Discussion on Transitional Shale Gas Accumulation Conditions from the Perspective of Source-Reservoir-Caprock Controlling Hydrocarbon: Examples from Permian Shanxi Formation and Taiyuan Formation in the Eastern Margin of Ordos Basin, NW China

Transitional shale gas, rich in resources, is expected to be a practical contributor the increase gas reserves and production China. Its exploration prospect has been demonstrated by several wells Daning-Jixian block on eastern margin of Ordos Basin. In this paper, Lower Permian Shanxi Formation (P1s) Taiyuan (P1t) Basin were compared for organic geochemical parameters, revealing that overflow fan + lagoon combination (OLC) third sub-member second member (P1s23) marine (MLC) first (P1t1) are most favorable intervals. The two intervals comparatively analyzed with respect mineral composition, brittleness, caprocks, preservation conditions. It found OLC P1s23 similar porosity much lower permeability than MLC P1t1 (or MLC1) BET surface area 10–15 m2/g, which smaller MLC1 (15–20 m2/g). Moreover, brittle content equivalent but brittleness index 33.73–62.36 (avg. 49.86), (53.34–58.27, or avg. 55.85). contains sandstones at both roof floor, higher interval, cannot serve as good physical seals. contrast, limestones which, together overlying coal seams, have hydrocarbon generation capacity can physically seal also fill it hydrocarbons, making superior shale. Due multi-lithologies developed transitional facies, besides matter enrichment, reservoir characteristics, necessary find suitable lithological ensure better preserved retained.