Much of the oil found in the history of the oil industry still remains in the ground in reservoirs that have been fully produced through primary and secondary recovery methods. Primary reserves are those produced first through pressure depletion (depletion or solution gas drive) within the reservoir or as a result of an active aquifer of water pushing water through the oil reservoir and sweeping the oil with it (water drive). Secondary reserves are those produced after primary recovery, generally derived from injecting water into the reservoir to maintain pressure and to push/sweep/drag oil to the producing well.

Tertiary reserves are derived from enhanced oil recovery (EOR) techniques that include steam flooding of heavy oil, surfactant flooding to reduce surface tension binding oil molecules to rock, polymer injections to plug permeability channels and force more efficient water flood sweep, and gas flooding. 

Gas floods can be either miscible or immiscible, wherein miscible means that the injected gas goes into solution with the oil and reduces viscosity (resistance to flow) and surface tension of oil and rock, while increasing oil swelling and localized pressure (known as formation “energy” or “drive”). Immiscible means that the injected gas does not go into solution and only provides formation energy (or drive) via incremental pressure, typically yielding only half the recovery of miscible floods.  Each technique is applicable to certain kinds of reservoirs and conditions.

CO2 miscible gas flooding is a major source of oil production in the U.S., particularly in West Texas, Wyoming and Mississippi where natural sources of CO2 can be obtained at reasonable cost.  CO2 applications are increasingly popular due to the increasing desire to sequestrate manufactured CO2. Denbury has reported that its CO2 floods in Mississippi are recovering an average of 17% of original oil in place, and has one mature project that is expected to recover approximately 20% of original oil in place. Evolution projects a more conservative recovery of 12-16% of OOIP at its Delhi CO2 project.

Recent industry published studies have focused on enhanced oil recovery, utilizing CO2 floods in the Louisiana, Mississippi, Alabama and Florida onshore areas. One study estimates that in Louisiana alone, there are 128 CO2 floodable reservoirs, with 16 billion barrels of original oil-in-place and over 9 billion barrels of oil remaining. The study was based on $40 oil, and high CO2 costs, resulting in an estimated 1.3 billion barrels of oil reserves to be economically produced through CO2 floods.  Substantial quantities of CO2 floodable reservoirs that are not within reasonable distance of current natural sources of CO2 exist along the Gulf Coast and in central and east Texas. Sourcing new supplies of CO2 could enable development of these potential reserves.