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Polyoxyalkyleneamine as shale inhibitor in water-based drilling fluids
Applied Clay Science 44 (2009) 265–268
Contents lists available at ScienceDirect
Applied Clay Science j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / c l a y
Polyoxyalkyleneamine as shale inhibitor in water-based drilling fluids Yuanzhi Qu a,⁎, Xiaoqing Lai a,b, Laifang Zou a, Yi'nao Su a a b
Research Institute of PetroChina Drilling Engineering Technology, Beijing 100097, China College of Petroleum Engineering, Yangtze University, Jingzhou, Hubei 434023, China
a r t i c l e
i n f o
Article history: Received 12 October 2008 Received in revised form 4 March 2009 Accepted 7 March 2009 Available online 21 March 2009 Keywords: Rheology Polyoxyalkykeneamine (POAM) Shale inhibitor Water-based drilling fluids
a b s t r a c t According to the conventional evaluation methods of drilling fluids, the inhibitive property of polyoxyalkyleneamine (POAM), which was prepared in the laboratory, to sodium montmorillonite (Na-MMT) was investigated, and the shale cuttings recovery ratio and the rheological properties of drilling fluids were measured before and after adding POAM in several water-based drilling fluids. The results showed that POAM was completely water-soluble, exhibited the superior performance to inhibit the hydration of Na-MMT and reduced the swelling or hydration of shale cuttings effectively. In addition, the determination of the biological toxicity and compatibility of POAM indicated that POAM was low toxic and compatible with other common drilling fluid additives. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Water-based drilling fluids may cause swelling of the clay minerals in shale formations that can create major problems for the drilling operations. According to statistics (Dzialowski et al., 1993), shales account for about 75% of the drilled sections in oil and gas wells, and cause approximately 90% of the wellbore instability-related problems during drilling operations. When water-sensitive shales are exposed to the conventional water-based drilling fluids, shales have an immediate tendency to take up water from the drilling fluid. Depending on the chemical characteristics of the shale, this can result in a rapid swelling or dispersion of the shale. Consequently, typical problems such as bit-balling, disintegration of cuttings, borehole wash-out, high torque and drag, and stuck pipe are often encountered as a result of water adsorption by water-sensitive shales (Steiger and Leung, 1992; van Oort et al., 1994). During the drilling practice in shale formations, various chemicals have been used to reduce clay mineral or shale swelling in water-based drilling fluids. Among the chemicals, salts such as potassium chloride, sodium chloride and divalent brines are the earliest and most widely used for inhibition of water-sensitive shales. The inhibitive method relies on the use of high concentration of salts. These salts somehow retard the hydration and swelling of water-sensitive shales through a variety of mechanism. However, these salts in large quantities adversely affect the environment. These salts also flocculate the clay minerals resulting in both high fluid losses and an almost complete loss of thixotropy. Further, increasing salinity often decreases the functional characteristics of drilling fluid additives. In the field application, polymer/KCl drilling fluids became ⁎ Corresponding author. Tel./fax: +86 10 62098361. E-mail address: [email protected] (Y. Qu). 0169-1317/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.clay.2009.03.003
popular (Clark et al., 1976; Twynam et al., 1994). A variety of polymers in combination with KCl were evaluated to achieve a higher level of shale inhibition as compared to KCl alone. However, surface swelling due to insufficient shale inhibition and high viscosity of polymers offered little partial success in providing the satisfactory results. Since drilling operations impact the surrounding environment, the drilling fluid additives should have low toxicity levels and should be easy to handle and to use to minimize the dangers of environmental pollution and harm to operators. It is desirable that additives work both onshore and offshore. As an excellent inhibitive agent, it should control the swelling of the clay minerals and drilled formations without adversely affecting the desired performance of other additives and the rheological properties of drilling fluids. In this paper, we evaluated the toxicity, inhibitive property and compatibility of polyoxyalkyleneamine as a shale inhibitive agent in water-based drilling fluids.
