摘要
In marine seismic exploration,especially in deep-water and hard ocean-bottom cases,free-surface multiples are strongly developed.Compared with primary waves,the wider illumination aperture of the multiples is beneficial for high-resolution seismic imaging.In this study,by introducing a new compound source composed of primaries and free-surface multiples and by ignoring internal multiples,we derive a new linearized forward problem(free-surface-multiple prediction model)under a weak-scattering assumption(i.e.,first-order Born approximation).On the basis of the new linearized problem,we propose a joint inversion-imaging method by simultaneously using the primaries and free-surface multiples under the general framework of least square inversion.To eliminate the crosstalk artifacts introduced by the cross-correlation of multiples with different orders,we prove that the crosstalk artifacts can be gradually eliminated during the inversion if a proper step length is selected.Synthetic-andfield-data tests demonstrate the effectiveness of the proposed method.
海上地震勘探中,很多情况下自由表面多次波强烈发育,通常被视为干扰噪声而压制处理。事实上,自由表面多次波与一次波一样,携带了有关地下介质的信息,而且照明孔径更宽,更有利于高精度成像。但是,在自由表面多次波与一次波的联合成像过程中,会产生非因果的Crosstalk假象。本文基于最小二乘反演成像方法,将一次波源和各阶多次反射波场与自由表面作用产生的二次源线性叠加成为“组合震源”,引入介质小扰动近似(Born近似),不考虑层间多次波,形成线性波传播方程。依据L2范数下数据逼近误差泛函定义一次反射波与自由表面多次波联合线性反演成像问题,分析该线性反问题的梯度项和基于此梯度项的迭代公式,得出迭代次数足够多和步长因子选择合适时,Crosstalk假象会随着迭代次数的增多而逐渐减弱的结论。最后分别采用理论合成数据与实际数据进行测试,证明了本论文所提出的一次反射波与自由表面多次波联合线性反演成像方法的有效性。
基金
the sponsors of the WPI group for their financial support
financially supported by the National Key R&D Program of China (Grant Number: 2018YFA0702503, 2019YFC0312004)
National Natural Science Foundation of China (Grant Number: 41774126)
Southern Marine Science and Engineering Guangdong Laboratory (Zhanjiang) (ZJW-2019-04)
National Science and Technology Major Project of China (Grant Number: 2016ZX05024-001, 2016ZX05006-002)。
