Numerical Simulation of the Fracture Propagation Mechanism during Supercritical Carbon Dioxide Fracturing in Shale Reservoirs

Abstract To investigate the fracture propagation mechanism during supercritical CO2 fracturing in shale reservoirs, a numerical model was proposed based on the displacement discontinuity method. The Peng–Robinson equation was introduced to determine the variations in CO2 properties during the fracturing process. Considering natural fracture distribution in shale reservoirs, the fracture propagation mechanisms during supercritical CO2 fracturing in shale reservoirs under different horizontal stress differences and matrix permeabilities were analyzed. The influence of the proportion of CO2 preenergizing on fracture morphology was discussed. The results obtained via numerical simulation show that supercritical CO2 is beneficial to create a more complex fracture network by activating natural fractures under the same horizontal stress difference. CO2 easily penetrates into the matrix near the fracture surfaces, increasing reservoir energy. However, when the permeability of shale reservoirs exceeds 0.04×10−3 μm2, substantial filtration of CO2 into the reservoir matrix occurs near the well bore, limiting the activation of natural fractures around the fracture tip. A higher proportion of CO2 preenergizing during fracturing is conducive to improve the fracture complexity while reducing the fracture aperture.