Why not CO2 Sequestration?

CO2, as the world's politicians are now learning, is a GreenHouse Gas (GHG) that is now warming the world. Mostly, this is because we are burning a lot of fossil fuels, which Gaia (or early life), locked up into coals and oils, largely to keep the earth cool by taking the CO2 from the primordial atmosphere.

For life to survive, at least life as we have come to know it, we have to reduce the volumes of CO2 we release. Already, we have increased the concentration of CO2 in our air from about 245 parts per million to around 320 ppm, and all predictions suggest that, unless we do something serious about it very soon it will reach 500ppm or much more within the next century or so. As well as making the earth hotter - indeed, there are fears that it could trigger a runaway effect that could make the earth as hot and inert as Venus - this may well have an impact on us and on the life with whom we share the planet. We live our whole lives immersed in the only atmosphere we have, and it has changed a lot from what our ancestors (even perhaps our grandparents) were used to.

This is what Kyoto is about. Building a set of international laws that help us all, fairly and honestly, limit the CO2 we form and release.

We can, of course, try and capture CO2 and lock it up where it does no harm to the atmosphere - the sequestration route. And there are ways of doing this:

  • Grow Trees, or other biomass. Of course, this idea is not new, as Gaia did a lot of this during Carboniferous times. And growing trees is undoubtedly a Good Thing. But we do not yet know how to convert trees into the dense solid, material we recognise as coal that can be safely locked away for the many millennia it has already existed. So it is undoubtedly better not to destroy coal, rather than to burn coal and try to make it again from growing trees.
  • Store CO2 itself. The general principle is that we take the coal (or oil or gas), burn it and extract the energy (probably in a most fantastically inefficient way), remove the CO2 from the combustion products, and put this CO2 back where it came from.

The trouble is that nobody has found a way of doing this safely. The establishment (scientific, political, industrial) seems to believe this can be done safely, by pumping the CO2, at very high pressures, back into the reservoirs from which we have extracted oil. Indeed, there are various projects, to try this out, and there are many reservoirs which do this to push more of the oil out of the reservoir, so called Enhanced Oil Recovery, or EOR. So there are old oil reservoirs which hold many millions of tons of CO2, and have done so for several years, even decades.

The Air Pollution and Climate Secretariat (www.airclim.org) has done a more thorough job of documenting the Carbon Capture and Storage (CCS) than I can, and an excellent report is available from them (Last gasp of the coal industry).

Let us have a little thought experiment: What happens when this CO2 escapes. For us in the UK it is perhaps most helpful to think if this as happening under the North Sea.

  1. The CO2 might escape slowly. So it will leak out, perhaps through some complex and slow route of porous rocks. So long as there is no life that gets suffocated on this route from reservoir to atmosphere, no great harm is done, although, of course, there is no benefit to the atmosphere, which ends up with the CO2 we tried to hide.
  2. The CO2 may escape fast, in some sort of catastrophic release lasting, perhaps, a few days. Given the huge pressures under which it would be stored, and the likely rapid corrosion of any leakage hole, this seems more plausible. An earthquake would be very good at opening such holes.

Before going into further detail of this scenario, let us review some things known about CO2:

  • It suffocates us. Too much CO2 in our air prevents us benefiting from breathing, and kills us quite quickly. It also kills all animal life.
  • It is heavier than air. Brewers learn early in their careers (or not at all) not to lean too far into a vat of fermenting brew, or it could suffocate them.
  • Put these two together, and what happened around Lake Enyos is one of the first warning we have had (at least that we know about). This incident killed some 1700 people, but there have been others since.

Now let us consider the North Sea:

  • There is a rumour of dead fish floating is the sea, but a fishing boat heading that way falls mysteriously silent.
  • A Sea Rescue Helicopter approaches the vessel, reports some sea foam, but also falls silent and crashes. Remember that virtually all our power sources depend on combustion that will be suffocated by high concentrations of CO2.
  • A ship approaching a patch of foamy water sinks. Bubbles in the water lower its density, so less can float in it. So a ship would suddenly find it was floating on air, and would sink.
  • The CO2 will, of course, be cold from expansion, enhancing its natural tendency to spread at low level. With luck, it might freeze a patch of sea for a while. At this point, there is virtually nothing that anybody can do except estimate what will happen. No planes can fly close. How quickly will the small leak grow, considering the huge pressures involved? Which way will the wind send the cloud? How much CO2 will escape? We could be in the position of the designer of the Titanic, able to calculate only how long we have left?
  • If the cloud headed for London, there is no possibility of evacuating the population in time. It could take less than 12 hours to reach the capital. But it might head for Norway or Scotland.

One of the most disturbing aspects of this scenario is that it never goes away. Unlike radiation, the CO2 stored underground has no half life. It does not become less risky as time passes. It is there until it escapes.

So I do not find this an attractive way to obtain our energy, and wish to see these risks (or future certainties) recognised by those contemplating the actions that lead to them. Hence this collection of information, and its release to the Web.

Fortunately, we do have time before this becomes commercially attractive. Unfortunately this is because the price of CO2 is ridiculously low, at about €20 per ton, and the costs of putting the CO2 back are far higher than that. So let us use this opportunity to prevent this ever happening.

David Hirst

Here are some links to relevant resources.

On Enhanced Oil Recovery

More later.

Updated 26th December 2008

Page Version 0.6, First released draft. 8th November 2002