7.5.3. Carbon Sequestration

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.

Benefits
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.

Hydrogen