Numerical insight into hydraulic fracture propagation in hot dry rock with complex natural fracture networks via fluid-solid coupling grain-based modeling

Abstract

Abundant natural fractures (NFs) in hot dry rock (HDR) reservoirs serve as a crucial element in hydraulic fracturing technology and reservoir production. Nevertheless, the interaction mechanism between hydraulic fractures (HFs) and natural fracture networks (NFNs) remains poorly understood. This study combines the novel hydro-grain-based model (hydro-GBM) and discrete fracture network (DFN) model to investigate the effects of in-situ stress, fracture number, and fracture length on hydraulic fracturing behaviors in mineral-scale granite with NFNs. Results indicate that as the complexity of NFs increases, the stress shadow effect is amplified during HF propagation, while the spatial arrangement of NFs governs the propagation of secondary paths. Additionally, a downward trend is observed in average activity levels of acoustic emission (AE) events and proportions of large events within NFs and matrix. Damage and activation degrees in both NFs and matrix decrease with an increase in the number of NFs. The inability of main hydraulic paths to propagate over long distances can be attributed to the dispersion of fracturing fluid and the rapid decay of pressure within densely distributed, short NFs. These numerical findings shed light on the process of HFs activating NFNs and provide valuable insights for enhancing heat extraction efficiency in HDR reservoirs.