Thinking through carbon sequestration

I've been trying to figure out what to say to my classes about carbon sequestration. As Brian mentioned in a comment, if we're going to lock carbon dioxide in rocks (well, artifically*), geologists are going to need to be involved.

I ought to be able to think through the problem from first principles. Carbon dioxide is part of all sorts of natural systems, after all. When it dissolves in water, it makes the weak acid that is responsible for much of the natural weathering of silicate minerals. It's released by metamorphic reactions, and the relative amounts of carbon dioxide and water in metamorphic fluids is important in determining which minerals are stable. It's one of several gasses that dissolve in magmas, and is important in its own ultra-weird magmas: carbonatites, which erupt molten baking soda in the East African Rift (and which concentrate rare earth elements in old deposits). At low temperatures, carbon dioxide, carbonic acid, bicarbonate, and carbonate ions make a fascinating buffer system. (I don't think I explained that one very well, the one time I taught environmental geochemistry. But it's still a fascinating system.)

And that's just the chemistry. There are also questions about fluid flow through rocks and fractures, and about possible rock fracture associated with high fluid pressures. It's hard to know exactly where to start, especially because the info sources that I've read don't try to explain things from first principles.

So how, exactly, is this carbon sequestration supposed to work, and how does it relate to all the various CO2 factoids that I've accumulated over time?

The answer depends on the rock and fluid involved, it seems. A number of possible environments have been proposed, and the issues are somewhat different for each one.

1) Use waste CO2 to enhance recovery of oil and gas. I was vaguely aware that carbon dioxide was used to help recover more oil from old oil fields (mostly because CO2 is produced near Durango - it's actually a commercially produced commodity). I didn't know much about how it works, though - was it used to increase the fluid pressure in the rock, and force the oil out, or did the CO2 dissolve in the oil and change its properties? It turns out that both happen. Yes, the carbon dioxide changes the fluid pressure. But it also dissolves in the oil and makes it flow more easily, which makes it possible to recover more of the oil.

This is already being done - in fact, carbon dioxide is produced commercially to be used in oil fields. So it makes sense to capture waste CO2 and use it instead. (Perhaps this should be considered CO2 recycling rather than sequestration, however - I assume that CO2 dissolved in the oil comes back to the surface with the oil. Not that there's anything wrong with recycling - make less waste, use if for useful purposes instead. But it doesn't take the CO2 away forever.)

2) Pump the CO2 into coal. The methane that adsorbs onto the surfaces of coal has become a commercially important source of natural gas (especially in the San Juan Basin, just south of Durango). Traditionally, the methane is released by pumping water out of the coal. But carbon dioxide also adsorbs onto the surfaces of coal. Maybe CO2 could be used to enhance coal-bed methane production, too.

This technique is being tried in my backyard. If it works, it's got a lot of potential, because coal-bed methane and coal-burning power plants (as a source of carbon dioxide) can be very near one another. (In fact, there are currently two coal-fired power plants near Farmington, New Mexico.) I don't know much about the surface chemistry of coal, so I don't have a good sense of what factors could make this work or not.

3) Pump the CO2 into deep, salty formation water. This is the target of the experiment that Lee Allison described today. I'm not entirely certain of the characteristics of the ideal "saline formation" sequestration project. I think the idea is that a) the salty water is isolated from useable groundwater, probably by some kind of low-permeability cap (like a classic oil reservoir would have); and b) the salty water would make a good chemical buffer for the carbonic acid. I'm not sure of the chemistry of the buffering - this is where I wish that I remembered the complications that happen in the systems of carbonic acid, bicarbonate, and carbonate when there's something in the system other than calcite and carbon dioxide. (I'm guessing that the high concentration of dissolved solids helps buffer the system, since the focus isn't entirely on limestones.) I'm also not sure how the dissolution of carbon dioxide in water affects the potential for problems with increased pore fluid pressure. (Increasing the amount of fluid in rock can make rock break. If you want to get oil out of the rock, this is a good thing; if you want to keep carbon dioxide from escaping, I'm guessing that it would be bad. Unless you can make the reservoir rock more permeable without breaking the less permeable cap?)

And this doesn't include ideas about using carbon dioxide to speed the weathering of silicates. (I think that's partly what's going on with the suggestions to sequester carbon dioxide in basalt, for instance.)

So I'm not sure how to discuss the issue in intro classes. I think I need more information. I would like to tell them about the ideas that have been proposed, however - particularly because some are happening in our own backyard.

*Carbon is naturally locked in rocks like coal, oil shale, and limestones. We let it out when we burn oil, coal, or natural gas, or when we make cement. But natural processes don't remove carbon as fast as we burn it for energy. So if we want to use fossil carbon for energy, and we don't want to deal with the consequences of putting all that carbon dioxide in the atmosphere, we've got to do something to speed up the process.

Sprawl and the solar energy space problem

I've been fascinated by solar energy since the late 70's, but I recognize that there are practical problems associated with using it to replace fossil fuels right now. Efficiency of photovoltaics, cost, storage... ok, yeah. But there's one problem that has had me scratching my head since I moved to the Southwest: finding a place to put the panels.

