Abstract: At present, it is in an early exploration stage of coal measure reservoir in the Permian Longtan Formation in Qijiang area, southeastern Sichuan Basin. There is a lack of clear understanding of fracturing quality of complex lithologies and fracture propagation characteristics of interbedding of shale, limestone, and coal rock, which needs to be further studied. In response to the above issues, experimental tests, fracturing physical simulation, and numerical simulation are conducted to analyze the fracturing quality and fracture propagation characteristics of Longtan Formation reservoir. The results show that there are significant differences in lithology, mineral composition, rock mechanical and in-situ stress parameters vertically of Longtan Formation reservoirs in various regions, and the reservoir is characterized by low brittle mineral content and poor brittleness as a whole, with the horizontal stress difference reaching up to 2–6 MPa between different rock types, making it difficult to propagate transverse fractures. The physical simulation result shows that due to the influence of lithologic boundary and stress difference coefficient, three types of fractures are observed in Longtan Formation, i.e., T-shaped fractures, passivation fractures, and transverse fractures, and the fracture pattern is mainly controlled by the strength of lithologic boundary. The numerical simulation of fracture propagation characteristics shows that the displacement, viscosity, and fracture initiation position have a significant influence on fracture propagation pattern. On this basis, the shale interval and mudstone interval intercalated with limestone and shale layers are optimally selected, and fracturing operation is implemented with a displacement of higher than 12 m³/min and a fracturing fluid viscosity of about 25 mPa·s to promote the transvers propagation of hydraulic fractures.

Key words: Sichuan Basin, Qijiang area, Longtan Formation, coal measure strata, hydraulic fracturing, fracture characteristics