Permeability and diffusivity measurements with the He-gas method of disturbed zone in rock samples cored from the full- scale experimental deposition holes in the TVO research tunnel

摘要

Six series of samples cored from the surfaces of two full-scale experimental deposition holes in the TVO Research Tunnel have been measured by a novel helium gas method in order to determine the existence of a disturbed zone close to the bored surface. First the recently introduced helium gas method for diffusion and permeability measurements on fractured and porous rock samples is briefly introduced, and the measuring techniques together with the mathematical models that are used to analyse the experimental results are discussed in some detail. The whole breakthrough curves of 30 samples have been measured, and the results have been analysed by the introduced models. As a result from the these fits, matrix porosities, effective diffusion coefficients and permeability coefficients of the gas phase have been determined. The measured diffusion and permeability coefficients both indicate the existence of a disturbed zone close to the bored surface. In the six series of samples that were analysed, the thickness of this zone varied between 17 and 21 mm. The maximal length of individual microcracks was estimated to be about 12 mm. Excluding the sample which supposedly is intersected by microcracks, the ratio of the diffusion coefficients of the disturbed zone and the intact rock was found to vary between 5 and 31, and the corresponding ratio of the permeabilities varied between 10 and 90. The diffusion coefficients of helium can also be estimated for water saturated samples, and similarly the hydraulic conductivities of the samples can be determined from their measured permeabilities. The values of these quantities are given in the concluding section. (orig.) (14 refs., 35 figs., 6 tabs.). (Atomindex citation 27:040808)