Enhanced CO2 extraction works by pushing the CO2 through the oilfield as a carrier of the oil, so what you get out of the extraction borehole is a mix of CO2 and oil, and the CO2 just vents back to the atmosphere during refining. Some fraction is left in the oilfield, but it's fairly minor.

The cost of the CO2 injection system is thus offset by the profits from the oil recovered; if this were to go to zero then the corporation would abandon it as an unprofitable exercise.