Compaction Driven Flow in Porosity Waves - A Threat to Caprock Integrity?

Compaction of porous rock is a mechanism to maintain or increase fluid overpressure and may lead to fluid focusing and the development of porosity waves. Such fluid transport may be much more efficient than Darcy flow or even fracturing and is predicted to play an important role in sedimentary basins, during crustal metamorphism and for mantle melt extraction. Here I investigate the possibility of porosity waves occurring during injection and storage of CO2 in aquifers. Reaction induced compaction may be expected in CO2 storage because of the large thermal, mechanical and chemical disequilibrium that is introduced to the system by human activity, and due to high reactivity of CO2 dissolved in brine. First results indicate that low permeability caprock may fail as a barrier to flow if significant viscous compaction occurs. In laboratory experiments, such deformation has been shown to take place due to the high reactivity of CO2-rich brine. However, the temporal and spatial scales for the onset of focused flow in porosity waves strongly depend on a set of poorly constrained parameters. Thus, more experimental and numerical work and comparison to field data is needed to correctly assess these coupled reaction-deformation-flow processes.