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Hydrophobic modified polymer based silica nanocomposite for improving shale stability in water-based drilling fluids
Journal of Petroleum Science and Engineering 153 (2017) 325–330
Contents lists available at ScienceDirect
Journal of Petroleum Science and Engineering journal homepage: www.elsevier.com/locate/petrol
Hydrophobic modified polymer based silica nanocomposite for improving shale stability in water-based drilling fluids
MARK
⁎
Jian-gen Xu , Zhengsong Qiu, Xin Zhao, Weian Huang School of Petroleum Engineering, China University of Petroleum, Qingdao, 266580, China
A R T I C L E I N F O
A BS T RAC T
Keywords: Nanocomposite Shale stability Water-based drilling fluids Shale hydration Pressure transmission
In this paper, a novel hydrophobic modified polymer based silica nanocomposite (NFC) was successfully prepared by emulsion polymerization and it was characterized by FTIR, PSD, TEM and TGA analysis. The results indicated that NFC possessed uni-modal distribution from 38 nm to 164 nm with the D50 value of about 72 nm and had good thermal stability. A variety of methods including the contact angle measurement, pressure transmission test, hot-rolling cuttings dispersion test and compatible test were adopted to evaluate the comprehensive effect of NFC on shale stability. And the shale cores before and after interacting with NFC were also characterized by scanning electron microscope (SEM) analysis. The experimental investigations revealed that NFC could effectively retard the pore pressure transmission and internally bridge and seal the pore-throats of shale. And it also exhibited preferable shale inhibition performance compared with KCl and JHC at the same concentration. After adsorption, the shale surface was more hydrophobic, which was more advantageous to shale stability. Furthermore, the compatibility test results confirmed that NFC had no negative effect on rheological performance and possessed a positive influence on filtration control performance of water-based drilling fluids.
1. Introduction In the drilling process, 75% of the formations drilled are shale formations and 90% of the wellbore instability problems are attributed to shale instability (Steiger and Leung, 1992; Zhang et al., 2013). Although a number of studies have been done on shale instability in the past decades, it has still been a critical issue in the petroleum industry (Van Oort, 2003; Liang et al., 2014). More importantly, shale gas, as a type of unconventional resource, has transformed the energy landscape around the world, but shale instability problems in the horizontal section greatly constrain its development (Zhou et al., 2016; Akhtarmanesh et al., 2013). Recent research shows that retarding pressure transmission is effective way to solve shale instability problems (Van Oort, 1997; Van Oort et al., 1996; Sharma et al., 2012). However, shale formations are characterized by low porosity and low permeability, and a filter cake cannot be formed on shale surface since the traditional additives for drilling fluids are too large to bridge and seal the nanopores of shale formations (Ewy and Morton, 2008). Therefore, how to plug the nanopores of shale formations is a vitally important work to solve shale instability problems. In recent years, the application of nano materials in drilling fluids has attracted great attention (Jain et al., 2015; Abdo and Haneef, 2012;
⁎
Corresponding author. E-mail address: [email protected] (J.-g. Xu).
http://dx.doi.org/10.1016/j.petrol.2017.04.013 Received 9 December 2016; Received in revised form 9 March 2017; Accepted 7 April 2017 Available online 08 April 2017 0920-4105/ © 2017 Elsevier B.V. All rights reserved.
Li et al., 2012). To solve the problems of shale instability, many researchers have done a lot of work. Non-modified silica nanoparticles were first introduced to solve the problems, but only a little effect has been achieved because the nanoparticles are easy to agglomerate and need large dosage to play a role (Cai et al., 2012; Baran and Cabrera, 2006). Some other researchers used polymer latex nanoparticles to bridge and seal the nanopores and microfractures of shale formations, and a certain achievement has been obtained (Liu et al., 2015; Xu et al., 2017). But the polymer latex prepared by emulsifier-free emulsion polymerization shows poor stability and contains low solid, it will be subject to restrictions for field applications. In addition, some research groups have reported the application of nano-emulsion as an effective drilling fluids additive for drilling shale formations (Tabibiazar et al., 2015). But it is unstable and shows poor temperature resistance. The use of nano-fillers for polymer matrix can combine the rigidity and thermal stability of inorganic nanomaterial with the toughness of polymers to create excellent properties (Ajayan et al., 2006; Zou et al., 2008). Therefore, the nanocomposite can overcome those disadvantages and may be a new approach to solve shale instability problems. Additionally，shale hydration is another important factor to cause borehole instability (Zhong et al., 2016; Shadizadeh et al., 2015). It has been reported that hydrophobic polymer can effectively inhibit
Journal of Petroleum Science and Engineering 153 (2017) 325–330
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a mechanical stirrer, a thermometer, and a dropping funnel. In brief, a certain amount of modified nano-silica was dispersed into deionized water in which SDS and OP-10 were dissolved, then 0.12 g of NaHCO3, 28 g of Styrene (St) and 12 g of Butyl acrylate (BA) were added into it and ultrasonically treated for 1 h. Secondly, they were transferred into the flask to be pre-emulsified under mechanical stirring and heated up to 75 °C for 1 h. Thirdly, KPS (0.24 g) was added into the flask to induce polymerization. The polymerization was then continued in the flask for another 3 h at 75 °C and finally cooled to room temperature.
the shale hydration (Gu et al., 2012). The synergistic effects of hydrophobic polymer and inorganic nanomaterial in the nanocomposite may result in superior sealing performance and good inhibition capacity to mitigate shale instability problems. In this paper, a novel hydrophobic modified polymer based silica nanocomposite (NFC), mainly used as a potential shale stabilizer in water-based drilling fluids for drilling troublesome shale formations, was prepared with Styrene (St), Butyl acrylate (BA) and nano-silica via emulsion polymerization. NFC could retard pressure transmission and decrease shale permeability to increase shale stability. More importantly, NFC could inhibit shale hydration as well. As per our knowledge, this is the first report on the application of hydrophobic modified polymer based silica nanocomposite as a potential shale stabilizer in water-based drilling fluids.
2.3. Characterization of NFC The chemical structures of NFC were characterized by Flourier transformation infrared spectroscopy (FT-IR, Nicolet 6700, USA). The particle size of NFC was determined based on dynamic light scattering by particle size distribution analyzer (PSD, Zetasizer Nano ZS90, the United Kingdom). The morphology of NFC was observed using transmission electron microscopy (TEM, JEOL JEM-2100UHR, Japan). The thermal stability of NFC was measured by thermo gravimetric analysis (TGA, Schwerzenbach, Switzerland).
