The relevance of dawsonite precipitation in CO2 sequestration in the Mihályi-Répcelak area, NW Hungary

A natural CO2 reservoir system with sandstone lithology has been studied in NW Hungary due to similarities with a large saline reservoir formation widespread in the whole of the Pannonian Basin (Central Europe), suggested to be one of the best candidates for industrial CO2 storage. A range of analytical techniques has been used on core samples from the CO2-containing sandstone layers representing a wide pressure (90-155 bar), temperature (79-95°C) and pore fluid composition range (TDS between 18 000 – 50 700 mg/l) to identify the mineralogy and textural characteristics of the natural reservoir. The only clear CO2-related feature in the studied lithology was the occurrence of dawsonite (NaAlCO3(OH)2) always in close textural relation with albite. This is in clear agreement with our geochemical modelling results, which also underline the presence of albite as a precondition for the crystallization of dawsonite at the given p-T-X conditions. Our results suggest that, at least in the Pannonian Basin, dawsonite may be an important mineral to safely sequester industrial CO2 in the subsurface.