川东南林滩场地区五峰组—龙马溪组页岩气藏压力演化及其地质意义

Pressure evolution of shale gas reservoirs in Wufeng-Longmaxi formations, Lintanchang area, southeast Sichuan Basin and its geological significance

唐建明 何建华 魏力民 李勇 邓虎成 李瑞雪 赵爽

TANG Jianming HE Jianhua WEI Limin LI Yong DENG Hucheng LI Ruixue ZHAO Shuang

中国石化 西南油气分公司 勘探开发研究院, 成都 610041 油气藏地质及开发工程全国重点实验室, 成都 610059 成都理工大学 能源学院, 成都 610059

Exploration & Production Research Institute, Southwest Petroleum Company, SINOPEC, Chengdu, Sichuan 610041, China State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu University of Technology, Chengdu, Sichuan 610059, China College of Energy Resources, Chengdu University of Technology, Chengdu, Sichuan 610059, China

川东南林滩场地区的上奥陶统五峰组—下志留统龙马溪组具备较好的勘探开发条件，查明该层系古流体压力演化对揭示页岩气成藏及逸散过程具有重要意义。以林滩场地区五峰组—龙马溪组页岩构造裂缝和流体超压裂缝脉体为研究对象，综合阴极发光观察、包裹体显微测温、激光拉曼分析及盆地模拟等技术手段查明该地区的古流体压力演化过程及其控制作用。研究表明：(1)林滩场地区经历了常压、微超压—常压、超压、泄压4个阶段，其中超压主要来源于生烃作用，泄压主要由页岩气逸散导致，且使气藏泄压54%。(2)五峰组—龙马溪组黑色页岩层系底部的裂缝存在两期脉体充填。第一期形成于沉降埋深阶段，时间在131~118 Ma，形成温度介于178~205 ℃，甲烷包裹体捕获压力为105.6~119.8 MPa；第二期形成于构造抬升阶段，时间在25~18 Ma，形成温度介于150~175 ℃，甲烷包裹体具有相对较低的盐度，其捕获压力介于80.8~92.1 MPa，较低的压力系数(1.37~1.49)指示气藏已发生大量逸散。(3)晚期构造运动，特别是喜马拉雅晚期的快速抬升是造成气藏逸散和泄压的根本原因。有机孔的圆度减弱、孔径减小表明储层物性变差。由于气藏形成和保存时间长，林滩场地区五峰组—龙马溪组页岩仍具备较好的勘探潜力。该研究有助于深化林滩场常压页岩气藏富集规律的认识，可为该地区页岩气勘探有利区的优选提供一定的理论支撑。

The Upper Ordovician Wufeng Formation-Lower Silurian Longmaxi Formation in Lintanchang area of the southeastern Sichuan Basin has good exploration and development conditions, and clarifying the paleo-fluid pressure evolution is of great significance for revealing the process of shale gas accumulation and fugitive emission. Taking the shale tectonic fractures and fluid overpressure fracture veins of the Wufeng-Longmaxi formations in Lintanchang area as the research object, the paleo-fluid pressure evolution process in this area and its controlling impact were investigated using cathodoluminescence, inclusion temperature measurement, laser Raman analysis, and basin simulation. The study shows that: (1) Lintanchang area has experienced four stages: normal pressure, mild overpressure to normal pressure, overpressure, and pressure relief. Overpressure is mainly due to hydrocarbon generation. Pressure relief is mainly caused by shale gas fugitive emission. The gas reservoir pressure relief reaches 54% of the initial pressure during the pressure relief stage. (2) There are two stages of vein filling in the fractures at the bottom of the black shale in the Wufeng-Longmaxi formations. The first stage is formed in the sedimentation and burial stage at 131-118 Ma, the temperature is 178-205 ℃, and the trapping pressure of methane inclusions is 105.6-119.8 MPa. The second stage is formed in the tectonic uplift stage at 25-18 Ma, the temperature is 150-175 ℃, the methane inclusions have relatively low salinity and its trapping pressure is 80.8-92.1 MPa. The low pressure coefficient (1.37-1.49) indicates that mass fugitive emission has occurred. (3) The late tectonic movement, especially the rapid uplift in the late Himalayan period, is the root cause of the fugitive emission and pressure relief of the gas reservoirs. The decrease of the roundness and pore size of the organic pores indicates the deterioration of reservoir physical properties. However, due to the long formation and preservation time of the gas reservoirs, the shale in the Wufeng-Longmaxi formations in Lintanchang area still has good exploration potential. This study is helpful to deepen the understanding of the accumulation mechanism of the normal-pressure shale gas reservoirs in Lintanchang area and can provide theoretical guidance for optimal selection of favorable shale gas exploration areas.

国家自然科学基金面上项目 42072182;四川省科技厅重点苗子项目 2022JDRC0103;四川省杰出青年科技人才项目 2020JDJQ0058

https://doi.org/10.11781/sysydz202304739