Web Date: March 9, 2012
Fracking Could Hinder Underground Carbon Storage
By breaking up rock formations deep underground, drilling companies can gain access to natural gas once thought unrecoverable. But drilling zones overlap significantly with places suitable for storing carbon dioxide below the surface, according to a new study (Environ. Sci. Technol., DOI: 10.1021/es2040015). As a result, researchers estimate that drilling could damage as much as 80% of U.S. carbon storage capacity.
Some scientists and lawmakers think that burying CO2 underground–instead of releasing it to the atmosphere–could reduce emissions and slow climate change. In a process called carbon capture and sequestration, facilities such as coal-burning power plants would capture the CO2 they produce and inject it deep below the ground. A layer of impermeable rock called caprock above the CO2 would prevent it from rising back to the surface. No large-scale sequestration projects have begun in the U.S., but the Meredosia Power Plant in Illinois could start sequestering CO2 in 2015.
Shale, a sedimentary rock formed from clay or mud, often makes good caprock, says Michael A. Celia, a professor of civil and environmental engineering at Princeton University. But shale can also contain natural gas, and breaking up the rock in order to extract gas–a process called hydraulic fracturing–leaves it unusable as caprock. Natural gas now accounts for 25% of the energy consumed in the U.S. and demand for it is increasing, according to the U.S. Geological Survey. So Celia wondered how large the geographic overlap is between areas of gas extraction and potential sites for carbon storage.
Using data from the Energy Information Administration and the Department of Energy, Celia and co-author Thomas Elliot identified locations suitable for carbon storage and places where gas extraction is occurring or likely to take place. They overlaid the data sets on a map and found that natural gas production could damage as much as 80% of the country’s carbon storage capacity.
Celia cautions that the study likely overestimates fracking’s impact on the amount of storage because the researchers did not account for sites with multiple caprocks stacked vertically. Such geological structures might enable drilling and carbon sequestration to take place in the same area.
Bruce Hill, a scientist at the Clean Air Task Force, a research and advocacy group, says the expansion of fracking won’t put an end to burying CO2 underground. The available underground storage capacity is so large, Hill says, that even if some of it became unusable, it wouldn’t be a “deal killer.” Department of Energy data suggest that the U.S. has enough storage capacity to hold its annual carbon emissions for 300 to 3,500 years.
There are also other ways to sequester CO2, Hill points out: Producers of CO2 could inject the gas into oil fields, a process that also increases the amount of oil that the field produces. Four power plant projects using this technique could start as soon as 2014, according to the Carbon Capture and Sequestration Technologies Program at the Massachusetts Institute of Technology.
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