Performance of immiscible and miscible CO2 injection process in a tight carbonate reservoir (experimental and simulation approach)

In this study, the technical feasibility of CO2 injection in a core sample of a tight carbonate reservoir was investigated under various operating conditions. First, the minimum miscibility pressure (MMP) of CO2/oil system was determined to be 1,907 Psia. The effects of the operating pressure as well as the injection flow rate of CO2 on the oil recovery were examined. The results showed that at the operating pressures far below the MMP, the ultimate oil recovery factor is considerably low and increases as the pressure approaches near-miscible condition. When injection pressure was increased to 2,000 Psia, the ultimate oil recovery factor reached 0.81 and further increase in injection pressure did not significantly improve the recovery factor. For injection pressures lower than MMP (i.e., immiscible condition), increasing injection flow rate of CO2 resulted in lower oil recovery, while at the pressures near and above the MMP, the ultimate oil recovery was much less dependent on CO2 injection flow rate. All the test results were simulated using the CMG package, ver. 2011 and attempt was made to history match the experimental results. In this process, relative permeability curves were used as matching parameter. The simulation results were in good agreement with experimental values.