Pore features of shale gas layer in Wufeng-Longmaxi formations in Fuling area of Sichuan Basin and the application to development

Shale porosity is an important factor affecting the gas-bearing capacity of shale. The pore characteristics of the upper gas layer from the Wufeng Formation to the first member of Longmaxi Formation were studied and compared with the lower gas layer by using argon plasma scanning electron microscopy (SEM), high pressure mercury intrusion and liquid nitrogen adsorption. Results show that the organic carbon content of the lower gas layer is high, the pores in the organic matter are dominant, the pore volume is mainly >0.02 mL/g, and the BET specific surface area is mainly >20 m²/g. The organic carbon content of the upper gas layer is low, the pores are mainly micro-fissures and clay mineral pores, the pore volume is mainly distributed from 0.016-0.02 mL/g, and the specific surface area is mainly 12-20 m²/g. Combined with a single well gas content test results, we found that organic carbon content has the best correlation with gas content, followed by specific surface area and porosity. An evaluation of the gas-bearing properties of the upper gas layer was carried out. Sub-layer ⑧ was considered as the best gas layer in the upper interval, while sub-layers ⑥ and ⑦ were the next best, and sub-layer ⑨ the worst.