Seismic Frequency Bandwidth Constraints in Deepwater Locations

Abstract

Abstract Deepwater environments typically involve an undercompacted overburden with low quality factor (Q) values associated with high rates of anelastic seismic 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, larger frequency bandwidth, and hence, better vertical and lateral resolution. We show how this misconception arises, and provide a quantitative demonstrate of the true factors affecting frequency content in deepwater seismic data. Overall, any pre-survey decision on source and streamer depths is a compromise between the pursuit of maximum frequency bandwidth (shallower source and streamer depths) and useful/recoverable S/N ratios in the data (deeper source and streamer depths), allowing for all possible noise mechanisms and operational constraints. It is unsurprising that the experience of the seismic industry in deepwater or high attenuation areas has consistently endorsed deeper rather than shallower source and streamer depths for yielding optimal data quality. As demonstrated in a deepwater 3D seismic example from the Philippines, the use of tight spatial sampling in both the inline and cross-line directions (i.e., the use of high-density 3D acquisition) is critical to avoid the loss of recorded high frequencies during processing, and to avoid noise and artifacts degrading both resolution and image quality. Furthermore, significant increases in trace density per square kilometre translate to significant increases in image quality, S/N ratio, and resolution.