孔隙压力和含水量对煤系高岭石吸附甲烷能量影响的分子模拟研究
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摘要
采用蒙特卡洛方法模拟计算了高岭石吸附甲烷的吸附能和范德华能及其随孔隙压力和含水量的变化规律,分析了高岭石吸附甲烷的微观机理。结果表明:随着孔隙压力的增大,高岭石吸附甲烷的范德华能和吸附能均呈先增大后趋于平衡的规律,符合Langmuir模型;随着含水量的增大,高岭石吸附甲烷的吸附能呈线性规律降低。高岭石中的水分子以氧原子端靠近高岭石孔壁表面、氢原子端远离孔壁表面的方式吸附,并占据了高岭石吸附甲烷的空间;高岭石对甲烷分子的吸附是典型的物理吸附,对水分子的吸附是物理与化学吸附并存;孔隙压力和含水量影响高岭石和甲烷分子间的距离,进而影响了高岭石和甲烷分子间范德华能的大小。研究结果从微观角度揭示了在松软低渗透煤层条件下,将水力压裂和卸压钻孔置于煤层顶底板岩层中,在富含黏土矿物的岩层中实施水力压裂和卸压有利于释放煤层气,为实现煤及其顶底板岩层中煤系气的一体化强化开采奠定了微观理论基础。
The Monte Carlo method was used to simulate and calculate the adsorption energy and Van Der Waals energy of methane adsorbed by kaolinite and its changing variation with pore pressure and moisture content. The microscopic mechanism of the adsorption of methane on kaolinite was theoretically analyzed. The results show that the Van der Waals energy and adsorption energy of methane adsorbed by kaolinite were increased firstly and then stable with increasing pore pressure, which was agreed with the Langmuir model. The adsorption energy of methane adsorbed on kaolinite decreased linearly with increasing water content. The water molecules in kaolinite were adsorbed in such a way that the oxygen atoms end near the surface of the kaolinite pore wall and the hydrogen atoms end away from the pore wall surface and occupy the space of methane adsorbed by kaolinite. The adsorption of methane molecules on kaolinite was a typical physical adsorption and the adsorption of water molecules was the coexistence of physical adsorption and chemical adsorption. Changes in water content and pore pressure had an effect on the distance between kaolinite and methane molecules, which in turn affects the Van der Waals forces. The research results revealed the mechanism of the effect of moisture on the adsorption of methane energy on kaolinite from the microscopic viewpoint. It is a micro-theoretical foundation for the integration of coal-series gas by placing hydraulic fracturing in the coal seam roof and floor strata under conditions of soft coal seams.
The Monte Carlo method was used to simulate and calculate the adsorption energy and Van Der Waals energy of methane adsorbed by kaolinite and its changing variation with pore pressure and moisture content. The microscopic mechanism of the adsorption of methane on kaolinite was theoretically analyzed. The results show that the Van der Waals energy and adsorption energy of methane adsorbed by kaolinite were increased firstly and then stable with increasing pore pressure, which was agreed with the Langmuir model. The adsorption energy of methane adsorbed on kaolinite decreased linearly with increasing water content. The water molecules in kaolinite were adsorbed in such a way that the oxygen atoms end near the surface of the kaolinite pore wall and the hydrogen atoms end away from the pore wall surface and occupy the space of methane adsorbed by kaolinite. The adsorption of methane molecules on kaolinite was a typical physical adsorption and the adsorption of water molecules was the coexistence of physical adsorption and chemical adsorption. Changes in water content and pore pressure had an effect on the distance between kaolinite and methane molecules, which in turn affects the Van der Waals forces. The research results revealed the mechanism of the effect of moisture on the adsorption of methane energy on kaolinite from the microscopic viewpoint. It is a micro-theoretical foundation for the integration of coal-series gas by placing hydraulic fracturing in the coal seam roof and floor strata under conditions of soft coal seams.
引文
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[26]韩永华,刘文礼,陈建华,等.羟基钙在高岭石两种(001)晶面的吸附机理[J].煤炭学报,2016,41(3):743-750.HAN Yonghua,LIU Wenli,CHEN Jianhua,et al.Adsorption mechanism of hydroxyl calcium on two kaolinite(001)surface[J].Journal of China Coal Society,2016,41(3):743-750.
[2]PASHIN J C.Coal as a petroleum source rock and reservoir rock[C]//Applied Coal Petrology,2008:227-262.
[3]WANG Y M,DONG D Z,HUA Y,et al.Quantitative characterization of reservoir space in the Lower Silurian Longmaxi Shale,southern Sichuan,China[J].Science China:Earth Sciences,2014,57(2):313-322.
[4]HOLMBOE M,Bourg I C.Molecular dynamics simulations of water and sodium diffusion in smectite interlayer nanopores as a function of pore size and temperature[J].Chemical Society Reviews,2014,42(8):3628-3646.
[5]唐书恒,范二平.富有机质页岩中主要黏土矿物吸附甲烷特性[J].煤炭学报,2014,39(8):1700-1706.TANG Shuheng,FAN Erping.Methane adsorption characteristics of clay minerals in organic-rich shales[J].Journal of China Coal Society,2014,39(8):1700-1706.
