Open Cut

MWD For Super-resolution Control Of R.A.B. Drilled Blast-hole Stand-off Distances

Open Cut » Drilling & Blasting

Published: May 17Project Number: C19023

Get ReportAuthor: Iain Mason | University of Sydney

Open-cut coal mine blasting losses are serious. Incorrect blast stand-off cost the equivalent of one unnecessary mine for every 10 existing Australian open cut mines. The 3D models now used to prescribe drill-bit direction are constrained in accuracy by pierce point affordability until production bits touch top-of-coal. Currently, coal overburden blast-hole drill-bits, directed by dead reckoning on a 10m x 10m grid, fly blind to depths set by interpolation of a 50m x 50m grid of reconnaissance pierce-points. The settings are inaccurate if the seam isn't flat. Blast damage would be cut if drill bits could be stopped short of coal.

Contributions of near-surface geophysics to raising pierce-point model resolution have been marginal so far, for benches are almost opaque to ground penetrating radar, & resonant seismically. In-fill drilling is too expensive unless it can be made an integral part of production. Many mines adjust the day's blast-hole depth by touching Top-of-Coal say on one blast-hole in five. Touch judging cutting depths of dark dust is valuable but not infallible.  Timing is critical. Drill bits can drop through a +/- 0.2m depth in less than ten seconds.

Drillers have tried for 80 years to automate touch judging, to update overburden maps in near-real time, to adjust target depth of the next hole by feeding forward results of drilling the last. Separately, fractional seconds behind real-time, blasthole drillers would like to be able to use forward looking near-bit tactile sensors to guide their bits as they close on Top-of-Coal. The usual rig logs - weight on bit, torque, air pressure, penetration rate - were never designed for rock recognition.  

But over the past decade drillbit-to-driller communications technology has matured to the point required for say extended reach oil well drillers to stop tricones precisely near a reservoir's cap by reading forward probing bit fields. Existing rods are cost engineered to survive 12-20 weeks sand-blasting. Rods are driven at a meter-a-minute, re- & de-couple every 10 mins. Grit is everywhere. Coal production is based on a rugged-replaceable-drill-rod technology into which comms wires are hard to retrofit.

We have established that cylindrical air-filled channels inside RAB drill strings can be used as they stand to retrofit operationally invisible, wideband communication links drillbit-to-driller. The installation of a wireless inside any Bowen Basin RAB string requires no change in rod re-supply. With prototyping we have established that the miniature, rugged, intelligent terminal transceivers needed, now embedded in mobile phones, can be lodged in existing counter-bore relief spaces, without significantly disrupting compressed air flows. Our development of a small, passive battery free, wireless top data swivel, should speed construction, installation &  testing of prototype look-ahead "radars", to see if they can first imperceptibly blend with, & then extend the existing practice of touching Top-of-Coal one blast-hole in five.

Related ACARP project reports, available from the ACARP website are C21005 and C24064.


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