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Rheological study of a water based oil well drilling fluid
Journal of Petroleum Science and Engineering 45 (2004) 123 – 128 www.elsevier.com/locate/petrol
Rheological study of a water based oil well drilling fluid Vikas Mahto, V.P. Sharma * Department of Petroleum Engineering, Indian School of Mines, Dhanbad-826004, Jharkhand, India Received 26 May 2003; accepted 30 March 2004
Abstract Organic polymers are commonly used to control the rheology and filtrate loss required for water-based drilling fluids. An ecologically-friendly water-based drilling fluid was developed by studying the rheological behavior of tamarind gum and polyanionic cellulose on bentonite water suspensions. The effect of drilling fluid filtrate on formation damage was also analyzed. The drilling fluid that was developed has better rheological properties and fluid loss control which are required for optimum performance of oil well drilling. In addition, the drilling fluid filtrate exhibits minimum formation damage on sandstone cores. D 2004 Elsevier B.V. All rights reserved. Keywords: Bentonite; Rheology; Formation damage; Polymer; Gel strength; Tamarind gum
1. Introduction The tamarind gum (from the tamarind tree, a most common tree in India) is a low cost viscosity modifier and may be used in drilling fluid formulation. The tamarind gum is a white to creamy, free flowing, powder. It has almost same the viscosity as guar gum at the same concentration in water, and it is seven times cheaper than guar gum (Khoja and Halbe, 2001). Chemically, it is a highly branched carbohydrate polymer. Its backbone consists of D-glucose units joined with (1 –4)h linkages similar to that of cellulose. It consists of a main chain of h-D(1– 4)-
* Corresponding author. Tel.: +91-326-220-6232; fax: +91-326220-6319. E-mail addresses: [email protected], [email protected] (V.P. Sharma). 0920-4105/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.petrol.2004.03.008
galactopyranosyl units with a side chain of a single xylopyranosyl unit attached to every second, third and fourth D-glucopyranosyl unit through an a-D(1 – 6) linkage. One galactopyranosyl unit is attached to one of the xylopyranosyl units through a h-D(1 –2) linkage (Parija et al., 2001). The polyanionic cellulose (PAC) is used as a fluid loss reducer for fresh water and salt-water muds, but it also acts as viscosity modifier in these systems (Bruton et al., 2000). PAC is available in two types (high or low viscosity grade), both of which impart the same degree of fluid loss control but different degrees of viscosity. The temperature stability of PAC is 149 jC (Plank, 1992) and is not subjected to bacterial degradation (Lummus and Azar, 1986). The bentonite clay used in drilling fluid is montmorillonite (Chilingarian and Vorabutr, 1983). It is added to fresh water to: (1) increase the hole cleaning properties, (2) reduce water seepage or filtration into
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permeable formation, (3) form a thin filter cake of low permeability, (4) promote hole stability in poorly cemented formations and (5) avoid or overcome loss of circulation. The high clay solids content of drilling fluid has several adverse effects: (1) greatly reduces the rate of penetration (Gatlin, 1960), (2) increased chances of differential sticking and (3) is the major cause of excessive torque and drag. Thus, low bentonite content is desired to control the total amount of solids. At low concentration, bentonite clay is unable to provide satisfactory rheological properties required for optimum performance in oil well drilling. Hence, polymers are added to achieve the desired result. Formation damage is the reduction of permeability near the well bore that results in a decrease of productivity/injectivity of an oil or gas well. It is caused by the invasion of foreign fluids and/or solids in the exposed section near the well bore. One of the basic functions of the drilling fluid is control of possible flow outs when high subsurface pressure is encountered thus the mud column pressure must exceed the formation pressure. As a result, the mud solids and filtrate enter the formation and cause damage (Jilani et al., 2002). The water based drilling fluid using organic polymers are safe and should be designed to minimize the amounts of solids and fluid invasion into the formation.
2. Experimental 2.1. Materials Three bentonite clay samples were obtained from the Kutch region, Gujarat, India. The tamarind gum was procured from Saiguru Food Industries, Mumbai and high viscosity polyanionic cellulose was obtained Table 1 Physico-chemical properties of bentonite clay samples Sample no.
A111 B222 C333
Properties Cation exchange capacity (meq./ 100 g clay)
Yield of clay (m3/ton clay)
Swelling index
81.66 80.0 83.33
8.6345 10 3 10.44 10 3 9.912 10 3
3.5 3.9 3.7
Table 2 Effect of concentration of bentonite (A111) on rheological properties of bentonite (A111) – water suspension Conc. of Apparent Plastic Yield Gelin Gel10 yp/lp bentonite viscosity viscosity point (N/m2) (N/m2) (s 1) (g/l) (cP) (cP) (N/m2) 10 20 30 40 50
1.25 1.5 2 2.25 3.25
1 1 1 1 2
0.25 0.5 1 1.25 1.25
0.25 0.375 0.5 0.5 0.5
0.25 0.75 1 1 1.125
500 1000 2000 2500 1250
from an oil field operation. The sandstone cores (sample no. 1: length = 2 cm, breadth = 1.8 cm; sample no. 2: length = 2.35 cm, breadth = 2.0 cm; sample no. 3: length = 1.4 cm, breadth = 1.8 cm) were selected from western Indian oil producing fields. 2.2. Experimental procedures The bentonite clay samples were dried by exposure to the sun for a few days. They were then crushed and screened through 200-mesh size sieve (0.074 mm). The samples were dried in an air oven at 100 F 2 jC. Initially, the swelling index (Mishra et al., 1985), yield of clay (Chilingarian and Vorabutr, 1983) and cation exchange capacity (Chilingarian and Vorabutr, 1983) of the clays were determined. Bentonite water suspensions were then prepared at different compositions and rheological properties (apparent viscosity, plastic viscosity, initial gel strength and 10 min gel strength) were measured. Then, an ideal bentonite concentration was chosen. These properties were again measured by adding ecologically-friendly organic polymers. Subsequently, the three most favourable mud systems were prepared from these three different clay suspensions and the drilling fluid combinations were hot rolled in a roller oven for 16 h to measure temperature stability. These muds were filtered through Whatman No. 50 filter paper using API fluid loss apparatus (Chilingarian and Vorabutr, 1983), then the filtrate obtained was used for formation damage studies. The formation damage studies were based on permeability reduction in a sand stone oil field core and experimental work was conducted using a Ruska Liquid Permeameter. The procedure adopted was to determine the permeability of filtrate and distilled water in core samples.
