1. INVESTIGATING THE EFFECTS OF COAL FORMATION
CONTAMINATION ON RHEOLOGICAL PROPERTIES OF WATER
BASED MUDS
MUHAMMAD HAFIZI BIN ZAINOL ABIDIN
PETROLEUM ENGINEERING
UNIVERSITI TEKNOLOGI PETRONAS
SEPTEMBER 2016

2. Investigating The Effect Of Coal Formation Contamination On Rheological
Properties Of Water Based Mud
by
Muhammad Hafizi bin Zainol Abidin
17552
A project dissertation submitted in partial
fulfilment of the requirement for the
Bachelor of Engineering (Hons)
(Petroleum Engineering)
SEPTEMBER 2016
Universiti Teknologi PETRONAS
32610, Bandar Seri Iskandar,
Perak Darul Ridzuan

3. ii
CERTIFICATION OF APPROVAL
Investigating The Effect Of Coal Formation Contamination On Rheological
Properties Of Water Based Mud
by
Muhammad Hafizi bin Zainol Abidin
17552
Project dissertation submitted to the
Petroleum Engineering Programme
Universiti Teknologi PETRONAS
in partial fulfilment of the requirement for the
BACHELOR OF ENGINEERING (Hons)
(PETROLEUM ENGINEERING)
Approved by,
__________________
(Mr. Asif Zamir)
UNIVERSITI TEKNOLOGI PETRONAS
BANDAR SERI ISKANDAR, PERAK
September 2016

4. iii
CERTIFICATION OF ORIGINALITY
This is to certify that I am responsible for the work submitted in this project, that the
original work is my own except as specified in the references and
acknowledgements, and that the original work contained herein have not been
undertaken or done by unspecified sources or persons.
________________
MUHAMMAD HAFIZI BIN ZAINOL ABIDIN

5. iv
ABSTRACT
Drilling in coal formation has emerged as one of the critical challenges in retrieving
unconventional energy, especially in the usage of the drilling fluids within the
operation. A comparative study will be made in this paper to investigate the effects
of different percentages of coal formation contamination into the water based muds
(WBM) as the base fluids during drilling operation downhole. A thorough research
including the effects on the rheological properties such as the density, viscosity, gel
strength, filtrate loss and yield point of each of the contaminated samples will be
made by the writer using the existing drilling mud preparation equipment. The coal
type that will be used throughout the experiment is lignite. The results shall be
included with the comparisons between the original WBM and different percentages
of contaminated muds. As a conclusion, this research will provide significant
information on the effects of lignite contamination on the rheological changes
experienced by the water based muds system.

6. v
ACKNOWLEDGEMENT
The utmost appreciation would be delivered to Allah The Almighty God for
giving the strength as well as the knowledge and ability to complete this Final Year
Project (FYP) II report within the stipulated time. A great appreciation to my
supervisor; Mr. Asif Zamir for his continuous guidance and examples throughout the
final year project period. A great thanks to both of my parents; Mr Zainol Abidin bin
Hasan and Mrs Mastura binti Azizan for their continuous motivation to during the
finishing period of this project. Not to forget, to all Drilling Mud Preparation and
Simulation laboratory technicians; Mr Khairunnizam bin Abdul Wahid and Mrs.
Hilmayeni binti Suardi for lending their help in my drilling mud preparation.
Besides, a big thanks to Mr Zulhusni as the laboratory technician in handling my coal
(lignite) samples using the Scanning Electron Microscope (SEM) equipement. All in
all, thank you to all the parties who are involved either directly or indirectly in
assisting me throughout the FYP period.
Thank you.

7. vi
TABLE OF CONTENTS
CERTIFICATION OF APPROVAL .......................................................................ii
CERTIFICATION OF ORIGINALITY.................................................................iii
ABSTRACT...............................................................................................................iv
ACKNOWLEDGEMENT......................................................................................... v
LIST OF TABLES ..................................................................................................viii
LIST OF FIGURES ..................................................................................................ix
CHAPTER 1: INTRODUCTION............................................................................. 1
1.1 Background of Study...................................................................... 1
1.2 Problem Statement.......................................................................... 2
1.3 Objective of Research..................................................................... 2
1.4 Scope of Study................................................................................ 3
CHAPTER 2: LITERATURE REVIEW................................................................. 4
2.1 Coal Formation and Coal Bed Methane (CBM): General Studies. 4
2.1.1Coal Ranks............................................................................... 4
2.1.2Surface Chemistry ................................................................... 5
2.1.3Coal Strength ........................................................................... 5
2.1.4 Mineral Matter........................................................................ 6
2.2 Drilling Fluids: General Overview................................................. 7
2.3 Water Based Muds and Industrial Types........................................ 7
2.4 Contamination in Drilling Fluids.................................................... 9

