Researchers find geosequestration of CO2 much safer than thought

A new study has revealed that storing carbon dioxide beneath the earth may be a safer and longer term method of reducing emissions in the atmosphere than previously thought. A team of NERC funded researchers at the University of Manchester, the University of Houston and the University of Toronto, found that carbon dioxide (CO2) has been naturally stored for up to 40 million years in CO2 gas fields in the Colorado Plateau and Rocky Mountains of the USA. Their findings are published in the geochemistry journal Geochimica et Cosmochimica Acta.

This is important news for those in the bioenergy community looking at the potential of coupling geosequestration to bioenergy production. When carbon capture and storage (CCS) technologies are applied to biomass power plants, a system that yields 'negative emissions' emerges - the most radical tool in the climate fight.

Ordinary renewables are all 'carbon neutral' at best, slightly carbon positive in practise. That is, they add small amounts of CO2 to the atmosphere over their lifecyle. But bio-energy with carbon storage (BECS) actively removes CO2 from the atmosphere and locks it up under ground. The difference is radical: whereas renewables like solar, non-CCS biomass, wind or hydropower yield between +15 to + 100 g of CO2 per kWh of electricity produced, carbon-negative bioenergy yields up to -1000g (that is, "minus", hence 'negative emissions' - see figure, click to enlarge).

Scientists have found that such BECS systems, if implemented on a global scale, can clean up the atmosphere and take us back to pre-industrial atmospheric CO2 levels by 2060. It is a feasible 'geo-engineering' concept that allows societies to function as normal, while not only eliminating their carbon emissions, but actually removing CO2 from the past. As more and more scientists call for radical steps to fight climate change, carbon-negative bioenergy might become one of the only instruments available to do so.

BECS systems put the carbon we pumped into the atmosphere since the Industrial Revolution back where it belongs: under ground. And the great thing is that, while doing so, renewable energy is generated (solar energy stored in biomass).

One of the hurdles standing in the way of adopting CCS has been doubts over the safety and permanence of geosequestration. The potential for leakage is often leveled against those who advocate CCS coupled to power plants that burn fossil fuels. A leak would mean a net contribution of carbon emissions. However, when coupled to biomass power plants, leakage is of lesser concern, because the CO2 is biogenic in origin. Leaks would not result in net CO2 emissions, because the fuel from which the gas was derived is carbon neutral from the start.

The new research however shows the safety argument against geosequestration might be exaggerated, as natural sites are shown to do the trick of storing CO2 gas safely for millions of years. The scientists took CO2 samples from five natural gas fields and measured their noble gases. Their findings allowed them to ‘fingerprint’ the Colorado CO2 for the first time:
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The results show that the gas in the fields has been released from molten magma within the Earth’s crust. In all of these fields, the last time the magma melted and CO2 was released was more than eight thousand years ago. In three of the fields, it last occurred over a million years ago, and in one it was at least 40 million years ago. This proves that the CO2 has been stored naturally and safely in the earth for periods between eight thousand years and 40 million years - Dr. Stuart Gilfillan, lead researcher

The scientists hope this study will pave the way for selection of similar safe sites for storage of CO2 from power plants in both the UK and abroad. Underground CO2 storage, in the correct place, should be a safe option to help us cope with emissions until we can develop cleaner energy sources. A suitable storage place for the UK could be in the North Sea, where similar rocks to those in the gas fields can be found, they say.

References:
Stuart M.V. Gilfillana, Chris J. Ballentine, Greg Holland, Dave Blagburn, Barbara Sherwood Lollar, Scott Stevens, Martin Schoell and Martin Cassidy, "The noble gas geochemistry of natural CO2 gas reservoirs from the Colorado Plateau and Rocky Mountain provinces, USA", Geochimica et Cosmochimica Acta, 15th February 2008, Vol 72, No. 4, p1174-1198.

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Scientific literature on negative emissions from biomass:
H. Audus and P. Freund, "Climate Change Mitigation by Biomass Gasificiation Combined with CO2 Capture and Storage", IEA Greenhouse Gas R&D Programme.

James S. Rhodesa and David W. Keithb, "Engineering economic analysis of biomass IGCC with carbon capture and storage", Biomass and Bioenergy, Volume 29, Issue 6, December 2005, Pages 440-450.

Noim Uddin and Leonardo Barreto, "Biomass-fired cogeneration systems with CO2 capture and storage", Renewable Energy, Volume 32, Issue 6, May 2007, Pages 1006-1019, doi:10.1016/j.renene.2006.04.009

Christian Azar, Kristian Lindgren, Eric Larson and Kenneth Möllersten, "Carbon Capture and Storage From Fossil Fuels and Biomass – Costs and Potential Role in Stabilizing the Atmosphere", Climatic Change, Volume 74, Numbers 1-3 / January, 2006, DOI 10.1007/s10584-005-3484-7

Further reading on negative emissions bioenergy and biofuels, and carbon capture techniques:
Peter Read and Jonathan Lermit, "Bio-Energy with Carbon Storage (BECS): a Sequential Decision Approach to the threat of Abrupt Climate Change", Energy, Volume 30, Issue 14, November 2005, Pages 2654-2671.

Stefan Grönkvist, Kenneth Möllersten, Kim Pingoud, "Equal Opportunity for Biomass in Greenhouse Gas Accounting of CO2 Capture and Storage: A Step Towards More Cost-Effective Climate Change Mitigation Regimes", Mitigation and Adaptation Strategies for Global Change, Volume 11, Numbers 5-6 / September, 2006, DOI 10.1007/s11027-006-9034-9

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