2. Experimental 2.1. Materials and reagents Encapsulating agent (UltraCap) and low viscous polyanionic cellulose (PAC-LV) were supplied by M-I SWACO in America. Modified starch, xanthan gum (XC), cationic inhibitor (CSW-1), carboxymethyl starch (CMS), viscosifier (80A51), filtration control agent (CMJ-2) and borehole-stabilizing agent (JYW-1) were all available in domestic market. Sodium-montmorillonite (Na-MMT) was made in Huai'an in Hebei in China. Polyoxyalkyleneamine (POAM) was synthesized according to the references (Rasshofer, 1985; Gbard, 1985; Larkin and Renken, 1988).
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Y. Qu et al. / Applied Clay Science 44 (2009) 265–268
Table 1 Dial readings of all samples at different rpm after adding Na-MMT (hot rolling for 16 h at 70 °C). Concentration of Na-MMT,%
Fresh Water ϕ600
ϕ300
ϕ3
G10'
ϕ600
2% KCl Solution ϕ300
ϕ3
G10'
ϕ600
2% CSW Solution ϕ300
ϕ3
G10'
ϕ600
2% POAM Solution ϕ300
ϕ3
G10'
2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0 22.5 25.0 27.5
2.5 18 43.5 104.5 – – – – – – –
1.4 13.5 34.5 86.5 – – – – – – –
0 5 20 54 – – – – – – –
0 13 46 77 – – – – – – –
2 2.5 3 5 12 24 59 138 – – –
1 1.5 2 3 9.5 20 54 130 – – –
0 0 0 2 5 12 36 65 – – –
0 0 0 2 4 20 42 86 – – –
2 2.5 4 4 6 10 25 40 82 236 –
1 1.5 2.5 3 4 7 20 32 68 220 –
0 0 0 0.5 1 3.5 8 11 30 106 –
0 0 0 0.5 0.5 4 11 14 32 144 –
1 1.5 2 2.5 3 3 3.5 4 5 6 10
1 1 1 1.5 2 2 3 3.5 4 5 7
0 0 0 0 0 0 0 0 1 2 4
0 0 0 0 0 0 1 0 1 2 5
– Indicates that the reading is greater than 300, no further readings were taken.
2.2. Rheological determination The rheological properties of the fluid samples in this study were measured using a model ZNN-D6 viscometer. The properties included apparent viscosity, plastic viscosity, yield point and gel strength. 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 (AV) = ϕ600/2 (cP) Plastic viscosity (PV) = ϕ600 − ϕ300 (cP) Yield point (YP) = ϕ600 − AV (N/m2). 2.3. Na-MMT and cuttings dispersion test The inhibitive agents in the mud systems should be sufficient to reduce the hydration and swelling of clay minerals in the shale cuttings. By a trial and error method of testing the combination of fresh water (or drilling fluids) and clay in the shale cuttings, the approximate amount of POAM present in the experimental systems was determinated and the concentration of POAM was about 2 wt.% of the systems. To demonstrate the inhibitive property of POAM, the experiments were designed to determine the maximum amount of Na-MMT that can be inhibited by 2 wt.% POAM solution over several days. All samples were adjusted to about pH 9 and treated with a 2.5 wt.% portion of Na-MMT at a medium rate of shear. After stirring for 30 min, the samples were hot rolled in a roller oven for 16 h at 70 °C. When the samples were cooled, their rheologies were recorded. All samples were treated again with Na-MMT as previously described. This procedure was carried out for each sample until they were too thick to measure. Before cuttings dispersion tests, the crystalline components of the cuttings were carried out by using Rigaku TTR-III X-ray diffractometer. Cuttings dispersion tests were performed by hot rolling 30 g shale
Fig. 1. Variation of apparent viscosity with Na-MMT concentration.