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Table 3 Effect of concentration of bentonite (B222) on rheological properties of bentonite (B222) – water suspension
Table 5 Rheological properties of 30 g/l (3% w/v) of bentonite clay – water suspension
Conc. of Apparent Plastic Yield Gelin Gel10 yp/lp bentonite viscosity viscosity point (N/m2) (N/m2) (s 1) (g/l) (cP) (cP) (N/m2)
Properties
Sample no. A111
B222
C333
Apparent viscosity (cP) Plastic viscosity (cP) Yield point (N/m2) Initial gel strength (N/m2) 10 min gel strength (N/m2)
2 1 1 0.5 1
2.5 1 1.5 0.5 1
2 1 1 0.5 1
10 20 30 40 50
1.5 2 2.5 2.75 3.75
1 1 1 1 2
0.5 1 1.5 1.75 1.75
0.375 0.5 0.5 0.5 0.5
0.5 0.75 2 2 2.5
1000 2000 3000 3500 1250
The apparent viscosity, plastic viscosity and yield point were calculated from 300 and 600 rpm readings using following formulas from API Recommended practice of Standard procedure for field testing drilling fluids (Recommended Practice, 1988): Apparent viscosity ðla Þ ¼ U600 =2 ðcPÞ Plastic viscosity ðlp Þ ¼ U600 U300 ðcPÞ Yield point ðyp Þ ¼ U300 lp 0:5 N=m2 ðlb=100 ft2 Þ
interlayer space and cause swelling of bentonite. The behaviour of bentonite water suspension is complex due to unisometric clay particles exposing different crystal faces, on which an electrical double layer can develop, which differs both in sign and the magnitude of the total surface potential (Singh and Sharma, 1997; Gungor, 2000). Consequently, the rheological characteristics in these suspensions are achieved by clay particle – clay particle and clay particle – water suspension. Table 5 summarizes the rheological properties of 30 g/l bentonite concentrations (3% w/v) in water with
Table 6 Effect of conc. of tamarind gum on rheological properties of 30 g/ l (3% w/v) of bentonite – water suspension (A111)
3. Results and discussion The swelling index, yield of clay and cation exchange capacity of the clays are listed in Table 1. The rheological properties of the bentonite water system at different clay concentrations were tabulated in Tables 2– 4. The bentonite clay consists of superimposed layers composed of two Si– O tetrahedral sheets framing an Al – O – OH octahedral sheet. In aqueous dispersion, water can penetrate into the
Conc. of Apparent Plastic Yield Gel10 yp/lp Gelin tamarind viscosity viscosity point (N/m2) (N/m2) (s 1) gum (g/l) (cP) (cP) (N/m2) 0.5 1 1.5 2 2.5
6.5 11.5 20 25 28.5
3.5 6 9 10 10
3 5.5 11 15 18.5
1.5 2 4.5 6 6.5
2.5 3 5.5 7 7
1710 1833 2400 3000 3700
Table 4 Effect of concentration of bentonite (C333) on rheological properties of bentonite (C333) – water suspension
Table 7 Effect of conc. of tamarind gum on rheological properties of 30 g/ l (3% w/v) of bentonite water suspension (B222)
Conc. of Apparent Plastic Yield Gel10 yp/lp Gelin bentonite viscosity viscosity point (N/m2) (N/m2) (s 1) (g/l) (cP) (cP) (N/m2)
Conc. of Apparent Plastic Yield Gel10 yp/lp Gelin tamarind viscosity viscosity point (N/m2) (N/m2) (s 1) gum (g/l) (cP) (cP) (N/m2)
10 20 30 40 50
0.5 1 1.5 2 2.5
1.25 1.5 2 2.5 3.5
1 1 1 1 2
0.25 0.5 1 1.5 1.5
0.375 0.5 0.5 0.5 0.5
0.5 1 1 1 1.25
500 1000 2000 3000 1500
6 11 14 21 23
3.5 6 7 9 9
2.5 5 7 12 14
1.5 2.5 3 5 5.5
2.5 3.5 4 6 6.5
1430 1660 2000 2660 3110
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Table 8 Effect of conc. of tamarind gum on rheological properties of 30 g/ l (3% w/v) bentonite – water suspension (C333)
Table 11 Effect of conc. of PAC on rheological properties of 30 g/l (3% w/v) of bentonite – water suspension (C333)
Conc. of Apparent Plastic Yield Gelin Gel10 yp/lp tamarind viscosity viscosity point (N/m2) (N/m2) (s 1) gum (g/l) (cP) (cP) (N/m2)
Conc. of Apparent Plastic Yield point Gelin Gel10 yp/lp PAC (g/l) viscosity viscosity (N/m2) (N/m2) (N/m2) (s 1) (cP) (cP)
0.5 1 1.5 2 2.5
1 2 3 4 5
7 11.5 15.5 18.5 21
4 6 7 7 8
3 5.5 8.5 11.5 13
1.5 2.5 3 4.5 5.5
3 3.5 4.5 5.5 6
1500 1830 2420 3280 3250
these clays. The 40 g/l bentonite concentrations (4% w/v) in water (Tables 2 – 4) shows a slight increase in apparent viscosity and yield point but there is no increase in plastic viscosity and gel strength. Because the solids content should be less for effective control of total solids in drilling fluid, 30 g/l bentonite (3% w/ v) concentration was selected for further study; 3% also is the normal concentration used in oil fields for drilling (Park et al., 1960; Elward-Berry and Darby, 1997). The rheological properties of bentonite at 3% conc. require further adjustment; thus, tamarind gum and PAC polymer were added.
