A Ghost-free Solution for Marine Seismic Acquisition

The ghost in marine seismic recording is the result of a reflection of the acoustic wavefield from the sea surface. Up-going waves are reflected back with reversed polarity, interfering constructively for certain frequencies and destructively for other frequencies dependent solely on source and receiver depths. Conventional marine seismic acquisition therefore involves a trade-off between the various frequency ranges. Recently a dual-sensor streamer, with collocated pressure and motion sensors, has been developed which removes the receiver ghost while maintaining the efficiency of towed streamer acquisition. A ghost-free source can be achieved with a time and depth distributed source using sub-sources deployed at specific depths and fired with specific firing time delays. The depths of the sub-sources are chosen such that the ghost functions are complementary, avoiding deep notches in the spectrum. Techniques for separating the wavefields from sub-sources have been developed that utilize the known firing time delays. The subsequent source ghost removal step involves re-combining those wavefields using well established techniques. De-ghosting or wavefield separation for source and receiver is based on first principle science and makes no restricting assumptions. The resultant seismic data has broader bandwidth both at the high end and the low end of the frequency spectrum.