Experimental study of swelling-induced crack self-sealing process in claystone samples with indirect water injection process

The self-sealing process of cracks in clayey rocks is considered as an essential mechanism for long-term confinement performance in deep geological disposal of radioactive waste. The swelling of clay minerals in these rocks plays a pivotal role in crack closure. In this work, we investigate the crack closure process and its impacts on transport properties in initially cracked samples of Callovo-Oxfordian claystone (COx). The novelty is to create an indirect crack hydration process, which is close to the field condition. For this purpose, an original experimental mock-up is designed. Four sets of samples are prepared and, respectively, drilled along the parallel direction to the bedding planes. The values of swelling pressure and water permeability are measured during the injection of water. The gas breakthrough pressure after crack sealing is also investigated. The experimental results suggest that the apparent swelling pressure of the cracked sample is higher than that of the intact sample. The swelling deformation is more important in samples parallel to the bedding planes than perpendicular to them. The results of this study also show that the gas breakthrough pressure of the cracked sample is strongly correlated with its swelling pressure. The water permeability after gas breakthrough test is further determined and it is observed that the gas-induced channels can be closed by water saturation. • An original experimental system is used to study self-sealing process in clayey rock. • A novel approach studies self-sealing without direct water injection into fracture. • Permeability, swelling and breakthrough pressure reflect self-sealing process. • Swelling pressure is an efficient indicator of self-sealing of cracks and fractures. • The gas breakthrough pressure is positively correlated with the swelling pressure.