BY Ararat Abdolla Abdulghafur

Transcription

1 THE EFFECT OF PROPER SELECTION OF DRILLING FLUID ON DRILLING OPERATION IN JAMBUR OIL FIELD BY Ararat Abdolla Abdulghafur ID. NO: Submitted to Department of Natural Resources Engineering And Management

2 THE EFFECT OF PROPER SELECTION OF DRILLING FLUID ON DRILLING OPERATION IN JAMBUR OIL FIELD BY Ararat Abdolla Abdulghafur Supervised by: Dr. Akram Hamoodi Lecturer in NREM University of Kurdistan-Hewlêr Ararat Abdolla I

3 THE EFFECT OF PROPER SELECTION OF DRILLING FLUID ON DRILLING OPERATION IN JAMBOUR OILFIELD BY Ararat Abdolla Abdolghafour Submitted in partial fulfillment of the requirement For The Degree of Bachelor of Engineering In Petroleum Engineering and Management Supervised By Dr. Akram Hamoodi Lecturer in NREM, University of Kurdistan-Hewlêr Ararat Abdolla II

4 DECLARATION I Ararat Abdolla Abdolghafour, hereby, state that the dissertation entitled The Effect of Proper selection of Drilling Fluid on Drilling Operation in Jambour Oilfield submitted to the department of Natural Resources Engineering and Management, University of Kurdistan Hewlêr is a partial fulfilment of the requirements for the award of bachelor of engineering in petroleum is partially my original work under the supervision and guidance of Dr. Akram Hamoodi, lecturer in NREM, University of Kurdistan Hewlêr. It has not previously formed the basis for the award of any degree, diploma, associate ship, fellowship or other similar title. Ararat Abdolla Abdolghafour Signature Place : University of Kurdistan Hewlêr Date : 30/06/2016 Ararat Abdolla III

5 CERTIFICATE This is to certify that the dissertation entitled The Effect of Proper Selection of drilling Fluid on Drilling Operation in Jambour Oilfield submitted by Ararat Abdolla Abdolghafour for the award of bachelor of engineering is a record of partial research work done under my guidance and supervision and it has not formed the basis for the award of any degree, diploma associate ship, fellowship or any other similar title and I also certify that the dissertation represents partially independent work on the part of the candidate. Dr. Akram Hamoodi Signature Place : University of Kurdistan Hewlêr Date : //2016 Ararat Abdolla IV

6 DEDICATED TO Mom and Dad There is no doubt that without their unconditional support I could not have completed this process. I would also like to dedicate this thesis to our Peshmarga martyred in clashes with Iranian Regime and ISIS. Ararat Abdolla V

7 ACKNOWLEDGMENTS I would like to wholeheartedly thank my supervisor Dr.Akram Hamoudi for his excellent guidance and supervision throughout the life of this thesis. It would have been impossible to finish it successfully without his assistance. Also, I would want to extend my gratitude to Mr. Ali and Bassil from IDEC Company. Without their help, it would have been really difficult to undergo the experiment. Furthermore, a huge appreciation goes to Dr. Mohammad Jameel for his unconditional support and help. Lastly, Rasty Saeed is the one who needs to be appreciated for what he did for me throughout the year. Ararat Abdolla Abdolghafour Ararat Abdolla VI

8 Abstract Drilling fluid is a very significant component of any drilling operation that needs proper attention. Drilling fluids have been continually improving since the day they were first used, because the drilling operations have regularly progressed. As the desire for high production rate and optimum drilling operation increases, the drilling fluid needs to modify to meet the maximum fulfillment of its functions. Moreover, one or more properties of the drilling fluid sometimes need to be altered to have a specific function done. Choosing a proper drilling fluid has always been a difficult task to overcome by drilling mud engineers. There are some factors such as the type of formation encountered, the range of temperature and pressure, the quality of water, environmental considerations which play a paramount role in the selection of the proper drilling fluid. Different types of drilling fluids execute different functions and have different limitation points and advantages. In this project, field data from Janbour Oilfield were used and analyzed. To add, salt saturated mud was designed in lab and compared with the mud the company had used to drill the second section of the well. The final result of this project indicates that the designed salt saturated mud was superior to the mud the company had used to drill the section. Lastly, KCl polymer mud is another choice that could be taken into consideration since it could drill through the section considering some of the governing factors affecting proper selection of drilling fluids. Key words: Key Words: Drilling Fluid, Salt Saturated Mud, Oil Based Mud, Sloughing Shale, Anhydrite, Lime Based Mud. Ararat Abdolla VII

9 Contents Abstract... VII Nomenclature... XI CHAPTER ONE... 1 INTRODUCTION Overview Objectives of Study... 1 CHAPTER TWO... 2 LITERATURE REVIEW... 2 CHAPTER THREE... 5 THEORETICAL BACKGROUND Drilling Fluid Drilling Fluid Functions Drilling Fluid Properties and Control Density Mud Weight Control Rheological Properties Viscosity Mud Viscosity Control Gel Strength, its measurement and control Filtration and its control Classification of Drilling Fluids Liquid Drilling Fluids Ararat Abdolla Clear Water Drilling Fluids Water-Based Muds Oil-Based Muds: VIII

10 3.4.2 Pneumatic Drilling Fluids: Air drilling fluid: Mist: Foam: Aerated (gasified) Mud: Selection of the Proper Drilling Fluid and its Effect on Drilling Operations The Type of Formation to be drilled: Shale Formations and the Proper Drilling Fluid(s) Used: Salt Formations and the Proper Drilling Fluid(s) Used: Anhydrite Formations and the Proper Drilling Fluid(s) Used: Offshore Formations and the Proper Drilling Fluid(s) Used: Trouble free- Areas and the Proper Drilling Fluid (s) Used: Lost Circulation Zones and the Proper Drilling Fluid (s) Used: The Temperature and Pressure of the Formation: Environmental Considerations: Makeup Water and its Availability: Cost: Chapter Four...25 Research Methodology...25 Chapter Five...26 Data Collection and Experimental Work Study Area: Well X Geological Structure of Lower Fars Interval: Characteristics of the Drilling Mud Used to Drill Well X Mud Losses Ararat Abdolla IX

11 5.6 Experimental Work: Chapter Six: Results and Discussion Mud types used to drill the Well Generally and Lower Fars Interval Specifically The Designed Salt Saturated Mud Comparison between the Oil Based Mud and Designed salt Saturated Mud Conclusions...42 Recommendations...43 References...44 Ararat Abdolla X

