February 12, 2014

What Is Geologic Sequestration?

Geologic sequestration of CO2 is commonly referred to as carbon capture and storage or CCS. The primary purpose of this process is to prevent carbon emissions from large industrial processes (e.g., power plants, cement and steel production facilities) from entering the atmosphere.

The first step of CCS is to capture CO2 emissions and compress them into a supercritical fluid form. Once compressed, the fluid CO2 is transported to an underground injection site. Transportation can occur in many ways, but pipeline transport is the most common and cost-effective method. The injection site pumps the fluid CO2 6,000 to 10,000 feet below the surface into a depleted oil field or saline rock formation where the CO2 is trapped in the geologic formation. After injection, the CO2 may absorb into brine water or react with minerals in the rock formation to form carbonate compounds.

Although CO2 injection has been used for decades to stimulate low-producing oil fields, the technology behind long-term storage of CO2 is new and still being developed. Currently, only a handful of industrial-size CCS projects are operating worldwide. The largest and most studied is found in southern Saskatchewan. Known as the Weyburn-Midale Project, CO2 emissions are captured from a coal-fired power plant in Beulah, North Dakota. The compressed CO2 is piped to two old oil fields in Canada and pumped underground at a rate of 9,400 tons per day. Researchers continue to monitor the site today for possible side effects discussed below. Additional information can be found at the Petroleum Technology Research Centre.

In 2007, Congress passed the Energy Independence and Security Act, directing the U.S. Geological Survey (USGS), in consultation with EPA and the Department of Energy (DOE), to develop a scientific basis for assessing the nation’s geologic storage capacity. The initial phase of that assessment was completed in 2012. Additionally, in 2009, DOE awarded twelve grants to companies for CCS projects. DOE plans to select three or four of these projects to proceed into Phase 2 for operational testing in 2015.

As very little is known about the long-term effects of geologic sequestration of CO2, many concerns are being studied in both the private and public sectors. Some of these concerns include:

The major concern is a large, sudden release of CO2 into the environment. A natural release of CO2 occurred at Lake Nyos in Cameroon in 1986, causing the deaths of 1,700 people and 3,500 livestock.

Geologic sequestration is a fascinating approach to managing captured CO2. Over the next few years, it will be interesting to observe whether the technical challenges can be successfully met.


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