© copyright by rashmi vijendra prasad 2014
TRANSCRIPT
© Copyright by Rashmi Vijendra Prasad 2014
All Rights Reserved
CHARACTERIZATION OF A NEW VEGETABLE
OIL BASED ESTER DRILLING FLUID
A Thesis
Presented to
the Faculty of the Department of Civil and Environmental Engineering
University of Houston
In Partial Fulfillment
of the Requirements for the Degree
Master of Science
in Civil Engineering
by
Rashmi Vijendra Prasad
August 2014
CHARACTERIZATION OF A NEW VEGETABLE OIL BASED ESTER DRILLING FLUID
Rashmi Vijendra Prasad
Approved:
Chair of the Committee Dr. Cumaraswamy Vipulanandan Professor Civil and Environmental Engineering Director of CIGMAT Director of THC-IT
Committee Members:
Dr. Kalyana Babu Nakshatrala Assistant Professor Civil and Environmental Engineering
Dr. Phaneendra Kondapi Sr. Technical Advisor Granherne/KBR
Suresh K. Khator, Associate Dean Kaspar J William, Professor and Chair Cullen College of Engineering Civil and Environmental Engineering
v
Acknowledgements
First and foremost I offer my sincerest gratitude to my advisor, Dr. Cumaraswamy
Vipulanandan, who has supported me throughout my thesis with his patience and
knowledge whilst allowing me the room to work in my own way. Without his
encouragement and effort this thesis would not have been completed or written. I thank
Dr. Kalyana Babu Nakshatrala and Dr. Phaneendra Kondapi, for serving on my thesis
committee. I would also like to thank my labmates, Aram, Dongmei, Jia, Kausar and
Ram for all their support, guidance and encouragement. I thank my parents and God for
always being with me.
Lastly, I would like to dedicate this work to my father Mr. A. S. Vijendra Prasad
for all his love and support all through my life without which nothing would have been
possible by me.
vi
CHARACTERIZATION OF A NEW VEGETABLE
OIL BASED ESTER DRILLING FLUID
An Abstract
of a
Thesis
Presented to
the Faculty of the Department of Civil and Environmental Engineering
University of Houston
In Partial Fulfillment
of the Requirements for the Degree
Master of Science
in Civil Engineering
by
Rashmi Vijendra Prasad
August 2014
vii
Abstract
This thesis presents a novel base fluid material for synthetic based drilling fluid
systems. The proposed vegetable oil based ester material is biodegradable in both aerobic
and anaerobic conditions as shown by the plate test and the UV spectrophotometric
analysis. It is also highly cost effective and fairly easy to synthesize. The vegetable oil
ester material is an insulator and has been modified using nanoparticles to adapt to the
resistivity measuring devices. Good sensing properties were observed in the presence of
additives like ferric nitrate with a drastic reduction of 90 % in the resistivity. The
optimum formulation of the proposed drilling fluid comprising minimal number of eco-
friendly additives was determined by experimental results. An in situ made UH-
Biosurfactant being a major component of the proposed drilling fluid blends the invert
emulsion improving its emulsion stability and also helps in reducing ester hydrolysis
when tested at a temperature of 75 oC. Though the proposed material is affected by salt
contamination, addition of a trivial amount of 0.1-0.5 % of nanoparticles would negate
the effects of salt contamination of the drilling fluid. Even otherwise, incorporation of at
least 0.5 % of nano materials would reduce the fluid loss by over 90 %. The UH-
Biosurfactant which enhances the properties of drilling fluid with a nominal quantity of 1
% is produced in a microbial fuel cell which recycles the used ester; hence proving to be
a completely sustainable system. A hyperbolic model was developed to predict the shear
behavior.
viii
TABLE OF CONTENTS
Acknowledgements ........................................................................................................... v
Abstract ............................................................................................................................ vii
TABLE OF CONTENTS .............................................................................................. viii
LIST OF FIGURES ......................................................................................................... xi
LIST OF TABLES .......................................................................................................... xv
CHAPTER 1 INTRODUCTION ..................................................................................... 1
1.1. Introduction to Drilling ..................................................................................... 1
1.1.1. Drilling Fluid Market ................................................................................. 2
1.1.2. Types Of Drilling Fluids ............................................................................. 3
1.1.3. Synthetic based muds (SBM) ..................................................................... 4
1.2. Soybean Oil ......................................................................................................... 6
1.3. The Ester Chemistry .......................................................................................... 6
1.4. Objectives ............................................................................................................ 7
1.5. Organization ....................................................................................................... 7
CHAPTER 2 LITERATURE REVIEW ......................................................................... 9
2.1. Introduction On Drilling And Drilling Fluids ................................................. 9
2.1.1. Viscosity, Fluid Loss and Density .............................................................. 9
2.1.2. Biodegradability ........................................................................................ 10
2.1.3. Sensing Property ....................................................................................... 11
2.2. Oil Based Drilling Fluids ................................................................................. 11
2.3. Synthetic Base Fluids ....................................................................................... 12
2.3.1. Ester Base Fluids ....................................................................................... 15
2.4. Hydrolysis of Ester ........................................................................................... 18
2.5. Effect of Temperature and Pressure on Ester Drilling Fluids ................... 19
2.6. Economics Of Synthetic Drilling Fluids ......................................................... 20
2.7. Fatty Acid Methyl Ester (FAME) ................................................................... 20
2.8. Summary ........................................................................................................... 21
ix
CHAPTER 3 MATERIALS AND METHODS ........................................................... 23
3.1. The Proposed Synthetic Base Fluid - FAME ................................................. 23
3.2. Transesterification ........................................................................................... 25
3.3. Drilling Fluid Formulation .............................................................................. 26
3.3.1. Additives .................................................................................................... 29
3.4. Experimental methods for drilling fluid system ............................................ 33
3.4.1. Rheology testing ........................................................................................ 33
3.4.2. Fluid loss measurement ............................................................................ 38
3.4.3. Density, Resistance, Conductivity and pH measurement...................... 39
3.4.4. UV Spectrophotometer ............................................................................. 41
3.5. Summary ........................................................................................................... 43
CHAPTER 4 CHARACTERIZATION OF SYNTHETIC VEGETABLE OIL
BASED DRILLING FLUID .......................................................................................... 44
4.1. Effect Of Nanoclay On Change In Type Of Vegetable Oil And Alcohol .... 44
4.1.1. Effect On Rheology ................................................................................... 44
4.1.2. Effect On Gel Strength ............................................................................. 46
4.1.3. Effect On Fluid Loss ................................................................................. 47
4.1.4. Effect On Electrical Resistivity ................................................................ 49
4.2. Comparison of OBM and SBM ....................................................................... 51
4.3. Effect Of Salt (NaCl) Contamination ............................................................. 53
4.3.1. Effect On Shear Stress .............................................................................. 53
4.3.2. Effect On Fluid Loss ................................................................................. 54
4.3.3. Effect On Thixotropy ................................................................................ 55
4.3.4. Effect On Thermal Stability ..................................................................... 59
4.3.5. Effect On Resistivity ................................................................................. 61
4.4. Remediation Of Salt (NaCl) Contamination .................................................. 62
4.4.1. Nanoclay..................................................................................................... 63
4.4.2. Nano Iron ................................................................................................... 66
4.4.3. Ferric Nitrate ............................................................................................. 69
CHAPTER 5 RECYCLING OF VEGETABLE OIL BASED ESTER DRILLING
FLUID .............................................................................................................................. 73
x
5.1. Microbial Fuel Cell........................................................................................... 73
5.1.1. Contamination Of Nanoclay In MFC Based Drilling Fluid System .... 75
5.1.2. Use Of Anode Solution Of MFC As An Effective Drilling Fluid Base . 78
5.2. Summary ........................................................................................................... 80
CHAPTER 6 MODELING ............................................................................................ 81
6.1. Rheological Models .......................................................................................... 81
6.2. Maximum Shear Stress .................................................................................... 83
6.3. Modeling Of Salt Contaminated Drilling Mud ............................................. 84
6.4. Modeling Of Remediation Using Nanoparticles ............................................ 88
CHAPTER 7 CONCLUSIONS AND RECOMMENDATIONS ................................ 90
7.1. Conclusions ....................................................................................................... 90
7.2. Recommendations & Future Work ................................................................ 91
REFERENCES ................................................................................................................ 93
xi
LIST OF FIGURES
Figure 1-1. Global Drilling Fluid Market Statistics (Markets And Markets, 2013) ... 2
Figure 1-2. Typical chemical formula of ester ................................................................ 6
Figure 2-1.Variation of kinematic viscosity with temperature for different base
fluids (Moritis, 2011) ....................................................................................................... 12
Figure 3-1. UV spectrum of Vegetable oil based Ester ................................................ 24
Figure 3-2. Variation of change in resistance (∆R/R0) with % volume of the
proposed base fluid ......................................................................................................... 24
Figure 3-3. Soybean oil Methyl ester Figure 3-4. Corn oil Methyl ester ................ 26
Figure 3-5. Proposed Drilling Fluid System ................................................................. 27
Figure 3-6. Variation of Shear stress with strain rate ................................................. 28
Figure 3-7. UV analysis of effect of UH-Biosurfactant ................................................ 28
Figure 3-8. Microbial Fuel Cell...................................................................................... 29
Figure 3-9. EDS of Nano iron particles ......................................................................... 31
Figure 3-10. SEM of UH-Biosurfactant ........................................................................ 32
Figure 3-11. SEM images of Iron oxide nanoparticles ................................................ 32
Figure 3-12. Some additives used in this study............................................................. 33
Figure 3-13. Digital Viscometer ..................................................................................... 35
Figure 3-14. Baroid FANN Viscometer ......................................................................... 36
Figure 3-15. Brookfield Viscometer .............................................................................. 37
Figure 3-16. Brookfield Viscometer – Spindles ............................................................ 38
Figure 3-17. Filter press experimental set up ............................................................... 39
Figure 3-18. pH meter and Conductivity Meter with Probes ..................................... 41
xii
Figure 3-19. Mud balance Figure 3-20. Digital resistivity meter ............ 41
Figure 3-21. UV Spectrophotometer ............................................................................. 42
Figure 4-1. Variation of viscosity with nanoclay concentration for CP ..................... 45
Figure 4-2. Variation of viscosity with nanoclay concentration for CM ................... 46
Figure 4-3. Filter Loss analysis of Corn Oil PVA based Ester (CP) .......................... 48
Figure 4-4. Filter Loss analysis of Corn Oil Methyl alcohol based Ester (CM) ........ 48
Figure 4-5. Variation of filtrate volume with time for SM .......................................... 49
Figure 4-6. Variation of Electrical property (∆R/R0) of CP ....................................... 50
Figure 4-7. Variation of Electrical property (∆R/R0) of CM ...................................... 50
Figure 4-8. Variation of Filtrate volume with time for mineral oil and ester drilling
fluid systems .................................................................................................................... 52
Figure 4-9. Variation of shear stress with shear rate with different percentages of
NaCl salt ........................................................................................................................... 54
Figure 4-10. Variation of filtrate volume with time ..................................................... 55
Figure 4-11. Variation of shear stress with strain rate during hysteresis for 1 % UH-
biosurfactant. ................................................................................................................... 56
Figure 4-12. Variation of shear stress with strain rate during hysteresis for 20 %
Salt. ................................................................................................................................... 57
Figure 4-13. Drilling fluid with 1% Biosurfactant + 5% NaCl .................................. 58
Figure 4-14. Drilling fluid with 1% Biosurfactant + 10% NaCl ................................ 58
Figure 4-15. Variation of viscosity with temperature .................................................. 59
Figure 4-16. Variation of shear of homogeneous vegetable oil based ester drilling
fluid during salt contamination at T=55oC ................................................................... 60
xiii
Figure 4-17. Variation of PV and YP of homogeneous vegetable oil based ester
drilling fluid during salt contamination at T=55 oC .................................................... 61
Figure 4-18. Variation of resistivity with %ester in water .......................................... 62
Figure 4-19. Variation of shear stress of 20% salt contaminated homogenized
vegetable oil based ester drilling fluid SM remediated with Nanoclay ...................... 65
Figure 4-20. Variation of fluid loss with percentage Nanoclay contaminated with
20% salt............................................................................................................................ 65
Figure 4-21. Variation of Fluid loss of 20% salt contaminated homogenized
vegetable oil based ester drilling fluid SM remediated with hydrophobic
nanoparticles ................................................................................................................... 67
Figure 4-22. Variation of shear behavior with percentage Nano iron ....................... 68
Figure 4-23. Variation of fluid loss with percentage Nano iron ................................. 68
Figure 4-24. Variation of resistivity with concentration of ferric nitrate .................. 70
Figure 4-25. Variation of Shear stress with strain rate ............................................... 71
Figure 4-26. Variation of filtrate volume with time for iron enhanced VEDF ......... 71
Figure 4-27. Variation of shear stress with strain rate of 20% salt contaminated
homogenized VEDF in the presence of ferric nitrate .................................................. 72
Figure 4-28. Variation of filtrate volume with time in the presence of hydrophobic
nanoparticles and ferric nitrate ..................................................................................... 72
Figure 5-1. Variation of voltage with time for MFC anode solution with 5mL of
FAME ............................................................................................................................... 74
Figure 5-2. Variation of Surface tension & pH for 10% salt ...................................... 76
Figure 5-3. Variation of Surface tension and pH for 10% salt + 3g NC .................... 76
xiv
Figure 5-4. Variation of OCV with time for 10% salt & 10% salt+3gNC ................. 77
Figure 5-5. Variation of fluid loss with time for drilling fluid samples with anode
solution ............................................................................................................................. 78
Figure 5-6. Variation of fluid loss with time for MFC samples .................................. 79
Figure 6-1. Shear variation for SM 0% salt sample .................................................... 85
Figure 6-2. Shear variation for SM 5% salt sample .................................................... 85
Figure 6-3. Shear variation for SM 10% salt sample .................................................. 86
Figure 6-4. Shear variation for SM 20% salt sample .................................................. 86
Figure 6-5. Behavior of consistency index A as a function of concentration of salt by
weight of water. ............................................................................................................... 87
Figure 6-6. Behavior of flow index B as a function of concentration of salt by weight
of water. ........................................................................................................................... 88
Figure 6-7. Variation of shear stress of 20% salt contaminated homogenized
vegetable oil based ester drilling fluid SM remediated with hydrophilic
nanoparticles ................................................................................................................... 89
xv
LIST OF TABLES
Table 2-1. Literature Review on drilling fluid formulation (Markets&Markets,
2013). ................................................................................................................................ 16
Contd. Table 2-1. Literature Review on drilling fluid formulation
(Markets&Markets, 2013). ............................................................................................. 17
Table 2-2. Typical Soybean Oil Methyl Alcohol profile (Gunstone, 1996) ................ 21
Table 3-1. Chemical composition of anode solution .................................................... 30
Table 3-2. Chemical composition of cathode solution ................................................. 30
Table 3-3. Chemical composition of salt bridge ........................................................... 30
Table 3-4. Viscosity calculations for Brookfield Viscometer ...................................... 37
Table 4-1. Rheological properties of SM with varying amounts of Nanoclay (NC) . 45
Table 4-2. Gel strength of CP samples .......................................................................... 46
Table 4-3. Gel strength of CM samples ......................................................................... 47
Table 4-4. API Fluid loss results of MO and CM samples .......................................... 52
Table 4-5. Rheology of MO and CM samples............................................................... 53
Table 4-6. Resistivity data of filtrate collected during API fluid loss experiment at
100 psi and 25 oC ............................................................................................................. 62
Table 4-7. Variation of rheological properties of 20 % salt contaminated VEDF with
different concentration of nanoclay. ............................................................................. 64
Table 5-1. Properties of Anode solution with 10 % NaCl ........................................... 77
Table 5-2. Properties of Anode solution with 10 % NaCl and 3 g Nanoclay ............. 77
Table 5-3. Rheology of various drilling fluids formulated using MFC Anode solution
and control vegetable oil based ester as base fluids ..................................................... 79
xvi
Table 5-4. Rheological properties of various base fluids ............................................. 80
Table 6-1. Hyperbolic model parameters for salt contaminated SM based drilling
fluid................................................................................................................................... 87
Table 6-2. Hyperbolic model parameters for 20% salt contaminated homogenized
vegetable oil based ester drilling fluid with varying concentration of nanoclay ....... 89
1
CHAPTER 1
INTRODUCTION
1.1. Introduction to Drilling
The ever growing demand for oil & gas is driving the global processes
of exploration and drilling for new resources in unexplored areas and deeper
formations. Drilling fluids also known as drilling muds are hydraulic fluids used in the
drilling industry to maintain the hydrostatic pressure, cool the drill bit, provide wellbore
stability and suspend the formation cuttings. The properties and formulation of drilling
fluids play a fundamental role in drilling operations (Shadravan & Amani, 2012). The
complex drilling fluids represent 15 to 18 % of the total cost (about $1 million) of
petroleum well drilling. Regular and routine incidents of hydrocarbon spills and blowouts
are common accidental situations encountered during drilling operations. These accidents
can be controlled rather effectively by shutting in the well with the help of the blowout
preventers and by changing the physical properties of the drilling fluid.
