Comparative studies on numerical sensitivity of different scenarios of enhanced oil recovery by water-alternating-gas (CO2) injection

Enhanced oil recovery by CO₂ injection technology (CO₂-EOR) plays a crucial role in enhancing oil production and the permanent sequestration of anthropogenic CO₂ in depleted oil reservoirs. However, the availability of CO₂ in oil field locations and its mobility in contrast with reservoir fluids are prime challenges in CO₂-EOR. The cost of CO₂ and its availability at the oil fields has prompted investigations on efficient injection of CO₂ at the fields to achieve the best sweep efficiency possible. Injection strategies such as water-alternating-gas (WAG), simultaneous vertical and horizontal WAG, simultaneous water injection into the aquifer and vertical WAG, water and gas injection simultaneously but separately (SS-WAG), and water and gas injection simultaneously but not separately (SNS-WAG) play a significant role, as well as the purity of CO₂. In this work, the significance of the above criteria was investigated individually and in combination. The coupled sequence of injection rate, soaking time, WAG ratio, and purity of injected CO₂ for enhancement of oil production were delineated. A realistic reservoir simulation model conceptualizing the CO₂-EOR system with five spot injection patterns was developed by the company CMG. The history-matched model that was developed was used to investigate the sensitivity of the coupled effects to the criteria listed above on oil recovery. Numerical investigations quantitatively emphasized that purity and soaking time of CO₂ have an inverse effect in the oil production rate and that SNS-WAG resulted in a better oil production rate than SS-WAG.