2. Materials and methods 2.1. Materials Styrene (St) and n-butyl acrylate (BA) were purchased from Sinopharm Chemical Reagent Co. Ltd (China) and were purified by vacuum distillation before use. SiO2 nanoparticles (7–40 nm) and octylphenol polyoxyethylene ether (OP-10) were obtained from Aladdin Reagent Co. Ltd (China). Ethanol, silane coupling agent KH570, sodium dodecyl sulfate (SDS), ethylic acid, potassium persulfate (KPS) and sodium bicarbonate (NaHCO3) were purchased from Sinopharm Chemical Reagent Co. Ltd (China) and used as received. Deionized water was used throughout the experiments. Shale samples in this study were obtained from Turpan Hami Basin, China. The detailed mineralogical composition of the shale samples was determined by XRD analysis and the results are presented in Table 1.
Firstly, NFC and non-modified silica nanoparticles were added into a certain amount of pre-hydrated sodium bentonite slurry respectively at a concentration of 0.5%. After magnetic stirring at least 24 h, the glass slides were uniformly coated using the dispersions and left airdried. Finally，a water droplet was dropped on the glass slide and the photos were recorded. The contact angle measurement was conducted on a contact angle tester (JC2000D, China) with the static sessile drop method.
2.2. Preparation of NFC
2.5. Pressure transmission test
Fig. 1 presents the preparation mechanism of NFC. The polymerization of NFC was divided into two steps. A certain amount of nanosilica was first dispersed into 100 mL ethanol dispersing medium with the aid of ultrasonic for 1 h. Then, KH570 was dissolved into ethanol dispersing medium with a little water according to the weight ratio of 1:1:18 for KH570/H2O/ethanol, and 1 mL ethylic acid was added into the dispersion with magnetic stirring for 30 min at room temperature. Secondly, the mixture of the above dispersion was loaded into a reaction flask, and vigorously stirred for 4 h at 75 °C using a mechanical stirrer to obtain KH570-modified nano-silica. Thirdly, the obtained KH570-modified nano-silica was washed several times with absolute ethanol, and dried at 60 °C for further use. The hydrophobic modified polymer based silica nanocomposite (NFC) as a potential shale stabilizer was prepared with Styrene (St), Butyl acrylate (BA) and KH570-modified nano-silica via emulsion polymerization. The polymerization reaction was carried out in a 250-mL four-necked flask which was equipped with a reflux condenser,
The pressure transmission test was adopted to evaluate the sealing performance of testing fluids, and through test results the permeability of shale cores could be calculated. The pressure transmission test was carried out on a simulation experiment device (Xu et al., 2005), and the test cell is shown in Fig. 2. For the test, 4.0 w/v% pre-hydrated sodium bentonite slurry was utilized as the base fluid. The axial compression and the confining pressure were maintained at 5 MPa all times, and the upstream pressure was elevated to 2 MPa. With initial downstream pressure 1 MPa, downstream pressure buildup was monitored subsequently to obtain the pressure transmission curves. In addition, the permeability of shale cores could be calculated by following formula (Xu and Qiu, 2006).
2.4. Contact angle measurement
⎛ P −P ⎞ ⎛ P −P ⎞ ln ⎜ P −mP (Lo, t ) ⎟ − ln ⎜ P −mP (Lo, t ) ⎟ m 2 1 ⎠ ⎝ m ⎠ ⎝ μβVL K= A t2 − t1
where K represents shale permeability, μm ; μ represents viscosity, mPa•s; β represents the static compression ratio, MPa−1; V represents the enclosed volume of downstream fluids, cm3; L represents the length of shale samples, cm; A represents the cross-sectional area of shale samples, cm2; t represents total experimental time, s; Pm represents the upstream pressure, MPa; Po represents the initial downstream pressure, MPa; P (L, t) represents the realtime downstream pressure, MPa. What is more, the shale cores were characterized before and after interacting with NFC by scanning electron microscope (SEM) analysis.
Table 1 Mineralogical composition of the shale samples. X-ray diffraction
Content (wt%)
Quartz Potassium feldspar Plagioclase Calcite Iron dolomite Clay mineral Kaolinite Chlorite Illite Illite/smectite mixed layer
20 6 29 28 2 15 3 3 12 82
(1) 2
2.6. Hot-rolling cuttings dispersion test Hot-rolling cuttings dispersion test was performed to evaluate 326
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Fig. 1. Schematic representation of NFC preparation.
Fig. 2. The schematic of the test cell for pressure transmission test.
NFC's ability to inhibit shale hydration and dispersion (Zhong et al., 2012). In this test, potassium chloride (KCl) and polymeric alcohol (JHC) as two frequently used shale inhibitors were chose to compare with NFC. Firstly, 50 g dried shale cuttings with sizes varying between 2.00 mm and 3.35 mm were added into the sealed tank which contained 350 mL testing fluid. Then, the sealed tank was hot rolled for 16 h at 77 °C. After hot rolling, the shale cuttings were screened using 40 mesh sieve, washed and dried at 105 °C for 4 h. Finally, the remaining cuttings were weighed to calculate the recovery rate.
Fig. 3. FT-IR spectra of the nanocomposite NFC.
3. Results and discussion 3.1. Characterization of NFC 3.1.1. FT-IR analysis Fig. 3 shows the FT-IR spectra of Poly(St-BA)/silica nanocomposite. In the spectrum of Poly(St-BA)/silica nanocomposite, the peaks at 1602 cm−1, 1493 cm−1 and 1452 cm−1 were associated with the characteristic vibration of benzene skeleton. Moreover, the peaks at 758 cm−1 and 697 cm−1 were the characteristic peaks of single substitution benzene ring, indicating that styrene took part in the polymerization reaction successfully. In addition, the stretching vibration peak of C˭O was 1728 cm−1, and the stretching vibration peak of C–O–C bond was 1155 cm−1, indicating that butyl acrylate was also involved in the polymerization reaction. What is more, the stretching vibration peak of Si–O–Si bond was 1098 cm−1. Therefore, through the FT-IR spectra, it can be seen that the Poly(St-BA)/silica nanocomposite was successfully prepared.