12 Nomenclature WBM= Water-Based Mud OBM= Oil-Based Mud SBM= Synthetic- Based Mud ROP= Rate of Penetration HPWBM= High Performance Water- Based Mud HPBDF= High Performance Brine Drilling Fluid KCl= Potassium Chloride HPHT= High Pressure High Temperature LC= Loss of Circulation Na +1 = Sodium Ca +2 = Calcium Cl -1 = Chloride CMC= Carboxyl Methyl Cellulose ρ m = Mud Density µ= Viscosity γ= Yield Point µ p = Plastic Viscosity lbs= Pound ft 2 = Feet Square ft 3 = Cubic Feet Ararat Abdolla XI

13 gr= Gram gal=gallon cc=cubic Centmeter D= Depth P h = Hydrostatic Pressure Ƭ= Shear Stress Y= Shear Rate k= Conversion Unit Factor Ararat Abdolla XII

14 List of Figures and Tables Table 3.1. Drilling Fluids types, composition and properties Table 5.1..The Characteristics of the Drilling Mud Table 5.2 Mud Losses Table 5.3 Salt Saturated Mud Formulation Table5.4.Saturated Mud Properties Table 6.1 Basic Properties of the Muds Figure 3.1..Complete loss of drilling fluid Figure 3.2..Partial loss of drilling fluid Figure 5.1. Map of Study Area Figure 5.2..Stratigraphical Column of the Well X Ararat Abdolla XIII

15 CHAPTER ONE INTRODUCTION 2.1 Overview Drilling fluid plays an important role in the process of completing a well and its overall cost. Historically, water was the only drilling fluid which was used to facilitate in the drilling operation. The first function done by drilling fluid was to carry the cuttings up to the surface from the bottom of the hole (Darley and Gray, 1988). Many drilling problems such as lost circulation, stuck pipe, shale caving and etc are influenced by drilling fluid properties and can be prevented eventually. Drilling fluids cover almost one fifth of the overall cost of drilling. They must be easy and simple to use, environmentally & ecologically friendly and not too expensive. The drilling fluids are usually designed to do numerous functions at once. They are required to suspend and remove cuttings around the drill bit and well bore, cool and lubricate the drill bit and the drill string, control down-hole pressure, evaluate the formation pressure and seal permeable formation (ASME Shale Shaker Committee, 2011). There are some governing agents that affect the proper selection of the drilling fluid. The type of formation encountered, temperature, ecological & environmental considerations need to be put into consideration when a proper selection of the drilling fluid is required (Bourgoyne Jr. et al.,1986). There are basically three types of drilling fluid that can be used in any mud system. Water base mud (WBM) comprises water as the continuous phase and is the most commonly used drilling fluid. Oil base mud (OBM) consists of oil as the continuous phase and diesel oil is the one used largely. Gas is composed of either air or natural gas and foaming agents are sometimes used (Darley and Gray, 1988). Resultantly, choosing an appropriate type of drilling fluid can greatly improve the drilling operation. An appropriate selection of the drilling mud is not only a big problem for mud engineers, but also for drilling engineers, drilling supervisors and production engineers. Usually a mud engineer is required to be on the rig site during the drilling operation to prevent any undesired problem and recalculate the properties of the drilling mud (Dhiman, 2012). Ararat Abdolla 1

16 Through this project, collected data related to drilling fluids from Janbour Formation would be analyzed and compared to the designed drilling fluids. It will be indicated that each type of drilling fluids can be properly used for a specific situation. This ultimately results in a safe and successful drilling operation since some drilling hazards can be effectively avoided by the proper drilling fluid chosen. 2.2 Objectives of Study The followings are the objectives of this project: Understanding the drilling fluids and their functions. Getting familiar to the different types of the drilling fluids, their properties, limitations and advantages. Analyzing field data. Designing a drilling fluid based on the given data. Comparing between the designed mud and the mud used by the company. Ararat Abdolla 1

17 CHAPTER TWO LITERATURE REVIEW Drilling fluids have always been a very important part of drilling engineering. Their proper functionality helps reduce many drilling problems. Therefore, proper and efficient understanding of drilling fluids is paramount in drilling industry. The effect of proper selection of drilling fluid on drilling operations has always been a very significant topic to discuss. Many people have had diverse experience with drilling fluids and their applications. In this chapter, different literature reviews from different people will be overviewed. Brandt et al., (1960) discussed a newly improved invert emulsion mud. The mud is free of inert solids and can be efficiently used in high temperature drilling (300F). The diversified salts of fatty acids form the emulsifier needed to produce the mud. They further explained that these muds could be used when high densities (up to 18 lb/gal) are required to control subsurface pressure, drilling productive zones and during perforation process. Ultimately, invert emulsion muds would prevent water or the mud to get into contact with the formation. Kelly Jr (1983) claimed that lignosulfonate muds (a type of water-based muds) are often considered to be a drilling fluid that could be used for almost any purpose. He further explains that this mud has special significance in drilling where high temperature formations might be countered, high density muds are needed, high tolerance for solids is required, low filter loss is desired, and high resistance to cement contamination, salt, anhydrite and gypsum formation is necessary. Christiansen (1991) asserts water-based mud (glycol and potassium chloride (KCL) polymer systems) replaced the oil based mud used by the Marsk Olie og Gas AS to drill horizontal wells due to discharge problems of the oil. A comparison between the two drilling fluids in terms of ROP, drag and torque, etc. was made, and it was indicated that the water based mud would show positive results in drilling horizontal wells. It was also mentioned that the oil based mud would still be used for those parts which cannot be drilled by water based mud. Halliday et al., (1998) explained that low density gas hydrate oppressive drilling fluid would be so efficient in deep water applications to inhibit and control gas hydrate. These fluids use low molecular weight organic compounds that are compatible with most water-based muds Ararat Abdolla 2

