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WBM & OBM Drilling Fluids.pptx

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WBM & OBM Drilling Fluids.pptx

  1. 1. WBM & OBM Drilling Fluids Function , Classification , Properties , calculations ‫ي‬ ‫ل‬ ‫ح‬ ‫ا‬ ‫س‬ ‫ال‬ ‫د‬ ‫ال‬ ‫خ‬ ‫سد‬ ‫ن‬ ‫ه‬ ‫م‬ ‫ال‬ ‫د‬ ‫ا‬ ‫د‬ ‫ع‬ ‫إ‬ ‫و‬ ‫ميم‬ ‫ص‬ ‫ت‬ 1
  2. 2. Functions of Drilling Fluids 2 You may not know that drilling fluid or mud has several important functions helping us achieve goal to drill well. I would like to share about the functions of drilling fluid as follows; 1. Transport cutting and dispose to surface – The drilling fluid brings the drilled material to the ground surface either by mud rheology and velocity. 2.Clean drill bits – As drilling fluid exits the bit jets, fluid velocity removes cutting from the bit teeth and bit body. This prevents bit ball up situation. 3.Provide hydrostatic pressure to control well while drilling – Hydrostatic pressure provided from drilling fluid is the primary well control. Mud weight should be high enough to control formation pressure while drilling. 4.Prevent excessive mud loss – While drilling, clay particle will form a thin layer over porous zones called “mud cake” or “filter cake”. Mud cake acts as barrier to prevent excessive drilling fluid loss into formation and provides wellbore stability.
  3. 3. Functions of Drilling Fluids 3 5.Prevent formation damage by using reservoir drill-in fluid – While drilling long reach zone in horizontal wells, the special drilling fluid will be utilized in order to prevent formation damage. 6.Provide hydraulic pressure to downhole assembly (BHA) as mud motor, measuring while drilling (MWD), logging while drilling (LWD), etc – Without enough hydraulic power, downhole tool will not be properly operated, hence, drilling fluid plays essential role to provide power to sophisticated downhole tool. 7. Facilitate downhole measurement as open hole logging, MWD, LWD, mud logging, etc – Mud will assist tool to measure everything downhole. 8.Lubricate drill string and BHA and cool the bit. The drill bit and BHA become hot due to friction during the drilling process. When the drilling fluid passes through the bit and exits the jets/nozzles, some extra heat is removed via mud.
  4. 4. Drilling fluids classification 4
  5. 5. Drilling Fluids properties WBM & OBM 5
  6. 6. Mud Weight and Its Importance in Drilling WBM & OBM 6 Mud weight or mud density is a weight of mud per unit volume. It is one of the most important drilling fluid properties because it controls formation pressure and it also helps wellbore stability. Mud weight is measured and reported in pounds per gallon (PPG), pounds per cubic feet (lb/ft3), or grams per milliliter (b/ml). Mud weight is normally measured by a conventional mud balance; however, if you have some air inside a fluid phase, reading from the conventional mud balance will give you an inaccurate number. Therefore, the most accurate method to measure the mud weight is with a pressurized mud balance. The pressurized mud balance looks like the convention one, but it has a pressurized sample cup. When you press a mud sample into the cup, any gas in a fluid phase is compressed to a very small volume so the mud weight measurement is more accurate.
  7. 7. Pressurized Mud Balance Conventional Mud Balance 7
  8. 8. What will happen if there is insufficient drilling fluid density ? 8 Well control The well will be in an underbalanced condition so any formation of fluids – gas, oil, and water- will enter into the wellbore. Wellbore collapse (wellbore instability) Mud weight will provide pressure to hole back formation. If mud weight is too small, wellbore may collapse.
  9. 9. What will happen if the mud weight is too high ? 9 Lost circulation If the hydrostatic pressure from mud column exceeds formation strength, it will cause a formation to break. Once the formation is broken, drilling fluids will be lost into the induced formation fractures. Decrease in rate of penetration Heavier mud weight will result in slower ROP because of hold down effect. Practically, while drilling, low mud weight is used at the beginning and mud weight will be increased , as the well is drilled deeper in order to optimize ROP and mitigate well control. Deferentially Stuck Pipe Since there are differences between formation pressure and hydrostatic pressure, there will be a lot of chances that a drill string will get deferentially stuck across permeable rocks. Formation damage The more mud weight that is in the well, the more mud filtration invades into porous formations. The invaded mud will cause damage to formation rocks.
