2009 Volume 50 Issue 4 Pages 238-247
Evaluation of the role of fractures as major water-conducting features in sedimentary rocks is indispensable for modelling and analyses of groundwater flow. We conducted core logging, acoustic televiewer logging and fluid electric conductivity logging in a borehole in Neogene sedimentary rocks, i.e., in the Koetoi and Wakkanai Formations in the Horonobe area Hokkaido, Japan, to evaluate the role of fractures as major water-conducting features. Few of the fractures in the Koetoi Formation are associated with water inflow points into the borehole, in contrast to the number of flowing fractures in the Wakkanai Formation. The relationship of fracture distributions and apertures to inflow points suggests that: 1) fracture interconnections in the Koetoi Formation are poor, while those in the Wakkanai Formation are expected to be more developed, at least more than in the Koetoi Formation, 2) fracture apertures in the Wakkanai Formation tend to be larger than those in the Koetoi Formation. These suggest that the Koetoi Formation would behave as a porous medium whereas the Wakkanai Formation would be behave hydrogeologically as a heterogeneous, fractured medium.
