| Due to the Tongwan Movement, large-scale weathering crust karstification developed in the Sinian Dengying Formation, Sichuan Basin. Taking Moxi area as a case, the residual thickness method and the impression method are respectively used to restore the paleogeomorphology of the fourth member of Dengying Formation based on the 3D seismic data and drilling data. Comprehensive analysis shows that the paleogeomorphology in Moxi area is undulating from southeast to northwest with locally karst peak, and it can be subdivided into two parts such as internal zone and marginal zone according to the sedimentary facies. In general there are three geomorphology units, i.e., karst platform, karst slope, and karst valley, while in Moxi area the karst slope can be subdivided into gentle slope, steep slope, and marginal highland based on the restored maps, by which five units developed. The development of karst reservoirs are jointly controlled by sedimentary facies, paleokarst geomorphology, and fault systems. In the internal zone, the karst platform has the weakest dissolution, with storage space of mainly pinhole, and smaller dissolved pores and cavities, while the gentle slope has stronger dissolution, with reservoir space dominated by larger dissolved pores. In the marginal zone, the karst slope has the strongest dissolution, with storage space of mainly honeycomb dissolved pores and cavities, and the karst intensity is also controlled by the fractures. It is shown that the karst slope with fracture system developed in the platform margin is the most favorable zone of the best quality reservoirs, and the karst platform in the internal zone can also be the next favorable play, especially with low exploration degree. |