18 especially salt muds. They also emphasized that these drilling fluids could be used to inhibit gas hydrate when low fracture gradients are faced during the process of drilling.. Bybee (2004) established a method to yield a designer mud that greatly strengthens fracture resistance during drilling in sand or shale formations. By continually adding bridging materials to the mud during drilling, the designer mud would be produced. The results showed good well bore stability and a reduction in mud losses. Lyons (2005) expressed that oil based muds are effective in drilling bothersome shales, deep & high-temperature wells, producing zones and formations such as salt and anhydrite which are water soluble. These muds would give high rate of penetration (ROP), reduce torque, minimize differential sticking and decrease bit balling. Klein et al., (2005) indicated that a newly designed water based mud would perform the same functions done by synthetic based muds (SBMs) to drill reactive gumbo shale segments in Gulf of Mexico. The water based mud can be easily designed by adding a polyamine shale inhibitor, an anti-accretion additive and a polymeric encapsulator. A field comparison between the new WBM and the SBM showed that the newly designed WBM would provide a higher ROP, no bit balling, good hydration protection, and economic stability. Azar and Samuel (2007) explained that proper selection of drilling fluids would result in some additional benefits beside the drilling fluids functions. It would result in reduction of formation damage & environmental impact and corrosion effects, and improvement in ROP and safety issues. They further clarified that the prosperity of drilling operations and the capability to minimize the cost are highly anticipated from the proper understanding and selection of drilling fluids. Lyons (2009) explained that aerated drilling fluids were first used to drill fractured rock formations and pore systems that would drain the standard fluids into the annulus. These fluids would avoid the dangerous impact of lost circulation segments. Yue et al., (2011) emphasizes on using synthetic drilling fluids in offshore drilling. These drilling fluids would result in high ROP, show outstanding rheological properties, high biodegradability and good ability in avoiding hydrate formations. They further elaborated that newly synthetic drilling fluids could be used since they can give constant rheological properties for a wide range of temperature. Dhiman (2012) conducted a study to prepare a drilling mud by adding barite, bentonite and hematite. He compared density, rheological properties and corrosion properties of these Ararat Abdolla 3

19 additives. The results indicated that hematite gave a higher value of density and rheological properties compared to barite for the same concentration. Moreover, the difference in the corrosion rates was too small that could be considered to be at the same level for the barite, bentonite and hematite. Witthayapanayanon, et al,. (2013) articulated a high performance water based mud (HPWBM) with the idea of complete inhibition for drilling offshore Cameroon. They developed HPWBM to reduce cost and time of drilling. The results met the anticipations by attaining high shale stability, inhibition of cuttings and clay, zero environmental effect, high ROP, minimized bit balling and torque. Falope et al,. (2014) stated that enhanced water based mud compared to synthetic oil based mud would be a better choice of use for drilling in deep formations of Niger Delta. Multifunctional polymeric additives added to water based mud would form this enhanced water based mud that is more environmentally friendly, cost effective and improves drilling efficiency. Compton et al,. (2015) developed a high performance brine drilling fluid (HPBDF) as a substitute for diesel oil-based mud to drill in Austic Chalk Formation. It was indicated that HPBDF would reduce the related cost and time of drilling. Moreover, the drilling fluid proved to give a higher value of ROP and a better well- bore stability compared to the diesel oil-based mud. Maliardi et al,. (2015) tried to use a high performance water-based mud instead of low weight calcium carbonate polymer muds to drill a highly fractured carbonate reservoir. Their aim was to decrease torque, increase ROP and improve the stability of the horizontal section of the well. Their results proved to be reasonable and reliable since an increase in ROP, a reduction in torque and an improvement in the stability of the extended section of the well could be observed. Ararat Abdolla 4

20 CHAPTER THREE THEORETICAL BACKGROUND 3.1 Drilling Fluid Drilling fluid is a very popular term which is frequently used in drilling industry. It is any fluid (liquid or gas) that is circulated continually down into the wellbore in rotary drilling process to fulfill some or all the required functions needed to have a safe drilling operation at the lowest cost possible (Azar and Samuel, 2007). Drilling mud is interchangeably used with drilling fluid, and it is basically a mixture of water and clay. It is habitually believed that most of the drilling problems (hazards) are somehow related to drilling fluid. Drilling fluid is of great importance and should be understood efficiently. The related cost of drilling fluid is small compared to the overall cost of the drilling operation, but its proper selection and application would affect the drilling cost and performance highly (Annis and Smith, 1996 & Mitchel and Miska, 2011). 3.2 Drilling Fluid Functions The following functions are the most significant functions done by drilling fluids in rotary drilling process. The functions performed by a drilling fluid differ and depend on the type of the drilling fluid used (ASME Shale Shaker Committee, 2011& Azar and Samuel, 2007& Bourgoyne Jr. et al.,1986 ). Remove drilled cuttings from the bottom of the well and carry them up to the surface. Control subsurface pressure (Pore Pressure) by exerting enough hydrostatic pressure. This is done to avoid the formation fluids from flowing into the well bore. Suspend the drilled cuttings when circulation process has halted. Cool and lubricate the bit and drill string. Form an impermeable mud cake on the wall of the well. And a drilling fluid should not do the followings in order to be able to perform the above functions properly: Cause corrosion Reduce ROP Ararat Abdolla 5

21 Be toxic Avoid formation evaluation Require high pump pressure Moreover, a drilling fluid must be environmentally friendly, easy to prepare, cheap and resistive to contaminations. The ability of a drilling fluid to reduce and dispose of the cuttings piled up at the bottom of the well bore and around the drill bit is of great essence. If the drilled cuttings are not removed efficiently, the capability of the drilling fluid would be affected and no sufficient hole cleaning would be achieved (ASME Shale Shaker Committee, 2011). 3.3 Drilling Fluid Properties and Control The properties of a drilling fluid have a great effect on the ability of a drilling fluid to perform its functions properly. To prevent expensive drilling problems, it is always required to have these properties field controlled and effectively maintained. It is paramount to test the properties to show any change occurring, determining the cause of the problem and thereby providing a proper solution (Azar and Samuel, 2007). The properties discussed in this project will be the followings: Density Rheological Properties Filtration Density Basically, density is the ratio of mass to volume, and it is measured in either pounds/gallon (lbs/gal), lbs/ft 3, or gram per cubic centimeter (gr/cc). Most tests done on mud density are still recorded in lbs/gal. However density is the more appropriate word, weight is more ideally used in association with mud. It is usually desired to have a mud weight close to that of water so that fracturing problems can be reduced easily and drilling rates optimized (Azar And Samuel, 2007). The most important function of mud weight is to calculate the hydrostatic pressure exerted by a column of mud on any point at any depth to control the formation pressure (Annis Ararat Abdolla 6

