To investigate the pore structure and adsorption capacity of illite with respect to methane in the Longmaxi Formation，isothermal adsorption experiments utilizing mercury intrusion，liquid nitrogen and low-temperature carbon dioxide techniques were applied to shale samples from Sichuan Basin.The adsorption characteristics of illite slit pores with different diameters were simulated using the Monte Carlo method.The results demonstrate that the pore volume and specific surface area of the shale are primarily supplied by pore diameters of less than 2nm.Illite is one of the primary components of the clay mineralogy within the shale and forms parallel or nearly-parallel plate pores.For pore sizes ranging from 0.5nm to 0.9nm (at 303.15K and 8MPa)，the methane molecules are affected by van der Waals and electrostatic forces，and the excess adsorption capacity of methane is big.When the pore size is bigger than 0.9nm，the methane adsorption is primarily affected by van der Waals forces，and the excessadsorption capacity of methane initially decreases，after which it remains unchanged with anincrease in the pore size.The free gas content increases with increasing pore diameters.The average equivalent adsorption heat reflects that the adsorption of methane onto illite is characterized by physical adsorption.During the adsorption process，when the pore size is between 0.5nm and 1.2nm，the average equivalent adsorption heat decreases rapidly with an increase of the pore diameter.When the pore size exceeds 1.2nm，the adsorption intensity between the methane molecules and the illite slit is essentially stable，and the average adsorption heat is 6.72kJ/mol.When the pore size is between 0.5nm and 0.8nm，the monolayer of methane is adsorbed onto the pore wall，and the local density of methane exhibits the characteristics of a single peak.When the pore size is between 0.8nm and 1.2nm，the adsorption mode changes from single-layer adsorption to double-layer adsorption，and the local density curve changes from unimodal to bimodal.When the pore size is bigger than 1.2nm，the free volume of methane adsorption can be big，and the local density curve is bimodal.
Tang Xin, Zhu Yan-ming, Guo Yuan-chen, Liu Yu, Zhou Xiao-yi
. Molecular simulation of methane adsorption within illite minerals in the shale of the Longmaxi Formation based on a grand canonical Monte Carlo method and pore size distribution[J]. Natural Gas Geoscience, 2018
, 29(12)
: 1809
-1816
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DOI: 10.11764/j.issn.1672-1926.2018.10.006
［1］Curtis J B.Fractured shale-gas systems[J].AAPG Bulletin,2002,86(11):1921.
[2]Ross D J K,Marc B R.The importance of shale composition and pore structure upon gas storage potential of shale gas reservoirs[J].Marine and Petroleum Geology,2009,26(6):916-927.
[3]Chen S B,Han Y F,Fu C Q,et al.Micro and nano-size pores of clay minerals in shale reservoirs:Implication for the accumulation of shale gas[J].Sedimentary Geology,2016,342:180-190.
[4]Chen S B,Zhu Y M,Qin Y,et al.Reservoir evaluation of the Lower Silurian Longmaxi Formation shale gas in the southern Sichuan Basin of China[J].Marine and Petroleum Geology,2014,57:619-630.
[5]Bowker K A.Recent development of the Barnett shale play,Fort Worth Basin:West Texas[J].Geological Society Bulletin，2003，42：1-11.
[6]Guo Qiulin,Chen Xiaoming,Song Huanqi,et al.Evolution and models of shale porosity during burial process[J].Natural Gas Geoscience,2013，24(3)：439-449.
郭秋麟,陈晓明,宋焕琪,等.泥页岩埋藏过程孔隙度演化与预测模型探讨[J].天然气地球科学,2013,24(3):439-449.
[7]Wilson B.Transistor I-V characteristics[J].Journal of Limnology,2003,69(supplement 1):33-44.
[8]Chen S B,Zhu Y M,Wang H Y,et al.Shale gas reservoir characterisation:A typical case in the southern Sichuan Basin of China[J].Energy,2011,36(11):6609-6616.
