Reservoir characteristics and control Factors of Sinian Dengying Formation in central Sichuan

Abstract：Research on Sinian Dengying Formation in central Sichuan by adopting combined macroscopic and microscopic methods shows that the main reservoir rocks are dolarenite, karst breccia, grained dolomite and algae dolomite, the reservoir space is dominated by emposieu and karst caves, and the reservoir is of relatively low quality, appearing as fracture-cavity type with low porosity and low permeability. The reservoir of Dengying Formation in the study area was formed by deposition and diagenesis. Dolarenite, grained dolomite and algae dolomite were deposited in a strong hydropower environment with the development of primary pores, which provided favorable material base for later strong karstification. 2nd member and 4th member were uplifted by Tongwan movement; hence the strata were exposed at the land surface for a long time and received atmospheric water together with mixed water reformation, leading to karstification. Through the weathering crust formed by karstification near the land surface, atmospheric fresh water and mixed water continued seeping into and dissolving the lower part of the formation. Strong karstification could create karstic collapse breccias and a great quantity of dissolution pore-caves in the lower part of the formation. Deposition and diagenesis provided favorable conditions for secondary porosity and improved the properties of reservoir rocks, while tectonic action in the later time formed a lot of cracks, providing the permeability for the reservoir.