22 and Smith, 1996 & Azar and Samuel, 2007). The hydrostatic pressure at any depth can be estimated by using the following equation: P h =k ρ m D Where, P h = hydrostatic pressure k= conversion unit factor ρ m = mud weight (density) Depending on the value of P h in psi, ρ m in lbs/gal, Depth in ft, the value of k would be in the above equation Mud Weight Control The control of mud weight is of great importance since it can greatly affect the performance of drilling fluid. There are some different materials which can be used to control the mud weight (increasing or decreasing it). Basically, mud weight is controlled either by adding chemical materials, diluting with water or using proper drilled solids equipment (Azar and Samuel, 2007). Sometimes, it is required to increase the density of the mud so that proper control of subsurface pressure can be achieved. Barite as a chemical material (Ba 2 SO 4 ) is usually used as a weighting material to add the weight of the drilling mud. It has some specific properties such as high specific gravity (4.3), inertness, low abrasiveness and cost. If the mud required to control the formation pressure maintains a density higher than required, some problems such as lost circulation, decrease of ROP, increase of differential pressure sticking and increase of mud cost would be the result (Annis and Smith, 1996). The drilled solids in the returned mud are mostly undesired and need to be disposed of. A proper use of shale shaker as a solids removal equipment would remove and decrease the amount of the drilled solids present in the mud. It is usually preferred to use a high speed screen shaker with 50 mesh followed by desilter, desander and mud cleaner to remove the drilled solids of un-weighted muds. Centrifuge is mostly used to remove cuttings of weighted muds. Mud weight is highly increased if the drilled solids are not properly and immediately removed, and this would cause unwanted problems. Dilution with water is also used but less effectively. It is used to reduce the density of the mud so that undesired situations could be easily avoided (Azar and Samuel, 2007). Ararat Abdolla 7

23 3.3.3 Rheological Properties Rheological properties of a drilling fluid play an important role in the process of performing some specific functions by the drilling fluid. These properties define the behavior of a drilling fluid to flow during the period of flow. Rheology is the study of deformation and flow of the matter (Ljones, 2013). Rheological properties of a drilling fluid consist of viscosity,gel strength and yield point Viscosity It is a very paramount property of any drilling fluid. It simply describes the fluid internal resistance to flow. It is also defined as the ratio of shear stress (Ƭ) to shear rate (γ) (Burke and Veil, 1995). Mathematically, it is expressed in the flowing equation: µ=ƭ/γ Drilling fluids are generally divided into two groups: Newtonian and Non-Newtonian fluids. Newtonian fluids are those fluids that have a constant viscosity and it can be shown in a linear line. The viscosity is not dependent on the shear rate. A plot drawn from Ƭ vs. γ would give a straight line with the viscosity being the slope. In a Newtonian fluid, the fluid would be able to flow even with a small amount of pressure being exerted. Light oil and water are example for non-newtonian fluids (Annis and Smith, 1996 & ASME Shale Shaker Committee. 2011, Azar and Samuel, 2007). For a Newtonian Fluid, Ƭ=µ*γ The field units of viscosity and shear rate are centipoise and lbs/100ft 2 respectively (Azar and Samuel, 2007). Non- Newtonian fluids such as most drilling fluids, and cement slurry need more than one parameter to describe the flow behavior of the fluid. The viscosity of a non-newtonian fluid is dependent on the shear rate. As shear rate increases, viscosity decreases and this is known as shear thinning.the viscous property of non-newtonian fluids can be approximated to show the flow behavior through either Bingham plastic model or power low model (Annis and Smith, 1996 & ASME Shale Shaker Committee, 2011 & Azar And Samuel, 2007). Newtonian fluids have an internal structure because they possess thixotropic property (Azar and Samuel, 2007). Ararat Abdolla 8

24 Since apparent viscosity of non-newtonian fluids is a combination of plastic viscosity and yield point, it is important to understand these two terms. Plastic viscosity (µ p ) is a portion of the fluid resistance to flow due to mechanical friction of the fluid. It is a function of the concentration of the solid particles present in the drilling fluid, and can be controlled by either mechanical means or dilution. Yield point (Y b ) is another portion of fluid resistance to flow due to electrochemical forces inside the fluid. Its unit is lbs/100ft 2 (Azar and Samuel, 2007) Mud Viscosity Control Generally a mud viscosity is a function of plastic viscosity and yield point. Viscosity can be controlled easily if each one of µ p and Y b is controlled effectively. Bentonite and polymers are most commonly used to increase viscosity. On the other hand, dilution with water is used to decrease viscosity, but if a large amount of liquid is desired in the mud, it would affect other properties. For this reason, thinners such as quebracho, lignosulfonate, tannins and lignite are alternatively used to reduce viscosity instead of dilution. Moreover, chemicals can be used to control an increase in yield point with no or little change in plastic viscosity. Lastly, a combination of dilution with water, chemical addition and solids removal can be used to control a simultaneous rise of Y b and µ p which results in control of viscosity (Azar and Samuel, 2007) Gel Strength, its measurement and control Gel strength is the minimum shear stress needed to initiate flow when the drilling fluid has been at rest for a while. In simple words, gel strength is a property which is formed when the fluid circulation has halted. Gel strength is the capability of the fluid to form a semi-solid structure (Gel) due to thixotropic properties. It is generally formed due to the interaction of the electrically charged solid particles (Annis and Smith, 1996). The produced gel becomes too strong as the time of quiescent increases, and this might cause many problems such as the need to have high re-circulation pressure by the mud pumps and slows down the separation process of the cuttings on the surface. Preferably, gel strength has to be high enough to suspend the drilled cutting efficiently during the halt of circulation (Darley and Gray, 1988).Gel strength and yield point both are a measurement of attractive (electrochemical) forces in the mud. Gel strength is different from yield point because it depends on time and is during the pause of circulation (Azar and Samuel, 2007). Ararat Abdolla 9

25 When gel strength is low, it might be increased by using bentonite. Thinners are usually used to reduce gel strength. Moreover, dilution with water is utilized to control gel strength when the mud is either contaminated by contaminants or high solids content is present. Lastly, flocculation increases gel strength and de-flocculation reduces it (Annis and Smith, 1996,Darley and Gray, 1988) Filtration and its control Filtration is one of the important properties of drilling fluids and requires proper and sufficient attention. It is described as the loss of the liquid phase of the drilling mud into the encountered permeable formation due to the positive differential pressure (difference between the hydrostatic pressure and the pore pressure) (Khodja et al, 2010). The liquid part of the drilling mud lost to the formation is called mud filtrate. Deposition of solid particles on the wall of the well forms the so-called mud cake (Azar and Samuel, 2007). Generally, there are two types of filtration: dynamic and static filtration. As the fluid is being circulated into the well, dynamic filtration occurs. Inversely, static filtration happens when the fluid is at rest (Annis and Smith, 1996). When the control of mud filtrate is concerned, it is usually required to decrease it. The following factors affect filtration property of drilling mud: Time Permeability of Mud cake Differential Pressure Solids Concentration Filtrate Viscosity Generally, most of the materials used to control (Increase) viscosity can be used to control (decrease) filtration. Bentonite can decrease filtration by forming a good mud cake. Carboxyl Methyl Cellulose (CMC) would reduce filtration by minimizing flocculation, but breaks down at 300F. Starch also is used as a fluid loss reducer by coating solids, but would break down at temperatures above 275F. Finally, lignosulfonate and lignite are also good materials used to control filtration by deflloculating the mud, but would start breaking down at 300F (Azar and Samuel, 2007). Ararat Abdolla 10

