Page "Carbon sink" Paragraph 32

CO < sub > 2 </ sub > has been injected into declining oil fields for more than 40 years, to increase oil recovery.

This option is attractive because the storage costs are offset by the sale of additional oil that is recovered.

Typically, 10 – 15 % additional recovery of the original oil in place is possible.

Further benefits are the existing infrastructure and the geophysical and geological information about the oil field that is available from the oil exploration.

Another benefit of injecting CO < sub > 2 </ sub > into Oil fields is that CO < sub > 2 </ sub > is soluble in oil.

Dissolving CO < sub > 2 </ sub > in oil lowers the viscosity of the oil and reduces its interfacial tension which increases the oils mobility.

All oil fields have a geological barrier preventing upward migration of oil.

As most oil and gas has been in place for millions to tens of millions of years, depleted oil and gas reservoirs can contain carbon dioxide for millennia.

Identified possible problems are the many ' leak ' opportunities provided by old oil wells, the need for high injection pressures and acidification which can damage the geological barrier.

Other disadvantages of old oil fields are their limited geographic distribution and depths, which require high injection pressures for sequestration.

Below a depth of about 1000 m, carbon dioxide is injected as a supercritical fluid, a material with the density of a liquid, but the viscosity and diffusivity of a gas.