INFLUENCE OF BEDDING PLANE STRENGTH ON EVOLUTION OF HYDRAULIC FRACTURE NETWORK

The bedding planes of unconventional oil and gas reservoirs, such as shale gas and coalbed methane, are relatively developed. The existence of bedding planes directly interferes with the expansion of hydraulic fractures. Different regions have different cementation degrees. It is of great significance to reveal the influence mechanism of the bedding plane on hydraulic fractures for understanding the formation and evolution of the hydraulic fracturing network. Therefore, based on Python programming, the global embedded 0-thickness cohesive element model with a bedding plane is established. Based on the model, the influence of the bedding plane strength on hydraulic fracture propagation is studied. Furthermore, the acoustic emission(AE)simulation is realized by MATLAB programming, which provides an important means for the fine study of the fracture propagation process. According to the numerical simulation results and AE data, it can be known that the propagation path of hydraulic fractures is determined by the maximum principal stress and the bedding plane. The strength of the bedding plane determines the proportion of the two. The weaker the bedding plane strength, the stronger the ability to capture hydraulic fractures. At this time, the fracture propagation path is dominated by the bedding plane. When the bedding plane strength is moderate, the phenomenon of cross-layer fracture and bedding fracture alternately appears, which shows the characteristics of intermittent dislocation fracture. So the fracture network is complex. During hydraulic fracturing, the tensile fracture is the dominant fracture type, and it is manifested in cross-layer fracture. There is a large fracture width, which is conducive to proppant migration and filling. However, the shear fracture is mostly manifested as the bedding slip fracture with a small crack width. Moreover, mineral heterogeneity can cause the asynchronous propagation of fractures and indirectly affect the complexity of fractures. Therefore, the fracturing construction design can be differentiated for reservoirs with different bedding plane strengths, to realize the efficient exploitation of unconventional tight oil and gas.