The Research And Forward Modeling Of The Suppression Method Of The Terrestrial Ghost Reflection

When the seismic source generates the wave motion below the low-velocity zone,some part of the wave motion which is called ghost propagates upward first and thenpropagates downward after encountering the bottom interface of the low-velocityzone. The existence of the ghost reflection would affect the frequency of the reflec-tions and reduce the seismic resolution, so it should be eliminated.Firstly, the paper presents a detailed analysis of the formation mechanism and thecharacteristics of the ghost reflection. After the analysis, the paper also have a re-search on the current methods of ghost suppression. Now there are varieties of meth-ods which have different principles on the suppression of ghost. Here the principleand the suppression effect of three methods which are designing the optimum shoot-ing depth, up-hole stacking, predictive de-convolution are analyzed and discussed indetail.In order to verify the feasibility of the methods which are proposed in this paper,the data of forward modeling are needed here. In this paper, the finite differencemethod is applied to simulate the seismic wave-field. After the suppression of thedispersion and the elimination of the artificial boundary, a reflection record whichcontains the ghost can be acquired based on the method above. The reflection recordprovides a theoretical data for the following method verifying.On the basis of studying the principles of surface-related multiple elimination, amethod of ghost suppression through combining the record of inverse vertical seismicprofiling (inverse VSP) with the record of conventional surface exploration is pro-posed. The ghost can be predicted through the convolution between the direct wave ofthe inverse VSP data and the reflection wave of the conventional surface exploration.After predicting, the predicted ghost, the derivative of the predicted ghost, the Hilberttransform of the predicted ghost and the derivative of the Hilbert transform are used tomatch through the multi-channel match for improving the amplitude and the phaseinformation. Finally, the suppression can be acquired by subtracting the matched pre-dicted ghost from the actual record. On the basis of researching the principle of dual-sensor technology, the paperproposed a method of suppressing ghost by combining the data of VSP with the dataof the inverse VSP according to the fact that the geophone detects the up-going anddown-going wave fields with opposite polarity. Ghost reflection belongs to theup-gonging wave fields in the data of inverse VSP but belongs to the down-gongingwave fields in the data of VSP, so the goal of suppressing ghost can be achieved bysumming the two records with a appropriate scaling coefficient.