Linear Gas Drives in High-Pressure Oil Reservoirs Compositional Simulation and Experimental Analysis

Abstract

This paper presents an analysis of the compositional process involved in the displacement of oil by high pressure gas injection as observed in laboratory experiments. Such an analysis is necessary in order to transpose these results to a field-wide scale for EOR projects. Therefore a two-fold compositional tool has been developed: The first function handles the Peng and Robinson equation of state to describe phase equilibria of multicomponent hydrocarbon mixtures. Based on thermodynamic considerations it computes either frontal or rear dynamic miscibility pressure as well as direct miscibility pressure of a gas/oil system.The second function simulates linear displacement of oil by gas involving compositional exchanges between phases (also based on P.R. equation of state) and their effect on flow parameters. Results of this compositional model are checked against laboratory experiments carried out on a field crude oil with three possible injection gases. This model yields a better understanding of various types of non-equilibrium gas drives and enhanced recoveries related to compositional transfers and mobility variations. A useful application is to select the most appropriate gas to be injected into a given field under reservoir conditions or after some depletion. It also shows how the notion of gas/oil relative permeability curves should be reviewed if a black-oil model is used to simulate flow of non-equilibrium fluids.