O f f s h o r e a n d o n s h o r e b r o a d b a n d s e i s m o l o g y 1382 The Leading Edge November 2013 SPECIAL SECTION: Offshore and onshore broadband seismologyCan land broadband seismic be as good as marine broadband?T he recent development of techniques to extend the bandwidth of marine towed-streamer surveys has significantly changed the marine seismic landscape. In fact, it has coined the new category of "broadband seismic," now synonymous with the marine towed-streamer market.The bandwidth challenge for marine towed-streamer seismic is well documented and is related to mitigating, or completely removing, the interference pattern from the interaction of the upgoing primary wave and its surface reflection (i.e., its ghost) at the source and receiver side. The interference results in the ghost notches in the amplitude spectrum which bound the useful bandwidth of the data at the high and low ends of the spectrum.Over the last few years, we have seen the proliferation of broadband solutions (which employ specific combinations of equipment, acquisition techniques, and processing methodologies) as well as standalone broadband processing treatments which can be applied in a variety of situations. The best broadband results to date have come from the solutions which have tackled both the receiver and source ghost notches to extend the seismic bandwidth to more than six octaves. Broadband benefitsBefore we consider whether we can achieve similar results with onshore surveys, let us try to qualitatively define the characteristics and benefits of six-octave bandwidth seismic that constitute our current benchmark. We will use data examples from a 3D narrow-azimuth survey using variabledepth streamer acquisition (SoubarasFigure 8. Case study 2. Broadband imaging onshore with six octaves. (a) Pre-STM of conventional " high-resolution" bandwidth of four octaves from 8 to 128 Hz. By adding additional octaves at the low-frequency end, we obtain (b) with six octaves starting from 2 Hz and a rich and detailed pre-STM image typical of the broadband marine examples shown in Figure 1. Data courtesy of PDO.

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Recent offshore discoveries in the Santos Basin have drawn attention to pre-salt targets; however, seismic imaging in the Santos Basin has proven to be challenging due to the complex geology and deep pre-salt targets. Variable-depth streamer acquisition is an emerging technology that provides opportunities to increase the usable bandwidth in both the low and high frequency ranges, gain stronger low frequency penetration, and reduce acquisition related noise. However, this new acquisition poses additional challenges to seismic processing, creating a need for new processing technologies and work flows. To overcome both the geological and acquisition-related challenges, we modify the processing work flow, then utilize a real field data set of variable-depth streamer acquisition to demonstrate that variable-depth acquisition combined with advanced processing techniques is beneficial to pre-salt imaging in the Santos Basin.

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