Very high resolution marine 3D seismics in shallow water environments
Missiaen, T.; Versteeg, W.; Henriet, J.-P. (2004). Very high resolution marine 3D seismics in shallow water environments, in: 32nd International Geological Congress, Florence, Italy, August 20-28, 2004. Abstract Volume. pp. 817 (Abstract 175-3)
In: (2004). 32nd International Geological Congress, Florence, Italy, August 20-28, 2004. Abstract Volume. IGC: Florence. 2 vols pp.
The adaptation of 3D techniques to very high resolution* shallow water studies has been progressing steadily over the last years. Cost-effective VHR 3D seismics is of great interest both in the field of engineering geophysics as well as for geological and geotechnical site investigations. Still, no well established practice for VHR 3D survey design seems to exist and few studies have been published on the relationship between acquisition parameters, processing costs and the quality of the processed data. (* the term "very high resolution" refers to mean source frequencies >1 kHz and expected resolution in the sub-meter range).The design of VHR 3D marine surveys does not simply reduce to a mere downscaling problem, it also requires specific strategies. The approach will not only depend on the geological target and the desired resolution, but will also be dictated by the field conditions and the available budget. The optimum acquisition strategy will necessarily be a compromise. On the one hand there is the need for high resolution and this requires the use of high frequencies. On the other hand there are the constraints placed on sampling - very high frequencies require very small sampling intervals.Working in shallow water environments will imply constraints on the acquisition geometry (trace interval, streamer spacing, line spacing, shot interval). Considering the frequency content of the seismic data and the desired resolution, accurate positioning is needed to prevent destructive stacking and obtain optimal imaging. Unfortunately, current navigation technology does not allow real-time positioning of the array elements with sufficient accuracy in a costeffective way, and additional geometry corrections may be needed.The compact, flexible acquisition system "Opus3D" developed at RCMG has allowed to further scale down the 3D seismic method to ultra-high resolutions and dm scale in a modest and cost-effective way, without requiring complex field procedures and processing. The system is designed for studies in shallow water, providing limited penetration and aimed at target sites of limited lateral extent. Acquisition and positioning constraints limit the acquisition system to nearshore studies. In protected areas and on rivers, canals and lakes the array may also be used as a stand-alone system.
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