The low-frequency seismic vibrator: design and experimental verification

Abstract

Extending the Vibroseis acquisition bandwidth towards low frequencies has become an increasing trend in land seismic exploration. It is clear that adding low-frequency content to seismic data can be beneficial to enabling waveform inversion for velocity model determination or refinement, improving the resolution of seismic data and obtaining structural information of deeper reservoirs. These geophysical benefits have been highlighted by many authors, for example Baeten et al. (2013) and Mahrooqi et al. (2012). However, using the Vibroseis method to acquire low frequency seismic data becomes very challenging. Owing to mechanical and hydraulic limitations, most conventional seismic vibrators cannot produce sufficient low-frequency force for transmission of seismic energy into deep ground below 10 Hz. Because of this fact many sweep design techniques aimed at enhancing the Vibroseis low-frequency contents have been developed (Bagaini 2006, 2008; Sallas 2010; Baeten 2011). These low frequency sweeps can enable conventional vibrators to shake as close as possible to their low-frequency mechanical limitations. Unfortunately, this approach requires a lower drive level and hence a slower sweep rate resulting in a longer sweep length. Therefore, the generation of extra low-frequency bandwidth with low frequency sweep methods usually has an impact on productivity.