Several borehole logging methods were tested in a 103m deep hole drilled in Inada Granite, Ibaraki, Japan to detect permeable fractures. Borehole camera logging is essential to judge whether a fracture is open. Water quality logging is effective to detect permeable fractures from which groundwater inflows. Hydrophone VSP logging is effective to detect a permeable fracture on condition that the fracture plane and wave direction make near right angle. Sonic logging seems to be effective to detect permeable fractures. Flow meter logging using heat pulse method was tested but not to be proven effective because of too low speed of vertical flow in the hole.
Double-packered permeable tests were performed on three representative depth sections (26, 85 and 100m deep) each of which is thought to have permeable fracture(s). All the three sections have permeability greatly larger than those of intact bedrocks. Groundwater samples were successfully collected from all the sections which proved effectiveness of this multiple application of borehole logging methods to detect permeable fractures. Water quality of all the samples from the three depth sections were measured to show neutral to weak alkaline Ca>Na-HCO3 type with almost no dissolved oxygen and electric conductivity three times as high as local surface waters. It is somewhat strange that even the shallowest groundwater has the same water quality as the deepest water has. This was probably because of the higher water head distribution with increasing depth. Under that condition the deepest groundwater flows into the shallowest section prior to sampling, which can make water quality of the shallowest section changed towards that of the deepest one.
