Experiment research on the CO₂ fracturing fracture propagation laws of tight sandstone

In order to improve the complexity of hydraulic fractures in the tight reservoirs with undeveloped natural fractures and beddings, CO₂ based tight sandstone fracturing was experimentally studied in the true triaxial fracturing simulation experiment system to analyze the effects of horizontal stress difference, fracturing fluid type and displacement on the propagation laws of hydraulic fractures. It is shown that the hydraulic fractures generated by supercritical CO₂ fracturing are morphologically the most complex, followed by those generated by liquid CO₂ fracturing and those generated by slick-water fracturing are the simplest. When liquid CO₂ fracturing is carried out, low horizontal stress difference (≤3 MPa) is beneficial to increasing the complexity of hydraulic fractures. Compared with the initial pressure of slick-water fracturing, that of liquid CO₂ fracturing is 22.1% lower and that of supercritical CO₂ fracturing is 28.2% lower. The fluid pressure increasing rate inside the wellbore and the initial pressure can be increased by increasing the displacement. It is experimentally proved that supercritical CO₂ fracturing can improve the complexity of fractures effectively.