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Broadband imaging via direct inversion of blended dispersed source array dataNormal access

Authors: M. Caporal, G. Blacquiere and M. Davydenko
Journal name: Geophysical Prospecting
Issue: Vol 66, No 5, June 2018 pp. 942 - 953
DOI: 10.1111/1365-2478.12584
Organisations: Wiley
Language: English
Info: Article, PDF ( 6.38Mb )

Summary:
Although seismic sources typically consist of identical broadband units alone, no physical constraint dictates the use of only one kind of device. We propose an acquisition method that involves the simultaneous exploitation of multiple types of sources during seismic surveys. It is suggested to replace (or support) traditional broadband sources with several devices individually transmitting diverse and reduced frequency bands and covering together the entire temporal and spatial bandwidth of interest. Together, these devices represent a so-called dispersed source array. As a consequence, the use of simpler sources becomes a practical proposition for seismic acquisition. In fact, the devices dedicated to the generation of the higher frequencies may be smaller and less powerful than the conventional sources, providing the acquisition system with increased operational flexibility and decreasing its environmental impact. Offshore, we can think of more manageable boats carrying air guns of different volumes or marine vibrators generating sweeps with different frequency ranges. On land, vibrator trucks of different sizes, specifically designed for the emission of particular frequency bands, are preferred. From a manufacturing point of view, such source units guarantee a more efficient acoustic energy transmission than today’s complex broadband alternatives, relaxing the low- versus high-frequency compromise. Furthermore, specific attention can be addressed to choose shot densities that are optimum for different devices according to their emitted bandwidth. In fact, since the sampling requirements depend on the maximum transmitted frequencies, the appropriate number of sources dedicated to the lower frequencies is relatively small, provided the signal-to-noise ratio requirements are met. Additionally, the method allows to rethink the way to address the ghost problem in marine seismic acquisition, permitting to tow different sources at different depths based on the devices’ individual central frequencies. As a consequence, the destructive interference of the ghost notches, including the one at 0Hz, is largelymitigated. Furthermore, blended acquisition (also known as simultaneous source acquisition) is part of the dispersed source array concept, improving the operational flexibility, cost efficiency, and signal-to-noise ratio. Based on theoretical considerations and numerical data examples, the advantages of this approach and its feasibility are demonstrated.

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