  10. 10. Hydrostatic and formation pressure 10
  11. 11. Sand Content Kit OBM & WBM A sand content kit is used for measuring the sand content in water based drilling mud or oil based drilling mud, comprising a 200-mesh sieve, a plastic funnel and a graduated glass tube that is calibrated to measure the sand content as a percentage. The 200-mesh sieve is designed to trap particles that are larger than 74 microns, which is much coarser than barite particles. However, the sieve will also trap other coarse particles (e.g. coarse Calcium Carbonate LCM particles), which could distort results if ignored. Every effort must be made to keep sand content as low as possible because it is extremely abrasive and can damage mud pumps and tubulars, as well as causing an undesirable increase in mud density. 11
  12. 12. Viscosity of Drilling Mud WBM & OBM 12 Viscosity describes a substance’s resistance to flow. High-viscosity drilling mud is typically described as “thick,” while low- viscosity mud is characterized as “thin”. In the oilfield , the following terms are used to describe drilling fluid viscosity and rheological properties. Two viscosities that will be described in this section are Funnel Viscosity and Plastic Viscosity.
  13. 13. Funnel Viscosity WBM & OBM The funnel viscosity is timed in seconds of drilling mud flowing through the Marsh Funnel Viscosity. The Marsh funnel is easy- to-use equipment that is used to quickly check viscosity of the mud. The Marsh funnel is dimensioned so that the outflow of time of one quart of freshwater (946 cc) at a temperature of 70 F ± 5 F (21 C ± 3 C) in 26 ± 0.5 seconds. 13
  14. 14. why the viscosity measured from the Marsh Funnel does not represent the true drilling mud viscosity. For all drilling mud, especially oil-based mud, temperate has an effect on the viscosity of a base fluid. The base fluid will be less thick once the temperature increases. It means that the funnel viscosity will decrease. The funnel viscosity measures at only one rate of shear, but the temperature each time of measurement is not constant. This is the reason why the viscosity measured from the Marsh Funnel does not represent the true drilling mud viscosity. On the drilling rig, this measurement of the mud viscosity is still useful because it is a quick and simple test for observing trends of drilling mud. In order to use the funnel viscosity effectively, personnel must record the values frequently. Then looking at a trend of funnel viscosity, it will indicate if there is any issue with drilling mud. Please remember that only a single point of the funnel viscosity cannot tell you anything about a condition of drilling mud. 15
  15. 15. Plastic Viscosity (PV) WBM & OBM Plastic Viscosity (PV) is a resistance of fluid to flow. According to the Bingham plastic model, the PV is the slope of shear stress and shear rate. Typically, the viscometer is utilized to measure shear rates at 600, 300, 200, 100, 6, and 3 revolutions per minute (rpm). In the field , the plastic viscosity can be calculated by a simple calculation shown below. Plastic Viscosity (PV) = Reading at 600 rpm – Reading at 300 rpm The unit of PV is Centi Poise (CP). For example determine PV from these reading values from a viscometer. Reading at 600 rpm = 56 Reading at 300 rpm = 35 Plastic Viscosity (PV) = 56 – 35 = 21 CP 15
  16. 16. Plastic Viscosity (PV) WBM & OBM 16 Any increase in solid content in drilling mud such as barite, drill solid, lost circulation material, etc., will result in higher plastic viscosity. In order to lower the plastic viscosity, solid content must be removed and it can be achieved by using solid control equipment and/or diluting drilling mud with base fluid. Fluid temperature will increase while drilling deeper therefore plastic viscosity of drilling mud will decrease because the viscosity of the base fluid decreases. Normally, the higher the mud weight, the higher plastic viscosity will be. However, if there is an increasing trend of plastic viscosity with constant mud weight, it means that there is an increase in drill solid content in a mud system. Moreover, if oil based mud is used, please keep in mind that water in oil based drilling fluid will act like a solid, and it will increase the plastic viscosity dramatically. It is very critical to ensure that amount of water in oil based mud is within the designed limit.
