CO2 mineral trapping comparison in different regions: predicted geochemical reactivity of the Precipice Sandstone reservoir and overlying Evergreen Formation

Injected CO2 streams may have geochemical reactivity to different rock types in a CO2 storage complex depending on solubility and formation water chemistry. The Precipice Sandstone and Evergreen Formation are a low-salinity reservoir-seal pair in the Surat Basin, Australia, targeted for potential CO(2 )storage. The kinetic geochemical CO2 reactivity of different rock facies from three regions were predicted over 30 and 1000 year time periods. No material CO2 mineral trapping in the quartz-rich Precipice Sandstone reservoir was predicted, owing to the low rock reactivity. Predicted CO(2 )mineral trapping in the Evergreen Formation was more variable due to different amounts of more reactive feldspars, clays, calcite and siderite. Predicted mineral trapping as siderite and ankerite was between 0.03 and 8.4 kg m(-3) CO2, and mainly depends on chlorite and plagioclase content. Predicted pH was between 5 and 7.5 after 1000 years. Pyrite precipitation was also predicted with SO(2 )present in the injectate. QEMSCAN and SEM-EDS (scanning electron microscopy and energy-dispersive spectroscopy) spot imaging of samples from the seal containing natural fractures filled by siderite, pyrite, clays, ankerite, calcite, barite and apatite represent a natural analogue for natural mineral trapping. These are in good agreement with our model predictions. This study suggests that, from a geochemical perspective, the Precipice Sandstone is a suitable storage reservoir, whereas mineral trapping would occur in the overlying Evergreen Formation.

Automated summary

This study predicted the CO2 storage potential of Precipice Sandstone and Evergreen Formation in the Surat Basin, Australia, and found that Precipice Sandstone is a suitable storage reservoir, while mineral trapping would occur in the overlying Evergreen Formation.