Deghosting Research On Marine Variable-depth Streamer Data

In marine seismic exploration,the reflection from the surface between sea and air is strong,so besides primaries,the receivers record ghosts which arise from the free surface.As the ghost has similar waveforms to the primary data,it will constructively and destructively interfere with the primary data,affect the amplitude,and even produce fraud events.Moreover,it will also lead to frequency notches and low frequency attenuation,which reduces the effective band limit of the recorded seismic data.It is known that the amplitude will show strong attenuation due to seismic wave dispersion when seismic signal penetrates through underground media.For this reason,conventional streamer acquisition is unable to meet the demand of seismic data processing and interpretation.Therefore,it is important to develop broadband,high signal-noise ratio(SNR)modeling,acquisition,processing technology with rich low,high frequency energy in order to acquire the target layer's signal accurately and achieve high precision,high resoulution imaging.Variable-depth streamer acquisition is an acquisition technique that using a depth profile varying with offset in order to use notch diversity.The seismic profiles get wider band after deghosting.Variable-depth Streamer contains more low frequency information.The marine seismic data acquired by conventional streamer acquisition suffers from the sea surface ghost,so the bandwidth is limited.The authors put forward a deghosting method which can suppress the receiver ghost and widen the frequency band.In this paper,firstly,the authors derive the formula to produce mirror records in frequency-space domain and search for the maximization of peak factor to estimate the delay time of upgoing wavefield and downgoing wavefield.Then take the optimal delay time into the formula to produce mirror data and obtain optimal mirror data.Ultimately,the optimal deghosted output can be calculated by using joint deconvolution algorithm.Meanwhile,the deghosting of synthetic data and marine variable-depth streamer data show that this deghosting method could suppress the ghost,reduce the spectral notches and acquire wider-band data.The acquisition mode can play well to get abundant useful information,especially strengthen the high-frequency energy.It provides a new thinking and good supplement in real high precision marine detection.This paper presents theoretical design principles for marine multi-level sources.Compared to a horizontal source,a multilevel source can be designed to improve low frequencies and reduce the ghost notch effect.Optimum depth combinations exist in the design.By considering both operational aspects and performance,we propose three or four levels in a multi-level source to be reasonable.