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Carbon Dioxide Sequestration in Saline Aquifers

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The USGS is pursuing research to reduce greenhouse gases in hopes of heading off global warming. Bob Rosenbauer of the Western Region Coastal and Marine Geology team (WRCMG) and Jim Bischoff, Scientist Emeritus with the Volcano Hazards team (formerly of WRCMG), have developed new technology to investigate the disposal of excess man-made carbon dioxide (CO2). The burning of fossil fuel has caused a continuous increase of atmospheric CO2 over the past 120 years. The role of CO2 as a greenhouse gas and its potential effect on global climate have been well documented in the scientific literature, and its mitigation has been the subject of several recent national scientific meetings, such as the First National Conference on Carbon Sequestration held in Washington, DC, in May 2001. Powerplants are a major source of this excess CO2, and although the capture of CO2 is a proven technology, its disposal and storage remain problematic.

diagram of experimental apparatus
Experimental scheme (drafted by Bruce Rogers, WRCMG) for determining the solubility of carbon dioxide in water and brines, using a fixed-volume reaction cell (labeled "Pressure Vessel" in diagram) and rotating furnace to simulate the pressures and temperatures of deep aquifers. Fluid or gas samples are withdrawn with a high-pressure syringe and transferred to a coulometer for carbon dioxide analysis. [larger version]

The team studying CO2 sequestration at Menlo Park, CA, has been joined by Tamer Koksalan, a Stanford University graduate student who is working with Stanford organic geochemist Mike Moldowan. A Mendenhall Postdoctoral Fellow will be added to the team in FY03.

This group within WRCMG hopes to short-circuit the emission of CO2 into the atmosphere by its geologic sequestration in deep-saline aquifers. In the sequestration process, CO2 captured from powerplant or other emissions would be pumped into deep-saline aquifers to isolate it from the atmosphere. The depths of these aquifers provide pressures high enough to keep the CO2 supercritical—in a single fluid phase with physical properties similar to those of a liquid rather than a gas. Some CO2 will become dissolved in the aquifer and can react with other dissolved salts in the brines and wallrock to form carbonate minerals that will permanently fix part of the CO2 as a rock. These aquifers are unsuitable as resources for drinking water.

This process, which is one of several proposed disposal mechanisms, has the advantages of permanence (by fixation of CO2 into carbonate minerals) and high capacity—there are many deep-saline aquifers of broad extent throughout the country. Many are located in regions with large coal-fired powerplants—a major source of excess CO2. The WRCMG study involves experiments to determine the solubility of CO2 in brines and the reactions between supercritical CO2 and fluids and host rocks that are characteristic of deep-saline aquifers.

Above left: An exploded view of the experimental apparatus for studying the interactions of carbon-dioxide-charged fluids and potential aquifer host rocks. [larger version]

Above right: A schematic (drafted by Bruce Rogers) of the apparatus. [larger version]

A rock sample and carbon-dioxide-charged brine are placed in the collapsible gold bag and subjected to temperatures and pressures typical of deep aquifers. We use the gold-lined exit tube and titanium sampling valve to withdraw samples of the fluid and monitor the progress of reactions during rock-water interactions.

In the Water/Rock Interaction Laboratory, we adapted technology originally designed to study hydrothermal systems to the investigation of CO2 sequestration. We designed and developed new reaction cells—containers in which we can mix components at different temperatures and pressures and observe the results—and new sampling and analytical procedures. The experimental scheme and new data on the solubility of CO2 in brines were presented at special sessions of the spring and fall meetings of the American Geophysical Union (AGU) in 2001.

An important aspect of the experimental work is to provide kinetic and thermodynamic data for modeling efforts being conducted by Yousif Kharaka and Jim Palandri (USGS, Water Resources) and Kevin Knauss (Lawrence Livermore National Laboratory).

This project is part of a national effort by government, industry, and academia to limit and dispose of greenhouse gases. Partial funding is being provided by the USGS Energy Resources Program (ERP) under the umbrella project "Assessment of Geologic Reservoirs for Carbon Dioxide Sequestration" headed by Bob Burruss (ERP). Coincidentally, Jon Kolak, a recent postdoctoral researcher with WRCMG, is now a Mendenhall Postdoctoral Fellow with the Energy Resources team in Reston, VA; Jon will be working on the potential environmental effects of CO2 sequestration in deep unminable coal beds and depleted oil reservoirs. We are cooperating with this work by adding methane, a greenhouse gas associated with coal and oil deposits, to our mix of experimental components. The U.S. Department of Energy (DOE) through the National Energy Technology Laboratory (NETL) is providing additional funding for some fundamental studies on supercritical CO2 in which Curt White, Sheila Hedges, and Don Harrison (all at NETL) are collaborating with the USGS effort.

Related Web Sites
Western Region Coastal & Marine Geology
U.S. Geological Survey (USGS)
Energy Resources Program
U.S. Geological Survey (USGS)
National Energy Technology Laboratory (NETL)
U.S. Department of Energy (DOE)
Conference Proceedings - First National Conference on Carbon Sequestration
U.S. Department of Energy (DOE)

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in this issue: Fieldwork cover story:
Contaminants Sampling Cruise - San Francisco

Ground-Truthing Coral Reef Maps

Research Shorebird Migration

CO2 in Saline Aquifers

Outreach Early Earth Day in Florida

Honduras Coral Reef Documentary Online

Girl Scouts

University Job Fair

Sea-Level Rise Lecture

Meetings Massachusetts Sea-level Rise Briefing

New Directions Workshop

Staff & Center News Floating Support Facility

Howell New Patuxent Director

WHFC Runners

Water-Column Optics Talks

Special Emphasis Program

New Employees

Mendenhall Fellow Presents Talk

Publications May Publications List

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