1. School of Earth, Atmospheric and Environmental Sciences, The University of Manchester, Oxford Road, Manchester M13 9PL, UK
2. Scottish Centre for Carbon Storage, School of GeoSciences, The University of Edinburgh, Grant Institute, Kings Buildings, West Mains Road, Edinburgh EH9 3JW, UK
3. Department of Geology, University of Toronto, 22 Russell Street, Toronto, Ontario M5S 3B1, Canada
4. Advanced Resources International, 4501 Fairfax Drive, Suite 910, Arlington, Virginia 22203-1661, USA
5. GasConsult International, 2808 Adeline Street #3, Berkeley, California 94703, USA
6. Department of Earth and Atmospheric Sciences, University of Houston, Houston, Texas 77204-5503, USA
7. China University of Geosciences, Wuhan City, 430074, China

Correspondence to: Stuart M. V. Gilfillan^1,2 Correspondence and requests for materials should be addressed to S.M.V.G. (Email: stuart.gilfillan@ed.ac.uk).

Abstract

Injecting CO₂ into deep geological strata is proposed as a safe and economically favourable means of storing CO₂ captured from industrial point sources^{1, 2, 3}. It is difficult, however, to assess the long-term consequences of CO₂ flooding in the subsurface from decadal observations of existing disposal sites^{1, 2}. Both the site design and long-term safety modelling critically depend on how and where CO₂ will be stored in the site over its lifetime^{2, 3, 4}. Within a geological storage site, the injected CO₂ can dissolve in solution or precipitate as carbonate minerals. Here we identify and quantify the principal mechanism of CO₂ fluid phase removal in nine natural gas fields in North America, China and Europe, using noble gas and carbon isotope tracers. The natural gas fields investigated in our study are dominated by a CO₂ phase and provide a natural analogue for assessing the geological storage of anthropogenic CO₂ over millennial timescales^{1, 2, 5, 6}. We find that in seven gas fields with siliciclastic or carbonate-dominated reservoir lithologies, dissolution in formation water at a pH of 5–5.8 is the sole major sink for CO₂. In two fields with siliciclastic reservoir lithologies, some CO₂ loss through precipitation as carbonate minerals cannot be ruled out, but can account for a maximum of 18 per cent of the loss of emplaced CO₂. In view of our findings that geological mineral fixation is a minor CO₂ trapping mechanism in natural gas fields, we suggest that long-term anthropogenic CO₂ storage models in similar geological systems should focus on the potential mobility of CO₂ dissolved in water.

1. School of Earth, Atmospheric and Environmental Sciences, The University of Manchester, Oxford Road, Manchester M13 9PL, UK
2. Scottish Centre for Carbon Storage, School of GeoSciences, The University of Edinburgh, Grant Institute, Kings Buildings, West Mains Road, Edinburgh EH9 3JW, UK
3. Department of Geology, University of Toronto, 22 Russell Street, Toronto, Ontario M5S 3B1, Canada
4. Advanced Resources International, 4501 Fairfax Drive, Suite 910, Arlington, Virginia 22203-1661, USA
5. GasConsult International, 2808 Adeline Street #3, Berkeley, California 94703, USA
6. Department of Earth and Atmospheric Sciences, University of Houston, Houston, Texas 77204-5503, USA
7. China University of Geosciences, Wuhan City, 430074, China

Correspondence to: Stuart M. V. Gilfillan^1,2 Correspondence and requests for materials should be addressed to S.M.V.G. (Email: stuart.gilfillan@ed.ac.uk).

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