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

• Preferential flow paths developed in the more permeable and reactive limestone.
• Alteration occurred at the cement–sandstone interface in the sandstone–cement core.
• Host rock permeability and reactivity are key to understand 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.