Coupling Immiscible CO2 Technology and Polymer Injection to Maximize EOR Performance for Heavy Oils

Abstract

Summary With approximately 90% of Saskatchewan's original heavy oil in place remaining in the ground, there is excellent potential for the application of enhanced oil recovery (EOR) methods and new technologies. The goal of the study discussed in this paper was to investigate if a new proposed process--coupling CO2 and polymer injection--can increase EOR performance for heavy oil reservoirs. The oil recovery performance of three EOR modes [water-alternating-gas (CO2 WAG) injection, polymer-alone flood and coupled CO2 and polymer injection] was compared in laboratory-scale linear coreflood tests in waterflooded cores. The immiscible CO2 WAG process recovered 15.3% original oil in place (OOIP) with 6.16 MSCF/stb gas utilization. Under a controlled maximum pressure drop across the core, the polymer-alone (0.4 wt%) flood produced an additional 12.93% OOIP above the initial waterflood recovery. However, the coupled CO2 and polymer injection process (using a polymer concentration of only 0.2 wt%) gave better recovery efficiency (18.7% OOIP) than the polymer-alone flood. Moreover, it had much better gas utilization than the CO2 WAG run, consuming only 2.0 MSCF/stb, or one-third of the amount of CO2 used in that run to recover the same amount of oil. This performance comparison demonstrates two of the biggest advantages of coupled CO2 and polymer injection: it can effectively reduce the pressure drop across the core and can obtain encouraging recovery if the optimal polymer concentration is added to the water.