"Our greatest responsibility is to be good ancestors."

-Jonas Salk

Monday, December 14, 2009

Carbon Sequestration Validation

So much for keeping a low profile at Fall AGU.

Oh well, as my putative scientific career finally evaporates altogether, I suppose it's good to have a mission. I'm going back to my self-defeating old habit of always being most interested in the things I know least about. This is pretty self-defeating scientifically, but maybe now that Revkin is semi-retired I can find a niche for myself as a science reporter. So consider me your man on the scene.

My favorite of the talks I attended today was by Sally Benson of Stanford, an invited talk on verifying carbon sequestration.

As another carbon sequestration speaker said, "it's all about the credits": energy interests aren't especially interested in carbon sequestration unless and until we put a price on carbon, but once we do so, they'll be very interested in it. Of course, this is a famously scrupulous and fastidious industrial sector, so we can presume they won't cut corners and just pump carbon randomly into pipes in the ground whether it will stay there or not. But just in case, perhaps it would be best if we could somehow discriminate actual sequestration from random pipes into the depths.

Sarcasm aside, there's little doubt that a significant amount of CO2 can be hidden underground. There's every evidence of serious people doing serious experiments to demonstrate all the pieces. And in the end, some form of sequestration is necessary to reverse carbon concentrations; whether it's what is now being called CCS or not, some way of taking carbon out of circulation in massive quantities is already the legacy of our generation, and likely of a generation or two to come.

It's the case that vast ancient deposits of methane remianed underground for millions of years. So gas can stay underground. It's also the case that we can pipe gas underground; the oil industry already does this to increase extraction. It makes sense, when you pull a resource fluid out, to pump its waste product into the same hole. (It's not really a hole. It's gaps in a granular medium. There never was an ocean of oil under that gusher.) But just because it's possible doesn't mean it's easy.

A leakage rate of 1% a year is as good as worthless. Even 0.1 % leaves only 37% of the gas underground after a millenium; you really have to get to 0.01% before the project starts doing substantial good (90% after a millenium) and a good goal is a leakage rate of 0.001% (99% after a millenium, 90% after 10,000 years).

And it's easy to get it wrong. Put too much gas underground (thereby avoiding building an expensive new facility) and you start inducing cracking in the cap rock (before I got to Texas, "cap rock" was not even in my vocabulary!) and your leakage rate starts to skyrocket.

Now in field tests, you can drill holes to check your theories, but in an actual deployment, I figure you can't be drilling too many holes to get samples. (I'm not actually sure about this, but my intuition rebels against making a swiss cheese out of your cap rock to make sure it is intact.) Anyway, Dr Benson's talk was about how to determine if you were getting the sequestration to work. The idea is that a regulator could refund you carbon points if you were successfully burying your carbon.

OK, so now there are two ways to proceed. You could try to measure the inventory, or you could try to measure the leakage. Both are problematic. You measure the inventory using seismic inversion; essentially sonar. The trouble with the sonar methods is twofold. First of all, it's messy: a lot of people make a career of having enough intuition to look at these things and find good places to explore or drill for this or that (usually that). Also, some CO2 dissolves or reacts. Even if your sonar were absolutely perfected you could easily lose 10 to 20% of your inventory. That is far too much uncertainty to be of use here.

The other approach is to look for leakage at the surface with arrays of sensitive CO2 detectors or isotopic measurements, to find sources of fossil carbon-based CO2 which is C-14 depleted. A source as "small" as 100 tons/year can be detected. Compare this to the rates of sequestration at a commercial site, on the order of 50 megatons of carbon inventory.

So that's sensitive enough. Are we done?

No, because the test is expensive and tightly focused in space, while the artificial reservoir is as large as 100 square kilometers. You have to kn ow eher to put the sensors. Here, though, is where seismic imaging does work. It can tell you something about the structure of the subsurface and give you good candidate locations to look for leaks.