2.7. Compatibility test The tested drilling fluid was prepared by adding 0.1 w/v% of modified starch, 3.0 w/v% KCl and 0.7 w/v% low viscosity polyanionic celluloses into 4.0 w/v% pre-hydrated sodium bentonite slurry at a high speed of 8000 rpm. After hot rolling at the appointed temperature 120 °C for 16 h in a XGRL-4 type rolling oven (Haitongda Company, China), the rheological and filtration control performance were measured. The compatibility of NFC in water-based drilling fluids was analyzed by comparing the rheological and filtration control performance of the tested drilling fluid with or without NFC. The rheological performance was determined with a ZNN-D6 rotating viscometer (Haitongda Company, China). The rheological parameters such as apparent viscosity, plastic viscosity and yield point were calculated from the high rotational speeds (600 and 300 rpm) according to the American Petroleum Institute (API) recommended practice. The filtration control performance was also tested by ZNS-2A filtration apparatus (Haitongda Company, China).
3.1.2. PSD analysis Fig. 4 presents the particle size distribution of the nanocomposite NFC in dilute aqueous solution. It can be concluded that the particle size distribution of the nanocomposite NFC was more concentrated, and the curve was a parabola. The particle size distribution was in the range of 38–164 nm and the medium particle size D50 value was 72 nm. Therefore, NFC can effectively seal the micro–nano scale porethroats and fractures of shale formations, and it was conducive to borehole stability.
Apparent Viscosity(AV) = Φ600 /2(mPa· s ) Plastic Viscosity(PV) = Φ600 −Φ300 (mPa· s )
3.1.3. TEM analysis Fig. 5 displays the TEM micrograph of the nanocomposite NFC in
Yield Point(YP) = (Φ300−PV)/2(Pa) 327
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3.2. Contact angle measurement Fig. 7 shows the test results of the contact angle measurement. It can be seen that the water contact angle for bentonite slurry was 22.0°, which showed a strong hydrophilic property. In particular, when 0.5 w/ v% non-modified silica nanoparticles was added, the hydrophilic property became stronger and the water contact angle for bentonite slurry containing 0.5 w/v% non-modified silica nanoparticles was only 14.3°. In the experiments, a phenomenon was observed that the water droplet spread quickly on the surface of the glass slide, indicating that non-modified silica nanoparticles were highly hydrophilic. After silica nanoparticles were grafted with hydrophobic polymer Poly(St-BA), the water contact angle for the nanocomposite was changed. When the bentonite slurry contained 0.5 w/v% NFC, the contact angle increased to around 60.2°, indicating that compared with non-modified silica nanoparticles the water wettability was significantly decreased. The shale surface was more hydrophobic and had a less affinity towards water, which was conducive to the reduction of water adsorption onto it (Zhong et al., 2015). Thus, NFC was advantageous to shale stability.
Fig. 4. Particle size distribution of diluted nanocomposite NFC.
3.3. Pressure transmission test The results of the pressure transmission test are presented in Fig. 8. It can be concluded that it took only around 40 min for shale cores to make the upstream and downstream pressure reach a balance, and 128 min for the base fluid. The growth rate of downstream pressure for shale and the base fluid was significantly higher than the base fluid containing 2.0 w/v% NFC, the time of which for making the upstream and downstream pressure reach a balance was about 503 min. According to formula (1), the shale permeability could be calculated based on pressure transmission test data. The permeability of shale core was 1.68×10−6 μm2. After interacting with the base fluid and the base fluid containing 2.0 w/v% NFC, it was decreased to 1.09×10−7 μm2 and 3.63×10−8 μm2, respectively. Results indicated that NFC could effectively retard pressure transmission and reduce the permeability of shale cores, thus it could be treated as a superior sealing agent. What is more, Fig. 9 shows the SEM photos of shale cores before and after interacting with NFC. It can clearly see that the nanoparticles could bridge and seal the pore throats and micro cracks of shale cores. A dense plugging film eventually formed on the shale surface, thereby improving shale stability in drilling process.
Fig. 5. TEM micrograph of diluted nanocomposite NFC.
dilute aqueous solution. It can be found that the particles were well dispersed and had regular spherical shape. The average particle size was around 70 nm, which was consistent with the D50 value (72 nm) of the PSD characterization results. Furthermore, the particles with coreshell structure indicated that the hydrophobic polymer Poly(St-BA) has been successfully grafted onto the surface of nano-silica particles.
3.4. Hot-rolling cuttings dispersion test
3.1.4. TGA analysis The thermal stability of NFC played a significant role for its application in drilling fluids. Fig. 6 shows the TGA curve of the prepared nanocomposite NFC. There was no obvious thermal decomposition until temperature increased up to 380 °C. Therefore, the newly prepared nanocomposite NFC maintained good thermal stability.
The inhibition performance of NFC was assessed by hot-rolling cuttings dispersion test with highly reactive shale cuttings. The results are shown in Fig. 10. It can be concluded that the shale recovery rate in tap water was 40.2%, indicating that the shale cuttings had strong hydration and dispersion capacity. After having conducted hot rolling of 0.5 w/v% NFC, 1.0 w/v% NFC, and 2.0 w/v% NFC, the recovery rate of them was 69.3%, 82.1%, and 90.7% respectively, showing that NFC had good capacity to prevent hydration and dispersion of shale cuttings in aqueous medium. In addition, the inhibition efficiency increased with the NFC concentration, and the inhibition performance of NFC was better than KCl and JHC at the same concentration. Therefore, NFC could act as a good shale inhibitor to maintain borehole stability. Through some literatures and the results obtained in this work, the inhibition mechanism of NFC for preventing shale hydration can be concluded (Gu et al., 2012; Ferreira et al., 2016; Amanullah and AlTahini, 2009). Because of its small particle size, large specific surface area and high surface energy, NFC has strong surface activity, and can be easily adsorbed onto the surface of clay particles. Furthermore, the adsorption capacity can be enhanced by a large number of residual bonds and active hydroxyl groups on the surface of NFC. In addition to van der Waals interactions, the clay particles surface has available sites to form a number of hydrogen bonds, thereby adsorbing more firmly.
Fig. 6. TGA curve of the nanocomposite NFC.
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Fig. 7. Test results of contact angle measurement, (a) bentonite slurry. (b) bentonite slurry containing 0.5 w/v% silica nanoparticles. (c) bentonite slurry containing 0.5 w/v% NFC.
Fig. 8. Pressure transmission test curves.
