Reducing Trapped Radiation: Geologic Sequestration in Unmineable Coal Seams
First, carbon dioxide could be injected into depleted oil and gas reservoirs, or “unmineable coal seams” – this type of carbon sequestration is not principally meant to sequester CO2 at all. Sequestration is a nice by-product. Injecting CO 2 into these types of reservoirs is aimed at using the CO2 to get additional hydrocarbon energy out of the ground. In the case of oil and gas, this is called “enhanced recovery” and in the case of coal, it is called “enhanced coal bed methane” (since the CO2 pushes out natural gas from the coal seam, rather than coal itself). This is illustrated in the figure below. The oil and gas industry has a tremendous amount of experience with using CO2 for enhanced recovery – the second figure shows the location of projects using CO2 injection for enhanced oil recovery in the US. Oil and gas companies operating in the North Sea have also been injecting CO2 into their reservoirs for years to stimulate additional oil and gas production. In some cases that CO2 is captured from a nearby power plant or industrial facility. In other cases, CO2 is captured from natural vents in the earth (as happens near locations with a lot of tectonic activity). Shale-gas wells are now being viewed as potential CO2 storage locations for decades into the future, once production from those wells begins to decline.