cuttings (6-10 mesh) in 300 mL different drilling muds for 16 h at 100 °C. Before hot rolling, all muds were adjusted to about pH 9. After hot rolling, the remaining cuttings were screened using a 40 mesh screen and washed with 10 wt.% KCl solution, dried and then weighted to obtain the percentage recovered of the cuttings in the different mud systems. 2.4. Biological toxicity and compatibility test The biological toxicity of the shale inhibition agent was measured by the Mysid shrimp test. A detail account of the procedure for measuring toxicity of drilling fluids is described in the reference (Duke et al., 1984). The compatibility test was carried out by measuring the change of rheological properties and filtrate loss of several mud systems before and after adding the shale inhibitive agent. Filtrate loss of drilling fluids was determinated by a filter press. The filtrate loss of the mud systems was measured in milliliters under 690 kPa of pressure through a special filter paper for 30 min. 3. Results and discussion 3.1. Effect of POAM on Na-MMT dispersion Rheological properties were measured for the different systems after adding Na-MMT (Table 1). The plots of apparent viscosity (AV), plastic viscosity (PV) and yield point (YP) of the samples versus NaMMT concentration were shown in Fig. 1–3 respectively. MMT in fresh water easily absorbed water and swelled greatly (Fig. 4). As a result, the viscosity of the system significantly increased, and the system was too thick to measure the rheological readings after adding 12.5 wt.% Na-MMT in fresh water. However, the other three systems exhibited the inhibitive property at different degree (Table 2).
Fig. 2. Variation of plastic viscosity with Na-MMT concentration.
Y. Qu et al. / Applied Clay Science 44 (2009) 265–268
267
Table 2 Summary of the crystalline minerals for the shale cuttings. Minerals
Content,%
Quartz Albite Calcite Clinochlore and Illite Total
32.9 16.7 16.2 34.2 100.0
Table 3 Recovery rate (%) of the shale cuttings in the different mud systems. Fig. 3. Variation of yield point with Na-MMT concentration.
Compared with fresh water, 2 wt.% KCl solution and 2 wt.% CSW solution, the 2 wt.% POAM solution exhibited the superior performance to inhibit the hydration and swelling of Na-MMT. Despite KCl can reduce the swelling and hydration of most clay minerals, especially smectite, it is only moderately effective for illite and may actually increase swelling of kaolins (van Oort, 1997; Santarelli and Carminati, 1995). As a kind of low molecular mass polyamines, the reaction of POAM with clay minerals can involve several mechanisms including hydrogen bonding, dipole interactions and ion exchange (Theng, 1974; Sithole and Guy, 1985). The molecules of POAM were adsorbed on the surfaces of clay minerals and compete with water molecules for reactive sites, which could serve to reduce clay mineral swelling. Low molecular mass amines can also be intercalated.
Test No.
Formulations of drilling fluid systems
Total recovered
1# 2#
11.5% Sodium formate + 1.3% Modified starch + 0.6%XC 11.5% Sodium formate + 1.3% Modified starch + 0.6%XC + 2%POAM 5%KCl + 0.5%UltraCap + 1%PAC-Lv + 0.5%XC (1.20 g/cm3 weighed with barite) 5%KCl + 0.5%UltraCap + 1%PAC-Lv + 0.5%XC + 2%POAM (1.20 g/cm3 weighed with barite) 5%KCl + 2%CSW-1 + 3%CMS + 0.2%80A51 + 0.3%XC + 2%CMJ-2 + 1%JYW-1 5%KCl + 2%CSW-1 + 3%CMS + 0.2%80A51 + 0.3%XC + 2%CMJ-2 + 1%JYW-1 + 2%POAM
67.0% 89.0%
3# 4# 5# 6#
72.3% 90.3% 59.3% 65.7%
Note: Continuous phase of all drilling fluid systems was fresh water.
cuttings had a high clay mineral content, POAM exhibited a good inhibiting property and reduced the swelling or hydration of shale cuttings effectively.
