Understanding the size and connectivity of pore spaces accessible to groundwater flow within a fracture is important for repository safety assessment. In this study, a novel, simple in situ method was developed to investigate the changes in pore connectivity within a fracture when fracture displacement occurs. The method utilizes a conventional packer system in a borehole. Fractures with low pore connectivity were investigated in situ by applying this method at the Horonobe Underground Research Laboratory. The test results demonstrated that pore connectivity remained stable, indicating no significant changes in rock permeability even when the fracture underwent lateral displacement. The containment performance of a rock formation can be estimated by combining this method with an investigation of groundwater flow-accessible pore size within a fracture, considering the potential lateral fracture displacement caused by future crustal movement.
 The results of this study can be used to estimate the long-term containment performance of the host rock in the geological disposal context and also to evaluate the sealing performance of reservoirs for carbon dioxide capture and storage.