Use of oil-soluble surfactant to reduce minimum miscibility pressure

In some low-permeable reservoirs, the miscibility pressure is far higher than the formation pressure, which makes it not feasible to have a CO2 miscible displacement. In this study, an oil-soluble surfactant, CAE, was designed and synthesized to reduce interfacial tension (IFT) and CO2-oil minimum miscible pressure (MMP), making it possible to release miscible displacement increasing oil recover. Experiment results showed that oil soluble surfactant can be dissolved in supercritical CO2 but not soluble in water. It is also found that the CAE preslug displacement has the higher displacement efficiency than displacement with the CAE dissolved in CO2. Based on a series of CAE preslug displacement experiments with varying CAE concentrations, the optimal injection concentration of CAE is 0.2%. Moreover the MMP determined under the CAE concentration of 0.2% is 6.1MPa lower than that of pure CO2 displacement. It reduces the MMP more than liquid gas preslug displacement (3.2MPa) when the same volume of liquid gas is used with the CAE used in CAE preslug displacement test.