甲烷在高岭石狭缝中吸附的分子模拟
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摘要
为了探究页岩储层中粘土矿物对甲烷的吸附机理,通过巨正则蒙特卡洛及分子动力学模拟方法,采用Materials Studio软件计算了缝宽为2、5、8 nm的高岭石狭缝在埋深为1、2、3、4、5 km的储层环境中对甲烷的吸附作用。结果表明:随着缝宽的增大,甲烷的绝对吸附量增大,等量吸附热减小;随着埋深的增大,甲烷的绝对吸附量和等量吸附热均先增大后减小,4 km时最大。且等量吸附热介于7～12 kJ/mol之间,小于42 kJ/mol,表明是物理吸附。甲烷沿垂直于高岭石壁面的方向出现吸附分层的现象,靠近壁面的为主要吸附层,然后依次是次要吸附层和游离层,三个吸附层的自扩散系数依次增大。
In order to explore the adsorption mechanism of methane in clay minerals under shale reservoirs,the grand canonical Monte Carlo and molecular dynamics simulation method was used to calculate the adsorption of methane in kaolinite slit with 2, 5, 8 nm slit width under the shale reservoirs whose buried depth was 1, 2, 3, 4, 5 km by using Materials Studio simulation software.The results indicate that as the slit width increases, the absolute adsorption quantity of methane increases and isosteric adsorption heat decreases; As the buried depth increases, both absolute adsorption quantity and isosteric adsorption heat of methane increase at first, then decrease, and they reach the maximum value when the buried depth is 4 km. Isosteric adsorption heat of methane is between 7 ～ 12 kJ/mol, which is less than 42 kJ/mol indicating that the adsorption is physical adsorption. Along the direction perpendicular to kaolinite wall, the adsorbed methane is layered. The layer that is adjacent to kaolinite wall is the main adsorption layer, the next is the secondary adsorption layer and then is the free layer. The order of self-diffusion coefficient of three adsorption layers is: main adsorption layer < secondary adsorption layer < free layer.
In order to explore the adsorption mechanism of methane in clay minerals under shale reservoirs,the grand canonical Monte Carlo and molecular dynamics simulation method was used to calculate the adsorption of methane in kaolinite slit with 2, 5, 8 nm slit width under the shale reservoirs whose buried depth was 1, 2, 3, 4, 5 km by using Materials Studio simulation software.The results indicate that as the slit width increases, the absolute adsorption quantity of methane increases and isosteric adsorption heat decreases; As the buried depth increases, both absolute adsorption quantity and isosteric adsorption heat of methane increase at first, then decrease, and they reach the maximum value when the buried depth is 4 km. Isosteric adsorption heat of methane is between 7 ～ 12 kJ/mol, which is less than 42 kJ/mol indicating that the adsorption is physical adsorption. Along the direction perpendicular to kaolinite wall, the adsorbed methane is layered. The layer that is adjacent to kaolinite wall is the main adsorption layer, the next is the secondary adsorption layer and then is the free layer. The order of self-diffusion coefficient of three adsorption layers is: main adsorption layer < secondary adsorption layer < free layer.
引文
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[2]Curtis J B.Fractured shale-gas systems[J].AAPG Bulletin,2002,86(11):1921-1938.
[3]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.
[4]Sui H,Yao J,Zhang L.Molecular Simulation of Shale Gas Adsorption and Diffusion in Clay Nanopores[J].Computation,2015,3(4):687-700.
[5]Kadoura A,Nair A K N,Sun S.Adsorption of carbon dioxide,methane,and their mixture by montmorillonite in the presence of water[J].Microporous and Mesoporous Materials,2016,225:331-341.
[6]Bish D L.Rietveld Refinement of the Kaolinite Structure at1.5 K[J].Clays and Clay Minerals,1993,41(6):738-744.
[7]周俊杰,李文静.高岭石电子结构的量化计算[J].工业技术创新,2014(3):258-262.
[8]李靖,李相方,王香增,等.页岩黏土孔隙含水饱和度分布及其对甲烷吸附的影响[J].力学学报,2016,48(5):1217-1228.
[9]王茂桢,柳少波,任拥军,等.页岩气储层粘土矿物孔隙特征及其甲烷吸附作用[J].地质论评,2015,61(1):207-216.
[10]Stephen L M,Barry D O,William A G.DREIDING:a generic force field for molecular simulations[J].Journal of Physical Chemistry,1990,94(26):8897-8909.
[11]刘玉婷.中外页岩气评价标准之比较研究[D].荆州:长江大学,2012.
[12]王斌,马正飞.烷烃在金属有机骨架MOF-5和Cu-BTC中吸附的蒙特卡罗模拟[J].南京工业大学学报:自科版,2008,30(3):38-42.
[13]周尚文,王红岩,薛华庆,等.页岩过剩吸附量与绝对吸附量的差异及页岩气储量计算新方法[J].天然气工业,2016,36(11):12-20.
[14]何映颉,杨洋,张廷山,等.石墨狭缝吸附页岩气的分子模拟[J].岩性油气藏,2016,28(6):88-94.
[15]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]吉利明,马向贤,夏燕青,等.黏土矿物甲烷吸附性能与微孔隙体积关系[J].天然气地球科学,2014,25(2):141-152.
[17]熊健,刘向君,梁利喜.甲烷在黏土矿物狭缝孔中吸附的分子模拟研究[J].煤炭学报,2017,42(4):959-968.
[18]刘春,张荣虎,张惠良,等.致密砂岩储层微孔隙成因类型及地质意义--以库车前陆冲断带超深层储层为例[J].石油学报,2017,38(2):150-159.