3.2. Effect of POAM on shale cuttings dispersion 3.3. Biological toxicity and compatibility of POAM Experimental cuttings were obtained from the shale formation of Chang-301 well depth of 1550 m in Yumen Oilfield. The samples were composed mainly of clay minerals, feldspar and quartz. The shale cuttings studied had a high clay fraction. Generally, shales with a high clay content should easily absorb water molecules and swell greatly. Shale cuttings were a clay-rich waste stream generated by the drilling process and could become unstable by the mechanisms similar to the hydration and swelling of clay minerals. The results of the shale cuttings dispersion tests (Table 3) indicated that the recovery rate of the shale cuttings increased after adding 2 wt.% POAM in three different mud systems. Especially for the former two mud systems, the recovery rate of the shale cuttings increased from 67.0% to 89.0% and from 72.3% to 90.3%, respectively. Since the shale
According to the reference (Duke et al., 1984), the biological toxicity of POAM was measured by the Mysid shrimp test and the LC50 of POAM was much greater than 30000 ppm. Generally, an LC50 value of greater than 30000 had been considered as environmental compatibility. As a shale inhibitive agent in water-based drilling fluids, POAM exhibited low toxicity and could be used both onshore and offshore. The results of the compatibility test were shown in Table 4. POAM had no influence on the rheological properties and filtrate loss of the mud systems before and after adding the shale inhibitive agent. This indicated that POAM did not change the performance of other additives and the rheological properties of drilling fluids. Thus,
Fig. 4. X-ray diffractograms of the shale cuttings of Chang-301 well depth of 1550 m in Yumen Oilfield. Note: Q = Quartz, A = Albite, C = Calcite; Cl = Clinochlore, I = Illite.
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Y. Qu et al. / Applied Clay Science 44 (2009) 265–268
References
Table 4 Effect of POAM on rheological properties of water-based drilling fluids. No. of test
ϕ600
ϕ300
ϕ3
G10'
API FL
AV
PV
YP
1# 2# 3# 4#
68 65 76 62
52 50 57 50
16 15 11 9
7 6.5 5 3.5
8.4 9.2 6 6.4
34 32.5 38 31
16 15 19 12
18 17.5 19 19
Note: The formulations of all mud systems were the same as in Table 3.
POAM could be compatible with the conventional additives in waterbased drilling fluids. 4. Conclusions A new shale inhibitive agent in water-based drilling fluids was described. POAM was an excellent shale inhibitive agent. Na-MMT dispersion tests, gel strength and relative viscosity measurements suggested that the addition of Na-MMT had little influence on the rheological properties of the POAM solution. POAM exhibited superior performance to inhibit the hydration and swelling of Na-MMT. In cuttings dispersion test, the recovery rate of the shale cuttings increased after adding 2 wt.% POAM in several water-based drilling fluids. The test indicated that POAM could suppress the hydration and swelling of shales effectively. The determination of toxicity and compatibility of POAM showed that POAM was environment-friendly and compatible with other conventional drilling fluid additives. Acknowledgements We would like to thank the financial support from PetroChina Fund under No. 2008A-2303 for this work.
Clark, R.K., Scheuerman, R.F., Rath, H., Van Larr, H.G., 1976. Polyacrylamide/potassiumchloride mud for drilling water-sensitive shales. J. Petrol. Technol. 28, 719–727. Duke, T.W., Parrish, P.R., Montgomery, R.M., 1984. Acute toxicity of eight laboratory prepared generic drilling fluids to mysids (mysidopsis). EPA-600/3-84-067. Dzialowski, A., Hale, A., Mahajan, S., 1993. Lubricity and wear of shale: effects of drilling fluids and mechanical parameters. SPE/IADC Drilling Conference. SPE, Amsterdam, p. 25730.. February. Gbard, S., 1985. Tris(polyoxaalky)amines (trident), a new class of solid-liquid phasetransfer catalysts. J. Org. Chem. 50 (20), 3717–3721. Larkin, J.M., Renken, T.L., 1988. Process for the preparation of polyoxalkylene polyamines. US 4766245. Rasshofer, W., 1985. Polyamines, a process for the production of polyamines and their use in the production of polyurethanes. US 4540720. Recommended practice, 1988. Standard procedure for field testing drilling fluids, 12th ed. . Recommended Practice, vol. 13. API, Washingtom, USA, pp. 7–9. B (RP 13B). Santarelli, F., Carminati, S., 1995. Do shales swell? A critical review of available evidence. SPE/IADC Drilling Conference. Amsterdam Netherlands. February. SPE/IADC 29421. Sithole, B.B., Guy, R.D., 1985. Interactions of secondary amines with bentonite clay and humic materials in dilute aqueous systems. Environ. Int. 11, 499–504. Steiger, R.P., Leung, P.K., 1992. Quantitative determination of the mechanical properties of shales. SPE Drilling Engineering, vol. 181. Theng, B.K.G., 1974. The chemistry of clay-organic reactions. Adam Hilger, London, pp. 84–92. Twynam, A.J., Caldwell, P.A., Meads, K., 1994. Glycol-enhanced water-based muds: Case history to demonstrate improve drilling efficiency in techtonocally stressed shales. SPE/IADC Drilling Conference. Dallas. February. SPE 27451. van Oort, E., 1997. Physico-chemical stabilization of shales. SPE International Symposium on Oilfield Chemistry. SPE, Houston. Texas, February, 37263. van Oort, E., Hale, A.H., Mody, F.K., Roy, S., 1994. Critical parameters in modeling the chemical aspects of borehole stability in shales and in designing improved waterbased shale drilling fluids. SPE 69th Annual Technical Conference and Exhibition. SPE, New Orleans, Los Angles, p. 28309. September.
