Abstract: Considering the supercritical CO2’s characteristics of low viscosity and no surface tension, it is expected to be a new type of fracturing method for unconventional oil and gas reservoir. In this paper, we finally build the initiation pressure models for supercritical CO2 fracturing through the establishment of pressurization rate model of fluid in the wellbore, and compare with the breakdown pressure of water and liquid CO2. The results show that: the breakdown pressure of supercritical CO2 fluid is 20.5% less than liquid CO2 fluid, which is 75.5% less than conventional hydraulic fracturing breakdown pressure, which shows that breakdown pressure is significantly affected by the low viscosity and low pressurization rate of supercritical CO2. The error of this model is only less than 3% compared with experimental data in the literature, so as to indicate that the model can provide guidance for the prediction of supercritical CO2 fracturing initiation pressure.

Key words: supercritical CO2, breakdown pressure, stress distribution around the wellbore