title: Solubility trapping in formation water as dominant CO(2) sink in natural gas fields.
abstract: Injecting CO(2) into deep geological strata is proposed as a safe and economically favourable means of storing CO(2) captured from industrial point sources. It is difficult, however, to assess the long-term consequences of CO(2) flooding in the subsurface from decadal observations of existing disposal sites. Both the site design and long-term safety modelling critically depend on how and where CO(2) will be stored in the site over its lifetime. Within a geological storage site, the injected CO(2) can dissolve in solution or precipitate as carbonate minerals. Here we identify and quantify the principal mechanism of CO(2) 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 CO(2) phase and provide a natural analogue for assessing the geological storage of anthropogenic CO(2) over millennial timescales. 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 CO(2). In two fields with siliciclastic reservoir lithologies, some CO(2) 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 CO(2). In view of our findings that geological mineral fixation is a minor CO(2) trapping mechanism in natural gas fields, we suggest that long-term anthropogenic CO(2) storage models in similar geological systems should focus on the potential mobility of CO(2) dissolved in water.
authors.affiliation: School of Earth, Atmospheric and Environmental Sciences, The University of Manchester, Oxford Road, Manchester M13 9PL, UK. stuart.gilfillan@ed.ac.uk
authors.forename: Stuart M V
authors.initials: SM
authors.lastname: Gilfillan
authors.forename: Barbara Sherwood
authors.initials: BS
authors.lastname: Lollar
authors.forename: Greg
authors.initials: G
authors.lastname: Holland
authors.forename: Dave
authors.initials: D
authors.lastname: Blagburn
authors.forename: Scott
authors.initials: S
authors.lastname: Stevens
authors.forename: Martin
authors.initials: M
authors.lastname: Schoell
authors.forename: Martin
authors.initials: M
authors.lastname: Cassidy
authors.forename: Zhenju
authors.initials: Z
authors.lastname: Ding
authors.forename: Zheng
authors.initials: Z
authors.lastname: Zhou
authors.forename: Georges
authors.initials: G
authors.lastname: Lacrampe-Couloume
authors.forename: Chris J
authors.initials: CJ
authors.lastname: Ballentine