Abstract

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 CO₂ 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 CO₂ 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 SO₂ 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.

Supplementary material: Additional model inputs, characterization and model images, and an excel file of QEMSCAN mineral and porosity components, are available at https://doi.org/10.6084/m9.figshare.c.5395393

Thematic collection: This article is part of the Geoscience for CO₂ storage collection available at: https://www.lyellcollection.org/cc/geoscience-for-co2-storage