A Numerical Study of Diphasic Multicomponent Flow

Abstract

Abstract This paper describes a general multicomponent two-phase flow model, taking into account convection, diffusion and thermodynamic exchange between phases. The main assumptions are: isothermal one-dimensional flow; two-phase flow (gas and liquid); each phase may be represented by a mixture of three components or groups of components. Actually, a great many recovery problems cannot be pictured by usual models because the oil and, in many cases, the injected fluid are not simple fluids and may bring about exchanges of components that considerably modify their characteristics. This is why efforts are now being made to develop "compositional" or "multicomponent" models capable of solving such situations. Generalization of the model to more complex systems can be considered. Cases treated may be any type of single- and two-phase flow, in particular any miscible process (e. g., high-pressure gas drive, condensing gas drive, slug displacement) and any diphasic processes with high mass exchange (e.g., displacement by carbon dioxide or flue gas). This model is working and has been successfully checked by experiments. Introduction Many investigations, broth experimental and theoretical, have been made on the recovery of oil from reservoirs. With regard to mathematical models, most of those conceived up to now have dealt with oil recovery by the injection of a fluid that is miscible or immiscible with the oil. For miscible drives, single-phase flow with a binary mixture and miscibility in all proportions is involved. In such an ideal situation oil recovery is theoretically total. For immiscible displacements flow is diphasic. Capillary pressure and relative permeability play a preponderant role. Since irreducible oil saturation preponderant role. Since irreducible oil saturation is inevitable, oil recovery can never be total. Actually, a great many recovery problems cannot be pictured by such models because the oil and, in many cases, the injected fluid are not simple fluids and may bring about exchanges of components that considerably modify their characteristics. This is why efforts are now being made to develop "compositional" or "multicomponent" models capable of solving such situations. Such a model is described here. It is designed to handle the most general case of the displacement of one fluid by another. This model offers the following possibilities.The fluids may be made up of more than two components.Flow may be entirely monophasic, entirely diphasic, or partially monophasic and diphasic.Miscibility may be partial or total.The material exchange between phases may take place under specific thermodynamic conditions. A model that is much closer to reality should provide more thorough knowledge of mass transfer provide more thorough knowledge of mass transfer mechanisms in a complex mixture as well as better oil recovery forecasting with the injection of a second fluid. DESCRIPTION OF THE MODEL In a porous formation, we will consider the displacement of a liquid hydrocarbon complex in place by another fluid that is injected into the place by another fluid that is injected into the formation. The injected fluid may be a gas or a liquid, containing or not containing hydrocarbons. We assume that the mass transfer in the transition zone between the displacing fluid and the displaced fluid occurs according to three mechanism: convection, diffusion and thermodynamic exchange between phases. We propose to study the flow thus described. The main assumptions are:flow is isothermal and one-dimensional;the porous medium is homogeneous and isotropic;there is no effect of gravity;there is a two-phase flow, i.e., oil and gaseach phase may be represented by a mixture of three components or three groups of components (e.g., C1, C2-6, C7+); SPEJ P. 171