Subsurface water-filled fracture detection by borehole radar: a case history

Borehole radar is a special mode of Ground Penetrating Radar. It has several distinguished features from surface radar. For examples, by means of borehole access to regions below the surface, the antennas can be located relatively close to the anomalies or targets to be measured, resulting in more precise targets response in deep subsurface applications. The experimental site is located on the top of a granite hill west of Beijing. There are a group of boreholes intersected by many fractures; both single-hole and cross-hole measurements were carried out. The measured data are processed and interpreted. The radial detecting range is more than 30 meters at this site. The subsurface fracture distribution can be imaged very clearly. Many fractures can be "seen", and their distance from borehole and their dip angle can be determined. The azimuth determinations for these fractures are possible in some situations. It is concluded that the borehole radar is an effective tool for subsurface imaging.