Underground storage of CO2 - page 2
Is the CO2 storage technique safe?
Nature shows us this is a serious option. Underground CO2 concentrations have been found during oil drilling, when they may be used as propellant to pump up the last drops. CO2 storage in sand layers below the bottom of the ocean is already being applied for natural gas extraction in the Sleipner gas field in the Norwegian sector of the North Sea. Storing CO2 in the subsoil is also quite similar to the way natural gas is stored underground.
Various underground storage options
Depleted oil and gas fields
Imagine natural gas and oil, pumped out of natural underground rocks' cavities, could be replaced with carbon dioxide. As stated before, CO2 is used as propellant to increase oil production. This clearly shows the underground storage possibilities.
Deep saline aquifers
Underground geological layers, which pores are filled with water, can also be used for CO2 storage. Since the salinity of the water in these layers is too high, it can not be used for drinking. That is why aquifers can be used as CO2 storage reservoirs. Injected carbon dioxide is then dissolved in the water of the rocks' pores. Deep aquifers offer a higher storage capacity than oil and gas fields.
Coal layers
Coal possesses all the right properties needed to store CO2. Moreover, the stored CO2 in coal layers can also be used to extract methane from these same layers. In the same way, CO2 is used as a propellant for the extraction of oil, it can perform the same function in the production of methane. By means of adsorption, CO2 attaches itself to coal and thus releases the methane from the coal. While two molecules of CO2 are needed to release one molecule of methane, the combustion of one molecule of methane releases only one molecule of CO2. This process has a net yield of one stored molecule of CO2.
Abandoned coalmines
Men have built coalmines to extract coal, and today these mines offer a huge underground storage area. Before this area can be used, certain conditions have to be fulfilled. For instance, the old mine shafts have to be made gastight. Furthermore, the surrounding coal layers, which had not been exploited, offer an extra storage capacity.