26 3.4 Classification of Drilling Fluids Selecting the proper type of drilling fluid plays a very paramount role in performing a safe and successful drilling operation in a very cost effective manner. Generally, drilling fluids are classified into the following two types based on their base phase (Azar and Samuel, 2007, Darley and Gray, 1988): Liquid Drilling Fluids Pneumatic Drilling Fluids Each type of drilling fluids has their own properties and composition. The following table would provide a general summary of drilling fluids types. More information on each type would be provided in the next section since complete knowledge on drilling fluids helps choose the most appropriate type needed to drill a specific formation. Table 3.1 Drilling Fluid Types, Composition and Properties (Azar and Samuel, 2007) Ararat Abdolla 11

27 3.4.1 Liquid Drilling Fluids The base phase in this type of drilling fluid is liquid (oil or water). It is classified into the following two types: Clear water drilling fluids Water-based muds Oil based-muds Generally, it is perceived that when a liquid is treated by clay such as bentonite or polymer, it would result in the formation of a drilling fluid called drilling mud. The followings are the primary phases of any drilling mud (Azar and Samuel, 2007): Continuous phase Dispersed phase Inert materials Chemicals Clear Water Drilling Fluids This drilling fluid consists of only water. This type is the most cost-effective and common liquid drilling fluid used when normal and trouble-free formations are encountered. This fluid has some good benefits such as prolonged bit life and higher ROPs. This fluid can t be used in water- sensitive formations and abnormal pressure regions (Azar and Samuel, 2007) Water-Based Muds Water-based muds (WBM) are the most common type of drilling muds which are mostly used. They are used in 90-95% of all drilling operations (Khodja et al, 2010).Water-based muds typically comprise an aggregate of liquids, solids, and chemicals, and in this case water is the continuous (base) phase (Shanker et al, 2010). The solids are divided into active and inert (inactive) solids. Active solids such as hydratable clay react with the liquid phase and the dissolved chemicals. Their activity is limited by adding chemicals, and this allows certain properties to be properly maintained. On the other hand, inert (inactive) materials such as barite do not react with the liquid (water) and the chemicals (Bourgoyne Jr, et al. 1986). Generally, WBM is divided into the following types: 1. non-inhibitive muds Ararat Abdolla 12

28 2. Inhibitive muds 3. Direct emulsion muds. 1.The non-inhibitive water-based muds These muds are the simplest type of WBM. These muds are cheap and easy to maintain and prepare. Though, their application stops when high-temperature formations, formations containing contaminants such as H 2 S, and dispersive formations will be faced. These muds contain the followings (Azar and Samuel, 2007): Clear water muds (spud mud), Bentonite-treated muds, Phosphate-treated muds, Gel chemical muds, Lignite/lignosulfonate muds. Importantly, phosphate-treated muds, gel-chemical treated muds and lignite/lignosulfonate muds are also called chemically-treated muds. Non-inhibitive simply means that the fluid does not contain inhibiting ions such as potassium (K + ), calcium (Ca +2 ) and chloride (Cl -1 ) to avoid hole problems (Rabia, 2002) A. Clear Water Muds (Spud mud): Clear water muds are inexpensive muds, and their ingredients are basically water and bentonite. These muds can be used when drilling surface hole is concerned (Azar and Samuel, 2007 & Darley and Gray, 1988 &Kelly Jr, 1983). B. Bentonite-Treated Muds: These muds are basically made by addition of bentonite to clear water. These muds are basically used to provide viscosity for enhanced cuttings-carrying capacity of the drilling mud. Moreover, they can avoid minor-hole sloughing problems and provide suspension of barite in weighted muds. Trouble-free shallow formations are usually drilled using these muds (Azar and Samuel, 2007). C. Lignite/Lignosulfonate Muds: These are those muds which are greatly treated with lignosulfonate along with lignite (two effective thinners). They have been formulated to stay stable up to 375F. These are usually used when low filter loss is required. A mud treated with lignosulfonate and lignite is effectively more resistant to chloride and calcium contamination (Azar and Samuel, 2007, Kelly Jr, 1983). Ararat Abdolla 13

29 D. Phosphate-Treated Muds: Phosphate-treated muds are used to control (decrease) viscosity when a bentonitetreated mud is contaminated by either magnesium or calcium ions. The addition of phosphates to bentonite muds results in formation of phosphate- treated muds. These muds become unstable when temperatures above 150F are encountered and are not efficient in controlling fluid loss. Their usage is restricted to shallow wells or top parts of a hole where fluid loss and temperature are not of real concern (Azar and Samuel, 2007). E. Gel-Chemical Muds: These muds consist of bentonite and a low concentration of thinners (quebracho or lignosulfonates). They possess almost the same applications of phosphates except they can tolerate deeper wells (Azar and Samuel, 2007). 2.The Inhibitive Muds: The inhibitive muds are those mud which contain inhibiting ions such as K +, Ca +2, and Cl -1 to control the wellbore stability. The inhibitive muds include calcium-based muds, salt water-based muds and potassium chloride (KCl)/ polymer muds (Azar and Samuel, 2007 & Rabia, 2002). A. Calcium-Based Muds: Calcium based muds are basically divided into gypsum and lime-based mud. This mud is formed by addition of either gypsum or lime to bentonite-treated mud. As a result of ion exchange between the sodium ions of the clay and the Ca +2 ions, this mud is formed. Lime mud is created by adding caustic soda, lime, thinners and a fluid loss controller to bentonite-treated mud. On the other side, gypsum mud is formulated by adding lignosulfonate and gypsum to bentonite-treated mud (Bleier, 1990). Lime muds can be utilized when limestone formation is encountered. Gypsum and anhydrite formations can be controlled by using gypsum mud. Lime/gypsum muds are usually used to drill shale formation and can avoid sloughing of shale (Darley and Gray, 1988 & Rabia, 2002). The calcium ions present in the mud would replace the sodium ions present on the clay particles. As a result, the wellbore would be stabilized and sloughing and heaving of the shale formation would be prevented. Lime muds can tolerate the maximum temperature of 300F, and gypsum muds can be used in subsurface temperatures up to 325F (Darley and Gray, 1988). Ararat Abdolla 14

