Only a small percentage of the petroleum in most oil fields can be recovered economically. One option to increase oil recovery is to pump CO2 into the reservoir to improve the flow of remaining oil through the pore space. After the oil-CO2 mixture reaches the surface, the CO2 is separated from the oil and recycled back to the reservoir. A side-effect of enhanced oil recovery is that a portion of the CO2 that was used to force oil out of the formation is sequestered in the reservoir’s pore space. CO2-EOR is currently used to optimize oil production, but can also be adjusted to boost the amount of carbon dioxide that stays sequestered in the reservoir.
CO2 has been used in the Permian Basin of Texas for three decades to enhance oil recovery. Most of the CO2 is supplied from natural sources in Colorado and New Mexico via pipeline, so there are currently few climate benefits in the process. But an experienced industry has developed and is capable of using anthropogenic CO2 (captured from fossil fuel burning power plants and industrial processes) for the same purpose. A large-scale coal gasification plant in North Dakota is currently capturing its CO2 and piping it to Weyburn, Canada where it is used for enhanced oil recovery. Other large anthropogenic CO2-EOR projects are under development.
Currently, CO2-EOR is used to produce about 250,000 barrels per day of oil in the U.S. that might otherwise not exist. A recent study by Advanced Resources International states that an additional 4 to 47 billion barrels of domestic resources could be economically recovered using CO2-EOR. The study notes that at least 8 billion tons of CO2 could be sequestered in the U.S. by using EOR. The carbon abatement cost of CO2-EOR varies according to field and the price of oil; in some cases in can have negative costs according to Battelle Memorial Institute.
Currently, regulations exist to govern CO2-EOR activities in order to prevent ground water contamination. However, there are no regulations to govern CO2-EOR activities operating with the purpose of permanently sequestering CO2. If and when the U.S. enacts a climate policy that requires CO2 mitigation, new standards will need to evolve that allow measuring and crediting of CO2 that is sequestered in oil fields. There are questions of “additionality” that must be addressed: some argue that the net climate impact of sequestering CO2 in an EOR operation is marginal because of the extra oil that is produced and then combusted. Others argue that the oil would still be produced elsewhere. Other complex regulatory issues such as plant siting, injection criteria, remediation options, and liability concerns must be addressed before CO2-EOR sequestration is widely deployed as a carbon mitigation technology.