[9]Sun Renyuan,Zhang Yunfei,Fan Kunkun,et al.Molecular simulations of adsorption characteristics of clay minerals in shale[J].Acta Chimica Sinica,2015,66(6):2118-2122.
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.
[10]Xuan P,Zhao J,Cao D.Adsorption of carbon dioxide of 1-site and 3-site models in pillared clays:A Gibbs ensemble Monte Carlo simulation[J].Journal of Colloid & Interface Science,2007,310(2):391-401.
[11]Do D D,Do H D,Nicholson D.Molecular simulation of excess isotherm and excess enthalpy change in gas-phase adsorption[J].The Journal of Physical Chemistry B,2009,113(4):1030-1040.
[12]Do D D,Do H D.Comparative adsorption of spherical argon and flexible n-butane in carbon slit pores:A GCMC computer simulation study[J].Colloids and Surfaces A:Physicochemical and Engineering Aspects,2005,252(1):7-20.
[13]Tan Z M,Gubbins K E.Adsorption in carbon micropores at supercritical temperatures[J].The Journal of Chemical Physics,1990,94(15):6061-6069.
[14]Jarvie D M,Hill R J,Ruble T E,et al.Unconventional shale-gas systems:The Mississippian Barnett shale of north-central Texas as one model for thermogenic shale-gas assessment[J].AAPG Bulletin,2007,91(4):475-499.
[15]Wang Jin.Methane Adsorption in Illite by Molecular Simulation [D].Taiyuan ：Taiyuan University of Technology,2015.
王晋.1M伊利石对甲烷吸附的分子模拟[D].太原：太原理工大学,2015.
[16]Wang Y,Zhu Y M,Chen S B,et al.Characteristics of the nanoscale pore structure in northwestern Hunan shale gas reservoirs using field emission scanning electron microscopy,high-pressure mercury intrusion,and gas adsorption[J].Energy & Fuels,2014,28(2):945-955.
[17]Drits V A,Zviagina B B,Mc Carty D K,et al.Factors responsible for the distribution of octahedral cations over trans- and cis-sites in dioctahedral 2:1 layer silicates [J].Clays Clay Minerals,2010,54:131-152.
[18]Wang Jin,Fang Xiaohong,Zeng Fangui.Structure modeling of illite-1M and its XRD simulation[J].Journal of the Chinese Ceramic Society,2015,43(8):1162-1166.
王晋,房晓红,曾凡桂.伊利石1M多型结构模型的构建及XRD模拟[J].硅酸盐学报,2015,43(8):1162-1166.
[19]Peng D Y,Robinson D B.A new two-constant equation of state[J].Minerva Ginecologica,1976,12(11/12):3069-3078.
[20]Mosher K,He J J,Liu Y Y,et al.Molecular simulation of methane adsorption in micro- and mesoporous carbons with applications to coal and gas shale systems[J].International Journal of Coal Geology,2013,109-110:36-44.
[21]Liu Y,ZhuY M,Li W,et al.Molecular simulation of methane adsorption in shale based on grand canonical Monte Carlo method and pore size distribution[J].Journal of Natural Gas Science and Engineering,2016,30:119-126.
[22]Chen S,Zhu Y M,Wang M,et al.Prospect conceiving of joint research and development of shale gas and coalbed methane in China[J].Energy and Power Engineering,2011,3(3):348-354.
[23]Dong Dazhong,Cheng Keming,Wang Yuman,et al.Forming conditions and characteristics of shale gas in the Lower Paleozoic of the Upper Yangtze region,China[J].Oil & Gas geology,2010,31(3):288-299.
董大忠,程克明,王玉满,等.中国上扬子区下古生界页岩气形成条件及特征[J].石油与天然气地质,2010,31(3):288-299.
[24]Xiong Jian，Liu Xiangjun，Liang Lixi .Molecular simulation on the adsorption behaviors of methane in montmorillonite slit pores[J].Acta Petrolei Sinica,2016,37(8):1021-1029.
熊健，刘向君，梁利喜.甲烷在蒙脱石狭缝孔中吸附行为的分子模拟[J].石油学报，2016，37（8）：1021-1029．
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