Study on the computational model and distribution characteristics of rock fracture energy induced by supercritical CO2 phase transition

Abstract

The current research on the energy distribution characteristics of supercritical CO₂ phase transition fracturing (CDPTF) is relatively lacking, particularly for effective quantitative calculation methods. This study develops models to calculate CO₂ shock wave and gas expansion energy, quantifying their roles in rock damage and energy distribution. Five field tests measured acoustic wave velocity, rock damage, and energy distribution during CO₂ rock fracturing. The results indicate that supercritical CO₂ creates large rock fragments, with a small crushing zone, forming numerous through-cracks on the surface and causing weak seismic effects. Additionally, the radius of rock failure ranges from 4.3 to 5.6 m, with gas expansion energy accounting for 84.36 % and shock wave energy only 15.64 %. Specifically, the average energy proportion of the shock wave used for rock fragmentation, crack formation, and surface vibration is 2.57 %, 12.13 %, and 1.94 %, respectively. The average energy proportion of gas expansion used for crack propagation is 42.15 %, while the energy used for gas ejection (i.e., wasted energy) accounts for 41.21 %, reflecting a relatively high overall energy efficiency. Furthermore, reducing the initial phase change pressure or increasing the tensile strength of the rock can effectively improve energy utilization efficiency. Minimizing gas leakage or applying the method in high-strength rock areas can further enhance the efficiency of gas expansion energy in rock fracturing. This study provides a theoretical basis for optimizing CDPTF energy utilization in rock fracturing.