NUMERICAL STUDY ON THE INTERACTIONS WITH WEAK INTERFACES FOR CO₂ AND HYDRAULIC FRACTURES USING THERMO-HYDRO-MECHANICAL COUPLED PHASE-FIELD MODEL

Carbon dioxide fracturing is an emerging technology for the stimulation of unconventional reservoirs; however, the interaction mechanism between fractures and weak interfaces remains less understood compared to hydraulic fracturing. To address this issue, we extended a thermo-hydro-mechanical phase-field model by incorporating the capillary effect between water and CO₂, establishing a fracturing model that accounts for weak interfaces. Comparative analyses were conducted to examine the interaction mechanisms of CO₂ and hydraulic fracturing under varying interfacial energy release rates, interaction angles, in-situ stresses, injection temperatures, and interfacial offsets. The results indicate that: (1)fractures deflect more and propagate along weaker interfaces, with CO₂ fractures exhibiting a stronger tendency to be attracted to weak interfaces; (2)hydraulic fracture propagation is largely insensitive to changes in interaction angle, whereas larger interaction angles restrict the deflection of CO₂ fractures; (3)lower stress differences enhance fracture deflection along weak interfaces for both fracture types, though CO₂ fractures show a greater propensity for interfacial deflection; (4)varying injection temperatures have minimal influence on hydraulic fracture-interface interaction but significantly affect CO₂ fracturing, with lower injection temperature differences limiting CO₂ fracture initiation; (5)when weak interfaces are offset in the direction away from fracture propagation, the complexity of both CO₂ and hydraulic fractures decreases and propagation behavior shifts, though CO₂ fractures remain more likely to be attracted to the interface. This study demonstrates that CO₂ fracturing is more sensitive to reservoir geomechanical properties when interacting with weak interfaces and is more conducive to forming complex fracture networks, providing theoretical support for predicting and evaluating the effectiveness of CO₂-based reservoir stimulation.