  17. 17. Several impacts of plastic viscosity on drilling operation are as follows; Equivalent Circulating Density (ECD) The more PV you have, the higher the ECD will be. Surge and Swab Pressure The PV has the same effect as ECD. If the PV increases, surge and swab pressure will also increase. Differential Sticking A chance for differential sticking will increase, especially in water based mud, when the plastic viscosity increases because of increases in solid content. Rate of Penetration (ROP) The ROP will be directly affected by the plastic viscosity. Thicker mud will have bigger hold down effect than thinner mud. Therefore, it causes in reduction in ROP. 17
  18. 18. Yield point WBM & OBM Yield Point (YP) is resistance of initial flow of fluid or the stress required in order to move the fluid. It can be simply stated that the Yield Point (YP) is the attractive force among colloidal particles in drilling fluid. As per Bingham plastic model, YP is the shear stress extrapolated to a shear rate of zero. Yield point can be calculated by the following formula. Yield Point (YP) = Reading at 300 rpm – Plastic Viscosity (PV) A unit of YP is lb/100 ft2. You can determine the Plastic Viscosity (PV) by this formula. Plastic Viscosity (PV) = Reading at 600 rpm – Reading at 300 rpm 18
  19. 19. Example 19 you have these values from the viscometer. Reading at 600 rpm = 56 Reading at 300 rpm = 35 Plastic Viscosity (PV) = 56 – 35 = 21 CP Yield Point (YP) = 35 – 21 = 14 lb/100 ft2 The YP indicates the ability of the drilling mud to carry cuttings to the surface. Moreover, frictional pressure loss is directly related to the YP. Higher YP will result in larger frictional pressure loss.
  20. 20. For water base mud , the YP will be increased with the following items 20 High temperature the high temperature environment tends to increase the YP in the water based mud. Contaminants such as carbon dioxide, salt, and anhydrite in the drilling fluids Over treatment of the drilling mud with lime or caustic soda
  21. 21. For oil based mud, the causes of increasing in YP are listed below; ‫ي‬ ‫ل‬ ‫ح‬ ‫ا‬ ‫س‬ ‫ال‬ ‫د‬ ‫ال‬ ‫خ‬ ‫سد‬ ‫ن‬ ‫ه‬ ‫م‬ ‫ال‬ ‫د‬ ‫ا‬ ‫د‬ ‫ع‬ ‫إ‬ ‫و‬ ‫ميم‬ ‫ص‬ ‫ت‬ 21 Drill solid the more drill solid you have, the more the YP will be. Treatment CO2 in the mud with lime (CaO) The lime (CaO) will chemically react with CO2 to form Calcium Carbonate (CaCO3) which will increase the YP. Low temperature in the oil based system, the low temperate will increase the viscosity and the YP. Please keep in mind that this is opposite to the water based system.
  22. 22. Operational impacts of the YP are as follows; 22 Equivalent Circulating Density (ECD) The ECD typically increases when the YP increases. Hole Cleaning Usually the larger diameter hole to be drilled, the higher the YP must be to support efficient hole cleaning.
  23. 23. Gel Strength and Operational Impact WBM & OBM 23 The gel strength is the shear stress of drilling mud that is measured at a low shear rate after the drilling mud has been static for a certain period of time. The gel strength is one of the most important drilling fluid properties because it demonstrates the ability of the drilling mud to suspend drill solid and weighting material when circulation is ceased.
  24. 24. How can gel strength is measured? 24 Gel strength measurement is made on viscometer using the 3-rpm reading, which will be recorded after stirring the drilling fluid at 600 rpm to break gel. The first reading is noted after the mud is in a static condition for 10 seconds. The second reading and the third reading will be 10 minutes and 30 minutes, respectively.
  25. 25. Why do we need to record the 3-rpm reading after 30 minutes? 25 The reason is that the 30 minute-reading will tell us whether the mud will significantly form the gel during extensive static periods like tripping out BHA or not. If the mud has high gel strength, it will create a high pump pressure in order to break circulation after the mud is static for a long time. Furthermore, increasing in a trend of 30-minute gel strength indicates a buildup of an ultra-fine solid. Therefore, the mud must be treated by adding chemicals or diluting it with fresh base fluid.
