Dwm in Onshore Environmental Sensitive Area

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Drilling Waste Management in

Onshore Environmental Sensitive Areas

Authors:

Mojtaba Kalhor Mohammadi, Curtin University of Technology, Western Australia

Co-authors:

A. Professor Jorge Sampaio, Curtin University of Technology, Western Australia

Dr. Koorosh Tahmasbi, Petroleum University of Technology, Iran

Dr. Frank Almassi,Baker Hughes Drilling Fluids, Perth, Australia

Abstracts

Drilling operations have always been considered by environmental agencies because of

generating large volumes of wastes during operation include drilling fluid, cuttings, rig

wash water, etc. Discharge of these wastes in the environment is the main concern and

requires waste management plan before starting the project in the drilling site.

Many practices and treatment have been introduced in the drilling site to treat and

manage of the drilling waste but there are still some issues about environmental friendly,

operational and cost effective practices in drilling operation.

This paper describes the dewatering process as a drilling waste management practices in

a drilling project in Western Australia. The main significant objective of this project is to

remain the operator in compliance with current regulations and the cost of waste

management practice. Also preplanning laboratory test has optimized chemical

consumption and helped to find out the dewatering efficiency in waste treatment.

1

Introduction

Environmental legislation in the exploration and production of oil and gas requires plans

for managing of wastes during operations by operators, service companies and

contractors. As the view of the waste generation, environmental agencies consider the

drilling as one of the important operation in exploration and production. During the


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Drilling Waste Management in Onshore Environmental Sensitive Areas

First Iranian Petroleum Engineering Congress 2

drilling operations large volumes of wastes is generated including drilling fluid, cuttings,

rig wash water, etc. Discharge of these wastes in environment is the main concern

because of their effects on the environment and there are some policies and regulations

on discharge of wastes by the environmental organizations and governments.

Environmental sensitive areas including islands, lakes, all areas surrounding the river and

life of animals and vegetations are considered by the environmental agencies.

Traditionally, drilling wastes were discharged in ocean or onsite location without any

concern about future environment problems.

Nowadays, preserving these environmental area considered as the global awareness has

been started from 1990s and the liability of the future environmental problem will be

remained by the initial waste producer in the site. There were two significant aspects in

managing of the drilling waste in onshore environmental sensitive areas; the first one is to

recognize harmful wastes, volume of wastes and limitation of the discharge. The second

one is to select an efficient, operational and economical option for waste management.

2 Drilling Waste Management

As a definition, Drilling Waste Management is a management system for selecting

optimal strategies, determining successful practices and technologies for treating the

drilling waste in a given geographical or environmental setting. Geographical locations

and environmental requirements play an important role to find proper management

systems in drilling sites.

Most of operators plan treatments and practices for waste management according to

drilling locations and limitations. Usually, limitations dictate by the environmental

organizations and governments. But an efficient drilling waste management system

follows goals including minimization of the drilling waste, reusing/recycling and efficient

disposal plan. To approach these goals, many practices introduce to drilling industry.

Traditionally, most of them were increased the well cost but during the last 10 years,

many cost effective options have been introduced to onshore and offshore drilling

industries.


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3 Case Study

The case study herein shows the drilling waste management practices in an onshore

environmental sensitive in Western Australia. Zero discharge practice in drilling

operation is one of the environmental requirements in WA. All operators must use waste

management plan during the drilling operation to manage drilling wastes including; drill

cutting, drilling fluids and waste water.

As the initial waste management plan, the drilling fluid was designed as water based mud

to reduce the environmental impact by providing technical requirements during drilling

operation. Collection and treatment of the generated waste water from tanks washing and

rig washing are the other waste management plan before final discharge in this project.

The main issue in this project was the liquid waste including remained drilling fluids after

operation for each section of the drilling. Collection of these wastes in reserve tanks and

hauling of them to shore was not the acceptable solution as there is still some issue about

spillage or leakage during hauling and shipping. On the other hand, volume of the liquid

waste, distance from disposal facility and cost of the shipping associated with

environmental concern. All of these reasons caused to plan onsite treatment on the

drilling waste before final discharge of wastes.

