Factors controlling enrichment and accumulation of Devonian–Carboniferous shale gas in the Yaziluo rift trough in the Yunnan–Guizhou–Guangxi region

Objective Compared with the Wufeng-Longmaxi Formation in the Sichuan Basin and its periphery, the Yunnan-Guizhou-Guangxi region has more complex conditions for the enrichment and accumulation of shale gas. Currently, the exploration degree of shale gas in the Yunnan-Guizhou-Guangxi region is relatively low, and the main factors controlling the enrichment and accumulation of shale gas are unclear. Methods This paper relies on a large number of studies from the basic surveys of shale gas and major special projects in the Yunnan-Guizhou-Guangxi region. The research includes the sedimentary characteristics, diagenesis, hydrocarbon generation, thermal evolution characteristics, shale reservoir characteristics, accumulation patterns, and preservation conditions of the Devonian-Carboniferous shale in the Yunnan-Guizhou-Guangxi region. Results The research indicated that the deposition of Devonian-Carboniferous organic-rich shale was mainly controlled by rift troughs, and the sweet spots of organic-rich shale were mainly formed in the transgressive system tract and the early highstand system tract of deep-water facies sedimentation. The regional sea level rise has brought abundant nutrients, promoting the wealth of organisms in the water body and generating strong biological productivity, which provides a good material basis for the formation of organic-rich sediments. Seismic interpretation reveals that most of the areas distributed along the main rift trough are greatly affected by destruction by late-stage tectonic activities, leading to the deterioration of the preservation conditions of shale gas. In contrast, the secondary rift troughs around the main rift trough have relatively stable structures, providing good conditions for the preservation of shale gas. Conclusion On this basis, the main controlling model for the enrichment and accumulation of shale gas in the Devonian-Carboniferous system in the Yunnan-Guizhou-Guangxi region is proposed: "rift trough deposition, deep-water lithofacies controlled hydrocarbon generation, and structural preservation in secondary rift troughs". The model has been confirmed through the drilling of multiple wells. [ Significance ] The results of this research can be used as a guide for the optimal selection of favorable shale gas areas and for the drilling of parameter wells in the future.