Unconventional CO2 Storage: CO2 Mineral Trapping Predicted in Characterized Shales, Sandstones, and Coal Seam Interburden

Abstract

Summary Carbon dioxide (CO2) capture from industrial sources including coal combustion, gas processing, cement or steel production, blue hydrogen, or direct air capture, and subsequent geological storage is part of the transition to reduce greenhouse gas emissions. Unconventional and conventional reservoirs provide opportunities for beneficial use such as enhanced recovery, supercritical CO2 (ScCO2) fracturing, and storage of gases such as CO2 and ancillary gases, or potentially hydrogen. The purpose of this study is to use Australian unconventional rock packages to understand the controls on CO2 reactivity and mineral trapping (the most secure form of storage) and compare the potential for CO2 storage. Characterization of core from the Surat, Eromanga, and Cooper basins, Australia, is used to populate CO2 and production water-rock reactivity models. Sensitivity to production water composition and temperature was also tested. Coal seam gas (CSG) reservoir interburden ranged from clay-rich mudstones to interlaminated sandstone and mudstone, and calcite cemented sandstones. The coal seam interburden samples contained high plagioclase and chlorite content. They were predicted to alter to carbonates calcite, ankerite, siderite, and dawsonite mineral trapping CO2. After 30 years, net mineral trapping varied from −0.1 to +0.3 kg CO2/m3, and pH was 4.6–4.9. Net mineral trapping after 1,000 years varied from 5.7 to 16.3 kg CO2/m3 and was 17.1 kg CO2/m3 with higher salinity water. The mineral content had the main control with different lithologies decreasing mineral trapping by 41 or 35% compared with a base case. Overlying plagioclase-rich sandstone trapped 17.1 kg CO2/m3 as calcite, ankerite, dawsonite, and siderite after 1,000 years with the pH increasing to 6. For the quartz-rich oil reservoir sandstone, however, only 0.3 kg CO2/m3 was trapped after 1,000 years. Gas shale and marine black oil shales contained high mica, chlorite, and feldspar content that could be converted to carbonate minerals, mineral trapping CO2. A marine black oil shale mineral trapped 8.3 and 13.9 kg CO2/m3 after 30 and 1,000 years, respectively, as siderite and ankerite. Unconventional reservoirs have a strong potential for mineral trapping during CO2 storage.