The chemistry and saturation states of subsurface fluids during the in situ mineralisation of CO2 and H2S at the CarbFix site in SW-Iceland

Sandra Snæbjörnsdóttir*, Eric H. Oelkers, Kiflom Mesfin, Edda Sif Aradóttir, Knud Dideriksen, Ingvi Gunnarsson, Einar Gunnlaugsson, Juerg M. Matter, Martin Stute, Sigurdur R. Gislason

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

44 Citations (Scopus)


In situ carbonation of basaltic rocks could provide a long-term carbon storage solution, which is essential for the success and public acceptance of carbon storage. To demonstrate the viability of this carbon storage solution, 175 tonnes (t) of pure CO2 and 73 tonnes (t) of a 75% CO2-24% H2S-1% H2-gas mixture were sequentially injected into basaltic rocks at the CarbFix site at Hellisheidi, SW-Iceland from January to August 2012. This paper reports the chemistry and saturation states with respect to potential secondary minerals of sub-surface fluids sampled prior to, during, and after the injections. All gases were dissolved in water during their injection into permeable basalts located at 500–800 m depth with temperatures ranging from 20 to 50 °C. A pH decrease and dissolved inorganic carbon (DIC) increase was observed in the first monitoring well, HN-04, about two weeks after each injection began. At storage reservoir target depth, this diverted monitoring well is located ∼125 m downstream from the injection well. A significant increase in H2S concentration, however, was not observed after the second injection. Sampled fluids from the HN-04 well show a rapid increase in Ca, Mg, and Fe concentration during the injections with a gradual decline in the following months. Calculations indicate that the sampled fluids are saturated with respect to siderite about four weeks after the injections began, and these fluids attained calcite saturation about three months after each injection. Pyrite is supersaturated prior to and during the mixed gas injection and in the following months. In July 2013, the HN-04 fluid sampling pump broke down due to calcite precipitation, verifying the carbonation of the injected CO2. Mass balance calculations, based on the recovery of non-reactive tracers co-injected into the subsurface together with the acid-gases, confirm that more than 95% of the CO2 injected into the subsurface was mineralised within a year, and essentially all of the injected H2S was mineralised within four months of its injection. These results demonstrate the viability of the in situ mineralisation of these gases in basaltic rocks as a long-term and safe storage solution for CO2 and H2S.

Original languageEnglish
Pages (from-to)87-102
Number of pages16
JournalInternational Journal of Greenhouse Gas Control
Publication statusPublished - 1 Mar 2017

Bibliographical note

Funding Information:
We acknowledge funding from the Reykjavik Energy; Environmental Fund of Reykjavik Energy; the European Commission through the projects CarbFix (EC coordinated action 283148), Min-GRO (MC-RTN-35488), Delta-Min (PITN-GA-2008-215360), and CO

Publisher Copyright:
© 2017 Elsevier Ltd

Other keywords

  • Basaltic rocks
  • Carbonation
  • CCS
  • Gas mixtures
  • Mineral storage
  • Mineral trapping
  • Solubility trapping
  • SulFix


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