Development of Wufeng Formation—Longmaxi Formation fault and shale gas preservation mechanism in Tiangongtang area, Sichuan Basin

The deep shale gas resources in the Tiangongtang area of the Sichuan Basin are rich, but the exploration degree is relatively low. At the same time, the complex structural development conditions in this region seriously restrict the results of shale gas exploration and development.Methods: This study is based on the shale geological features and seismic data of the research area, using typical well data and balance profile restoration to investigate the fault development characteristics in the area and their effects on shale gas preservation.Results:The study shows that: ① In the Tiangongtang area, the Wufeng Formation — Longmaxi Formation primarily develops four levels of fractures, with level Ⅰ fractures mainly developed in the structural edge areas, level Ⅲ and Ⅳ fractures dominant in the north, and level Ⅱ, Ⅲ, and Ⅳ fractures primarily developed in the south. ② The formation of fractures in the Tiangong Tang area is mainly divided into three stages: during the late Yanshan period, SN compression formed fractures predominantly in the NW and NWW directions; in the early Himalayan period, NNE—SSW compression formed fractures mainly in the NW direction; since the mid- Himalayan period, NWW—SEE regional tectonic strike- slip stress has resulted in the formation of NE- dominant fractures. ③ The influence of fractures on shale gas retention is characterized by an increased gas content the further away one is from the fault; different scales of fractures have varying impacts on shale gas retention. When the distance from level Ⅰ fractures exceeds 5 km, level Ⅱ fractures are between 3~5 km, and level Ⅲ fractures exceed 2 km, the gas content exceeds 3.0 m3/t, indicating good shale gas retention conditions; level Ⅳ fractures have a minimal impact on shale gas retention.Conclusions: The development of faults varies significantly across different stages of burial evolution. During the burial stage, fault development is minimal, and its impact on shale gas preservation is negligible. During the slow uplift stage, large- scale fault development caused by compressive uplift severely damages preservation conditions. During the rapid uplift stage, fault development and reactivation further exacerbate shale gas loss.The study clarifies the shale gas preservation mechanism in the Tiangongtang area, providing theoretical support for further exploration and development.