The hydraulic fracturing of conglomerates with combined impacts of interface and gravel heterogeneity

Hydraulic fracturing (HF) is a crucial technique for enhancing production in low-permeability conglomerate reservoirs. The presence of diverse materials such as matrix, gravel, and the gravel–matrix interface introduces significant heterogeneity in these conglomerates. This heterogeneity poses substantial challenges in predicting and controlling the propagation paths of HFs. We investigate the impacts of the mechanical properties of the interface and gravel on hydraulic fracture (HF) propagation based on the global pore-pressure cohesive zone element method, which is validated against existing experimental results. We apply two distinct geological models: the individual conglomerate model with uniformly sized gravels and the heterogeneous conglomerate model with composite gravels. Results indicate that HF propagation favors the path with the lowest critical fracture energy. Variations in the mechanical properties of the gravel and interface significantly influence the HF propagation path, affecting both the morphology of the fracture and the timing of gravel penetration. We further construct a phase diagram to characterize the combined effects of interface and gravel properties on the HF mode, which facilitates the rapid determination of the penetration-to-deflection ratio and enables the effective prediction of the fracture extension modes.