Comparison of Geological Conditions and Prospects of Exploration Potential of Shale Gas in Upper Permian Wujiaping Formation and Longtan Formation, Sichuan Basin

Manfei Chen ^1,2,3 Jiajing Yang ^1* Zhiyuan Lu ⁴ Ying Ming ¹ Hua Wang ¹ Siyu Chen ⁴ Wenjing Zhang ¹

• ¹ Exploration and Development Research Institute of China Petroleum Southwest Oil and Gas Field Company, Cheng'du, China
• ² China University of Petroleum, Beijing, Beijing, Beijing, China
• ³ Sichuan Key Laboratory of Shale Gas Evaluation and Exploitation, Sichuan, China
• ⁴ School of Geosciences, Yangtze University, Wuhan, Hebei Province, China

Shale gas serves as a crucial transitional energy source during the ongoing energy transformation.The development of the Longmaxi Formation shale gas field in the Sichuan Basin has intensified the search for new alternative stratigraphic sequences, which is now a key focus in shale gas exploration.The Upper Permian Longtan and Wujiaping Formations, characterized by contemporaneous heterotopic facies, have exhibited promising hydrocarbon indications in previous drilling activities.To assess the resource potential and exploration prospects of these formations, this study employed various experimental methods, including shale gas content measurement, field emission scanning electron microscopy (FE-SEM), total organic carbon (TOC) analysis, vitrinite reflectance (Ro), and X-ray diffraction (XRD). These techniques facilitated a systematic investigation of gas-bearing characteristics, organic geochemical properties, reservoir spaces, and mineral compositions, thereby establishing comprehensive evaluation criteria for favorable exploration zones and geological resource calculations. Results reveal that the Longtan Formation, characterized by sea-land transitional facies, comprises multiple thin shale layers with a thickness ranging from 0.5 to 20.0 meters. Its average TOC content is 2.7%, with kerogen types II2 and III, and Ro values ranging from 1.4% to 2.8%. The reservoir space primarily consists of interlayer pores in clay minerals, displaying an average porosity of 4.5%, an average brittle mineral content of 41.7%, and an average gas content of 5.0 m³/t. The favorable zone is located in the Guangan-Zigang-Shibao region, exhibiting a resource abundance of approximately 1.60 × 10⁸ m³/km². The Wujiaping Formation, belonging to deep-water shelf facies, features a single-layer thickness of 6 to 12.0 meters, an average TOC content of 3.5%, kerogen types I and II1, and Ro values ranging from 2.0% to 2.8%. Its reservoir space is mainly comprised of organic matter pores, with an average porosity of 5.5% and an average brittle mineral content of 76.6%. The average gas content in the shale section at the top of the Wujiaping Formation can reach 8 m³/t, with a favorable area in the Dazhou Liangping block, showcasing a resource abundance of 3.30 × 10⁸ m³/km². Both formations present significant exploration prospects, offering essential support for shale gas development in the Sichuan Basin.