Numerical Simulation of Shale Reservoir Fluid-Driven Fracture Network Morphology Based on Global CZM

There are a large number of natural fractures in shale reservoirs, which brings great challenges to hydraulic fracturing. Activating natural fractures in the reservoir can form a complex fracture network, enhance fracturing effects and increase shale gas production. Reservoir geological conditions (low in-situ stress, natural fracture distribution and cement strength) and operation parameters (fracturing fluid viscosity and injection rate) all have an important influence on fracture network propagation. In this paper, a two-dimensional hydraulic fracturing fluid-mechanic coupling numerical model for shale reservoirs with natural fractures is established. Based on the global cohesive zone model, the influence of geological conditions and operation parameters on the propagation of hydraulic fracture network and the fracturing process is studied. Numerical simulation results show that when the horizontal in-situ stress difference, approach angle and cement strength are low, it is easier to form a complex fracture network. Research on the construction parameters found that when the viscosity of the fracturing fluid is low, it is easier to form a complex network of fractures, but the length of the fractures is shorter; on the contrary, the fractures are straight and long. Besides, increasing the injection rate is beneficial to increase the complexity of the fracture network, while increasing the initiation pressure and width of the principal fracture, reducing the risk of sand plugging. Finally, this paper also proposes an optimization solution for hydraulic fracturing operation based on the numerical simulation results.