Simulation of the Alcohol-Slug Process Using the "Cell Model"

Abstract

Abstract The similarity of the mechanism of miscible displacement to the functioning of packed columns has led to suggestions that the "theoretical plate" concept might be a useful mathematical model for the simulation of miscible displacement processes. Such a model would rest on the assumption that the porespace of a linear porous medium is equivalent to a certain number of "plates"or cells and that, in each cell, only a fraction of the fluid volume ismovable. During displacement, the movable volume from each cell moves on toeach succeeding cell, establishing equilibria with the respective stationary volumes. When two phases are present in the model, relative phase mobilities, as governed by viscosities and phase saturations, will affect the movable fractionin each cell. If, in addition, there is interphase transfer of material, the equilibrium condition for each cell is governed by the amounts and mutual solubilities of the components. While the procedure is quite general, thepresent study is confined to various ternary water-hydrocarbon-alcohol systems.To expedite computations, general mathematical relations were developed for thebinodal curves and tie lines. These were necessary to obtain the phase volumes and compositions for any over-all cell composition. Expressions for phasemobility ratios as functions of saturations were also used. The validity of the model has been demonstrated by comparisons of efflux histories for alcohol displacements of oil and water as obtained from the model and from laboratory experiments. Introduction It has been known for some time that a sufficient volume of certain lower alcohols will effectively displace all or most of the oil and water contacted in an oil-water porous medium system. As alcohols are considerably more expensive than equal volumes of recovered oil, an economically successful process requires that only a finite volume or slug of alcohol displace the oil and water.