Significant gas discovery in the Lower Cambrian Longwangmiao Formation in Sichuan basin has received wide attention on the time-equivalent Shilongdong Formation in Western Hunan-Hubei area. In order to provide guidance to the regional evaluation of reservoir in Western Hunan-Hubei area, detailed research has been carried out with methods including observation of outcrop, thin section, casted thin section, and cathode luminescence analysis. Based on the research of several outcrops in Eastern Hubei-Chongqing and Western Hunan-Hubei area, typical weathering crust karst features have been observed. Miaoliangzi-Dingzhai cross section has been chosen as the typical section in Enshi Xianfeng area for detailed research. The surface karstificated zone is 3 meters in thickness, composed of weathering layer and collapse breccia layer. The underlying strata have been affected by meteoric water leaching and dissolution due to faults and fracture system. And the meteoric water dissolution reaches as far as hundreds meters. According to the cement types and dissolution features, the vertical seepage flow zone and horizontal subsurface flow zone have been distinguished. Lithology is overall dense in the research area, but high quality reservoir with high porosity and permeability exists in some area, especially in the surface karstificated zone. In the vertical seepage flow zone and horizontal subsurface flow zone, pore space is lost due to late silicification, and only minor pore space is preserved. According to the discussion of diagenesis process and reservoir development, high quality reservoir is mainly controlled by supergene karstification, burial dissolution, and dolomitization. It is speculated that regional unconformity karsts are present in the research area, which are related to Xingkai movement during early Cambrian. This research is important to the regional evaluation of reservoir in Eastern Hubei-Chongqing and Western Hunan-Hubei area.

Shilongdong  /  karst  /  reservoir