AN EXPERIMENTAL STUDY TO CHARACTERIZE PHYSICAL ROCK PROPERTY CHANGES DURING REACTION OF CO2 WITH BASALTS AND BASANITES OF THE AUCKLAND VOLCANIC FIELD

CO₂, water and basalts are known to react in volcanic environments. Mineral sequestration of anthropogenic CO₂ is one of the proposed solutions to capture and decrease CO₂ emissions. This involves dissolution of naturally occurring iron, magnesium and calcium rich minerals, when in contact with CO₂ dissolved in water to form carbonate minerals. Basalts are thought to be one of the promising rock types for mineral sequestration of CO₂ by creating such hydrothermal mineral alterations. Rock-fluid interactions occurring during the mineral carbonation process alter the rock structure, resulting in changes in the rock’s storage and fluid transport properties (especially porosity and permeability). In order to characterize these changes, experiments of CO₂ - rich water interactions with young basalts and basanites (less than 0.3 Ma) of the Auckland Volcanic Field were studied over 140-days reaction period. Here we quantify the changes in the rock microstructure and type of secondary mineral precipitation on basalt and basanite rocks having similar chemical composition but different porosity, permeability and pore geometries, before and after reaction with CO₂. Electron microprobe analysis confirmed the precipitation of Fe-Mg carbonates with different morphologies. Sample with the lowest crystallinity favoured maximum carbonate precipitation indicating the dependence of dissolution rate and secondary mineral precipitation on crystallinity. A 15% increase in porosity and 3-orders of magnitude increase in permeability was observed in the same sample opening new questions on the effect of these rock-fluid reactions on the pore network. All other samples showed very low increase in porosity and high decrease in permeability. These observations were confirmed by Nuclear Magnetic Resonance (NMR) and ultrasonic velocities. This project will provide useful insights for carbon capture and storage and volcanic research by further investigating the effect of rock-fluid reaction on the pore network.