8. vii
CHAPTER 3: METHODOLOGY.......................................................................... 10
3.1 Research Methodology................................................................. 10
3.2 Laboratory Project Workflows..................................................... 11
3.3 Project Gantt Chart....................................................................... 12
3.4 Project Milestone.......................................................................... 13
3.5 Experimental Procedures.............................................................. 14
3.5.1 Lignite grains preparation .................................................. 17
3.5.2 WBM and Lignite-Contaminated Mud Preparation........... 19
3.5.3 Mud Rheological Properties Testing.................................. 20
CHAPTER 4: RESULTSANDDISCUSSION ....................................................... 23
4.1 Data Gathering from Experiment................................................. 23
4.2 Results and Analysis..................................................................... 24
4.2.1 Density Analysis................................................................. 26
4.2.2 Viscosity Analysis.............................................................. 27
4.2.3 Yield Point Analysis........................................................... 29
4.2.4 Gel Strength Analysis......................................................... 30
4.2.5 Filtration Loss Analysis...................................................... 32
CHAPTER 5: CONCLUSION................................................................................ 38
REFERENCES......................................................................................................... 39

9. viii
LIST OF TABLES
Table 2.1.: Coal Classes by ASTM………………………………………………..3-4.
Table 2.2: Coal Strength Measurement by Hardglove Index…………..…………….5
Table 2.3: Drilling Fluids Roles………………………………………………….......6
Table 2.4: Different WBM Types Applied in the Industry………………………..7-8
Table 3.1: Gantt Chart……………………………………………………………....11
Table 3.2: Chemical Substances and Laboratory Equipment Used…………..….....14
Table 3.3: Water Based Muds (WBM) Rheological Features......………...……..…15
Table 4.1: Tests formulation (Pure and lignite-contaminated WBM)………….…..19
Table 4.2: Experimental Tests Master Data Readings…………..………………24-25
Table 4.3: Density Readings………………………………………...……………..26
Table 4.4: Plastic Viscosity Properties…………..………………..…….…………29
Table 4.5: Yield Point Properties…………….……………………….....…………30
Table 4.6: Gel Strength Properties……………….……………………….….…….32
Table 4.7: Filtration Loss (LPLT) Readings………………………….……………33

10. ix
LIST OF FIGURES
Figure 3.1: Laboratory ProjectWorkflows……………………………...…………..10
Figure 3.2: Project Milestone…………………………………..……….…………..13
Figure 3.3: Coal Rocks……………………………………...………….….………..17
Figure 3.4: Coal grains………………………………………………………………17
Figure 3.5: Sieving Machine………………………………………………………...18
Figure 3.6: Size of one of the coal grains…………………………………………...18
Figure 3.7: Barite……………………………………………………………………19
Figure 3.8: Bentonite………………………………………………………………..19
Figure 3.9: Laboratory Mud Balance………………………………………………..20
Figure 3.10: Laboratory Mud Multimixer…………………………………………..21
Figure 3.11: Laboratory FANN 35 Viscometer……………………………………..22
Figure 3.12: Low Pressure Low Temperature (LPLT) Filter Press………………....22
Figure 4.1: Density Plot Against Coal Percentages………………….…..………….26
Figure 4.2: Plastic Viscosity Plot Against Coal Percentages……………………….28
Figure 4.3: Yield Point Plot Against Coal Percentages…………………………….30
Figure 4.4: Gel Strength Plot Against Coal Percentages……………………...……32
Figure 4.5: Filtration Loss Plot Against Coal Percentages………………………....37
Figure 4.6: Filter Cake Thickness Plot Against Coal Percentages……………..…..37

11. 1
CHAPTER 1
INTRODUCTION
1.1 Background of Study
In this era, the aggressiveness of unconventional energy resources such as
shale gas and coal bed methane (CBM) is inevitable to be explored and produced
compared to years ago. The production capacity for these resources had successfully
penetrated the conventional energy market that the world’s holds from years ago
until this present time. North America had proven their capabilities in pioneering the
technologies that enable the unconventional energy to be drilled and brought to
surface with less cost consumptions as well as improving productivity margins
(World Energy Council, 2016).
In the United States alone, CBM had contributed a total of 11.7% of the gas
being produced (Baltoiu & Warren, 2008). Therefore, deploying the appropriate
drilling operations are important due to the distinctiveness of coal that requires larger
consideration to safeguard coal productivity (Barr, 2009). One of the important
drilling operation’s segments are the usage of drilling fluids or known also as drilling
mud (Shafie, Farahbod & Zargar, 2015). Conventionally, drilling fluids can be
widely categorized as Water Based Mud (WBM), Oil Based Muds (OBM), Synthetic
Based Mud (SBM), emulsions, invert emulsions, air, foam fluids as well as few
highly customized drilling fluids. (Shah, Shanker, & Ogugbue, 2010). There are
many drilling mud problems that may occur at the down hole. According to
Adekomaya & Olafuyi (2011), there are the possibilities whereby the drilling mud
composition is altered due to the presence of contamination coming by crushed rocks
from the drilled formation.

12. 2
In this research, a thorough investigation shall be made on the effects of
different percentages of coal formation contamination on various rheological
properties of the drilling fluid such as viscosity, gel strength, filtrate loss, yield point
as well as density. For the purpose of the study, WBM will be taken as the base
fluid.
1.2 Problem Statement
In drilling operations, formations debris that had been drilled have the
tendency to fall off and shall contaminate the drilling muds inside the annulus.
Therefore, this research will study the changes occurring at the rheological
characteristics of water based muds (WBM) that are invaded by different percentages
of coal grains.
1.3 Objective of Research
In this research, there are two (2) objectives that had been outlined in order to
attain possible solutions to the problem statement:
i. To compare the rheological properties of non-contaminated water based
muds (WBM) as well as lignite-contaminated WBM.
ii. To study the consequences of different percentages of lignite formation
contamination on the rheological properties of WBM.

