A laboratory study on near-miscible CO2 injection in Steelman reservoir

Miscible flooding is considered unsuitable for some reservoirs in southeast Saskatchewan because of high CO2 minimum miscibility pressure or operating pressure constraints. Therefore, the effectiveness of near-miscible CO, in jection was assessed for the Steelman reservoir in a laboratory study. The minimum miscibility pressures (MMP) were estimated for Steelman reservoir f luids with pure CO, and CO2-hydrocarbon gas mixtures, the partially flashed reservoir fluids and the dead oils with pure CO,. The results of MMP studi es demonstrated (1) addition of ethane or propane can reduce CO2 MMP greatl y; and (2) achieving a miscible CO, flood in the Steelman reservoir could b e possible at a lower operating pressure than the measured CO, MMP, by part ially depleting the reservoir. Asphaltene flocculation tests showed that, a fter the onset point, flocculation increased linearly with gas concentratio n, but that the presence of brine had a negligible effect. Three tertiary C O2 coreflood tests were conducted with Steelman reservoir fluids a;the rese rvoir temperature. These results showed that the microscopic displacement e fficiency during the CO, injection stage improved with the operating pressu re in the near-miscible region, but no dramatic change in oil recovery was observed with a change in operating pressure.