Numerical Simulation of Multi-Fracture Propagation Based on the Extended Finite Element Method

Abstract

Multi-stage, multi-cluster fracturing in horizontal wells is widely used as one of the most effective methods for unconventional reservoir transformation. This study is based on the extended finite element method and establishes a multi-hydraulic fracturing propagation model that couples rock damage, stress, and fluid flow, and the influence of horizontal stress difference and cluster spacing on fracture propagation is quantitatively analyzed. The simulation results show that changes in horizontal stress differences and inter-cluster spacing have a significant impact on the final propagation morphology of hydraulic fractures, and the change of the fracture initiation sequence forms different stress shadow areas, which in turn affects the propagation morphology of the fractures. When two fractures simultaneously propagate, they will eventually form a “repulsive” deviation, and a smaller stress difference and a decrease in inter-cluster spacing will lead to a more significant deviation of the fracture. Specifically, when the horizontal stress difference is 4 MPa and the cluster spacing is 6 m, the offset of the fracture tip along the direction of minimum horizontal principal stress is about 1.6 m, compared to the initial perforation position. When two fractures propagate sequentially, the fractures do not significantly deviate and propagate along the direction of maximum horizontal principal stress. When fractures propagate sequentially, the stress difference has little effect on the morphology of the fracture, but changes in inter-cluster spacing will significantly affect the length of the fracture. This study quantifies the effect of inter-fracture interference on fracture propagation morphology, providing guidance for optimizing the construction parameters of multi-stage hydraulic fracturing.