CGGVeritas has a long history of tailoring acquisition parameters to meet client requirements, including low frequency acquisition. We offer an extensive library of modeling, processing and analysis tools including source modeling software. This allows us to evaluate the trade-offs in bandwidth that result from putting the source and streamer at various depths, and from changing the configuration of the source.
Superior Bandwidth recorded by Sentinel Solid Streamers
The Sentinel streamer gives unrivalled low frequency recording, with the best low-noise characteristics in the industry. Dual sensor streamers have no particular benefits for low frequency recording as they use only the hydrophone at low frequencies, the geophones are used to infill the higher frequency cable ghost notch.
The streamer hydrophone group capacitance and differential input impedance form an analogue low-cut filter on the streamer. These differences in the low-cut filter have a significant impact on the low frequencies recordable, e.g. there is 5dB difference in signal at 5Hz between the latest 2Hz Sentinel streamer and previous Syntrak fluid systems. As the frequencies get lower the difference increases.
Analysis of the frequencies of the recent TIDES data recorded by CGGVeritas as part of the Tsunami prediction project offshore Indonesia showed that useful data below 2.5 Hz was being recorded, giving an extra octave in bandwidth at the low end compared with conventional recording. This data was recorded using Sentinel solid streamers with an 8.5m source depth, and 22.5m cable depth.
Benefits of Low Frequency Recording
Seal Sentinel electronics allow a lower analog low-cut filter to be used in recording, providing:
- Better penetration of the Earth and imaging of deep targets,
- Improves ability to see below highly scattering or absorbing geology, especially useful for sub-salt and sub-basalt and below any complex overburden
- Enhanced steep dip imaging
- Greater bandwidth for seismic inversion, providing better reservoir characterization
- Low frequencies for full waveform inversion to provide better velocity models
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The Tupi discovery offshore Brazil. The data were recorded by CGGVeritas using
Sentinel Solid Streamers and imaged using Reverse Time Migration. |
