The mechanisms and rates of fracture sealing in carbonates

Geological observations, seismic data as well as laboratory experiments have shown that faults lithify and recover their strength (heal) during inter-seismic periods. The mechanical-chemical process of fault healing is a key in understanding many aspects of fault behavior, such as earthquake recurrence and rupture dynamics, but is also pivotal for the application of deep geothermal energy, CO₂ sequestration and the underground storage of radioactive waste. In this contribution we investigate the mechanical-chemical recovery of fractures in carbonates at upper crustal conditions. In the upper crust, fractures are dominantly sealed through mineral precipitation from supersaturated fluids that are chemically out of equilibrium with the host rock. Such fracture sealing processes are inferred to be either relatively fast under high fluid availability and through mineral precipitation from supersaturated fluids (advective transport) or relatively slow by dissolution-precipitation processes, also known as self-sealing (diffusive transport). In order to improve the understanding of the mechanism and rate of the damage-recovery cycle of fractures, this project investigates how different sealing mechanisms (advection vs. diffusion) as well as fracture sealing rates are coupled. For this purpose, observations from natural vein systems are combined together with fracture sealing experiments with a percolation cell apparatus. In order to quantitatively document the sealing process, the selected rock samples are analyzed by laboratory-based X-ray computed microtomography and scanning electron microscopy. In summary, this work will advance knowledge about the damage-recovery cycle in fractured carbonates through the investigation of sealing processes active at the microscale.