Recent advancements in deep water drilling has unfolded the existence of
challenging geological and environmental conditions. Water Based Muds (WBM) which
are widely used in the current scenario are found to be highly unsuitable for shale
formations and deep water drilling. Hence there is great scope for research in the field of
Synthetic Drilling Fluids (SDF) towards the development of an eco-friendly Oil Based
Mud (OBM).
2
1.1.1. Drilling Fluid Market
The ever increasing hydrocarbon demand coupled with deep water drilling is
driving the growth of the drilling fluid industry very quickly over the last decade. The
global market for drilling fluids was valued at USD 7.20 billion in 2011 and is now likely
to reach USD 12.31 billion by 2018. Usage of drilling fluids for offshore purposes
accounted for 30% of the total market in 2012 (Markets&Markets, 2013). The global
industry analysis report published by Transparency Market Research showed that North
America has always been the leading market for drilling fluids with over 55 % of the
global market share in 2012 (Markets&Markets, 2013).
Figure 1-1. Global Drilling Fluid Market Statistics (Markets And Markets, 2013)
Figure 1-1 shows that North America has the maximum drilling fluid market
share. According to Energy Information Administration (EIA Annual Report, 2013), the
global expenditure on exploration and development of oil and gas industry increased by 5
3
% which accounted for $18 billion in 2013. However, growing environmental concerns
regarding the use and disposal of drilling fluids coupled with geopolitical issues are
expected to hinder the market growth.
1.1.2. Types Of Drilling Fluids
Drilling fluids are made up of continuous phase and internal phase. The base
fluids form the continuous phase and water/brine form the internal phase. Other
additives include weighting agents, fluid loss agents, emulsifiers and viscosifying agent.
Drilling fluids are of 3 main types namely water, oil and synthetic based drilling fluids.
They are categorized by the type of base fluid and differ widely in their applications.
(i) Water based – Mainly consists of bentonite and water. Weighting agents like
calcium carbonate or barium sulfate are commonly used. Water based muds are
the most commonly used drilling fluids since they are easy to manufacture and are
inexpensive. The main concern with WBM is the thermal degradation of chemical
additives that often occurs while drilling high temperature wells. Such
degradation can lead to strong variations in rheological and filtration
characteristics and loss of fluid properties (Melbouci & Sau Arjun, 2006).
Moreover, even if no degradation of components occurs, the viscosity of hydro-
soluble polymer solutions commonly used in drilling fluid formulations strongly
decreases at high temperatures. Improperly formulated and maintained drilling
fluid systems can cause significant near-wellbore formation damage and create
potential for the plugging of screens and slotted liners (Pitoni et al. 1999).
(ii) Oil based – Mainly consists of oil, water/brine and surfactant. The base oils may
be mineral oil, low toxicity mineral oil or diesel oil (Caenn. R. et al. 2011). Oil
4
based muds surmounted water based muds whiles drilling through shale as they
offered excellent stabilization against filtration loss. In difficult drilling situations
such as horizontal, deep wells and reactive shale formations, drillers usually rely
upon oil based muds. Despite their high-performance properties, OBMs are costly
to dispose-off and contain toxic materials, such as mineral oil as one of their
major ingredients which makes them environmentally unsuitable for current
usage. The only drawback in oil based muds was that they are very less or not
biodegradable. A major drawback of OBMs is their poor biodegradability in
aerobic conditions. Most importantly, they show very slow degradation in
anaerobic conditions which are typical on the seafloor and thus in the pile of drill
cuttings dumped overboard from the drilling platform. This led to the extended
research in the area of synthetic drilling fluids (Salleh M. K. et al. 2011)
(iii) Synthetic based – Mainly consists of synthetic fluid, water/brine and surfactant.
They are similar to OBMs in rheological properties but with an edge of
biodegradability. Their non-toxic nature makes them different and favors greater
usage in the industry. However, in the milieu of having so many advantages lies
the disadvantage of having the highest cost compared to the other drilling fluids.
1.1.3. Synthetic based muds (SBM)
Water based muds are cheap and can be formulated with easily available
ingredients. When it comes to drilling through shale formations, water based muds
cannot be used due to very high filtration loss. Shale formations are fine grained
sedimentary rocks made of clay minerals, calcite and quartz. These rocks show high
fissility and are mainly composed of silt sized particles of clay (Qianheng & Baoguo,
5
2008). Often, wellbore instability issues are encountered in these formations which is
due to the dispersion of the clay into ultra-fine colloidal particles and this has a direct
impact on the drilling fluid properties (Khodja.M. et al. 2010, Hunter T. N. et al. 2008).
United States has over 20% of land covered by shale formations which represent
75% of all formations drilled by the oil & gas industry. The best suited material for such
formations is Oil Based Mud. OBMs are highly effective due to their low fluid loss and
high temperature and pressure tolerance. OBMs rules the industry for a long time until
the environmental problem caused by their disposal was realized. Abidance by the
Environmental Protection Agency (EPA) and cost has been a major concern which
sojourns the usage of oil based muds. Low aromatic mineral oils as well as synthetic oils
have been replacing the highly aromatic oils (e.g. diesel) in the oil and gas industry.
However, as environmental legislation become more stringent, even the newer and less
polluting mineral and synthetic oils in vogue now may be pronounced unsuitable because
of their non-biodegradability. In fact, in many parts of the world, including countries like
the USA, United Kingdom, Holland, Norway, Nigeria and Australia, the use of diesel and
mineral oil-based drilling fluids in offshore operations has already been either severely
restricted or banned because of their toxicity and bio-accumulation (Salleh & Tapavicza,
2011). This led to the breakthrough in the field of drilling fluids research when
researchers began to study the use of different materials which could abide by the EPA
standards but also possess the excellent physical properties of OBMs during the 1990s.
Synthetic based muds could be either emulsions or invert emulsions. Emulsion is a
generic term to describe a mixture of oil in water. An invert emulsion means it has more
quantity of oil in the continuous phase and lesser quantity of water/brine in the internal
6
phase i.e. the invert emulsion system has oil in the external phase and water/brine in the
continuous phase (Zanten R. V. et al. 2012).
1.2. Soybean Oil
There is a wide variety of vegetable oils available. Soybean oil is a vegetable oil
extracted from the soybean seeds and is one of the most widely consumed cooking oils.
Chemicals derived from soybean oil are used to control cholesterol. Soybean seed
contains about 30 % carbohydrate, 38 % protein, 18 % oil and 14 % moisture, ash and
hull. 100 g of soybean oil contains 16 g saturated fat, 23 g monounsaturated fat, 58 g
polyunsaturated fat with a smoke point of 257 oC (Ivanov D. S. et al. 2011).
1.3. The Ester Chemistry
Esters are derivatives of oxacids and hydroxyl compounds consisting of a
carbonyl next to to an ether linkage. It can also be defined as an organic compound made
by replacing the hydrogen of an acid by an alkyl or other organic group. Many naturally
occurring fats and essential oils are esters of fatty acids. Animal and vegetable fats and
oils are just big complicated esters. The difference between a fat (like butter) and an oil
(like sunflower oil) is simply in the melting points of the mixture of esters they contain. If
the melting points are below room temperature, it will be a liquid - oil. If the melting
points are above room temperature, it will be a solid - a fat. (Chemistry Guide – UK)
Figure 1-2. Typical chemical formula of ester
7
1.4. Objectives
The overall objective of this research was to develop and characterize a vegetable
oil based ester drilling fluid system. The specific objectives of this study are as follows:
1) Develop and characterize various types of vegetable oil based ester drilling fluids
(VEDF)
2) To investigate the sensing properties of VEDF
3) To study the effect of salt contamination on the VEDF
4) Use microbial fuel cell (MFC) to recycle the salt contaminated VEDF
5) Model the behavior of VEDF
1.5. Organization
This thesis is organized into 6 chapters. Chapter 1 provides an introduction about
the drilling fluids. The types and characteristics of drilling fluids have been described in
detail. It also elaborates on the advantages and disadvantages of the different drilling
fluid technologies.
Chapter 2 deals with the literature review explaining the past research in the field
of synthetic drilling fluids. Issues related to procurement and costing of the currently
available materials have also been discussed. This chapter also explains the reason why
the current research is important.
Chapter 3 discusses the characterization of the proposed base fluid material for
synthetic group of drilling fluids. The advantage of using the proposed material over
available oil based muds in terms of rheology has been assessed.
Chapter 4 explains the effect of sodium chloride salt contamination on the
rheology and fluid loss of the proposed material. The effect of nano materials to
8
remediate salt contamination has been investigated and experimental results of the same
have been presented. An effective method for real time monitoring of the drilling fluid
based on its resistivity measurements has been proposed.
Chapter 5 deals with the biodegradability of the material. Experimental results
which show their capability to modify the properties of an MFC have been presented in
this chapter. Also, plate test proving the ability of serratia sp. to survive in this material
have been has been discussed.
Chapter 6 discusses the characteristics of proposed hyperbolic model and how it
interprets the rheology of this drilling fluid. The advantages of this model compared to
the ones currently employed in the industry for predictions have also been discussed.
Chapter 7 summarizes the results from the thesis. This chapter also includes the
original contributions of this research and recommendations for future work.
9
CHAPTER 2
LITERATURE REVIEW
2.1. Introduction On Drilling And Drilling Fluids
The history of drilling could be separated into 3 different periods namely the
experimental era from ancient times to 1901, the era of practice from 1901 to 1928 and
finally the era of science and research from 1928 to present (Irfan H. 2000). Drilling
could be onshore or offshore; conventional, horizontal, slant or directional drilling. A
major difference between onshore and offshore drilling is the type of the drilling
platform. Also, in offshore drilling the drill pipe must pass through the water column
before entering the seafloor or lake. These type (offshore) of wells have been drilled in
waters as deep as 10,000 ft. Drilling operations require various types of lubricants to ease
the process. Drilling fluids mainly provide hydrostatic pressure for wellbore stability,
lubrication to reduce frictional losses and viscosity to suspend cuttings. These drilling
fluids can be formulated with different properties depending upon the requirements of the
project. The various properties which are generally under consideration are briefly
discussed below.
2.1.1. Viscosity, Fluid Loss and Density
Viscosity in simple words describes the thickness of the fluid. It is the measure of
the resistance offered by the fluid towards flow. Amin R.A.M. 2010 reported the plastic
viscosity of vegetable oil based ester drilling fluids lying in the range of 22 – 30 cP.
Hydrolysis of esters occur when water is added to ester in the presence of an acidic or
basic environment. Hydrolysis is triggered by higher temperature. This also increases the
10
viscosity of the material. Very high viscosity is also not desirable say Maghrabi. S. et al.
2013, since it will cause high equivalent circulating density (ECD).
