Carbon dioxide flooding

[2] When the injected CO2 and residual oil are miscible, the physical forces holding the two fluids apart effectively disappears.

This results in a viscosity reduction of the hydrocarbon and makes it easier to displace the crude oil from the rock pores and sweep it to the production well.

[4] One reason this occurs is because the injected CO2 can flow into the minute pores that are unavailable to oil and water.

[7] Injecting the CO2 too fast will allow the CO2 to channel from the injector directly to a producing well without mobilizing any oil.

Injecting CO2 too quickly may fracture the formation, which may again allow channeling from the injector to any or all of the producing wells.

[2][6][8] Also, injecting CO2 may migrate fines, which are small particles of clay and minerals, may plug the pores and prevent the mobilization of oil through the formation.

[10][6] This method reduces the chances of unwanted channeling, and increases the amounts of oil that may be recovered as opposed to the more common CO2 injection water alternating gas process (WAG) or by following a soak of CO2 with steam.

[1][2][8] For medium or light oils with a high API gravity, fluids or gases that are less viscous themselves can be used.

[1] In cases where the reservoir is filled with extremely heavy oil or bitumen, steam injection, or other methods that employ heat, are much more commonly favored so that the mobility or viscosity of the oil can be lowered and the extraction will become easier.

[13] Since then, the process has become extensively used in the Permian basin region of the US and is now more recently is being pursued in many different states.