Immiscible CO2 Flooding through Horizontal Wells

Abstract

The CO2 immiscible process is a potentially viable method of enhanced oil recovery (EOR) for heavy oil reservoirs. In an immiscible CO2 process, part of the injected CO2 is absorbed into the reservoir fluids and part forms a free-gas phase in the reservoir. Three groups of well configurations were mainly used: (1) vertical injection and vertical production wells, (2) vertical injection and horizontal production wells, and (3) horizontal injection and horizontal production wells. In immiscible CO2 injection, highest recovery was obtained by vertical injection-horizontal production (VI-HP), followed by vertical injection-vertical production (VI-VP), and the least by horizontal injection-horizontal production (HI-HP). In VI-HP well configuration, the best recovery was obtained as 15.1% OOIP. In continuous CO2 injection experiments, oil recovery for the VI-HP well configuration was higher than that of the other well configurations. The lowest ultimate recovery was obtained from HI-HP well configuration. The distance between the horizontal injector and horizontal producer was another important factor for the displacement of oil. In all runs, CO2 breakthrough occurred very early, showing the dominance of viscous forces and relatively small effect of mass transfer between CO2 and oil. The total oil recovery varied considerably because of the differences in injection rates and because of the unstable displacement. As a whole, oil recovery increased with an increase in the injection rate of CO2. The cumulative gas-oil ratio (GOR) appeared to be sensitive to the gas injection rate for all well configurations. An increase in oil recovery with injection rate during initial stages of the runs was affected by the cumulative GOR.