Formation and types of natural gas reservoirs of the Tangyuan fault depression in Yi-Shu graben

Based on drilling, logging and geochemical data from 32 wells, the depositional and tectonic evolution of the Tangyuan fault depression were studied and the gas accumulation conditions and gas reservoir types were analyzed. Based on interpretation of 2D and 3D seismic data, a structure map of each layer was plotted and the trap types developed in various structural layers were found and confirmed. The source rock of the Tangyuan fault depression was mainly developed in the Cretaceous and in the Eogene Wuyun Formation, Xinʹancun Formation, Dalianhe Formation Member 1 and Baoquanling Formation Member 1. The reservoirs are of similar age and include the Eogene Wuyun Formation, Xinʹancun Formation, Dalianhe Member 2 and Baoquanling Member 2. The caprock was developed in the Dalianhe and Baoquanling Member 1. There are three types of source-reservoir-caprock assemblages present which include self-generating & self-preserving, lower-generating & upper-preserving and new-bed-generating & old-bed-preserving. Drilling has demonstrated that there are two types of gas reservoirs, a composition lithologic-structural gas reservoir and a lithologic gas reservoir. With reference to the seismic data and known reservoir data in adjacent areas, it is estimated that there may also be structural gas reservoirs and stratigraphic gas reservoirs.