13. 3
1.4 Scope of Study
In this research, the scope of study is mainly related to the coal formation
invasion towards drilling fluids. However, for the purpose of the research, water
based muds (WBM) is opted to be studied. A structured laboratory experiment shall
be performed in order to investigate various percentages of coal formation
contamination onto the rheological properties of WBM such as viscosity, gel
strength, filtrate loss, yield point and density. The results obtained from the
experiment will be analysed and discussed in the paper.

14. 4
CHAPTER 2
2LITERATURE REVIEW
2.1 Coal Formation and Coal Bed Methane (CBM): General Studies
Coal is a type of sedimentary rock that was originated on Earth’s surface
resulting from accumulation of both organic and inorganic materials. This process is
undergone by coal through chemical, mechanical and biological process namely as
coalification. (Barr, 2009). Coal is majorly made up of organic plant constituents
such as woods, leaves, plant stems as well as other parts of both land and aquatic
plants (ALL Consulting, 2004).
2.1.1 Coal Ranks
Coal rank on the other hand is the measurement used on the physical
appearance and chemical changes occurring within coalification process on
the coal edifices and constituents. (Barr, 2009). Coal rank classes had been
stated by American Society for Testing and Materials (ASTM) and are
presented in table as follows;
Table 2.1: Coal Classes by ASTM (Barr, 2009)
ASTM Rank Classes Major Rank Categories
Peat Peat (Low Rank)
Lignite A
LigniteLignite A
Sub Bituminous A,B and C

15. 5
High Volatile Bituminous C
High Volatile Bituminous B
Bituminous
High Volatile Bituminous A
Medium Volatile
Bituminous
Low Volatile Bituminous
Semi - anhracite
Anthracite (High Rank)Anthracite
Meta - anthracite
2.1.2 Surface Chemistry
This part of coal studies is mainly on the qualitative determination of
coals reactivity with water. A hypothesis is made as such; coals with a lower
rank shall prone to be in hydrophilic states whereas coals in higher rank will
exhibit hydrophobic states. Hydrophilic states of coal will become more
reactive towards water. This condition is mandatory in drilling zones where
may be the coal is either in dry or wet that contain high salinity. This is
because high salinity effect on coal will results in high reactivity towards
fresh water. Hydrophilic coal seams also shall promote in water clogging in
cleats (Barr, 2009).
2.1.3 Coal Strength
Coal strength is one of the criteria that is being induced by coal seam
coalification process. The greater the pressure and heat on the coal layers, the
greater the density of the coal will be. However, the pore sizes of the coal
rocks shall diminish. This condition will result in decreasing water content
inside the coal and eventually leads to high fragility and dry. The following
table will show the measurement of coal strength based on the Hardglove
Grindability (Barr, 2009).

16. 6
Table 2.2: Coal Strength Measurement by Hardglove Index (Barr, 2009)
Coal Rank USC Value (psi)
Anthracite (High Rank) 1780
Low Volatile Bituminous 490
Medium Volatile Bituminous 497
High Volatile Bituminous A 1050
High Volatile Bituminous A 4800
High Volatile Bituminous A 5930
Lignite (Low Rank) 9400
2.1.4 Mineral Matter
Mineral matter identification shall deliver the amount of clay in coal
sample retrieved as well as shale samples that may be located near above or
below the coal formation. Proximate analysis is able in identifying the ash
content as well as inorganic content that permits for coal characterisation
purposes (Barr, 2009).

17. 7
2.2 Drilling Fluids: General Overview
As one of fundamental elements within drilling operations, selecting a proper
drilling muds itself is considered vital to ensure high quality production is attained as
well as achieving industrial effectiveness. Therefore, this paper will outline certain
functions of drilling muds within the industry (Kristensen, 2013).
Table 2.3: Drilling fluids roles (Kristensen, 2013)
Functions Description
Hole cleaning agent - Responsible in flowing the drill cuttings out
from the wellbore to surface as this is important
in ensuring the hole is fully cleaned for
completion program to take part (Kristensen,
2013).
Bit lubrication - Provides smoothening effects for bit operation
and towards drill string in horizontal realm wells
(Kristensen, 2013).
Buoyancy to bit - Holds the bit submersed to reduce weight of drill
string on hook load (Kristensen, 2013).
Wellbore stability
agent
- Maintaining the wellbore integrity regardless of
chemical reaction occurring downhole
(Kristensen, 2013).
2.3 Water Based Muds and Industrial Types
Despite of development of various drilling fluids nowadays, water based
muds (WBM) is still considered relevant within the industry (Nagre, Zhao,
Frimpong, & Owusu, 2015). Using water as base fluids, WBM is applied due its
environmental tolerance by which its drilled debris can be disposed straightforwardly
(Shah et. al., 2010). WBM consists of four (4) basic components namely: a) Water as
continuous phase of the fluids b) Active colloidal solids c) Inert solids and d)

