Study of the Mechanisms of Carbon Dioxide Flooding and Applications to More Efficient EOR Projects

Abstract

Abstract The mechanisms of carbon dioxide flooding at pressures below the minimum miscibility pressure (MMP) were studied using a numerical model of a slim tube to determine a means of increasing the efficiency of such floods. Results of these studies indicate that, in multiple contact flooding (MCF), the gas phase at the liquid-gas front approaches a constant composition denoting a bank of solvent approaching conditions of miscibility, but not achieving it because of the quantity of methane, nitrogen, and other light gases that overwhelms it. The ethane plus components (C2+) composed approximately five percent of the reservoir gas phase. This constant compositional gas phase formed early in the flood and persisted throughout the flood until eventual gas breakthrough. A simulated low-temperature flash of the reservoir gas phase produced a solvent that contained more than 75 percent ethane and propane. Slugs of this solvent were used to produce miscible displacements with CO2 gas at pressures 40 percent below the MMP. These findings were confirmed in further studies using fluids from several other reservoirs.