9.5 16.5 23 31.5 41
7 11 13 17 20
2.5 5.5 10 14.5 21
1.25 2 3.5 6.5 8.5
5.5 11.5 16 22.5 27.5
710 1000 1538 1700 2100
3.1. Effect of tamarind gum The effect of tamarind gum on the rheological properties is shown in Tables 6 – 8 . Since the tamarind gum is a carbohydrate polymer (Parija et al., 2001; Whistler and Bemiller, 1973) and it consists mainly hydroxyl groups; the increase in apparent viscosity, plastic viscosity, yield point, yield point/plastic viscosity ratio, initial gel strength and 10 min gel strength with increase of the concentration of tamarind gum may be due to hydrogen bonding of hydroxyl group of tamarind gum with clay.
Table 9 Effect of conc. of PAC on rheological properties of 30 g/l (3% w/v) of bentonite – water suspension (A111)
Table 12 Effect of conc. of tamarind gum on rheological properties of 1 g PAC and 30 g bentonite/l of bentonite – water suspension (A111)
Conc. of Apparent Plastic Yield Gelin Gel10 yp/lp PAC (g/l) viscosity viscosity point (N/m2) (N/m2) (s 1) (cP) (cP) (N/m2)
Conc. of Apparent Plastic Yield Gel10 yp/lp Gelin tamarind viscosity viscosity point (N/m2) (N/m2) (s 1) gum (g/l) (cP) (cP) (N/m2)
1 2 3 4 5
0.5 1 1.5 2 2.5
11.5 16 26 33 41
7 10 14 17 20
4.5 6 12 16 21
1.75 2.5 3.5 6 9
7 12.5 15 24 30
1280 1200 1710 1880 2100
13 19.5 27.5 35 48
8 11 13 14 16
5 8.5 14.5 21 32
1.5 3 5.5 9 14.5
4 6 9.5 12 16.5
1250 1540 2230 3000 4000
Table 10 Effect of conc. of PAC on rheological properties of 30 g/l (3% w/v) of bentonite – water suspension (B222)
Table 13 Effect of conc. of tamarind gum on rheological properties of 1 g PAC and 30 g bentonite/l of bentonite – water suspension (B222)
Conc. of Apparent Plastic Yield Gelin Gel10 yp/lp PAC (g/l) viscosity viscosity point (N/m2) (N/m2) (s 1) (cP) (cP) (N/m2)
Conc. of Apparent Plastic Yield Gelin Gel10 yp/lp tamarind viscosity viscosity point (N/m2) (N/m2) (s 1) gum (g/l) (cP) (cP) (N/m2)
1 2 3 4 5
0.5 1 1.5 2 2.5
9.5 15.0 22.5 37 40
7 9 13 18 18
2.5 6 9.5 19 22
1.25 2 3 5 8.5
4.5 9 15.5 22 28.5
710 1330 1460 2110 2440
12 15.5 22.5 28.5 40
7 9 12 12 16
5 6.5 10.5 16.5 24
1.25 2 4 6 10
6 6.5 8 9 12.5
1420 1440 1750 2750 3000
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Table 14 Effect of conc. of tamarind gum on rheological properties of 1 g PAC and 30 g bentonite/l of bentonite – water suspension (C333)
Table 16 Measurement of permeability of distilled water and mud filtrate A on core sample 1
Conc. of Apparent Plastic Yield Gelin Gel10 yp/lp tamarind viscosity viscosity point (N/m2) (N/m2) (s 1) gum (g/l) (cP) (cP) (N/m2)
Properties
Distilled water
Mud filtrate A
pH Viscosity (cP) at 25 jC Permeability (K, md)
7 0.896 234.85
8.3 0.976 182.73
0.5 1 1.5 2 2.5
11 16 21 24 27
8 9 9 10 12
3 7 12 14 15
1.5 2.5 3 5 7
4 6 7 7.5 8
750 1550 2660 2800 2500
3.2. Effect of PAC Tables 9– 11 show that viscosity (apparent, plastic), yield point, yield point/plastic viscosity ratio and gel strengths increases with an increase in PAC concentrations. Due to anionic nature of PAC, the adsorption and flocculation occurs as a result of hydrogen bonding between solid surfaces and the hydroxyl groups on the polymer (Gungor, 2000).
