Enhanced Vibroseis. The next step in improving land 2D - 4D

Abstract

The field of vibroseis has seen various advances over recent decades which have been mostly of a gross nature. These include the development and operation of heavier vibrators, improvements in positioning and tracking, the deployment and control of larger numbers of vibrators acting either as part of a fleet or as individual sources. More subtly, improved QC brought about by incorporation into the source decoder of sufficient recording channels which may better define vibroseis signatures has also been available to suitably equipped crews. Meanwhile, some seismic land recording systems also have been able to keep up with these source-related improvements, with the majority of advances made in cableless and hybrid systems which can work with large numbers of independent sources thanks to real time QC options, ease of deployment and a mix-and-match approach of recording system architectures. The basic assumptions in terms of the frequency and force put into the ground, however, remain fixed on the notion of weighted sum ground force (WSGF) as espoused by Sallas in the 1980's. Most source control equipment and QC methods are still built on the premise that this is a sufficiently good approximation for most circumstances. However, even basic testing with load cells and/or down hole sensors reveal that this assumption is poor at low frequencies, and potentially significantly inaccurate at high frequencies. The problems resulting from this incorrect WSGF-approach are important limiting factors in terms of taking the next steps in vibroseis productivity and data quality improvement. This is true not only for typical land 2D/3D surveys but also the shortcomings of the WSGF approach may seriously limit the progress that may be made on land 4Ds where far more accurate understanding of source characteristics is essential. Initial results using The Enhanced Vibroseis method shows the potential to solve many of these issues and may be seen as the next major step the industry needs to make to progress this form of land acquisition