Solvent Flooding Displacement Efficiency in Relation to Ternary Phase Behavior

The chief objective of the study was to exercise control on the system phase behavior through the use of mixtures of two alcohols exhibiting opposite phase behavior characteristics in the alcohol-hydrocarbon-water system involved. Such systems were employed in displacements in porous media to ascertain their effectiveness. Introduction Displacement of oil and water in a porous medium by a mutually miscible alcohol or other solvent has been the subject of numerous investigations. This process, in spite of its limited scope as an oil recovery method, has certain mechanistic features that are of value in gaining an understanding of some of the newer recovery techniques (e.g., the Maraflood* process). The works of Gatlin and Slobod, proposing piston-like displacement of oil and water by a miscible alcohol; of Taber et al., describing the displacement mechanism in terms of the ternary phase behavior involved; and of Holm and Csaszar, defining displacement mechanism in terms of phase velocity ratio, are major contributions in this area. In a later work, Taber and Meyer suggested the addition of small amounts of oil and water (as the case may be) to the alcohol used for displacement, since this helped to obtain piston-like displacements with systems that are usually characterized by the efficient displacement of either oil or water. APPARATUS, EXPERIMENTAL PROCEDURE, AND SIMULATOR PROCEDURE, AND SIMULATOR The procedure employed for determining the equilibrium phase behavior of ternary systems involved the titration of a hydrocarbon-water (or brine) mixture by the particular solvent (pure alcohol, or alcohol mixture) for the determination of the binodal curve, and the analysis by refractive index measurement of ternary mixtures having known compositions for the determination of the tie lines. Since the procedure is valid for strictly ternary systems, its use in this case where essentially quaternary systems are involved would yield the total alcohol content rather than the correct proportion of each alcohol. The ternary diagrams presented should be viewed with this limitation in mind. presented should be viewed with this limitation in mind. The apparatus used for experimental runs in porous media consisted of a positive displacement Ruska pump and a core encased in a steel pipe. Suitable sampling apparatus and auxiliary equipment were employed. Most runs consisted of injecting a slug of the particular solvent into a core initially containing a residual oil (waterflood) or irreducible water saturation, at a constant rate, and then following the slug by water or brine. The effluent samples collected were analyzed for the hydrocarbon, water and alcohol in order to plot the production histories. Complete experimental details and fluid production histories. Complete experimental details and fluid properties are given in Ref. 6. Table 1 lists the properties properties are given in Ref. 6. Table 1 lists the properties of the porous media used. Computer simulations of some of the experimental runs, as well as exploratory simulations, were carried out using the method earlier reported. The method basically consists in the representation of a porous medium by a certain number of cells containing immobile oil (or oleic) and water (or aqueous) fractions into which alcohol is injected in a stepwise manner allowing for phase changes. SPEJ P. 89