Evaluation of the forward-looking capability of conventional borehole radar

Abstract

There is a strong need to develop real-time imaging technologies to enable the driller to 'see' the subsurface structures ahead of the drill-bit and around the borehole during borehole drilling. One of the ways to realise such imaging while drilling is to use borehole radar (BHR) techniques. In this paper, a conventional non-directional mono-static BHR will be evaluated for its forward-looking capability by using the data collected at an abandoned mine site at Brukunga, South Australia. Here we demonstrate that the conventional BHR can be electrically coupled on to a conductive wire or drill-rod whilst a guided wave is induced along the axial wire or drill string making it possible for imaging ahead of the drill-bit by integrating the BHR with the steel drill string. The drill-rod ahead of the BHR acts as a forward-looking antenna. When the guided wave travels to the end of the drill-bit, part of the energy is reflected by the drill-bit and the remaining energy radiates in front of the drill-bit, and is reflected by the geological/electrical discontinuities, recorded by the BHR. The forward-looking capability of the BHR is about 2-6m in the tested borehole section.