不同阶次自由表面相关多次波预测与成像方法

Prediction and migration of different order surface-related multiples

海水与空气间的强波阻抗界面使得海洋地震数据普遍发育自由表面相关多次波,多次波信息的利用是提高海洋地震资料成像品质的新突破点.近年来发展了一系列多次波成像方法,干涉假象是制约其应用推广的关键问题之一.为了避免假象影响,本文提出了不同阶次自由表面相关多次波预测与成像方法,首先,修改了传统SRME(表面相关多次波衰减)方法中的边界条件,通过多次波升阶次与匹配相减的方法预测出不同阶次自由表面相关多次波;其次,基于单程波偏移算子和"面炮"偏移策略,以一次反射波或第(N-1)阶自由表面相关多次波为下行波场正向延拓,以第1阶多次或第N阶多次波为上行波场逆向延拓,并在每一层互相关成像得到第1阶或N阶多次波单独成像.本方法避免了低阶多次波和高阶多次波产生的相关假象,且相对于全波算子的偏移方法具有较高的计算效率,增强了多次波成像方法的实用性.单层模型和三层模型测试验证了本方法的正确性,并在我国某深海探区实际资料处理中得到了成功应用.相对于传统一次波成像,分阶次多次波成像具有更高的照明均衡度、垂向分辨率和信噪比.本研究表明,海洋多次波成像是一次波成像的有力补充,对于稳定海底沉积的深海地区,具有一定的应用前景.

Due to strong impedance between air and water,marine seismic data widely exist surface-related multiples.Application of multiples is a new breakthrough for improving image quality in marine seismic data processing.Recently,series of multiple imaging methods are developed.However,the strong artifacts limit their application.In order to avoid artifacts,we proposed a method of prediction and migration of different orders surface-related multiples.First,boundary of traditional SRME was modified by lifting order of multiples and adaptive subtraction to predict different order multiples;second,based on one-way wave-equation migration operator and "area shot" migration strategies,migration of first order or N th order multiple at each depth step was obtained by forward propagated primaries or the ( N -1)th order multiple crosscorrelation with backward propagated first order multiples or the N th order multiples.The advantage of our approach is less artifact from crosscorrelation between lower order multiples and higher order multiples.It also has higher calculation efficiency,which is more suitable for real data processing.One layer and three layers model test verified our method and we also successfully applied it to a deep marine field data.Compared to migration of primaries,it has more balanced illumination,vertical resolution and S/N ratio.In conclusion,migration of multiples is a good supplementary to migration of primaries for area with stable sea bottom,which also has potential value for future marine data processing.