4 Theory

Theory of the dewatering process is based on pH controlling of the drilling fluid wastes

and surface charge of fines and ultra fines. In the pH range of the drilling fluids that is

typically being between 7 to 11, ultra fine particles in the drilling fluids tend to be

charged negatively. These negative charges repel the particles and prevent from clumping

of the particles. This causes difficulty in removing the ultra fine particles even with a

high-speed centrifuge with 2000 g force. To solve this problem, it is necessary to treat the

drilling fluids or waste fluids chemically to agglomerate the solids to make them large

enough to be removed by a high-speed centrifuge. The process of agglomeration to create

large, dense clusters requires two steps:

1. Destabilize the submicron particles so they no longer repel each other. This is easily

achieved by lowering the pH from its original pH to approximately 5.5.


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2. Flocculate, bundle, or wrap together to create large dense clusters.

These two steps can be accomplished by sequentially adding three chemicals; or

sometimes only one or two chemical additives can accomplish all three steps. Today,

ranges of polymers produce by companies with different molecular weight of cationic

coagulants, non-ionic, anionic and cationic flocculants.

Figure 1- Schematic procedure of dewatering

4.1Technical Consideration

As the technical consideration, dewatering process requires laboratory procedures such as

jar test to select the proper coagulants and flocculants. But there is a problem in finding

the optimum dosage/concentration of chemicals in jar test. Optimization of chemical

concentration is necessary in the dewatering process. Otherwise, it increases the cost of

chemical consumption in the field. To approaching this goal, series of the laboratory tests

have been done to select the proper chemicals and the proper dosages of them by

centrifuge simulation as the additional procedure to common jar test. This has helped to

simulate the separation process as the field condition to obtain the optimum chemical

dosage in the dewatering process and also find out the dewatering efficiency in reducing

the waste volume and monitoring the quality of the produced water in the dewatering

process.

Bridging Flocculation

Polymer chains can"bridge" particles tocreate larger masses thatsettle out

Charge Neutralization

Like charged particlesrepel removal of chargecan enable particles toapproach close enough

to coagulate


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5 Results

Initially, pH of the drilling fluid waste reduced to neutralized point with different

percentage of wastes with water. Monitoring of pH has shown that 50% dilution of the

waste with water has reduced the concentration of acid to 50% in comparison with the

25% water dilution (Figure 2). Mixing the waste with water helps to destroy the balance

of the chemicals in the drilling fluids especially the portion of the polymers in it. Also, it

is cost effective to reduce the consumed volume of the acid by adding water.

In the next step, different volumes of the flocculants have been added to compare the

settlement of the solids during the time. This has helped to find the proper flocculants for

dewatering. (Figure3). The initial concentration of the flocculant obtains by comparing

the solid settlements within the first minutes after adding the flocculant in figure 3. As

figure 3 has showed after a certain concentration, solids precipitation has remained

constant as concentration graphs overlap on each other but this is not the optimum

concentration. Until this step it is possible to introduce the proper flocculant with the

initial concentration.

5

5.5

6

6.5

7

7.5

8

8.5

9

9.5

1010.5

11

11.5

12

0 5000 10000 15000 20000 25000 30000 35000

Concentr ation of Acid (ppm)

pH

No Dilution, Real

Waste25% Dilution of

w ater50% Dilution of

w ater

Figure 2-pH control of the drilling fluids waste

Dilution of the waste with water is effective on reducing the concentration of pH control chemicals and

helps to better mixing of the acid with waste in a lower time as desired in the dewatering process. 50%

dilution of water reduces the required acid to 14000 ppm from the initial value (29000 ppm) at the

neutralized point.


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0

2

4

6

8

10

12

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32Time,Min

SolidsPrecipitation(%

)

40ppm 80ppm 120ppm 160ppm 200ppm

Figure 3-Solid precipitation with different concentration of the flocculantIn the dewatering process, flocculation must be considered within the first minutes after adding flocculant.

As the figure shows, solids precipitation increases as the concentration of the polymer increases until 160

ppm. More than 160 ppm overdosing occurs as there is no increase in the solid precipitation in the first

minutes.