The arguments seem to assume that the energy must be produced on land that's currently open space, disrupting the ecosystems more than a coal mine. But I look around me and see the ecosystems disrupted anyway... by shopping malls and big box stores and parking lots. And I've wondered: why couldn't all those rooftops be used to generate electricity?

Well, it turns out that they can be.

According to the New York Times, stores as diverse as Wal-Mart and Whole Foods are installing solar panels on their roofs. The efforts are concentrated in places with major tax incentives (which include New Jersey and Connecticut, which don't strike me as the best places for solar power) - the panels are still too expensive to compete with coal and natural gas. But if the costs change... Arizona and New Mexico, I'm looking at you.

And if that works, you know, they could cover those acres of parking lots with roofs, if they want more space.

Resources, environment, and teaching intro geoscience in the 21st century

The Teaching Intro Geoscience workshop ended with small-group discussions about what's different about teaching intro geo courses in the 21st century. The discussion was spurred by the workshop's tag - the On the Cutting Edge series features lots of workshops on "Teaching X in the 21st Century" (where X has equaled petrology, structural geology, hydrology, sedimentary geology, geophysics, geomorphology, and intro geoscience), but we weren't talking as much about what's new as about how to teach effectively, period.

The summary of the discussion hasn't been uploaded yet, and I don't remember it well enough to summarize it. (As a friend likes to say, "I've slept since then.") But I want to talk about something that I was thinking about, but didn't say (because I was talking too much already).

The geosciences are central to understanding and dealing with big problems that humans are dealing with right now. We've said this in the past, but suddenly the geosciences are on the front page of newspapers (even when there hasn't been an earthquake, a volcanic eruption, or a flood) and are central to election issues. High prices for gasoline and natural gas, and the proposed solutions (wind, sun, nuclear, geothermal, new drilling offshore, oil shale, gas from shale, coal gasification, coal-bed methane), and the potential environmental costs of the various solutions (global warming, nuclear waste disposal, impacts from mining everything from coal to the components of solar panels, oil spills, groundwater contamination) - geoscientists contribute to understanding all of these things. For as long as I've been in geology, we've been talking about this stuff, but during the last fifteen years, few of these issues have grabbed students' attention. But the world is different - different again, for those of us shaped by the economy of the 1970's, but different for the first time for the majority of intro students.

The misconceptions we've got to deal with are overwhelming. I've recently realized that many people don't realize that methane (the greenhouse gas released by burping cows, among many other sources) is the scientific name for natural gas (the stuff that heats their home, and the fuel that T. Boone Pickens wants to use to replace gasoline in cars). And that natural gas is different from oil (and the various things that come from crude oil, such as gasoline and diesel fuel and #2 fuel oil and plastics and asphalt), but that propane can be produced from both natural gas and crude oil. And that coal gasification and coal-bed methane are different things. And that the sun's light hits Earth at different angles in the summer and winter (and that the sun is not closer in the Northern Hemisphere summer), and if you want to design effective home solar panels, you should think about that. And that the direction the wind blows depends on many things, and isn't the same all the time. And... and... and...

I don't handle resource geology very well. I'm one of those people who has taught it at the end of the semester, crammed into one discussion, and it hasn't usually gone well. (Not even when I start it by making students brainstorm a list of all the resources that they use when driving to the mountains to go skiing.) Part of the problem is my background: I grew up in the 70's as one of the "damn Yankees freez[ing] in the dark" and got into geology in the 80's because I liked water, and I became a hard-rock geologist in the early 90's, when the only resource geologists getting jobs were hydrologists. But maybe my background could also be a strength now. I've never worked for oil or mining (and was briefly an environmental geochemist), but I know plenty of people who do. (That's one side effect of being the past president of an AAPG-affiliated society.) I've taken oil money (Arco funded my graduate advisor, and Chevron, Shell, and Mobil had all endowed funds that supported graduate students), but am familiar with the overwhelming evidence for human-caused climate change. (I read the literature, I've been a member of AGU, I know climate researchers and trust their competence as scientists.) I don't think that demonizing either environmentalists or oil/gas/mining companies gets us anywhere close to solving the tough problems we've got to deal with.

So I'm thinking about what to do. I'm teaching Earth Systems Science, which gives me both opportunities and constraints. I can't simply structure an entire intro course around resource problems (though that could make a good topical intro course), but I can fit resources into the theme of big geochemical cycles. (Too bad I don't really structure my course using an earth systems approach - my one attempt left students saying "Earth is a complex system and we can't understand it," which was not the response I had hoped for.) Maybe I can use resource issues as case studies for discussions of all sorts. Maybe I should find a way to talk about organic stuff (like petroleum and coal) in my minerals section - they aren't minerals (because they're organic), but they are important chemical components of rocks. I could talk about what makes oil, coal, and natural gas in my discussion of sedimentary rocks. I could figure out some way to talk about fracture mechanics (and why cracks are important for both water and natural gas, and why they are potentially dangerous in places like the Crandall Canyon mine collapse) when I'm talking about earthquakes and structural geology. I already talk about climate change, but I could work in some kind of final brainstorming session that ties everything together. (Was that vague? I swear, before I do anything in class my instructions will be more specific.)

What would you do? What misconceptions have you encountered about resources? How would you deal with them - especially when it comes to misconceptions that are entrenched in political beliefs, from the Right or the Left?