30 B. Salt-Based Muds: These are the collective terminology for a drilling fluid in which its liquid phase (water) is being saturated with salt (NaCl). The water is either fresh or sea water. Basically, these muds are composed of fresh or sea water, prehydrated bentonite or attapulgite, CMC) and optionally lignosulfonate. These muds are used where salt sections are to be drilled, sloughing of shale is prone to encounter and are also utilized in offshore drilling by adding polymer (For building viscosity) to the mud (Azar and Samuel, 2007 & Kelly Jr, 1983 & Rabia, 2002). It must be taken into consideration that solubility of salt increases with temperature. In this case, the system is better to be aggregated with extra salt to reimburse for the increased temperature at subsurface conditions (Rabia, 2002). Salt-water based muds have a relatively high solids tolerance, but it all depends on the weight of the mud. Their temperature stability depends on the degradation temperature of their minimum stable component (Kelly Jr, 1983). C. KCl /Polymer muds: KCl muds are the most appropriate type of water-based muds used to drill watersensitive shale formations. The potassium ions replace the sodium (Na +1 ) or the calcium (Ca +2 ) ions present on the interlayers of the clay, and KCl mud is formed as a result. Fast drilling at minimum solids content can be obtained through these muds. KCl muds are mostly used in shale formations and avoid the hydration and sloughing of shale (Azar and Samuel, 2007 & Darley and Gray, 1988). On the other hand, polymer muds are very close to clear water muds since they possess low solids content. These muds are formed by adding polymer to the mud. Fast drilling through competent rocks could be attained through polymer muds (Darley and Gray, 1988). Polymer muds have some advantages (Azar and Samuel, 2007): Providing good fluid loss control Viscosifying the mud Providing good well-bore stability at high temperature zones Extending the yield of bentonite 3.Direct Emulsion muds: These are a type water-based mud in which oil (diesel oil) is added to the mud followed by an emulsifying agent such as organic colloids or soaps to stabilize the emulsion. The added oil is the dispersed phase and is considered to play the role of solid particles. The oil is emulsified in the water and is kept as discontinuous and small droplets (Bourgoyne Jr. et al 1986). The percentage of the oil in the water is around 10%. Direct emulsion muds are easy to Ararat Abdolla 15

31 prepare. These muds possess a high price, and it is difficult to analyze the cuttings transported by them to the surface. Though these muds can be useful in providing the following applications (Jha et al. 2014): Decrease the sloughing of shale and negative effect on productive areas. Increase ROP Provide good lubrication, less torque and improved life of bit Resist corrosion Not affected by contaminants (Compared to other water based muds) Oil-Based Muds: This is another type of liquid drilling fluids. These muds are basically quite similar to WBM in composition except the liquid phase (continuous phase) is oil (diesel or synthetics) (Azar and Samuel, 2007 & Bourgoyne Jr,T.A. et al & Erickson et al, 1988 & Khodja et al & Rabia, 2002 & Shanker et al, 2010). These muds are usually used when the performance of WBM is not sufficient (Khodja et al, 2010). Diesel oil is usually used as the continuous phase since it has high flash point and low pour point. These muds are usually composed of diesel oil, asphalt, emulsifier and water (2-10 %) (Darley and Gray, 1988).Their advantages include (Azar and Samuel, 2007 & Erickson et al & Shanker et al, 2010): Outstanding fluid loss control Stable at high temperatures Good shale sloughing and swelling inhibition Sufficient lubrication to drill bit and string Avoiding corrosion Moreover, they could be used in coring, completion and releasing stuck pipe. Oil based muds just like all the other fluids have some drawbacks. These muds are expensive to use and not environmentally/ecologically friendly (Annis and Smith, 1996). In the early 1990s, the disposal of cuttings into the ocean from wells drilled by oil based muds was inhibited. Generally oil based muds can be divided into the following sub types: 1. Invert Emulsion muds 2. Synthetic based muds Ararat Abdolla 16

32 1. Invert Emulsion Muds: These muds are described as OBMs to which water (usually brine) is added. The water droplets are emulsified and dispersed in the oil. Oil is the external (continuous) phase and water takes up the internal (discontinuous) phase (Bleier 1990 & Bourgoyne Jr. et al & Jha et al, 2014). The water added is always more than 5%, and it adds in some benefits. The properties of the invert emulsion rely on the percentage of water used. High emulsified water concentration results in less fire hazards related to the oil muds (Fraser, 1992). The emulsifying agent is usually first added to the oil and then water is added. The Invert emulsion muds usually consist of diesel oil, water (brine), organophilic clays (provide additional fluid loss and viscosity control) fatty acids for water emulsification, barite (weighting material) and polymer are usually utilized to provide additional rheology control (Myers, 1993). Invert emulsion muds have several potential advantages. They are utilized to avoid sloughing/swelling of shale formations (Myers, 1993 & Schlumberger Oilfield Glossary, 2015). Their maintenance cost is low (Darley and Gray, 1988). They can give excellent viscosity/fluid loss control and are resistant to contaminants such as salt, anhydrite and gypsum (Jha, et al & Kelly Jr, 1983). They also provide an increase in well bore stability and ROP (Shanker et al, 2010). On the other hand, invert emulsion muds possess some pitfalls. They are unstable at high temperature and pressures (Shanker et al. 2010). These are expensive to use and are not much environmentally friendly (Myers, 1993). 2. Synthetic Based muds (SBM): SBMs were an evolution made to the OBMs and introduced to solve problems (especially environmental problems) created by OBMs. The composition of SBMs is just similar to OBMs except the external phase is a synthetic drilling fluid such as alpha olefins, isomerized olefins or normal alkanes. These muds are designed to act as a low toxic oil based mud (Rabia, 2002). The use and development of SBMs is quite new and continues to progress. SBMs equivalently to OBMs are utilized in shale formations, high subsurface temperatures, in salt formation and where the WBMs would not function properly. SBMs have several beneficial advantages. They reduce drilling time which results in less air emission. SBMs provide good lubrication and reduced friction. They increase ROP and avoid problems such as stuck pipe (Burke and veil, 1995). Since they can be recycled, less waste is yielded. SBMs are less toxic and more environmentally friendly compared to OBMs (Burke and veil, 1995 & Shanker et al, 2010). The biggest disadvantage of SBMs is that they are more expensive than OBMs; however Ararat Abdolla 17

