In situ diffusion experiment in granite: phase I.
A program of in situ experiments, supported by laboratory studies, was initiated to study diffusion in sparsely fractured rock (SFR), with a goal of developing an understanding of diffusion processes within intact crystalline rock. Phase I of the in situ diffusion experiment was started in 1996, with the purpose of developing a methodology for estimating diffusion parameter values. Four in situ diffusion experiments, using a conservative iodide tracer, were performed in highly stressed SFR at a depth of 450 m in the Underground Research Laboratory (URL). The experiments, performed over a 2 year period, yielded rock permeability estimates of 2 x 10(-21) m(2) and effective diffusion coefficients varying from 2.1 x 10(-14) to 1.9 x 10(-13) m(2)/s, which were estimated using the MOTIF code. The in situ diffusion profiles reveal a characteristic "dog leg" pattern, with iodide concentrations decreasing rapidly within a centimeter of the open borehole wall. It is hypothesized that this is an artifact of local stress redistribution and creation of a zone of increased constrictivity close to the borehole wall. A comparison of estimated in situ and laboratory diffusivities and permeabilities provides evidence that the physical properties of rock samples removed from high-stress regimes change. As a result of the lessons learnt during Phase I, a Phase II in situ program has been initiated to improve our general understanding of diffusion in SFR.
Vilks
P
P
AECL, Whiteshell Laboratories, Pinawa, Manitoba, Canada R0E 1L0. vilksp@aecl.ca
Cramer
J J
JJ
Jensen
M
M
Miller
N H
NH
Miller
H G
HG
Stanchell
F W
FW
D004058:Diffusion; D055593:Geological Phenomena; D005844:Geology; D008962:Models, Theoretical; D010539:Permeability; D011850:Radioactive Waste; D012822:Silicon Dioxide / Q000737:chemistry*; D018505:Waste Management
D011850:Radioactive Waste; C007886:granite; D012822:Silicon Dioxide