Fluid loss can be defined by the API as the amount of water coming out through
the filter paper at a pressure 100 psi after 30 mins. The spurt loss is termed as the fluid
loss at the end of 7.5 mins. The fluid loss of iso-parafinic oil and esters were reported by
Patel. A. and Ali. S. 2003 as 10-15 mL with the addition of many chemical additives at
high pressure high temperature (HPHT) conditions.
Density is known to be the ratio of mass of the material to its volume. As reported
by (Patel. A. and Ali. S. 2003; Ismail A.R. 2001; Growcock. F. B. and Patel. A. D. 2011)
we can say that the range of density for drilling fluids could be from 7 ppg to 16 ppg
depending upon the formation type and the drilling conditions.
2.1.2. Biodegradability
Disposability is a very important property undiscussed while designing a drilling
fluid system. Operators are worried about the high initial investment and neglect the ease
disposability offered by the synthetic base fluids. Ester is considered to be the most easily
biodegradable synthetic base fluid showing an LC50 concentration of 20000 mg/kg
(Offshore-Mag article, October 2011).
It is known that water based muds and oil based muds are not preferred these
days, due to environmental concerns. Bentonite is the mainly found in WBMs and OBMs
majorly contain mineral or diesel oil which are proven to be highly toxic. Water based
muds which are less toxic are preferred for normal drilling operations. However for deep
water drilling purposes, water based muds are not recommended. Instead, OBMs are used
as they have greater temperature tolerance (Ismail A.R. 2001). Environmental Protection
11
Agency (EPA) has imposed strict guidelines on the operators to protect the environment
and promote the use of biodegradable materials. The oil based mud normally create short
or long term disasters and hence there is a great need the develop alternatives. The release
of ester-based fluids into the global drilling fluids market initiated the era of synthetic-
based invert drilling fluids. The biodegradation and toxicity performance of esters is
considered to be the best among all synthetic based fluids currently used in the industry
(Burrows. K. et al. 2001).
2.1.3. Sensing Property
Monitoring the performance of the drilling fluid constantly while drilling is very
important. At present less research has been made in improving the sensing properties of
a drilling fluid. Since the resistivity of the ester is very high of the order of terra ohms, no
work has been done to modify the material so as to sense its resistivity changes with
changes in the material (Corach. J. et al. 2012).
2.2. Oil Based Drilling Fluids
Oil based mud is a fluid system containing oil as he continuous phase and droplets
of water as dispersed phase emulsified in oil. Typically the oil based muds contain 2 to
25 % of dispersed phase but this can be increased up to 50 % to reduce the cost and
toxicity. Oil based muds (Marks. R. E. et al. 1988) are normally nonconductive and
precludes the use of those logging tools which involve the passage of current through the
formations. Even though the low aromatic mineral oils replaced the diesel oils in oil
based muds, the persisting oil on the drilled cuttings causing toxic environment in marine
systems gave rise to greater interest in finding out better alternatives. Diesel and other
mineral oil-based muds have a high kinematic viscosity that yields high ECDs that could
12
result in drilling problems such as induced fracturing and lost circulation. Drilling in the
gulf needed low ECDs because of the narrow pressure range between the pore pressure
and the fracture gradient as explained in Fig 2-1 (Moritis, 2011). Nanoparticles have
helped in developing yield stress and improving the emulsion stability in case of oil based
mud (Agarwal. S. et al. 2011)
Figure 2-1.Variation of kinematic viscosity with temperature for different base
fluids (Moritis, 2011)
2.3. Synthetic Base Fluids
The Norwegian regulatory authority defines a synthetic base fluids (Neff. J.M. et
al. 2000) as “A drilling fluid where the base fluid consists of non-water soluble organic
compounds and where neither the base fluid nor the additives are of petroleum origin.” In
the drilling fluid industry, the term “oil” is used for liquids prepared from distillation of
petroleum, whereas the term “synthetic” or “synthetic fluid” is reserved for non-aqueous
liquids prepared from the reaction of fundamental organic building blocks, such as
ethylene or methane. The revolution in OBMs began in the early 1990s with the advent of
synthetic-based drilling fluids. The primary reason was biodegradability of the residual
13
oil on drilled cuttings. The primary concern was the fate of oily drilled cuttings,
especially those discharged into the sea during offshore drilling operations. Sampling of
cuttings mounds on the seafloor revealed that not only the mounds themselves, but vast
areas around them, had become anoxic and were essentially devoid of life. A base fluid
that would anaerobically biodegrade might solve this problem. The search for such fluids
led to esters, in the belief that their “built-in oxygen” would enable these materials to
biodegrade without the assistance of dissolved oxygen. Vegetable and animal oils – many
of them natural esters – were tried but failed to meet performance and/or HSE standards.
However, an ester prepared from a natural fatty acid and an alcohol, showed much more
promise, and it became the first commercial “synthetic” fluid. Other synthetic fluids soon
followed, including acetals, alkylbenzenes and an assortment of aliphatic hydrocarbons
derived from ethylene. Today the most commonly used synthetic fluid is an internal
olefin with a carbon chain length of C16-C18. (Growcock. F. B. and Patel. A. D. 2011).
Drilling fluid is used to aid the drilling of boreholes into the earth. Often used
while drilling oil and natural gas wells and on exploration drilling rigs, drilling fluids are
also used for much simpler boreholes, such as water wells. (Christopher. J. and John. A.
V) Liquid drilling fluid is often called drilling mud. The EPA regulations, however, are
based on mud technology - that is, water-based drilling fluids (WBFs) and oil-based
muds (OBMs) - that was available when the regulations were developed. Although EPA
requirements appear to have been a major driver behind the development of Synthetic
Based Muds (SBM), concern is now focused on the inhibiting effect of discharge
limitations on use of alternative mud technologies. (wikipedia)
14
The synthetic based fluids (SBF) used in drilling fluid systems may be a hydrocarbon,
ether, ester, or acetal. Synthetic hydrocarbons include normal (linear) paraffins (LPs),
linear-α-olefins (LAOs), poly-α-olefins (PAOs), and internal olefins (IOs) (Jackson. A.
1987). Most drilling in the Gulf of Mexico currently is with WBFs. When WBFs are not
suitable and OBFs are not selected, IO and LAO SBFs are extensively employed. SBFs
are a relatively new class of drilling muds that are particularly useful for deepwater and
deviated hole drilling. They were developed to combine the technical advantages of oil
based drilling fluids (OBF) with the low persistence and toxicity of WBFs. In an SBF, the
continuous liquid phase is a well-characterized synthetic organic compound. Salt brine
usually is dispersed in the synthetic phase to form an emulsion (Burke. C. J. and Veil. J.
A. 1995). Invert emulsion drilling fluids generally face problems pertaining to barite sag,
high surge/swab pressures and excess equivalent density. By omitting clay from the
drilling fluid system, rate of penetration can be improved and surge pressures can be
substantially reduced (Zanten. R. et al. 2012)
Shell Chemicals define SDF as the following: “In basic terms, "synthetic" applies
to the process by which the end product was manufactured, where the ending molecules
of the process are not normally found in nature. Fluids from chemical processes are
defined as being "synthetic", while fluids extracted from refinery streams are generally
defined as being oil-based.” In order to define "synthetic", as it applies to drilling fluids,
the non-aqueous drilling fluids (NADF) offshore disposal regulations as legislated in
several parts of the world were reviewed. Schlumberger claims that M-I SWACO was the
first to develop a synthetic-based drilling fluid system exhibiting the highest level of
drilling and environmental performance. Baroid Fluid Services defines bioremediation as
15
the biological treatment of hydrocarbon contaminated waste (most commonly oil-based
or synthetic-based mud drill cuttings) with microorganisms that will metabolize the
hydrocarbons, converting them to water and carbon dioxide (www.halliburton.com,
www.slb.com, www.shell.com). As drilling applications become more complex and
environmental regulations tighten, researchers continue to focus on developing synthetic-
based drilling fluids.
2.3.1. Ester Base Fluids
In 1985, development began on a fully biodegradable base fluid at the request of
operators facing restrictions on the use of and discharges from conventional oil base
fluids. Esters were found to be the most suitable naturally derived base fluids in terms of
potential for use in drilling fluids, being exceptional lubricants, and showing low toxicity
and a high degree of both aerobic and anaerobic biodegradability. Ester fluid provides
similar shale stabilization and superior lubricity to mineral oil-based mud, and yet also
satisfies environmental parameters.
The first trial of the conventional ester-based fluid in February 1990, took place in
Norwegian waters and was a technical and economic success. Since then, nearly 400
wells have been drilled worldwide using this C12-C14 ester-based system (Offshore
Magazine, 2011). The release of ester-based fluids into the global drilling fluids market
initiated the era of synthetic-based invert drilling fluids (Gray & Grioni, 1969). Following
the success of esters, other drilling fluids classed as synthetics were formulated, but these
synthetics have not matched the environmental performance of vegetable oil based ester
drilling fluids. One of the most important criteria that they have failed to meet is that of
16
biodegradability; additionally, some have been rejected as a result of poor eco
toxicological or technical performance.
A low viscosity base fluid is required to give operators the choice of using a
system that fulfils more technically demanding requirements than existing ester-based
systems, with a lower oil to water ratio, hence reducing the amount of base fluid
discharge (Burrows. K. et al., 2001).
High biodegradability and relatively low toxicity have long made esters
universally recognized as the best base fluids for synthetic-based muds in regards to
environmental performance. A major limiting factor in the use of ester-based fluids,
particularly in deep water, is the inherently high kinematic viscosity, a condition that is
magnified in the cold temperatures encountered in deep water risers. (Terrens. G. W. et
al. 1998). These higher viscosities are believed to be especially critical in deep water
wells where lack of overburden causes a severely narrowed window between pore
pressures and fracture gradients. Other implications of these higher viscosities include
limitations on oil/water ratios, mud weights, and drill solids tolerance.
Table 2-1. Literature Review on drilling fluid formulation (Markets&Markets,
2013).
Sl No Reference
Drilling
Fluid
type
Base fluid /
Water ratioTests Method PV (cP)
YP
(lb/100
ft2)
Resistivity Remarks
1R.A.M Amin et
al. (2010)
Methyl/
Ethylexy
l Ester
Based
80/20Brookfield Model
LVDV-III22-30 7 to 36
not
measured
On
contamination
with salt water,
PV increases and
YP reduces
2
Adeleye Sanmi
Apaleke et al.
(2012)
Canola
Oil
Based
90/10 & 80/20
mud balance,
viscometer, HPHT
single cell
filtration loss
tester, hot olling
oven with cells,
electrical stabiliy
tester.
53 & 59 7 & 29not
measured
Density is 8ppg.
Reducing the
oil/water ratio is
a challenge
because stability
reduces. CMC is
toxic.
17
Contd. Table 2-2. Literature Review on drilling fluid formulation
(Markets&Markets, 2013).
Sl No Reference
Drilling
Fluid
type
Base fluid /
Water ratioTests Method PV (cP)
YP
(lb/100
ft2)
Resistivity Remarks
3
J.Corach, PA
Sorichetti & SD
Romano (2012)
FAME of
Corn,
Canola
oil
NADielectric
spectroscopyNA NA
conductivi
ty of
FAME of
corn &
canola oil
is of the
order 1E-
10.
The resisitivity
of these FAMEs
are nearly of the
order of terra
ohm.
4A Patel and S Ali
(2003)
Isoparafi
nic oil &
Ester
70/30, 75/25,
90/10HPHT filter loss 29-59 20-63
not
measured
HPHT FL is
studied
5Burrows K et al.
(2001)
Internal
Olefin
Base
Fluid
(C8)
70/30FANN 75 and 35
Viscometers
65
(11lb/g
al);
86(14lb
/gal)
36(11lb
/gal);
44(14lb
/gal)
not
measured
15-17ppg
density.10% sea
water
contamination
caused increase
in YP
6
Lirio Quintero,
Shannon et al.
(1999)
Ester 85/15
FANN 35
Viscometer, HPHT
Filterloss,
Electrical stability
tester.
24-41
not
measur
ed
not
measured
HPHT FL is
studied
7Growcock and
Frederick (1996)
Ester,
ether,
PAO
80/20
HPHT filter loss,
Low shear
rheology meter
not
measur
ed
not
measur
ed
not
measured
For thermal
stability, higher
emulsifier
concentration is
required
8
Mohammed and
Mohammed
(2009)
diesel
oil95/5
FANN 35
Viscometer, HPHT
Filterloss,
Electrical stability
tester.
25 40not
measured
Effect of
emulsifier on
rheology is more
prominent at
room temp than
high temp
Remarks NA
differen
t types
of oil are
used
80/20 commonly
used
Viscosity and
HPHT filter loss
are the major
parameters
governing the
characterization
of SBM
25-40 7 to 40
This
parameter
has not
been
studied
on drilling
fluids
zero fluid loss in
the presence of
salt
contamination
has not been
attained yet for
ester based
drilling fluids
18
2.4. Hydrolysis of Ester
Technically, hydrolysis is a reaction with water. These reactions are exactly the
reverse of those used to prepare ester from vegetable oil and alcohol. The only difference
is that a base catalyst is used in esterification process. Example of an ester hydrolysis is
given below:
CH3CH2COOCH3 + H2O CH3CH2COOH + CH3OH Eq 1
Methyl Propanoate Propaonic Acid Methanol
In the absence of any other external source, the vegetable oil based ester drilling
fluid is a homogeneous system made of water and ester. Hydrolysis of ester is dangerous
as it degrades the ester into its components. Once degraded, the properties of ester
undergoes an obvious change and hence would no longer be useful as a drilling fluid.
Hence, before using the material as a drilling fluid it is important to know about the
hydrolysis mechanisms of ester. Hydrolysis is triggered by high temperature but would
also occur at normal room temperature at lower rates. The pH of the proposed ester is in
the range of 8-9 and hence is categorized as basic. Hence the mechanism of ester
hydrolysis under basic conditions are necessary to be understood.
