Numerical simulation and optimization study of the complex fracture network in naturally fractured reservoirs

Multi-fractured horizontal wells are widely used for unconventional reservoir development since the hydraulic fracture (HF) could stimulate natural fractures (NF) to form a complex fracture network (CFN), which will significantly increase the productivity. So accurately characterizing and optimally designing the fracture network configuration are essential to unconventional reservoir development. Facing this urgent request, a numerical study for the complex fracture network is proposed. The displacement discontinuity method (DDM), together with the fluid flow function, is adopted to simulate the HF dynamic propagation which couples the rock and fluid mechanics. A power-law function is adopted to describe the distribution of natural fractures. Then a fracture crossing criterion is used to determine the interaction of HF and NF to simulate the CFN configuration. Based on the CFN numerical model, the effects of different operational and geological parameters, such as the HF spacing and various NF distribution fields, are investigated. Furthermore, a CFN optimization framework is established to achieve the optimal design of CFN under complex geological conditions, in which a clustering-loop method together with a whale optimization algorithm (WOA) is employed to maintain the accuracy while reducing the calculation time. Multiple CFN placement methods are simulated and optimized and the optimal CFN under a complex naturally fractured reservoir is finally obtained. This numerical simulation and optimization approach makes an effort to the study of CFN configuration and unconventional reservoir development.