CO2 Enhanced Oil Recovery (EOR)
While there other, larger scale approaches to CO2 sequestration, CO2 EOR is applicable in many mature oil fields in the world. CO2 is often a preferred injected fluid which is miscible with oil and lowers its viscosity. This improves resource recovery and reduces the need to drill new and expensive wells (deep off-shore, in the Arctic etc.)
CO2 is injected and partially recovered as oil is produced. Over time a large net quantity of CO2 remains underground.
Ironically, the cost and availability of CO2 is often the limiting factor in using CO2 EOR. By colocating a production plant for electricity, hydrogen or ammonia at or near the well-head a large and stable source of CO2 can be made available to support the EOR operation.
The net CO2 emissions from the natural gas and coal which supplies the plant is nearly zero, because the by-product CO2 is recovered, purified and permanently sequestered.