This contribution consists of two parts. First, an equation of state (EOS) applicable to the PVT of oil and gas mixtures is introduced. Matching the second virial coefficient for the equation of state with the second virial coefficient for the square-well fluids, a new temperature dependence is found for the parameter α of the equation of state. Using this parameter, the equation of state is extended to heavy hydrocarbons up to n -octacosane. This equation of state not only is applied to hydrocarbons but to non-hydrocarbons as well. The average absolute error for predicting the vapor pressure and saturated liquid density of hydrocarbons, non-hydrocarbons, polar compounds and associating fluids were found to be 1.7% and 2.6%, respectively. Then, this modified equation of state is used to calculate the minimum miscibility pressure (MMP) for displacing two oil mixtures using two gas mixtures. Application of widely used PR and SRK equations of state for the same systems in calculating minimum miscibility pressure is also discussed.
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