频谱替换无拉伸动校正及其应用

Spectral Borrowing Nonstretch NMO Correction and Its Application

传统动校正通常应用于叠加前的共中心点道集(CMP),是地震资料处理环节中至关重要的一步,动校正的效果将直接影响到后续的叠加及其他处理。在浅层和大偏移距情况下,传统动校正引起的子波拉伸、波形畸变尤为明显,其直接导致频带向低频方向移动,严重影响了叠加效果。解决动校正拉伸的问题通常选择的方法是外切除,然而,对于浅层地震同相轴而言,数据量本身就少且动校拉伸严重,使用外切除必然影响浅层地震数据的分辨率和保真度。基于此阐述了一种无拉伸动校正的方法,即将CMP道集变换到频率域,取零偏移距道的相位谱替换其他偏移距道的相位谱,并保持振幅谱不变,之后通过反傅里叶变换得到动校正后的CMP道集。该方法自动避免了传统动校正中的拉伸现象及其导致的大偏移距数据切除效应,产生了更好的叠加效果,且可以有效保持地震数据的AVO现象;同时,不需要地下介质的速度信息。合成模型和实际数据的处理结果进一步验证了本文方法的有效性。

The conventional normal moveout(NMO)correction,applied to CMP gather before stacking,is a key step in seismic data processing,and its effects will have an influence on stack and subsequent processing.It is particularly obvious that conventional NMO correction generates a stretch of wavelets and waveform distortion under the circumstance of shallow layers and large offsets,which results in decrease in frequency.In general,the external mute is a solution to the problem of a stretch of NMO.However,for shallow seismic events,the number of total traces of CMP is small and the stretch is severe.In this condition,the resolution and fidelity will be decreased if the stretch is muted.Therefore,this paper has proposed an improved nonstretch NMO correction approach.Firstly,the CMP data is transformed from CMP gather to frequency domain,then the phase spectrum of zero-offset trace is used to substitute the original traces in CMP gather while keeping the amplitude spectrum unchangeable.Finally,it receives CMP gather through NMO correction by transforming inverse discrete Fourier.Moreover,this method avoids the undesirable stretch effects that are present in the conventional NMO and can also keep AVO effectively in seismic data.Meanwhiles it does not need velocity information of media subsurface.The synthetic examples and results of processing field data demonstrate that the presented approach is valid and applicable.