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Areas of Research in Geologic CO2 Sequestration
Sequestration Storage Capacity of Subsurface Traps: The typical approach to CO2 sequestration assessments involves estimating the sequestration capacity of a geologic formation, i.e. the volume or mass of CO2 that can be stored in a geologic formation, such as saline reservoirs, coal beds, or petroleum reservoirs. However, determining the volume necessary to sequester the CO2 emissions from point sources is an important frame of reference for CO2 sequestration assessments. Therefore, the USGS has proposed an assessment methodology for determining the geologic capacity necessary for individual CO2 sequestration projects. (Brennan and Burruss, 2003; 2006)
Data Analysis for Assessment of CO2 Storage Options: Depleted oil and gas reservoirs and coal beds that can not be mined because of quality and technological restrictions are possible reservoirs for CO2 sequestration. Therefore, it is necessary to know the geographic relationship between the potential geologic reservoirs for CO2 seqeustration and the CO2 emission point sources. This means analyzing the available data on CO2 point-source emissions, reservoir field size distributions, volumes of fluid production, and other data types using geostatistical and geospatial methods.
Chemical Reactions Involved with Geologic CO2 Sequestration: CO2 reacts with water to produce an extremely acidic solution, capable of dissolving minerals and releasing metals to solution Although the capture of CO2 from power plant emissions is a proven technology, the disposal and storage of CO2 remain problematic. There are major uncertainties involving the environmental impact and long term storage associated with the disposal of CO2 in deep reservoirs. Carbonate minerals are integral to the integrity of the reservoirs helping seal pores and fractures in the cap rock, If dissolved, seals could release CO2 and contaminated brine into overlying aquifers that supply drinking and irrigation water. Moreover, the acid solution could corrode the cement seals plugging 25 million abandoned oil or gas wells in the United States.
Natural Analogues for CO2 Sequestration: Little is known about the long term fate of CO2 sequestered in geologic reservoirs. However, there are natural gas fields with high CO2 concentrations, and fields of nearly pure CO2, where the CO2 has been in place for long periods of time. Our goal is to determine the source of CO2 in the reservoir, how long the CO2 has been in place, if the CO2 concentration has remained constant or fluctuated though time, and if the CO2 has interacted with other fluids and/or minerals in the reservoir. Determining the behavior of CO2 in various geologic reservoirs will provide information that will be of critical importance in selecting optimal geologic sequestration targets for CO2.
Major Issues in Geological Sequestration of CO2
Industrial Infrastructure. To process, transport, and store CO2, industrial infrastructure much larger than the size of the current US natural gas industry infrastructure may be required. Replacement of existing generating capacity with new technology will require major investments in capital equipment. Even if high technology, “zero emissions” coal or gas fired powerplants are developed, the CO2 or carbonate effluent will need to be transported and stored. Although most powerplants are associated with sedimentary basins with opportunities to store CO2 in oil and gas reservoirs, coal beds, or brine formations, by far the largest storage capacity is in the oceans, requiring long distance transportation both onshore and in the oceans, either in pipelines or in tanker ships.
U.S. Natural Gas Pipeline Network
(Source: Energy Information Administration, Office
of Oil & Gas, Natural Gas Division, Gas Transportation
Information System)
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U.S. Department of the Interior |
U.S. Geological Survey
