Sometime in 2001,
probably at a one-hectare site on a depleted oil reservoir in Texas
or California, a slug of carbon dioxide (CO2) will be injected
some 600 m (2000 ft) into the ground. But it won’t be pure CO2.
It may be tagged with helium, argon, and other noble-gas tracers introduced
into the injected stream at various known concentrations in a regular
pattern, providing a "chemical wave" signature. It may also contain
intentionally introduced isotopes of carbon, hydrogen, nitrogen, and
oxygen whose ratios could shed light on the effects of the injected
CO2 on the site's geochemistry and on the ability of the
underground formation to trap the CO2.
a hydrologist in ORNL's Environmental Sciences Division (ESD) who developed
the concept of tagging CO2 with a chemical wave, and David
Cole, a geochemist in ORNL's Chemical and Analytical Sciences Division,
will use noble gas and isotopic tracers in injected CO2 to
help determine whether and how long the site will securely store, or
sequester, the CO2. The tagged CO2 will be introduced
at injection wells and sampled as it migrates through return wells,
a hundred or so meters away. Moline will measure the chemical wave signal
in the sampled gas using a portable gas chromatograph. Cole will measure
isotope ratios in gas and fluid samples using mass spectrometry.
should help answer these questions about injected CO2: Where
did it go? How fast does it move? How long will it stay? Could it leak
back into the atmosphere, thereby contributing to greenhouse gas levels?
showing both terrestrial and geological sequestration of carbon
dioxide emissions from a coal-fired plant. Rendering by LeJean
Hardin and Jamie Payne.
The ORNL results
should also help address these questions about the selected site for
CO2 injection: Is this a suitable or unsuitable site for
carbon sequestration? What are the optimal depths, temperatures, and
pressures for carbon sequestration in this reservoir? How much injected
CO2 is dissolved in underground fluid, trapped in pores,
or adsorbed on rock? How much CO2 can be stored at this site?
Moline says that
the noble-gas tracers should provide useful information because they
are inert, so they do not interact with subsurface rock and fluids in
the same way as the isotopic tracers do. She will be looking for an
attenuation of the chemical wave signature when she samples for CO2
and noble gases. A diminished signal for CO2 relative to
the noble gases will indicate how much of the injected CO2
has been "lost" during transportthat is, sequestered.
Cole says that analysis
of the isotope tracers should help scientists better understand the
interactions between the injected CO2 and the site geochemistry.
"When a bubble of carbon gas is injected into the formation," he says,
"it may displace the water there. Some of the CO2 will be
dissolved in the fluid, and the CO2-bearing fluid will interact
with the underground rock. Our tracer studies may show whether minerals
are precipitated from the CO2-bearing fluid to the rock,
whether minerals in the rock are dissolved in the fluid, and whether
the fluid affects the permeability or porosity of the rock in the formation."
These ORNL scientists
are participating in the geological sequestration (GEO-SEQ) project
sponsored by DOE's Office of Fossil Energy. They are helping to study
the effects of injecting CO2 into depleted oil reservoirs,
brine formations, and coal beds. Participants in this three-year project
on geologic sequestration of CO2 include Lawrence Berkeley,
Lawrence Livermore, and Oak Ridge national laboratories, in cooperation
with Chevron, Texaco, Pan Canadian Resources, Shell CO2 Co.,
BP-Amoco, Statoil, the Alberta Research Council Consortium, Stanford
University, and the Texas Bureau of Economic Geology. One goal of the
work is to determine whether CO2 injection can result in
economic benefitsenhanced oil recovery and production of methane
from coal beds—as well as sequestration.
In these studies,
we will be studying whether the injection of CO2 changes
the formation," Cole says. "For example, CO2 interacting
with brine, which is mineral-rich saltwater, may lead to changes in
the fluid chemistry that could either increase or decrease the porosity-permeability
characteristics of the saline aquifer, depending on its mineral composition."
