Evaluation of the role of fractures as the major water-conducting features in Neogene sedimentary rocks

Funaki, Hironori ; Ishii, Eiichi   ; Tokiwa, Tetsuya

Evaluation of the role of fracture as the major water-conducting feature in sedimentary rocks is indispensable information to carry out the modelling and analysis of the groundwater flow. We conduct core logging, acoustic televiewer logging and fluid electric conductivity logging at a borehole to clarify the relationship between fracture and flow point. As a result, most of the fractures in the Koetoi Formation don't have a function as major water-conducting features, but some of the fractures in the Wakkanai Formation do. The further statistical analysis indicates; (1) fracture interconnectivity in the Koetoi Formation is poor, while that in the Wakkanai Formation exists to some extent, (2) fracture aperture in the Wakkanai Formation tends to be more than that in the Koetoi Formation. These suggest that the Koetoi Formation would be porous medium and the Wakkanai Formation would be stronger in property as fractured medium than the Koetoi Formation.