Energy balance of a drill-bit seismic source, part 2: Drill-bit versus conventional seismic sources

The radiation properties of a downhole drill-bit seismic source are related to the amplitude and frequency of the forces exerted by the working bit. The main vibration modes of roller-cone and polycrystalline diamond compact (PDC) bits are investigated under different drilling conditions. The analysis includes vibrations produced by teeth indention, multilobed patterns, bouncing with periodic and random effects, single-cutter forces, stick-slip and whirling effects, mud-pressure modulation forces, and bit wear. Drill-bit radiation properties are calculated using the results obtained in part 1 of this paper and are numerically compared to the radiation of conventional vertical seismic profiling (VSP) sources.