Fig. 10. Shale cuttings recoveries of different inhibitors.
What is more, after grafted with hydrophobic polymer Poly(St-BA), the surface of NFC is covered with the polymer chains and become more hydrophobic. When NFC solution is in contact with shale, a hydrophobic film can be formed on shale surface by adsorption. Therefore, the clay minerals hydration can be effectively inhibited as the entrance of water molecules into clay particles clearance is restricted by the hydrophobic film. The aforementioned facts can prove that NFC has good shale inhibition performance.
Table 2 Rheological and filtration control performance of the tested drilling fluid.
3.5. Compatibility test After hot rolling at the appointed temperature 120 °C for 16 h in a XGRL-4 type rolling oven, the rheological and filtration control performance of the tested drilling fluid with or without 2.0 w/v% NFC were measured. The test results are shown in Table 2. It can be concluded that NFC had no negative effect on rheological performance
Parameter
Before adding
After adding
600 rpm 300 rpm AV (mPa.s) PV (mPa.s) YP (Pa) YP/PV API FL (mL)
36 22 18 14 4 0.29 6.6
40 25 20 15 5 0.33 5.2
and had a positive influence on filtration control performance of waterbased drilling fluids. Therefore, the newly prepared nanocomposite NFC could be a good shale stabilizer in water-based drilling fluids.
Fig. 9. SEM photos of shale cores, (a) before testing and (b) after interacting with the base fluid containing 2.0 w/v% NFC.
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for water-based drilling fluids. Appl. Clay Sci. 132–133, 122–132. Gu, C., Di, Q., Jing, B., Shi, W., 2012. Mechanism of hydrophobic nano-SiO2 material in inhibiting clay swelling. Acta Pet. Sin. 6, 016. Jain, R., Mahto, V., Sharma, V.P., 2015. Evaluation of polyacrylamide grafted polyethylene glycol/silica nanocomposite as potential additive in water based drilling mud for reactive shale formation. J. Nat. Gas. Sci. Eng. 26, 526–537. Li, G.R., Zhang, J.H., Zhao, H.Z., Hou, Y.G., 2012. Nanotechnology to improve sealing ability of drilling fluids for shale with micro-cracks during drilling. In SPE International Oilfield Nanotechnology Conference and Exhibition. Society of Petroleum Engineers. Liang, C., Chen, M., Jin, Y., Lu, Y., 2014. Wellbore stability model for shale gas reservoir considering the coupling of multi-weakness planes and porous flow. J. Nat. Gas. Sci. Eng. 21, 364–378. Liu, J.Y., Qiu, Z.S., Huang, W.A., 2015. Novel latex particles and aluminum complexes as potential shale stabilizers in water-based drilling fluids. J. Pet. Sci. Eng. 135, 433–441. Shadizadeh, S.R., Moslemizadeh, A., Dezaki, A.S., 2015. A novel nonionic surfactant for inhibiting shale hydration. Appl. Clay Sci. 118, 74–86. Sharma, M.M., Chenevert, M.E., Guo, Q., Ji, L., Friedheim, J., Zhang, R., 2012. A new family of nanoparticle based drilling fluids. In SPE Annual Technical Conference and Exhibition. Society of Petroleum Engineers. Steiger, R., Leung, P.K., 1992. Quantitative determination of the mechanical properties of shales. SPE Paper 18024, SPE Drilling Engineering, 7(3), 181-185. Tabibiazar, M., Davaran, S., Hashemi, M., Homayonirad, A., Rasoulzadeh, F., Hamishehkar, H., Mohammadifar, M.A., 2015. Design and fabrication of a foodgrade albumin-stabilized nanoemulsion. Food Hydrocoll. 44, 220–228. Van Oort, E., 1997. Physico-chemical stabilization of shales. In International Symposium on Oilfield Chemistry. Society of Petroleum Engineers. Van Oort, E., 2003. On the physical and chemical stability of shales. J. Pet. Sci. Eng. 38 (3), 213–235. Van Oort, E., Hale, A.H., Mody, F.K., Roy, S., 1996. Transport in shales and the design of improved water-based shale drilling fluids. SPE Drill. Complet. 11 (3), 137–146. Xu, J., Qiu, Z., Huang, W., Zhao, X., 2017. Preparation and performance properties of polymer latex sdnl in water-based drilling fluids for drilling troublesome shale formations. J. Nat. Gas. Sci. Eng. 37, 462–470. Xu, J.F., Qiu, Z.S., 2006. Simulation test equipment of coupled hydra-mechanics of shales. J. Chin. Univ. Pet. (Ed. Nat. Sci.) 30 (3), 63–66. Xu, J.F., Qiu, Z.S., Lyu, K.H., 2005. Pressure transmission testing technology and simulation equipment for hydra-mechanics coupling of shale. Aca Pet. Sin. 27 (2), 26–27. Zhang, S., Qiu, Z., Huang, W., Cao, J., Luo, X., 2013. Characterization of a novel aluminum-based shale stabilizer. J. Pet. Sci. Eng. 103, 36–40. Zhong, H., Qiu, Z., Huang, W., Cao, J., 2012. Poly (oxypropylene)-amidoamine modified bentonite as potential shale inhibitor in water-based drilling fluids. Appl. Clay Sci., S. 67–68 (5), 36–43. Zhong, H.Y., Qiu, Z.S., Sun, D., Zhang, D.M., Huang, W.A., 2015. Inhibitive properties comparison of different polyetheramines in water-based drilling fluid. J. Nat. Gas. Sci. Eng. 26, 99–107. Zhong, H., Qiu, Z., Zhang, D., Tang, Z., Huang, W., Wang, W., 2016. Inhibiting shale hydration and dispersion with amine-terminated polyamidoamine dendrimers. J. Nat. Gas. Sci. Eng. 28, 52–60. Zhou, S., Xue, H., Guo, W., Li, X., 2016. A new nuclear magnetic resonance permeability model of shale of Longmaxi Formation in southern Sichuan Basin. J. China Univ. Pet. (Ed. Nat. Sci.) 40 (1), 56–61. Zou, H., Wu, S., Shen, J., 2008. Polymer/silica nanocomposites: preparation, characterization, properties, and applications. Chem. Rev. 108 (9), 3893–3957.
