Accumulation conditions and controlling factors for the enrichment of shale oil and gas in the Jurassic Qianfoya Formation, Yuanba area, Sichuan Basin

Taking key wells such as Yuanye 3 in the Yuanba area of the Sichuan Basin as examples, the accumulation conditions of continental shale oil and gas in the Middle Jurassic Qianfoya Formation in this area have been evaluated based on core observation and experimental analysis. The organic-rich mudstone of the Qianfoya Formation has high porosity and good oil and gas content. It is the main reservoir lithofacies type, while the physical properties of limestone and sandstone interlayers are relatively poorer. The pores are mainly inorganic ones, accounting for approximately 60% to 80% of the total porosity. Compared with marine shale, the proportion of micropores is lower and the content of macropores is higher, which is conducive to the production of shale oil and gas. The fourth section of the lower part of the second member of the Qianfoya Formation is dominated by organic-rich mudstone, with a high shale-to-stratum ratio, an average porosity of 5.43%, and an average total organic carbon (TOC) content of 1.72%. The free hydrocarbon content (S₁) of frozen sample pyrolysis is 2.63 mg/g, and the average total gas content is 1.51 m³/t, showing a good oil-bearing property and favorable geological conditions for the formation of continental shale oil and gas. Comparative analysis with other wells has indicated that half-deep lacustrine facies is the most favorable sedimentary facies belt, providing basic material for oil and gas enrichment, and high maturity and fracture development is the important condition for oil and gas enrichment.