Characteristics and gas bearing properties of gas shale reservoirs in Wufeng-Longmaxi formations, Zigong region

Shale exploration in multiple regions of the Sichuan Basin has achieved breakthroughs, with stable production growth in shale gas extraction from the Luzhou and Changning areas. The Zigong region, adjacent to the Luzhou block, has shown promising exploration potential for the Wufeng-Longmaxi formations shale based on preliminary studies. However, insufficient research on shale reservoir characteristics and gas-bearing properties in this area has severely hindered further shale gas exploration. This study investigates the reservoir characteristics and gas-bearing properties of the Wufeng-Longmaxi formations shale in the Zigong area through experimental analyses, including X-ray diffraction, field emission scanning electron microscopy, overburden pressure porosity tests, and organic carbon analysis. A comparative analysis with the neighboring Luzhou block was also conducted. The results indicate that the Wufeng-Longmaxi formations shale in Zigong exhibits high organic matter abundance, with an average total organic carbon (TOC) content of 2.80%, and is in an overmature stage, characterized by an average vitrinite reflectance (Ro) of 2.49%. The reservoir exhibits relatively high porosity (average 4.81%), with diverse pore types such as inorganic mineral pores and organic matter pores. The shale is characterized by high quartz content, low clay content, and high brittle mineral content, with average brittle index values (brittleness index Ⅰ and Ⅱ) of 55.71% and 68.77%, respectively, indicating favorable brittleness. The shale reservoir pressure coefficient exceeds 2.0, and the gas content ranges from 3.28 m³/t to 5.98 m³/t, demonstrating favorable gas-bearing capacity. Compared to the Luzhou area, the Zigong region exhibits higher porosity, thermal maturity, and brittleness indices, while the TOC and gas content are slightly lower. Both regions share similar pore types. Overall, the Wufeng-Longmaxi formations shale in the Zigong area exhibits excellent reservoir properties, which is conducive to the enrichment and accumulation of deep shale gas.