Research On The Mechanism Of Ghost And Deghosting Method For Marine Seismic Data

Ghost is a kind of very strong interference wave in marine seismic exploration, itfollows up the primary wave tightly and can also be received by the hydrophone in thetowed-streamer. The ghost events and the primary events are mixed together on the record,and it’s very difficult to separate them from each other, which is disadvantageous for thefollow-up interpretation work. What’s more, because of the effect of ghost, a series ofnotches come into being in the spectra of seismic data which limit the bandwidth. As a result,a part of meaningful low frequency and high frequency component is lost, especially somelow frequency component which is very meaningful for the image of very deep targets. Forthis reason, it’s very necessary to remove the ghost in the seismic data.Two vertical towed-streamers at different depths are used to acquire two sets of seismicdata in the over/under streamer method. Combining the seismic data acquired by the overstreamer and the under streamer during data processing, the upgoing wavefield including noghost can be separated out, then the ghost can be removed.In this paper, the forward modeling of marine seismic wavefield including ghost is firstcompleted by staggered-grid higher-order finite difference method, then by analysing itswavefield characteristics, we study the effect of ghost on the seismic record. Then from aresearch on the mechanism of ghost, we analyse the effect of ghost on bandwidth. By spectralanalysis we draw a conclusion that because of the effect of ghost, a series of notches indeedcome into being in the spectra of seismic data, which limit the bandwidth. Finally we analysethe theory of the method put forward by Sonneland and Posthumous, then a program iswritten based on a deep understanding of their ideas. The test on the model and actual dataproves that the over/under streamer method can be successfully used to remove the ghost.After deghosting by over/under streamer method, the ghost events following the primaryevents tightly are removed and the primary events are more clear and continuous on the seismic record. Besides, the notches in the spectra are removed and the missing energy in theFK spectra is compensated, then the bandwidth is extended and the low frequency componentis raised.