Enhancing directional propagation characteristics of hydraulic fractures in hot dry rock: Insights from multi-lateral wells

Hydraulic fracturing serves as a critical technology for extracting thermal energy from hot dry rock reservoirs by stimulating the reservoir and establishing efficient flow pathways. Nevertheless, this approach faces several significant and persistent challenges, including difficulties in controlling hydraulic fracture propagation and the resultant poor connectivity. To address these issues, this study proposes a multi-lateral well hydraulic fracturing approach to guide fracture growth directionally. Laboratory-scale fracturing experiments were performed on granite samples under simulated triaxial stress and elevated temperatures, comparing three well configurations: vertical, single-lateral, and multi-lateral wells. The induced fracture surfaces were reconstructed digitally by high-resolution 3D optical scanning. This process was employed to characterize the morphology of hydraulic fractures and to evaluate the guiding performance for the lateral well design. The results indicate that fracture propagation is primarily governed by in situ stress, regardless of rock temperature in vertical well hydraulic fracturing. In single-lateral well fracturing, the lateral well dominates the fracture extension under low-temperature conditions. However, its guiding effectiveness diminishes as rock temperature increases. In contrast, multi-lateral well hydraulic fracturing maintains a stronger guiding capability even at high temperatures, thereby enhancing inter-well connectivity. Furthermore, fracture roughness parameters and tortuosity increase with rock temperature. This tendency becomes particularly pronounced at elevated temperatures. Multi-lateral well hydraulic fracturing significantly reduces fracture roughness and tortuosity, which contributes to improved fracture conductivity. This study provides new insights into achieving directional connectivity between injection and production wells in an Enhanced Geothermal System.