Thermo-hydro-mechanical coupling simulation for fracture propagation in CO2 fracturing based on phase-field model

CO2 fracturing is extensive used in unconventional oil and gas reservoir, geothermal resources, metal uranium mining, and CO2 geological storage. At present, the fluid-solid coupling model for fracture propagation with CO2 does not consider the influence of heat exchange between CO2 fracturing fluid and the formation, which leads to the deviation between the simulation results and field. Based on the phase-field models, considering the thermal stress and CO2 physical properties change induce by thermal effect, a Thermo-hydro-mechanical coupling model is established for CO2 fracturing. This paper studies the influence of formation horizontal stress difference, approaching angle and fracturing fluid injection temperature. The results indicate that, compared with hydraulic fracturing, CO2 fracturing can significantly reduce the fracture initiation pressure and time, and obtain a more complex fracture morphology with the same stress difference. For natural fractures, the approaching angle is linearly related to the initiation pressure and initiation time of opening new fractures. With the growth of approaching angle, the initiation pressure and initiation time increase respectively. The fracture shows increase in fracture morphology complexity induced by a stronger thermal stress with the growth of temperature dif-ferences. CO2 fracturing simulation thermal stress should be considered for a precision of fracture morphology.

Automated summary

In this paper, a thermo-hydro-mechanical coupling model is established to study the influence of formation horizontal stress difference, approaching angle, and fracturing fluid injection temperature on CO2 fracturing. The results show that compared with hydraulic fracturing, CO2 fracturing can significantly reduce the fracture initiation pressure and time, and obtain a more complex fracture morphology. The approaching angle is linearly related to the initiation pressure and initiation time of opening new fractures.