Research On Deghosting Method Of Ocean Bottom Seismic Exploration

In the Ocean Bottom Nodes(OBN)seismic exploration,the sea surface itself is a very strong reflection interface,which will produce ghost waves in the received data.The ghost wave interference forms false inphase in seismic records,and the trap effect appears in the frequency spectrum,resulting in the missing of some effective information in the effective wave frequency band,thus losing the effective signal of primary reflection,which reduces the resolution of seismic information and affects the accuracy of seismic data interpretation.Therefore,some measures must be taken to eliminate the ghost waves in the seabed seismic records.OBN seismic double detection signal acquisition data suppression method is mainly to put piezoelectric acceleration detector(hydrophone)and vertical velocity detector(geophone)at the bottom of the sea at the same time to collect seismic signals.In this paper,the physical structure,mechanical characteristics and working principle of piezoelectric detector and vertical velocity detector are analyzed,and the characteristics and differences between them are described.That is to say,the response polarity of the water detector and the land detector in the upstream wave field is the same,while the response polarity in the downstream wave field is opposite,and in the spectrum of the signals collected by the two geophones,the trap caused by the ghost wave is complementary.On the basis of this theory,it is shown that the ghost wave can be suppressed and the trap effect caused by the ghost wave can be eliminated by using the method of double detection acquisition,that is,double detection synthesis technology,after adding the seismic data obtained by two kinds of geophones.There are some differences in frequency,phase and amplitude between water record and land record,so it is impossible to synthesize them directly.After introducing the matching method of frequency,phase and amplitude between water and land inspection records,aiming at frequency matching,based on the original spectral whitening method,the author proposes to introduce the wavelet spectral whitening method into the frequency matching processing of double detection synthesis,and gets better processing results than the ordinary spectral whitening method.It is proved that the wavelet spectral whitening method is feasible and effective for frequency matching of double-check data.Then,the wavelet denoising is applied to suppress the ghost wave and noise after the double detection synthesis processing for the first time,and the SNR of the processing results is improved.A theoretical forward model is designed to simulate the generation and elimination of ghost waves in OBN seismic exploration.It is illustrated that the matching of amplitude,phase and frequency of double detection is an indispensable step in the process of double detection synthesis,and it is verified that the double detection technology can eliminate ghost waves and the trap effect caused by ghost waves.Finally,the actual OBN data are processed by double-check synthesis,and its effect is verified.It is proved that the double-check synthesis technology has obvious effect on the suppression of ghost wave in the OBN seismic exploration data.