Influence of mesoscopic heterogeneity on fracture behavior in high-temperature granite subjected to CO2 fracturing

Hot dry rock (HDR) geothermal resources are a clean, efficient, and renewable energy source. Investigating the fracturing behavior of HDR under fluid injection is crucial for enhancing geothermal energy extraction. At the micro-scale, the mineralogical distribution within granite exhibits pronounced heterogeneity, which significantly influences the stimulation efficiency of Enhanced Geothermal Systems (EGS) reservoirs. To evaluate the impact of mesoscopic heterogeneity on CO2 fracturing in granite, we conducted a series of CO2 fracturing experiments using three types of granite specimens with varying degrees of heterogeneity (a heterogeneity factor R was introduced to quantitatively characterize the degree of heterogeneity in the granite specimens.). These tests were performed under real-time high-temperature conditions ranging from room temperature to 300 °C. Experimental results indicate that the breakdown pressure of CO2 fracturing is consistently lower in granite specimens with higher heterogeneity (larger R-values). To quantitatively assess the complexity of the resulting stimulation, both fractal dimensions and topological parameters were utilized. These metrics were found to be positively correlated with the degree of heterogeneity. Such findings suggest that granite with more pronounced heterogeneity is more sensitive to thermal effects, which promotes mechanical degradation and the development of a more intricate, well-connected fracture network for Enhanced Geothermal Systems (EGS).