Exploration potential and targets of the Permian shale gas in the Yangtze region, South China

Despite significant exploration breakthroughs, the exploration potential and targets of the Permian shale gas in the Yangtze region, South China remain poorly understood due to factors such as complex sedimentary facies variation, differentiated source rock-reservoir combination conditions, and varying tectonic activity-induced preservation conditions. A systematic investigation of the characteristics and distribution, exploration potential, and preservation conditions of the Permian shale sequences, proposes the exploration prospects and targets of the Permian shale gas in the Yangtze region. The results indicate that the studied Permian shales in the Yangtze region are of two types, namely the marine and marine-continental transitional shales, which comprise three suites of organic-rich shales, i. e., the Gufeng, Longtan (Wujiaping), and Dalong formations. The shale distribution is governed by the continental-margin (intracontinental) rift basins and intracratonic depression basins. Specifically, the marine-continental transitional shales of the Longtan Formation are mainly seen in the intracratonic depression basins in the western and southeastern parts of the Yangtze region, while the marine shales of the Gufeng (Wujiaping) and Dalong formations occur predominantly in the continental-margin (intracontinental) rift basins along the northern margin of the Yangtze region. The marine shales exhibit high brittle mineral content, high total organic carbon (TOC) content, well-developed organic pores, and high gas content. In contrast, the marine-continental transitional shales show high TOC content, moderate thermal evolution, well-developed inorganic pores, and generally low, highly variable gas content. Tectonic activities and associated preservation conditions represent critical factors controlling the exploration potential of the Permian shale gas in the Yangtze region. Areas with weak tectonic deformations, such as the western Hubei Province and the Sichuan, Jianghan, and Subei basins, exhibit favorable preservation conditions, thus holding considerable exploration potential. To address geological engineering challenges and accelerate the exploration and production of the Permian shale gas in the Yangtze region, it is recommended to intensify research on fine-grained sedimentary facies zone delineation, dynamic evolutionary patterns of shale gas enrichment, comprehensive evaluation metrics for shale gas preservation conditions, and adaptive technical systems for reservoir stimulation.