Real-time prediction of coal top through guided borehole radar wave imaging for open cut blast-hole drilling

The aim of this project was to demonstrate the feasibility of integrating a BHR onto a drilling string for coal-top prediction during blast-hole drilling.  The project asked two questions:

• Can downhole radar data be communicated to the driller in the cab fast enough for real-time processing and visualisation?
• Can a BHR, embedded on the drill string, generate the look ahead waves needed to detect coal and other key strata ahead of the drill bit?

The questions were successfully answered through the following key achievements:

• Wireless communication between the downhole BHR and the driller through the air column in normal drill rods was demonstrated by using a modified, waterproofed Raspberry Pi 4 based dual band (2.4 GHz and 5 GHz) communication system located on an operational drill bit, as a downhole transponder. Communication daughter boards of JEHR radars have been adapted to stream data wirelessly between drill bit and driller via a Raspberry Pi data-stream organiser & repeater, and integrated with a drill stabiliser
• Field tests indicate that this communication system can wirelessly transmit downhole data at least 60 m up hole through air-filled drill rods, on both ISM bands if the rod joint ID exceeds 80mm, on the 5 GHz band if the joint ID exceeds 34mm which will meet most blasthole drilling needs for Australian open-cut mines. Our system has a high data transmission rate (up to 58 Mbps for 2.4 GHz wireless LAN and 114 Mbps for 5 GHz wireless LAN).
• Wireless calls for minimal alteration to the drill rig. The top drive of at least some RAB rigs might provide a pathway for data transmission not only for the borehole-radar based bit navigation above coal-top but also for other downhole rock recognition and navigation Measurement-While-Drilling (MWD) or Logging-While-Drilling (LWD) technologies. There may be no need for a top data swivel.
• Software for a real-time radar data processing, visualisation, automated seam-prediction, and warning system has been prototyped and demonstrated in both the laboratory and field trials.
• Numerical modelling study using Computer Simulation Technology (CST) Studio Suite indicates that integrating BHR antennas onto the drill string can both selectively generate look-ahead (TE11 mode) waves for coal top imaging and then switch into a feel-ahead TEM mode to map rock resistivity immediately ahead of the drill bit in real time with high resolution, both key to RAB drill bit navigation technology, down to and past the bit.
• A field trial using BHR radar transmitter (Tx) and memory logging receiver (Rx) boards from JEH Radar Consulting has established that BHR waves can be coupled onto a fully powered up drill-string to drive two types of guided borehole radar waves, TEM for “feel-ahead” and TE11 for “look-ahead”. Both have been launched in both laboratory and field trials by antennas close-coupled and conformal with the drill-stabiliser.

This project has successfully demonstrated, through theoretical (numerical) and experimental investigations, the feasibility of integrating a BHR onto a drill-string for top of coal prediction.