To find the optimum concentration of the acid to reduce pH, solid separation versus

different concentration of the acid has been compared. According to the figure 4, after a

certain concentration, the solid separation has remained constant as there is not much

increase in the solid percentage. This concentration is the optimum value for the pH

reduction. To find the optimum concentration of flocculants, the same procedure has been

done with adding different concentration of the flocculant and centrifuging for one

minute. Comparing results in figure 5 shows that by increasing the concentration of the

flocculant the solid precipitation increases but the difference is eligible for the last two

samples in each experiment, and it can be understand more concentration of the

flocculant cause overdosing. Also, feeling the produced water after centrifuging has

showed the amount of polymeric flocculant in the water. Figure 6 shows the completedewatering process after centrifuging.


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0

10

20

30

40

50

60

0 3000 6000 9000 11000 14000 17000 20000

Concentration (ppm)

SolidsSeparation(%)

Figure 4-Solid precipitation versus concentration of the acid

Centrifuging of the sample after adding acid has shown that there is not more affect on the solid separation

after 17000 ppm. This concentration of acid can be the optimum value in the lab scale

0

5

10

15

20

25

30

35

40

45

0 40 80 120 160Concentr ation (ppm )

Solids

Separation(%)

Only Polymer (withou t Acid)Acid = 5700 pp mAcid = 11500 ppmAcid = 17200 ppmAcid = 23000 ppm

Figure 5-Solid precipitation with different concentration of the acid

and flocculants after centrifuge

This graph has provided the solid separation with different concentration of acid and polymer. There is over

dosing on the last two column of the graph as there is not much difference on solid precipitation for 160

ppm of polymer.


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Figure 6- Dewatering simulation of the drilling fluids waste

by the laboratory centrifuge scale

5.1Economical Consideration

Dewatering has become common in many instances, especially as technology has

advanced and the units have become less expensive. Using cost effective practices such

as dewatering process to get the clear water from drilling wastes reduce operating costs

and also reduce the concern about the environment for exploration and production

companies.The main benefit of the dewatering process is providing the acceptable format of the

waste discharging. As the economical consideration, the cost of hauling of the waste to

disposal facilities has reduced significantly. In addition the produced water was used as

the recycle water in the system. So the cost of used water in the circulation system is

reduced. The only concern about this process is the quality of the produced water that

must be considered by controlling the pH and other extra ions in the produced water that

must be control in the field.

6 Conclusion

In conclusion, drilling waste management is the decision of using proper technologies

and practices according to environmental requirements to reduce the environmental


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impacts and cost of the waste management plan. The dewatering process describe herein

is one of the efficient treatments to treat the waste before discharging that has been an

expensive technology for many years. But it has been changed to a cost effective option

in drilling site with more flexibility.

Finally, optimization of the chemical consumption in the waste treatment is the hidden

part in the waste management practices that can change expensive practices to the cost

effective solutions. The volume of the drilling fluid waste reduces to at least 50% of the

initial volume after dewatering process with production of the water that can be released

or reused in the drilling system as required.

Acknowledgment

The authors wish to acknowledge the support and assistance provided by Baker Hughes

Drilling Fluids Company in Perth, especially Marc Quesnel; Distric Manager- Drilling

Fluids and Chris Hargreaves; Senior Co-Ordinator, Simon Geraghty; Project

Management Consultant, Dusan Andovski; Fluids Laboratory Technician.

Also special thanks to Dr. Emmazadeh; Petroleum University of Technology and also

Professor R.T. Rajeswaran; Curtin University of Technology.

References

[1] Veil, J.A, Drilling Waste Management: Past, Present, and Future, SPE Annual Technical

Conference and Exhibition, 2002.

[2]

Muhammad Ali, Reinhard J. Oswald and Umar Iqbal, SPE Annual Technical Conference,

OMV'S DRILLING WASTE MANAGEMENT A PROACTIVE APPROACH,2004

[3] Drilling Fluid Processing Handbook , Chapter 16 ,ASME Shale Shaker Committee, 2004

[4]

Guide to Dewatering Drilling Fluids, Ciba Co. , 1999[5] Dobias, B. ,Coagulation and Flocculation : Theory and application, 1993

[6] Briji M., Engineering Foundation Conference, Flocculation, Sedimentation and

Consolidation, 1985

Dwm in Onshore Environmental Sensitive Area

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