重庆周缘下志留统龙马溪组和下寒武统牛蹄塘组页岩有机质孔隙发育及演化特征

针对重庆周缘下志留统龙马溪组和下寒武统牛蹄塘组2套海相页岩已经进行了规模勘探与开发，但2套页岩的产气效果却存在较大差别，其中龙马溪组页岩产气量大，稳产时间长；牛蹄塘组页岩产气量小，稳产时间短。因此，以重庆周缘龙马溪组和牛蹄塘组页岩样品为研究对象，通过有机碳含量测试、全岩XRD分析、等效镜质体反射率测试、聚焦离子束扫描电子显微镜（FIB-SEM）及聚焦离子束氦离子显微镜（FIB-HIM）观察，结合地层埋藏史及生烃演化史分析，对2套页岩的有机质孔隙及演化特征进行了研究。研究结果表明：2套页岩的有机质孔隙发育特征存在较大差别。龙马溪组页岩固体干酪根内有机质孔隙数量少、孔径小，连通性差；但龙马溪组页岩迁移有机质内部孔隙数量多、孔径大，连通性好；牛蹄塘组页岩固体干酪根内不发育孔隙，而迁移有机质内部孔隙数量少、孔径小及连通性差；影响2套页岩有机质孔隙发育的最重要的因素是热演化程度。牛蹄塘组页岩固体干酪根孔隙由于过度演化而大量消失，只保留少量的迁移有机质孔隙；而龙马溪组页岩由于热演化程度适中，发育大量的迁移有机质孔隙，固体干酪根只保留少量孔隙。适宜的热演化程度能够保证页岩有机质孔隙的大量发育期和生烃高峰期的耦合，为页岩气生成之后第一时间得到有效赋存提供必要的有机质孔隙。针对中国南方下寒武统牛蹄塘组页岩气的勘探开发应重点寻找热演化程度适中（2.0%O<3.0%），即分布在古隆起边缘的页岩分布区。

Organic matter pores and evolution characteristics of shales in the Lower Silurian Longmaxi Formation and the Lower Cambrian Niutitang Formation in periphery of Chongqing

In the periphery of Chongqing,two sets of marine shale gas have been carried out for the exploration and development.However,there are significant differences in the gas production of the two formations of shale,in which the shale production of the Longmaxi Formation is large and the stable production time is long.The production of the Niutitang shale is small and the stable production period is short.For the samples from the Longmaxi and Niutitang Formations in Chongqing,and XRD analysis,equivalent vitrinite reflectance test,focused ion beam scanning electron microscope and focused ion beam helium ion microscope were used to study the organic matter pores development,and stratigraphic burial and evolution history were also studied to clarify evolution of organic matter pores.The results show that there are significant differences in the organic pore development characteristics of the two formations shale.The solid kerogen of the Longmaxi shale has a small number of pores,a small pore size and poor connectivity.However,the migrated organic matter in the Longmaxi shale has a large number of pores,large pore size,and better connectivity.There is no pore in the solid kerogen of Niutitang shale,but there are a few pores with small pore size and poor connectivity in the migrated organic matter.The most important factor affecting the organic matter pore development of the two formations shale is the degree of thermal evolution.Organic matter pores of kerogen in the Niutitang shale has disappeared due to excessive evolution,leaving only a small amount of pores in migrated organic matter.However,due to the moderate thermal evolution of the Longmaxi shale,a large number of migrated organic matter pores are developed,and solid kerogen only retains a small amount of pores.The optimum thermal evolution degree can ensure the best match between the massive development period of organic matter pores and the hydrocarbon generation peak,and provide necessary storage space for shale gas.For the exploration and development of shale gas of Niutitang shale,we should focus on finding the shale with moderate degree of thermal evolution (2.0%O<3.0%) that distributed around in ancient uplift.