Millions of years ago, carbon sequestration occurred when plant and animal matter were buried and compressed in layers of rock.
Mining operations have been pushing deeper into these layers of rock to extract fossil fuels. Burning these fuels has the opposite effect of carbon sequestration, releasing carbon dioxide back into the atmosphere.
Natural gas wells, for example, drilled thousands of feet into the earth to remove gases trapped in porous rock. The porous rock, typically shale or sandstone, is capped by layers of other impermeable rock layers, which keeps the gases from escaping, until they are punctured by a well, of course.
In order to reduce carbon emissions, carbon capture technology can remove carbon dioxide from the exhaust on factories and even vehicles, but the question is what to do with it. Some can be fed into greenhouses and to chemical plants, which sequester carbon in plants or plastics, eliminating it from the atmosphere. Interestingly, the very wells natural gas was extracted from can also be used for carbon sequestration. The same rock layers that held natural gas in check for millennia can also be used to bury carbon dioxide, but there is always the question of how to monitor it.
Electrical Resistance Tomography [ERT] makes use of a series of electrodes and sensors to track the movement and concentration of carbon dioxide underground. Previous attempts to monitor carbon sequestration projects only got as deep as 2,100ft, but many places that can be used to store carbon are much deeper. Lawrence Livermore National Laboratory [LLNL], in California, has adapted the technology to go deeper than ever before with an ERT system to measure a carbon sequestration project in Cranfield, Mississippi. Injecting some one million tons of carbon dioxide into wells more than 10,000ft deep, LLNL used ERT to monitor the movements of the gas. Such a deep ERT system can open up new wells for carbon sequestration as well as monitor them for capacity and leaks.