Geological characteristics and controlling parameters of shale gas accumulation in the Shanxi Formation, Yan’an area, Ordos Basin

Abstract Shale gas, a key unconventional energy resource, has become increasingly important in global energy production. In the current global context, as energy demands rise and the need for sustainable resources intensifies, the exploitation of shale gas presents a significant opportunity. In China, shale gas exploration holds great promise, especially in the Ordos Basin, which is considered a major contributor to the nation’s future energy portfolio. The Shanxi Formation in the Ordos Basin is rich in shale gas resources, with recent exploration breakthroughs positioning it as a strategic replacement field for future reserve expansion and production enhancement. To analyze the geological characteristics of shale gas accumulation and its main controlling factors of gas-bearing capacity in the Shanxi Formation, this study systematically analyzed the mineralogical, geochemical, reservoir properties, and adsorption–desorption characteristics of the shale using data from three new wells, including well logging, core samples, and experimental testing in the Yan’an area. The findings revealed that the Shanxi Formation shale exhibits large single-layer thickness, excellent lateral continuity, and high organic matter abundance with Type III kerogen. Coupled with coal seams, it forms high-quality gas source rocks characterized by high thermal maturity. The shale demonstrated favorable fracturability and gas storage capacity due to its high brittle mineral content (brittleness index: 44.63%) and a well-developed nanoscale pore-fracture network (specific surface area: 3.84 m2/g; pore volume: 0.0103 cm3/g). Field validation showed a desorbed gas content average of 1.137 m3/t, and horizontal well tests achieved an absolute open flow exceeding 5.3 × 104 m3/d, confirming its potential for commercial development. This study highlighted the critical roles of organic matter abundance, thermal maturity, and pore structure in controlling gas content, providing a scientific foundation for efficient shale gas exploration and hydraulic fracturing optimization in the Ordos Basin. These results hold significant implications for advancing large-scale shale gas reserve expansion in the Yan’an area.