The deep blue C

As a palaeontologist specializing in old, weird sea-life, I have never been very useful.  Good company but of little practical value, my headstone will say.

"There is much pleasure to be gained from useless knowledge."

In the last few months, though, this has begun to change.  By a combination of opportunity and availability, I have suddenly found myself working in two very topical areas of applied Earth science: shale gas, and carbon capture and storage.

The former is the more media-bewitching, perhaps because it allows journalists to use the word 'fracking' with schoolboy abandon.  The latter, however, is a bit less easily dramatized, so it tends to get a lot less attention.  This is a pity, because CCS is potentially very important to our energy future, and Yorkshire looks set to play a key role in its development.

NASA map of global atmospheric carbon dioxide, July 2008.

If there's a moment to do so in the midst of our shivering, the recent cold snap should make us think about how best to power Britain.  Only a numpty would argue against us moving in a greener direction, but the cost, complexity and politics of renewables means we won't be weaned off fossil fuels any time soon.  An inspection of the sources of UK daily power consumption shows just how far we have to go.

As a consequence, stepping stones are needed to reduce our greenhouse gas emissions.  CCS is one possibility, and as its goal is the permanent geological storage of carbon dioxide, this is a step in which the stones are critical.

The basic premise of carbon capture and storage is as follows:

1. Fit chemical filters to power stations and other major emitters, capturing CO2 before it is released into the atmosphere;

2. Condense the captured CO2 into a 'supercritical' state and use gas pipelines to transport it out to the North Sea;

3. Inject the CO2 into rock formations deep beneath the sea, from which it cannot escape.

Hey presto! A major shrinkage in our carbon footprint.

Carbon-dated footprints

Of course, it's not that simple.  The technology is already available for all three stages - the Norwegians have been capturing and storing carbon in their giant North Sea gas field, Sleipner, since 1996 - but the UK has never managed to integrate them.

That looks like it's about to change, though, with the recent Budget announcing major financial support for two CCS proposals, including Yorkshire's own White Rose Project, based at Drax power station.  The funding doesn't guarantee the projects will happen, but it is at least a statement of intent.

A vast volume of storage space is present in the rocks beneath the North Sea; huge quantities of CO2 could be sequestered in networks of tiny pore spaces.  One of the remaining uncertainties, though - and the one I have become involved in trying to understand - is how geological variabilities affect where the carbon dioxide goes once it is injected into the rocks.

Sandstones make the best prospects, as not only are they porous, but the pores are interconnected.  This permeability enables the injected carbon dioxide to move as a plume through the rock and fill the reservoir.  If the sandstone is a saline aquifer - a reservoir full of extremely salty brine - the CO2 will begin to dissolve into the saltwater.  Eventually, the CO2 will become trapped in the pore spaces and precipitate as a cement in between the grains.

Image from CO2 CRC, Australia.

This isn't a fast process, so you need to know the injected carbon dioxide will not only fill the chosen reservoir, but stay there.  When choosing a geological site for storage, then, you need large bodies of sandstones that aren't faulted or fractured.  You also need them to be overlain by an impermeable cap rock.

Conveniently for the White Rose project then, the Triassic sandstones off the East Yorkshire coast look very promising indeed.  They were deposited by desert rivers about 250 million years ago, when Britain lay in much warmer climes.  Eventually the desert sands got buried and turned into sandstone, and - later on - folded by tectonic forces into gentle domes.

Triassic Yorkshire

These sandstones have few faults in them, are often filled with brine, and are capped by impermeable salts or shales, making them extremely attractive CCS reservoirs.  The Crown Estate, which owns the seabed to a distance of 12 nautical miles* and holds the rights for carbon storage out to the continental shelf, has recognized this.  In a statement issued a few weeks before the Budget, they gave the National Grid permission to look into storing CO2 in a saline aquifer 70km offshore of Filey Bay.

Exploratory drilling into the reservoir could start as early as May.  With the North Sea gas pipeline coming onshore at Easington, and the Drax power station employing carbon capture technology, Yorkshire's CCS elements begin to come together promisingly.

As Easi as CCS

Doing all this isn't going to be cheap, but development costs might be offset by selling some of the captured CO2 to petroleum companies.  This might sound a bit odd, but injecting it into petroleum reservoirs is a proven method of enhanced oil recovery, or EOR.  It could provide two years' worth of UK oil supplies from existing fields, and would be lower impact than opening up new ones.

Not unreasonably, some people are sceptical of CCS, arguing that it will just allow the continued exploitation of fossil fuels, without facilitating a move towards greener energy.  They could be right; I think it depends on the political will to put a long-term renewable energy plan in place.  There may be ways to make the White Rose Project greener, though, so Yorkshire's role in powering Britain cleanly could be even more important than it already looks to be.

Furthermore, if they are going to build a slew of new fossil-fuelled power stations, the government should follow the advice of the Institution of Mechanical Engineers and ensure they are all fitted with CCS technology.

This would send out a stronger message of intent, especially if UK interest in shale gas takes off.  But that's another fracking story.

*and right down to the centre of the Earth, which leads me to imagine the Queen sitting in Buckingham Palace of an evening, poring over seismic cross-sections of the British Isles, planning how best to imitate Jules Verne.