Abstract: In recent years, Huagang Formation in the central inversion structural belt in Xihu Sag is a major exploration target in the East China Sea Basin. However, due to the influence of multi-stage tectonic activities and diagenesis, the reservoirs exhibit strong heterogeneity, and the genesis of high-quality reservoirs remains unclear. Taking structure “B” as an example, and integrating with core observation, mineral composition analysis, scanning electron microscopy, high-pressure mercury injection, and imaging logging data, reservoir stress distribution, fracture development characteristics, and the tectono-diagenetic reservoir-controlling mechanisms have systematically been analyzed. The tectonic stress in the study area displays a distinct three-segment zonation. The shallow zone is dominated by extensional stress, with regularly oriented fractures developed, and the middle zone is characterized by intense stress disturbance and diffuse fracture orientations, while the deep zone is governed by compressive–shear stress, with concentrated and large-angle fractures developed. There are significant differences in stress concentration, fracture connectivity, and diagenetic fluid activity in different structural positions (fault core, fractured zone, and host zone). Considering the combined effects of tectonic stress and diagenesis, Huagang Formation reservoirs are classified into six types of tectono-diagenetic facies, and their planar distribution characteristics have been clarified. These facies alternate spatially among the fault core, fractured zone, and host zone, with high-quality reservoirs predominantly developed in strong dissolution facies zones characterized by high fracture connectivity and open diagenetic system. Overall, reservoir heterogeneity in the study area was controlled by multi-scale coupling of tectonic stress, fracture system, and diagenetic process, and a reservoir-controlling model of “stress-dominant–fluid-driving–facies zone differentiation” was proposed based on tectono-diagenetic facies analysis. The study results provide a geological basis for high-quality reservoir prediction and zonal evaluation in strike-slip fault zones.

Key words: tight sandstone, tectono-diagenetic facies, strike-slip fault, Huagang Formation, Xihu Sag