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The structural evolution and sedimentary differentiation of the Sichuan Basin in China are complex, with intricate reservoir pore structures that significantly impact shale gas production. This study examines the complexity and heterogeneity of the microscopic pore structures in the deep marine shale reservoir in the Longmaxi Formation. Pore structure characterization techniques are used to compare deep and shallow–medium marine shales, and siliceous and silty shales. The results reveal the factors influencing pore structure and their impact on exploration and development. The key points are as follows: (1) The pore structure of deep siliceous shale is the most complex due to its diverse range of pore development patterns, pore types, and sizes. (2) The box dimension of full pore size is about 1.52 for deep marine shale and 1.46 for shallow–medium shale. Organic matter (OM) content, the degree of pore development, and inorganic mineral content all correlate positively with the complexity of the pore structure in deep marine shale, which affects the formation of high-quality reservoirs. (3) Lateral heterogeneity of pore structures shows strong regional variations in the study area. Heterogeneity is more pronounced in the deep marine shale than in the medium and shallow shale formations. OM mesopores significantly influence the overall heterogeneity of the shale pore system. The deep marine shale reservoir is situated in an area with strong regional variations. The pore structure of high-quality reservoirs is more complex than those of shallow–medium marine shales, displaying notable heterogeneity. Pore structures with fractal dimension values close to that of the shallow–medium formations (box dimensions within 1.5) offer promising targets for the exploration and development of deep marine shale gas. [ABSTRACT FROM AUTHOR]

For the purpose of clarifying the seismic response characteristics of fractured-cavity reservoirs of Dengying Formation in the central Sichuan Basin, the paper first intends to establish three geological models of fracture cave reservoirs based on drilling, logging, and core data of the Dengying Formation in the central Sichuan Basin. Then, the formation reflection is calculated with reference to anisotropic Horizontal Transverse Isotropy (HTI) medium. Finally, further research on Amplitude Variation with Azimuth (AVAZ) seismic forward modeling has been conducted to clarify the seismic response characteristics of different reservoir types in the study area. The results suggest that: Seismic response characteristics of fractured-cavity reservoirs are controlled by incident angle and azimuth angle of seismic waves in different types of reservoirs. The incident angle of the seismic wave controls the difference in amplitude caused by different micro-fracture densities, and the azimuth angle controls the identification ability of the micro-fracture direction. The increase in incident angle brings about a gradual decline in amplitude. The magnitude reaches the highest when the azimuth is parallel to the normal direction of the fracture surface; however, it'll come down to the lowest as the azimuth is perpendicular to the normal direction of the fracture surface. The fracture density fails to affect the amplitude as long as the azimuth angle is parallel to the direction of the fracture. However, the decreased amplitude reflects the increasing fracture density as the azimuth angle is identical to the normal direction of the fracture surface. The comparison between the theoretical model of three different types of fractured-cavity reservoirs and the actual uphole trace shows that the model has high accuracy. The prospect of seismic identification of fractured-cavern reservoirs, based on the results, can provide us with feasible and applicable evidence for future research on seismic identification of reservoirs and prediction of fracture distribution in the Dengying Formation of central Sichuan. [ABSTRACT FROM AUTHOR]

Shale in the Wufeng Formation of the upper Ordovician and Longmaxi Formation of lower Silurian in the Sichuan Basin and its surrounding area is widespread. Shale gas resources are abundant. Shale gas in the Wufeng Formation and the Longmaxi Formation in the basin has been a major breakthrough. The basin margin transition zone in southeastern Chongqing is in an intense tectonic activity area, which is more complicated and special than the stable stratum in the basin. Therefore, it is necessary to put forward higher requirements for preservation conditions and enrichment pattern evaluation of shale gas. Therefore, in view of the complicated structural pattern of the basin margin transition zone in southeastern Chongqing, the preservation conditions and reservoir forming patterns are analyzed through structural evolution, uplift and denudation, fault development, structural styles, roof and floor conditions, and formation pressure. The results show that the main reason for the formation of normal pressure is the late uplift, denudation and fault development. The pressure coefficient from the basin to the outer layer is changed from overpressure to normal pressure, and structural transformation forms the preservation form of shale gas with narrow and steep residual anticline, wide residual syncline and residual slope. The preservation condition evaluation of normal shale gas should be based on structural factors such as structural evolution, structural style, uplift and denudation degree and fault development degree, with formation pressure coefficient as reference condition, combined with material basic conditions such as roof and floor conditions and formation thickness. The findings of this study can help for better understanding of the "sweet spot" prediction of normal pressure shale gas in complex structural area. [ABSTRACT FROM AUTHOR]