Analysis and significance of shale reservoir differences between Wujiaping Formation in Hongxing area and Longmaxi Formation in Jiaoshiba area, eastern Sichuan Basin

In the Hongxing area of the eastern Sichuan Basin, the Permian Wujiaping Formation developed a set of black, silicon-rich, and carbon-rich shale reservoirs, which are currently pivotal for enhancing shale gas reserves and production in the region. These shale reservoirs show strong similarities with the lower sections (layers ① to ③) of the gas-bearing shale in the Longmaxi Formation of the Jiaoshiba area in terms of sedimentary environment, shale quality, and gas content. Both formations are characterized by high carbon, silicon, and gas contents. However, in later stages of development, the shale gas reservoirs of the Wujiaping Formation were significantly less productive compared to those in the Longmaxi Formation in the Jiaoshiba area. To address this, the study analyzes the differences in reservoir quality and gas content between the two shale sets and their primary controlling factors. The results reveal that the shale reservoir in the Wujiaping Formation is characterized by a low silica mineral content and a high carbonate mineral content. Although it has a high organic carbon content, the kerogen types and organic matter are relatively poorer. The pore structure is marked by less developed organic matter pores and lamellar fractures, with smaller pore sizes. Overall, its reservoir physical properties and gas content are slightly inferior to those of the Longmaxi Formation shale in the Jiaoshiba area. Comparative analysis suggests that differences in sedimentary backgrounds and processes lead to primary quality differences in mineral and lithological composition, lamellation, and kerogen types between the two shale reservoirs. These differences form the material basis for variations in physical properties and gas content. Furthermore, differences in subsequent structural preservation conditions and other macro-geological factors lead to significant disparities between the two reservoirs in terms of pore types, sizes, porosity, and gas content. In addition, the study explores the impact of these distinctive characte-ristics on the development effectiveness of the two reservoirs and proposes corresponding engineering and technological strategies tailored to the differences in the development of these reservoirs.