18. 8
Additional chemicals. There are few types of WBM practiced in the industry. The
table below will list four (4) major types of WBM used (Shafie et. al., 2015).
Table 2.4: Different WBM Types Applied in the Industry (Shafie et. al., 2015)
WBM Types Description
Clear Water
- Freshwater and brine is deployed when drilling
of hard formations. This mud is pumped into
downhole and it will react with clay or shale
contained in the formations. Water will liquefy
the clays and shall be moved up to surface as
muds (Shafie et. al., 2015).
Calcium Muds
- Calcium is very useful in drilling zones with
high content of gypsum and anhydrite as these
formations are prone to calcium invasion
(Shafie et. al., 2015).
Lignosulphate
- This mud is suggested for drilling zones with:
a) high mud densities
b) moderately high temperature
c) great tolerance for contamination of drilled
cuttings
d) less filter loss is then needed
(Shafie et. al., 2015).
Potassium Chloride
(KCL) / Polymer
- Foundation elements consists of:
a) Fresh water/ sea water
b) Potassium chloride
c) Inhibiting polymers
d) Viscosity building polymer
e) Alleviated starch
f) Caustic soda
(Shafie et. al., 2015).

19. 9
In order to study the behaviour of WBM performance, the rheological
properties should be studied. According to Adekomaya and Olafuyi (2011) the
rheological characterisations of the muds are very much related to plastic viscosity,
yield point, mud weight, fluid loss, gel strength as well as electrical stability. These
properties are important in order for the drilled hole to be cleaned during drilling
operations, barite suspension and throughout solids separation process (Eke &
Ezenweichu, 2015).
2.4 Contamination in Drilling Fluids
According to Ezenweichu (2015), contaminants are considered as any
possible kinds of materials i.e. solid, liquid or gas by which these substances shall
lead to unfavourable implications towards drilling fluids either physically or
chemically. Adekomaya and Olafuyi (2011) had also stressed out that geographical
position of reservoirs, the depths, as well as classification of formation to be drilled
are among the factors that contribute to mud composition.
As drilling operations progresses, drilled debris such as formation rocks and
low-yielding clays will have the tendency to contaminate the muds inside the annulus
(Ezenwuchi, 2015). Severe contamination of debris within the wellbore will
ultimately promotes to one of the critical issue of drilling operations which is less
efficient of hole cleaning. This event will then shall tailored to more serious
occurrences such as stuck pipe, formation collapse and loss circulation (Adekomaya
& Olafuyi, 2011). Besides contaminating the composition of drilling muds, fluids
contamination also has the possibility in contributing to the wellbore instability,
unprecise wellbore positioning as well as time wastage throughout drilling operations
(Kumapayi, Bello, Akintola, Dala, Mohamed, &, Olafuyi, 2014).

20. 10
CHAPTER 3
3METHODOLOGY
3.1 Research Methodology
As the research is mainly to thoroughly investigates the effects of coal
formation contamination on rheological properties of water based muds (WBM),
therefore, a structured flow of scientific laboratory procedures should be listed from
the beginning up until the end. Before the rheological tests are performed, the lignite
itself must be carefully grind as this element is the manipulated variable within the
experiment.
Below are the required substances and laboratory tools as well as WBM
rheological features that will be studied.

21. 11
3.2 Laboratory Project Workflows
Figure 3.1: Laboratory Project Workflows
Final report writing and presentation
Results compilation and complete data tabulation
Comparison analysis on rheological properties is done
Rheological properties of WBM added with lignite is measured
Different lignite percentage is added to the pure WBM
Rheological properties of pure WBM is measured
Pure Water Based Muds (WBM) formulation is made

22. 12
3.3 Project Gantt Chart (Table 3.1: Project Gantt Chart)
Item
Week Number
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
FYP Topic
selection
HOLIDAY
Research
methodology
identification
HOLIDAY
Mud
formulation
training & HSE
briefing
HOLIDAY
Lab booking
confirmation
HOLIDAY
WBM
preparation and
rheology test
HOLIDAY
Coal grains
preparation
HOLIDAY
Mud rheology
tests (Different
lignite %)
HOLIDAY
Data gathering
& analysis
HOLIDAY
FYP II
presentation
preparation
HOLIDAY

23. 13
3.4 Project Milestone
Figure 3.2: Project Milestone
Week 2 -
6 (FYP I)
• Confirmation on project title, preparation and submission of Extended
Proposal for research project
Week 7
(FYP I)
• Studied the drilling mud preparation at Drilling Mud Preparation
Laboratory in Block 15
• Obtained permission to enter lab for FYP purposes
Week 9 –
10 (FYP
I)
• Performed WBM chemical composition and formulation with guidance
from Supervisor
• Laboratory experiment for making pure WBM and 5% additional of coal
formation
Week 11
(FYP I)
• FYP 1 Proposal Defense
Week 12 –
Week 14
(FYP I)
• Editing the Extended Proposal with preliminary results obtained and
submission of Interim Report
Week 15 -
18 (FYP
II)
• Rheological properties tests based on different percentages of lignite
formation
Week 19 -
22 (FYP
II)
• Data gathering based on experimental works and complete data analysis
• Final report documentation
Week 23 –
24 (FYP
II)
• FYP II Presentation preparation

