粘土ゲルが充填した多孔質媒体中の水の制限拡散の計測

Restricted diffusion of water in clay gel saturated porous media

大窪 貴洋; 山口 真*

Okubo, Takahiro; Yamaguchi, Makoto*

磁場勾配NMR法により、粘土ゲルが充填したガラスビーズ層中の水の自己拡散係数の拡散時間依存性を測定した。測定にあたっては、6ms以下の短い拡散時間に対して振動磁場勾配を用いる手法、6200msといった長い拡散時間に対しては、対磁場勾配パルスを適用して測定を行った。これら測定から得られた水の自己拡散係数の拡散時間依存性を解析することにより、粘土ゲル充填ガラスビーズ層の比表面積及び屈曲度を評価した。

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, , and tortuosity, , are extracted by analyzing the diffusion coefficient of fluid molecules as a function of diffusion time, . Since and 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 and for water and clay gel saturated porous media modeled by glass beads beds. 17 interval bipolar gradient stimulated echo ( ms ms) and oscillating gradient spin echo sequences ( ms 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 and .