Broadband Pseudo-random Vibratory Sweeps for Productivity Enhancement

Abstract

Increasing the vibratory seismic bandwidth especially on the low end brought new challenges. To reach deeper signal penetration, to improve reflection continuity and to enhance inversion solutions, broadband non-linear sweeps were introduced to overcome the mechanic and hydraulic limitations of a standard seismic vibrator. The main disadvantage is the substantially longer non-linear sweep length compared to the length of an equivalent energy linear sweep. Pseudo-random sweeps are also tested and applied with success, but have not gathered enough momentum for widespread use yet. We have developed a global optimisation method and defined constraints to produce broadband pseudo-random sweep sequences, which have the potential to replace broadband non-linear sweeps with satisfactory quality while reducing sweep length to increase productivity. The optimisation process could incorporate the need for higher sweep energy, lower spectral fluctuations and also keeping vibrator limitations, the control parameters which are unavailable in the standard software given by the vibrator manufacturers. Our numerical calculations show that optimised broadband pseudo-random sweeps have the potential for a few percentage productivity increase in normal applications, but several hundred percentage enhancement in urban seismic measurements, where resonance effect reductions are also on our side.