Contents lists available at ScienceDirect
Applied Clay Science j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / c l a y
Polyoxyalkyleneamine as shale inhibitor in water-based drilling fluids Yuanzhi Qu a,⁎, Xiaoqing Lai a,b, Laifang Zou a, Yi'nao Su a a b
Research Institute of PetroChina Drilling Engineering Technology, Beijing 100097, China College of Petroleum Engineering, Yangtze University, Jingzhou, Hubei 434023, China
a r t i c l e
i n f o
Article history: Received 12 October 2008 Received in revised form 4 March 2009 Accepted 7 March 2009 Available online 21 March 2009 Keywords: Rheology Polyoxyalkykeneamine (POAM) Shale inhibitor Water-based drilling fluids
a b s t r a c t According to the conventional evaluation methods of drilling fluids, the inhibitive property of polyoxyalkyleneamine (POAM), which was prepared in the laboratory, to sodium montmorillonite (Na-MMT) was investigated, and the shale cuttings recovery ratio and the rheological properties of drilling fluids were measured before and after adding POAM in several water-based drilling fluids. The results showed that POAM was completely water-soluble, exhibited the superior performance to inhibit the hydration of Na-MMT and reduced the swelling or hydration of shale cuttings effectively. In addition, the determination of the biological toxicity and compatibility of POAM indicated that POAM was low toxic and compatible with other common drilling fluid additives. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Water-based drilling fluids may cause swelling of the clay minerals in shale formations that can create major problems for the drilling operations. According to statistics (Dzialowski et al., 1993), shales account for about 75% of the drilled sections in oil and gas wells, and cause approximately 90% of the wellbore instability-related problems during drilling operations. When water-sensitive shales are exposed to the conventional water-based drilling fluids, shales have an immediate tendency to take up water from the drilling fluid. Depending on the chemical characteristics of the shale, this can result in a rapid swelling or dispersion of the shale. Consequently, typical problems such as bit-balling, disintegration of cuttings, borehole wash-out, high torque and drag, and stuck pipe are often encountered as a result of water adsorption by water-sensitive shales (Steiger and Leung, 1992; van Oort et al., 1994). During the drilling practice in shale formations, various chemicals have been used to reduce clay mineral or shale swelling in water-based drilling fluids. Among the chemicals, salts such as potassium chloride, sodium chloride and divalent brines are the earliest and most widely used for inhibition of water-sensitive shales. The inhibitive method relies on the use of high concentration of salts. These salts somehow retard the hydration and swelling of water-sensitive shales through a variety of mechanism. However, these salts in large quantities adversely affect the environment. These salts also flocculate the clay minerals resulting in both high fluid losses and an almost complete loss of thixotropy. Further, increasing salinity often decreases the functional characteristics of drilling fluid additives. In the field application, polymer/KCl drilling fluids became ⁎ Corresponding author. Tel./fax: +86 10 62098361. E-mail address: [email protected] (Y. Qu). 0169-1317/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.clay.2009.03.003
popular (Clark et al., 1976; Twynam et al., 1994). A variety of polymers in combination with KCl were evaluated to achieve a higher level of shale inhibition as compared to KCl alone. However, surface swelling due to insufficient shale inhibition and high viscosity of polymers offered little partial success in providing the satisfactory results. Since drilling operations impact the surrounding environment, the drilling fluid additives should have low toxicity levels and should be easy to handle and to use to minimize the dangers of environmental pollution and harm to operators. It is desirable that additives work both onshore and offshore. As an excellent inhibitive agent, it should control the swelling of the clay minerals and drilled formations without adversely affecting the desired performance of other additives and the rheological properties of drilling fluids. In this paper, we evaluated the toxicity, inhibitive property and compatibility of polyoxyalkyleneamine as a shale inhibitive agent in water-based drilling fluids.
