Your article reported Houston University research which claims that "governments wanting to use carbon capture and storage have overestimated its value" (US paper raises doubts over viability of carbon capture, 26 April).

The carbon dioxide storage method injects the gas into the microscopic pores of reservoir sediments below 800 metres underground, in order to reduce atmospheric levels of this greenhouse gas. Scientists internationally are attempting to evaluate it. The argument you report is derived from a notorious pair of articles by Michael Economides and Christine Ehlig-Economides.

Economides says: "It would be hard to inject CO₂ into a closed system without eventually producing so much pressure that it fractured the rock and allowed the carbon to migrate to other zones and possibly escape to the surface." That proposition is clearly wrong. The largest storage site in the world has injected 12m tonnes of CO₂ over the last 13 years, not "a million tonnes over three years" as they asserted.

Consider the oil trapped in subsurface reservoirs. It is well understood that oil is not generated where it is discovered, but has moved many kilometres vertically and laterally through layers of sediment. That informs petroleum geologists (such as us) and should inform petroleum engineers (such as Economides and his co-author) that a reservoir is not a "closed system", but transmits fluids to its surroundings. The pressure spreads into a large subsurface volume (like a leaky car tyre) and does not increase in the reservoir rocks as they suggest.

The Economides calculations rely on bizarre assumptions, leading to the erroneous claim that "it would take a reservoir the size of a small US state to hold the CO₂ produced by one power station". Their argument is, literally, full of holes. Firstly, storage capacity estimates differ between the first and second of their articles by a factor of 10, with no explanation and no change in their conclusions. Secondly, the calculation assumes that the "small US state" is underlain by just one reservoir, just 10 metres thick.

Economides professes that "geologists [do] not understand flow and the laws of physics", but he clearly fails to understand the geology. Multiple porous sandstones often exist below ground, with cumulative thicknesses of many hundreds of metres. Thirdly, there have been some 20 experiments of CO₂ injection over the past decade. Only one has experienced the alleged pressure problem of "a bicycle pump against the wall".

By contrast, detailed work on six continents has convinced hundreds of impartial geoscientists that massive capacity for CO₂ storage exists. The UK is especially fortunate as rocks similar to those which host our oil are anticipated to store 100 years of CO₂ from all north-west Europe's power plants. This can buy us time while truly sustainable energy sources develop to limit climate change. But climate change is something else Economides and his co-author don't believe in.

Stuart Haszeldine and Martin Blunt

www.gusrdian.co.uk

04 May 2010