oa Research on the Applicability of CO2 Enhanced Oil Recovery in Lacustrine Shale Formation

CO2 prepad fracturing is a promising recovery approach for shale oil reservoirs. However, some of the field tests missed forecasts in the recovery. Therefore, a targeted investigation is demanded to clarify the potential effects of CO2 on shale oil production. Based on the nano-mechanical analysis and physical model simulation tests of cores, this research explored the patterns of the effects of CO2 on the microscopic mechanical properties of the fracture surface and fracture conductivity of shale and clarified the EOR performance of CO2 for different crude oil. It is shown that CO2 has great effects on the microscopic mechanical properties of the shale fracture surface, the indentation depth into the shale surface grows at the same load, with an average increase of about 16% after CO2 treatment. It means deeper proppant embedment into the fracture surface is expected under the same confining pressure, and thus the fracture flow conductivity is degraded. For the low-viscosity Qingshankou oil, the EOR performance of CO2 presents no prominent improvement, compared with that of surfactants. Therefore, attention shall be paid to the potential damage caused by CO2 prepad fracturing when recovering the pure-shale-type shale oil reservoir of the Qingshankou Formation.