Modeling of Pressure Dependence of Interfacial Tension Behaviors of a Complex Supercritical CO2 + Live Crude Oil System Using a Basic Parachor Expression

In the CO2 injection based enhanced oil recovery (EOR) operations; injected supercritical CO2 interacts with reservoir crude oil in a multiple-contact fashion to develop a low IFT condition between the two phases that plays a crucial role in achieving low residual oil saturation. In case of oil reservoirs, depending on the pressure, temperature, and composition of the gas and oil, injection of supercritical CO2 can be under either immiscible or miscible modes. As described by Al-Mjeni et al. , “in an immiscible flood, gas and oil remain distinct phases. Gas invades the rock as a nonwetting phase, displacing oil from the largest pores first. However, when they are miscible, gas and oil form one phase. This mixing typically causes the oil volume to swell while lowering the IFT between the oil phase and water. Displacement by miscible-gas injection can be highly efficient for recovering oil”. Wallace et al. state that “as reservoir pressure enters the near-miscible range (0.8 to 0.95 of minimum miscibility pressure), the vaporization of light hydrocarbon components from the crude oil into the CO2 vapor phase begins, the mixing of CO2 and oil phases progresses, and the IFT of the system is lowered, all contributing to improved oil recovery efficiency”. It had prompted researchers to experimentally investigate and theoretically model the pressure dependence of complex supercritical CO2 + crude oil systems at elevated pressures and temperatures.

Hsu et al, Nagarajan and Robinson, Nagarajan et al, and Gasem et al. are among early researchers who used the experime

ntally measured input data (phase compositions and densities of the equilibrium liquid and vapor phases) to model the experimental IFT behaviors of complex but standard supercritical CO2 + hydrocarbon systems using a basic parachor expression. Based on Modern physics and an experimental database, Schechter and Guo suggested the use of a critical scaling exponent 3.88 in the parachor equation.