24. 14
3.5 Experimental Procedures
There are few chemical substances and laboratory apparatus that should be
taken into consideration before proceeding with the experimental procedures. Table
3.4.1 will show the chemical substances and laboratory apparatus that shall be used.
In Table 3.4.2, the techniques for measuring the fluid properties are shown.
Table 3.2: Chemical Substances and Laboratory Equipment Used
Chemical Substances Laboratory Equipment
1. Fresh water based muds (WBM)
2. Lignite rocks (In grains sizes)
3. Barite
4. Bentonite/ Clay/ Montmorillonite
1. Laboratory mortar and pestle
2. Sieving Machine
3. Scanning Electron Microscope
(SEM)
4. Mass balance
5. Mud balance
6. Variable Speed Viscometer
7. Low Pressure Low Temperature
(LPLT) Standard API Filter
Press

25. 15
Table 3.3: Water Based Muds (WBM) Rheological Features
Rheological
Features
Laboratory
Equipment
Explanation
Coal Grains
1. Pestle and
mortar
2. Sieving
Machine
3. Scanning
Electron
Microscope
(SEM)
 To evenly sizing the coal grains
before adding them into the basic
WBM formulation.
Mass of
Additives
Mass Balancer
 To exactly measure the required mass
of additives to be added to the
formulation.
Fluid Density Mud Balance
 Identifying the WBM density in unit
of (lb/gal) through direct reading.
Fluid
Viscosity
FANN (Model 35A)
Viscometer
 Needed to determine the following:
1. Plastic Viscosity in unit of (cp),
300600  p
Yield Point
FANN (Model 35A)
Viscometer
 Needed to determine the following:
Yield Point in unit of (lb/100 ft2
),
pby   300
Gel Strength
FANN (Model 35A)
Viscometer
 WBM sample is to be stirred
approximately for 15 seconds at dial
reading of 600 RPM.
 The sample is to be left at rest state
while concurrently the dial maximum
deflection values just before the Gel
disrupted are taken.

26. 16
 Gel Strength is measured in unit of
(lb/100 ft2
)
Filtrate Loss
Low Pressure Low
Temperature
(LPLT) Standard
API Filter Press
 The filtrate results are observed and
gathered for any specified recesses up
until 30 minutes.
 No additional calculation is required.

27. 17
3.5.1 Lignite grains preparation
1. The lignite sample that was retrieved from the supervisor will be crushed
using pestle and mortar from the laboratory.
2. Then the lignite samples are sieved using sieving machine to ensure the range
of sizings.
3. The crushed coal samples were then being measured under the Scanning
Electron Microscope (SEM) to observe its shapes after being crushed.
Figure 3.3: Coal rocks
Figure 3.4: Coal grains

28. 18
Figure 3.5: Sieving Machine
Figure 3.6: Size of one of the coal grains

29. 19
3.5.2 WBM and Lignite-Contaminated Mud Preparation
1. A 350 ml of water is put into a beaker and shall be transferred into a beaker.
2. A piece of paper is folded into two sides for the grains to be placed.
3. The mass reading of mass balancer apparatus is set to zero.
4. Spatula is used to take barite from the container onto the mud balancer.
5. Steps number 1 – 4 is repeated for bentonite.
6. The pure water is taken to Multi-Mixer for mixing purposes.
7. Stopwatch is used during mixing process to measure the required mixing time
prior to addition of other additives (e.g. coal grains).
8. After the mixing process is complete, mud density is measured using the mud
balancer.
9. The reading of the density of mud is taken when the mud balancer is in
equilibrium position.
Figure 3.7: Barite
Figure 3.8: Bentonite

30. 20
3.5.3 Mud Rheological Properties Testing
1. The density of the muds are being measured using the Mud Balancer.
i) The mud is poured into the mud container until the mud filled up the
whole container.
ii) The mud balance is being adjusted until an equilibrium point is
reached. A static position of the bubble within the calibration meter
indicates the final reading for the density.
Figure 3.9: Laboratory Mud Balance
2. The rheological properties of the mud are tested using FANN (Model 35 A)
Viscometer and Standard API Filter Press.
3. For the properties of viscosity, yield point and gel strength, the following
procedures are taken into account:
i) The mud container is locked on top of the viscometer and is shall be
unlocked when doing cleaning (Used for attaching the mud container
onto the viscometer)
ii) The mixed mud should be poured into the mud container until the
maximum line of the container is reached.
iii) The mud container (filled with the mud) will be attached to the
viscometer until it covers two holes of the equipment.