Are we happy yet? Benson thinks so.

I have some doubts, myself. (The following is not part of Benson's talk but speculation of my own.)

The time scales are at issue. How long between springing a leak and detecting it? It seems like it could easily be decades before the leak erupts to the surface: very fast by geological standards but very slow by commercial ones.

Commercially, as a carbon combustion business, I want to be rewarded for my good deeds (really, non-penalized for my non-bad deeds) immediately. But as a government, I don;t want to credit you with the sequestered carbon until it doesn't leak. Most businesses will not take a thousand year lead time on their investments. So the problem, ultimately, isn't technical. It's the same old social problem. We don't know how to think on long enough time scales to make incentives for effective carbon sequestration work. Or so it looks to me. Did I miss something?


Elmar said...

Much safer than pumping CO2 underground: mineral sequestration. http://www.springerlink.com/content/78528604337v3773/

Unknown said...

Hi Michael, long-time reader, first time commenter!

I was wondering if you know much about the work of the Indian scientists who published on the carbonophage (what's the right term for this?) bacteria? They consume the carbon dioxide and leave behind calcium carbonate. This could potentially reduce the leakage, as well as the total gas stored in the deposit? I think maybe more likely to be important as a cement to fill the holes and cracks in the Swiss cheese than to make much of a dent in the total volume of gas. Though, I'm not sure what kind of conditions they are tolerant of, which would no doubt be critically important.

Trying to track down the publication in the meantime.

Lou Grinzo said...

As for the "will it work" part, I don't think you missed anything. I'm highly skeptical of CCS technology, as much I want it to work. (Getting close to the massive CO2 reductions needed in the US will be vastly easier if we can master CCS technology.)

Also, there's the issue of liability. A corporation pumps a bazillion tons of CO2 into various holes in the ground, and 20 years later a previously unknown fault causes a massive CO2 release that results in hundreds of human deaths. Then what? Once we decide who pays ow much to whom, what happens to all the other CO2 pumped into the ground before and immediately after this incident? Do we then abandon CCS?

Michael Tobis said...

Elmar, thanks for your comment.

Paul, same. I'm no expert on CCS and I haven't heard of this. Let us know if you track it down, thanks!

Michael Tobis said...

Lou, I don't think the sort of gas release you postulate is plausible. Else it would already be happening with natural gas. 100 tons per year which would constitute a leak sounds like a lot, but it only amounts to a diffuse source of a few hundred pounds per day, which amounts to the same amount of stuffiness as if a few hundred people were breathing.

The toxic risk, if any, is from the pipelines. However, pipelines for toxic gases already exist, and I believe commercial CO2 pipelines already traverse Albuquerque shipping Colorado mineral CO2 deposits to the Permian Basin oil extraction region in Texas for enhanced oil recovery.

I think this isn't a big issue.

The issue I am raising is the incentive to overfill the reservoir and crack it. This amounts to paying companies to do something that would be useful if they did X amount of it and useless if they did 2X, where X is not easily determined.

Michael Tobis said...

Wilmot McCutcheon adds the following on Energy Collective:

The U.S. Government Accountability Office (GAO), in a report dated 9-30-08 http://www.gao.gov/products/GAO-08-1080 showed that CO2 sequestration is a dubious proposition. Not only might CO2 eventually leak out to the atmosphere, but there could also be localized eruptions that could kill people. Sequestration involves pumping huge amounts of CO2 underground at very high pressure and hoping that there will be no earthquakes or caprock fractures that might breach containment. We are talking about billions of tons each year. One 600 MW coal plant produces 5 million tons of CO2 each year, and the enhanced oil recovery (EOR) needs of the entire Permian Basin in Texas are only 7 million tons. So what is the alternative? Cracking CO2 by electrolysis, to produce carbon monoxide which can be used for synfuel. See http://www.freepatentsonline.com/y2009/0200176.html The energy for cracking (5.5 eV) should come from wind and solar, providing a way for renewable energy to be used without connecting to the grid.

