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

Abstract

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. Index Terms-Borehole radar (BHR), guided electromagnetic (EM) wave, imaging.1545-598X

Fracture identification by reflected guided borehole radar waves

“…When a BHR is attached to conductive cables at its top and bottom or is operated in a borehole filled with conductive mud or water, both up-and down-going waves guided by the borehole will be induced (Mason et al, 2008;Zhou and van de Werken, 2015). When guided waves, travelling along the borehole, hit geological discontinuities, they may be reflected, then detected by the BHR receiver.…”

“…We have found (Mason et al, 2008;Zhou and van de Werken, 2015;Mao and Zhou, 2017) that if a BHR is attached to a conductive wire or runs in a conductive saline water-filled borehole, then reflected guided borehole radar waves, travelling along the borehole, are often recorded. They can interfere with normal BHR surveys and can be suppressed (Huo et al, 2018).…”

“…They can interfere with normal BHR surveys and can be suppressed (Huo et al, 2018). However, drill-string guided BHR waves can be used for seeing ahead of the drill-bit (Zhou and van de Werken, 2015;Mao and Zhou, 2017;Zhou and Madden, 2018) and detecting geological interfaces especially for those interfaces sub-perpendicular to the borehole (Mason et al, 2008;Zhou and van de Werken, 2015).…”

Coal top detection by conductively guided borehole radar wave imaging for open cut blast‐hole drilling

“…). Zhou and van de Werken () advocated that the guided waves along a drill string can act as a forward‐looking event for imaging ahead of the drill bit while drilling boreholes. Through field experiments with different configurations, they also demonstrated that the guided BHR waves can be used for recognition of geological boundaries along the borehole.…”

“…Although the feasibility of look‐ahead capability of the guided BHR wave imaging has been demonstrated in both Zhou and van de Werken () and Mao and Zhou (), the forward‐looking characteristics and factors affecting the forward‐looking events in the open‐cut environment, such as overburden and coal seam thickness, have not been investigated. This section provides some analysis of these factors on guided BHR wave imaging for predicting the top of the coal seam and more information can be found in Zhou and Madden ().…”