(GRS-704) Self-Sealing of Fractures in indurated Claystones

C.-L. Zhang, A. Rogalski, O. Czaikowski

Contract No. 02E11627

In the framework of the European Joint Programme on Radioactive Waste Management (EURAD) – Work Package 6 – GAS, GRS investigated gas transport and impact on self-sealing of fractures in the indurated Callovo-Oxfordian (COX) and Opalinus (OPA) clay-stones. Core samples were extracted from four lithological facies relatively rich in clay mineral, carbonate and quartz, respectively. They were artificially cracked to different fracture intensities. Self-sealing of the fractures was measured by fracture closure, water permeability variation, gas penetration, and recovery of gas-induced pathways. Most of the fractured samples exhibited a dramatic reduction in water permeability to very low levels close to that of the intact clay rocks, depending on their mineralogical composition, fracture intensity, confining stress, and load duration. The self-sealing capacity of the clay-rich samples is higher than that of the carbonate-rich and sandy ones. Significant effects of sample size and fracture intensity were identified. The sealed fractures become gas-tight for certain injection pressures. However, the measured gas breakthrough pres-sures are still lower than the confining stresses. The gas-induced pathways can reseal when contacting water. These important findings imply that fractures that will be generated by excavation of a repository in such a clay host rock can seal with time.