The modeling of rapid multiphase flow of reservoir fluids in wells and the non-equilibrium partial separation of dissolved gases from the metastable oil and water phases is discussed and reviewed. The effect of non-equilibrium on the deviation of the pressure distribution along the wells from the equilibrium model predictions is delineated. The multi-phase 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 solution of the set of differential equations is obtained numerically under a typical scenario involving the constant gas, oil, and water production rates at the wellhead. It is demonstrated that the nonequilibrium pressure distribution in the well deviates significantly from the equilibrium results depending on the local relaxation time, which vary along the well. The present models can be incorporated into the conventional reservoir simulations for accurate description of the effect of the actual multi-phase well-fluid behavior under non-equilibrium flow conditions. The models are applicable with two-phase (oil/gas and water/gas) and three-phase (oil/water/gas) well fluid systems.
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