Table 15 Properties of favorable drilling fluid: mud A is 30 g bentonite, 1 g PAC and 1 g tamarind/l water; mud B is 30 g bentonite, 1 g PAC and 1.5 g tamarind/l water; mud A is 30 g bentonite, 1 g PAC and 1.5 g tamarind/l water
3.3. Combined effect of tamarind gum and PAC The apparent viscosity, plastic viscosity and yield point, yield point/plastic viscosity and gel strengths of the mixture containing 0.1% PAC and 3% bentonite increases with increase in the concentration of tamarind gum as evident from Tables 12 –14. The high yield point/plastic viscosity ratio indicates that it is a shear thinning mud which is desirable for drilling fluid as it sets to a gel, which is sufficient to suspend the cuttings when circulation is stopped and which breaks up quickly to a thin fluid when it is agitated by resumption of drilling (Gray and Darley, 1981). The rheological properties of optimum combinations developed from the above studies have been found to be stable at 75 jC as shown in Table 15. 3.4. Formation damage study
Properties Drilling fluid combination Mud A
Mud B
Mud C
Ambient Hot Ambient Hot Ambient Hot rolling temp. rolling temp. rolling temp. for for for 16 h at 16 h at 16 h at 75 jC 75 jC 75 jC Apparent viscosity (cP) Plastic viscosity (cP) Yield point (N/m2) Initial gel strength (N/m2) 10 min gel strength (N/m2) API fluid loss (ml)
19.5
11
20.5
22.5
23
21
21.5
11
12
12
9
10.5
10.5
11
12
11.5
3
3
4
4
3
3.5
6
6
8
8
7
7
8.5
12.5
12
12
12
12.5
10
12
From Tables 16– 18, observations indicated that the permeability to mud filtrate was less than that of
Table 17 Measurement of permeability of distilled water and mud filtrate B on core sample 2 Properties
Distilled water
Mud filtrate B
pH Viscosity (cP) at 25 jC Permeability (K, md)
7 0.896 82.78
8.6 0.977 64.99
Table 18 Measurement of permeability of distilled water and mud filtrate C on core sample 3 Properties
Distilled water
Mud filtrate C
pH Viscosity (cP) at 25 jC Permeability (K, md)
7.0 0.896 193.4
8.5 0.977 149.40
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permeability to distilled water. This is due to (1) adsorption of polymers on silica surfaces and on the edge of clay lattice (Bennion et al., 2000) and (2) migration of fine clay particles from filtrate into the formation (Bennion, 1999; Masikewich and Bennion, 1999). Formation damage caused by these formulations of drilling fluids is less, probably because of less adsorption of polymer on the core due to less polymer concentration. The low pH also may be the contributing factor of less formation damage. At low pH, dissolution of silica and subsequently releasing of fines inside the formation is less (Gray and Darley, 1981; Bagci et al., 2000). 4. Conclusions (1) Tamarind gum drilling fluids are seven times less expensive than guar gum drilling fluids and tamarind gum is readily available in India, thus is a more suitable drilling fluid. (2) Combinations of tamarind gum, PAC and bentonite clay produce favorable rheological properties and optimum fluid loss at very low concentrations. In addition, its effect on formation damage is less than guar gum drilling fluids. Acknowledgements The authors thank Council of Scientific and Industrial Research, New Delhi, India for providing financial assistance for this work. References Bagci, S., Kok, M.V., Turksoy, U., 2000. Determination of formation damage in limestone reservoirs and its effect on production. JPSE 28, 1 – 12 (October). Bennion, B., 1999. Formation damage—the impairment of the invisible and uncontrollable, resulting in an indeterminate reduction of the unquantifiable. J. Can. Pet. Technol. 38 (2), 11 – 17.
Bennion, D.B., Thomas, F.B., Jamaluddin, A.K.M., Ma, T., 2000. Using under balanced drilling to reduce invasive formation damage and improve well productivity—an update. J. Can. Pet. Technol. 39 (7), 53 – 60. Bruton, J., Mercer, R., Paul, D., 2000. The application of new generation CaCl2 mud systems in the Deepwater Gulf of Mexico. IADC/SPE Drilling Conf., New Orleans, February. SPE 59051. Chilingarian, G.V., Vorabutr, P., 1983. 1st ed. Drilling and Drilling Fluids, vol. 50, 133. Elsevier, Amsterdam, Netherlands, pp. 149 – 151. Elward-Berry, J., Darby, J.B., 1997. Rheologically stable, nontoxic, high temperature, water based drilling fluid. SPE Drill. Complet., 158 – 162 (September). Gatlin, C., 1960. Petroleum Engineering: Drilling and Well Completions. Prentice-Hall, Englewood Cliffs, New Jersey, p. 125. Gray, G.R., Darley, H.C.H., 1981. 4th ed. Composition and Properties of Oil Well Fluids, vol. 270 – 272. Gulf Publishing Company, Houston, Texas, p. 495. Gungor, N., 2000. Effect of the adsorption of surfactants on the rheology of Na-bentonite slurries. J. Appl. Polym. Sci. 75, 107 – 110. Jilani, S.Z., Menouar, H., Al-Majed, A.A., Khan, M.A., 2002. Effect of overbalance pressure on formation damage. JPSE 36, 97 – 109. Khoja, A.K., Halbe, A.V., 2001. Scope for the use of tamarind kernel powder as a thickner in textile printing. Man-Made Textiles in India (October) 403 – 407. Lummus, J.C., Azar, J.J., 1986. Drilling Fluids Optimization—A Practical Field Approach, vol. 112. PennWell Publishing, Tulsa, Oklahoma, p. 160. Masikewich, J., Bennion, D.B., 1999. Fluid design to meet reservoir issues—a process. J. Can. Pet. Technol. 38 (1), 61 – 71. Mishra, G.C., Pandey, N.K., Pandey, P.K., 1985. Greases from Indian Bentonite, Indian. J. Chem. Technol. 23, 190 – 194. Parija, S., Misra, M., Mohanti, A.K., 2001. Studies of natural gum adhesives: an overview. J. Macromol. Sci., Polymer Rev. C41 (3), 175 – 197. Park, A., Scott Jr., P.P., Lummus, J.L., 1960. Maintaining low solids drilling fluids. Oil Gas J., 81 – 84 (May). Plank, J.P., 1992. Water based muds using synthetic polymers developed for high temperature drilling. Oil Gas J. 90 (5), 40 – 45. Recommended Practice, 1988. Standard procedure for field testing drilling fluids, 12th ed. Recommended Practice, vol. 13 B (RP 13B). API, Washington, USA, pp. 7 – 9. Singh, P.K., Sharma, V.P., 1997. Effects of electrolytes on zeta potential of beneficiated Indian Bentonites. J. Sci. Ind. Res. 56, 281 – 287. Whistler, R.L., Bemiller, J.N., 1973. Industrial Gums, 2nd ed. Academic Press, New York, USA, pp. 370 – 411.
