CO2 storage and EOR in an underdeveloped field: A techno-economic-environmental study

Abstract Geologic sequestration of carbon dioxide (CO 2 ) is considered an important technology for mitigating the increasing level of atmospheric CO 2 . One of the most common methods for CO 2 geologic sequestration is to inject CO 2 into depleted oil reservoirs, which recovers part of the remaining oil after the primary and secondary recovery methods. Unlike previous studies, this research investigated practical opportunities of CO 2 sequestration and EOR in underdeveloped oil fields, which are not fully depleted and contain only a few wells. A realistic compositional simulation model was constructed to represent a carbonate oil reservoir in the Gulf of Mexico Basin. A series of CO 2 water-alternating-gas (WAG) injection strategies was studied by varying operational conditions and analyzed for oil recovery and CO 2 storage. A comprehensive economic model was developed to evaluate the net present value (NPV) and used for varying scenarios with, for example, carbon storage incentive and oil price. Results indicated an inverse relationship between oil recovery and CO 2 storage. That is, a displacement pressure above the minimum miscibility pressure (MMP) yielded maximal CO 2 storage, but a suboptimal level of oil recovery. This contrasts with the widely known observations for CO 2 -EOR/sequestration in developed oil fields, where operating above MMP maximizes both oil recovery and CO 2 storage. Furthermore, the resulting net utilization factors from the cases of operating pressure above the MMP were smaller than those of typical CO 2 -EOR operations. Analysis showed that pressure management using a small number of wells in an underdeveloped oil field can play an important role in optimizing CO 2 -EOR/storage because oil recovery comes not only from CO 2 -EOR mechanisms, but also from oil flow potentials induced by the limited number of wells. Under the current economic conditions, NPVs were positive even without factoring in the carbon storage incentive (i.e., 45Q tax credit) accrual for the case studied. However, the CO 2 -WAG scenarios with the greatest NPVs were associated with the smallest amounts of CO 2 storage and net utilization factor, which was not desirable from the environmental viewpoint. A synergistic scenario was possible to increase CO 2 storage, net utilization factor and NPV together by proper adjustments in carbon storage incentive according to oil price.