Reaction under BASIC conditions:
1) The mechanism shown below leads to acyl-oxygen cleavage.
2) The mechanism is supported by experiments using O labeled compounds and
esters of chiral alcohols.
H+(aq)
19
3) This reaction is known as "saponification" because it is the basis of making soap
from glycerol tri-esters in fats.
4) The mechanism is an example of the reactive system type.
2.5. Effect of Temperature and Pressure on Ester Drilling
Fluids
Literature showed that both pressure and temperature had effects on the viscous behavior
of the non-aqueous drilling fluids. According to Hermoso. J. et al. 2014, the yield stress
values increase linearly with pressure. The pressure influence on yielding behaviour has
been associated with the compression effect of different resulting organoclay
microstructures.
Mechanism of the base hydrolysis of esters:
1) Step 1: The hydroxide nucleophiles attacks at the electrophilic C of the ester
C=O, breaking the p bond and creating the tetrahedral intermediate.
2) Step 2: The intermediate collapses, reforming the C=O
results in the loss of the leaving group the alkoxide, RO- , leading to the
carboxylic acid.
3) Step 3: An acid / base reaction. A very rapid equilibrium where the alkoxide, RO-
functions as a base deprotonating the carboxylic acid, RCO2H, (an acidic work
up would allow the carboxylic acid to be obtained from the reaction).
20
2.6. Economics Of Synthetic Drilling Fluids
The cost of non-aqueous synthetic base fluids that are used to make drilling fluids
has always been higher than that of water since water is a naturally available material
while synthetic base fluids are manufactured and processed. Hence, when synthetic fluids
were introduced as replacements for oils in offshore operations to enable direct discharge
of cuttings to the sea, the initial drilling fluid cost almost doubled. However, the actual
cost incurred by the operator for using SBMs are those for loss of residual fluid on
cuttings, losses downhole (mainly through lost circulation) and rental of the fluid
returned to the service company for reconditioning and re-use. Furthermore, use of
synthetic base fluid does not require expensive collection, transportation and onshore
disposal of cuttings. Thus, for drilling in reactive, deep and/or hot formations, which
usually is more efficient with SBMs than with WBMs, the net cost of using SBM is
significantly less than WBMs, though their initial costs may still be higher (Growcock. F.
B. and Patel. A. D. 2011). Currently, the operators in the drilling industry are more
concerned about the initial cost than the long term savings and other valuable benefits
and hence still hesitate to invest upon synthetic drilling fluids.
2.7. Fatty Acid Methyl Ester (FAME)
Soybean oil is a vegetable oil extracted from the seeds of the soybean. It is one of
the most widely consumed cooking oils. Fatty acid methyl esters (FAME) are a type
of fatty acid ester that can be produced by an alkali-catalyzed reaction
between fats or fatty acids and alcohol. The molecules in biodiesel are primarily FAMEs,
usually obtained from vegetable oils by transesterification. The composition of a typical
21
Soybean oil Methyl alcohol ester (SM) can be obtained by conducting gas
chromatography. The FAMEs are generally composed of a mixture of esters as
mentioned in Table 3.1. This material is currently being used in the transformer industry
as an insulator and also extensively used in the fuel industry as biodiesel.
Eq 2
Table 2-3. Typical Soybean Oil Methyl Alcohol profile (Gunstone, 1996)
Fatty Acid % Weight
Molecular
Weight Chemical Formula
Palmitic 12 270.46 C15H31CO2CH3
Stearic 5 298.52 C17H35CO2CH3
Oleic 25 296.5 C17H33CO2CH3
Linoleic 52 294.48 CH3(CH2)4CH=CHCH2CH=CH(CH2)7 CO2CH3
Linolenic 6 292.46 CH3(CH2CH=CH)3(CH2)7 CO2CH3
2.8. Summary
Based on the literature survey pertaining to the drilling fluid formulations the
following can be summarized:
1) Resistivity has neither been reported nor used as a means to monitor the
properties of the drilling fluid.
2) Water based muds are not suitable for shale formations due to high fluid loss.
3) Salt water contamination causes an increase in the plastic viscosity and reduces
the yield stress.
Alcohol Oil Glycerine Ester
22
4) All the drilling fluid formulations currently used have atleast 3 to 4 different
additives namely viscosifier, fluid loss reducer, densfier, primary emulsifier,
surfactant and secondary emulsifier; other than the base fluid and water/brine for
enhancing various properties. Hence we see an increased cost of the final product.
5) There is a need to develop a drilling fluid which has properties as that of synthetic
drilling muds but are also cost effective.
23
CHAPTER 3
MATERIALS AND METHODS
3.1. The Proposed Synthetic Base Fluid - FAME
Selection of a base fluid needs through scrutiny and various factors are
considered. The following criteria were assessed before proposing the base fluid.
1) Availability and commercial terms of base fluid at location
2) Drilling environment - formation temperature stability or pressures that will be
encountered
3) Operator policy and local legislation, local content requirement, toxicity, health
and safety issues
In the current study, fig. 3-1 shows the UV spectrophotometric print of the
proposed vegetable oil based ester base fluid. With the help of some research papers
which have already been published, the individual peaks of the constituent esters were
identified and highlighted in the plot. The first would be methyl oleate which picks up the
UV peak at 220 nm. The next one to show up on the plot is methyl linoleate at 270 nm
followed by methyl stearate at 290 nm. The last constituent recorded by the
spectrophotometer was methyl palmitate whose peak was seen at 324 nm (Qingsu, et al.,
2006). Figure 3-2 shows the sensibility of resistivity to change in the concentration of the
proposed base fluid with water by weight.
24
Figure 3-1. UV spectrum of Vegetable oil based Ester
Figure 3-2. Variation of change in resistance (∆R/R0) with % volume of the
proposed base fluid
2
2.5
3
3.5
4
4.5
5
5.5
6
6.5
7
190 240 290 340 390 440
Ab
sorb
ance
(A
o)
Wavelength (nm)
biodiesel
0
5000000
10000000
15000000
20000000
25000000
30000000
0 5 10 15 20 25 30 35 40
Ch
ange
in r
esis
tance
(∆
R/R
0)
Volume of biodiesel in water (%)
Methyl Palmitate
Methyl Stearate
Methyl Oleate
Methyl Linoleate
25
3.2. Transesterification
The proposed material is a C15-C17 long chained ester synthesized in-house.
Trans-esterification of methanol which is a 1-C chained sugar alcohol and vegetable oil
was carried out in the university laboratory under room temperature and atmospheric
pressure (Noureddini. H. and Zhu. D. 1997, Freedman. B. et al. 1986).
Firstly 1g of the catalyst NaOH was dissolved in 50mL of methanol inside a glass
beaker covered tightly by an aluminum sheet. The aluminum sheet was removed and
covered again at regular intervals to allow the heat and pressure to escape since this
reaction is exothermic. The mixing was done by placing the glass beaker on a magnetic
stirrer at a particular constant rpm. The mixing was done for approximately 30 minutes
until the entire NaOH was dissolved. This was followed by the addition of 250 mL of the
chosen vegetable oil into the glass beaker and the mixture was stirred for approximately 3
hours. After a uniform solution was obtained the glass beaker was kept aside in an
undisturbed state for at least 6hrs covered completely by the aluminum sheet. The
solution is kept in this condition until all the glycerin has settled down and clear ester
remains at the top portion. The ester and glycerin can be differentiated easily by the
visible color difference. The ester is later decanted and used as the base fluid for further
studies on drilling fluid.
In the current study, esters were prepared with alcohol as methanol and polyvinyl
alcohol and catalyst as NaOH. Vegetable oils manufactured from co and soybean were
used to study the variation in the properties.
26
Figure 3-3. Soybean oil Methyl ester Figure 3-4. Corn oil Methyl ester
3.3. Drilling Fluid Formulation
The basic components of this system is water and fatty acid methyl ester of
soybean oil. Formulation of drilling fluid began with choosing the appropriate base fluid
to water ratio. After referring to a wide gamut of literature, a fluid to water ratio of 60:40
was finalized. The reason behind this choice was to use the least possible amount of base
fluid to reduce the overall cost of the drilling fluid system. For the same reason, a
limitation was kept on the number of additives to be used in the formulation. The drilling
fluid when mixed in the mixer turns out to be a white milky homogeneous fluid. A
standard order of mixing has been followed throughout the research. Firstly water is
mixed with base fluid for 60 seconds followed by addition of the surfactant. This mixture
is again mixed for 60 seconds. Further addition of additives would be given a mixing of
an extra 60 seconds.
Figure 3-5 shows the final drilling fluid system containing water, ester and UH-
biosurfactant. The mix is homogeneous and white in color with a sweet odor. Figure 3-6
shows the variation of shear stress with strain rate measured using digital viscometer.
From this figure, it can be concluded that there exists a yield stress for the emulsion
ESTER
GLYCERIN
27
which is not seen either in water or ester. The drastic change in viscosity of the invert
emulsion indicates the reaction between the ester and water causing a more dense mix.
Figure 3-7 shows the UV print of biosurfactant in the vegetable oil based ester
base fluid. The plot clearly shows that methyl linoleate and methyl stearate undergo
chemical modifications while the rest of the esters in FAME remain unaltered. These
modifications help in understanding the possible causes for the changes occurring in the
stability of the base fluid due to the presence of UH-biosurfactant.
UH-biosurfactant has also proved to reduce the hydrolysis at higher temperatures.
Table 3-1 explains the increase in the absorbance as the concentration of UH-
biosurfactant is increased.
Figure 3-5. Proposed Drilling Fluid System
Vegetable oil based ester drilling fluid (VEDF)
Mixer jar
28
Figure 3-6. Variation of Shear stress with strain rate
Figure 3-7. UV analysis of effect of UH-Biosurfactant
0
5
10
15
20
25
30
35
40
45
50
0 200 400 600 800 1000 1200
Sh
ear
Str
ess
(dyn
es/c
m2)
Strain Rate (sec-1)
100% ester
100% water
60%ester+40%water
0
1
2
3
4
5
6
7
150 200 250 300 350 400 450
Abso
rban
ce (
Ao)
Wavelength (nm)
DI water
Ester
Ester+Biosurfactant
Methyl Linoleate (modified)
Methyl Stearate (modified)
29
3.3.1. Additives
Several materials were used during this study to enhance the properties of drilling
fluid. However while formulating, it was always kept in mind that only the most
important and unavoidable additives would be used in the drilling fluid; in the least
possible quantities. One of the main objective of this study was to use additives which
would not cause any harm to the environment.
i. Surfactant: The surfactant used in this study is the UH-Biosurfactant which has
been synthesized biologically in an MFC in the UH laboratory under controlled
conditions. MFC is expanded as microbial fuel cell. These are biological fuel
cells or bio-electrochemical systems that drive a current by using bacteria and
mimicking bacterial interactions found in nature. In this study, a two chambered
MFC was used to produce UH-Biosurfactant. The two chambers are anode and
cathode with a salt bridge connecting them. Salt bridge is provided to facilitate the
movement of electrons.
Figure 3-8. Microbial Fuel Cell
Resistance measurement
Salt bridge
Cathode chamber
Anode chamber
Oxygen supply
30
Table 3-1. Chemical composition of anode solution
Chemical Composition Chemical Formula Quantity
Potassium Phosphate Dibasic K2HPO4 1.33 g/L
Potassium Phosphate Monobasic KH2PO4 0.5 g/L
Magnesium Sulphate MgSO4 0.5 g/L
Potassium Chloride KCl 0.1 g/L
Sodium Nitrate NaNO3 2 g/L
Vegetable Oil - 10 mL/L
Yeast extract - 0.5 g/L
Serratia sp. - 50 mL/L
Table 3-2. Chemical composition of cathode solution
Chemical Composition Chemical Formula Quantity (g/L)
Potassium Phosphate Dibasic K2HPO4 1.33
Potassium Phosphate Monobasic KH2PO4 0.5
Magnesium Sulphate MgSO4 0.5
Potassium Chloride KCl 0.1
Sodium Nitrate NaNO3 2
Table 3-3. Chemical composition of salt bridge
Chemical Composition Chemical Formula Quantity (g/L)
Potassium Phosphate Dibasic K2HPO4 1.33
Potassium Phosphate Monobasic KH2PO4 0.5
Magnesium Sulphate MgSO4 0.5
Potassium Chloride KCl 0.1
Sodium Nitrate NaNO3 2
Agar - 15
Anode chamber has Serratia.sp. bacteria. The production of biosurfactant
is maximum during the first 24hrs of the installation of MFC. They begin to
appear as yellowish white flakes floating in the anode chamber. These flakes are
31
later collected in small bowls and dried under atmospheric pressure and room
temperature. The dry flakes are then powdered fine for further use.
ii. Nano particles: materials whose size is in the nano scale are called nano particles.
Nano sciences is gaining great interest due to the excellent flexibility offered by
them in their physical and chemical properties. In this study, nano clay (NC) of
bentonite origin and nano iron oxide (NI) have been used to enhance various
properties of the drilling fluid system. These materials were ordered from Sigma
Aldrich Company. The size of these is between 50 – 100 nm. This was confirmed
by the results obtained by SEM (Scanning Electron Microscope) and EDS
(Energy Dispersive X-ray Spectroscopy) as shown in figures 3-8 to 3-10.
Figure 3-9. EDS of Nano iron particles
Energy (Kev)
Co
un
ts
32
Figure 3-10. SEM of UH-Biosurfactant
Figure 3-11. SEM images of Iron oxide nanoparticles
iii. Sodium Chloride salt (contaminant): sodium chloride crystals of Sigma Aldrich
make were used as a contaminant to quantify the effect of salt contamination in
33
drilling fluids which is the most common contamination occurring in this
industry.
iv. Ferric Chloride: lavender crystals of ferric chloride have been used to help reduce
the effect of salt contamination in the drilling fluid system.