  26. 26. Causes of Increasing in Gel Strength of Water Based Mud 26 The following causes will lead to high gel strength in the water based mud. • Bacteria • Ultra fine solid • Salt • Chemical contamination such as lime, gypsum, cement, and anhydrite • Acid gases such as Carbon Dioxide (CO2), and Hydrogen Sulphide (H2S)
  27. 27. Causes of Increasing in Gel Strength of Oil Based Mud 27 For an oil based drilling fluid, there are several points that will cause high gel strength in the mud system as follows. • Over treatment with organic gelling material • Build up of fine solid particles in the mud
  28. 28. Operational Impact of Excessive Gel Strength 28 Circulating Pressure Excessive gel strength will lead to high pump initiation pressure to break circulation after mud is in a static condition for a period of time. High pump pressure may result in formation fracture and lost circulation. Cutting Suspension Low gel strength indicates inability to suspend cuttings. It can lead to pipe stuck and hole pack off due to insufficient cutting suspension. Barite Sag Barite sag is a situation where barite cannot be suspended by drilling mud because of low gel strength. It can be seen that when large fluctuation of mud density coming out of hole.
  29. 29. Apparent viscosity WBM & OBM 29 The viscosity of a fluid measured at the shear rate specified by API. In the Bingham plastic rheology model, apparent viscosity (AV) is one-half of the dial reading at 600 rpm (1,022 sec–1 shear rate) using a direct- indicating, rotational viscometer. For example, a 600-rpm dial reading is 50 and the AV is 50/2, or 25 cP.
  30. 30. API Fluid Loss Test WBM API Fluid Loss Test (low-pressure, low-temperature filtration test) is a test used to measure a filtration of mud with ambient temperature and 100 psi differential pressure. The API fluid loss testing equipment is shown Figure How will the drilling mud be tested? Place a filter Add the sample into the testing chamber Place the chamber in the testing kit Apply 100 psi pressure Record volume for 30 minutes; at the end of the test the volume of filtrate will be recorded. Record thickness of filter cake 30
  31. 31. Filtration 31 If drilling fluid has good fluid loss property, it will show a thin and impermeable mud cake. Please keep in mind that this test is based on the surface condition, and it may be in error because it does not simulate down hole conditions. The API fluid loss test can lead you to the wrong conclusion, because at the surface condition the test demonstrates very good fluid loss and a very thin filter cake. When the drilling mud is in a downhole condition, wellbore temperature and pressure can dramatically change drilling fluid properties . The best way to test the fluid loss is to simulate wellbore condition at high pressure high temperature in order to see what the fluid loss property will be. The procedure is called” HTHP Fluid Loss.”
  32. 32. 32
  33. 33. HTHP Fluid Loss Test WBM & OBM The HTHP fluid loss test is similar to the API test because it indicates information on drilling mud filtration into the formation under a static condition over a certain period of time . For the HTHP fluid test, both temperature and pressure can be varied to represent an expected downhole condition. The HTHP testing equipment has a heating jacket so you can heat up the drilling fluid sample to the expected wellbore temperature. Typically, the recommended temperature in the heating jacket should be above the estimated temperate of about 25 F to 50 F. The test pressure is normally at 500 psi differential pressure. Normal test conditions are 150 F and 500 psi differential pressure and the maximum allowable test temperature is 300 F with the standard equipment. Mud filter cake thickness must be maintained below 2 mm. The HTHP test is performed for 30 minutes, just like the API fluid lost test. 33
  34. 34. Drilling Operational Impacts of Fluid Loss 34 Formation damage If the drilling mud does not have good fluid loss property, fluid with small particles in the drilling mud can be invaded into formations and it will cause formation damage. This will directly affect the production rate of the well once it starts producing. Differential sticking The drilling fluid that has bad fluid loss will form a very soft and thick mud cake across permeable formations. This can lead to differential sticking because of an increase in the contact area between formation and drill string. Torque and drag A thick mud cake across porous zones can be easily formed because the drilling mud has high fluid loss values. The thicker the mud cake is, the more torque and drag are experienced while performing the drilling and tripping operations.
