Abstract: The supercritical CO₂ fracturing technology is yet to be improved,and the mechanisms of fracture generation and propagation are still not clear at present.In order to get an in-depth understanding of hydraulic fracture propagation behaviors and geometry under supercritical CO₂ fracturing,we introduced the Pen-Robinson equation to simulate the process of supercritical CO₂ fracturing,based on the displacement discontinuity boundary element method.Combined with lab physical simulation experiments,the differences of hydraulic fracture propagation behaviors and geometry between conventional fracturing with water-based fluid and fracturing with supercritical CO₂ in the shale reservoir were discussed.The results show that the pressurization in the pores of surrounding rocks will function to reduce the constraint of in-situ stress on fracture propagation,thanks to the diffusivity and good permeability of supercritical CO₂,and in turn the initiation pressure for fractures is lower than that of conventional fracturing.The incremental volumetric strain generated during and the failure of fractures after supercritical CO₂ fracturing are higher than those under conventional fracturing,thus the fracture geometry under supercritical CO₂ fracturing is more complex than that under fracturing with water-based fluid; meanwhile,the fracture plane under supercritical CO₂ fracturing is more complex and uneven,and has higher tortuosity than that under conventional fracturing with water-based fluid.

Key words: fracture propagation, fracture geometry, natural weak plane, supercritical CO₂, hydraulic fracturing, shale reservoir