Techno-Economic-Environmental Analysis of CO2 Storage and EOR in an Underdeveloped Field

Abstract Geological sequestration of carbon dioxide (CO2) is considered an important technology for mitigating the increasing level of atmospheric CO2. One of the most common methods for CO2 geological sequestration is to inject CO2 into depleted oil reservoirs, which recovers part of the remaining oil that has been unrecovered by simpler methods of oil recovery (e.g., water injection). Previous studies have shown that such CO2-enhanced oil recovery (CO2-EOR) effectively serves as a CO2 sequestration method because a successful CO2-EOR typically results from efficient displacement of resident fluids (water and oil) at thermodynamic conditions such that CO2 of a large density (e.g., 15 mol/L as supercritical CO2) can develop multicontact miscibility with the reservoir oil. Unlike previous studies, this research investigates practical opportunities of CO2 sequestration and CO2-EOR in underdeveloped oil fields, which are not fully depleted with only a few wells. A realistic compositional simulation model was constructed to represent a carbonate oil reservoir in the Gulf of Mexico Basin. Based on the history-matched simulation model, a series of CO2 water-alternating-gas (WAG) injection strategies was studied by varying operational conditions (i.e., CO2 and water injection rates, production rate, and WAG cycle) and analyzed for oil recovery and carbon storage. A comprehensive economic model was developed to evaluate the net present value (NPV) and used for varying scenarios with, for example, 45Q tax credit and oil price. Results indicated an inverse relationship between oil recovery and CO2 storage. That is, a displacement pressure above the minimum miscibility pressure (MMP) yielded maximal CO2 storage, but a suboptimal level of oil recovery. This contrasts with the widely known observations for CO2-EOR/sequestration in developed oil fields, where operating above MMP maximizes both oil recovery and CO2 storage. Analysis showed that pressure management using a small number of wells in an underdeveloped oil field can play an important role in optimizing CO2-EOR/storage because oil recovery comes not only from CO2-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 45Q tax credit accrual for the case studied. However, the CO2-WAG scenarios with the greatest NPVs were associated with the smallest amounts of CO2 storage, which was not desirable from the environmental viewpoint. A synergistic scenario was possible to increase CO2 storage and NPV together by proper adjustments in carbon tax credit according to oil price.