  35. 35. Mud Filter Cake WBM & OBM Mud filter cake is a layer formed by solid particles in drilling mud against porous zones due to differential pressure between hydrostatic pressure and formation pressure. For the drilling operation, it is preferred to have a filter cake that is impermeable and thin. Practically, the filter cake from API or HTHP fluid loss test should be less than or equal to 1/16 inch. If drilling fluid is not in a good shape, which results in a thick filter cake in the wellbore, it will lead to a stuck pipe situation and high torque/drag. 35
  36. 36. How will the filter cake impact on a drilling operation? 36 Differential sticking If mud filter cake is thick, a contact area between drilling string or any kind of tubular will be increased. When drilling into permeable zones that are severely overbalanced, the drill stem will have high chance to get differentially stuck across these zones. Moreover, not only can the drilling string get stuck, the logging tool could be stuck across the permeable sands as well. Torque and drag Under dynamic conditions such as drilling, working pipe, etc., if drilling mud has a thick filter cake across the wall of the wellbore, torque will increase. Furthermore, a thick wall filter cake will result in high drag while tripping out of the hole or logging.
  37. 37. 37
  38. 38. Solid Content in Drill Mud WBM & OBM Solid content is a fraction of the total solid in drilling mud, and it always increases while drilling ahead because of drilling solid (cuttings), mud chemical additives and weighting material. Solid content refers to soluble and insoluble solid content in the drilling fluid system. There are three types of solid contents as listed below; Soluble material such as salt Insoluble high gravity solid (HGS) such as weighting agents (barite, calcium carbonate, hematite, etc.) Insoluble low gravity solid (LGS) or drilled solid such as solids particles from‫ل‬ ‫ي‬ c‫ا‬ ‫ح‬ u‫ال‬ ‫س‬ t‫د‬ t‫خ‬ ‫ال‬ in‫س‬ g‫ه‬ ‫ن‬ ‫د‬ s ‫ال‬ ‫م‬ ‫دادعإ‬ ‫و‬ ‫ت‬ ‫ص‬ ‫م‬ ‫ي‬ ‫م‬ 39
  39. 39. Solid content 39 The drill solids are the worst solid content in the drilling fluid because it gradually deteriorates mud properties. Moreover, if its particle size is less than 5 microns, these drill solids cannot be removed by mechanical methods, and they will stay in the mud forever. Generally, the drill solids will take up 6-7 percent of the total mud volume. Since the drilled solid content is very important, it must be checked daily. For good drilling practices, the drilled solid should be tested twice a day by retorting. The upper limit of the drill solid faction should be 6-7 % by volume or approximately 55 – 60 lb/bbl. Another critical value besides low gravity solid (LGS) and high gravity solid (HGS) is the average density of weighting materials in drilling fluid. The weighting materials such as Barite, Calcium Carbonate, Hematite, etc., have a specific gravity above 2.7. Table 1 demonstrates some important specific gravity of weighting materials. However, the drilled solids usually have a specific gravity about 2.6. Hence, drill solids will reduce average solid density when mixed in the drilling fluid. Normally, the acceptable value of the average solid density is about 3.8 or higher. If this value is below 3.8, it indicates that there may be too much low gravity solid in the mud.
  40. 40. Retort Retort 50 ml Retort 10 ml 40
  41. 41. The operational impacts of solid content Equivalent Circulating Density (ECD) ECD will be higher if the solid content increases. Excessive ECD will lead to formation fracture and a loss circulation issue. Differential Sticking The filter cake will be thick and sticky, if there are a lot of low gravity solids in the drilling mud. Due to this reason, the potential of getting deferentially stuck across permeable formations is increased. Rate of penetration High concentration of the solid content will reduce the overall rate of penetration. There are three solid contents added into the system. The first two contents are weighting material and chemicals which are needed to maintain good mud properties. The last one is the drill solid which can be controlled by mechanical methods. If the drill solid content is not controlled properly, drilling performance will decrease. Surge/swab pressure The excessive surge and swab pressures result from the high amount of solid contents in the fluid system. 41
  42. 42. What is the difference between drill solids and barite? 42 Drill Solid: It is solid particles from formation generated while drilling. Its specific gravity is about 2.6 which is normally defined as Low Gravity Solid (LGS). Drill solid can increase mud weight; however, it will degrade mud properties such as Yield Point, viscosity, gel strength, etc. If mud excessively gets drill solid, drilling fluid properties especially rheology (Yield Point, viscosity) will be higher and mud cake with a lot of drill solid will be poor quality. Higher rheology will lead to more required energy in order to make circulation. In addition, poor mud cake can also lead to pipe struck situation. In order to control drill solid content in mud, solid control equipment as shale shakers, desanders, desilters and centrifuges must be operated properly and effectively. Barite: It is the weighting agent with specific gravity about 4.2 normally called High Gravity Solid HGS . Both Drill solid and Barite are able to be weighting agent; however, Barite does not degrade other mud properties such as PV, YP, gel strength, etc.
