Analyses of vibrator performance using long and short sweeps

Abstract

There appears to be a growing interest in improving subsurface seismic imaging by increasing spatial sampling as a result of increased receiver and/or source density. Cost-effectively improving spatial sampling, however, requires increased vibrator productivity. Some high-productivity techniques now used in survey operations are slip-sweep and independent simultaneous shooting (ISS). However, there is a debate that such methods should be used only by vibrator groups with short sweeps or single vibrators with long sweeps. Can we remove all in-field signal-to-noise enhancement processes and rely strictly on the seismic processing of high trace-density volumes? This paper focuses on the vibrator itself and determines the vibrator performance when driven by short and long sweeps. The experimental results demonstrate that a minimum sweep length is required to avoid significant degradation in vibrator performance at low frequencies (below 20 Hz). Above 20 Hz, the force power spectra with various sweep lengths remain consistent. Moreover, when coupling is poor, a short sweep will produce a better spectrum of the vibrator ground force than a long sweep.