2. Experimental 2.1. Materials and reagents Encapsulating agent (UltraCap) and low viscous polyanionic cellulose (PAC-LV) were supplied by M-I SWACO in America. Modified starch, xanthan gum (XC), cationic inhibitor (CSW-1), carboxymethyl starch (CMS), viscosifier (80A51), filtration control agent (CMJ-2) and borehole-stabilizing agent (JYW-1) were all available in domestic market. Sodium-montmorillonite (Na-MMT) was made in Huai'an in Hebei in China. Polyoxyalkyleneamine (POAM) was synthesized according to the references (Rasshofer, 1985; Gbard, 1985; Larkin and Renken, 1988).
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Y. Qu et al. / Applied Clay Science 44 (2009) 265–268
Table 1 Dial readings of all samples at different rpm after adding Na-MMT (hot rolling for 16 h at 70 °C). Concentration of Na-MMT,%
Fresh Water ϕ600
ϕ300
ϕ3
G10'
ϕ600
2% KCl Solution ϕ300
ϕ3
G10'
ϕ600
2% CSW Solution ϕ300
ϕ3
G10'
ϕ600
2% POAM Solution ϕ300
ϕ3
G10'
2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0 22.5 25.0 27.5
2.5 18 43.5 104.5 – – – – – – –
1.4 13.5 34.5 86.5 – – – – – – –
0 5 20 54 – – – – – – –
0 13 46 77 – – – – – – –
2 2.5 3 5 12 24 59 138 – – –
1 1.5 2 3 9.5 20 54 130 – – –
0 0 0 2 5 12 36 65 – – –
0 0 0 2 4 20 42 86 – – –
2 2.5 4 4 6 10 25 40 82 236 –
1 1.5 2.5 3 4 7 20 32 68 220 –
0 0 0 0.5 1 3.5 8 11 30 106 –
0 0 0 0.5 0.5 4 11 14 32 144 –
1 1.5 2 2.5 3 3 3.5 4 5 6 10
1 1 1 1.5 2 2 3 3.5 4 5 7
0 0 0 0 0 0 0 0 1 2 4
0 0 0 0 0 0 1 0 1 2 5
– Indicates that the reading is greater than 300, no further readings were taken.
