flooding is the practice of injecting CO2
into oil reservoirs to recover additional oil.
In the oil reservoir, the CO2
dissolves into the oil, makes it more mobile, and allows it to move more easily toward the
production wells. In many cases, water is injected after the CO2
to help move the oil along. Since the 1970s, the injection
into aging oil reservoirs in West Texas has resulted in the production of more than 1 billion incremental barrels of
The crude oil produced from a CO2
enhanced oil recovery (EOR) operation contains dissolved CO2
. At the surface, the dissolved CO2
is separated from the oil, and the CO2
is then compressed and reinjected.
Each time CO2
is injected, some of the CO2
remains underground, permanently trapped in the oil-bearing rock formation. This trapped
does not return to the surface in the produced crude oil.
To make up for the CO2
that remains trapped in the oil reservoir, the CO2
flood operator purchases additional CO2
. The operator then
combines this new CO2
that the operator has separated from the crude oil. In this way, the proper amount of CO2
for injection into the underground oil reservoir.
EOR projects are designed to be active for decades, and each project has many cycles of CO2
injection. With each cycle, another portion
that is injected becomes permanently trapped in the reservoir. By the end of the flood, virtually all of the CO2
that has been
purchased and brought to the field is permanently trapped or “sequestered” in the reservoir. As a result, hundreds of millions of tons
are currently trapped underground in oil fields in the United States and around the world.
Historically, most of the CO2
for oil field floods has come from natural underground accumulations of CO2
. The CO2
from these geologic
deposits is limited in volume, and economics restrict its use to within a couple of hundred miles of where it occurs. In contrast,
anthropogenic (or human made) sources of CO2
are widespread. As more and more oil fields mature, the need for CO2
EOR will increase,
and the potential for EOR using anthropogenic CO2
will increase as well. 1,2
EOR using anthropogenic CO2
represents a prime opportunity
for reducing the CO2
emissions from large-scale sources like power plants, gas- and oil-processing plants, and ethanol facilities.
- Bradley, T., The CO2 enhanced oil recovery story: Kinder Morgan CO2 Company.
docs.nrdc.org/globalWarming/files/glo_09031101c.pdf (accessed March 2010).
- National Resources Defense Council, 2008, Tapping into stranded domestic oil - enhanced oil recovery with carbon dioxide is a win-win-win.
www.nrdc.org/energy/eor.pdf (accessed March 2010).