Research on the characteristics of paleo-structural stress field and prediction of tectonic fractures in shale reservoirs of the Yichang Slope area in Western Hubei, China

The western Yichang area in Hubei Province serves as a key exploration target for shale gas in the Silurian Longmaxi Formation along the peripheral margin of the South China Basin. Since the Mesozoic, the Yichang Slope Zone has been subjected to multi-tectonic system controls, resulting in complex paleotectonic stress field distribution. The development patterns of structurally controlled fractures remain unclear, and favorable shale gas preservation zones influenced by tectonic fractures require further investigation-factors that significantly hinder shale gas development in this region.This study integrates seismic data, well logging data, laboratory analyses, and field outcrop observations with structural interpretation, finite element numerical simulation, and rock fracture criteria to analyze paleotectonic stress field characteristics. By reconstructing the distribution patterns of paleostress fields and predicting structural fracture development, we further delineate favorable zones for shale gas preservation and enrichment.Results demonstrate that the Yichang Slope Zone experienced two major tectonic events-the early and late Middle Yanshanian periods-with its primary structural framework established during the late Middle Yanshanian. The area predominantly develops conjugate shear fractures with SSE and NE orientations, formed under near E-W compressive stress fields generated by the Qinling-Dabie orogeny. The fracture coefficient of Longmaxi Formation shale ranges between 0.69 and 1.11, with values of 0.9–1.02 observed in the eastern study area, indicating a concealed fracture development stage that represents optimal conditions for shale gas preservation and accumulation.By combining field-observed fracture characteristics with numerical simulation results, this research successfully predicts structural fracture distribution patterns, providing critical geological guidance for shale gas exploration and development in the study area. Furthermore, the methodology offers valuable references for fracture prediction in other multi-phase tectonic deformation regions.