2.2. Rheological determination The rheological properties of the fluid samples in this study were measured using a model ZNN-D6 viscometer. The properties included apparent viscosity, plastic viscosity, yield point and gel strength. 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 (AV) = ϕ600/2 (cP) Plastic viscosity (PV) = ϕ600 − ϕ300 (cP) Yield point (YP) = ϕ600 − AV (N/m2). 2.3. Na-MMT and cuttings dispersion test The inhibitive agents in the mud systems should be sufficient to reduce the hydration and swelling of clay minerals in the shale cuttings. By a trial and error method of testing the combination of fresh water (or drilling fluids) and clay in the shale cuttings, the approximate amount of POAM present in the experimental systems was determinated and the concentration of POAM was about 2 wt.% of the systems. To demonstrate the inhibitive property of POAM, the experiments were designed to determine the maximum amount of Na-MMT that can be inhibited by 2 wt.% POAM solution over several days. All samples were adjusted to about pH 9 and treated with a 2.5 wt.% portion of Na-MMT at a medium rate of shear. After stirring for 30 min, the samples were hot rolled in a roller oven for 16 h at 70 °C. When the samples were cooled, their rheologies were recorded. All samples were treated again with Na-MMT as previously described. This procedure was carried out for each sample until they were too thick to measure. Before cuttings dispersion tests, the crystalline components of the cuttings were carried out by using Rigaku TTR-III X-ray diffractometer. Cuttings dispersion tests were performed by hot rolling 30 g shale
Fig. 1. Variation of apparent viscosity with Na-MMT concentration.
cuttings (6-10 mesh) in 300 mL different drilling muds for 16 h at 100 °C. Before hot rolling, all muds were adjusted to about pH 9. After hot rolling, the remaining cuttings were screened using a 40 mesh screen and washed with 10 wt.% KCl solution, dried and then weighted to obtain the percentage recovered of the cuttings in the different mud systems. 2.4. Biological toxicity and compatibility test The biological toxicity of the shale inhibition agent was measured by the Mysid shrimp test. A detail account of the procedure for measuring toxicity of drilling fluids is described in the reference (Duke et al., 1984). The compatibility test was carried out by measuring the change of rheological properties and filtrate loss of several mud systems before and after adding the shale inhibitive agent. Filtrate loss of drilling fluids was determinated by a filter press. The filtrate loss of the mud systems was measured in milliliters under 690 kPa of pressure through a special filter paper for 30 min. 3. Results and discussion 3.1. Effect of POAM on Na-MMT dispersion Rheological properties were measured for the different systems after adding Na-MMT (Table 1). The plots of apparent viscosity (AV), plastic viscosity (PV) and yield point (YP) of the samples versus NaMMT concentration were shown in Fig. 1–3 respectively. MMT in fresh water easily absorbed water and swelled greatly (Fig. 4). As a result, the viscosity of the system significantly increased, and the system was too thick to measure the rheological readings after adding 12.5 wt.% Na-MMT in fresh water. However, the other three systems exhibited the inhibitive property at different degree (Table 2).
Fig. 2. Variation of plastic viscosity with Na-MMT concentration.
Y. Qu et al. / Applied Clay Science 44 (2009) 265–268
267
Table 2 Summary of the crystalline minerals for the shale cuttings. Minerals
Content,%
Quartz Albite Calcite Clinochlore and Illite Total
32.9 16.7 16.2 34.2 100.0
Table 3 Recovery rate (%) of the shale cuttings in the different mud systems. Fig. 3. Variation of yield point with Na-MMT concentration.
Compared with fresh water, 2 wt.% KCl solution and 2 wt.% CSW solution, the 2 wt.% POAM solution exhibited the superior performance to inhibit the hydration and swelling of Na-MMT. Despite KCl can reduce the swelling and hydration of most clay minerals, especially smectite, it is only moderately effective for illite and may actually increase swelling of kaolins (van Oort, 1997; Santarelli and Carminati, 1995). As a kind of low molecular mass polyamines, the reaction of POAM with clay minerals can involve several mechanisms including hydrogen bonding, dipole interactions and ion exchange (Theng, 1974; Sithole and Guy, 1985). The molecules of POAM were adsorbed on the surfaces of clay minerals and compete with water molecules for reactive sites, which could serve to reduce clay mineral swelling. Low molecular mass amines can also be intercalated.
Test No.
