Propagation of hydraulic fracture under the joint impact of bedding planes and natural fractures in shale reservoirs

The generation of the complex fracture network through hydraulic fracturing is a prerequisite for economic exploitation of shale gas. Bedding planes and natural fractures in shale reservoirs exert a direct impact on the propagation of hydraulic fracture and the formation of the complex fracture network. Based on theoretical analysis and flow-stress-damage coupled approach, the propagation of hydraulic fracture under the joint impact of the bedding planes and the natural fractures is studied. The results show the main factors that influence the fracture propagation are the horizontal principal stress difference, the minimum horizontal principal stress, the approaching angle of bedding plane (AABP), the intersection angle of natural fracture (IANF), and the cohesion of the reservoir matrix and the bedding plane. The bigger the horizontal principal stress difference is and the smaller AABP and the cohesion are, the more likely hydraulic fracture will propagate toward the direction of the maximum horizontal principle stress; the smaller AABP and the cohesion are, the more easily it will propagate along the bedding planes; AABP and IANF are the key factors that affect the fracture network formation and both of them bear a negative correlation on the principal stress difference for the formation of the fracture network; the smaller the stress difference and the cohesion difference between the bedding plane and the reservoir matrix are, and AABP is close to IANF and they are in the middle of its value range, the more easily the fracture network forms. The research results are of great significance to reveal the propagation law of hydraulic fracture and the formation of the complex fracture network in shale reservoirs and the efficient exploitation of shale gas.