黔北寒武系牛蹄塘组页岩孔隙分形表征  

Fractal characterization of pore structure in Cambrian Niutitang shale in northern Guizhou,southwestern China

作　　者：唐玄[1] 郑逢赞 梁国栋 马子杰 张家政 王玉芳 张同伟 TANG Xuan;ZHENG Fengzan;LIANG Guodong;MA Zijie;ZHANG Jiazheng;WANG Yufang;ZHANG Tongwei(MNR Key Laboratory for Strategic Evaluation of Shale Gas Resources,China University of Geosciences(Beijing),Beijing 100083,China;Guizhou Engineering Technology Research Center for Goalbed Methane and Shale Gas,Guiyang 550000,China;Oil and Gas Resources Survey Center of China Geological Survey,Beijing 100083,China;Bureau of Economic Geology,Jackson School of Geosciences,The University of Texas at Austin,Austin,TX 78713,USA)

机构地区：[1]中国地质大学(北京)自然资源部页岩气资源战略评价重点实验室,北京100083 [2]贵州省煤层气页岩气工程技术研究中心,贵州贵阳550000 [3]中国地质调查局油气资源调查中心,北京100083 [4]Bureau of Economic Geology,Jackson School of Geosciences,The University of Texas at Austin,Austin,TX 78713,USA

出　　处：《地学前缘》2023年第3期110-123,共14页Earth Science Frontiers

基　　金：国家自然科学基金项目(41730421,41972132);中央高校基本科研业务费项目(35832020051)。

摘　　要：页岩的孔隙结构是影响页岩气赋存和流动的关键因素,分形维数可以用来定量描述页岩孔隙结构的复杂程度。以黔北地区牛蹄塘组富有机质页岩为例,在扫描电镜、页岩地球化学和矿物组成分析基础上,利用高压压汞和低温氮气吸/脱附法研究了页岩孔隙结构特征参数,利用FHH模型计算了孔隙分形维数,讨论了孔隙结构的影响因素。研究发现:(1)下寒武统牛蹄塘组富有机质页岩石英含量为39.0%~68.4%;黏土矿物含量为11.5%~28.2%;有机碳含量为2.77%~5.81%,平均为3.81%;有机质成熟度高。(2)氮气吸脱附数据显示BET比表面积为11.954~21.744 m^(2)/g,平均为14.572 m^(2)/g;总孔体积为0.0186~0.0259 cm^(3)/g,平均为0.0214 cm^(3)/g;平均孔径范围在4.773~7.025 nm,平均为5.967 nm。微孔对总比表面积贡献大,而中孔和宏孔对孔隙体积贡献大。(3)基于低温氮气吸附数据获得的页岩孔隙分形维数D_(1)和D_(2)分布相对集中(D_(1)为2.65~2.71,D_(2)为2.79~2.85),压汞数据的大孔隙分形维数分布范围宽(D_(Hg)为2.21~2.81),分形维数显示牛蹄塘组富有机质页岩具有以微孔为主的复杂孔隙结构和高度非均质性,孔隙发育具有多重分形特征。(4)分形维数D_(2)与有机碳含量和微孔体积有明显的正相关关系,显示分形维数D_(2)可用于有机质孔隙结构表征,而矿物组成对分形维数没有明显影响。研究区牛蹄塘组页岩分形维数与龙马溪组产气页岩较为接近,指示本区页岩具有较好的孔隙结构。Pore structure is the key factor affecting the distribution and flow of shale gas,and fractal analysis can be used to quantitatively characterize the complex pore structures in shale.To better understand the porous structure of the organic-rich shale from the Lower Cambrian Niutitang Formation in northern Guizhou Province,southeastern China,shale samples from Well ZK,Songtao area,are analyzed to determine the pore parameters using high-pressure mercury injection and low-temperature nitrogen adsorption methods,combined with scanning electron microscope observation,shale geochemistry and mineral composition analysis.The pore fractal dimensions are calculated by FHH model,and the influencing factors for pore structure are discussed.To summarize:(1)the quartz content in the organic-rich shale ranges between 39%68.4%;clay content,11.5%28.2%;organic carbon content,2.77%5.81%(average 3.81%);while kerogen is mainly of type I,with high thermal maturity.(2)The BET specific surface area ranges between 11.95421.744 m^(2)/g(average 14.572 m^(2)/g);total pore volume,0.01860.0259 cm^(3)/g(average 0.0214 cm^(3)/g);and average pore size,4.7737.025 nm(average 5.967 nm).Micropores contribute largely to the total specific surface area;while mesopores and macropores account for a large proportion of pore volume.(3)The organic-rich shale has complex pore structure dominated by micropores,with high heterogeneity and multifractal characteristics.The pore fractal dimensions D_(1) and D_(2) obtained from low-temperature nitrogen adsorption data have narrow pore-size distributions(D_(1),2.652.71;D_(2),2.792.85),while mercury injection data yield a wider pore-size distribution for macropores(D_(Hg) between 2.212.81).(4)D_(2) is positively correlated with TOC content and micropore volume,and mineral composition has no significant effect on pore fractal dimensions.The fractal dimension of the Niutitang shale in the study area is similar to that of the gas-producing Longmaxi shale,indicating shales of this area have good pore structure.

关 键 词：孔隙结构 分形维数 牛蹄塘组 高压压汞 黔北地区 

分 类 号：P618.130.2[天文地球—矿床学] P534.41[天文地球—地质学]