Seismic investigative method for soil layers, lying under the sea

摘要

1394533 Seismic prospecting CHEVRON RESEARCH CO 7 May 1973 [5 May 1972] 21732/73 Heading H4D In a marine seismic prospecting system a seismic source and hydrophone streamer are moved by a single boat which traverses a straight course line, the trailing end of the streamer has a steerable paravane assembly so that the trailing end moves along a line parallel to but offset laterally from the course line, and the instantaneous positions of the hydrophones relative to the boat are determined by digitally timing the travel of sonic pulses from a transmitter aboard the boat to a series of target transducers on the streamer. The trailing end offset results in successive locations of the hydrophones and source point defining a twodimensional grid of centre points (where each centre point is mid-way between a source point and associated hydrophone location) which can be arranged to give three-dimensional common depth point coverage of the subsurface. The hydrophone position determination preferably occurs between actuation of the seismic source and receipt of the resulting seismic reflection signals. The determination involves counting clock pulses and recording the counts on a header portion of a magnetic tape. The seismic reflection data, together with recording amplifier binary gain, navigational and other data, are then recorded on the tape in digital format (details given), the reflection data from individual hydrophones being multiplexed prior to conversion to digital form. For subsequent computer processing of the seismic data the counts recorded on the header portion are combined with the navigational data to derive the absolute (geodetic) positions of the hydrophones so that the centre point grid can be associated accurately with the subsurface.