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DATA PROCESSING & INTERPRETATION 


A new broadband solution takes to the water


 A superior broadband marine seismic solution offers a new combination of leading equipment, unique acquisition techniques and patented de-ghosting and imaging technology to provide better subsurface images. Jo Firth reports.


W


henever seismic data is acquired, the reflections recorded have different frequencies, and the


difference between the highest and lowest frequencies is the bandwidth. Te broader the bandwidth, the sharper the wavelet and the higher the resolution of the resulting seismic image. However, complications arise when data


is acquired with a large bandwidth. Different sources produce different bandwidth signals, the Earth quickly attenuates higher frequencies, there are issues with just how much of any signal is preserved by the receivers, and the data needs to be appropriately processed once recorded. Te solution lies in answering the challenges that are under our control, ie source and receiver bandwidth and high-fidelity processing as unfortunately we cannot change the Earth’s behaviour.


Fig. 1 BroadSeis produces an ideal wavelet, with the best signal-to-noise ratio and best low-frequency content.


Seeking the best solution Te seismic industry now widely accepts the importance of recording the full range of frequencies (low as well as high)


to achieve high-resolution imaging. At one end of the scale, high-fidelity, low- frequency data provides clear imaging of deep targets, as well as greater stability for undertaking inversion. At the other end, higher frequencies are important for high-resolution imaging of important shallow features such as thin beds and small sedimentary traps. When the streamers are towed at greater depths, this reduces sea-state noise and improves low-frequency signal-to-noise ratios. Te drawback is that the streamers record a ‘ghost’ signal, the reflection of data back down to the streamer from the sea surface, causing a notch in the amplitude spectrum which comes in at lower frequencies as the cable gets deeper – 100Hz at 7.5m streamer depth and 50Hz at 15m. Up to now this has resulted in a choice between recording shallow for high frequencies or deep for noise-free low frequencies. Te BroadSeis solution developed by


CGGVeritas acquires both the low and high frequencies with each Sercel Sentinel solid


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