水銀圧入法による岩石の空隙寸法分布測定

Abstract

岩石の空隙構造は透水係数等の物性値を大きく左右するため，その代表的なパラメータである有効空隙率および空隙寸法の分布特性を定量的に評価することが重要である．世界各地から採取された15種類の岩石の計108個の試料について，水銀圧入法によりそれらの有効空隙率と空隙寸法分布を測定したデータを取りまとめ，各種岩石の空隙構造の特徴を報告する．岩石の種類，年代と産地の違いによって，有効空隙率と空隙の寸法分布特性が大きく異なり，かつ，その空隙寸法分布の特性は空隙率との相関性が必ずしもあるとは限らないことが明らかになった．岩石の空隙寸法分布を測定する手段として，水銀圧入式ポロシメータは比較的実施簡便で，測定データの信頼性と再現性も本研究により確認された．ただし，有効空隙率の小さい（例えば，1％未満）緻密な深成岩の場合は，空隙半径の大きい範囲における測定結果が誤差を含む可能性がある．

Pore structure of rocks strongly influences permeability and other physical properties, therefore quantitative measurements of porosity and pore size distribution of rock samples are necessary and important in engineering geology. We collected total 108 rock samples of 15 rock types and measured their porosity and pore size distribution by the mercury intrusion porosimetry method and report the data and characterize the pore size distribution in this paper. Porosity and pore size distribution of rocks significantly vary with rock type, geological age and their locality. Moreover, the characteristics of pore size distribution did not show a unique correlation with the porosity of the same rock sample. Therefore, to evaluate pore size distribution of rocks is essential and useful for discussing fluid transportation related with rock pore structure. Mercury intrusion porosimetry is a useful method for pore size distribution measurements, and its reliability and repeatability were confirmed through this experimental study. For low-porosity（e.g. ＜1％）rocks, however, measured results of pore size distribution in large-size range（e.g. around 100μm）might have some error probably due to roughness of rock sample surfaces.