Digital Simulation of Hydraulic Fracturing in Laminated Shale Formation Containing Varying Bedding Planes

Large-scale hydraulic fracturing is a prevalent technique for exploiting low-porosity and low-permeability shale reservoirs. The propagation and morphology of the hydraulic fracture in the laminated shale formations are significantly influenced by densely developed bedding planes, which can be classified into three categories: continuous, transitional, and discontinuous, with each characterized by distinct properties. This categorization complicates the prediction of the fracture propagation and the optimization of fracturing plans. In this research, a comparative study was proposed to describe fracture propagation and morphology in laminated shale with different types of bedding planes, employing the hydromechanically coupled discrete element method (DEM). The simulation results revealed that bedding planes of different types produce distinct impacts on the fracture propagation, leading to diverse fracture morphologies. In particular, it was found that the plane thickness affected the fracture propagation under low permeability, but the impact was insignificant under high permeability. Under different orientation angles, the continuous bedding planes showed distinct impacts on fracture propagation, while the transitional and discontinuous bedding planes consistently captured the hydraulic fracture. Moreover, the fluid viscosity and injection rate significantly influenced continuous and transitional bedding planes while having a minor effect on the discontinuous bedding planes. The optimal injection schemes incorporating varying injection rates or fluid viscosities were investigated. In addition, the impacts of small-scale bedding planes on fracture propagation were revealed. Furthermore, the bottom hole pressure variation and seismic event distribution were presented to provide complementary evidence of the fracture propagation. The simulation results can promote a comprehensive understanding of the fracture development in shale reservoirs.