Basic Research Needs for Geosciences - Energetics Meetings and ...

INTRODUCTIONfraction of the carbon dioxide produced from fossil energy conversion be captured and storedaway from the atmosphere (see sidebar on Scenarios for greenhouse gas emissions). Porous,subsurface geologic rock formations offer potential locations for long-term storage of carbondioxide.Nuclear power is another component of the global energy equation. Nuclear power plants supplyabout 0.9 terawatts of the world’s present rate of energy use, much less than fossil fuel-basedsystems, but a significant fraction—one that could increase to replace part of the fossil fuelbasedenergy production (see sidebar on Scenarios for greenhouse gas emissions). Nuclearenergy produces no CO 2 but instead generates substantial amounts of radioactive materials, a factthat has both environmental and security implications. To sustain nuclear energy generation, andeven more so to increase generation by a factor of up to 10 over the next century, it is necessaryto safely store radioactive waste in underground repositories. Several countries, including theU.S., have programs in progress to develop underground nuclear waste repositories. If nuclearenergy production is to expand, many more suitable sites for underground storage need to beidentified and characterized, and suitable approaches to underground storage need to beengineered for each site.SUBSURFACE GEOLOGIC STORAGE SCIENCEThis report outlines the scientific challenges that must be addressed if subsurface geologicsystems are to be used to store safely the products of energy use, particularly those from electricpower generation. The report covers issues that pertain to both CO 2 sequestration and nuclearwaste isolation. Both issues are included as a basis for this report because the scientificcommunities involved in the relevant research overlap, as do the underlying fundamental scienceissues. The specific technical challenges are different (see Appendix 1: Technical PerspectivesResource Document).Storage of carbon in the subsurface involves introduction of supercritical CO 2 into rockformations beneath the surface of the Earth, typically at depths of 1000 to 4000 meters. AlthoughCO 2 is a relatively benign substance, the volume being considered is large. If developed to itsenvisioned potential, geologic sequestration will entail the pumping of CO 2 into the ground atroughly the rate we are extracting petroleum today. To have the desired impact on theatmospheric carbon budget, CO 2 must be efficiently retained underground for hundreds of years.Storage of nuclear waste in the subsurface involves a smaller volume of material, and shallowerburial depths of roughly 500 meters. But by virtue of its radioactivity and toxicity, nuclear wastemust be confined carefully, and because of long half-lives, it must be sequestered for a long time,even by geological standards. Current regulations indicate that a U.S. repository will need to beeffective for ten thousand to one million years.Any underground storage system will have to account for the natural characteristics ofsubsurface rock formations; some are advantageous for storage, while others are not. Thecrosscutting consideration is that when foreign materials are emplaced in subsurface rockformations, they change the chemical and physical environment. Understanding and predictingthese changes are important for determining how the subsurface will perform as a storagecontainer. In the case of CO 2 , a cold but low-density fluid is injected and is allowed to find its2 Basic Research Needs for Geosciences: Facilitating 21 st Century Energy Systems