Effect of Crude Oil Properties on the Interfacial Tension of Crude Oil/CO₂ Under HPHT Conditions

Injection of carbon dioxide (CO₂) is an effective method to improve oil recovery from hydrocarbon reservoirs. The interfacial tension (IFT) between CO₂ and crude oil is a critical parameter during CO₂ flooding. IFT of different crude oils in compressed carbon dioxide was measured at different pressures and temperatures. The minimum miscibility and first-contact miscibility pressures were calculated using vanishing IFT analysis. The minimum miscibility pressure is significantly affected by temperature with less dependency on the crude oil composition. The first-contact miscibility pressure was found to be more sensitive to temperature and crude composition. Measured IFT values at different pressure and temperature conditions were correlated to crude oil density and acid number using a wide range of crude gravity and total acid number. These properties are simple and less costly to measure but they directly reflect the effect of crude oil composition on IFT as a function of pressure. This new approach of correlating IFT between CO2 and crude oil under reservoir conditions will improve the simulation of CO2 EOR projects under reservoir conditions.