33 this drawback could be compensated greatly if the drilled cuttings are properly disposed of Pneumatic Drilling Fluids: These drilling fluids can usually be used where WBMs and OBMs cannot be used efficiently. These fluids are basically utilized in loss circulation zones, under balanced drilling operations and depleted (low pressure) reservoirs. They usually give higher ROP and less formation damage, control loss circulation zones, and enhance the bit life. On the other hand, they cannot be used properly if water is present. Their drawbacks would be corrosion and hole erosion (Azar and Samuel, 2007). These types can be further subdivided into the following (Azar and Samuel, 2007 & lyons et al, 2009 & Rabia, 2002): Air drilling fluid Mist Foam Aerated (Gasified) mud Air drilling fluid: This is the simplest form of pneumatic drilling fluids since it only comprises air. Usually the maximum ROP would be achieved by using air since minimum hydrostatic pressure would be exerted on bottom of the well bore. Air drilling has some advantages. It gives high ROP in dense formations and has good solids carrying capacity (Azar and Samuel, 2007 & Boscher and Ruda, 2005). Moreover, it improves the bit life, reduces formation damage and control loss circulation zones. This mud loses its effectiveness in the presence of water (from the formation) and corrosion is one of the problems related to air drilling fluid when there is no enough air supply (Boscher and Ruda, 2005) Mist: This is when water is added to the airstream. Mist drilling can do almost the same functions of air drilling fluid. It is usually utilized when small amount of influx water usually flow into the well bore (Azar and Samuel, 2007 & Boscher and Ruda, 2005) Ararat Abdolla 18

34 Foam: Foam drilling happens when water and a surfactant are added to the airstream. This is usually used when the volume of water entering the well bore increases that cannot be controlled by mist drilling. Compared to air drilling, it gives higher drilled solids carrying capacity, reduced erosion, increased wellbore stability, less water volume required. Foam drilling loses its efficiency when high pressure formations are encountered, because the hydrostatic pressure by the foam is too low that causes the wellbore to become unstable, or the water flow is high that cannot be controlled by the foam (Boscher and Ruda, 2005) Aerated (gasified) Mud: This is another type of pneumatic drilling fluids. Aerated mud is composed of an incompressible drilling fluid with compressed air or gas. Aerated mud gives higher ROPs compared to conventional muds, and controls loss of circulation effectively (Boscher and Ruda, 2005 & Putra, 2008). This can be greatly utilized in underbalanced drilling (Azar and Samuel, 2007). Furthermore, reduced formation damage and hole-pressure control are two other advantages of aerated mud (Putra, 2008). Besides its advantages, it causes some problems. The biggest pitfall of this mud is that it causes high corrosion to the drill pipes (Boscher and Ruda, 2005 & Putra, 2008). 3.5 Selection of the Proper Drilling Fluid and its Effect on Drilling Operations Proper selection of a drilling fluid is very significant to the prosperity of a drilling operation. Clearly, no drilling fluid can be used in all circumstance (Bleier, 1990). However there are many factors governing the proper selection of a drilling fluid, the main ones are the followings. The type of formation to be drilled The temperature and pressure of the formation Environmental considerations Makeup water and its availability Cost Ararat Abdolla 19

35 3.5.1 The Type of Formation to be drilled: This is one of the most important factors affecting the selection of an appropriate drilling fluid. Depending on the sensitivity of the drilled formation to the drilling fluid and the resulting problems, the most suitable drilling fluid can be easily selected. Various formations such as (shale, salt, anhydrite, offshore and lost circulation zone) with the type(s) used to drill them are going to be discussed and clarified Shale Formations and the Proper Drilling Fluid(s) Used: Shale Formations are predominantly the most encountered formations during the process of drilling. These formations are the most difficult and problematic formations to drill. They comprise approximately over 75% of drilled formations in the whole world (Azar and Samuel, 2007 & Chukwu et al, 1993). Shale formations cause many unwanted problems such as stuck pipe and difficulty in logging &completion operations if proper drilling fluids is not used. As a result, safe and cost- effective drilling through shale formation could be attained through the properly selected drilling mud type. While drilling shale formations, there are many types of drilling fluids that can be efficiently used to avoid all the problems that might occur. Different types of WBMs such as lime, KCl, salt, gypsum, and polymer muds can be effectively used to drill shale formations (Bleier, 1990). Invert emulsion muds could be a good choice of drilling mud used to drill shale formations. Moreover, OBMs have shown to be good and reliable drilling muds while encountering reactive shales. OBMs used to drill shale formations offer excellent wellbore stability, low formation damage, reduced stuck pipe and good lubrication (Bloys et al, 1994). Lastly, SBMs can also be used to drill shale sections Salt Formations and the Proper Drilling Fluid(s) Used: Sometimes, a salt section might be encountered while the process of drilling is underway. Not any drilling fluid could be used to drill salt zone of a formation. The type of drilling fluid used usually depends on the thickness of the salt section. Un-saturated salt muds are usually used when the salt segment is thin (not too thick). The most proper types of drilling muds used to drill thick sections of salt are OBM and saturated salt mud (Azar and Samuel, 2007 & Bleier, 1990). Through the proper use of these muds, problems caused by salt sections Ararat Abdolla 20

36 such as hole enlargement can be effectively avoided Anhydrite Formations and the Proper Drilling Fluid(s) Used: Not always limestone, shale or salt sections are to be drilled, but anhydrite sections are sometimes prone to be encountered. When bentonite-treated water mud is used to drill these formations, the Ca +2 ions start releasing and interact with the mud. This is the reason why not any mud could be used to drill these formations. Lime muds/ gypsum muds are the best types of drilling muds utilized to drill through anhydrite formations since they can tolerate the polluting ions (Azar and Samuel, 2007) Offshore Formations and the Proper Drilling Fluid(s) Used: In offshore drilling the process of solids removal should be fulfilled very intensively. Since the cuttings/solids have to be discharged into the sea, not any drilling mud could be used. OBMs have always been used to drill offshore formations, but their usage was prohibited in 1970s due to environmental considerations. SBMs have always shown to be effective drilling muds used in offshore drilling. They are mostly used since they are environmentally accepted and can dispose of the drilled cuttings safely (Schlumberger Oilfield Glossary, 2015). Waterbased muds are seldom used in offshore drilling, but salt water muds could be effective. Certain polymers added to salt water muds (viscosifying the mud) can give excellent results in drilling offshore (Azar and Samuel, 2007) Trouble free- Areas and the Proper Drilling Fluid (s) Used: Drilling trouble free- areas is way easier and less costly compared to drilling troublesome zones. Many low-priced and simply formed muds can be used to drill these areas since almost no problem is faced. Unweighted-gel freshwater muds, muds treated lightly with lignoslufonates, and lignite muds are some of the most proper and cheapest muds that can be efficiently utilized to drill these areas (Bleier, 1990) Lost Circulation Zones and the Proper Drilling Fluid (s) Used: Loss of circulation (LC) adds to the overall cost and time of any drilling operation. LC is defined as the partial or complete loss of drilling mud to the formation through zones called thief zones (Darley and Gray, 1988 & Jha et al, 2014). The partial loss is when a part of the drilling fluid would return back to the surface. On the other side, the complete loss of drilling fluid results Ararat Abdolla 21

