LARAMIE — Wyoming has taken an active approach toward research into the viability of long-term geologic carbon dioxide (CO₂) storage.

Research for carbon capture technology is ongoing at the University of Wyoming: the Carbon Management Institute was formed to study CO₂ storage in the structure of the earth’s crust, and the Enhanced Oil Recovery Institute evaluates CO₂storage when the chemical compound is used to enhance oil recovery from the state’s oil reservoirs.

These entities, among others, are striving to maintain coal as a viable resource in Wyoming. Wyoming’s abundant coal resources provide 7 percent of the energy produced in the United States, yet burning coal releases CO₂ into the atmosphere. As greenhouse gas emissions face increasing regulatory pressure and public scrutiny, developing the technology to capture, compress, and store CO₂ emissions in geologic traps may be fundamental to Wyoming’s future energy economy.

Carbon dioxide is a simple molecule composed of one carbon and two oxygen atoms. This naturally-occurring molecule comprises less than 0.04 percent of the air humans breathe.

Carbon dioxide is released to the atmosphere from both natural and anthropogenic (human) processes.

Natural sources—The most common natural sources of CO₂ include the respiration and decay of living things, forest fires, the melting of permafrost, and limestone weathering. Emissions from volcanoes also fall under this category. A limited amount of CO₂ is emitted from hot springs and geysers.

Natural CO₂ is also common in petroleum and natural gas reservoirs. The CO₂ in these reservoirs was generated along with the oil and gas through bacterial and thermogenic processes.

Anthropogenic sources—The largest global source of anthropogenic or human-made CO₂ is the combustion of fossil fuels such as coal, oil, and gas in power plants, automobiles, and industrial facilities.

The anthropogenic CO₂ component of the atmosphere has been growing steadily since the Industrial Revolution (1760-1850). Over the past 800,000 years, atmospheric levels of CO₂ naturally fluctuated from 171 to nearly 300 ppm (Lüthi and others, 2008).

As of March 2013, the monthly mean atmospheric CO₂ concentration recorded at the Mauna Loa Observatory in Hawaii was 397.3 ppm (Tans, and Keeling, 2013) — higher than any observed over the past 800,000 years (Lüthi and others, 2008).

Geologic CO₂ Storage

To help reduce anthropogenic CO₂ emissions, several alternatives have been proposed that would remove CO₂ (and other gases) from the emissions stream. One of these alternatives is geologic CO₂ storage, often termed carbon sequestration or carbon capture and storage (CCS).

The long-term strategy of geologic storage is to collect and store CO₂that would otherwise be released to the atmosphere from point sources such as coal-fired power plants, chemical plants, refineries, and natural gas plants and compressor stations. In principle, CO₂ is injected into the subsurface as a supercritical fluid, where it remains in place for an appropriate amount of time.

There are numerous options for where and how to store CO₂ within a geologic basin, including abandoned and unmineable coal seams, depleted or uneconomic petroleum reservoirs, and saline aquifers, defined as aquifers containing groundwater with greater than 10,000 mg/L total dissolved solids, which is significantly above the national standards of 500 mg/L for drinking water.

Geologic Storage Assessment of CO₂ in the Laramide Basins in Wyoming

The subject of this investigation is the potential for long-term geologic storage of anthropogenic CO₂ within the Laramide basins of Wyoming.

Laramide basins are fault-bounded basins that formed between basement-cored mountain ranges during the Late Cretaceous to Early Eocene Laramide orogeny (~80–55 Ma). These basins formed by basement-rooted reverse faults with as much as tens of kilometers of vertical offset. Laramide basins are found from northern Mexico through Canada.

The Laramide basins evaluated for this study include the Greater Green River, Wind River, Bighorn, Powder River, Hanna, and Denver basins.

U.S. EPA’s Class VI Geologic CO₂ Storage Wells in Wyoming

Carbon dioxide capture and geologic storage has not yet occurred at an industrial scale in the United States or elsewhere. However, with the potential for future geologic storage, the U.S. Environmental Protection Agency (EPA) and the Wyoming Department of Environmental Quality (DEQ), under the guidelines of the Safe Drinking Water Act’s Underground Injection Control program, have developed regulations for safely storing CO₂deep underground in geologic formations. In particular, Class VI wells have been designated as a new well class for CO₂ sequestration.