31. 21
iv) Different dial readings, Θ (eg. 3 RPM, 6RPM, 100 RPM, 200 RPM,
300 RPM and 600 RPM) is taken after a certain mixing time.
v) For gel strength; procedures number 1 – 4 is repeated with additional
usage of high and low button the lower sides of the viscometer. For
every 15 seconds, the dial reading is set manually to 3 RPM and the
deflection value on the reading is measured. 10 seconds is needed for
the mud to rest before being repeated again.
vi) For yield point; the value is attained from the formula.
vii)Below is required formula for calculating the mud viscosity after the
dial readings had been obtained:
 Plastic Viscosity in unit of (cp),
300600  p
 Apparent Viscosity in unit of (cp),
2
600
 a
 Yield Point in unit of (lb/100 ft2
),
pby   300
Figure 3.10: Laboratory Mud Multimixer

32. 22
Figure 3.11: Laboratory FANN 35 Viscometer
4. The fluid loss from the mud are being measured using the Low Pressure Low
Temperature (LPLT) filter press and every five minutes, the reading of the
fluid loss is recorded.
5. The filter cake is measured after 30 minutes of fluid loss using a Vernier
calliper on a filter paper.
Figure 3.12: Low Pressure Low Temperature (LPLT) Filter Press

33. 23
CHAPTER 4
4RESULTS AND DISCUSSION
4.1 Data Gathering from Experiment
From the experiment, the results that are expected to be yield is on how much
the coal-based contaminants can affect the rheological characteristics of the WBM.
Various kinds of properties of the WBM are studied such as density, viscosity, yield
point, gel strength and filtrate loss for the purpose and proper results will be
tabulated accordingly and detailed analysis on the results will be performed.
According to Mahto and Jain (2013), the coal additives (in their research which was
the fly ash), that were added are 1%, 2% and 3%. Thus, with reference to Mahto
et.al (2013), the percentage of coal additives added into the mud are; 0.5%, 1.0%,
1.5%, 2.0%, 2.5% and 3.0%.
Below is the mud formulation that is used for pure WBM and the additional
of coal contaminants percentage. The mud density will be the controlled variable
within the experiment.
Table 4.1: WBM formulation (Non – contaminated and contaminated WBM)
Water (g) 320 320 320 320 320 320 320
Barite (g) 10 10 10 10 10 10 10
Bentonite (g) 25 25 25 25 25 25 25
Lignite
Percentage (%)
0 0.5 1 1.5 2 2.5 3
Coal Mass (g) 0 1.8 3.6 5.3 7.1 8.9 10.7

34. 24
4.2 Results and Analysis
Table 4.2: Experimental Tests Master Data
Test T1 T2 T3 T4 T5 T6 T7
Remarks
Base Case (0%
lignite)
WBM + 0.5%
lignite
WBM + 1.0 %
lignite
WBM + 1.5 %
lignite
WBM + 2.0 %
lignite
WBM + 2.5 %
lignite
WBM + 3.0 %
lignite
600 RPM 40 43 54 63 59 66 71
6 RPM 12 19 30 36 39 38 53
200 RPM 29 30 43 50 47 48 58
300 RPM 27 32 44 54 56 59 65
3 RPM 17 18 38 39 40 40 57
100 RPM 25 26 40 45 43 45 56
Plastic
Viscosity (cp)
13 11 10 9 8 7 6
Yield Point
(lb/100 ft2)
14 22 44 45 48 52 59
10 seconds Gel 24 26 41 41 39 41 50

35. 25
Strength
(lb/100 ft2)
10 minutes Gel
Strength
(lb/100 ft2)
49 39 47 46 45 44 54
API Fluid Loss
(ml)
14.5 13.0 12.5 11.5 10.0 9.0 7.5
Filter Cake
Thickness
(mm)
4.05 3.69 3.68 3.26 3.16 2.15 2.14

36. 26
4.2.1 Density Analysis
Table 4.3: Density readings
Lignite
Percentages (%)
0 0.5 1 1.5 2 2.5 3
Lignite Mass (g) 0 1.8 3.6 5.3 7.1 8.9 10.7
Density (ppg) 8.6 8.7 8.8 8.9 9.0 9.1 9.3
Figure 4.1: WBM Density Plot Against Coal Percentages
According to Figure 4.1, the general trend exhibited an increase in the density
of the mud. The density starts with the value of 8.7 ppg for 0%. From the percentage
of lignite addition for which at 0.5%, 1%, 1.5%, 2% and 2.5%, the density increases
linearly with the respective value of 8.7 ppg, 8.8 ppg, 8.9 ppg, 9.0 ppg and 9.1 ppg.
The increase of the density reach its top value of 9.3 ppg, when there is an addition
of the coal percentage of 3%. This is the stopping point for the experiment whereby
8.6
8.7
8.8
8.9
9
9.1
9.3
8.2
8.4
8.6
8.8
9
9.2
9.4
0 0.5 1 1.5 2 2.5 3
Density(ppg)
Coal Percentages (%)
Density Plot Against Coal (Lignite) Percentages
Density (ppg) Linear (Density (ppg))

37. 27
it can be seen that the general trend for density of the WBM added with coal is
increasing. The density will be increased as the mass amount of the sample increases
with a constant volume. This abide to the rule of the density for which it is the ratio
between the mass and volume.
𝜌 =
𝑚
𝑣
Noted that, if the density is high, one of the anticipated problem is lower rate of
penetration (ROP). This happened due to the recirculation of excessive drilled
cuttings within the mud system.
4.2.2 Viscosity Analysis
Table 4.4: Viscosity Properties
Lignite Percentage
(%)
Lignite Mass (g)
Plastic Viscosity (Θ600 - Θ300)
(cp)
0 0 13
0.5 1.8 11
1 3.6 10
1.5 5.3 9
2 7.1 8
2.5 8.9 7
3 10.7 6

