Truly broadband data bring high resolution and layer differentiation. The reduced sidelobes create sharper wavelets for greater clarity. The six octaves of data recorded by BroadSeisTM provide high resolution shallow data as well as low frequencies for subsalt penetration. In order to achieve sufficient bandwidth in areas where high frequencies are limited, it is necessary to extend the low frequencies. Lower frequencies are affected less by attenuation, and provide greater accuracy and stability for seismic inversion.
In this example from the fast track PSDM processing from CGG's Santos Basin multi-client data, the broad bandwidth from BroadSeis provides improved pre-salt imaging over conventional surveys, even with GWE deghosting.
Conventional marine streamer acquisition lacks sufficient signal-to-noise ratio in the 2-7 Hz bandwidth due to streamer depth, streamer tow noise, source array configuration, source depth and source bubble. Using BroadSeis we routinely record frequencies down to 2.5 Hz, providing three octaves of data below 20 Hz.
Good signal-to-noise ratio data at low frequency need to be recorded, Deghosting techniques that only boost the low frequencies will not provide the same strength of signal as truly broadband data that have been recorded. Due to the proprietary curved shape of BroadSeis streamers, the average tow depth is significantly deeper than that of other acquisition geometries, which increases the signal-to-noise both by being below the swell and due to the steeper slope of the receiver ghost notch. In addition, Sentinel solid streamers are renowned for their low-noise properties, especially at low frequencies, and have been shown to be 10-15 dB quieter at 5 Hz than gel streamers in vibration tank tests.
We see the same improvements in data quality on the Eastern side of the Atlantic. In this example from our multi-client data in Block 21 there is clear imaging of the base salt and pre-salt structures as well as fine definition of the post-salt.
In addition to extending the low frequencies subsalt imaging is often enhanced by acquiring long offsets and increasing the range of azimuths. The improved sampling enhances illumination as well as improving noise and multiple attenuation.
Broadest bandwidth, best low frequencies deliver accurate models for better decisions. Choose BroadSeis at all stages from exploration to production.
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