Figure 3-12. Some additives used in this study
3.4. Experimental methods for drilling fluid system
Having formulated the control drilling fluid system containing base fluid ester,
water and UH-Biosurfactant, the drilling fluid had to be tested for various properties
which included rheological studies and fluid loss tests. The following API approved
methods were used to test the drilling fluid.
3.4.1. Rheology testing
Rheology of a drilling fluid refers to its physical behavior. It is the study of the
deformation of fluids, the core elements are viscosity, friction pressure loss and the fluids
velocity profile. Viscosity (µ) is the fluids internal resistance to its forced flow, or in
other words how thick the fluid is. As have been shown previously the viscosity has an
influence on the fluid loss properties. The viscosity however influences different tasks in
Nano Iron Nano Clay UH-Biosurfactant
34
the circulating system. For the fluid to have good cleaning properties the viscosity of the
drilling fluid should be as low as possible. When the drilling cuttings have been removed
from under the bit the viscosity should be high to transport the cuttings all the way to the
top of the well. Especially in highly deviated wells the viscosity needs to be high due to
the smaller path the particles can fall. It is also preferable that the drilling fluid is less
viscous for the surface pumps. The pumps require less energy when the viscosity is low.
Too high viscosity can also lead to severe drilling problems when running the drill string
up or down (surge and swab problems). The drilling fluid must be designed with these
problems in mind (Growcock. F. B. and Patel. A. D. 2011).
A fluid does not necessarily have one determined viscosity, it can vary depending
on the shear rate. Only Newtonian fluids have a determined viscosity, the most typical
Newtonian fluid is water. However drilling fluids are not always Newtonian, most often
they are non- Newtonian. There are different kinds of non-Newtonian fluids. In order to
determine what kind it is, a rheology profile must be made. This is made by measuring
the shear stress versus shear rate. Shear stress τ is defined as an applied force, F, acting
along a unit surface area, A. γ is the shear rate. It is defined as the velocity gradient or in
other words, the change in velocity of a fluid moving in the x-axis with respect to another
layer a unit distance away along a perpendicular axis, typically the y-axis or the r-axis in
a polar coordinate system (Burrows. K. et al., 2001). The modelling of this parameter will
be further explained in Chapter 6.
The properties related to rheology of a fluid are plastic and apparent viscosity and
its shear stress at a given strain rate. These measurements have been taken using the
digital viscometer. The viscometer is computerized and offers digital data collection
35
provision. The instrument measures apparent viscosity at different strain rates ranging
from 0.1 to 1700 s-1. The motor speeds range from 1 rpm to 600 rpm and the temperature
can be controlled upto 85 oC. The Bingham Plastic model was chosen to get the viscosity
and shear data.
Figure 3-13. Digital Viscometer
Also, before the UH-laboratory was equipped with digital viscometer, Baroid
FANN Viscometer was used to determine the plastic viscosity (PV), apparent viscosity
(AV), yield stress (YP) and gel strength by subjecting all samples to 300 rpm and 600
rpm as per API standards. The calculations are done as follows (Burrows. K. et al., 2001):
PV (cP) = 600 rpm reading – 300 rpm reading Eq 3
YP (lb/ft3) = 300 rpm reading – PV (cP) Eq 4
AV (cP) = 600 rpm reading / 2 Eq 5
36
Figure 3-14. Baroid FANN Viscometer
Low shear stresses at a given strain were calculated using measurements made
from Brookfield Viscometer. The viscometer consists of an arrangement to change 6
spindles of different sizes. The dial readings are further used to calculate the viscosity as
shown in
Table 3-4.
37
Table 3-4. Viscosity calculations for Brookfield Viscometer
LV SPINDLE FACTOR
SPEED SPINDLE NUMBER
1 or 61 2 or 62 3 or 63 4 or 64
0.3 200 1000 4000 20000
0.6 100 500 2000 10000
1.5 40 200 800 4000
3 20 100 400 2000
6 10 50 200 1000
12 5 25 100 500
30 2 10 40 200
60 1 5 20 100
K = 1000
Figure 3-15. Brookfield Viscometer
38
Figure 3-16. Brookfield Viscometer – Spindles
3.4.2. Fluid loss measurement
The easiest way to determine the filtration properties of a fluid is to use a filter
press. In the experiments done in this report a standard API filter press with compressed
air was used. The pressure source delivered air with a pressure of 100 psi. The
experiments were always started with thorough cleaning and drying of the base cap,
rubber gasket, screen and the filter cell. The cell was then sealed to the base cap and
filled with mud with approximately 4 inch from the top. After that the cell was carefully
placed into the frame and the regulator from the pressure source was gradually opened
(within 3 seconds). This was the most critical step as the cell sometimes was leaking. If
that were the case the cell was disassembled and the experiment was started over again. If
the cell was not leaking the timer was started and the filtrate volume was measured after
1, 2, 3, 5, 7.5, 10, 15, 20, 30 minutes. After 30 minutes, the drilling fluid was discarded
and the height of the mud cake was measured to the closest 0.5 mm.
39
Figure 3-17. Filter press experimental set up
3.4.3. Density, Resistance, Conductivity and pH measurement
The ability of drilling fluids to carry the drill cuttings from well bore to top
surface depends on various factors of which density plays a major role. Density of the
mixes were measured using the mud balance.
The electrical resistance offered by a homogeneous unit cube of material to the
flow of a direct current of uniform density between opposite faces of the cube. Also
called specific resistance, it is an intrinsic, bulk (not thin-film) property of a material.
Resistivity is usually determined by calculation from the measurement of electrical
resistance of samples having a known length and uniform cross section according to the
following equation, where ρ is the resistivity, R is the measured resistance, A is the cross-
sectional area, and l is the length. In the mks system (SI), the unit of resistivity is the
ohm-meter (Ωm).
40
The formula for electrical resistivity is
ρ =RA/l Eq 6
Conductivity is measured by using a conductivity meter and a probe of Baroid
make. A salt solution with 618 g/L of NaCl salt solution is made in DI water which is the
calibration solution. The probe is cleaned in DI water and placed in the calibration
solution. The digital conductivity meter is now calibrated to show a reading 1414 µs at
room temperature 25 oC (+/-5 oC). The electrical resistivity was measured using the API
device (Ofite Resistivity Meter) which internally employs the two probe method as
shown in figure 3-18. This parameter was measured to study the sensing property of the
drilling fluid.
The pH is similarly measured using pH probe of Baroid make as shown in figure
3-18. pH meter is calibrated using 3 different standard solutions of pH 4, 7 and 10.
Calibration is done by dipping a clean probe into the standard solutions and adjusting the
reading in the digital pH meter. Density was measured using the industry standard device
called mud balance as shown in figure 3-19. Figure 3-20 shows the digital resistivity
meter used to measure the resistivity of the fluids. This instrument directly shows the
resistivity readings in Ωm.
41
Figure 3-18. pH meter and Conductivity Meter with Probes
Figure 3-19. Mud balance Figure 3-20. Digital resistivity meter
3.4.4. UV Spectrophotometer
UV analysis was done using UV spectrophotometer of CECIL Company, model
1020 S scanning. Figure 3-19 shows the spectrophotometer with the digital display and
the sample chamber. The instrument was calibrated using DI water which has to give a
42
constant absorbance at any given wavelength. It was found that the spectrophotometer
available in UH laboratory could be calibrated only as absorbance 2 for DI water instead
of 0. Hence all observations were made accordingly recalculating as per the DI water
calibration. The parametric inputs given to the spectrophotometer before running the
samples were as follows:
Initial wavelength chosen was 200 nm
Final wavelength chosen was 900 nm
Wavelength speed was chosen to be 100 nm per minute
Having done the calibration with DI water, the 0th absorbance was set at the value 2.
Hence all the plots begin with a minimum value of 2.
Figure 3-21. UV Spectrophotometer
43
3.5. Summary
Chapter 3 can be summarized as follows:
UV results showed that the synthesized material was FAME, mixture of
methyl oleate, methyl linoleate, methyl stearate and methyl palmitate esters.
API fluid loss is measured at a standard pressure of 100 psi upto 30 minutes.
The digital viscometer has a temperature limitation of 85 oC
LCR meter and Resistivity meter were used to measure resistance at 23±2ºC.
Viscosity, fluid loss and resistivity were measured to characterize the
synthetic drilling mud.
44
CHAPTER 4
CHARACTERIZATION OF SYNTHETIC
VEGETABLE OIL BASED ESTER DRILLING
FLUID
The proposed material was characterized in order to assess its adaptability as a
synthetic base fluid in a drilling fluid system. Characterization of the vegetable oil based
ester drilling fluid was done in 2 stages. The first one concentrated on the rheology and
the second one on the biodegradability aspect of FAME.
4.1. Effect Of Nanoclay On Change In Type Of Vegetable Oil
And Alcohol
In order to enhance the properties of the drilling fluid, effect of bentonite based nanoclay
(NC) was studied on the following drilling fluids with the below listed materials as base
fluids. Drilling fluids of different base fluids were tested for fluid loss and rheology to
show the consistency of the nanoclay additive used.
VEDFCM – VEDF made using corn oil and methyl alcohol
VEDFCP – VEDF made using corn oil and polyvinyl alcohol
VEDFSM – VEDF made using soybean oil and methyl alcohol
4.1.1. Effect On Rheology
Regarding the viscosity and yield point it can be observed that the effect of
nanoclay on VEDFCP is more detrimental than that on VEDFCM samples. This can be
45
seen in figures 4-1 and 4-2. VEDFCM is found to be more stable showing little or no
change in the plastic viscosity and yield point while a decreasing trend can be noticed in
case of VEDFCP samples. Hence it can be inferred that the effect of varying base fluids
for vegetable oil based ester drilling fluids is found in case of rheology i.e. plastic
viscosity and yield point. In case of the VEDFSM samples, an increase in the YP/PV ratio
was observed as tabulated in table 4-1. Based on these results the critical concentration of
nanoclay for this vegetable oil based ester drilling fluid can be assessed.
Table 4-1. Rheological properties of SM with varying amounts of Nanoclay (NC)
%NC
PV
(cP)
YP
(lb/100ft2) YP/PV
GS 10sec
(lb/100ft2)
GS 10min
(lb/100ft2)
Resistivity
(Ωm)
30
mins
fluid
loss
(mL)
0 26.5 8.5 0.3 4 5 504.0 73
0.5 27.7 20.6 0.7 9 10 68.1 5.25
1 29.3 29.5 1.0 12 12 42 5
1.5 25.6 28.0 1.1 11 11 24 11
Figure 4-1. Variation of viscosity with nanoclay concentration for CP
0
20
40
60
80
100
120
140
CP_0 CP_0.5 CP_1 CP_1.5
PV
AV
Sample
Vis
cosi
ty µ
(cP
)
46
Figure 4-2. Variation of viscosity with nanoclay concentration for CM
4.1.2. Effect On Gel Strength
Gel strength of a drilling fluid is defined as the Results show that the addition of
low dosage of NC even as less as 0.5% would improve the stability of the mix to a
considerable extent. This is due to the binding effect offered by the nanoclay towards
water as it is hydrophilic in nature. The gel strength results have been tabulated in tables
4-2 and 4-3.
Table 4-2. Gel strength of CP samples
% NC GS 10sec GS 10min
0 76 80
0.5 50 18
1.0 42 43
1.5 60 61
0
10
20
30
40
50
60
CM_0 CM_0.5 CM_1
PV
AV
Sample
Vis
cosi
ty µ
(cP
)
47
Table 4-3. Gel strength of CM samples
% NC GS 10sec GS 10min
0 54 45
0.5 60 60
1.0 62 62
4.1.3. Effect On Fluid Loss
The base fluid ester used to make the drilling fluid was synthesized using soybean
oil, corn oil, methyl alcohol and polyvinyl alcohol. The control sample of vegetable oil
based ester drilling fluid had 40 % water and 60 % ester and 1 % UH-Biosurfactant by
weight of ester. Bentonite based nanoclay was added as a percentage by weight of ester
content in the drilling fluid and was varied up to 1.5 %. The fluid loss was measured
using standard filter press device. The electrical resistivity of every sample was measured
by using a digital resistivity meter. These tests were conducted at room temperature. The
fluid loss test was conducted under 100 psi pressure.
The results indicate that irrespective of the type of drilling fluid base, nanoclay is
a highly promising additive for fluid loss reduction. Figures 4-3, 4-4 and 4-5 show that
using nanoclay as an additive in vegetable oil based ester drilling fluids would reduce the
fluid loss drastically even at a low concentration of 0.5 %. This result is irrespective of
the type of vegetable oil or alcohol used during the manufacture of the base fluid. A
reduction of over 90 % was found in all the tested samples indicating that the nanoclay
interacted with the ester.
48
Figure 4-3. Filter Loss analysis of Corn Oil PVA based Ester (CP)
Figure 4-4. Filter Loss analysis of Corn Oil Methyl alcohol based Ester (CM)
0
50
100
150
200
250
300
350
400
0 5 10 15 20 25 30 35
0% NC
0.5% NC
1.0% NC
1.5% NC
Time (mins)
Fil
trat
e V
olu
me
(mL
)
0
50
100
150
200
250
300
350
400
0 5 10 15 20 25 30 35
0% NC0.5% NC1.0% NC1.5% NC
Time (min)
Fil
trat
e V
olu
me
(mL
)
49
Figure 4-5. Variation of filtrate volume with time for SM
4.1.4. Effect On Electrical Resistivity
Figures 4-6 and 4-7 describe the variation of ∆R/R0 with time during the fluid loss
test. Results show that addition of nanoclay into vegetable oil based ester drilling fluid in
low concentrations would reduce ∆R/R0 factor and hence the resistivity of the material
drastically which shows that the resistivity of the drilling fluid could be used effectively
as a monitoring or sensing tool. It can be observed that the fluctuations reduce and the
curve flattens with the addition of nanoclay which would again aid in the monitoring
purpose for further contaminations. During the fluid loss test, loss of water occurs i.e.
loss of material occurs. This causes a change in the concentration and composition of the
drilling fluid which is brilliantly captured by the change in ∆R/R0. This shows that ∆R/R0
and hence resistivity; can be used as an excellent monitoring tool.
