Feasibility evaluation of CO2 EOR and storage in tight oil reservoirs: A demonstration project in the Ordos Basin

Among the techniques to mitigate CO2 emissions into atmosphere, CO2 geological storage is the only option for gigaton removal of CO2. This study performs a pilot test of CO2-EOR and storage in a tight reservoir of Baibao oilfield, located at the Ordos Basin of China. Two scenarios: CO2 injection through two newly drilled wells and total nine wells, with two CO2 injection schemes: continuous injection (CI) and water alternative gas (WAG) injection, are considered. Simulation results show that both CO2 injection schemes can substantially increase oil production, compared to the current waterflooding. To be more specific, WAG, in contrast to CI, increases oil production by 7.9% and 16.2% for the two- and nine-injection well scenarios, respectively. Yet, as for CO2 storage, WAG, compared with CI, finally leads to a decrease of stored CO2 by 9.6% and 15%, for the two- and nine-CO2 injection well scenarios, respectively. From the aspect of CO2 utilization efficiency, net CO2 utilization ratio of WAG is smaller than the one from CI regardless of the number of CO2 injection well. Besides, for the two- and nine-injection well scenarios, maximum net utilization ratios are achieved after 7–8 years’ and 4–5 years’ injections, respectively. The sensitive analyses reveal that the impact of CO2 injection rate of WAG on total oil production is more significant than the water injection in WAG. Water injection rate in WAG negatively affects the total CO2 storage and CO2 net utilization ratio whereas the higher CO2 injection rate dramatically increases the total CO2 storage. Overall, this study not only sheds light on achieving double-win goal via CO2 injection, but also can be a valuable reference for other CO2-EOR and storage pilot tests in tight reservoirs.