Experiment of supercritical CO2 fracturing: Invalid experimental data analysis and enlightenment

Supercritical CO2 (SC-CO2) fracturing is considered as a new efficient and waterless fracturing technology for unconventional oil and gas stimulation. This process also can realize the CO2 sequestration and reduce the release of greenhouse gas. In order to further reveal the advantages and characteristics of SC-CO2 fracturing, laboratory fracturing experiments with shale were carried out. It was found that some rock samples could be fractured as expected while some other rock samples had higher initiation pressures that obviously deviated from normal value, furthermore several samples were not even able to be fractured. We found that when cementing the wellbore with resin glue, the additional glue would block the remaining space between the wellbore and the shale sample. Thus, the rock samples could hardly be fractured or fractured with extra high initiation pressures approaching the maximum limit of experimental equipment (55.0 MPa). In this case, dozen or more fractions with irregular shapes would be produced after the rock sample was destroyed, accompanied by strong breaking sound. Based on the results, a new method of SC-CO2 impact fracturing is proposed, which impacts and fractures the reservoir by building and instantly releasing pressure at bottom hole. This method may significantly improve the number of fractures and fracture connection in the reservoir, and realize efficient developments of unconventional oil and gas.