0
10
20
30
40
50
60
70
80
0 5 10 15 20 25 30 35
Fil
trat
e vo
lum
e (m
L)
Time (min)
0% NC
0.5% NC
1.0% NC
1.5% NC
50
Figure 4-6. Variation of Electrical property (∆R/R0) of CP
Figure 4-7. Variation of Electrical property (∆R/R0) of CM
0
0.5
1
1.5
2
2.5
3
0 5 10 15 20 25 30 35
0% NC
0.5% NC
1.0% NC
1.5% NC
Time (mins)
ΔR
/R0
0
0.5
1
1.5
2
2.5
3
0 5 10 15 20 25 30 35
0% NC
0.5% NC
1.0% NC
1.5% NC
Time (mins)
∆R
/R0
51
4.2. Comparison of OBM and SBM
Samples of vegetable oil based ester/water ratio 60/40 were prepared and mixed
for 60 sec. Nanoclay was later added to the mixture and thoroughly mixed for another 60
sec. Fluid loss test was conducted at room temperature and 100 psi pressure as per API
standards. From the below table 4-4 it can be clearly seen that as expected, the presence
of nanoclay significantly reduced the fluid loss of both corn oil methyl alcohol (CM) and
mineral oil (MO) based drilling fluids. This effect was more pronounced in the proposed
material than the mineral oil based drilling fluid as seen in figure 4-8. A fluid loss
reduction of over 90% was found in all the samples tested which is highly desirable from
a good drilling fluid system. CM samples showed better resistance to fluid loss than the
MO samples. Table 4-5 explains the rheology of all the samples tested at room
temperature.
52
Table 4-4. API Fluid loss results of MO and CM samples
Figure 4-8. Variation of Filtrate volume with time for mineral oil and ester drilling
fluid systems
0
50
100
150
200
250
300
350
400
0 5 10 15 20 25 30 35
Fil
tra
te V
olu
me
(mL
)
Time (min)
MO- 0%NC
MO- 0.5%NC
MO- 1%NC
CM- 0%NC
CM- 0.5%NC
CM- 1%NC
Sample MO CM
%NC 0% 0.50% 1% 0% 0.50% 1%
Time
(min) FL (mL) FL (mL) FL (mL) FL (mL) FL (mL) FL (mL)
0 0 0 0 0 0 0
2 170 4.8 4 160 7 3.8
4 190 6.6 5 248 7.5 4
6 220 8.6 6 280 7.8 4.4
8 240 9.2 7 290 8 4.6
10 260 12 7.6 310 8.5 4.8
12 280 13 8.4 320 9 5
14 290 14.6 9 320 9.2 5.2
16 310 15.6 9.8 325 9.5 5.4
18 325 16.6 10.4 330 9.8 5.6
20 340 17.6 11 330 9.8 5.8
22 350 18.6 11.6 330 9.9 6
24 360 19.6 12.2 331 10 6.2
26 380 20.6 12.6 335 10 6.4
28 21.6 13.2 335 10.05 6.7
30 22.4 13.6 336 10.05 6.8
53
Table 4-5. Rheology of MO and CM samples
Sample
MO-
0%NC
MO-
0.5%NC
MO-
1.0%NC
CM-
0%NC
CM-
0.5%NC
CM-
1.0%NC
300 57 60 58 74 78 80
600 117 121 120 98 100 108
PV (cP) 60 61 62 24 22 28
AV (cP) 58.5 60.5 60 49 50 54
YP (lb/100ft2) 3 1 4 50 56 52
4.3. Effect Of Salt (NaCl) Contamination
Salt contamination studies are necessary on drilling fluids since it is more likely
to come across salt formations during offshore drilling. The study was planned to
investigate the effect of sodium chloride salt contamination of vegetable oil based ester
drilling fluid on its shear stress, fluid loss, yield stress and plastic viscosity.
4.3.1. Effect On Shear Stress
Samples of vegetable oil based ester/water ratio 60/40 homogenized with 1% UH-
biosurfactant were prepared and NaCl salt ranging from 0 to 20% by weight of water by
mixing them for 60 seconds in the mixer. The shear analysis was done using the digital
viscometer. As shown in Fig. 4-9, addition of salt increased the shear stress of the
material at a given shear strain rate.
54
Figure 4-9. Variation of shear stress with shear rate with different percentages of
NaCl salt
4.3.2. Effect On Fluid Loss
Even though we see an increase in the viscosity which represents the thickening
of the material, we generally expect thicker fluids to possess greater resistance to fluid
loss. However, in case of this vegetable oil based ester drilling fluid, there is a dramatic
increase in the fluid loss with % salt contamination as seen in Fig. 4-10. This is due to the
reduction in the yield stress. Though the material is getting thicker, its emulsion stability
and thixotropy reduces with increase in salt content. However, this effect of salt can be
reduced by increasing the UH-biosurfactant concentration.
0
10
20
30
40
50
60
70
80
0 200 400 600 800 1000 1200
Shea
r S
tres
s (
dyn
es/c
m2)
Strain Rate (sec-1)
0% salt
5% salt
10% salt
20% salt
hyperbolic model
55
Figure 4-10. Variation of filtrate volume with time
4.3.3. Effect On Thixotropy
Thixotropy is a shear thinning property. Certain gels or fluids that are thick
(viscous) under static conditions will flow (become thin, less viscous) over time when
shaken, agitated, or otherwise stressed. They then take a fixed time to return to a more
viscous state. Thixotropy is an important parameter to access the stability of an invert
emulsion. Samples of different percentages of salt were prepared and tested for 1cycle of
hysteresis i.e. the samples were subjected to loading followed by unloading of shear rate
varying from 0 – 1020 sec-1.
Initially, two samples of soybean oil methyl alcohol vegetable oil based ester
drilling fluid of vegetable oil ester/water ratio 60/40 were prepared with 1% UH-
biosurfactant and 20 % NaCl salt added by weight of vegetable oil based ester and water
respectively. The tests were conducted using digital viscometer. Viscosity, yield point,
0
20
40
60
80
100
120
0 5 10 15 20 25 30 35
Fil
trat
e vo
lum
e (m
L)
Time (min)
0% salt
5% salt
10% salt
20% salt
56
0
5
10
15
20
25
30
35
40
0 200 400 600 800 1000 1200
Shea
r S
tres
s (d
ynes
/cm
2)
Strain Rate (sec-1)
gel strength and shear parameters were calculated. All tests were conducted at room
temperature and atmospheric pressure.
It can be seen in Fig. 4-11 and Fig. 4-12 that the vegetable oil based ester drilling
fluid system follows elastic hysteresis. The directions in the curves show that the material
needs less energy to deform while loading than that of unloading. This can be attributed
to the emulsion stability of the material i.e. with time, the emulsion is not stable and the
soap formed during hydrolysis settles down rapidly causing more energy requirement for
deformation under shear during unloading. The down-curve (unloading) does not usually
follow the same path as that of the up-curve because of the structural breakdown of the
drilling fluid with the increase of shear rate. This shows that the material requires a
surfactant or an emulsifier to hold the emulsion stable without any phase separations.
Figure 4-11. Variation of shear stress with strain rate during hysteresis for 1 % UH-
biosurfactant.
57
Figure 4-12. Variation of shear stress with strain rate during hysteresis for 20 %
Salt.
To investigate the effect of surfactant on the emulsion stability of the
contaminated vegetable oil based ester drilling fluid, samples of CM based muds with
60/40 ester to water ratio were prepared. Shear tests were done at a temperature of 25 oC
with digital viscometer. The samples were subjected to 3 cycles of loading and unloading
at varying shear stress. It can be seen in Fig. 4-13 and Fig. 4-14 that in the presence of
UH-Biosurfactant, salt contamination improves the stability of the material making the
shear stress vary with shear rate almost linearly.
0
10
20
30
40
50
60
70
0 200 400 600 800 1000 1200
Sh
ear
Str
ess
(dyn
es/c
m2)
Strain Rate (sec-1)
58
Figure 4-13. Drilling fluid with 1% Biosurfactant + 5% NaCl
Figure 4-14. Drilling fluid with 1% Biosurfactant + 10% NaCl
0
5
10
15
20
25
30
35
40
45
0 200 400 600 800 1000 1200
Sh
ear
Str
ess
(dyn
es/c
m2)
Strain Rate (sec-1)
cycle 1
cycle 2
cycle 3
0
5
10
15
20
25
30
35
40
45
0 200 400 600 800 1000 1200
Sh
ear
Str
ess
(dynes
/cm
2)
Strain Rate (sec-1)
cycle 1
cycle 2
cycle 3
59
0
1
2
3
4
5
6
0 10 20 30 40 50 60 70 80 90
Vis
cosi
ty (
cP)
Temperature (oC)
100 rpm
300 rpm
600 rpm
4.3.4. Effect On Thermal Stability
The proposed base oil was tested for its thermal stability. 400 mL of the material
was taken in the beaker and was tested in digital viscometer. The fluid was subjected to
varying shear stresses at 25 oC, 35 oC, 45 oC, 65 oC and 85 oC temperatures. Fig. 4-15
shows the variation of plastic viscosity with temperature. From the Fig. 4-15 it can be
inferred that irrespective of the strain rate, the viscosity reduces at higher temperature.
This means the material is unstable with changes in temperature. Stabilization and
optimization strategies shall be discussed in the following sections.
Figure 4-15. Variation of viscosity with temperature
The vegetable oil based ester drilling fluid has 60 % ester and 40 % water,
homogenized with 1 % UH-Biosurfactant by weight of ester. Salt content was varied
from 0 to 20 % to investigate the effect of salt on the rheology of the vegetable oil based
ester drilling fluid at elevated temperature of 55 oC. The test was conducted using the
60
digital viscometer. The results plotted in Fig. 4-16 shows that even in the presence of
biosurfactant, the mix was unstable with no salt contamination at higher temperature. As
the contamination increased, the mix showed greater shear stress and lower plastic
viscosity as seen in Fig. 4-17. Also, there was a drastic increase in the yield point as
indicated by the shear stress at 20 % salt contamination. This shows that the material is
stable until 10 % salt contamination but begins to degrade with contamination > 10 %.
The stability can be further established by fluid loss results at T=55 oC which has been
recommended for future work.
Figure 4-16. Variation of shear of homogeneous vegetable oil based ester drilling
fluid during salt contamination at T=55oC
0
5
10
15
20
25
0 200 400 600 800 1000 1200
Shea
r S
tres
s (d
ynes
/cm
2)
Strain Rate (sec-1)
0%
5%
10%
20%
61
Figure 4-17. Variation of PV and YP of homogeneous vegetable oil based ester
drilling fluid during salt contamination at T=55 oC
4.3.5. Effect On Resistivity
Change brought in the resistivity of the drilling fluid due to variation in the ester
quantity was captured by using conductivity meter readings and shown in the Fig. 4-
18. From table 4-6 the percentage ester could be estimated by measuring resistivity of
the filtrate and matching it with the resistivity data for known % ester. The below data
implies that as resistivity reduces, the % ester in filtrate also reduces and this could be
due to the reaction of ester with salt to form soap. i.e. as the concentration of brine in
the drilling fluid increases, the %loss of ester with the filtrate reduces and hence the
contamination of formation due to lost fluid could be reduced.
Table 4-7 shows the effect of salt on different properties of VEDF. A solution
with a higher (more positive) reduction potential than the new species will have a
tendency to gain electrons from the new species (i.e. to be reduced by oxidizing the
0
5
10
15
20
25
30
35
0 5 10
PV
an
d Y
P
% Salt contamination by weight of water
PV
YP
62
new species) and a solution with a lower (more negative) reduction potential will
have a tendency to lose electrons to the new species (i.e. to be oxidized by reducing
the new species). From the table 4-7 it is clearly seen that salt contamination alters the
stability of the material and reduces its corrosive property.
Figure 4-18. Variation of resistivity with %ester in water
Table 4-6. Resistivity data of filtrate collected during API fluid loss experiment at
100 psi and 25 oC
Conductivity unit(semens) Resistivity interpolated %ester in
filtrate %salt
0.1 micro 100000 64.58 5
2.3 micro 4347.82 46.8 10
121.4 milli 0.08 33.24 20
4.4. Remediation Of Salt (NaCl) Contamination
The objective of this study was to investigate the effect of different materials on
the fluid loss and electrical properties of an vegetable oil based ester drilling fluid
23.5
24
24.5
25
25.5
26
26.5
27
0 5 10 15 20 25 30 35
Res
isti
vit
y(Ω
m)
Weight of ester in water (%)
63
homogenized by UH-Biosurfactant. As seen in the previous sections, the effect of salt
contamination especially on fluid loss; was on the incremental side. The remediation
strategy to reduce the effect of salt contamination involved the comparison of 3 different
remediation materials.
Nanoclay - a hydrophillic nanoparticle
Nano iron – a hydrophobic nano particle
Ferric nitrate – a soluble crystalline compound
were tested to remediate the effect of sodium chloride on the proposed material.
4.4.1. Nanoclay
The vegetable oil based ester drilling fluid contaminated with salt were tested for
remediation with nanoclay. Literature says that nanoclay has been widely used in the
water based muds due to its excellent properties and hydrophilic nature. Since water is
one of the main components of synthetic drilling mud as well, nanoclay was tested in this
study. The base fluid ester used to make the drilling fluid was synthesized using soybean
oil and methyl alcohol (SM). The control sample of vegetable oil based ester drilling
fluid had 40 % water and 60 % vegetable oil based ester and was homogenized with 1%
UH-Biosurfactant by weight of ester. All samples were contaminated with 20 % sodium
chloride salt by weight of water. 20 % was chosen since it would be close to the
maximum solubility of sodium chloride in water. Bentonite based nanoclay was added as
a percentage by weight of ester content in the drilling fluid and was varied up to 1.5 %.
The fluid loss was measured using standard HPHT device.