4. Conclusion Novel hydrophobic modified polymer based silica nanocomposite (NFC) was successfully prepared as a potential shale stabilizer in waterbased drilling fluids. Its particle size distribution was between 38 nm and 164 nm with D50 value of about 72 nm and the newly prepared shale stabilizer NFC had good thermal stability. What is more, NFC could effectively retard pressure transmission and decrease shale permeability. The nanoparticles could bridge and seal the pore throats and micro cracks of shale cores. A dense plugging film could eventually form on the shale surface, thereby improving shale stability. Meanwhile, NFC had good shale inhibition performance. At the concentration of 2%, the recovery rate of the shale sample was 90.7%, indicating that NFC exhibited superior shale inhibition performance compared with KCl and JHC at the same concentration. Furthermore, the adsorption of NFC could make the shale surface become more hydrophobic, which was more beneficial to shale stability. Overall, NFC had great potential to be a superior shale stabilizer in water-based drilling fluids for drilling troublesome shale formations. Acknowledgments This work was financially supported by the National Key Basic Research Special Foundation of China (2015CB251205)， National Natural Science Foundation of China (51474236) and China Postdoctoral Science Foundation (2015M580618; 2016T90658). References Abdo, J., Haneef, M.D., 2012. Nano-enhanced drilling fluids: pioneering approach to overcome uncompromising drilling problems. J. Energy Resour. Technol. 134 (1), 014501. Ajayan, P.M., Schadler, L.S., Braun, P.V., 2006. Nanocomposite science and technology. John Wiley & Sons. Akhtarmanesh, S., Shahrabi, M.A., Atashnezhad, A., 2013. Improvement of wellbore stability in shale using nanoparticles. J. Pet. Sci. Eng. 112, 290–295. Amanullah, M., Al-Tahini, A.M., 2009. Nano-technology-its significance in smart fluid development for oil and gas field application. In SPE Saudi Arabia Section Technical Symposium. Society of Petroleum Engineers. Baran, J.R., Cabrera, O.J., 2006. U.S. Patent No. 7,033,975. Washington, DC: U.S. Patent and Trademark Office. Cai, J.H., Chenevert, M.E., Sharma, M.M., Friedheim, J.E., 2012. Decreasing water invasion into Atoka shale using nonmodified silica nanoparticles. SPE Drill. Complet. 27 (01), 103–112. Ewy, R.T., Morton, E.K., 2008. Wellbore stability performance of water base mud additives. Soc. Pet. Eng.. Ferreira, C.C., Teixeira, G.T., Lachter, E.R., Nascimento, R.S.V., 2016. Partially hydrophobized hyperbranched polyglycerols as non-ionic reactive shale inhibitors
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Contents lists available at ScienceDirect
Journal of Petroleum Science and Engineering journal homepage: www.elsevier.com/locate/petrol
Hydrophobic modified polymer based silica nanocomposite for improving shale stability in water-based drilling fluids
MARK
⁎
Jian-gen Xu , Zhengsong Qiu, Xin Zhao, Weian Huang School of Petroleum Engineering, China University of Petroleum, Qingdao, 266580, China
A R T I C L E I N F O
A BS T RAC T
Keywords: Nanocomposite Shale stability Water-based drilling fluids Shale hydration Pressure transmission
In this paper, a novel hydrophobic modified polymer based silica nanocomposite (NFC) was successfully prepared by emulsion polymerization and it was characterized by FTIR, PSD, TEM and TGA analysis. The results indicated that NFC possessed uni-modal distribution from 38 nm to 164 nm with the D50 value of about 72 nm and had good thermal stability. A variety of methods including the contact angle measurement, pressure transmission test, hot-rolling cuttings dispersion test and compatible test were adopted to evaluate the comprehensive effect of NFC on shale stability. And the shale cores before and after interacting with NFC were also characterized by scanning electron microscope (SEM) analysis. The experimental investigations revealed that NFC could effectively retard the pore pressure transmission and internally bridge and seal the pore-throats of shale. And it also exhibited preferable shale inhibition performance compared with KCl and JHC at the same concentration. After adsorption, the shale surface was more hydrophobic, which was more advantageous to shale stability. Furthermore, the compatibility test results confirmed that NFC had no negative effect on rheological performance and possessed a positive influence on filtration control performance of water-based drilling fluids.
1. Introduction In the drilling process, 75% of the formations drilled are shale formations and 90% of the wellbore instability problems are attributed to shale instability (Steiger and Leung, 1992; Zhang et al., 2013). Although a number of studies have been done on shale instability in the past decades, it has still been a critical issue in the petroleum industry (Van Oort, 2003; Liang et al., 2014). More importantly, shale gas, as a type of unconventional resource, has transformed the energy landscape around the world, but shale instability problems in the horizontal section greatly constrain its development (Zhou et al., 2016; Akhtarmanesh et al., 2013). Recent research shows that retarding pressure transmission is effective way to solve shale instability problems (Van Oort, 1997; Van Oort et al., 1996; Sharma et al., 2012). However, shale formations are characterized by low porosity and low permeability, and a filter cake cannot be formed on shale surface since the traditional additives for drilling fluids are too large to bridge and seal the nanopores of shale formations (Ewy and Morton, 2008). Therefore, how to plug the nanopores of shale formations is a vitally important work to solve shale instability problems. In recent years, the application of nano materials in drilling fluids has attracted great attention (Jain et al., 2015; Abdo and Haneef, 2012;
⁎
Corresponding author. E-mail address: [email protected] (J.-g. Xu).
http://dx.doi.org/10.1016/j.petrol.2017.04.013 Received 9 December 2016; Received in revised form 9 March 2017; Accepted 7 April 2017 Available online 08 April 2017 0920-4105/ © 2017 Elsevier B.V. All rights reserved.
