Improving predictions of equation of state by modifying its parameters for super critical components of hydrocarbon reservoir fluids

The parameters of equations of state of van der Waals type have been generally correlated by matching the properties of pure substances, and extended to mixtures by employing mixing rules commonly with binary interaction parameters. It is proposed to use equilibrium data on binary systems to determine the attraction term in equations of state (EOS) for super critical components instead of data of pure substances. The proposed method was applied to the Peng-Robinson EOS, as an example, resulting in a significant improvement in predicting the phase behaviour of different types of fluids. As no binary interaction parameters are required in this method the computational requirement for flash calculations is drastically reduced for fluids with many components. The proposed method is particularly advantageous for predicting fluid phase equilibria in compositional reservoir simulators, where the reservoir fluid can be described with any desirable number of components without any significant increase in computational time.