Pore Structure Characteristics of Shale Reservoir of the Lower Qian 4 Member in the Wangchang Anticline of the Qianjiang Sag

The analyses of X-ray powder diffraction,porosity and permeability,high pressure mercury,nitrogen adsorption,Micro-CT scanning,and FIB-SEM were performed,aiming to understand the pore structure characteristics of the shale reservoir and discuss the controlling factors of the superiority of rock physical property of of different lithologies of the 14th cyclotherm of the Lower Qian4 Member in the Wangchang anticline of the Qianjiang sag. Studies show that the reservoir consists mainly of dolomite (40.5% on average),calcite (10.4% on average),feldspar (16.5% on average),clay minerals (11.2% on average),anhydrite (10.8% on average),and quartz (5.9% on average); the rock is "high-medium porosity (average 17.6%) and very low permeability (average 0.043 6 mD)" type; high macropore rate (79.7% on average) within each lithology (except argillaceous limestone) contributes to excellent porosity,and the correlation between dolomite and calcite content and macopore and micropore rate indicates that dolomitization is closely related to the formation of macropore. Dolomiticzation along with calcite precipiatation lays the foundation of poor permeability,and the positive correlation between anhydrite content and geometrical tortuosity indicates the enhancement of the space complexity of the pore throat and the deterioration of permeability. The less connecting number (main peak at 3) and the low efficiency of mercury withdrawal (40% on average) reflect poor connectivity which also has a certain effect on permeability.