Li et al., 2012). To solve the problems of shale instability, many researchers have done a lot of work. Non-modified silica nanoparticles were first introduced to solve the problems, but only a little effect has been achieved because the nanoparticles are easy to agglomerate and need large dosage to play a role (Cai et al., 2012; Baran and Cabrera, 2006). Some other researchers used polymer latex nanoparticles to bridge and seal the nanopores and microfractures of shale formations, and a certain achievement has been obtained (Liu et al., 2015; Xu et al., 2017). But the polymer latex prepared by emulsifier-free emulsion polymerization shows poor stability and contains low solid, it will be subject to restrictions for field applications. In addition, some research groups have reported the application of nano-emulsion as an effective drilling fluids additive for drilling shale formations (Tabibiazar et al., 2015). But it is unstable and shows poor temperature resistance. The use of nano-fillers for polymer matrix can combine the rigidity and thermal stability of inorganic nanomaterial with the toughness of polymers to create excellent properties (Ajayan et al., 2006; Zou et al., 2008). Therefore, the nanocomposite can overcome those disadvantages and may be a new approach to solve shale instability problems. Additionally，shale hydration is another important factor to cause borehole instability (Zhong et al., 2016; Shadizadeh et al., 2015). It has been reported that hydrophobic polymer can effectively inhibit
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a mechanical stirrer, a thermometer, and a dropping funnel. In brief, a certain amount of modified nano-silica was dispersed into deionized water in which SDS and OP-10 were dissolved, then 0.12 g of NaHCO3, 28 g of Styrene (St) and 12 g of Butyl acrylate (BA) were added into it and ultrasonically treated for 1 h. Secondly, they were transferred into the flask to be pre-emulsified under mechanical stirring and heated up to 75 °C for 1 h. Thirdly, KPS (0.24 g) was added into the flask to induce polymerization. The polymerization was then continued in the flask for another 3 h at 75 °C and finally cooled to room temperature.
the shale hydration (Gu et al., 2012). The synergistic effects of hydrophobic polymer and inorganic nanomaterial in the nanocomposite may result in superior sealing performance and good inhibition capacity to mitigate shale instability problems. In this paper, a novel hydrophobic modified polymer based silica nanocomposite (NFC), mainly used as a potential shale stabilizer in water-based drilling fluids for drilling troublesome shale formations, was prepared with Styrene (St), Butyl acrylate (BA) and nano-silica via emulsion polymerization. NFC could retard pressure transmission and decrease shale permeability to increase shale stability. More importantly, NFC could inhibit shale hydration as well. As per our knowledge, this is the first report on the application of hydrophobic modified polymer based silica nanocomposite as a potential shale stabilizer in water-based drilling fluids.
2.3. Characterization of NFC The chemical structures of NFC were characterized by Flourier transformation infrared spectroscopy (FT-IR, Nicolet 6700, USA). The particle size of NFC was determined based on dynamic light scattering by particle size distribution analyzer (PSD, Zetasizer Nano ZS90, the United Kingdom). The morphology of NFC was observed using transmission electron microscopy (TEM, JEOL JEM-2100UHR, Japan). The thermal stability of NFC was measured by thermo gravimetric analysis (TGA, Schwerzenbach, Switzerland).
2. Materials and methods 2.1. Materials Styrene (St) and n-butyl acrylate (BA) were purchased from Sinopharm Chemical Reagent Co. Ltd (China) and were purified by vacuum distillation before use. SiO2 nanoparticles (7–40 nm) and octylphenol polyoxyethylene ether (OP-10) were obtained from Aladdin Reagent Co. Ltd (China). Ethanol, silane coupling agent KH570, sodium dodecyl sulfate (SDS), ethylic acid, potassium persulfate (KPS) and sodium bicarbonate (NaHCO3) were purchased from Sinopharm Chemical Reagent Co. Ltd (China) and used as received. Deionized water was used throughout the experiments. Shale samples in this study were obtained from Turpan Hami Basin, China. The detailed mineralogical composition of the shale samples was determined by XRD analysis and the results are presented in Table 1.
Firstly, NFC and non-modified silica nanoparticles were added into a certain amount of pre-hydrated sodium bentonite slurry respectively at a concentration of 0.5%. After magnetic stirring at least 24 h, the glass slides were uniformly coated using the dispersions and left airdried. Finally，a water droplet was dropped on the glass slide and the photos were recorded. The contact angle measurement was conducted on a contact angle tester (JC2000D, China) with the static sessile drop method.
2.2. Preparation of NFC
2.5. Pressure transmission test
Fig. 1 presents the preparation mechanism of NFC. The polymerization of NFC was divided into two steps. A certain amount of nanosilica was first dispersed into 100 mL ethanol dispersing medium with the aid of ultrasonic for 1 h. Then, KH570 was dissolved into ethanol dispersing medium with a little water according to the weight ratio of 1:1:18 for KH570/H2O/ethanol, and 1 mL ethylic acid was added into the dispersion with magnetic stirring for 30 min at room temperature. Secondly, the mixture of the above dispersion was loaded into a reaction flask, and vigorously stirred for 4 h at 75 °C using a mechanical stirrer to obtain KH570-modified nano-silica. Thirdly, the obtained KH570-modified nano-silica was washed several times with absolute ethanol, and dried at 60 °C for further use. The hydrophobic modified polymer based silica nanocomposite (NFC) as a potential shale stabilizer was prepared with Styrene (St), Butyl acrylate (BA) and KH570-modified nano-silica via emulsion polymerization. The polymerization reaction was carried out in a 250-mL four-necked flask which was equipped with a reflux condenser,
The pressure transmission test was adopted to evaluate the sealing performance of testing fluids, and through test results the permeability of shale cores could be calculated. The pressure transmission test was carried out on a simulation experiment device (Xu et al., 2005), and the test cell is shown in Fig. 2. For the test, 4.0 w/v% pre-hydrated sodium bentonite slurry was utilized as the base fluid. The axial compression and the confining pressure were maintained at 5 MPa all times, and the upstream pressure was elevated to 2 MPa. With initial downstream pressure 1 MPa, downstream pressure buildup was monitored subsequently to obtain the pressure transmission curves. In addition, the permeability of shale cores could be calculated by following formula (Xu and Qiu, 2006).
2.4. Contact angle measurement
⎛ P −P ⎞ ⎛ P −P ⎞ ln ⎜ P −mP (Lo, t ) ⎟ − ln ⎜ P −mP (Lo, t ) ⎟ m 2 1 ⎠ ⎝ m ⎠ ⎝ μβVL K= A t2 − t1
where K represents shale permeability, μm ; μ represents viscosity, mPa•s; β represents the static compression ratio, MPa−1; V represents the enclosed volume of downstream fluids, cm3; L represents the length of shale samples, cm; A represents the cross-sectional area of shale samples, cm2; t represents total experimental time, s; Pm represents the upstream pressure, MPa; Po represents the initial downstream pressure, MPa; P (L, t) represents the realtime downstream pressure, MPa. What is more, the shale cores were characterized before and after interacting with NFC by scanning electron microscope (SEM) analysis.
