Including Nonequilibrium Relaxation in Models for Rapid Multiphase Flow in Wells

Abstract

Summary The modeling of rapid flow of multiphase reservoir fluids in wells involving nonequilibrium partial separation of dissolved gases from the metastable oil and water phases is reviewed and formulated. The multiphase-fluid flow is described by means of the differential mass, momentum, and energy-balance equations along the well. The rate of gas transfer from the metastable liquid phases to the gas phase is expressed in terms of the relaxation time determined by the prevailing gas-phase volume fraction and the pressure and temperature conditions. The differential equations are solved numerically under a typical scenario involving the constant gas-, oil-, and water-production rates at the wellhead. It is demonstrated that the nonequilibrium saturation and pressure distributions in wells deviate from the equilibrium results, depending on the variation of the local relaxation time along the well. It is concluded that inclusion of nonequilibrium relaxation effects in models for rapid multiphase flow in wells is required.