Rheological study of a water based oil well drilling fluid Vikas Mahto, V.P. Sharma * Department of Petroleum Engineering, Indian School of Mines, Dhanbad-826004, Jharkhand, India Received 26 May 2003; accepted 30 March 2004
Abstract Organic polymers are commonly used to control the rheology and filtrate loss required for water-based drilling fluids. An ecologically-friendly water-based drilling fluid was developed by studying the rheological behavior of tamarind gum and polyanionic cellulose on bentonite water suspensions. The effect of drilling fluid filtrate on formation damage was also analyzed. The drilling fluid that was developed has better rheological properties and fluid loss control which are required for optimum performance of oil well drilling. In addition, the drilling fluid filtrate exhibits minimum formation damage on sandstone cores. D 2004 Elsevier B.V. All rights reserved. Keywords: Bentonite; Rheology; Formation damage; Polymer; Gel strength; Tamarind gum
1. Introduction The tamarind gum (from the tamarind tree, a most common tree in India) is a low cost viscosity modifier and may be used in drilling fluid formulation. The tamarind gum is a white to creamy, free flowing, powder. It has almost same the viscosity as guar gum at the same concentration in water, and it is seven times cheaper than guar gum (Khoja and Halbe, 2001). Chemically, it is a highly branched carbohydrate polymer. Its backbone consists of D-glucose units joined with (1 –4)h linkages similar to that of cellulose. It consists of a main chain of h-D(1– 4)-
* Corresponding author. Tel.: +91-326-220-6232; fax: +91-326220-6319. E-mail addresses: [email protected], [email protected] (V.P. Sharma). 0920-4105/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.petrol.2004.03.008
galactopyranosyl units with a side chain of a single xylopyranosyl unit attached to every second, third and fourth D-glucopyranosyl unit through an a-D(1 – 6) linkage. One galactopyranosyl unit is attached to one of the xylopyranosyl units through a h-D(1 –2) linkage (Parija et al., 2001). The polyanionic cellulose (PAC) is used as a fluid loss reducer for fresh water and salt-water muds, but it also acts as viscosity modifier in these systems (Bruton et al., 2000). PAC is available in two types (high or low viscosity grade), both of which impart the same degree of fluid loss control but different degrees of viscosity. The temperature stability of PAC is 149 jC (Plank, 1992) and is not subjected to bacterial degradation (Lummus and Azar, 1986). The bentonite clay used in drilling fluid is montmorillonite (Chilingarian and Vorabutr, 1983). It is added to fresh water to: (1) increase the hole cleaning properties, (2) reduce water seepage or filtration into
124
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permeable formation, (3) form a thin filter cake of low permeability, (4) promote hole stability in poorly cemented formations and (5) avoid or overcome loss of circulation. The high clay solids content of drilling fluid has several adverse effects: (1) greatly reduces the rate of penetration (Gatlin, 1960), (2) increased chances of differential sticking and (3) is the major cause of excessive torque and drag. Thus, low bentonite content is desired to control the total amount of solids. At low concentration, bentonite clay is unable to provide satisfactory rheological properties required for optimum performance in oil well drilling. Hence, polymers are added to achieve the desired result. Formation damage is the reduction of permeability near the well bore that results in a decrease of productivity/injectivity of an oil or gas well. It is caused by the invasion of foreign fluids and/or solids in the exposed section near the well bore. One of the basic functions of the drilling fluid is control of possible flow outs when high subsurface pressure is encountered thus the mud column pressure must exceed the formation pressure. As a result, the mud solids and filtrate enter the formation and cause damage (Jilani et al., 2002). The water based drilling fluid using organic polymers are safe and should be designed to minimize the amounts of solids and fluid invasion into the formation.
2. Experimental 2.1. Materials Three bentonite clay samples were obtained from the Kutch region, Gujarat, India. The tamarind gum was procured from Saiguru Food Industries, Mumbai and high viscosity polyanionic cellulose was obtained Table 1 Physico-chemical properties of bentonite clay samples Sample no.
A111 B222 C333
Properties Cation exchange capacity (meq./ 100 g clay)
Yield of clay (m3/ton clay)
Swelling index
81.66 80.0 83.33
8.6345 10 3 10.44 10 3 9.912 10 3
3.5 3.9 3.7
Table 2 Effect of concentration of bentonite (A111) on rheological properties of bentonite (A111) – water suspension Conc. of Apparent Plastic Yield Gelin Gel10 yp/lp bentonite viscosity viscosity point (N/m2) (N/m2) (s 1) (g/l) (cP) (cP) (N/m2) 10 20 30 40 50
1.25 1.5 2 2.25 3.25
1 1 1 1 2
0.25 0.5 1 1.25 1.25
0.25 0.375 0.5 0.5 0.5
0.25 0.75 1 1 1.125
500 1000 2000 2500 1250
from an oil field operation. The sandstone cores (sample no. 1: length = 2 cm, breadth = 1.8 cm; sample no. 2: length = 2.35 cm, breadth = 2.0 cm; sample no. 3: length = 1.4 cm, breadth = 1.8 cm) were selected from western Indian oil producing fields. 2.2. Experimental procedures The bentonite clay samples were dried by exposure to the sun for a few days. They were then crushed and screened through 200-mesh size sieve (0.074 mm). The samples were dried in an air oven at 100 F 2 jC. Initially, the swelling index (Mishra et al., 1985), yield of clay (Chilingarian and Vorabutr, 1983) and cation exchange capacity (Chilingarian and Vorabutr, 1983) of the clays were determined. Bentonite water suspensions were then prepared at different compositions and rheological properties (apparent viscosity, plastic viscosity, initial gel strength and 10 min gel strength) were measured. Then, an ideal bentonite concentration was chosen. These properties were again measured by adding ecologically-friendly organic polymers. Subsequently, the three most favourable mud systems were prepared from these three different clay suspensions and the drilling fluid combinations were hot rolled in a roller oven for 16 h to measure temperature stability. These muds were filtered through Whatman No. 50 filter paper using API fluid loss apparatus (Chilingarian and Vorabutr, 1983), then the filtrate obtained was used for formation damage studies. The formation damage studies were based on permeability reduction in a sand stone oil field core and experimental work was conducted using a Ruska Liquid Permeameter. The procedure adopted was to determine the permeability of filtrate and distilled water in core samples.