  43. 43. Alkalinity WBM pH is a value representing the hydrogen ion concentration in liquid and it is used to indicate acidity or alkalinity of drilling mud. The pH is presented in a numerical value (0-14), which means an inverse measurement of hydrogen concentration in the fluid. The pH formula is listed below; pH = -log10[H] Where: H is the hydrogen ion concentration in mol. According to the pH formula, the more hydrogen atoms present, the more acidity of substance is but the pH valve decreases. Generally speaking, a pH of 7 means neutral. Fluids with a pH above 7 are considered as being alkaline. On the other hand , the fluids with pH below 7 are defined as being acidic. In the drilling mud, there are three main chemical components involved in Alkalinity of drilling fluid, which are bicarbonate ions (HCO –) , hydroxyl ions (OH–) 3 and The Alkalinity means ions that will reduce the acidity. In order to get accurate measurements for the pH, using a pH meter instead of using a pH paper is recommended because it will give more accurate pH figures. Additionally, pH meters must be calibrated fr eq ‫ي‬ u ‫ح‬ ‫ل‬ e ‫س‬ ‫ا‬ n ‫ال‬ ‫د‬ t ‫ل‬ l ‫اخ‬ y. ‫نهمال‬‫د‬‫س‬ ‫دادعإ‬ ‫و‬ ‫ت‬ ‫ص‬ ‫م‬ ‫ي‬ ‫م‬ 44
  44. 44. pH in Drilling Mud (Water Based Mud) pH strips pH meter 44
  45. 45. Cause of a decrease in pH of drilling Mud 45 There are many factors that can cause reduction in pH of drilling mud as listed below; Water contamination The water contamination or water influx will decrease pH in the drilling fluid because water is neutral. Carbonate or Bicarbonate With these two chemical molecules, the pH of drilling mud will be reduced. Acid gases as Carbon dioxide (CO2) and Sulphur Dioxide (H2S) If there are acid gases mixing in the system, the pH will decrease. Additionally, acid gas has bad effect on mud properties. The rheology of the mud as PV, YP, and gel strength will increase, but Pm and Pf will decrease due to loss of pH. Anhydrite Chemical components of Anhydrite will neutralize hydrogen ions in the mud so pH of drilling mud will drop. It is important to increase mud pH while drilling Anhydrite formation.
  46. 46. Pm = phenolphthalein of mud WBM 46 Pm stands for “phenolphthalein end point of the mud” and it indicates quantities of Potassium Hydroxide (KOH), caustic soda, cement, etc., in the water base mud. The Pm refers to the amount of acid required to reduce the pH of mud to 8.3. The Pm test includes the effect of both dissolved and non-dissolved bases and salts in drilling fluid. Especially in lime mud, Pm is used to determine the ratio of insoluble lime to soluble lime in the filtrate.
  47. 47. Pf = phenolphthalein of filtrate WBM 47 Pf stands for the phenolphthalein alkalinity of the mud filtrate. Pf is different from the Pm because it tests the affect of only dissolved bases and salts. However, Pm includes the effect of both dissolved and non-dissolved bases and salts in drilling mud.
  48. 48. Mf = methyl orange of filtrate WBM 48 Mf stands for the methyl orange alkalinity end point of mud filtrate and the definition of the methyl orange alkalinity is the amount acid used to reduce the pH to 4.3. According to the API test, Pm, Pf and Mf are shown in a daily mud report and all the figures are reported in cubic centimeters of 0.02N sulfuric acid per cubic centimeter of drilling fluid sample.
