基于最小二乘反演的各向异性逆时偏移角度域共成像点道集提取方法研究

Study on least-squares-inversion based angle-domain common imaging gathers from anisotropic reverse time migration

因不受多路径假象影响,角度域共成像点道集在偏移速度分析、振幅随反射角变化分析以及地震属性解释中起着至关重要的作用.逆时偏移成像技术采用精确的地震波动理论,因此基于逆时偏移的角度域共成像点道集提取方法能够适用于任意复杂构造,且算法精度高、稳健性强.然而,在实际中,受速度不准、采集孔径有限、照明不均以及偏移算子不精确等因素影响,逆时偏移角度域共成像点道集分辨率低、振幅不均衡、存在低波数假象.如何获得高质量的角度域共成像点道集,是油气勘探急需解决的难题.在前人研究基础上,通过将角度域共成像点道集的提取作为反演问题,本文提出一种基于最小二乘反演的各向异性逆时偏移角度域共成像点道集提取方法.该方法可以改善角度域共成像点道集的分辨率、信噪比以及振幅均衡性.典型模型数值试算表明了该方法的可行性和有效性.

Free from the interference of artifacts caused by multipath of seismic wave,Angle-Domain Common Imaging Gathers(ADCIGs)play an important role in Migration Velocity Analysis(MVA),Amplitude Variation with Angle(AVA)analysis,and seismic attribute interpretation.Accurate seismic wave theory is applied in prestack Reverse Time Migration(RTM),which makes the method of extracting ADCIGs from RTM available for any complex subsurface structure with high accuracy and strong robustness.In practice,however,ADCIGs often suffer from poor resolution,unbalanced amplitude behavior,and low-wavenumber artifacts because of inaccurate migration velocity,limited recording aperture,uneven illumination,and inaccuracies of the migration operator.It is an urgent issue to obtain high-quality ADCIGs in oil and gas exploration.On the basis of previous studies,we propose a new method of extracting ADCIGs from RTM in anisotropic media based on least-squares inversion to improve its quality by posing the extracting of ADCIGs from RTM as an inverse problem whose misfit function measures the difference between simulated and observed data.The proposed method can generate high-quality ADCIGs with higher resolution,fewer artifacts,and improved amplitude coherency across different reflection angles.Several numerical results of typical models demonstrate the feasibility and effectiveness of the proposed method.