Data acquisition of groundwater flow and mass transport properties in sedimentary rocks, 2; Considerations of mass transport properties based on pore size distribution, chemical composition and air permeability of the Horonobe specimen

Hara, Akio

Pore size distribution, chemical composition and air permeability are analyzed on diatomaceous mudstone specimens of Koetoi and Wakkanai formation sampled from boreholes HDB-1, HDB-2 and HDB-5 which drilled by Japan Nuclear Cycle Development Institute in Horonobe area Hokkaido Japan. Permeability of Koetoi and Wakkanai formation is related to diagenetic facis changes of diatom fossils. Diatom fossils are belonging to Opal-A facies in the specimens of Koetoi formation. Pore size distribution of Koetoi formation concentrated around 1000 angstrom and permeability is higher than Wakkanai formation. In Wakkanai formation, diagenetic facies of diatomaceous fossil is changes into Opal-CT facies and pore size distribution concentrates between 20 to 40 angstrom and permeability declines abruptly. The specimen which includes high SiO content tend to have low permeability and high concentration of pore radius distribution between 20 to 40 angstrom. The degree of concentration should be caused to reducing permeability. A specimen sampled at 600m depth the formation boundary has high porosity and permeability than the specimen sampled around 200 to 300m depth below the formation boundary. The lowest permeability within the Koetoi and Wakkanai formation is observed in the Wakkanai formation at 200 to 300m depth of the formation boundary between Koetoi and Wakkanai formation. These strata have possibility of functioning as a seal rock, which can keep the high pressure and disturb ground water flow.