure Analysis - Well Indications
Overpressure Analysis
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Drilling engineering
The parameters that this tool can measure at bottomhole and make available to thesurface in real time are:
Wellbore inclination Wellbore direction
Drilled formation resistivity Neutron log Temperature Bit Torque Weight on bit
Overpressure Analysis
Measurement while Drilling (MWD)
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Drilling engineering
Fracturing Gradient
Fracturing Gradient
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Drilling engineering
Pressure Gradients (referred to RKB), expressed in Kg/cm2/10m, are:
Pore Gradient or Pore Pressure Gradient.
Sediment Gradient or Overburden Gradient (GOV).
Fracturing Gradient - Knowledge of the fracturing gradient curve along the well
profile is of fundamental importance, together with pore gradient:
>To plan the well. It allows to determine the best casing points in function of two
parameters:
choke margin
differential pressure
>To drill the well. It allows to operate safely while drilling the well, and in case of kick
or blow-out control.
Fracturing Gradient
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Leak - Off Test (Lot)
Formation Integrity Test (Fit)
Leak-Off Test
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PURPOSE OF LOT
To check the real Fracturing value, after a casing string has been run.
To check the real Fracturing value, after drilling through a layer with highporosity and/or permeability.
Leak Off Test
Formation Integrity Test
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It consists in a check of a formations resistance to a predetermined pressure. This pressure
value corresponds to the highest mud density that is going to be employed during drillingoperations.
The procedure is similar to that of LOT, the only difference being that an engineer wont look forthe leak point, but will stop pumping once the predetermined pressure value has been reached.
Mill cement and shoe, and drill maximum 10m of new hole.
Circulate mud in the well, and uniform mud density.
Close the BOPs.
Pump with a low flow rate (1/4 - 1/2 bbl/min), and plot pumped volume and pressure values.
Stop pumping when the predetermined pressure value has been reached (pumping pressureplus mud pressure).
Formation Integrity Test
Rotary Drilling Bits
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Drilling engineering
y g
Bit Selection
Rotary Drilling Bits
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Drilling engineering
Bit Selection
Theoretically, bit selection is a simple procedure. Select the proper bit based
on:
Type of formation to be drilled
Type of drilling fluid being used
Strength and characteristics of BHA
Capability of surface equipment (pumps, rotary, drawworks, etc) to
supply the power needed
Unfortunately, downhole conditions are too unpredictable and changeable for
this to happen.
Rotary Drilling Bits
Rotary Drilling Bits
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Drilling engineering
The most important consideration affecting bit design is the type of rock that the
bit will be drilling:
Is the formation hard or soft?
Is it composed of abrasive sand?
Is it a sticky, heavy shale?
Is is porous chalk?
One bit to drill all these formations would be ideal. However, no single bit can do
this with equal efficiency.
Bit Selection
Rotary Drilling Bits
Rotary Drilling Bits
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Drilling engineering
The hardness of a rock depends upon its strength of cementation. Sand can
range from a tightly fused matrix to an unconsolidated matrix.
Bit Selection: Formation Hardness
Soft Soft shales, clays, weak sandstones, salt, gypsum, anhydrite
Medium Hard limestones, sandstones, dolomite, hard shales
Hard Chert, dolomite, sandy shales
Extremely Hard Quatzite, chert, basalt
Rotary Drilling Bits
Rotary Drilling Bits
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Drilling engineering
The abrasiveness of a rock can range from low abrasiveness to very abrasive for
each formation hardness.
Bit Selection: Formation Abrasiveness
Low abrasion Clays, shales, limestones, basalt
High abrasion Mixtures of clay and limestone with sand
y g
Rotary Drilling Bits
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Optimizing Drilling Parameters
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Rotary Drilling Bits
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As the bit drills, it eventually starts to wear out.
The teeth that crush the formation begin to wear down. The bearings that allow
the cones to turn start to wear out and fail.
The more weight put on the bit and the faster it turns - the greater the wear, yetthe faster it drills.
As the bit wears out, it will not drill as efficiently, and the ROP decreases.
Eventually the bit slows down so much that it is not economical to leave it in the
hole any longer, so it is pulled from the hole and replaced with another.