ORNL's role in
GEO-SEQ is to evaluate and demonstrate monitoring technologies, with
a goal of selecting ones that are safe and that work best in verifying
that carbon has been sequestered. GEO-SEQ's other tasks are to (1) develop
methods to sequester CO2 in enhanced oil recovery, sites,
depleted gas reservoirs, and saline aquifers; (2) enhance and compare
computer simulation models for predicting, assessing, and optimizing
geologic sequestration in brine, oil, gas, and coal-bed methane formations;
and (3) improve the methodology and information available to assess
the sequestration capacity of different sites.
to slowing the buildup of greenhouse gases in the atmosphere is to minimize
losses of carbon and nitrogen from disturbed lands. ORNL and Pacific
Northwest National Laboratory have joined Ohio State University and
Virginia Polytechnic Institute and State University in a two-year project
funded by DOE's Office of Fossil Energy to find ways to improve the
natural carbon uptake of lands disturbed by mining, highway construction,
or poor management practices. For this purpose, they are studying the
use of soil enhancers made from the wastes of coal-fired power plants
and sewage treatment facilities. The research is being done at sites
in Kentucky, Ohio, and West Virginia. Tony Palumbo, John McCarthy, Gary
Jacobs, Jizhong Zhou, Jeff Amthor, and Patrick Mulholland, all of ESD,
will study the impact on soil carbon of reclaiming disturbed lands by
planting them with grasses and trees (e.g., pines and poplars) and fertilizing
them with coal fly ash and sewage waste.
strip mine site is a source of acid mine drainage (note the amber
color) to the environment.
fly ash to clay soil makes it friendlier for plant growth, we hope that
more carbon will be built up in the soil," Palumbo says. "We will measure
soil organic carbon before and after each site is planted. We may plant
grass first because it will remove boron and other toxins from the fly
ash so they don't adversely affect tree growth. On the other hand, we
may find that toxic fly-ash metals will get tied up with organic compounds
in the sewage sludge, making them less of a threat to the trees."
in progress is turning this degraded land into a site that could
reduce soil erosion and sequester more carbon.
If carbon tax
credits are granted in the United States, landowners will have more
of an economic incentive to exercise stewardship over lands they must
reclaim to comply with state and federal laws. They will want their
reclaimed sites to receive credit for sequestering carbon.
"We will also
measure nitrogen releases from the soil to determine whether ammonia
in sewage sludge is being converted to nitrous oxide, a greenhouse gas,"
Palumbo says. "We will study ways to manipulate the soil, perhaps by
wetting it and introducing specific microorganisms, to minimize nitrous
The project's findings
as to what works and what doesn't in reclaiming land to increase carbon
storage will be transferred to mine reclamation firms and other interested
industrial companies. This effort is part of the activities of DOE's
Center for Research on Enhancing Carbon Sequestration in Terrestrial
Ecosystems (CSiTE), which is co-managed by Jacobs.
In a project funded
by DOE's Office of Fossil Energy, Tommy Phelps, an ESD microbiologist,
proposes to build a football-field-sized pond 30 m (100 ft) deep next
to a coal-fired power plant. The object of his research is to see if
carbon captured from the coal plant and injected into the pond will
be successfully sequestered. To sequester carbon in the pond, Phelps
plans to introduce the TOR-39 bacteria that he discovered in 1993 in
Virginia. The pond will also receive iron leached from coal fly-ash
"These bacteria feed on
carbon and respire iron, converting it to magnetite," Phelps says. "They
also do not need oxygen or light, so they thrive anywhere in the pond."
ESD show that TOR-39 bacteria in water can also make micron-sized particles
of iron carbonate (siderite) from iron hydroxide and carbon dioxide
introduced into the test tube. "We believe that these bacteria can combine
carbon dioxide from the coal plant with iron in the water to produce
iron carbonate," Phelps says. "The iron carbonate will sink into the
pond sediments, sequestering the carbon."
are sinking their talents into interesting approaches to carbon sequestration
in the hope of delaying climate change.
DOE Center for Research on Enhancing Carbon Sequestion in Terrestrial