Formulations of drilling fluid systems
Total recovered
1# 2#
11.5% Sodium formate + 1.3% Modified starch + 0.6%XC 11.5% Sodium formate + 1.3% Modified starch + 0.6%XC + 2%POAM 5%KCl + 0.5%UltraCap + 1%PAC-Lv + 0.5%XC (1.20 g/cm3 weighed with barite) 5%KCl + 0.5%UltraCap + 1%PAC-Lv + 0.5%XC + 2%POAM (1.20 g/cm3 weighed with barite) 5%KCl + 2%CSW-1 + 3%CMS + 0.2%80A51 + 0.3%XC + 2%CMJ-2 + 1%JYW-1 5%KCl + 2%CSW-1 + 3%CMS + 0.2%80A51 + 0.3%XC + 2%CMJ-2 + 1%JYW-1 + 2%POAM
67.0% 89.0%
3# 4# 5# 6#
72.3% 90.3% 59.3% 65.7%
Note: Continuous phase of all drilling fluid systems was fresh water.
cuttings had a high clay mineral content, POAM exhibited a good inhibiting property and reduced the swelling or hydration of shale cuttings effectively.
3.2. Effect of POAM on shale cuttings dispersion 3.3. Biological toxicity and compatibility of POAM Experimental cuttings were obtained from the shale formation of Chang-301 well depth of 1550 m in Yumen Oilfield. The samples were composed mainly of clay minerals, feldspar and quartz. The shale cuttings studied had a high clay fraction. Generally, shales with a high clay content should easily absorb water molecules and swell greatly. Shale cuttings were a clay-rich waste stream generated by the drilling process and could become unstable by the mechanisms similar to the hydration and swelling of clay minerals. The results of the shale cuttings dispersion tests (Table 3) indicated that the recovery rate of the shale cuttings increased after adding 2 wt.% POAM in three different mud systems. Especially for the former two mud systems, the recovery rate of the shale cuttings increased from 67.0% to 89.0% and from 72.3% to 90.3%, respectively. Since the shale
According to the reference (Duke et al., 1984), the biological toxicity of POAM was measured by the Mysid shrimp test and the LC50 of POAM was much greater than 30000 ppm. Generally, an LC50 value of greater than 30000 had been considered as environmental compatibility. As a shale inhibitive agent in water-based drilling fluids, POAM exhibited low toxicity and could be used both onshore and offshore. The results of the compatibility test were shown in Table 4. POAM had no influence on the rheological properties and filtrate loss of the mud systems before and after adding the shale inhibitive agent. This indicated that POAM did not change the performance of other additives and the rheological properties of drilling fluids. Thus,
Fig. 4. X-ray diffractograms of the shale cuttings of Chang-301 well depth of 1550 m in Yumen Oilfield. Note: Q = Quartz, A = Albite, C = Calcite; Cl = Clinochlore, I = Illite.
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Y. Qu et al. / Applied Clay Science 44 (2009) 265–268
References
Table 4 Effect of POAM on rheological properties of water-based drilling fluids. No. of test
ϕ600
ϕ300
ϕ3
G10'
API FL
AV
PV
YP
1# 2# 3# 4#
68 65 76 62
52 50 57 50
16 15 11 9
7 6.5 5 3.5
8.4 9.2 6 6.4
34 32.5 38 31
16 15 19 12
18 17.5 19 19
Note: The formulations of all mud systems were the same as in Table 3.
POAM could be compatible with the conventional additives in waterbased drilling fluids. 4. Conclusions A new shale inhibitive agent in water-based drilling fluids was described. POAM was an excellent shale inhibitive agent. Na-MMT dispersion tests, gel strength and relative viscosity measurements suggested that the addition of Na-MMT had little influence on the rheological properties of the POAM solution. POAM exhibited superior performance to inhibit the hydration and swelling of Na-MMT. In cuttings dispersion test, the recovery rate of the shale cuttings increased after adding 2 wt.% POAM in several water-based drilling fluids. The test indicated that POAM could suppress the hydration and swelling of shales effectively. The determination of toxicity and compatibility of POAM showed that POAM was environment-friendly and compatible with other conventional drilling fluid additives. Acknowledgements We would like to thank the financial support from PetroChina Fund under No. 2008A-2303 for this work.
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