37 in the flow of the whole mud into the formation without any return (Azar and Samuel, 2007). In the flowing figures, partial and complete loss of drilling fluids could be easily seen. Figure 3.1 Complete Loss of Drilling Fuid (Azar and Samuel, 2007) Figure 3.2 Partial Loss of Drilling Fluid (Azar and Samuel, 2007) As a result, using the proper type of drilling fluids to drill these zones is paramount. When loss of circulation zone is encountered, sealing off the zone is of high necessity. Lost circulation materials are usually used to control loss of circulation. The most used lost circulation materials are fibrous, granular and flaked. These materials exist in fine, medium or course sizes to shut off the low to medium zones of lost circulation. If the loss of circulation is severe, plugs are then utilized to seal off the zone (Azar and Samuel, 2007). Furthermore, when LC zone is anticipated to drill, either the density of the fluid is reduced, foam or air drilling is used, or the region of LC is cased off (Boscher and Ruda, 2005). Finally, if it is in advance expected that huge volume of drilling mud might be lost, aerated fluid would be the best type to use considering maintenance and cost (Bleier, 1990). Ararat Abdolla 22

38 3.5.2 The Temperature and Pressure of the Formation: The effect of pressure and temperature on the rheological properties of drilling fluids is of great importance when deep wells are drilled. Since the difference between the fracture and pore pressure becomes too small in these cases, cautious evaluation of pressure and temperature is required to control possible kicks and damages to the hydraulics (Bjorkevoll and Rommetveit, 1997). Any drilling fluid chosen to drill high pressure high temperature (HPHT) formations has to be thermally stable and provide excellent rheological properties. Polymer muds have appeared to be effective drilling muds to drill HPHT formations since they can provide high filtration control, good rheological properties and excellent thermal stability (Jianghua, 2012). Moreover, OBMs have always been the most favored type of drilling mud in HPHT drilling. OBMs are very effective to use when HTHP formations are encountered due to their tolerance to high temperature and pressure (Azar and Samuel, 2007). To mention, due to their environmental consideration and high cost, researchers have been trying to develop a new type of water based mud that can almost perform the same functions of OBMs. Lastly, lignosulfonate muds can also be used when high pressure and temperature sections are faced. They have been designed in a way that can tolerate temperatures up to 375F (Kelly, 1983) Environmental Considerations: The impacts of the drilling fluids and the drilled cuttings on the environment have to always be taken into real consideration; however they might be treated properly prior to the drilling process. Different drilling fluids have been prohibited due to their effects on the environment. OBMs have mostly been chosen to perform in different situations, but their environmental impacts have predominantly been their permit restriction. In offshore drilling, SBMs and mineral oil based muds are commonly preferred to OBMs (Azar and Samuel, 2007). SBMs have appeared to be environmentally acceptable because of their low toxicity and better discharge of cuttings compared to OBMs. To add, water base muds are the most environmental friendly type of drilling fluids. Generally, WBM are way more environmentally acceptable compared to high cost OBMs (Bourgoyne Jr et al, 1986). Lastly, environmental considerations have caused the prohibition of salt muds in some Ararat Abdolla 23

39 areas and high chromium treated muds in some others (Bleier, 1990) Makeup Water and its Availability: Makeup water is one of the factors that play a significant role in the selection of a proper mud system required. It is of high consideration to evaluate the chemical composition and the source of the makeup water before choosing the mud system. In addition, the amount of Mg +2, Ca +2, and Cl -1 must be estimated to help choose the most proper mud highly compatible with the chemical composition of the makeup water. Ultimately, the cost of mud treatment can be easily reduced if enough information on the source and availability of the makeup water is available. In offshore, since seawater is the most economical type of water used frequently, the mud should be chosen accordingly (Azar and Samuel, 2007) Cost: Drilling fluids cost has always been a very vital factor that has greatly affected the process of selecting the proper required mud. Water based mud types are generally costeffective, and this makes them become workable in various situations. On the other side, despite their strong advantages, oil based muds (OBMs) have always been characterized to be expensive and costly. This is a disadvantage of OBMs generally that makes them unfeasible in some cases. The cost of OBMs becomes too high when they are formulated from synthetic and mineral base (Amani et al. 2012). Ararat Abdolla 24

40 Chapter Four Research Methodology Proper selection of drilling fluid would affect any undertaken drilling operation positively. Drilling fluids play a very important role in drilling operations, and one should be sufficiently experienced when dealing with drilling fluids. Various drilling fluids are usually used to drill different formation types. The main objective of this project is to analyze the effect of proper selection of drilling fluid on drilling operation. Therefore the following methodology would be utilized to evaluate the objective. In order to make the project stronger and more meaningful, real data of a well in Jambour Oil Field Located in Kirkuk (provided by North Oil Company) are going to be used. It was not easy to get these data, but through diligence I managed to obtain them. The project would have been almost meaningless without having these data. The focus would be on analyzing the mud which was used to drill the second interval (Lower Fars) and also evaluating the overall mud system used to drill the well. Moreover, through lab experiment, Salt Saturated Mud mud would be designed; its properties would be measured and compared with the mud the company has used to drill the second section of the well. The more proper mud between the one used by the company and designed one in the lab would be selected based on the governing factors (discussed in theoretical background) affecting the proper selection of drilling fluids. Lastly, considering the lithology of the interval, some other drilling fluids that could be used to drill such section would be suggested. Ararat Abdolla 25

41 Chapter Five Data Collection and Experimental Work The data to be used in this project were obtained from North Oil Company located in Kirkuk City of Iraq. The data are related to well X (The name and Number of the well to stay confidential), and the focus would be on the second interval of the well. Furthermore, the results of the lab experiment done would be analyzed and compared with the result of the second interval of this well. 5.1 Study Area: Jambour Oil Field is the study area of this project. The collected data are related to a well drilled in this oil field. Jambour is located in Kirkuk City of Iraq. Its latitude and longitude coordinates are and respectively. Figure 5.1: Map of Study Area Ararat Abdolla 26