Self-sealing tests were carried out on cylindrical samples artificially cracked on one-third of the diameter with a perfectly controlled aperture. Water was then injected into the crack. An innovative cell was used that had been developed, the body of which is transparent to X-rays. The sample could fully rotate in the nanotomograph, allowing a 3D reconstruction of images before, during and after tests, a visualization of the evolution of the cracked zone, and a quantification of the variations in crack volume during self-sealing. Permeability measurements were made to quantify the influence of self-sealing on flows. In the present work, two facies of claystone with different CaCO₃ contents were tested. In the clay-rich sample, an important but not total, reduction in volume was observed, as well as a large decrease in permeability, even if a safe claystone value was not recovered and a two-phase kinematic occurred. On the CaCO₃-rich samples, a small volume reduction of the fracture was observed with a small decrease in water permeability. The influence of the mineralogy on the self-sealing capacity of the claystone was demonstrated and a threshold of carbonate content of around 40% was exhibited to discriminate samples able to self-seal from those that were not.