Factors affecting self‐sealing of geological faults due to CO 2 ‐leakage

Injecting anthropogenic CO 2 into the subsurface is suggested for climate change mitigation. However, leakage of CO 2 from its target storage formation is a concern. In the event of leakage, permeability in leakage pathways such as faults may get altered due to mineral reactions induced by CO 2 ‐enriched water, thus influencing the migration and fate of the CO 2 . An example of such fault permeability alteration is found in the Little Grand Wash Fault zone (LGWF), where the fault outcrops show fractures filled with calcium carbonate. To test the nature, extent, and time‐frame of such fault ‘self‐sealing’, we developed reactive flow simulations based on hydrogeological conditions of the LGWF. We measured LGWF water chemistry and conducted an x‐ray powder diffraction (XRD) analysis of the fault‐rock to constrain the model geochemistry. We hypothesized that the choice of parameters for relative permeability, capillary pressure, and reaction kinetics will have a huge impact on the fault sealing predictions. Simulation results showed that precipitation of calcite in the top portion of the fault led to a decrease in porosity of the damage zone from a value of 40% to ∼ 2 % . Over a simulation time of 1000 years, porosity in the damage zone showed self‐enhancing behavior in the bottom portion and self‐sealing behavior in the top portion of the fault. We found that the results were most sensitive to the relative permeability parameters and the fault architecture. A major conclusion from this analysis is that, under similar conditions, some faults are likely to seal over time. © 2017 Society of Chemical Industry and John Wiley & Sons, Ltd.