Evolution of Microcracks in Damaged Natural Salt: Insights from 4D imaging

Rocksalt formations are critical candidates for storing natural gas, hydrogen, compressed air energy, and radioactive waste. While pure, undisturbed rock salt deposits exhibit low porosity and impermeability when buried deeply, excavation leads to near-field microcracking and dilatancy in the salt, increasing porosity and permeability. Over time, the connectivity of brine- or water-vapor-filled microcrack networks in deformation-damaged salt is expected to decrease, partly due to dissolution-precipitation healing. In this study, we employ 4D (time-resolved 3D) microtomography to investigate the long-term evolution of dilated grain boundary and microcrack networks developed in deformation-damaged natural salt through brine-assisted processes. Our findings reveal substantial microstructural modification and healing occurring over periods ranging from days to a few months. Cracks and dilated grain boundaries undergo crystallographic faceting, necking, and migration, effectively "recrystallizing" the material and resulting in increased tortuosity and decreased connectivity of the crack network. Understanding the complex interplay between microcracking, healing, and permeability changes in deformation-damaged rock salt is of utmost importance for optimizing storage and disposal applications in geomechanics and physical chemistry. Our research contributes valuable insights to this field and informs the sustainable development and management of rock salt formations for diverse energy storage and waste management needs.