Vertical Cable Marine Seismic Acquisition

Abstract

Abstract This paper will examine and compare the moored vertical cable with the towed streamer techniques of seismic acquisition. Advances in computer speed have made previously impractical seismic data processing, like pre-slack migration of 3-D data sets, an everyday possibility. thus opening the door to alternatives in marine acquisition. Vertical cable and towed streamer acquisition techniques are compared in this paper with regards their seismic imaging potential. We show that for complex geologic structures the vertical cable acquisition acquires a more uniform distribution of reflection points from a reflector at depth and thus the possibility of a better seismic image than the streamer. Introduction Seismic imaging problems continue to plague explorationists who require clearer Images of the reservoirs they are mapping. 3-D technology was, and is a revolution in seismic imaging techniques, that offers a solution to imaging problems. The 3-D revolution of the 80's did not extend to the physical geometry of marine acquisition. Of course marine data was acquired with closely spaced lines and processed in the 3-D fashion but the acquisition continued using the usual geometry as the 2-D. What was different was upgraded source navigation and better streamer positioning accuracy. The 3-D technology improved the seismic images especially the accuracy of the position of the reflectors in the cross line direction. However as we attempt to image ever more difficult geologic structures it is necessary to critically examine our imaging technology for possible improvement. 'Towed streamers are without a doubt a very efficient method of acquiring seismic data. We should not overlook their deficiencies because they are so cost effective. One deficiency is that the streamer geometry is very rigid and difficult to reconfigure. Other acquisition geometries may offer advantages that are revealed in the improved seismic images possible, this is especially true for seismic data that is migrated before stack as compared to post-stack migrated data. As computers become more efficient it becomes feasible to migrate massive seismic data sets pre-stack, that were considered impractical a few years ago. The seismic Imaging scenario that evolved in the 1970's and 80'swas composed of two major parts, the streamer acquisition technique followed by the post-stack migration processing methods and both were dictated by the available technology of the day in acquisition and computer processing. Towed Streamer 3-0 Besides the technology limitations, the seismic imaging scenario of the 70's and 80's reflected our concepts of the earth's geology. Other than saltdomes we tended to think of the geology as being resolvable into dip and strike components for acquisition design. Then the proper thing to do in theacquisition was to align the seismic acquisition lines and thus the streamer, with the geologic dip. This would allow the finer spatial sampling to be acquired in the dip direction. One result is that the acquisition has a preferred direction. The processing involved mid-point binning. correction to zero range and poststack migration. This was a consistent scenario from geologic concept to seismic acquisition and on to processing.