Effect of non-equilibrium mass transfer in miscible gas recovery processes

Abstract

The mass transfer equilibrium is a condition usually assumed to solve EOS and flash equations. However, this condition is not always true for all reservoirs, especially in regions near high-rate gas wells. For such wells, the fluids take seconds to run through a gridblock near the wellbore, and there is not enough time to achieve the equilibrium mass transfer. This paper presents a model to evaluate the non-equilibrium condition based on an empirical correlation from the literature. It takes into account the effects of diffusion coefficients and gas velocity to calculate the non-equilibrium saturations of the components. The simulation is performed in a gas-condensate reservoir, and the results are compared with the ones obtained with the local-equilibrium consideration. The simulator used was the UTCOMP compositional simulator, developed at The University of Texas at Austin.