Potential Leakage and Toxicity Problems with CO2 Sequestration
31 July 2006
|Cross-well seismic difference tomogram of the Frio Brine project shows the CO2 plume.|
Results from a field test on CO2 sequestration in an old brine-filled oil reservoir suggest that the mixture of CO2 and brine dissolves minerals in the rock walls, including carbonate, that could lead to pathways in the rock through which the gas could escape.
In a paper published in the July edition of Geology, the researchers in the Frio Brine Pilot also note the potential for the mobilization of toxic trace metals and toxic organic compounds.
The Frio Brine Pilot was the first test of closely monitored CO2 injection in a brine formation in the United States, and was funded by the Department of Energy (DOE) National Energy Technology Laboratory (NETL) under the leadership of the Bureau of Economic Geology (BEG) at the Jackson School of Geosciences, The University of Texas at Austin, with major collaboration from GEO-SEQ, a national lab consortium led by Lawrence Berkeley National Laboratory (LBNL).
The researchers injected 1,600 metric tons of CO2 1,500 meters down into a sandstone site representative of a target for large-volume storage. The sandstones of the Oligocene Frio Formation are part of a thick, regionally extensive sandstone trend that underlies a concentration of industrial sources and power plants along the Gulf Coast of the United States.
|Monitoring strategy at Frio.|
The team then measured and monitored the CO2 plume using a diverse suite of technologies in three intervals: the injection zone, the area above the injection zone, and the shallow near-surface environment.
Each monitoring strategy used a preinjection and one or more postinjection measurements. Wireline logging, pressure and temperature measurement, and geochemical sampling were also conducted during injection, and at follow-up intervals subsequent to the injection.
While the sequestration to-date has been successful—there have been no detected CO2 leakages—the researchers conclude in their latest published assessment of on-going findings and analysis that the chemistry of the process might prove problematic.
Fluid samples obtained from the injection and observation wells before CO2 injection showed a Na-Ca-Cl–type brine with 93,000 mg/L total dissolved solids (TDS) at near saturation with CH4 at reservoir conditions.
Following CO2 breakthrough, samples showed sharp drops in pH (6.5–5.7), pronounced increases in alkalinity (100–3,000 mg/L as HCO3) and Fe (30–1,100 mg/L), and significant shifts in the isotopic compositions of H2O, dissolved inorganic carbon (DIC), and CH4.
Geochemical modeling indicates that brine pH would have dropped lower but for the buffering by dissolution of carbonate and iron oxyhydroxides.
This rapid dissolution of carbonate and other minerals could ultimately create pathways in the rock seals or well cements for CO2 and brine leakage. Dissolution of minerals, especially iron oxyhydroxides, could mobilize toxic trace metals and, where residual oil or suitable organics are present, the injected CO2 could also mobilize toxic organic compounds.
Environmental impacts could be major if large brine volumes with mobilized toxic metals and organics migrated into potable groundwater.
“Gas-water-rock interactions in Frio Formation following CO2 injection: Implications for the storage of greenhouse gases in sedimentary basins”; Y.K. Kharaka, D.R. Cole, S.D. Hovorka, W.D. Gunter, K.G. Knauss, B.M. Freifeld; Geology: Vol. 34, No. 7, pp. 577–580 doi: 10.1130/G22357.1
Monitoring CO2 storage in brine formations: lessons learned from the Frio field test one year post injection
Sounds like the same issue with storing nuclear waste; it works now, but how long does it work?
Posted by: John Ard | 31 July 2006 at 08:01 AM
It doesn't matter. By the time we get serious about sequestration, it will be too late.
Posted by: t | 31 July 2006 at 08:10 AM
Geological evolution and events, combined with human intervention will provide pathways for the sequestered gas to migrate to the surface. The same way natural gas and oil find its way to the surface, is the same way sequestered CO2 will get back into the atmosphere.
Posted by: allen Z | 31 July 2006 at 08:56 AM
Depending on the site/depth/process chosen, it may take anywhere from weeks (poorly chosen and managed projects) to millions of years (due to changes in plate tectonics and climate-erosion patterns).
Posted by: allen Z | 31 July 2006 at 08:58 AM
Why don't you just plant Jathropa trees on the not yet affected site. Jathropa trees love Co2 and their seeds make a good Biodiesel feedstock.
Look, no handwringing required.
Posted by: Joseph | 31 July 2006 at 09:03 AM
On the other hand, who wants a minefield of suffocating gas, waiting to be released? Who wants a Lake Nyos in Kansas or Saxony?
Posted by: allen Z | 31 July 2006 at 09:09 AM
I think the factors that will kill CCS are the capital cost, power penalty and need for subsidies, not gas leakage. Meanwhile the fossil fuel industry has had a great few years telling us the CO2 problem was solved. They didn't see the contradiction in telling us that coalbed methane needs to be drilled and tapped as it will always migrate to the surface.
BTW nuclear waste is supposed to buried in deep dry rocks in containers that prevent reaction with the host rock. If nongaseous nuclear waste escaped it should migrate down, not up.
Posted by: Aussie | 31 July 2006 at 09:35 AM
So little faith. One report of a field test comes out. Panic. Anyone notice the words 'suggests', 'if', 'could', 'potential'?
Read this again " While the sequestration to-date has been successful—there have been no detected CO2 leakages—"
I have never thought sequestering would be cost effective at the scales needed to make any difference. But thoughts are not facts and it should be thoroughly evaluated.
There are ways sequestering might work even if the first tests disappoint. Perhaps only some formations will have troubles. Other sinks, with slightly different geology might work well. Adding other chemicals might prevent problems with toxic metals and carbonate (even if those actually are problems which is not proven). Average leakage may be so slow it doesn't matter - is it 1% a day or 1% a century -we don't know.
The neighbors dog will have more effedt on your life than this report.
Posted by: K | 31 July 2006 at 10:48 AM
Good timing. I'll add a link to this post from mine. It's about the problems with geosequestration in general (mostly an overview taken from Tim Flannery's The Weather Makers):
Posted by: Michael G. Richard | 31 July 2006 at 11:06 AM
Could we tap into the sequestered CO2 to feed algae ponds that make alt fuels. Would sequestering then be cost effective?
Posted by: joseph | 31 July 2006 at 11:56 AM
This new study is an argument for using mineral carbonation instead of physical trapping. Mineral carbonation is exothermic, so the CO2 cannot escape without an external energy source.
Posted by: Paul Dietz | 31 July 2006 at 12:47 PM
Yes, but piping/transporting the gas from gas source to a production site would be better, unless the algae has significant downtime, like winter. Additionally, the water would be acidic.
Posted by: allen Z | 31 July 2006 at 02:03 PM
This is the rag-doll epilepsy typical of environmental news media. No science involved, just reflexive doom-seeking. If it ain't doom, it ain't environmental news, friends. Get the data, dukov.
Posted by: Juarez | 31 July 2006 at 05:41 PM