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125
Table 3 Effect of concentration of bentonite (B222) on rheological properties of bentonite (B222) – water suspension
Table 5 Rheological properties of 30 g/l (3% w/v) of bentonite clay – water suspension
Conc. of Apparent Plastic Yield Gelin Gel10 yp/lp bentonite viscosity viscosity point (N/m2) (N/m2) (s 1) (g/l) (cP) (cP) (N/m2)
Properties
Sample no. A111
B222
C333
Apparent viscosity (cP) Plastic viscosity (cP) Yield point (N/m2) Initial gel strength (N/m2) 10 min gel strength (N/m2)
2 1 1 0.5 1
2.5 1 1.5 0.5 1
2 1 1 0.5 1
10 20 30 40 50
1.5 2 2.5 2.75 3.75
1 1 1 1 2
0.5 1 1.5 1.75 1.75
0.375 0.5 0.5 0.5 0.5
0.5 0.75 2 2 2.5
1000 2000 3000 3500 1250
The apparent viscosity, plastic viscosity and yield point were calculated from 300 and 600 rpm readings using following formulas from API Recommended practice of Standard procedure for field testing drilling fluids (Recommended Practice, 1988): Apparent viscosity ðla Þ ¼ U600 =2 ðcPÞ Plastic viscosity ðlp Þ ¼ U600 U300 ðcPÞ Yield point ðyp Þ ¼ U300 lp 0:5 N=m2 ðlb=100 ft2 Þ
interlayer space and cause swelling of bentonite. The behaviour of bentonite water suspension is complex due to unisometric clay particles exposing different crystal faces, on which an electrical double layer can develop, which differs both in sign and the magnitude of the total surface potential (Singh and Sharma, 1997; Gungor, 2000). Consequently, the rheological characteristics in these suspensions are achieved by clay particle – clay particle and clay particle – water suspension. Table 5 summarizes the rheological properties of 30 g/l bentonite concentrations (3% w/v) in water with
Table 6 Effect of conc. of tamarind gum on rheological properties of 30 g/ l (3% w/v) of bentonite – water suspension (A111)
3. Results and discussion The swelling index, yield of clay and cation exchange capacity of the clays are listed in Table 1. The rheological properties of the bentonite water system at different clay concentrations were tabulated in Tables 2– 4. The bentonite clay consists of superimposed layers composed of two Si– O tetrahedral sheets framing an Al – O – OH octahedral sheet. In aqueous dispersion, water can penetrate into the
Conc. of Apparent Plastic Yield Gel10 yp/lp Gelin tamarind viscosity viscosity point (N/m2) (N/m2) (s 1) gum (g/l) (cP) (cP) (N/m2) 0.5 1 1.5 2 2.5
6.5 11.5 20 25 28.5
3.5 6 9 10 10
3 5.5 11 15 18.5
1.5 2 4.5 6 6.5
2.5 3 5.5 7 7
1710 1833 2400 3000 3700
Table 4 Effect of concentration of bentonite (C333) on rheological properties of bentonite (C333) – water suspension
Table 7 Effect of conc. of tamarind gum on rheological properties of 30 g/ l (3% w/v) of bentonite water suspension (B222)
Conc. of Apparent Plastic Yield Gel10 yp/lp Gelin bentonite viscosity viscosity point (N/m2) (N/m2) (s 1) (g/l) (cP) (cP) (N/m2)
Conc. of Apparent Plastic Yield Gel10 yp/lp Gelin tamarind viscosity viscosity point (N/m2) (N/m2) (s 1) gum (g/l) (cP) (cP) (N/m2)
10 20 30 40 50
0.5 1 1.5 2 2.5
1.25 1.5 2 2.5 3.5
1 1 1 1 2
0.25 0.5 1 1.5 1.5
0.375 0.5 0.5 0.5 0.5
0.5 1 1 1 1.25
500 1000 2000 3000 1500
6 11 14 21 23
3.5 6 7 9 9
2.5 5 7 12 14
1.5 2.5 3 5 5.5
2.5 3.5 4 6 6.5
1430 1660 2000 2660 3110
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Table 8 Effect of conc. of tamarind gum on rheological properties of 30 g/ l (3% w/v) bentonite – water suspension (C333)
Table 11 Effect of conc. of PAC on rheological properties of 30 g/l (3% w/v) of bentonite – water suspension (C333)
Conc. of Apparent Plastic Yield Gelin Gel10 yp/lp tamarind viscosity viscosity point (N/m2) (N/m2) (s 1) gum (g/l) (cP) (cP) (N/m2)
Conc. of Apparent Plastic Yield point Gelin Gel10 yp/lp PAC (g/l) viscosity viscosity (N/m2) (N/m2) (N/m2) (s 1) (cP) (cP)
0.5 1 1.5 2 2.5
1 2 3 4 5
7 11.5 15.5 18.5 21
4 6 7 7 8
3 5.5 8.5 11.5 13
1.5 2.5 3 4.5 5.5
3 3.5 4.5 5.5 6
1500 1830 2420 3280 3250
these clays. The 40 g/l bentonite concentrations (4% w/v) in water (Tables 2 – 4) shows a slight increase in apparent viscosity and yield point but there is no increase in plastic viscosity and gel strength. Because the solids content should be less for effective control of total solids in drilling fluid, 30 g/l bentonite (3% w/ v) concentration was selected for further study; 3% also is the normal concentration used in oil fields for drilling (Park et al., 1960; Elward-Berry and Darby, 1997). The rheological properties of bentonite at 3% conc. require further adjustment; thus, tamarind gum and PAC polymer were added.
