We compared and analyzed hard-rock drilling elastic energy emission between diamond-impregnated coring and reverse-circulation (RC) percussion drilling methods from an experiment at Brukunga, South Australia. The two drilling mechanisms generated very different seismic wavefields. This comparison emphasized their energy radiation differences and signal characteristics. From the field data, by investigating the raw data energy, frequency analysis, and crosscorrelation tests, the seismic records from percussive RC drilling provided a strong indication that the drill-bit energy could be suitable for drill-bit seismic imaging purposes; the energy radiation from the percussive RC bit could also provide high-resolution images with borehole seismic acquisition. In contrast, at comparable drilling conditions the coring drilling using a diamond-impregnated coring bit was quiet, the radiated acoustic energy from this drilling mechanism was difficult to detect by a surface receiver array, and there was no convincing visible drill-bit signal observed in the experiment.
We use the direct wave interferometry migration with coherency measurement to image the diamond drill-bit. The sucess of such imaging can prove if the direct waves from the drill-bit can be detected. The drilling signals usually contain strong narrow band inteference noises. We suggest to use interferometry by deconvolution for migration, which widens the cross spectrum, hence the weak coherent features can be better observed. Additionally, we suggest to integrate coherent measurement of semblance or Multiple Signal Classification (MUSIC) into the algorithm in order to detect weak drill-bit signal. We test both methods with a synthetic and a diamond drill-bit seismic-while-drilling (SWD) field data. MUSIC coherency shows relatively better spatial resolution in contrast to semblance method. It also demonstrates better detectability of weak signal than summation and semblance. Our field SWD data also indicates that the interferometry migration can image the diamond drill-bit with appropriate survey parameters, and the MUSIC method achieves a high spatial resolution.
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