衰减干涉假象的海洋一次波与多次波同时成像方法

Imaging marine primary and multiple simultaneously with interferential artifact attenuation

海水与空气间的强波阻抗差使得海洋地震资料普遍发育自由表面相关多次波,如何利用好多次波所携带的有效信息已成为提高海洋地震资料成像品质的新突破点.基于面炮偏移的一次波与多次波同时成像方法能够避免多次波预测精度的影响,但是,正向传播的震源子波与反向延拓的自由表面相关多次波所产生的干涉假象严重制约了该技术的应用,本文提出了一种基于单程波偏移算子,可在成像域压制干涉假象的一次波与多次波同时成像方法.其中包含了三个步骤:第一,传统单程波偏移成像方法中的震源子波替换为一次波、多次波与震源子波,初始上行延拓波场为一次波与多次波,基于单程波算子的波场延拓与互相关成像条件的应用得到包含干涉假象的一次波与多次波同时成像;第二,以子波为震源,自由表面相关多次波为记录,按照传统单程波偏移成像方法得到干涉假象;第三,基于最小二乘匹配滤波算法,将第一步的成像结果与第二步的干涉假象进行匹配相减,得到干涉假象衰减后的一次波与多次波同时成像,避开了由于实际资料子波无法准确提取而造成一次波与多次波对成像能量级的不一致性.Sigsbee2B模型测试验证了本方法的有效性,并在我国某探区深海实际资料处理中得到了成功应用,深层基底得到了清晰刻画,并且照明均衡度明显改善.

There widely exist multiples in marine seismic data due to strong impedance between air and water. How to use well multiples is a new breakthrough for improving image quality of marine seismic data processing. Area shot migration based primary and multiple imaging can avoid the influence on multiples prediction, but artifacts caused by cross correlation between forward propagated wavelets and backward propagated multiples limits its application. In this paper, we propose to image primary and multiples simultaneously with artifacts attenuation based on the one-way wave-equation method. It contains three steps：First, the source in conventional migration is replaced by records including primaries and free-surface multiples, together with a wavelet. A backward propagated primary is replaced by primaries and multiples. Imaging conditions are used to obtain the image containing real structure and artifact. Second, the wavelet serves as the source and backward propagated primaries are replaced by free-surface related multiples. Also, imaging conditions are used to generate artifacts. Third, artifacts obtained in second step are adaptively subtracted from the image from the first step which contains real structure and artifacts, avoiding the uncertainty of wavelets in real data processing. Sigsbee2B model test proves its validity, and the application to a deep marine area shows that this method can clearly delineate the basement at depth with remarkably improved balanced illumination.