9.5 16.5 23 31.5 41
7 11 13 17 20
2.5 5.5 10 14.5 21
1.25 2 3.5 6.5 8.5
5.5 11.5 16 22.5 27.5
710 1000 1538 1700 2100
3.1. Effect of tamarind gum The effect of tamarind gum on the rheological properties is shown in Tables 6 – 8 . Since the tamarind gum is a carbohydrate polymer (Parija et al., 2001; Whistler and Bemiller, 1973) and it consists mainly hydroxyl groups; the increase in apparent viscosity, plastic viscosity, yield point, yield point/plastic viscosity ratio, initial gel strength and 10 min gel strength with increase of the concentration of tamarind gum may be due to hydrogen bonding of hydroxyl group of tamarind gum with clay.
Table 9 Effect of conc. of PAC on rheological properties of 30 g/l (3% w/v) of bentonite – water suspension (A111)
Table 12 Effect of conc. of tamarind gum on rheological properties of 1 g PAC and 30 g bentonite/l of bentonite – water suspension (A111)
Conc. of Apparent Plastic Yield Gelin Gel10 yp/lp PAC (g/l) viscosity viscosity point (N/m2) (N/m2) (s 1) (cP) (cP) (N/m2)
Conc. of Apparent Plastic Yield Gel10 yp/lp Gelin tamarind viscosity viscosity point (N/m2) (N/m2) (s 1) gum (g/l) (cP) (cP) (N/m2)
1 2 3 4 5
0.5 1 1.5 2 2.5
11.5 16 26 33 41
7 10 14 17 20
4.5 6 12 16 21
1.75 2.5 3.5 6 9
7 12.5 15 24 30
1280 1200 1710 1880 2100
13 19.5 27.5 35 48
8 11 13 14 16
5 8.5 14.5 21 32
1.5 3 5.5 9 14.5
4 6 9.5 12 16.5
1250 1540 2230 3000 4000
Table 10 Effect of conc. of PAC on rheological properties of 30 g/l (3% w/v) of bentonite – water suspension (B222)
Table 13 Effect of conc. of tamarind gum on rheological properties of 1 g PAC and 30 g bentonite/l of bentonite – water suspension (B222)
Conc. of Apparent Plastic Yield Gelin Gel10 yp/lp PAC (g/l) viscosity viscosity point (N/m2) (N/m2) (s 1) (cP) (cP) (N/m2)
Conc. of Apparent Plastic Yield Gelin Gel10 yp/lp tamarind viscosity viscosity point (N/m2) (N/m2) (s 1) gum (g/l) (cP) (cP) (N/m2)
1 2 3 4 5
0.5 1 1.5 2 2.5
9.5 15.0 22.5 37 40
7 9 13 18 18
2.5 6 9.5 19 22
1.25 2 3 5 8.5
4.5 9 15.5 22 28.5
710 1330 1460 2110 2440
12 15.5 22.5 28.5 40
7 9 12 12 16
5 6.5 10.5 16.5 24
1.25 2 4 6 10
6 6.5 8 9 12.5
1420 1440 1750 2750 3000
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Table 14 Effect of conc. of tamarind gum on rheological properties of 1 g PAC and 30 g bentonite/l of bentonite – water suspension (C333)
Table 16 Measurement of permeability of distilled water and mud filtrate A on core sample 1
Conc. of Apparent Plastic Yield Gelin Gel10 yp/lp tamarind viscosity viscosity point (N/m2) (N/m2) (s 1) gum (g/l) (cP) (cP) (N/m2)
Properties
Distilled water
Mud filtrate A
pH Viscosity (cP) at 25 jC Permeability (K, md)
7 0.896 234.85
8.3 0.976 182.73
0.5 1 1.5 2 2.5
11 16 21 24 27
8 9 9 10 12
3 7 12 14 15
1.5 2.5 3 5 7
4 6 7 7.5 8
750 1550 2660 2800 2500
3.2. Effect of PAC Tables 9– 11 show that viscosity (apparent, plastic), yield point, yield point/plastic viscosity ratio and gel strengths increases with an increase in PAC concentrations. Due to anionic nature of PAC, the adsorption and flocculation occurs as a result of hydrogen bonding between solid surfaces and the hydroxyl groups on the polymer (Gungor, 2000).
