Carbon dioxide capture from industrial sources including coal combustion, gas processing, cement or steel production or direct air capture, and geological storage is part of the transition to reduce greenhouse gas emissions. Conventional CO2 geological storage involves injection of supercritical CO2 into a suitable reservoir with a structural trap from an overlying seal. Unconventional and conventional reservoirs provide opportunities for beneficial use such as enhanced recovery, supercritical CO2 fracturing, and storage of gases such as CO2 and ancillary gases, or potentially hydrogen. The purpose of this study is to use Australian examples of unconventional rock packages to understand the controls on CO2 reactivity and mineral trapping (the most secure form of storage) and to demonstrate if there is potential for storage in unconventional reservoirs. Characterization of core from the Surat, Eromanga, and Cooper basins, is used to populate geochemical models and compare the potential for mineral trapping of CO2. Interburden from a coal seam gas reservoir ranged from clay rich mudstones to interlaminated and calcite cemented sandstones. The interburden samples contained high plagioclase and chlorite mineral content and these were predicted in geochemical dissolved CO2-production water-rock reactivity models to alter to calcite, ankerite, siderite and dawsonite mineral trapping 4 – 12 kg CO2 per m3. CO2 mineral trapping as siderite and ankerite in quartz rich oil sandstone was predicted to be lower than in interburden. Gas shale samples and black oil shales also contained a high mica, chlorite and feldspar content that can be converted to carbonate minerals, mineral trapping CO2. Unconventional rock packages have strong potential for mineral trapping during CO2 storage. In future a combination of characterization, CO2 experiments and models should be performed for reservoirs and seals from sites of interest to understand initial changes to poro-perm. Several sandstones characterized here showed indicators of natural CO2 or acidic fluid alteration with carbonates and clays filling natural fractures. Characterizing regions, where gases have been stored naturally and carbonates precipitated are valuable to validate long term predictions. Understanding the CO2 storage potential of different reservoirs will also have applicability to future hydrogen storage.

This content is only available via PDF.
You can access this article if you purchase or spend a download.