Oil and gas exploration potential of continental shale of Lianggaoshan Formation of Middle Jurassic in Qijiang area of southeastern Sichuan

Advancements in evaluation and development technologies have established continental shale oil and gas as vital future alternative energy sources for China. Recently, exploratory wells drilled in the Lianggaoshan Formation shale segment of the Middle Jurassic in the Qijiang area, southeastern Sichuan, have shown promising oil and gas indications. To clarify the basic geological characteristics of shale oil and gas in this area, the organic-rich shale of the Lianggaoshan Formation in the southeastern Qijiang area was chosen as the subject of study. Based on core observations and laboratory analyses, an evaluation of the basic geological conditions for shale oil and gas in the second section of the Lianggaoshan Formation in the Qijiang area was conducted. This was combined with high-quality shale seismic prediction and structural preservation condition assessments to identify exploration potential and direct future exploration efforts. Using typical wells in the Qijiang area as case studies, resource potential analysis was performed by integrating organic geochemical characteristics, thermal maturity, reservoir physical properties, and oil and gas bearing characteristics. Results indicate that the high-quality shale in the lower subsection of the second member of the Lianggaoshan Formation spans an extensive area of 4 569 km², with thickness ranging from 20 to 39 m. Controlled by semi-deep lacustrine facies, this shale exhibits an average organic carbon content of 1.3% to 1.6%, with organic matter types predominantly Ⅱ₁ to Ⅱ₂, and vitrinite reflectance values between 1.00% and 1.29%. These characteristics suggest significant hydrocarbon generation potential and promising measured oil and gas content. The high-quality shale is characterized by high gamma-ray (GR) readings, high acoustic time difference, and low density. Seismic waveform classification and acoustic impedance inversion techniques identified the Dingshan, Dongxi, and Guanshengchang areas as regions of concentrated shale thickness. These areas feature large, broad, and gentle synclines with favorable drilling results, indicating good overall preservation conditions. The main burial depths ranges from 1 000 to 3 500 m, with uniform structural stress and good compressibility. In summary, the analysis indicates that the continental shale in the Lianggaoshan Formation of the Qijiang area possesses favorable preservation conditions and substantial shale oil resources exceeding 500×10⁶ t, offering significant exploration potential. This evaluation provides a strategic framework for expanding exploration efforts in continental shale oil and gas within the Sichuan Basin.