  49. 49. Alkalinity cases 49 Pf and Mf are based on the mud filtrate tests that will help people know about ions in the drilling mud. There are three cases regarding Pf and Mf. First case: Pf and Mf are similar in value to each other. It indicates that the ions (hydroxyl ions) are the main contributor to the mud alkalinity. Second case: If Pf is low but the Mf is high, it indicates that bicarbonate ions are in the mud. Third case: if both figures (Pf and Mf) are high, it means that carbonate ions are in the mud system.
  50. 50. Total Hardness Content in WBM & OBM “Total Hardness” or “Water Hardness” is a measurement of calcium (Ca2+) and magnesium (Mg 2+) ions in water base mud and oil base mud .The total of both soluble ions of calcium (Ca2+) and magnesium (Mg 2+) is given by titration with standard Versenate solution. 50
  51. 51. What will be happening if you have a lot of total hardness in your drilling mud? • Bad mud cake (thick and mushy) • High fluid loss • Flocculation of clay content • Less polymer effectiveness • Ineffective chemical treatment For most of the water base mud, the acceptable value of total hardness must be below 300 mg/L. If the lime drilling mud is used, it is acceptable to have a higher value but is should be kept below 400 mg/L. 51
  52. 52. Chloride Content in WBM 52 The chloride comes from salt in the formation, and chloride concentration can be determined by titration with a silver nitrate solution .The amount of chloride must be checked frequently . If there are any abnormal changes in the chloride content, it can be an indication of drilling into a salt formation or taking water influx from drilled formations Why is it so important to maintain the amount of chloride in the drilling fluids? The chloride is used to prevent a shale swelling problem. How can the chloride content be maintained? The chloride content in the drilling fluid can be maintained by adding salts such as potassium chloride (KCl) and sodium chloride (NaCl). If potassium chloride (KCl) is used, it is imperative to have sufficient potassium ions to react with the clay content from the formation. Generally, 3 – 4% KCL is recommended for normal drilling. However, it may require increasing the concentration of KCl if you are drilling into formations which have a lot of reactive clay content.
  53. 53. Potassium Ion & KCL In Drilling Fluid Test It is important to monitor and control the Potassium ion concentration for Water Based Mud systems that use Potassium for Shale Inhibition because it will deplete as it is adsorbed onto shales . Depletion needs to be monitored and effective inhibition levels need to be maintained in the mud system. The Potassium ion concentration is determined by adding excess Sodium Perchlorate to a measured volume of mud filtrate to precipitate out Potassium Perchlorate. The precipitate is then centrifuged and the volume of the compacted precipitate is converted to Potassium ion concentration by reference to a calibration curve, which must be prepared using the test reagents at the rig site (see overleaf). 53
  54. 54. Glycol Concentration Test in WBM Glycol is generally used in KCl-Polymer fluid systems when enhanced Shale Inhibition is required. Glycol will be lost through adsorption on exposed shale formations in the wellbore and on the cuttings, and the glycol depletion rate will be a function of drilling Penetration Rate (ROP) and Cuttings size. The glycol concentration test in drilling mud ( Refractometer ) therefore needs to be monitored to ensure that levels are maintained for effective shale inhibition. 54
  55. 55. Methylene Blue Test (MBT) WBM Methylene Blue Test (MBT) or Cation Exchange Capacity is used to determine the amount of reactive clay (clay-like materials) in a water base mud. A methylene blue dye (a cation dye) is utilized for this test because it powerfully magnetizes the negative ions in the clay . Typically, the test is reported in terms of the reactive clay concentration in pounds per barrel, bentonite equivalent. Same as other mud properties, tracking the MBT and observed for trend changes are required in order to maintain good mud conditions. If an increase in MBT is observed, it indicates that the drill solid concentration in the drilling mud increases. For a good drilling operation, the MBT should be kept at 15 lb/barrel or less. 56