Optimizing Drilling Parameters
y g
Rotary Drilling Bits
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Drill bit optimization can be viewed as having 3 distinct phases:
Selecting the proper bit for the drilling conditions
Monitoring the drilling conditions on the well so that the drilling
performance is at least equal to the best well in the area
Implementing a bit weight/rotary speed program from theoretical
calculations that will improve drilling performance above the best wells
in the area
Optimizing Drilling Parameters
y g
Rotary Drilling Bits
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There is a known relationship between drilling rate and rotary speed:
Soft formations: drilling rate is directly proportional to rotary speed
Hard formations: ROP decreases with increased RPM
In hard formations, the cutting action of the bit requires that the teeth first
penetrate the formation and then scrape or gouge out the formation. If the RPM
is too fast, the teeth will not have enough time to fully penetrate the formation
before they get pulled out again as the bit rotates.
Optimizing Drilling Parameters: Rotary Speed
Rotary Drilling Bits
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Drilling rates increase in close proportion to rotary speed, providing -
Bottom hole cleaning is adequate.
Unless the cuttings already produced are cleaned out of the path of the bit assoon as possible, the bit will end up cutting the cuttings, when it could be used
to cut virgin rock.
Optimizing Drilling Parameters: Hole Cleaning
Rotary Drilling Bits
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Low solids content mud will give a better rate of penetration in a similar fashion
to low mud overbalance.
It is not clear exactly why, but it is speculated that the mud solids may slow
down the equalization of pressure under the chip.
With a solids-free system, the drilling fluid can more easily penetrate past the
chip to reduce the hold down effect.
Optimizing Drilling Parameters: Mud Solids and ROP
Rotary Drilling Bits
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Drilling engineering
The ROP of any drill bit is limited by the ability of the mud to clean the bottom of
the hole.
The goal of the hydraulics program is to remove the cuttings from the face of the
bit as soon as they are dislodged.
If the cuttings are not quickly removed, the bit will end up cutting them again,
needlessly.
Using the proper nozzles to increase the flow rate and increase the speed at
which the mud flow hits the bottom will increase ROP.
HOWEVER
Optimizing Drilling Parameters: Hydraulics
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Casing Design
Casing Profile
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30" CP
20" csg
9 5/8" csg
8 1/2 hole
13 3/8"csg
standard" profile
Casing Design - Casing Profile
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Role Of The Casing - Conductor Pipe
The depth at which the conductor pipe (C.P.) will be fixed must allow the mud to circulate to
the surface.
Isolate surface unconsolidated formation.
Shallow gas.
Casing Design - Casing Profile
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Role Of The Intermediate Casing
Allow a greater choke margin ( 40 kg/cm
2
).
One or more intermediate casing string may be required to isolate different targets.
Isolate formations with different pressure gradients.
Etc.
Casing Design - Casing Profile
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Role Of The Production Casing
The production casing string will serve to isolate the productive intervals, to facilitate properreservoir maintenance and/or prevent the influx of undesired fluids.
This is the string through which the well will be completed, produced and controlled
throughout its life.
Diameter.
Thickness (or weight in lb/ft).
Casing Design - Casing Profile
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Role Of The Liner
CASING DESIGN (CASING PROFILE)
Role of the LINER
INTERMEDIATE LINER
PRODUCTION LINER
Casing Point
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P3
P2
P1
P4
De
pthm
Depth 2
Depth 1
Depth 3
Depth 4
PORE PRESSURE
FRACTURING
PRESSURE
Pressure
Casing Profile
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30" CP
20" csg
9 5/8" csg
8 1/2" Hole
13 3/8" csg
Slim"
Casing Profile
133/8" CP
95/8" csg
7" csg
5" csg
4 1/2 Hole
Standard
Casing Profile
Casing Profile
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Standard"Profile
(5 casingstrings)
Lean"Profile
(5 casingstrings)18 5/8
30 CP
24 1/2
133/8
9 5/8
8 1/2
Hole
24 1/2 CP
16
18 5/8
133/8
9 5/8
8 1/2Hole
Casing Design
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Casing Threads
NON API
ANTARES DALMINE BIG OMEGA MANNESMAN FJWP HYDRIL VAM VALLOREC
etc..
