Acoustic emission analysis for rock–bit interactions in impregnated diamond core drilling

•Impregnated diamond drilling performance were analysed by Acoustic Emission (AE).•Bit wear and state of the bit were inferred from the signal analysis.•Strong relations between drilling operational parameters and AE were established.•AE monitoring can improve the drilling performance in deep explorations.

Our goal was to determine the relationship between acoustic emission (AE) signals and diamond drill bit wear in order to gather and interpret data to allow overall improvement of drilling performance. Achieving improved performance required investigating various drilling parameters to understand the characteristics of the AE signals in terms of their interaction with the operational parameters of the drilling apparatus. Echidna drill apparatus that simulates field exploration diamond drilling on a small scale was used to monitor AEs during rock–bit interaction. AE sensors were attached to both the drill and the rock in question to record acoustic signals being emitted during the process of drilling. Two different types of tests were conducted – step tests and wear tests. Step tests on the Echidna drill included stepping down the depth of cut from 130 µm to 0 µm, while the cutting speed remained constant. Wear tests, again using the Echidna drill, involved accelerating the wear rate of the drill bit by using it to cut highly abrasive rock in two different ways. Based on the step test results, a series of linear relationships were developed. These relationships make it possible to estimate the depth of cut, weight on the bit (WOB) and torque on the bit (TOB) by simply using the time spectrum of the AE signals. Wear tests also showed that AE amplitudes start to trend down as wear begins to accelerate.