Optimum Timing for Miscible CO2-EOR after Waterflooding in a Tight Sandstone Formation

In this paper, CO2 dissolution into a light oil/reservoir brine and optimum timing for CO2 enhanced oil recovery (CO2-EOR) after waterflooding in a tight sandstone formation are experimentally studied. First, the gas–oil ratio (GOR) of CO2-saturated light oil and the gas–water ratio (GWR) of CO2-saturated reservoir brine are measured by using a PVT system. The measured GOR is found to be approximately six times of the measured GWR at the same pressure and temperature. Second, the equilibrium interfacial tensions (IFTs) between the light oil/reservoir brine and CO2 are measured at different equilibrium pressures and the actual reservoir temperature by applying the axisymmetric drop shape analysis (ADSA) technique for the pendant drop case. The measured equilibrium IFT between the light oil and CO2 is about one-third to one tenth of that between the reservoir brine and CO2 under the same test conditions. Third, the minimum miscibility pressure (MMP) between the light oil and CO2 is determined to be 11.0 MPa...

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