Pore structure characteristics and development patterns of different structural parts of the Wufeng-Longmaxi formations shale in western Chongqing

The Longmaxi Formation in western Chongqing has abundant shale gas resources, but the characteristics and productivity of shale reservoirs in different structural parts vary significantly, and its understanding is still unclear. This study comprehensively utilized methods such as TOC, whole rock mineral analysis, multi-scale observation of core scanning electron microscopy, gas adsorption experiments, and pressure holding core gas content testing to compare and analyze the reservoir characteristics and pore structure differences of shale in different structural parts such as slopes and synclines in the Da􀆳an area of western Chongqing. The study explored the controlling role of pore structure on gas content and identified favorable exploration areas. The research results indicate that: 1) shale in the synclinal zone is characterized by "porous and few fractures", with a high degree of organic pore development. The fractures are mainly diagenetic fractures and abnormally high-pressure fractures, while structural fractures are not developed; in the slope area, fractures are developed and mainly structural cracks, with weaker development of organic pores. 2) The pore structure shows significant differentiation: the volume of micropores and mesopores in shale in the inclined zone is higher than that in the slope zone, while micropores and mesopores in the anticline zone have a slight advantage over surface area. 3) There are differences in the control mechanisms of gas content: the gas content of shale in the syncline zone is mainly regulated by the mesoporous pore structure, with less influence from micropores; on the contrary, in the slope area, the gas content is mainly controlled by the microporous structure. The research results provide a theoretical basis for the optimal selection and exploration development of shale gas exploration targets in the Longmaxi Formation in western Chongqing.