Could it be that economics isn’t the biggest hurdle standing in the way of our goal of safely locking away carbon dioxide  using carbon capture and storage (CCS)? Two engineering professors in the US are arguing that the physical challenges of CCS have been wildly underestimated.

Christine Ehlig-Economides of Texas A&M University and Michael J. Economides of the University of Houston have published a paper in the Journal of Petroleum Science and Engineering stating that underground geologic reservoirs would have to be five to 20 times larger than previously estimated to store any volume of liquid or supercritical (behaving partly as a gas, partly as a liquid).

That limitation, the authors write, “renders geologic sequestration of CO2 a profoundly non-feasible option for the management of CO2 emissions.”

That conclusion strikes a blow for many who have viewed CCS as one of the best ways to reduce carbon emissions from coal-fired power plants so we can continue to use fossil fuels without worsening climate change.

Ehlig-Economides and Economides examined two of the leading proposed strategies for CCS: 1) enhanced oil recovery — that is, flooding depleting oil fields to force out the remaining oil, replacing it with liquid carbon dioxide — and 2) injecting carbon dioxide into an already depleted oil or gas reservoir or a deep saline aquifer. They conclude that previous studies haven’t realistically taken into account the pressure limitations of such reservoirs, leading to “sever” underestimates in how much underground volume would be needed for carbon storage.

“There are already some data that seem to warn of problems in the very few existing injection projects,” the authors write. They point to Sleipner, a CCS project in the North Sea, which has achieved only one-third the carbon dioxide injection volumes that would be required for a single 500-megawatt coal-fired power plant. They further note that the project has seen “significant leakage to overlying layers.”

Examining the carbon dioxide storage capacity required for one coal plant, which produces about 3 million tonnes of CO2 a year, Ehlig-Economides and Economides calculate that 30 years of storage at 1,000 pounds per square inch could require an underground aquifer with an area of 1,371 square miles, which is just under the size of the state of Rhode Island.

“Conversely,” they conclude, “for more moderate size reservoirs, still the size of Alaska’s Prudhoe Bay reservoir, and with moderate permeability there would be a need for hundreds of wells. Neither of these bodes well for geological CO2 sequestration and the findings of this work clearly suggest that it is not a practical means to provide any substantive
reduction in CO2 emissions, although it has been repeatedly presented as such by others.”

In an article about the new findings, The Guardian reported that the British Geological Survey was examining the study and planned to prepare its own peer-reviewed analysis of Ehlig-Economides’ and Economides’ calculations.

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