Mechanism of hydraulic fracture propagation and the uneven propagation behavior of multiple clusters in shale oil reservoirs

Abstract

China possesses substantial shale oil and gas resources, a significant portion of which is recoverable. Hydraulic fracturing technology plays an essential role in enhancing oil recovery. However, accurately predicting the propagation of hydraulic fractures in complex reservoirs remains challenging due to the inherent weakness of shale formations. Based on the discrete element method (DEM), a coupled hydraulic fracturing model that incorporates perforation erosion and flow distribution was developed. This model simulates the mechanical interactions between hydraulic fractures and natural weak planes, providing insights into fracture morphology, perforation erosion, flow distribution, and net pressure inversion. Results show that low cementation interface angles facilitate vertical fracture propagation, while higher angles restrict vertical propagation by capturing fractures. Due to shear stress concentration, bedding planes limit vertical propagation through shear failure, and natural fracture zones exacerbate non-uniform propagation by inducing stress perturbations. Furthermore, the degree of non-uniform fracture propagation is influenced by flow distribution, which is significantly affected by perforation friction. The findings reveal the mechanisms of hydraulic fracture propagation and the uneven propagation behavior of multiple fracture clusters, offering a theoretical foundation for understanding the governing principles of hydraulic fracture behavior, particularly in explaining the non-uniform propagation of multi-cluster hydraulic fractures in layered reservoirs.