  56. 56. Water Phase Salinity of OBM Water phase salinity WPS is a factor showing the activity level of salt in oil based mud. In order to control the water phase salinity, salt is added into the drilling fluid. The salt added into the system will be dissolved by water in the mud; therefore, the chloride content will increase. By increasing the chloride concentration (adding salt), the activity level in the mud will decrease. Salt is added in order to create an activity level which is equal to or less than formation water. Therefore, the water phase in the mud will not move into formation and cause a clay swelling issue. Practically, calcium chloride (CaCl2) or sodium chloride (NaCl) is the chemical to be used. 56
  57. 57. When salt must be added into the mud system? Typically, while drilling with oil based mud, cuttings are generally dry, hard, and easy to break into pieces. However, if the cuttings come together in big pieces and are wet, it may increase salt content in the drilling fluid. The reason is that water in the mud moves into formations and swells the clay particles in the formation. Swelled clay causes wet and mushy cuttings. 57
  58. 58. Functions and Importance of Electrical Stability of Oil Based Mud The Electrical Stability (ES) is one of the vital properties for oil based mud. It shows the voltage of the current flowing in the mud. The ES number represents the mud emulsion stability. The more ES is; the more the emulsion stability is. Oil based fluid is a non-conductive material. Therefore, the base fluid will not transfer any current. Only the water phase in the mud will conduct the electricity. If the mud has good emulsion, you will have high ES figures. On the other hand, if the emulsion of the mud is bad, you will have low ES value. The Electrical Stability (ES) is obtained from an electrical stability tester kit as in the figure There are several factors that can weaken the emulsion, such as oil/water ratio, solid content, pressure, temperature, some types of weighting material, etc 59
  59. 59. What the Electrical Stability (ES) will tell us? 59 If ES is lower than a normal mud specification, it indicates that there is something unusual in the mud such as water or salts, which will make emulsion of the oil based mud in bad shape. Moreover, the ES can be utilized to determine an interface between water and oil based mud while displacing water with oil based fluid. For good drilling practices, it is required to frequently monitor the ES level and watch for any unusual changes. Changes in the ES can be seen while drilling into green cement or while adding any conductive material as stated earlier. These known factors affecting the ES must be noted in order to prevent any confusion when interpreting the mud’s property.
  60. 60. Alkalinity Excess Lime (Oil Based Mud Properties) For most of oil based mud, lime (Ca(OH)2) is used in the system in order to perform a chemical reaction with fatty acid emulsifiers. Typically, 3 to 5 lb/bbl of lime is added in the drilling mud so that there is enough hydroxide (OH-1) ions to keep the emulsion stability in good shape. Moreover, lime (Ca(OH)2) will control acid gases such as H2S and CO2. The following chemical equations demonstrate how lime reacts with H2S and CO2, respectively. Ca(OH)2 + H2S -> CaS + 2(H2O) Ca(OH)2 + CO2 -> CaCO3 + H2O 60
  61. 61. Calculate Oil-Water Ratio from Retort Data Oil Water Ratio (OWR) is a figure representing the fraction of oil and water in oil based drilling mud. Generally speaking, it is a ratio between the percent oil in liquid phase and the percent water in liquid phase. In order to determine OWR, volume of oil/water/solid in drilling mud comes from a retort analysis. A sample of oil based mud is controlled burnt in a retort kit at required temperature. When the mud is heated, water and oil will be extracted out and solid is left in the retort kit. The retort analysis report shows percentage of each component by volume so we use data from the retort analysis to determine oil water ratio. 61
  62. 62. how to calculate oil water ratio from retort data. 62 a) % oil in liquid phase = (% by volume oil x 100) / (% by volume oil + % by volume water) b) % water in liquid phase = (% by volume water x 100) ÷ (% by volume oil + % by volume water) c)Result: The oil/water ratio equals to the percent oil in liquid phase and the percent water in liquid phase.
  63. 63. Example 63 Determine oil water ratio from following information Data from a retort analysis: % by volume oil = 56 % by volume water = 14 % by volume solids = 30 Solution: a) % oil in liquid phase = (56 x 100) ÷ (56+14) % oil in liquid phase = 80 b) % water in liquid phase = (14 x 100) ÷ (56+14) % water in liquid phase = 20 c) According to this retort report, the oil/water ratio equals to 80/20.