INFLUENCE OF NATURAL FRACTURE ON HYDRAULIC-FRACTURE PROPAGATION OF HOT DRY ROCK RESERVOIR WITHIN THE GONGHE BASIN

The commercial development of Hot Dry Rock(HDR)resources currently depends on Enhanced Geothermal Systems(EGS),where natural fracture networks play a decisive role in reservoir connectivity. While significant theoretical and experimental research has clarified fracture propagation mechanisms in HDR,a comprehensive evaluation of hydraulic fracture behavior—accounting for actual in-situ stress conditions, reservoir rock heterogeneity, and complex natural fractures—remains insufficiently studied in real-world EGS stimulation processes. Focusing on the Gonghe HDR demonstration site in Qinghai Province, this study first characterizes the three-dimensional distribution of natural fractures and quantitatively analyzes the influence of the present-day stress regime on fracture reactivation and propagation. By integrating treatment data with microseismic and time-frequency electromagnetic monitoring, we assessed how pre-existing natural fractures control hydraulic-fracture propagation within the Gonghe granite reservoir. The research reveals that natural fractures in the Gonghe Basin HDR are predominantly oriented NW and NE. Their spatial distribution, controlled by multi-stage tectonic superposition, exhibits strong heterogeneity. At low injection volumes, the rock's intrinsic mechanical properties promote hydraulic fracture initiation along pre-existing natural fractures. As stimulation intensity increases, hydraulic fractures at the Gonghe site evolve from initially following natural fractures to reorienting toward the direction controlled by the maximum principal stress, resulting in a hybrid propagation pattern. The resulting fracture network is dominated by shear and strike-slip failure modes. These findings enhance the mechanistic understanding of hydraulic stimulation in HDR reservoirs and provide a quantitative basis for optimizing EGS design.