No abstract

No abstract

No abstract

INTRODUCTIONOur research into rock permeabilities at elevated T and P was initiated in 1975 and intended to address the problem of constructing a model for formation of skarn-hosted ore deposits. Most research on such settings has concentrated on mechanisms of melt intrusion and intrusive body formation, changes in temperature fields and stresses inside and in the vicinity of the intrusive body, the thermodynamic properties of melts, fluids and associated solutions, or the infiltration effects themselves. The infiltration and cumulative properties of a fluid environment itself, i.e. the rock matrix which hosts and is converted to skarn and ore, have been less well studied, despite the fact that rock permeability controls the scale and trends of ore-metasomatic processes. At the time we began this study, the available information on deep rock permeability largely reflected the needs of the petroleum and gas industry, and permeability experiments were generally conducted to 150 a C and a few hundreds of atmospheres. The physical-chemical conditions of skarn formation, however, required knowledge of permeability to 600-700 a C and 1-2 kbar. In the works of Fatt and Davis (1952), Brace et al. (1968), andZoback andByerlee (1975), permeability measurements were made to 4-5 kbar at room temperature. Unfortunately, none of the studies provided a means of predicting permeability values at high temperatures Fluids in the Crust: Equlibrium and transport properties.

An 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 of in situ permeability 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 possible in situ permeability 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.