38. 28
Figure 4.2: Plastic Viscosity Plot Against Coal Percentages
Plastic visocity is the defined as the resistance of the fluid flow that is caused
by the particles friction of the mud in the liquid phase.The viscosity performance of
the coal - water based muds are greatly depending on the amount concentration of
the solids added.
From Figure 4.2, it can be concluded that plastic viscosity of the WBM is
decreasing alongwith the addition of coal. The value for plastic viscosity begins with
13 centipoise (cp) for 0% lignite added. However, as the addition of coal increases to
1%, 1.5%, 2%, 2.5% and 3%, the value for plastic viscosity is decreasing linearly.
The lowest plastic viscosity value of the lignite contaminated-water based muds is at
6 cp for the addition of coal at 3%.
In general, the trend of the plastic viscosity itself is decreasing when addition
of the lignite increases. Clay or bentonite is the main component for making the
water based mud system alongside with barite as the weighting agent. Clay or
bentonite itself has the properties of controlling the viscosity of a mud by making its
own particles to deflocculate in the system. The coal that is being added is a lignite
type of coal. It had been known that, lignite itself has the content of humic acid that
is able to increase the colloidal stability of the clay particles within the water based
system. This means that, the particles do not easily settled down at the bottom
13
11
10
9
8
7
6
0
2
4
6
8
10
12
14
0 0.5 1 1.5 2 2.5 3 3.5
PlasticViscosity(cp)
Coal Percentages (%)
Plastic Viscosity Plot Against Coal (Lignite) Percentages
Plastic Viscosity (600 - 300) Linear (Plastic Viscosity (600 - 300))

39. 29
surface of the mud and be can retain their positions within the mud system.
Therefore, the trend of the viscosity is reducing when addition of coal is increasing
towards the system.
4.2.3 Yield Point Analysis
Table 4.5: Yield Point Properties
Lignite
Percentages (%)
0 0.5 1 1.5 2 2.5 3
Lignite Mass (g) 0 1.8 3.6 5.3 7.1 8.9 10.7
Yield Point (Θ300
- PV) (lb/100 ft2)
14 22 44 45 48 52 59
Figure 4.3: Yield Point Plot Against Coal Percentages
14
22
44 45 48
52
59
0
10
20
30
40
50
60
70
0 0.5 1 1.5 2 2.5 3
YieldPoint(lb/100ft2)
Coal Percentages (%)
Yield Point Plot Against Coal (Lignite) Percentages
YP Linear (YP)

40. 30
Figure 4.3 shows that yield point value of the water based muds is increasing
with the addition of lignite percentages. Yield point can be defined as the ability for
the drilling mud to suspend cuttings and to carry them back to surface from
downhole. It can also be noted as the initial stress required to initiate the fluid to
move.
Initially, the reading of the yield point is at 14 lb/100ft2
. As the lignite is
added to the formulation, the trend increases from 22 lb/100ft2
for 0.5% up until 59
lb/100ft2
. Noticed that there is a sharp increase from 22 lb/100ft2
to 44 lb/100ft2
before the trend increases at 45 lb/100ft2
until 59 lb/100ft2
.
From the trend above, it can be said that contamination of lignite formation
into the formulation of water based muds shall deliver a good impact in terms of
lifting up cuttings. This is because, larger yield point value will give good ability in
lifting drilled cuttings up to the surface through the annulus. However, in real drilling
application, the water based muds will experience pressure loss due to high value of
yield point.
4.2.4 Gel Strength Analysis
Table 4.6: WBM Gel Strength
Lignite Percentages (%) 0 0.5 1 1.5 2 2.5 3
Lignite Mass (g) 0 1.8 3.6 5.3 7.1 8.9 10.7
10 seconds (s) 24 26 41 41 39 41 50
10 minutes (min) 49 39 47 46 45 44 54

41. 31
Figure 4.4: Gel Strength Plot Against Coal Percentages
Figure 4.4 indicates the graph of gel strength for both ten seconds as well as
ten minutes time interval. Gel strength is the ability for a drilling fluid to form any
internal structures in the mode of static or in stagnant motion. It can also be
conisedered as the pressure needed to initiate the flow after the mud is held in a
certain motionless period. Besides that, gel strength is also be defined as the
properties for which it can hold the drilled cuttings in suspension after the flow is
ceased. The longer the static position time, the harder the internal particles structures
within the mud as larger pressure is required to start the fluid flow to as usual
movement. The larger the coal percentages, the longer the stagnation time and hence,
the greater the gel strength.
From Figure 4.4, generally the trends for both of the time period is
increasing. For example, in ten seconds plot, the trend starts with 24 lb/100 ft2
and at
the end of 3% lignite addition, the gel strength value reached at 50 lb/100 ft2
. This
implies that the increment is more than 25 lb/100 ft2
. Overall, it can be concluded
that the lignite-contamintaed drilling muds require a high value of minimum stress or
24
26
41 41
39
41
5049
39
47 46 45 44
54
0
10
20
30
40
50
60
0 0.5 1 1.5 2 2.5 3
GelStrength(lb/100ft2)
Coal Percentages (%)
Gel Strength Plot Against Coal (Lignite) Percentages
10 seconds (s) 10 minutes (min)