Table 1 Mineralogical composition of the shale samples. X-ray diffraction
Content (wt%)
Quartz Potassium feldspar Plagioclase Calcite Iron dolomite Clay mineral Kaolinite Chlorite Illite Illite/smectite mixed layer
20 6 29 28 2 15 3 3 12 82
(1) 2
2.6. Hot-rolling cuttings dispersion test Hot-rolling cuttings dispersion test was performed to evaluate 326
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Fig. 1. Schematic representation of NFC preparation.
Fig. 2. The schematic of the test cell for pressure transmission test.
NFC's ability to inhibit shale hydration and dispersion (Zhong et al., 2012). In this test, potassium chloride (KCl) and polymeric alcohol (JHC) as two frequently used shale inhibitors were chose to compare with NFC. Firstly, 50 g dried shale cuttings with sizes varying between 2.00 mm and 3.35 mm were added into the sealed tank which contained 350 mL testing fluid. Then, the sealed tank was hot rolled for 16 h at 77 °C. After hot rolling, the shale cuttings were screened using 40 mesh sieve, washed and dried at 105 °C for 4 h. Finally, the remaining cuttings were weighed to calculate the recovery rate.
Fig. 3. FT-IR spectra of the nanocomposite NFC.
3. Results and discussion 3.1. Characterization of NFC 3.1.1. FT-IR analysis Fig. 3 shows the FT-IR spectra of Poly(St-BA)/silica nanocomposite. In the spectrum of Poly(St-BA)/silica nanocomposite, the peaks at 1602 cm−1, 1493 cm−1 and 1452 cm−1 were associated with the characteristic vibration of benzene skeleton. Moreover, the peaks at 758 cm−1 and 697 cm−1 were the characteristic peaks of single substitution benzene ring, indicating that styrene took part in the polymerization reaction successfully. In addition, the stretching vibration peak of C˭O was 1728 cm−1, and the stretching vibration peak of C–O–C bond was 1155 cm−1, indicating that butyl acrylate was also involved in the polymerization reaction. What is more, the stretching vibration peak of Si–O–Si bond was 1098 cm−1. Therefore, through the FT-IR spectra, it can be seen that the Poly(St-BA)/silica nanocomposite was successfully prepared.
2.7. Compatibility test The tested drilling fluid was prepared by adding 0.1 w/v% of modified starch, 3.0 w/v% KCl and 0.7 w/v% low viscosity polyanionic celluloses into 4.0 w/v% pre-hydrated sodium bentonite slurry at a high speed of 8000 rpm. After hot rolling at the appointed temperature 120 °C for 16 h in a XGRL-4 type rolling oven (Haitongda Company, China), the rheological and filtration control performance were measured. The compatibility of NFC in water-based drilling fluids was analyzed by comparing the rheological and filtration control performance of the tested drilling fluid with or without NFC. The rheological performance was determined with a ZNN-D6 rotating viscometer (Haitongda Company, China). The rheological parameters such as apparent viscosity, plastic viscosity and yield point were calculated from the high rotational speeds (600 and 300 rpm) according to the American Petroleum Institute (API) recommended practice. The filtration control performance was also tested by ZNS-2A filtration apparatus (Haitongda Company, China).
3.1.2. PSD analysis Fig. 4 presents the particle size distribution of the nanocomposite NFC in dilute aqueous solution. It can be concluded that the particle size distribution of the nanocomposite NFC was more concentrated, and the curve was a parabola. The particle size distribution was in the range of 38–164 nm and the medium particle size D50 value was 72 nm. Therefore, NFC can effectively seal the micro–nano scale porethroats and fractures of shale formations, and it was conducive to borehole stability.
Apparent Viscosity(AV) = Φ600 /2(mPa· s ) Plastic Viscosity(PV) = Φ600 −Φ300 (mPa· s )
3.1.3. TEM analysis Fig. 5 displays the TEM micrograph of the nanocomposite NFC in
Yield Point(YP) = (Φ300−PV)/2(Pa) 327
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3.2. Contact angle measurement Fig. 7 shows the test results of the contact angle measurement. It can be seen that the water contact angle for bentonite slurry was 22.0°, which showed a strong hydrophilic property. In particular, when 0.5 w/ v% non-modified silica nanoparticles was added, the hydrophilic property became stronger and the water contact angle for bentonite slurry containing 0.5 w/v% non-modified silica nanoparticles was only 14.3°. In the experiments, a phenomenon was observed that the water droplet spread quickly on the surface of the glass slide, indicating that non-modified silica nanoparticles were highly hydrophilic. After silica nanoparticles were grafted with hydrophobic polymer Poly(St-BA), the water contact angle for the nanocomposite was changed. When the bentonite slurry contained 0.5 w/v% NFC, the contact angle increased to around 60.2°, indicating that compared with non-modified silica nanoparticles the water wettability was significantly decreased. The shale surface was more hydrophobic and had a less affinity towards water, which was conducive to the reduction of water adsorption onto it (Zhong et al., 2015). Thus, NFC was advantageous to shale stability.
Fig. 4. Particle size distribution of diluted nanocomposite NFC.
3.3. Pressure transmission test The results of the pressure transmission test are presented in Fig. 8. It can be concluded that it took only around 40 min for shale cores to make the upstream and downstream pressure reach a balance, and 128 min for the base fluid. The growth rate of downstream pressure for shale and the base fluid was significantly higher than the base fluid containing 2.0 w/v% NFC, the time of which for making the upstream and downstream pressure reach a balance was about 503 min. According to formula (1), the shale permeability could be calculated based on pressure transmission test data. The permeability of shale core was 1.68×10−6 μm2. After interacting with the base fluid and the base fluid containing 2.0 w/v% NFC, it was decreased to 1.09×10−7 μm2 and 3.63×10−8 μm2, respectively. Results indicated that NFC could effectively retard pressure transmission and reduce the permeability of shale cores, thus it could be treated as a superior sealing agent. What is more, Fig. 9 shows the SEM photos of shale cores before and after interacting with NFC. It can clearly see that the nanoparticles could bridge and seal the pore throats and micro cracks of shale cores. A dense plugging film eventually formed on the shale surface, thereby improving shale stability in drilling process.
