Opening Versus Self-Sealing Behaviour Of Single Fractures In Mudstone Caprocks During CO2 Migration

Reactions between CO2 and CO2-charged brines and mudrocks may inhibit CO2 leakage via the precipitation of carbonate minerals or via swelling of clay minerals or enhance leakage via the corrosion of carbonate cements. The timescales for the potential self-sealing behaviour, and/or the magnitudes of the permeability enhancements are uncertain. Laboratory experiments can provide constraints on the intrinsic fracture permeabilities, but the quantification of permeability changes following reaction or under conditions of multiphase flow is challenging in the laboratory. Reactive transport modelling (RTM) provides a numerical laboratory in which the intrinsic permeabilities of rough fractures, and the coupling of the flow and reaction processes, can be investigated. A modified local cubic law (MLCL) is used to model rough fracture permeability, and coupling of permeability-porosity changes to mineralization and clay swelling. The results show that the intrinsic permeability of self-affine fractures is primarily dependent on the roughness and degree of correlation between the two fracture surfaces, and that with increasing roughness the simulated fracture permeabilities are systematically lower than permeabilities predicted from the fracture aperture mean using a cubic law. The dependence of fracture permeabilities on reactions is investigated, and the relationship between mineralization behaviour and fluid residence time is discussed.