Carbon sequestration, also termed carbon storage, is the permanent storage of carbon dioxide (CO2), usually in deep geologic formations. Industrially-generated CO2 -- resulting from fossil fuel combustion, gasification, and other industrial processes -- is injected as a supercritical fluid into geologic reservoirs, where it is held in place by natural traps and seals. Carbon storage is one approach to minimizing atmospheric emissions of man-made CO2.
As discussed elsewhere, the main purpose of CO2 EOR such as the Weyburn Project is tertiary recovery of crude oil, but in effect substantial CO2 remains sequestered/stored as a result.
Current Status of CO2 Storage
CO2 storage is currently underway in the United States and around the world. Large, commercial-scale projects, like the Sleipner CO2 Storage Site in Norway and the Weyburn-Midale CO2 Project in Canada, have been injecting CO2 into geologic storage formations more than a decade. Each of these projects stores more than 1 million tons of CO2 per year. Large-scale efforts are currently underway in Africa, China, Australia, and Europe, as well. These commercial-scale projects are demonstrating that large volumes of CO2 can be safely and permanently stored. In addition, a number of smaller pilot projects are underway in different parts of the world to determine suitable locations and technologies for future long-term CO2 storage. In addition, a number of smaller pilot projects are underway in different parts of the world to determine suitable locations and technologies for future long-term CO2 storage. To date, more than 300 CO2 storage projects have been carried out worldwide. For a detailed, and periodically updated listing of CO2 storage projects around the world, refer to NETL's Carbon Capture, Utilization, and Storage (CCUS) Database.
Monitoring, Verification, and Accounting
An important part of carbon storage is monitoring, verification, and accounting (MVA) for the CO2 during and after injection. Geochemical sampling and geophysical imaging are used to track the CO2 plume as it is injected into the reservoir and monitor its location and lateral extent for months and years after injection. The goal is to verify that the CO2 remains permanently stored in the formation. These MVA technologies are likely to provide the basis for establishing carbon credit trading markets in the future. NETL's Carbon Storage Program has developed a detailed technical guide on MVA of CO2 stored in deep geologic formations, which provides a very thorough discussion of this subject.
Carbon capture and storage is an important component of our nation's CO2 emissions management strategy. Studies have demonstrated that CO2 storage in geologic formations can account for up to 55 percent of the emissions mitigation needed to stabilize and ultimately reduce concentrations of CO2 in the atmosphere.