基于低温CO2吸附的煤和页岩微孔结构分形分析  

Fractal analysis of micropore structures in coal and shale based on low-temperature CO2 adsorption

作　　者：熊益华 周尚文[2] 焦鹏飞 杨明伟 周军平[3] 韦伟[1] 蔡建超[1] XIONG Yi-hua;ZHOU Shang-wen;JIAO Peng-fei;YANG Ming-wei;ZHOU Jun-ping;WEI Wei;CAI Jian-chao(Institute of Geophysics and Geomatics,China University of Geosciefices,Wuhan 430074,China;PetroChina Research Institute of Petroleum Exploration and Development,Beijing 100083,China;The State Key Laboratory of Coal Mine Disaster Dynamics and Contrul,Chongqing University,Chongqing 400044,China)

机构地区：[1]中国地质大学地球物理与空间信息学院,湖北武汉430074 [2]中国石油勘探开发研究院,北京100083 [3]重庆大学煤矿灾害动力学与控制国家重点实验室,重庆400044

出　　处：《天然气地球科学》2020年第7期1028-1040,共13页Natural Gas Geoscience

基　　金：国家科技重大专项(编号:2017ZX05035002-002);国家自然科学基金(编号:41722403)联合资助~~。

摘　　要：分形维数是分析煤和页岩微观孔隙结构的重要参数之一。目前主要是基于低温N2吸附数据进而利用Frenkel-Halsey-Hill(FHH)模型,获得煤和页岩中孔(2~50 nm)与宏孔(>50 nm)的表面粗糙分形维数,对其微孔(<2 nm)分形维数的研究还较少。为深入研究煤和页岩的微孔特征,基于微孔填充与孔径分布理论,对比分析了煤和页岩微孔结构的分形特征。选取煤和页岩样品进行低温CO2吸附实验,计算并分析两者的微孔分形维数。结果表明:煤的微孔分形维数分布在2.6~2.8之间,平均为2.75;页岩的微孔分形维数分布在2.8~2.9之间,平均为2.88。煤的微孔比表面积分布在100~300 m2/g之间;页岩的微孔比表面积集中在15~30 m2/g之间,页岩的孔隙分布零散且数量少,说明分形维数越大,微孔结构更加复杂。此外,分别对煤与页岩的微孔分形维数、表面粗糙分形维数进行了对比,发现虽然煤的微孔比表面积均远大于页岩,但其孔径分布、孔隙结构比页岩简单,微孔分形维数小于页岩。同时,由于中孔、宏孔数量少,比表面积小,孔隙表面较为光滑,煤的表面粗糙分形维数小于页岩。微孔分形维数和表面粗糙分形维数分别受微孔结构复杂程度与中孔、宏孔表面粗糙程度的影响,微孔结构越复杂,中孔、宏孔表面越粗糙,分形维数越大。An effective method to accurately characterize and quantify the pore structure of coal and shale is a key issue. At present,the fractal dimension of surface roughness(D2)of coal and shale is mainly analyzed based on the low-temperature nitrogen adsorption experiments and Frenkel-Halsey-Hill(FHH)model,but the micropore fractal dimension(Dm)is still rarely studied. This paper based on the micropore-filling theory and micropore-aperture distribution theory,a Dm model of coal and shale was proposed. The low-temperature CO2 adsorption experiments were done,and the fractal analysis of CO2 adsorption isotherms corresponding to coal and shale samples were carried out by using the Dmmethod. The results show that the Dm of coal is ranging from 2.6 to 2.8,with an average of 2.75,while that of shale ranges from 2.8 to 2.9,with an average of 2.88. The specific surface area of micropore of shale is ranging from 15 m2/g to 30 m2/g,while the specific surface area of micro-pore of coal is ranging from 100 m2/g to 300 m2/g. It shows that the pore distribution of shale is scattered and the number of pore is small,indicating that shale has a more complicated and heterogeneous micropore struc-ture. The Dm and D2 are compared. The pore volume and specific surface area of micropore of coal are much larger than that of macropores,and the micropore structure is more complex. Meanwhile,the small number of mesopores and macropores,small specific surface area and smooth pore surface,make Dm of coal larger than D2. Dm and D2 are respectively affected by the complexity of microporous structure and the roughness of mesopore and macropore surface. Complex micropore structure and rough pore surface will increase the fractal dimension.

关 键 词：微孔分形维数 FHH模型 低温CO2吸附 低温N2吸附 

分 类 号：TE151[石油与天然气工程—油气勘探]