Experimental Studies Of Low Ift Displacement By CO2 Injection

Abstract

Abstract An experimental technique is described for isolating the influence of low interfacial tension (IFT) from the influence of other CO2 displacement mechanisms. Also, the capillary number concept was extended to correlate the displacement efficiencies of the CO2-oil systems. Experimental results indicate that low IFT displacement by CO2 is an effective recovery mechanism. Introduction The use of CO2 as an enhanced oil recovery agent in petroleum reservoirs has been investigated both in the laboratory and in the field. Several recovery mechanisms were identified among which those most often considered were: swelling, viscosity reduction, and vaporization and extraction of portions of oil. A CO2 displacement may be either immiscible or miscible portions of oil. A CO2 displacement may be either immiscible or miscible depending on injection gas composition, reservoir oil composition, reservoir temperature, and pressure. The concept of low IFT flooding has been extensively studied for surfactant and micellar enhanced oil recovery processes; however, the literature shows no investigations of the influence of low IFT on CO2 displacement efficiency. During CO2 flooding, low IFT occurs simultaneously with vaporization, swelling, and viscosity reduction, making its influence difficult to isolate. In this paper we discuss an experimental technique designed to isolate low IFT effects. EXPERIMENTAL TECHNIQUE The following procedure was used to isolate the effect of IFT on CO2 displacement efficiency from other CO2 displacement mechanisms:CO2 and reservoir oil were mixed at the desired temperature, pressure, and CO2-to-oil mole ratio.The mixture was brought to equilibrium.Compositions, densities, and viscosities of the equilibrated oil and gas, as well as the IFT between phases were measured. IFT measurements used the pendant drop method.The core was saturated with the equilibrated oil as described below.The equilibrated oil was displaced from the core with equilibrated gas. As the displacing gas and reservoir oil were preequilibrated, their compositions and physical properties, including IFT, remained constant during displacement. Injection rate was also constant. The pressure drop across the core was kept at a minimum to preserve the equilibrium between the displacing gas and the displaced liquid. Each experiment consisted of three stages:Bringing the core to the experimental stage. This included the following operations:saturating the core with brine,measuring permeability to brine, anddisplacing the brine with several volumes of equilibrated oil to a specified irreducible water saturation, Swi.Performing the displacement. The equilibrated gas was injected at a constant rate, and the pressure drop across the core was continuously recorded.