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

Abstract Carbon dioxide (CO 2 ) enhanced oil recovery (EOR) will likely be the primary means of geologic CO 2 storage during the early stages of commercial-scale carbon capture and storage (CCS) because of the inherent economic incentives as well as the abundant experience and demonstrated success in the United States, where CO 2 EOR has been employed since 1974. The work presented here estimates CO 2 storage efficiency factors in CO 2 EOR operations using a unique industry database of CO 2 EOR sites and 12 different reservoir simulation models. The simulation models encompass fluvial clastic and shallow shelf carbonate depositional environments for reservoir depths of 1219 and 2438 m (4000 and 8000 feet) and 7.6-, 20-, and 64-m (25-, 66-, and 209-foot)-thick pay zones. A novel statistical modeling technique incorporating the Michaelis–Menten function is used to generate empirical percentile estimates of CO 2 storage efficiency factors. West Texas San Andres dolomite water alternating gas (WAG) CO 2 flood performance data were used to derive P10, P50, and P90 CO 2 storage efficiency factors of 0.76, 1.28, and 1.74 Mscf/STB (stock tank barrel) of original oil in place. Median CO 2 storage efficiency factors from continuous CO 2 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 CO 2 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 CO 2 storage resource estimates in oil reservoirs during CO 2 EOR operations (as opposed to storage following depletion) and the uncertainty associated with those estimates.