Results show that the nanoparticles of clay do interact with the ester causing
drastic changes in the rheology and fluid loss properties. Table 4-8 describes the
64
rheological data obtained from digital viscometer calculated using Bingham-plastic
model. Observing the gel strength data, the behavior of nanoclay based ester drilling fluid
can be assessed. With a uniform gel strength at the end of 10minutes, it can be concluded
that an addition of even 0.5 % nanoclay produces a physically stable mix.
Fig. 4-19 shows that there is an increase in the shear stress with the concentration
of nanoclay. Also it can be observed that the trend is perfectly incremental with increase
in nanoclay concentration at lower strain rate. At higher strain rates, shear stress increases
with nanoclay only upto 1 % above which the material begins to degrade. At a given
strain rate of 1021.4 sec-1, a change of +50 % is caused in the shear stress by the addition
of 1.5 % of nanoclay.
Fig. 4-20 explains the effect of nanoclay on fluid loss of the vegetable oil based
ester drilling fluid. This effect is synchronous with that on the shear stress i.e. there is a
continuous reduction in the fluid loss until an addition of upto 1 % of nanoclay. Whereas
at 1.5 % nanoclay an increase in fluid loss can be noticed. This along with the shear
behavior shows that there exists a critical concentration for nanoclay above which a
negative effect is caused.
Table 4-7. Variation of rheological properties of 20 % salt contaminated VEDF with
different concentration of nanoclay.
%Nc PV (cP) YP
(lb/100ft2)
YP/PV GS 10sec
(lb/100ft2)
GS 10min
(lb/100ft2)
0 19.6 2.9 0.15 3 4
0.5 26.7 7.5 0.28 9 9
1 27.2 8.0 0.29 10 10
1.5 23.9 8.4 0.35 10 10
65
Figure 4-19. Variation of shear stress of 20% salt contaminated homogenized
vegetable oil based ester drilling fluid SM remediated with Nanoclay
Figure 4-20. Variation of fluid loss with percentage Nanoclay contaminated with
20% salt
0
10
20
30
40
50
60
70
80
90
0 200 400 600 800 1000 1200
Sh
ear
Str
ess
(dyn
es/c
m2)
Strain Rate (sec-1)
0% Np
0.5% Np
1.0% Np
1.5% Np
hyperbolic model
0
10
20
30
40
50
60
70
80
0 5 10 15 20 25 30 35
Fil
trat
e volu
me
(mL
)
Time (min)
0% NC
0.5% NC
1.0% NC
1.5% NC
66
4.4.2. Nano Iron
It is known that iron particles are biodegradable and can be converted into
enzymes. Since bentonite is not a green material, it was decided to choose nano iron as an
additive to enhance the properties of the salt contaminated vegetable oil based ester
drilling fluid. The control sample of vegetable oil based ester drilling fluid had 40 %
water and 60 % SM ester and was homogenized with 1% UH-Biosurfactant by weight of
ester. Contaminated samples had 20 % sodium chloride salt by weight of water. 20 %
was chosen since it would be close to the maximum solubility of sodium chloride in
water. Nano-iron was added as a percentage by weight of ester content in the drilling
fluid and was varied up to 0.5 %. Rheological measurements were made using digital
viscometer at 25 oC and fluid loss measurements were made using filter press.
Fig. 4-22 shows the effect of nano iron on contaminated vegetable oil based ester
drilling fluid. The nano iron had greater effect on rheology than nano clay which could be
attributed to its hydrophobic nature. An increase of 150% was observed in the
contaminated mud after addition of 0.5 % nano iron which proves better performance of
nano iron than nano clay; both in terms of remediation as well as economics. Addition of
0.1 % nano iron can bring an increase of 250 % in the shear stress which is
commendable. Another interesting point to note is that an increase in the nano iron
content would affect the shear stress only at strain rates above 500 sec-1. Which means
the effect of nano iron would not be pronounced at low strain rates. Density showed an
increase due to addition of nanoiron which is observed in Fig. 4-21.
67
Fig. 4-23 shows the variation of fluid loss with time. Nano iron showed excellent
remediation to contaminated mud concerning its fluid loss. There was a very minor
difference found in fluid loss due to contamination of drilling fluid enhanced with 0.5 %
NI. This shows the stability of the mud. A small amount of NI like 0.1 % would reduce
the fluid loss by more than 80%.
Figure 4-21. Variation of Fluid loss of 20% salt contaminated homogenized
vegetable oil based ester drilling fluid SM remediated with hydrophobic
nanoparticles
5.5
7.09
9.42
8.8 9
8
0
1
2
3
4
5
6
7
8
9
10
0.1% NI 0.5% NI 0.5% NI + 20% salt
Pro
per
ty
% Additives
Density
(ppg)
pH
68
Figure 4-22. Variation of shear behavior with percentage Nano iron
Figure 4-23. Variation of fluid loss with percentage Nano iron
0
20
40
60
80
100
120
140
160
180
0 200 400 600 800 1000 1200
Sh
ear
Str
ess
(dyn
es/c
m2)
Strain Rate (sec-1)
0% salt
20%salt
0.1% NI
0.5% NI
0.5%NI+20%salt
0
20
40
60
80
100
120
0 5 10 15 20 25 30 35
Fil
trat
e V
olu
me
(mL
)
Time (min)
0% salt
20% salt
0.1% NI
0.5% NI
0.5%NI+20%salt
69
4.4.3. Ferric Nitrate
Since nano particles are very expensive, it wouldn’t be advisable to use them in
large quantities. Hence, in order to reach the objective of proposing a system with
biodegradable and highly economical mud, ferric nitrate was chosen. Ferric nitrate was
mainly chosen after positive results with nano iron was observed. The effect of ferric
nitrate as a salt contamination remediation additive was investigated on salt contaminated
mud.
Fig. 4-24 plots the variation of resistivity caused by the presence of ferric nitrate
in SM ester. The plot clearly indicates that the material responds positively towards the
objective of proposing an electrically sensible drilling fluid. A drastic reduction of over
2000 % was seen in the resistivity of the ester.
Fig. 4-25 shows the comparison of effect of ferric nitrate with that of nano iron on
the shear stress of the mud at different strain rates. Various mixes of drilling fluid
containing 40 % water and 60 % SM ester homogenized with 1% UH-Biosurfactant by
weight of ester were prepared. Contaminated samples had 20 % sodium chloride salt by
weight of water. Fig. 4-25 explains that the shear behavior of ferric nitrate is comparable
to that of 0.1 % NI. When contaminated by salt, the rheological properties of ferric nitrate
treated drilling fluid shows better performance than NI treated mud. This observation is
supported by the radical increase in shear stress from 54 dynes/cm2 to 194 dynes/cm2 at a
maximum strain rate of 1021 sec-1.
The variation of fluid loss with time is plotted in the Fig. 4-26. The results
indicate that though there a drastic increase in the shear stress, fluid loss is very little
affected by the presence of ferric nitrate in vegetable oil based ester drilling fluid. While
70
observing the behavior of ferric nitrate as an additive for remediation of salt
contamination, it can be observed that there is a reduction seen in the fluid loss. This
probable reason for this reduction is the reaction between salt and ferric nitrate causing a
250 % increase in the shear stress at strain rate of 1021 sec-1 and over 150 % reduction in
fluid loss.
Fig. 4-27 and Fig. 4-28 show the effect of ferric nitrate on uncontaminated
vegetable oil based ester drilling fluid. From Fig. 4-27 it can be seen that there is a drastic
increase of 250 % in the shear stress at a strain rate of 1021 sec-1.
Figure 4-24. Variation of resistivity with concentration of ferric nitrate
0
5
10
15
20
25
30
0 5 10 15 20 25
Res
isti
vit
y(Ω
m)
Weight of FeNO3 (%)
71
Figure 4-25. Variation of Shear stress with strain rate
Figure 4-26. Variation of filtrate volume with time for iron enhanced VEDF
0
50
100
150
200
250
0 200 400 600 800 1000 1200
Sh
ear
stre
ss (
dyn
es/c
m2)
Strain Rate (sec-1)
0% salt
20%salt
0.1% NI
0.5% NI
0.5%NI+20%salt
0
20
40
60
80
100
120
140
0 5 10 15 20 25 30 35
Fil
trat
e V
olu
me
(mL
)
Time (min)
0% salt
20% salt
0.1% NI
0.5% NI
0.5%NI+20%salt
0.5%FeNO3
0.5%FeNO3+20%salt
72
Figure 4-27. Variation of shear stress with strain rate of 20% salt contaminated
homogenized VEDF in the presence of ferric nitrate
Figure 4-28. Variation of filtrate volume with time in the presence of hydrophobic
nanoparticles and ferric nitrate
0
50
100
150
200
250
0 200 400 600 800 1000 1200
Sh
ear
stre
ss (
dyn
es/c
m2)
Strain rate (sec-1)
0% FENO3
0.5%FENO3
0
20
40
60
80
100
120
0 0.5 5
Flu
id l
oss
(m
L)
Weight of FeNO3 (%)
0
0.5
73
CHAPTER 5
RECYCLING OF VEGETABLE OIL BASED ESTER
DRILLING FLUID
5.1. Microbial Fuel Cell
MFC is expanded as microbial fuel cell. These are biological fuel cells or bio-
electrochemical systems that drive a current by using bacteria and mimicking bacterial
interactions found in nature. In this study, Serratia.sp. bacteria was used in the anode
chamber.
There were 2 objectives behind studying the behavior of the proposed ester in MFC.
MFC was used to show the biodegradability of the proposed base fluid.
Possibilities of the drilling fluid to be recycled using an MFC
Using recycled ester as drilling fluid
Literature shows that the proposed base fluid is biodegradable using LC 50 and EC 50
tests. No studies have been done so far using an MFC to study the properties of the ester
showing the uniqueness of this study. The principle behind an MFC could be simply
explained as the metabolism of the bacteria by feeding on to the vegetable oil which is
generally added to the anode chamber (Rabaey.K. et al. 2005). During this metabolism,
the vegetable oil is degraded and this process produces electrons which are captured by
the anode and cathode probes generating electricity. Another interesting point to note
would be that the UH-biosurfactant was produced by this MFC using vegetable oil and
serratia sp. bacteria in anode chamber.
74
Fig. 5-1 explains the change in open circuit voltage (OCV) and closed circuit
voltage (CCV) with time. The analysis showed that presence of ester improves the
production of electricity in the MFC. It can also be concluded that the degradation of
FAME is occurring in the presence of bacteria Serratia .sp. Microorganisms metabolize
glycerin first and then the long chain esters. Also, studies have shown that the voltage
obtained by using an external resistance of 1000 Ω was of the order of 0.500 V (Kim
B.H. et al. 2007; Wei J. et al. 2011). With 5 mL of ester in the anode chamber, OCV of
the same order was achieved using an external resistance of 100 KΩ. Hence values of
voltage (OCV) with ester in anode are considerably higher compared to those with
vegetable oil in anode. This is an indication towards the good biodegradability of the
proposed vegetable oil vegetable oil based ester.
Figure 5-1. Variation of voltage with time for MFC anode solution with 5mL of
FAME
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 50 100 150 200 250 300 350 400
open circuit voltage
closed circuit voltage
Time (hrs)
Vo
ltag
e (v
olt
s)
75
5.1.1. Contamination Of Nanoclay In MFC Based Drilling Fluid System
In this study, samples of anode solutions contaminated with 10 % salt and 10 %
salt treated with 3 g of NC in the anode chamber were investigated for pH and surface
tension to determine the effect of salt and nanoclay on the biosurfactant production in the
anode chamber of MFC. Instruments used were pH meter, API resistivity meter, filter
press and tensiometer. All tests were conducted in room temperature and atmospheric
pressure.
From literature we know that ideally the drilling fluids are made to be alkaline,
Fig. 5-2 to Fig. 5-3 show that the addition of nanoclay in anode not only keeps the pH in
the alkaline range, but also stabilizes the pH. A reduction in the surface tension shows the
production of biosurfactant in the anode chamber. The tables 5-1 and 5-2 show that
majority of the changes in the parameters measured occurred within the 1st 24hrs of the
experiment. After which a reduction in OCV indicates the degradation of the Serratia sp.
bacteria. In the presence of salt, it degradation of bacteria is accelerated which is seen in
Fig. 5-4.
Fluid loss test was conducted using filter press at room temperature and 100 psi
pressure for all the samples after running the MFC for 1week. Fig. 5-5 shows the
variation of fluid loss with time. The plot indicated that there is an increase of 13.5 % in
the fluid loss due to salt contamination. However, using nanoparticles the effect of salt
contamination can be controlled upto 60 %, without harming the bacteria. Hence, the
used vegetable oil based ester drilling fluid can be recycled using an MFC and the
properties of which can be enhanced using nanoparticles.
76
Figure 5-2. Variation of Surface tension & pH for 10% salt
Figure 5-3. Variation of Surface tension and pH for 10% salt + 3g NC
0
10
20
30
40
50
60
day1 day3 day4
surface tension
pH
Linear (surface tension)
Surf
ace
ten
sio
n (
dyn
es/c
m2
)&
pH
0
10
20
30
40
50
60
day1 day2 day8
surface tension
pH
Linear (surface tension)
Su
rfac
e te
nsi
on
(dynes
/cm
2)
& p
H
77
Table 5-1. Properties of Anode solution with 10 % NaCl
10 % salt
Parameter day1 day3 day4
Surface Tension (dynes/cm2) 48 28 39
pH 7 6.64 6.73
Resistivity (Ωm) 0.087 0.11 0.099
Table 5-2. Properties of Anode solution with 10 % NaCl and 3 g Nanoclay
10 % salt + 3 g NC
Parameter day1 day2 day8
Surface Tension (dynes/cm2) 51 42 43.5
pH 7.23 7.49 7.33
Resistivity (Ωm) 0.103 0.105 0.156
Figure 5-4. Variation of OCV with time for 10% salt & 10% salt+3gNC
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 1000 2000 3000 4000 5000 6000 7000
10% salt+3g NC 10% salt
Time (mins)
OC
V(v
)
78
Figure 5-5. Variation of fluid loss with time for drilling fluid samples with anode
solution
5.1.2. Use Of Anode Solution Of MFC As An Effective Drilling Fluid
Base
The study was continued towards the third objective of this section. The MFC
based drilling fluid was compared with the control drilling fluid consisting of 60 %
vegetable oil based ester, 40 % water and 1% UH-biosurfactant by weight of vegetable
oil based ester. The anode solution tested was of more than a week old. Fig. 5-6 shows
that the anode solution could be used as a drilling fluid provided we increase its viscosity
by adding certain viscosifying agents as shown in table 5-3. The very low viscosity could
be due to the increase in water volume and in the production of biosurfactant and
production of vegetable oil based ester in the presence of Soybean oil, methanol and
0
10
20
30
40
50
60
70
80
90
100
0 5 10 15 20 25 30 35
0% salt
10% salt
10%salt + 3gNC
Fil
trat
e V
olu
me
(mL
)
Time (mins)
79
NaOH in the anode chamber. It must be noted that the anode solution were not mixed
with any further additives like nanoparticles or biosurfactant.
