Main controlling factors of shale gas enrichment and high yield: a case study of Wufeng-Longmaxi formations in Fuling area, Sichuan Basin

The controlling factors of shale gas enrichment and yield were discussed based on core observation, geochemical analysis, logging and seismic data of marine shale collected from the Wufeng-Longmaxi formations in the Fuling area of Sichuan Basin. Total organic carbon content, micro-to nano-scale pores and preservation conditions are the main controlling factors for shale gas enrichment. The total organic carbon content is not only an important parameter for evaluating original shale quality, but also affects micro-to nano-scale pore development. The preservation condition is important for shale gas enrichment. The high yield of shale gas is affected by brittle mineral content, burial depth, structural morphology and fractures. The higher the brittle mineral content, the better the compressibility of shale and the better the effect of fracturing. In addition, burial depth and structure features have great effect on crustal stress, and thus have significant influence on fracturing. Natural fracture development leads to directional pressure relief during fracturing, and it is difficult to form an effective and complex permeability mesh.