42. 32
pressure in order to put the mud back into motion at each time whenever the drilling
operations are halted. High gel strength value is also desired as it shows how capable
the contaminated muds to suspend the drilled cuttings within the mud system.
4.2.5 Filtration Loss Analysis
Table 4.7: Filtration Loss (LPLT) Readings
Coal Percentage
(%)
Time (min)
Filtration Loss
(ml)
Filter Cake
Thickness (mm)
0
5 7
4.05
10 9.5
15 10.5
20 11.5
25 12.5
30 14.5
0.5
5 7
10 8.5
15 10.0

43. 33
20 11.5
3.69
25 12.5
30 13.0
1
5 7.5
3.68
10 8.5
15 9.0
20 11.0
25 12.0
30 12.5
1.5
5 7.0
3.26
10 7.5
15 8.5
20 9.5
25 10.0

44. 34
30 11.5
2
5 6.5
3.16
10 7.5
15 8.0
20 8.0
25 9.0
30 10.0
2.5
5 6.0
2.15
10 6.5
15 7.0
20 7.0
25 8.0
30 9.0
3
5 5.5
2.14
10 6.0

45. 35
15 6.5
20 6.5
25 7.5
30 7.5
Figure 4.5: Filtration Loss Plot Against Coal Percentages
14.5
13 12.5
11.5
10
9
7.5
0
2
4
6
8
10
12
14
16
3 2.5 2 1.5 1 0.5 0
FiltrationLoss(ml)
Coal Percentages (%)
Filtration Loss Plot Against Coal (Lignite) Percentages
Filtration Loss (ml) Linear (Filtration Loss (ml))

46. 36
Figure 4.6: Filter Cake Thickness Plot Against Coal Percentages
Figure 4.5 demonstrates the plot of filtration loss of all the samples for lignite
contaminated-water based muds. In general, fluid loss is defined as the leakage of
liquid phase within drilling mud system into the formation from the annulus.
Continous build up of solid content on the filter paper or known as filter cake should
be avoided.
In Figure 4.5, it can be observed that the amount of fluid loss is decreasing as
lignite is added into the formulation. Initially, the 0% lignite, the amount of fluid loss
is 14.5 milliliter (ml). This value is still acceptable according to American Petroleum
Institute (API) recommendation for which its value is 15 ml maximum. By the end of
3%, the amount of fluid that is loss is 7.5 ml.
As being mentioned earlier, lignite contain a type of organic acid known as
humic acid or fluvic acid. This acid is developed during continous depositional of
dead plants and animals on layers of earth. Contamination of lignite within bentonite
– water system increases the colloidal stability of the clay particles. This process is
done through the adorption on bentonite from the lignite. Knowing that lignite is one
4.05
3.69 3.68
3.26 3.16
2.15 2.14
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
0 0.5 1 1.5 2 2.5 3 3.5
FilterCakeThickness(mm)
Coal Percentages (%)
Filter Cake Thickness Plot Against Coal (Lignite)
Percentages
Filter Cake Thickness (mm) Linear (Filter Cake Thickness (mm))

47. 37
of a good deflocculant agent, clay particles are held in their positions within the mud
system without having to flocculate with each other and settled down at the bottom.
This is because both bentonite and humic acids exhibit negatively charged particles
downhole especially if the drilling vicinity is of alkaline. Hence, repulsion occurs
between those two components.
Figure 4.6 on the other hand, explained on the decreasing trend of filter cake
thickness when addition of lignite is increasing towards the water based muds
formulation. It can be concluded that filter cake thickness itself is directly
proportional to filtration loss. This is because, as filtration loss is decreasing, the
filter cake is also become thinner. An indication of a good filter cake is not just only
thin, but it must also be impermeable. This is to prevent any fluid loss into the
formation matrix. There will be major problem to the well if the filter cake is thick.
Such problem includes pipe sticking due to the constriction within the wellbore
especially in the event of drilling in deviated or horizontal wells. Since the clay
particles are greatly dispersed and do not bind to each other, therefore, they will
make a great barrier to the filter cake. Thus, fluid loss shall be minimized due to the
strong ‘shield’ existed within the filter cake formed.

48. 38
CHAPTER 5
CONCLUSION
Coal formation reservoirs are considered one of the unconventional resources
nowadays. However, continuous research and development of technologies and
engineering marvels to retrieve the energy is increasingly fast.
From this research, it can be observed that density of the mud shows an
increase trend due to different percentages of lignite contamination. In industry point
of view, increasing density of mud indicates a serious issue that will occur later on
such as decrease in rate of penetration (ROP) due to excessive recirculation of drilled
cuttings.
Besides that, plastic viscosity shows a decrease trend due to deflocculation
properties of contaminated water based muds. However, the value for yield point as
well as gel strength demonstrated an increase trend. These two fluid rheological
characteristics explained on how good the contaminated water based muds in
suspending and lifting up drilled cuttings to the surface that were initially positioned
at downhole. However, drawbacks such as pressure loss should be paid attention to if
continuous contamination of lignite is occuring within the water based muds system.
Moreover, lignite contaminated water based muds showed a great filtration
loss and filter cake thickness due to its deflocculating characteristics.

49. 39
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