31 December 2010

Geo-engineering II

Is there doubt about that we are playing very dangerous games with climate? No. There is no doubt at all that greenhouse gases are called greenhouse gases for a reason, and there is no doubt that we are hurling insane qualities of them into the atmosphere. There is also no doubt about that the system is somewhat inert, so that if you do that, and you don’t immediately suffer the consequences, it doesn’t mean there are no consequences. We have an excellent record, from air bubbles in ice cores, of past levels of such gases. And we know very well levels such as we have today have not occurred in the last ~900.000 years. And for going back further we rely on less ideal evidence, but that evidence shows clearly the last time we had so much CO2 in the atmosphere was 55 million years ago. We also know we are now changing the system at a speed that is seen rarely in the geological record, and if we see such large and rapid changes in the past they tend to be associated with mass extinctions. And there will be plenty of people who wish to brush all that aside and say it’s a left-wing conspiracy, but you need a certain flexibility of mind to do that. I’m not that flexible. I worry my head off. And I’m interested in the question of what we can still do to limit the damage.

The best thing to do would be simply not produce that much greenhouse gases anymore. How? Knowledgeable people have written excellent books about that, and I have in turn written about these on my blog. Let’s say it again; read the books by Tim Jackson, Chris Goodall and George Monbiot!
But it’s good to have several irons in the fire. We won’t stop exhausting large amounts of greenhouse gases tomorrow. So what about making sure that the methane we produce is used instead of letting it leak away into the atmosphere, and that the CO2 we produce is stored? That way we reduce our impact, even before we have weaned ourselves off fossil fuels.

We produce greenhouse gases all over the place. A cow burps, a car rides from A to B, I turn the central heating on… it’s not very concentrated. But heavy industry tends to exhaust lots of it at discrete places. They could, and with a financial incentive, they would capture it, and deal with it. How? This is another branch of geoengineering: carbon capture and storage (CCS). It requires some logistics. The best equipped are the oil companies. They produce lots of CO2, and they routinely transport fluids over large distances. So where to store it? There’s, as far as I know, a few options: in the deep sea, in minerals, in unmineable coal seams, in water-bearing geological formations, in salt caves, and in empty oil and gas fields.

I object to CO2 storage in the deep sea. It’s not very stable! The idea is that the CO2 is supercritical at such pressures, and would sit there, which that’s bad enough as it is; it would kill any life at that level. And I don’t trust the stability. The CO2 may bubble up when disturbed by a submarine landslide or an earthquake; it may get dissolved in the sea water with disastrous consequences… bad idea!

Storing CO2 in minerals is quite innocent; CO2 incorporated in a mineral to form a carbonate isn’t going anywhere anytime soon. The problem here is that you don’t tend to find large enough amounts of receptive minerals just lying around.

If you have coal seams that are so difficult to mine that mining them would cost more fuel that it would yield it might still be energetically viable to drill a hole into them, and pump CO2 in. CO2 sticks to coal better than methane does, so you get rid of it in a safe way, and you get methane for free! If you then burn that, and pump the thus produced CO2 back into the coal seam, you may get yourself some nice low-CO2 fuel.

If you have no coal seams around you may just pump your CO2 underground, if you have a layer of rock that’s permeable, and will hold the CO2, with a non-permeable layer on top of that. Porous rock will normally be water-filled, so you just turn the still water into sparkling water and Bob’s your uncle. Just make sure the CO2 can’t go anywhere, but there’s plenty of geological structures that provide that.

Salt is very impermeable, and occurs in big blobs in the subsurface. Sometimes these are used for salt winning, and in that case there’s space in them for CO2. Geologically they’re not stable, but on human time scales they are.

The storage space I like most is empty oil and gas fields. Especially gas fields. They have proven they can contain gas for millions of years. So they can also do it for a little bit longer. And there will already be a pipeline leading to them. And there will be a plant somewhere near, and that plant could be extended to include equipment that catches the CO2, if it doesn’t already have it. Oil and gas exploration often goes hand in hand, and oil refinery produces lots of CO2. Oil companies already pump CO2 into their oil reservoirs to make the oil less viscous, so in many places the entire infrastructure would already be in place. So all works together to allow at least one big player in CO2 exhaust to tidily get rid of its CO2!

I sometimes advocate this practice. And I’ve heard strange objections. People have seriously voiced the concern you would get land subsidence where you inject CO2. Subsidence? If you just empty a gas field you might get that. If you refill it with another fluid you avoid it. Another advantage.

Is this already done? Yes. Is there a financial incentive? To a certain extent. There is such a thing as carbon tax in many countries, but it’s still too low to really provide a strong push. Would an increased carbon tax move CO2-fuming industries to countries with no such tax? Perhaps, but I have never heard of this effect due to the initial establishment of carbon tax in the various countries.

Can it go wrong? Yes. Anything can go wrong. But chances are slim. A methane molecule is much smaller than a CO2 molecule, so a reservoir that can contain methane can contain CO2. Except, of course, that these reservoirs have been drilled into. But if you keep the pressure within limits the risk is small.

So should we do this? I think so!

1 comment:

Nils Gudmund said...

Thank you for this timely artcle.Happy nuew year to you!