oa Seismic Frequency Bandwidth Constraints in Deepwater Locations

Deepwater environments typically involve an undercompacted overburden with low quality (Q) factor values (high rates of anelastic attenuation). Rugose water bottom characteristics and complex stratigraphic styles collectively yield surface seismic data that has a small frequency bandwidth and a poor signal-to-noise content. A common misconception associates shallow seismic source and streamer towing depth with increased high frequency amplitudes, larger frequency range, and larger frequency bandwidth (and hence, better vertical resolution). We demonstrate how this misconception arises, and provide a quantitative demonstrate of the true factors affecting frequency content in deepwater data. Noise attenuation is particularly difficult in deepwater areas, as out-of-the-plane (3D) noise generating mechanisms are typically abundant. Standard 2D noise filters are ineffective, thereby degrading an already restricted frequency bandwidth. Consequently, “true” 3D processing algorithms must be applied to remove all noise types. This invokes a critical requirement that the seismic wavefield is densely sampled in both the inline and cross-line shooting directions, and that specific shooting strategies are employed during the 3D acquisition experiment. Overall, we demonstrate how to optimally acquire 3D seismic data in deepwater areas, so that the maximum possible frequency bandwidth, with optimal signal-to-noise ratio, can be both acquired and imaged.