Table 15 Properties of favorable drilling fluid: mud A is 30 g bentonite, 1 g PAC and 1 g tamarind/l water; mud B is 30 g bentonite, 1 g PAC and 1.5 g tamarind/l water; mud A is 30 g bentonite, 1 g PAC and 1.5 g tamarind/l water
3.3. Combined effect of tamarind gum and PAC The apparent viscosity, plastic viscosity and yield point, yield point/plastic viscosity and gel strengths of the mixture containing 0.1% PAC and 3% bentonite increases with increase in the concentration of tamarind gum as evident from Tables 12 –14. The high yield point/plastic viscosity ratio indicates that it is a shear thinning mud which is desirable for drilling fluid as it sets to a gel, which is sufficient to suspend the cuttings when circulation is stopped and which breaks up quickly to a thin fluid when it is agitated by resumption of drilling (Gray and Darley, 1981). The rheological properties of optimum combinations developed from the above studies have been found to be stable at 75 jC as shown in Table 15. 3.4. Formation damage study
Properties Drilling fluid combination Mud A
Mud B
Mud C
Ambient Hot Ambient Hot Ambient Hot rolling temp. rolling temp. rolling temp. for for for 16 h at 16 h at 16 h at 75 jC 75 jC 75 jC Apparent viscosity (cP) Plastic viscosity (cP) Yield point (N/m2) Initial gel strength (N/m2) 10 min gel strength (N/m2) API fluid loss (ml)
19.5
11
20.5
22.5
23
21
21.5
11
12
12
9
10.5
10.5
11
12
11.5
3
3
4
4
3
3.5
6
6
8
8
7
7
8.5
12.5
12
12
12
12.5
10
12
From Tables 16– 18, observations indicated that the permeability to mud filtrate was less than that of
Table 17 Measurement of permeability of distilled water and mud filtrate B on core sample 2 Properties
Distilled water
Mud filtrate B
pH Viscosity (cP) at 25 jC Permeability (K, md)
7 0.896 82.78
8.6 0.977 64.99
Table 18 Measurement of permeability of distilled water and mud filtrate C on core sample 3 Properties
Distilled water
Mud filtrate C
pH Viscosity (cP) at 25 jC Permeability (K, md)
7.0 0.896 193.4
8.5 0.977 149.40
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permeability to distilled water. This is due to (1) adsorption of polymers on silica surfaces and on the edge of clay lattice (Bennion et al., 2000) and (2) migration of fine clay particles from filtrate into the formation (Bennion, 1999; Masikewich and Bennion, 1999). Formation damage caused by these formulations of drilling fluids is less, probably because of less adsorption of polymer on the core due to less polymer concentration. The low pH also may be the contributing factor of less formation damage. At low pH, dissolution of silica and subsequently releasing of fines inside the formation is less (Gray and Darley, 1981; Bagci et al., 2000). 4. Conclusions (1) Tamarind gum drilling fluids are seven times less expensive than guar gum drilling fluids and tamarind gum is readily available in India, thus is a more suitable drilling fluid. (2) Combinations of tamarind gum, PAC and bentonite clay produce favorable rheological properties and optimum fluid loss at very low concentrations. In addition, its effect on formation damage is less than guar gum drilling fluids. Acknowledgements The authors thank Council of Scientific and Industrial Research, New Delhi, India for providing financial assistance for this work. References Bagci, S., Kok, M.V., Turksoy, U., 2000. Determination of formation damage in limestone reservoirs and its effect on production. JPSE 28, 1 – 12 (October). Bennion, B., 1999. Formation damage—the impairment of the invisible and uncontrollable, resulting in an indeterminate reduction of the unquantifiable. J. Can. Pet. Technol. 38 (2), 11 – 17.
Bennion, D.B., Thomas, F.B., Jamaluddin, A.K.M., Ma, T., 2000. Using under balanced drilling to reduce invasive formation damage and improve well productivity—an update. J. Can. Pet. Technol. 39 (7), 53 – 60. Bruton, J., Mercer, R., Paul, D., 2000. The application of new generation CaCl2 mud systems in the Deepwater Gulf of Mexico. IADC/SPE Drilling Conf., New Orleans, February. SPE 59051. Chilingarian, G.V., Vorabutr, P., 1983. 1st ed. Drilling and Drilling Fluids, vol. 50, 133. Elsevier, Amsterdam, Netherlands, pp. 149 – 151. Elward-Berry, J., Darby, J.B., 1997. Rheologically stable, nontoxic, high temperature, water based drilling fluid. SPE Drill. Complet., 158 – 162 (September). Gatlin, C., 1960. Petroleum Engineering: Drilling and Well Completions. Prentice-Hall, Englewood Cliffs, New Jersey, p. 125. Gray, G.R., Darley, H.C.H., 1981. 4th ed. Composition and Properties of Oil Well Fluids, vol. 270 – 272. Gulf Publishing Company, Houston, Texas, p. 495. Gungor, N., 2000. Effect of the adsorption of surfactants on the rheology of Na-bentonite slurries. J. Appl. Polym. Sci. 75, 107 – 110. Jilani, S.Z., Menouar, H., Al-Majed, A.A., Khan, M.A., 2002. Effect of overbalance pressure on formation damage. JPSE 36, 97 – 109. Khoja, A.K., Halbe, A.V., 2001. Scope for the use of tamarind kernel powder as a thickner in textile printing. Man-Made Textiles in India (October) 403 – 407. Lummus, J.C., Azar, J.J., 1986. Drilling Fluids Optimization—A Practical Field Approach, vol. 112. PennWell Publishing, Tulsa, Oklahoma, p. 160. Masikewich, J., Bennion, D.B., 1999. Fluid design to meet reservoir issues—a process. J. Can. Pet. Technol. 38 (1), 61 – 71. Mishra, G.C., Pandey, N.K., Pandey, P.K., 1985. Greases from Indian Bentonite, Indian. J. Chem. Technol. 23, 190 – 194. Parija, S., Misra, M., Mohanti, A.K., 2001. Studies of natural gum adhesives: an overview. J. Macromol. Sci., Polymer Rev. C41 (3), 175 – 197. Park, A., Scott Jr., P.P., Lummus, J.L., 1960. Maintaining low solids drilling fluids. Oil Gas J., 81 – 84 (May). Plank, J.P., 1992. Water based muds using synthetic polymers developed for high temperature drilling. Oil Gas J. 90 (5), 40 – 45. Recommended Practice, 1988. Standard procedure for field testing drilling fluids, 12th ed. Recommended Practice, vol. 13 B (RP 13B). API, Washington, USA, pp. 7 – 9. Singh, P.K., Sharma, V.P., 1997. Effects of electrolytes on zeta potential of beneficiated Indian Bentonites. J. Sci. Ind. Res. 56, 281 – 287. Whistler, R.L., Bemiller, J.N., 1973. Industrial Gums, 2nd ed. Academic Press, New York, USA, pp. 370 – 411.