Examining the Potential of Immiscible CO2 for Gravity-assisted Enhanced Oil Recovery and Storage

Abstract

This paper investigates the effectiveness of gravity-assisted immiscible CO2 injection for enhanced oil recovery and CO2 storage with three-phase heterogeneous reservoir simulation. Two types of immiscible injection are considered: constant, uninterrupted CO2 injection, and alternating CO2 injection, the latter of which entails interchanging periods of CO2 injection with periods of well inactivity. These injection strategies are applied to four different oil types to evaluate recovery and storage potentials. Enhanced oil recovery is very effective with 40° API oil, achieving ultimate field recoveries of 80.63 percent for constant CO2 injection and 63.77 percent for alternating CO2 injection. CO2 injection is far less effective for heavier oils. Constant CO2 injection generally produces more oil than alternating injection, given the greater amount of CO2 injected. When controlling for total CO2 injected, however, the two injection methods produce oil equally well. The alternating injection method is more efficient at storing CO2 than the constant injection method for the same quantity of CO2 injected across all oil types. For 40° API oil, the alternating method is as high as 16 percent more efficient, the best of all four oils examined. The increased storage efficiency coupled with the lack of additional oil production indicates that CO2 is finding space for storage by displacing water accumulated during an initializing water-flood. Evidence of significant water displacement by CO2 supports the legitimacy of the long term goal of CO2 sequestration into saline aquifers.