Characteristics analysis of Da'anzhai shale gas (oil) reservoirs in eastern Sichuan Basin

Abstract: Based on the core and field section observation and microscopic section in combination with analysis of geology, drilling and physical properties data, this paper discusses in detail sedimentary facies and reservoir characteristics of Da'anzhai member in eastern Sichuan Basin. The division scheme of sedimentary facies in Da'anzhai member is put forward, which argues that the transitional parts at the edge, on the slope and on the semi-deep lake biasing deep lake side are favorable for developing heterogeneity and shale gas (oil) reservoirs, that reservoirs of Da'anzhai member in the study area belong to ultra-low porosity and permeability pore fracture type reservoirs, whose reservoir space comprises of fracture, intracrystalline pore, eroded micro-pores, solution openings and dissolved caves, dominated by fractures, with solution openings and dissolved caves taking the second place. In addition, compaction, pressure solution, cavity filling, silicification and cementation are main factors adversely affect reservoir quality, while dissolution and rupture process improve reservoir quality. Therefore, The development of reservoirs in Da'anzhai member is not only controlled by sedimentary facies, rock type, diagenesis and tectonics but also affected by content of organic carbon, maturity of organic, brittle mineral content, thickness and buried depth of shale in the study area.