We have performed tests at the Boart Longyear drilling test site at Brukunga, South Australia, with grouted geophone sensor strings in nearby drillholes that demonstrate the feasibility of using diamond drilling process as a source to gather high quality seismic velocity data in the earth. These geophone sensor strings and the seismic while drilling methodology develop dare envisaged for 'life of mine' sensing and geological characterisation. Thus, various tests have been performed to evaluate whether the gathered data might be useful for various future applications from advanced exploration and geological characterisation through to mining and extraction. Various modifications of the seismic string installation with respect to 1-C and 3-C sensor pods and grouting method were trialled and all configurations were generally found useful. However, some configurations are better suited for tomography and others better for later micro-seismic analysis. The drill as a seismic source was found to be rich in both P and S wave modes with reasonable energy from 10 Hz to over 500 Hz, at distances of up to 200m from the diamond drill bit. Small modifications to the drilling procedure allowed us to perform checks on the data quality and acquisition system. The lack of a measured 'zero-time' or measured source signature with the SWD creates serious challenges for implementing conventional cross-well tomography algorithms with the drill-cutting as a seismic source in one hole and the geophone string in another. Thus, the tomography inversion algorithms must be changed, and a good reference velocity model used as a starting seed for inversion. This is where the slight modifications to drilling procedure may provide extra data. A configuration of two boreholes with permanent sensors and the drilling of another hole in line with the first two allows cross-correlation methods to reasonably extract travel times. However, the repeating pattern of energy generated by the seismic source due to drill rotation at 10-40 Hz presents challenges to this approach too, which we partially overcome with use of time-gating via a reference velocity model collected via straight-forward Zero Offset vertical seismic profiles. Despite challenges, seismic while drilling with diamond drill rigs in conjunction with geophone sensor arrays is feasible and should provide every useful life-of-mine data.

Open-Access Online Publication: May 31, 2023