We desire increased useful bandwidth in our seismic surveys: higher frequencies to increase resolution, and lower frequencies for deeper penetration and in particular to enable better velocity-model-building by full-waveform inversion. To design an acquisition strategy to achieve these goals we must understand both the signal produced by our sources and the noise to be overcome. What matters is signal-to-noise, not signal or noise alone. We examine two ocean-bottom node datasets from the Atlantis field in the deep water Gulf of Mexico to learn more.
We find that the primary source of noise above about 4 Hz is seismic interference. The signal and noise are of similar character and the signal-to-noise ratio is thus approximately constant with frequency. Instead of increasing our signal, we may instead use the predictable nature of the noise to better attenuate it. Below 2 Hz the noise is dominated by the natural microseismic background of the earth, which rapidly in amplitude with decreasing frequency. In contrast, below about 7 Hz airguns in amplitude at about 16 dB / octave. Below 2 Hz the signal-to-noise ratio thus declines precipitously with decreasing frequency. New acquisition paradigms may be required to meet the low-frequency challenge.
Presentation Date: Tuesday, October 18, 2016
Start Time: 3:45:00 PM
Location: 163/165
Presentation Type: ORAL