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Report No.

Restricted diffusion of water in clay gel saturated porous media

Okubo, Takahiro; Yamaguchi, Makoto*

The time-dependent diffusion coefficients of fluid molecules in confining geometries have been studied by NMR experiments with magnetic gradient. The characteristics of porous media such as the ratio of the surface area to pore volume, $$S/V_p$$, and tortuosity, $$Upsilon$$, are extracted by analyzing the diffusion coefficient of fluid molecules as a function of diffusion time, $$D_{eff}$$. Since $$S/V_p$$ and $$Upsilon$$ are related to permeability, it have been a very powerful technique for investigating the transport phenomena of fluids in porous media. Therefore, we attempted to apply these methods to clay saturated porous media which would be considered as barrier environment in geological disposal system of high-level radioactive waste. NMR measurements of time-dependent diffusion coefficient were performed to estimate $$S/V_p$$ and $$Upsilon$$ for water and clay gel saturated porous media modeled by glass beads beds. 17 interval bipolar gradient stimulated echo$cite{3}$ ($$D_{eff} = 6$$ ms $$sim 200$$ ms) and oscillating gradient spin echo sequences ($$D_{eff} = 0.625$$ ms $$sim 5.626$$ ms) were used to measure time-dependent diffusioncoefficients. Mitra equation and Pade approximation were applied to analyze time-dependent diffusion coefficient for the purpose of extracting $$Upsilon$$ and $$S/V_p$$.



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