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

Type Article
Date 2020-09
Language English
Author(s) Colin FlorentORCID1, Ker StephanORCID1, Marsset Bruno1
Affiliation(s) 1 : Ifremer, REM-GM, 3 Centre de Brest, BP 70, 29280 Plouzané, France
Source Geophysics (1942-2156) (Society of Exploration Geophysicists), 2020-09 , Vol. 85 , N. 5 , P. A31-V414
DOI 10.1190/geo2019-0686.1
Abstract

Very High-Resolution (VHR) marine seismic reflection helps to identify and characterize potential geohazards occurring in the upper part (300 m) of the sub-seafloor. Whereas the lateral and vertical resolutions achieved in shallow water depth (<200 m) using conventional surface-towed technology are adequate, these resolutions quickly deteriorate at greater water depths. SYSIF (SYstème SIsmique Fond), 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 as both the source and receivers are constantly moving with respect to each other according to the towing configuration. We present a new workflow that allows the application of conventional processing algorithms to extended deep-towed seismic datasets. 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 where the source and receiver depth vary separately and do not share the same acquisition datum. We designed a dedicated datuming algorithm to shift the source and receivers to the same datum. The procedure thus allows the application of conventional processing algorithms to perform both velocity analysis and depth imaging and therefore allowing access to the full potential of the seismic system. We 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.

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