Fig. 5. TEM micrograph of diluted nanocomposite NFC.
dilute aqueous solution. It can be found that the particles were well dispersed and had regular spherical shape. The average particle size was around 70 nm, which was consistent with the D50 value (72 nm) of the PSD characterization results. Furthermore, the particles with coreshell structure indicated that the hydrophobic polymer Poly(St-BA) has been successfully grafted onto the surface of nano-silica particles.
3.4. Hot-rolling cuttings dispersion test
3.1.4. TGA analysis The thermal stability of NFC played a significant role for its application in drilling fluids. Fig. 6 shows the TGA curve of the prepared nanocomposite NFC. There was no obvious thermal decomposition until temperature increased up to 380 °C. Therefore, the newly prepared nanocomposite NFC maintained good thermal stability.
The inhibition performance of NFC was assessed by hot-rolling cuttings dispersion test with highly reactive shale cuttings. The results are shown in Fig. 10. It can be concluded that the shale recovery rate in tap water was 40.2%, indicating that the shale cuttings had strong hydration and dispersion capacity. After having conducted hot rolling of 0.5 w/v% NFC, 1.0 w/v% NFC, and 2.0 w/v% NFC, the recovery rate of them was 69.3%, 82.1%, and 90.7% respectively, showing that NFC had good capacity to prevent hydration and dispersion of shale cuttings in aqueous medium. In addition, the inhibition efficiency increased with the NFC concentration, and the inhibition performance of NFC was better than KCl and JHC at the same concentration. Therefore, NFC could act as a good shale inhibitor to maintain borehole stability. Through some literatures and the results obtained in this work, the inhibition mechanism of NFC for preventing shale hydration can be concluded (Gu et al., 2012; Ferreira et al., 2016; Amanullah and AlTahini, 2009). Because of its small particle size, large specific surface area and high surface energy, NFC has strong surface activity, and can be easily adsorbed onto the surface of clay particles. Furthermore, the adsorption capacity can be enhanced by a large number of residual bonds and active hydroxyl groups on the surface of NFC. In addition to van der Waals interactions, the clay particles surface has available sites to form a number of hydrogen bonds, thereby adsorbing more firmly.
Fig. 6. TGA curve of the nanocomposite NFC.
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Fig. 7. Test results of contact angle measurement, (a) bentonite slurry. (b) bentonite slurry containing 0.5 w/v% silica nanoparticles. (c) bentonite slurry containing 0.5 w/v% NFC.
Fig. 8. Pressure transmission test curves.
Fig. 10. Shale cuttings recoveries of different inhibitors.
What is more, after grafted with hydrophobic polymer Poly(St-BA), the surface of NFC is covered with the polymer chains and become more hydrophobic. When NFC solution is in contact with shale, a hydrophobic film can be formed on shale surface by adsorption. Therefore, the clay minerals hydration can be effectively inhibited as the entrance of water molecules into clay particles clearance is restricted by the hydrophobic film. The aforementioned facts can prove that NFC has good shale inhibition performance.
Table 2 Rheological and filtration control performance of the tested drilling fluid.
3.5. Compatibility test After hot rolling at the appointed temperature 120 °C for 16 h in a XGRL-4 type rolling oven, the rheological and filtration control performance of the tested drilling fluid with or without 2.0 w/v% NFC were measured. The test results are shown in Table 2. It can be concluded that NFC had no negative effect on rheological performance
Parameter
Before adding
After adding
600 rpm 300 rpm AV (mPa.s) PV (mPa.s) YP (Pa) YP/PV API FL (mL)
36 22 18 14 4 0.29 6.6
40 25 20 15 5 0.33 5.2
and had a positive influence on filtration control performance of waterbased drilling fluids. Therefore, the newly prepared nanocomposite NFC could be a good shale stabilizer in water-based drilling fluids.
Fig. 9. SEM photos of shale cores, (a) before testing and (b) after interacting with the base fluid containing 2.0 w/v% NFC.
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4. Conclusion Novel hydrophobic modified polymer based silica nanocomposite (NFC) was successfully prepared as a potential shale stabilizer in waterbased drilling fluids. Its particle size distribution was between 38 nm and 164 nm with D50 value of about 72 nm and the newly prepared shale stabilizer NFC had good thermal stability. What is more, NFC could effectively retard pressure transmission and decrease shale permeability. The nanoparticles could bridge and seal the pore throats and micro cracks of shale cores. A dense plugging film could eventually form on the shale surface, thereby improving shale stability. Meanwhile, NFC had good shale inhibition performance. At the concentration of 2%, the recovery rate of the shale sample was 90.7%, indicating that NFC exhibited superior shale inhibition performance compared with KCl and JHC at the same concentration. Furthermore, the adsorption of NFC could make the shale surface become more hydrophobic, which was more beneficial to shale stability. Overall, NFC had great potential to be a superior shale stabilizer in water-based drilling fluids for drilling troublesome shale formations. Acknowledgments This work was financially supported by the National Key Basic Research Special Foundation of China (2015CB251205)， National Natural Science Foundation of China (51474236) and China Postdoctoral Science Foundation (2015M580618; 2016T90658). References Abdo, J., Haneef, M.D., 2012. Nano-enhanced drilling fluids: pioneering approach to overcome uncompromising drilling problems. J. Energy Resour. Technol. 134 (1), 014501. Ajayan, P.M., Schadler, L.S., Braun, P.V., 2006. Nanocomposite science and technology. John Wiley & Sons. Akhtarmanesh, S., Shahrabi, M.A., Atashnezhad, A., 2013. Improvement of wellbore stability in shale using nanoparticles. J. Pet. Sci. Eng. 112, 290–295. Amanullah, M., Al-Tahini, A.M., 2009. Nano-technology-its significance in smart fluid development for oil and gas field application. In SPE Saudi Arabia Section Technical Symposium. Society of Petroleum Engineers. Baran, J.R., Cabrera, O.J., 2006. U.S. Patent No. 7,033,975. Washington, DC: U.S. Patent and Trademark Office. Cai, J.H., Chenevert, M.E., Sharma, M.M., Friedheim, J.E., 2012. Decreasing water invasion into Atoka shale using nonmodified silica nanoparticles. SPE Drill. Complet. 27 (01), 103–112. Ewy, R.T., Morton, E.K., 2008. Wellbore stability performance of water base mud additives. Soc. Pet. Eng.. Ferreira, C.C., Teixeira, G.T., Lachter, E.R., Nascimento, R.S.V., 2016. Partially hydrophobized hyperbranched polyglycerols as non-ionic reactive shale inhibitors
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