Fine-scale velocity distribution revealed by datuming of very-high-resolution deep-towed seismic data: Example of a shallow-gas system from the western Black Sea

Abstract

Very-high-resolution (VHR) marine seismic reflection helps to identify and characterize potential geohazards occurring in the upper part (300 m) of the subseafloor. Although the lateral and vertical resolutions achieved in shallow water depths ([Formula: see text]) using conventional surface-towed technology are adequate, these resolutions quickly deteriorate at greater water depths. The SYstème SIsmique de Fond (SYSIF), a multichannel deep-towed seismic system, has been designed to acquire VHR data (frequency bandwidth [220–1050 Hz] and vertical resolution of 0.6 m) at great water depths. However, the processing of deep-towed multichannel data is challenging because the source and the receivers are constantly moving with respect to each other according to the towing configuration. We have introduced a new workflow that allows the application of conventional processing algorithms to extended deep-towed seismic data sets. First, a relocation of the source and receivers is necessary to obtain a sufficiently accurate acquisition geometry. Variations along the profile in the depth of the deep-towed system result in a complex geometry in which the source and receiver depth vary separately and do not share the same acquisition datum. We have designed a dedicated datuming algorithm to shift the source and receivers to the same datum. Thus, the procedure allows the application of conventional processing algorithms to perform velocity analysis and depth imaging and therefore allows access to the full potential of the seismic system. We have successfully applied this methodology to deep-towed multichannel data from the western Black Sea. In particular, the derived velocity model highlights shallow gas charged anticline structures with unrivaled resolution.