Caprock Remains Water Wet Under Geologic CO2 Storage Conditions

Abstract

Carbon storage technology is primarily targeted in saline formations, which is a porous rock matrix filled with brine, sealed with a low permeability caprock. There are significant variations of CO2 wetting properties, typically reported in the literature as contact angle of CO2 and brine interacting with a rock material, suggesting that CO2 could become wetting under geostorage conditions and negatively impact containment effectiveness. Here, we performed the first controlled laboratory measurements of CO2-brine contact angles on shale rocks from low permeability sealing formations with distinctive mineralogic properties—calcite-rich, quartz-rich, and dolomite-rich. We targeted temperatures at 40° and 100°C, pressures at 8.3, 34.5, and 62.1 MPa, and salinity at 35,000 and 260,000 ppm. Results show no significant change in contact angle with mineralogy, temperature, pressure, salinity, and CO2 bubble size. We conclude that caprocks will remain water-wet at geologic CO2 storage conditions and will not lose their capillary sealing capacity.