The role of host rock properties in determining potential CO₂ migration pathways

This work examines CO₂-brine-cement-rock interactions and the associated permeability changes to understand the role of host rocks in determining CO₂ migration pathways into groundwater aquifers under conditions relevant to geological carbon sequestration. Composite sandstone-cement and limestone-cement cores were used for an eight-day flow-through experiment. X-ray Micro-CT imaging revealed that CO₂-brine-cement interaction predominated at the sandstone-cement interface, leading to a permeability increase by a factor of three. In the limestone-cement core, however, the CO₂-rich flow diverted itself primarily into the higher permeability limestone, creating wormholes and a dominant flow path inside the limestone, resulting in a permeability increase by a factor of twenty four. Mass balance measurement indicates that the limestone-cement core lost about three times more of its original mass compared to the sandstone-cement core. These observations suggest differing CO₂ migration pathways into underground drinking water resources through preferential pathways in host rocks.