<center>Geological Sequestration of Greenhouse Gases:<br>Opportunities for Industry Academe Research Partnerships</center>

Abstract
The causes, effects, realities, and projections of global warming are currently highly contested and controversial issues. One of approache under consideration by the U.S. Department of Energy (DOE) and the international community that has the potential to reduce atmospheric carbon dioxide (CO2) concentrations is injection of CO2 into the subsurface (geologic sequestration). Input from environmental and petroleum geoscientists is needed in order for society to clearly understand the costs and benefits of geologic sequestration.
Geologic targets for CO2 sequestration include brine-bearing formations (those containing nonpotable waters) and mature or abandoned oil and gas reservoirs. Two possible benefits of geologic sequestration include safe storage of large volumes of CO2 over long periods of time using existing technologies and also economic benefits from value-added approaches. Value-added approaches include enhanced oil recovery (EOR) through CO2 flooding as well as injection of CO2 for pressure maintenance, which might allow simultaneous production from oil legs and gas caps. Sequestration risks include (1) leakage of injected CO2 through natural pathways (e.g., faults and fractures) over tens or hundreds of years; (2) pressurization of brine-bearing formations, resulting in leakage of brine into shallow, potable water sources; and (3) leakage through improperly abandoned or cemented well bores that could create asphyxiation hazards.
Research projects to identify constraints on successful geologic sequestration have been undertaken, as have initial studies on the economics of using CO2 from power-plant exhaust streams in EOR. Further research is needed to plan and carry out field-scale pilot projects in both brine-bearing formations and oil and gas reservoirs. Such pilot projects would allow evaluation of engineering, safety, and economic issues.
Introduction
About 85% of U.S. energy comes from the combustion of fossil fuels. On the basis of current economic factors, these fuels are expected to continue to dominate energy sources well into the 21st century. Greenhouse gases, volumetrically dominated by carbon dioxide (CO2) that is released by energy production (electricity generation, transportation, etc.), are an unavoidable byproduct of this process. In response to evidence suggesting a link between CO2 emissions and global warming, the U.S. Department of Energy (DOE) has sponsored research into technologies that might reduce CO2 emissions into the atmosphere.
Why should geologists and oil and gas companies be interested in these activities? Because one of the potential solutions to the CO2 emission problem is to capture CO2 from power-plant and refinery emissions and inject it into the subsurface, thereby "sequestering" the gas. Likely subsurface targets include brine-bearing formations adjacent to or under existing oil and gas reservoirs, brine-bearing formations that regionally underlie fresh-water aquifers, abandoned or mature oil and gas reservoirs (enhanced oil recovery EOR), and unminable coalbeds (enhanced coalbed methane production). Now is the time for interested groups to provide input toward understanding these sequestration methods in order to guide safe practices and to evaluate the potential economic benefits of CO2 sequestration.
Available Funding - The Carbon Sequestration Program, established by the DOE (U.S. Department of Energy, 2000), published anticipated requirements in funding to achieve its goals through 2015. The purpose of this funding is to build scientific understanding of the geologic sequestration process, upon which a national carbon sequestration policy could be built. To reduce the costs and risks, federal agencies (such as DOE) are partnering with industry, academe, foreign countries, and international organizations. The Bureau of Economic Geology, The University of Texas at Austin, has been involved in past partnering projects that have evaluated controls on geologic sequestration in both brine-bearing formations and abandoned or mature oil and gas reservoirs (through enhanced oil recovery involving CO2 flooding). Future DOE partnerships regarding geologic sequestration will focus increasingly on modeling and design of field-scale pilot projects to demonstrate technologies and evaluate safety issues. Monitoring of air and aquifers around pilot sites is needed, as is investigation of impacts of CO2-associated corrosion on pipelines and well casing and tubing and documentation of economic constraints on successful sequestration/EOR projects.
Current and proposed DOE funding supports partnering opportunities that target a combination of method assessment and public outreach, conceptual research and development, bench-scale prototype development, field-scale pilot testing, and large-scale project operation and monitoring. Funding will increase from about $9 million in 2000 to a maximum of $85 million in 2008, tapering off to $40 million in 2015. This funding will address research, not only in geologic sequestration, but also in CO2 capture and separation technology, terrestrial and oceanic sequestration, advanced concepts, and crosscutting activities.
Sequestering CO2 in the Subsurface
Benefits - Using existing technology, large volumes of CO2 can be injected into the subsurface and effectively isolated from the atmosphere and potable ground water for long (geologic) periods. Between deep brine-bearing formations and depleted oil and gas reservoirs, as much as 1,000 years' worth of CO2 emissions could be safely sequestered in an environment that is likely to remain stable over long periods (hundreds of thousands of years or more). And because of past activities in deep-well injection of waste and oil-field injection of CO2 for EOR purposes, the mechanics and impact of these activities are well understood. Brine-bearing porous and permeable formations are an attractive and economic target for many CO2 sources such as power plants because they underlie many parts of the United States. This allows injection at the site of the emissions, removing the need to construct a pipeline to transport the gas to another location for injection, such as an oil field. Because brine-bearing units are largely unused, subsurface rights to such formations should be available.
Where opportunities for injection into mature or abandoned oil and gas reservoirs exist, economic benefits can be derived from the injection of CO2. Additionally, a study is being undertaken at Lawrence Berkeley National Laboratories to investigate whether injection of CO2 at the gas-water contact of producing gas reservoirs might effectively maintain reservoir pressure and prevent edge-water influx. Success in this study may raise the question of whether injection at a gas-oil contact might allow simultaneous production of oil and an overlying gas cap while maintaining reservoir energy and preventing edge-water influx. Such a method may allow faster production of hydrocarbons, potentially increasing near-term cash flow and ultimate field economics.
Risks - Risks associated with subsurface sequestration of CO2 center main