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:

Leaks of CO₂ to the surface, endangering the ecosystem and human health;
CO₂ contamination of potable water supplies, resulting in a decrease in pH and increase in solubilized minerals;
Seismic activity caused by CO₂ injection; and
Seismic activity rupturing a CO₂ reservoir.

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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This document addresses issues of a general nature related to the federal RCRA regulations. Persons evaluating specific circumstances dealing with the RCRA regulations should review state and local laws and regulations, which may be more stringent than federal requirements. In addition, the assistance of a qualified professional should be enlisted to address any site-specific circumstances.