Conductively Guided Borehole Radar Wave for Imaging Ahead of a Drill Bit

A guided wave is induced along a conductive logging cable or a conductive water-filled borehole during borehole radar (BHR) surveying. Such a guided wave is normally considered as unwanted interference to normal BHR waves and needs to be suppressed, either through BHR designs or data processing. In this letter, we advocate that the guided wave can be coupled onto a drill string, which can act as a forward-looking antenna for imaging ahead of the drill bit while drilling. Using data collected by a monostatic BHR with different configurations at an abandoned mine site in Brukunga, South Australia, we demonstrate that the forward-looking capability of the BHR is about 2-6 m in the tested borehole section.