Quantifying CO2 storage efficiency factors in hydrocarbon reservoirs: A detailed look at CO2 enhanced oil recovery

West Texas San Andres dolomite water alternating gas (WAG) CO2 flood performance data were used to derive P10, P50, and P90 CO2 storage efficiency factors of 0.76, 1.28, and 1.74 Mscf/STB (stock tank barrel) of original oil in place. Median CO2 storage efficiency factors from continuous CO2 injection following conventional waterflood varied from 15% to 61% and 8% to 40% for fluvial clastic and shallow shelf carbonate simulation models, respectively, while those from WAG injection varied from 14% to 42% and 8% to 31%, respectively. Variation in the CO2 storage efficiency factors was largely attributable to reservoir depth (a surrogate for reservoir pressure and temperature) and lithology (clastic versus carbonate). The results of this work provide practical information that can be used to quantify CO2 storage resource estimates in oil reservoirs during CO2 EOR operations (as opposed to storage following depletion) and the uncertainty associated with those estimates.