API Standard
SHORT THREAD COUPLING
LONG THREAD COUPLING
BUTTRESS THREAD
EXTREME LINE THREAD
Casing Design
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Safety Factor
COLLAPSE 1.1 ALL
BURST 1.05 H40 - J/K55
1.1 C75 - P110
1.2 Q125
TENSION 1.7 C95
1.8 > C95
Casing Design
M i St
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Main Stresses
BURSTBURST
COLLAPSECOLLAPSE
TENSIONTENSION
Casing Cementing
T Of C t
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Top Of Cement
1. Surface Casing
a) Offshore wells
b) Offshore wells
> From Jack-up / Fixed Platform
- Exploration wells - Development wells
> From Floating Rig
Casing Cementing
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2. INTERMEDIATE CASING
The main aim of the rise of the cement in the annuls is to restore the hydraulic conditions in
the well after the borehole has been drilled (avoid communication between formations withdifferent pressure gradient and containing different hydrocarbons), isolate overpressure
zones; temperature problems.
a) Onshore wells
b) Offshore wells
> From Jack-up / Fixed Platform
> From Floating Rig
Well Heads
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The well heads available on the market have working pressure of :
- 2.000 psi
- 3.000 psi
- 5.000 psi
- 10.000 psi
- 15.000 psi
- Theselected WORKING PRESSURE of the well head is according to the
maximum formation pressure predicted at bottom hole.
- In thepresence of CO2 or H2S special steels will have to be used in
accordance with corrosion Standards.
Well Heads
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Well heads for:
Onshore andJack-up Rigs
Semisubs or Drilling Ships (subsea well heads)
Onshore and Jack-up Rigs
A. Conventional well head.
B. UNITIZED well head (compact well head).
Christmas Tree
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Bop Selection
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The pressure rating of the BOPs must be higher than the maximum pressurepredicted at the well head (with the exception of the annular preventer).
- BOP for DRILLING
- BOP for PRODUCTION TEST
Wellhead
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Blow-out
Preventers
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BO-019-GIA-0066-E
Cement Job
Cementing Jobs
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Primary cementing
Cement plug
Cement squeeze
Primary Cementing
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Primary Cementing
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Primary cementing means the cementing of the casings or liners of a well.
All the casings and liners of a well must be cemented except for some liners,
normally those with slots for the passage of the produced fluids and which, once
positioned in the well, are simply left anchored to and suspended from the casing
above.
So surface, intermediate and production casings are all cemented with slurries of
different properties and formulas to take into account the different well parameters at
the depth at which they are positioned.
Calculating a Primary Cementing
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previous
csg shoe
csg shoe
csg collartail cement
lead cement
excess (..%) in
open hole
mud
Two-stage Primary Cementing
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Casing can be cemented in one or two stages.
Cementing is one-stage when the work is completed in one step; that is, when all the
cement is placed where needed in a single job.
Instead, cementing is two-stage when the annulus is filled with cement in two steps; during
the first step the cement is placed in the lower part of the annulus followed by a second
step when the cement is placed in the top part of the annulus.
Cement Plug
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These are operations which may be necessary at any point during the construction or life
of the well.
During drilling, to solve serious lost circulation problems (lost circulation plug), or when
the bit has to be deviated from vertical drilling (kick-off plug).
During production, when levels which are no longer economically viable or levels which
produce water or gas have to be shut-in.
At the end of the wells producing life when, in accordance with mining laws, a well has to
be shut-in with a given number of cement plugs (abandon plugs).
Cement Squeeze
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Cement squeeze means the forced pumping of slurry inside the rock to create a solidsleeve which acts as a barrier so that fluids do not flow into or out of the rock.
A squeeze is often a remedial job and takes place during a wells producing life.
A squeeze is a difficult operation to plan because many variables are involved:
appropriate formula of the slurry
squeeze pressure
pumping rate
type of formation and its permeability
Cement Squeeze
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BOP or
Hydrill(closed)
the pressure applied
during the squeeze
acts along the entirelength of the casing
P of the
squeeze
Cement Squeeze
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lower packer which isolates the
squeeze zone
squeeze packer
tubing string
or drill pipe
casing
shot interval
to be closed stinger
slurry
Examples Of Problematic Cement Jobs
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Figure 1
Figure 1 shows a typical case of cement
channelling where the casing rests on the
wall of the well.
The result will be the formation of an
excess of filtration deposit and a film which
adheres to the casing . Even if the slurry
had completely filled the annulus, its
adherence to the casing would not beperfect.
Examples Of Problematic Cement Jobs
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Figure 2
The eccentricity of the casing inside the
borehole favours the settling of the cement
through the mud. Moreover, the cavities of
the borehole will have collected viscous mud
and cuttings.
Figure 2 shows an excessive formation of
cake at the two permeable zones.
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