Geologic Sequestration in Deep Saline Aquifers

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Reducing Trapped Radiation: Geologic Sequestration in Deep Saline Aquifers

The second geologic option for long-term carbon sequestration involves the injection of CO2 into deep saline aquifers. A saline aquifer is basically a large underground salt water deposit. Once the CO2 is injected, it would react chemically with the salt water to form “precipitates” – solid chunks of material that cannot leak up back into the atmosphere. While not nearly as common as injecting CO2 for enhanced oil recovery, carbon sequestration in saline aquifers is being practiced in Norway. The same logic behind long-term sequestration in saline aquifers had lead to some proposals for long-term CO2 injection in deep ocean formations. While this might work from a technical perspective, it’s not clear whether the unintended consequences of increased ocean acidification would be worth the benefits of carbon sequestration (remember those coral reefs?). At this point, there are few serious proposals for sequestration in the deep ocean.

 CCS Schematic. Injection wells go 7,000ft underground under soil which is an ‘impermeable seal’. The injections wells lead to a power plant
CCS Schematic (Subsurface depth to scale, 5,280 feet equals one mile)
Source: US Environmental Protection Agency

Of all geoengineering options besides terrestrial sequestration, geologic storage of CO2 is the one that is practiced most often today, but even so, the number of active projects is relatively low. See this map from the Massachusetts Institute of Technology, which has pinpointed the location of currently operating and planned carbon sequestration projects.Most involve enhanced oil/gas recovery, or coal-bed methane. Few projects are sequestering carbon dioxide simply to avoid venting the CO2 into the atmosphere. A large number of projects with this particular goal have been canceled in recent years. There are two inter-related reasons for this. The first is regulatory uncertainty. Most of the world has not adopted a sufficiently stringent framework for greenhouse-gas emissions reductions to provide any economic incentives for widespread carbon sequestration. In some countries, such as the US, regulations that would govern the long-term injection of CO2 into geologic reservoirs, other than for enhanced oil or gas recovery, have not yet been developed. No sane investor or company is going to put their money into carbon sequestration until all of the rules are in place (and when the rules provide an economic incentive for sequestration). Second, the use of CO2 for enhanced oil recovery, in particular, can be profitable under some circumstances if oil prices are high enough. In contrast, the “market” for avoided CO2 emissions is not very well developed in most parts of the world.