Anonymous said...

I'm worried about the volumes of gas. Basic zero order magnitude estimate.

The volume of carbon will expand thousand fold when it is burned. You can't put it undergrounds because there is no space for it. So for every coal mine you need 999 other similar size empty spaces to put the CO2 to. It doesn't compute.

Unless you do something fancy like very high pressures or cold temperatures.

But not as a gas.

Sequester coal. It's by far the most efficient way to store CO2.

Sam said...

Hi Michael - I am a post-doc for Prof. Benson and I just wanted to point out that the surface monitoring technology Prof. Benson highlighted to obtain a ~100tCO2 monitoring resolution at the surface was not dependent on the measurement of C14, but rather the measurement of C13.

This measurement can be done much more cheaply and quickly than C14 and we are involved in research showing that it can be deployed over the large spatial scales (~100km^2) and at the resolution required (see presentation H13I-04).

Steve Bloom said...

The long-term leakage issue is much less important if the CO2 is from biomass burning.

Unknown said...

Ahh, found it!

I'm reading it now. They isolated the enzyme and are talking about using it in reactor tanks, also the activity of the enzyme might not work too well at such high concentrations of carbon dioxide. Not sure if subterranean hydrocarbon deposits would work so well, at least not yet.

David B. Benson said...

Paul --- COuld you kindly scan in the title, authors and abstract. Most of us won't have access to the Nova Scotia Agriculturla School library...

Unknown said...

Oh, sorry David. Forgot about the proxy...

Ramanan, R., Kannan, K., Sivanesan, S. D., Mudliar, S., Kaur, S., Tripathi, A. K., and Chakrabarti, T., 2009. Bio-sequestration of carbon dioxide using carbonic anhydrase enzyme purified from Citrobacter freundii. World Journal of Microbiology and Biotechnology, 29, 981-987.

The increase in the atmospheric concentrations of one of the vital green house gasses, carbon dioxide, due to anthropogenic interventions has led to several undesirable consequences such as global warming and related changes. In the global effort to combat the predicted disaster, several CO2 capture and storage technologies are being deliberated. One of the most promising biological carbon dioxide sequestration technologies is the enzyme catalyzed carbon dioxide sequestration into bicarbonates which was endeavored in this study with a purified C. freundii SW3 b-carbonic anhydrase (CA). An extensive screening process for biological sequestration using CA has been defined. Six bacteria with high CA activity were screened out of 102 colonies based on plate assay and
presence of CA in these bacteria was further emphasized by activity staining and Western blot. The identity of selected bacteria was confirmed by 16S rDNA analysis. CA was purified to homogeneity from C. freundii SW3 by subsequent gel filtration and ion exchange chromatography which resulted in a 24 kDa polypeptide and this is in accordance with the Western blot results. The effect of host on metal ions, cations and anions which influence activity of the enzyme in sequestration studies suggests that mercury and HCO3- ion almost completely inhibit the enzyme whereas sulfate ion and zinc enhances carbonic anhydrase activity. Calcium carbonate deposition was observed in calcium chloride solution saturated with carbon dioxide catalyzed by purified enzyme and whereas a sharp decrease in calcium carbonate formation has been noted in purified enzyme samples inhibited by EDTA and cetazolamide.

David B. Benson said...

Paul --- Thanks.

SOmebody might care to try this with peridotite or even just basalt.

Hank Roberts said...

> The time scales are at issue.
> How long between springing a
> leak and detecting it?

Well, consider an analogous situation -- doing an environmental impact report, where if your chosen consultant finds any of a list of threatened or endangered species (or perhaps a far longer list of species that should be on the official list but haven't been studied yet, that only the biologists know about).

In other words, if the result of finding a problem is a huge expense or loss of money, but the result of not finding a problem is business as usual -- what will happen? In the short term, that is.