四川盆地东南缘二叠系茅口组一段页岩气藏地质特征及富集模式

四川盆地东南缘(川东南)二叠系茅口组一段(茅一段)认识程度较低,以野外露头和钻井岩心等为基础,利用矿物岩石学、地球化学、普通薄片和氩离子抛光扫描电镜等实验分析资料,结合测井和地震属性预测技术,开展沉积相、烃源岩、储层物性及储集类型等研究,明确了茅一段页岩气地质特征及成藏富集模式。主要得到3点认识:(1)茅一段处于碳酸盐岩台地较深水外缓坡相,主要发育深灰色-灰黑色炭质泥岩、灰质泥岩、泥质灰岩和生屑灰岩4种岩性,炭质泥岩和灰质泥岩具有较高TOC(0.5%～5.1%),适中的热演化程度(R_o2.0%～2.3%),具备良好的烃源基础,为新类型非典型性页岩气;(2)茅一段发育有机质孔、溶蚀孔、粒缘缝和收缩缝等储集空间类型,形成"孔-缝-网"储集复合体,其中炭质泥岩和灰质泥岩主要发育有机质孔、粘土矿物收缩缝和层理缝,泥质灰岩和生屑灰岩主要发育溶蚀孔、粒缘缝、收缩缝和高角度缝;(3)茅一段页岩气具有"源储一体、连片分布、构造-裂缝双重控藏"的成藏富集模式,研究区茅一段连续分布面积超过7 000 km²,地质资源量超5 000×10⁸ ...

Geological characteristics and enrichment pattern of Permian Mao 1 Member shale gas reservoirs at the southeastern margin of Sichuan Basin

To understand the shale gas reservoirs in the first member of the Permian Maokou Formation(Mao 1 Member)in the southeastern margin of Sichuan Basin(southeastern Sichuan Basin),we combined outcrop and core observation,mineralogical and geochemical data,thin section analysis and scanning electron microscopic results of argon ion beam cross sections,with logging and seismic attribute prediction techniques to study their sedimentary facies,source rocks,reservoir properties and types.The geological characteristics and gas enrichment pattern of the Mao 1 Member shale were revealed and summarized as:(1)The member is located in the relatively deep-water gentle slope of a carbonate platform and comprised of well-developed dark gray-gray black carbonaceous mudstone,calcareous mudstone,argillaceous limestone and bioclastic limestone.The carbonaceous and calcareous mudstone,among others,with relatively high TOC(0.5%-5.1%)and moderate thermal maturity(R o:2.0-2.3),are potential hydrocarbon source rocks with possible new-type atypical shale gas.(2)The reservoir space in the member including organic matter pores,dissolution pores,grain boundary fractures,and constricted fissures,may form a reservoir complex of“pore-fracture-network”.The carbonaceous mudstone and calcareous mudstone are dominated by organic matter pores,clay mineral shrinkage cracks and bedding-parallel fractures,while argillaceous limestone and bioclastic limestone mainly develop dissolution pores,grain boundary fractures,contraction fissures and high-angle cracks.(3)The shale gas enrichment in the member can be generally described as“integrated continuous source-reservoir assemblages controlled dually by structures and fractures”,and results in an estimated geological resource volume of more than 500 BCM continuously distributed in an area of more than 7000 km 2.It therefore has great exploration potential for shale gas.The research results are of great significance to improving the understanding of the new-type shale gas geology and guiding the shale gas exploration in southeastern Sichuan Basin.