Rock-fluid interactions in geothermal reservoir systems and the implications for carbon sequestration

• Main Author: Belshaw, Grace
• Format: Thesis
• Language: English
• Published: 2022
• Subjects: Iceland
• Online Access: http://eprints.nottingham.ac.uk/67351/; https://eprints.nottingham.ac.uk/67351/1/Thesis_GraceBelshaw_ammended.pdf

This thesis aims to examine whether andesitic rock samples are likely to be good targets for permanent carbon sequestration via mineral trapping, as an alternative to basaltic-type reservoirs which have been proven to be successful. The CarbFix project in Iceland and the Wallula Basalt Pilot Scale project both reported results from field scale studies that suggested carbonation reactions had occurred within just two years in basaltic-type reservoirs, which is a significant improvement on the thousands of years needed for other geological carbon storage methods to be considered permanent. Carbon dioxide was successfully sequestered in these systems, after mineral dissolution reactions with the injected acidic fluids, which released divalent cations able to combine with the dissolved CO2 and precipitate carbonate minerals. However, there is a significant lack of research examining whether alternative volcanic rocks such as andesite may also be suitable. If alternative volcanic rocks can also be utilised as targets for permanent carbon sequestration in short timescales, this would expand the accessibility of the CarbFix project to more global locations and help mitigate the impacts of rising CO2 concentrations in the atmosphere. Rock samples from the region of Rantau Dedap on the Island of Sumatra, Indonesia, were first characterised in detail to examine their mineralogical and chemical compositions, with results indicating they were of andesitic composition. Batch reactor experiments were conducted under elevated temperatures of 100oC and pH values close to 3 using crushed andesite type rock samples, to simulate carbon sequestration conditions close to the site of injection. The release of silicon into the experimental fluids was used to calculate a bulk rock dissolution rate of the order 10-11 mol/m2/s for the andesite type rocks, which is roughly 1-2 orders of magnitude slower than reported basaltic dissolution rates. Mineral dissolution in basaltic systems is considered to be the rate limiting step in the ...