The Linear Displacement of Oil from Porous Media by Enriched Gas

Abstract

Abstract This paper presents a method for predicting the manner in which oil will be displaced from a porous body by enriched gas. The calculations apply to a gas rich enough to give a partially, but not a completely, miscible displacement. The method - a three-component, two-phase analysis - takes into account condensation of some of the intermediate hydrocarbons from the injected gas into the oil, as well as enhanced volatility of heavier hydrocarbons at elevated pressures and temperatures. The condensation swells the oil and decreases its viscosity, thus aiding in its recovery. The calculations have been extended to apply to actual crude oil-natural gas systems by arranging the components into three groups according to their volatility. As an approximation, each group is then treated as a single component in the analysis. The influence of an angle of dip for an inclined displacement is also taken into account. The recovery predictions are corroborated by experiments which used both consolidated sand cores and unconsolidated glass beads. In some of these tests, actual live crude oil was displaced by amulticomponent gas typical of enriched gases used in oil fields. Introduction This paper presents a method for predicting the amount of oil that can be displaced from a homogeneous, linear, porous body at various stages during the injection of enriched, or "wet", gas. The porous body can be in either a horizontal or an inclined position. This type of displacement is sometimes known as "condensing gas drive". The method is developed especially for the case in which the injected gas is enriched enough to be partially, but not completely, miscible with the reservoir oil. The need for a calculative procedure for this type of operation is emphasized by the number of field projects where completely miscible drives are not practical, but where near-miscible conditions are feasible.