[6]侯宇光,何生,易积正,等.页岩孔隙结构对甲烷吸附能力的影响[J].石油勘探与开发,2014,41(2):248-256.HOU Yuguang,HE Sheng,YI Jizheng,et al.Effect of pore structure on methane adsorption capacity of shales[J].Petroleum Exploration and Development,2014,41(2):248-256.
[7]JI L,ZHANG T,MILLIKEN K L,et al.Experimental investigation of main controls to methane adsorption in clay-rich rocks[J].Applied Geochemistry,2012,27(12):2533-2545.
[8]LIU D,YUAN P,LIU H,et al.High-pressure adsorption of methane on montmorillonite,kaolinite and illite[J].Applied Clay Science,2013,85(11):25-30.
[9]JIN Z,FIROOZABADI A.Effect of water on methane and carbon dioxide sorption in clay minerals by Monte Carlo simulations[J].Fluid Phase Equilibria,2014,382:10-20.
[10]BILLEMONT P,COASNE B,DE W G.Adsorption of carbon dioxide,methane,and their mixtures in porous carbons:effect of surface chemistry,water content,and pore disorder[J].Langmuir the Acs Journal of Surfaces&Colloids,2013,29(10):3328-38.
[11]孙仁远,张云飞,范坤坤,等.页岩中黏土矿物吸附特性分子模拟[J].化工学报,2015,66(6):2118-2122.SUN Renyuan,ZHANG Yunfei,FAN Kunkun,et al.Molecular simulation of adsorption characteristics of clay minerals in shale[J].CIESC Journal,2015,66(6):2118-2122.
[12]隋宏光,姚军.页岩黏土矿物CH4/CO2吸附规律的分子模拟[J].东北石油大学学报,2016,40(2):90-98.SUI Hongguang,YAO Jun.Molecular Simulation of Adsorption Law of CH4/CO2 in shale clay minerals[J].Journal of Northeast Petroleum University,2016,40(2):90-98.
[13]ZHANG J,CLENNELL M B,DEWHURST D N,et al.Combined monte carlo and molecular dynamics simulation of methane adsorption on dry and moist coal[J].Fuel,2014,122(15):186-197.
[14]FISK S,WIDOM B.Structure and free energy of the interface between fluid phases in equilibrium near the critical point[J].The Journal of Chemical Physics,1969,50(8):3219-3227.
[15]BISH D L.Rietveld refinement of non-hydrogen atomic positions in kaolinite[J].Clays&Clay Minerals,1989,37(4):289-296.
[16]MAYO S L,OLAFSON B D,GODDARD W A.Ageneric force field for molecular simulations[J].Journal of Physical Chemistry,1990,94(26):8897-8909.
[17]蔡治勇,曾丹苓,刘娟芳.分子动力学模拟中的变截断半径算法[J].工程热物理学报,2006,27(4):556-558.CAI Zhiyong,ZENG Danling,LIU Juanfang.Acomputational method with variable cutoff radium in molecular dynamics simulation[J].Journal of Engineering Thermophysics,2006,27(4):556-558.
[18]MARTIN M G,SIEPMANN J I.Transferable potentials for phase equilibria.1 united-atom description of nalkanes[J].Journal of Physical Chemistry B,1998,102:2569-2577.
[19]赵安平.季冻区路基土冻胀的微观机理研究[D].长春:吉林大学,2008.
[20]SHULYAK R S,PRIMACHENKO V V,ZOLOTUKHINA L N,et al.Investigating chalganovsk kaolin deposits[J].Refractories,1992,33(5/6):323-325.
[21]TALU O,MYERS A L.Molecular simulation of adsorption:Gibbs dividing surface and comparison with experiment[J].Aiche Journal,2010,47(5):1160-1168.
[22]聂百胜,段三明.煤吸附瓦斯的本质[J].太原理工大学学报,1998,29(4):417-421.NIE Baisheng,DUAN Sanming.The adsorption essence of gas on coal surface[J].Journal of Taiyuan University of Technology,1998,29(4):417-421.
[23]PRAUSNITZ J M,LICHTENTHALER R N,de Azevedo E G.Molecular thermodynamics of fluid-phase equilibria[M].Beijing:Chemical Industry Press,1999:32-48.
[24]曹明礼,曹明贺.非金属纳米矿物材料[M].北京:化学工业出版社,2006:62-79.
[25]熊健,刘向君,梁利喜.石英吸附甲烷的蒙特卡罗研究[J].天然气地球科学,2016,27(8):1532-1540.XIONG Jian,LIU Xiangjun,LIANG Lixi.Adsorption of methane in quartz by grand canonical monte carlo simulation[J].Natural Gas Geoscience,2016,27(8):1532-1540.
[26]韩永华,刘文礼,陈建华,等.羟基钙在高岭石两种(001)晶面的吸附机理[J].煤炭学报,2016,41(3):743-750.HAN Yonghua,LIU Wenli,CHEN Jianhua,et al.Adsorption mechanism of hydroxyl calcium on two kaolinite(001)surface[J].Journal of China Coal Society,2016,41(3):743-750.