Figure 5-6. Variation of fluid loss with time for MFC samples
Table 5-3. Rheology of various drilling fluids formulated using MFC Anode solution
and control vegetable oil based ester as base fluids
Viscosity
300
rpm 600rpm PV AV YP YP/PV
GS
10sec
GS
10min
SPVA vegetable oil based
ester 4 10 6 5 0 0 2 2
Ing SM ester 5 10 5 5 0 0 7 5
CP control 144 253 109 126.5 35 0.321101 76 80
0
50
100
150
200
250
300
350
400
0 5 10 15 20 25 30
SP ester
naoh+S+M
CP
Time (sec)
Fil
trat
e vo
lum
e (m
L)
Anode solution of
Control drilling
fluid
80
Table 5-4. Rheological properties of various base fluids
Sample PV YP YP/PV GS 10sec GS 10min
MFC solution 5 1 0.2 7 5
SM control 26.5 8.5 0.3 4 5
5.2. Summary
From this chapter the following can be concluded.
1) MFC can be successfully used to recycle the VEDF as demonstrated by the
voltage data and biosurfactant production.
2) Salt contamination reduced the OCV of MFC and hence its productivity was
reduced.
3) Nanoparticles can be employed to enhance the properties of the recycled
VEDF.
81
CHAPTER 6
MODELING
Drilling fluids generally behave as yield-pseudoplastic fluids. This behavior is
characterized by a non-linear proportionality between shear stress and shear rate in excess
of the yield stress. An accurate rheological model relating shear stress to shear rate in
drilling fluids is always required for the proper evaluation of wellbore hydraulics. In this
chapter the shear properties of the proposed drilling fluid have been modelled by
introducing a new hyperbolic model.
6.1. Rheological Models
Several rheological models were proposed to describe this behavior. Currently the
industry uses Bingham-Plastic model and Herschel Bulkley model extensively. Though
the power law and Bingham plastic models showed extensive user friendly properties, it
failed to capture the yield stress associated with every fluid. This shall be explained in the
following sections.
6.1.1. Bingham-Plastic
One of the most popular rheological models is the Bingham-Plastic model .This
two-constant model considers a direct proportionality between shear stress and shear rate
in excess of the yield stress, τy .The constant of proportionality is defined as the plastic
viscosity, µp. However, this model fai1s in defining the non-linear characteristics of the
fluids considered in this study. Nakshatrala et al. 2009 say the notion of the existence of a
82
Bingham fluid is invalid since there always exists a yield stress for every fluid which has
not been captured by the Bingham-Plastic model.
6.1.2. Power Law
The power law describes the fluids without yield stress characterized by a
nonlinear flow curve. However, the model considering no yield stress becomes
inadequate in describing the rheological reality. In the following equation, shear stress
τ is related to the strain rate γ with k and n as model parameters.
∗
Eq 7
6.1.3. Herschel-Bulkley
This three parameter model, proposed by Herschel and Bulkley, describes the
behavior of yield-pseudoplastics.
∗
Eq 8
6.1.4. Proposed model – Hyperbolic model
The proposed model is of high accuracy in predicting the rheology of drilling
fluids. It takes the following form
Eq 9
where το = yield stress, τ = shear stress, lbf/100 ft2
γ = shear rate, sec-1
, A = consistency
index and B = flow behavior index. The proposed hyperbolic model is a very powerful
model and obeys the second law of thermodynamics.
83
ll ≤ int and τ * > 0
For viscous fluids: 0 < τ < ∞, = 0
The variation of shear stress with strain rate was modeled using the proposed
hyperbolic model and compared with the two most widely used models in the industry
namely Power-Law model and Herschel-Bulkley model. Samples contaminated with
different percentages of salt were studied. Samples of ester/water ratio 60/40
homogenized with 1% UH-biosurfactant were prepared and NaCl salt ranging from 0 to
20% by weight of water by mixing them for 60 seconds in the mixer. The shear tests were
done using the Brookfield viscometer manually. Calculations were made based on
Durgueil. E. J. 1987.
6.2. Maximum Shear Stress
The proposed hyperbolic model has a maximum limiting shear stress that the fluid will
experience at relatively higher rate of shear strains. The prediction of limiting stress τmax
makes this model unique and different from the existing models.
=
∗
=
> 0 ⇒ > 0
=
!< 0 ⇒ # > 0
Also when the strain rate approaches 0 i.e. → ∞ ⇒τmax = $
+ Eq 10
Hence it can be seen that there exists a limit on the maximum shear stress produced by
the fluid at relatively higher rates of shear strain which is clearly predicted by the
proposed hyperbolic model.
84
6.3. Modeling Of Salt Contaminated Drilling Mud
Fig. 6-1 to Fig. 6-4 describe the variation of shear stress with strain rate for
different salt contaminated samples of vegetable oil based ester drilling fluid. The plots
indicate that the proposed hyperbolic model predicts the shear behavior of the vegetable
oil based ester drilling fluid with much more accuracy than that of the other two models
in this study. The power law model shows 0 yield stress which is not acceptable
compared to the available data.
Fig. 6-1, it can be easily noticed that the hyperbolic model is the best in predicting
the behavior of uncontaminated vegetable oil based ester drilling mud. Table 6-1 shows
the model parameters A and B of hyperbolic model. Parameter A is the consistency of the
mix while B is the flow index. Effects of salt contamination has been captured by this
model very accurately showing the changes in the stability.
Fig. 6-5 and Fig. 6-6 show the behavior of hyperbolic model parameters A and B
with % salt contamination. From these plots it is clear that the consistency of vegetable
oil based ester drilling fluid increases with salt contamination which relates to the
viscosity of the mud. The flowability of the in case of vegetable oil based ester drilling
fluid reduces with the contamination which relates to the yield stress or the ease with
which the mud can flow.
85
Figure 6-1. Shear variation for SM 0% salt sample
Figure 6-2. Shear variation for SM 5% salt sample
0
50
100
150
200
250
0 2 4 6 8 10 12 14 16 18
experimental
power law
herschel bulkley model
hyperbolic model
Shear rate (1/s)
Sh
ea
r st
ress
(d
yn
es/
cm2
)
0
20
40
60
80
100
120
140
0 5 10 15 20
experimental
power law
herschel bulkley
hyperbolic
Shear rate (1/s)
Sh
ea
r st
ress
(d
yn
es/
cm2
)
86
Figure 6-3. Shear variation for SM 10% salt sample
Figure 6-4. Shear variation for SM 20% salt sample
0
50
100
150
200
250
0 5 10 15 20
experimental
power law
herschel bulkley
hyerbolic
Shear rate (1/s)
Sh
ea
r st
ress
(d
yn
es/
cm2
)
0
100
200
300
400
500
600
700
800
900
1000
0 5 10 15 20
experimental
power law
herschel bulkley
hyperbolic
Shear rate (1/s)
Sh
ea
r st
ress
(d
yn
es/
cm2
)
87
Table 6-1. Hyperbolic model parameters for salt contaminated SM based drilling
fluid
Sample A B Yield point %&
(lb/ft3)
R2
SM0 18.73 0.016 22.00 0.99
SM5 30 0.01 44.59 0.97
SM10 24 0.014 53.34 0.98
SM20 32.3 0.012 104.02 0.91
Figure 6-5. Behavior of consistency index A as a function of concentration of salt by
weight of water.
y = -0.0176x2 + 0.8999x + 20.697
0
5
10
15
20
25
30
35
0 5 10 15 20 25
Hyper
boli
c M
odel
par
amet
er A
Percentage NaCl by weight
88
Figure 6-6. Behavior of flow index B as a function of concentration of salt by weight
of water.
6.4. Modelling Of Remediation Using Nanoparticles
In this thesis hyperbolic model is proposed which could be used as an effective
mathematical tool to study the effect of various contaminations on the shear behavior of
biodiesel based synthetic drilling fluid. The present study deals with variation of yield
stress with various concentrations of additives which have been correlated by the
proposed hyperbolic model. The remediation analysis was carried out using nanoclay
which are hydrophilic nanoparticles.
Table 6-2 shows the hyperbolic model parameters for salt contaminated
homogenized vegetable oil based ester drilling fluid with varying concentration of
nanoclay. From Fig. 5-7 it can be observed that the effect of nanoparticles on the
contaminated mud can very well be captured by hyperbolic model. Table 5-2 analyses the
consistency and flow index from the hyperbolic model. There is a drastic change in both
y = 2E-05x2 - 0.0005x + 0.0149
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
0.018
0 5 10 15 20 25
Hyp
erb
oli
c M
od
el p
aram
eter
B
Percentage NaCl by weight
89
the parameters from 0% to 0.5% nanoclay indicating that the nanoclay is affecting the
physical properties of the invert emulsion mud. There is a drastic increment in the yield
stress and a drop in the viscosity showing the reversal effect of nanoparticles as compared
to that of salt contamination as seen in Table 6-1.
Table 6-2. Hyperbolic model parameters for 20% salt contaminated homogenized
vegetable oil based ester drilling fluid with varying concentration of nanoclay
%NC YP A B R2
0 2.91 14.31 0.0054 0.98
0.5 7.55 7.95 0.0052 0.99
1 8.04 9.07 0.0044 0.99
1.5 8.45 8.24 0.0057 0.99
Figure 6-7. Variation of shear stress of 20% salt contaminated homogenized
vegetable oil based ester drilling fluid SM remediated with hydrophilic
nanoparticles
0
10
20
30
40
50
60
70
80
90
0 200 400 600 800 1000 1200
Shea
r S
tres
s (d
ynes
/cm
2)
Strain Rate (sec-1)
0% Np
0.5% Np
1.0% Np
1.5% Np
hyperbolic model
90
CHAPTER 7
CONCLUSIONS AND RECOMMENDATIONS
7.1. Conclusions
This study focused on the introduction of a new application for an existing
material and enhancing its properties to match the requirements. FAME was studied
for its properties as a synthetic base fluid. Based on the study, the following
conclusions were drawn.
a. Introduction of FAME as a synthetic base fluid was successfully backed by
the rheological and fluid loss study results.
b. Resistivity is sensitive to salt contamination and remediation of the drilling
fluid. Hence it could be used as an effective tool to monitor the performance
of the drilling fluid at real time conditions.
c. The electrical resistivity reduced considerably with the addition of
nanoparticles. It was found that a critical concentration of 1% nanoparticles
gave the best rheological and fluid loss results for the proposed material.
d. Salt contamination reduces the emulsion stability of the drilling fluid. It also
affects the PV and YP of the drilling fluid.
e. Nanoparticles affected the filtration loss of the proposed vegetable oil based
ester drilling fluid system. Nanoparticles can be used as an effective material
to retrieve the lost properties of vegetable oil based ester drilling fluids during
salt contamination.
91
f. A very low percentage of 0.5% of nanoparticles in vegetable oil based ester
drilling fluid reduced the fluid loss by over 90% which is commendable. This
effect was more pronounced in synthetic mud than that of a mineral oil based
mud.
g. Addition of nanoparticles also showed an increasing effect on the YP/PV ratio
which determines the improving stability of the drilling fluid.
h. UH-biosurfactant produced in an MFC is successfully used as an emulsifier to
improve the stability of the invert emulsion. Since the same MFC could be
used to recycle the used-vegetable oil based ester drilling mud, the proposed
drilling fluid system can be called a “self-sufficient system.”
i. Anode solution in a 1week used MFC could be used as an effective base fluid
for drilling fluid formulations by modifying its viscosity using suitable
additives.
j. The proposed hyperbolic model accurately predicts the rheological behavior
of the synthetic mud showing the effects of various additives at room
temperature.
7.2. Recommendations & Future Work
The following recommendations for the future work are suggested
a. This study has been limited to room temperature and a pressure of 100 psi for
fluid loss tests. Hence further analysis of the behavior of the mud at higher
temperatures ranging from 85 oC and above as well as pressures greater than
1000 psi could be done.
92
b. The material FAME is used in the transformer industry as an excellent
insulator. The current study shows that addition of nanoparticles reduces its
electrical resistivity. Hence a new study could be planned to improve the
sensing property of the proposed drilling fluid.
c. A deeper study on the chemical effects of nanoparticles such as nano clay and
nano iron during the synthesis of the ester could be done. They will definitely
effect the rate of reaction and this could be studied using FTIR and gas
chromatographic characterization.
d. Esters are bound to get hydrolyzed at higher temperatures. Hence the effect of
UH-biosurfactant could be studied under different temperatures using UV
method to correlate the rate of hydrolysis with surfactant concentration.
e. It is now known that MFC can be used to recycle the ester based mud. A
detailed quantification can be done by adding different concentration of ester
in MFC and analyzing the UV, surface tension, pH and resistivity data.
93
REFERENCES
Agarwal, S., Tran, P., Martello, D., Soong, Y., & Gupta, R. (2011). Research Shows
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