A method for imposing residual oil saturation in compositional simulation of miscible gas injection processes is proposed. It is based on use of alpha-factors found by a simple analytic calculation.

The method is validated on a one-dimensional model, then applied to full field simulations of miscible gas injection in the Deep Jusepin reservoir in Venezuela. In this case, the alpha-factor approach was judged to have been successful, improving the physical representation of the process and probably making the simulation results more realistic.

Finally, the method is compared with other possible approaches, principally (a) excluding a specified amount of oil from the flash calculations, or (b) using a dual porosity model.

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