Permeability of rock samples from the Kola and KTB superdeep boreholes at highP-Tparameters as related to the problem of underground disposal of radioactive waste

Abstract

AbstractAn experimental study of the samples collected from a depth of 3.8–11.4 km in the Kola and KTB superdeep boreholes, and from the Earth’s surface at the Kola drilling site was carried out at temperatures up to 600°C and pressures up to 150 MPa. The study was focused on the estimation ofin situpermeability of the deep-seated rocks, their palaeopermeability during metamorphic transformations, and their protective properties for HLW disposal. Permeability dependencies on pressure and temperature were obtained. An increase in confining pressure leads to a decrease in rock sample permeability. The temperature trends obtained are of different types: permeability may decrease within the entire temperature range, or it may firstly decrease, reach its minimum and then decrease. It was found that this permeability behaviour is due to rock microstructure transformations caused by the competing effects of temperature and effective pressure. A possiblein situpermeability trend for the superdeep section was proposed. A numerical simulation of convective transport was performed in order to determine a safe depth for the HLW well repository. The estimates obtained show that HLW well repositories can be used safely at relatively shallow depths.