Kate Mackenzie A very technical CCS controversy

Carbon capture and sequestration is nothing if not controversial. The cost, effectiveness and the public reaction to extracting CO2 from coal- or gas-fired plants and storing it underground are still hotly debated, and likely will continue to be until a commercial-scale power generation CCS project is fully up and running.

Two Texas-based engineers last year pointed out what they see as an unavoidable technical flaw in the whole proposition: the pure limitations of how much CO2 can be stored. Their work has drawn strong criticism from four geologists.

The authors of the original reports, Christine Economides-Ehlig of Texas A&M University and husband Michael Economides of Houston University, presented a paper to a Society of Petroleum Engineers conference, and this year had a journal article published which attracted the attention of the Guardian. Economides outlined the work on his blog at the Houston Chronicle’s website:

The conclusions are quite negative and, in fact, sobering. Earlier published reports on the potential for sequestration fail to address the necessity of storing CO2 in a closed system. Our calculations suggest that the volume of liquid or supercritical CO2 to be disposed cannot exceed more than about 1% of pore space. This will require from 5 to 20 times more underground reservoir volume than has been envisioned by many, and it renders geologic sequestration of CO2 a profoundly non-feasible option for the management of CO2 emissions. Kyoto Protocol or successor accords would imply orders of magnitude larger problem than anything possible as CCS.

The full paper looks at existing CO2 sequestration carried out in enhanced oil recovery (EOR), in deep saline aquifers and in depleted hydrocarbon reservoirs to show that CCS is not possible on the scale expected of it, for climate change mitigation purposes.

However CCS is nothing if not technically complex, either. Four geologists from the UK and Canada have written a rebuttal of Economides’ and Economides-Ehlig’s paper, arguing that:

In essence, this unusual theory assumes that storage of CO2 will be injected to the deep subsurface into a sealed container, with no-flow of existing water through the lid, sides, or base. Un-surprisingly, if extra CO2 fluid is added to a sealed container, the pressure within the container will increase.

The problem, they say, is the assumptions on which this is based:

The most profound error, is that the subsurface is not made of sealed boxes. If it were, then oil and gas would not have been able to move for tens or hundreds of kilometers laterally and vertically, to be caught in the traps where these fluids are discovered today. The oil industry would not exist.

There are other errors, they add; most importantly the assumption that the reservoir is only 30 metres thick. The authors in their full response say that between them they have analysed 20 CO2 injection, only one of which experienced a severe pressure problem and nine of which operate – or could operate – at industrial scale.