Micro-pore characteristics of shale in Zhanhua Sag, Bohai Bay Basin

The micro-pore structure of shale is a key contol of shale oil and gas accumulation and seepage. The micro-pore structure of the continental shale in the Shahejie Formation in the Zhanhua Sag was analyzed by using argon-ion polishing SEM, CO₂ adsorption, N₂ adsorption, MIP and NMR. The shale displays six kinds of pores, including organic, intergranular, intragranular, intercrystalline, dissolution pores and micro-cracks. Micropores, mesopores and macropores are all developed. The micropore specific surface area accounts for about 61.52% of the total specific surface area, providing the main space for shale oil and gas adsorption. The mesopores and macropores provide most pore volume, accounting for 49.99% and 41.19%, respectively, which play a major role in the storage and migration of shale oil and gas. The shale porosity is 4.08%-7.04% and the effective porosity is 0.11%-0.64%, which means that pore connectivity is poor.