摘要
双程波方程逆时深度偏移是复杂介质高精度成像的有效技术,但其结果中通常包含成像方法引起的噪音和假象,一般的滤波方法会破坏成像剖面上的振幅,其中的假象也会给后续地质解释带来困扰.将波场进行方向分解然后实现入射波与反射波的相关成像能够有效地消除这类成像噪音,并提高逆时偏移成像质量.波传播方向的分解通常在频率波数域实现,它会占用大量的存储和计算资源,不便于在沿时间外推的逆时深度偏移中应用.本文提出解析时间波场外推方法,可以在时间外推的每个时间片上实现波传播方向的显式分解,逆时深度偏移中利用分解后的炮检波场进行对应的相关运算,实现成像噪音和成像信号的分离.在模型和实际数据上的测试表明,相比于常规互相关逆时偏移成像结果,本文方法能够有效地消除低频成像噪音和特殊地质构造导致的成像假象.
Two-way wave equation based reverse time migration is powerful in imaging complex area.However,its result usually contains imaging noise which poses challenge to seismic interpretation.The imaging amplitude would be distorted by simple noise filter. Wavefield separation imaging condition is an effective way to suppress the imaging noise and enhance the imaging quality.Conventionally,the wavefield separation is achieved in frequency wavenumber domain which cannot be conveniently implemented in time domain reverse time migration.We propose the analytical wavefield extrapolation method which can efficiently separate wavefield into its directional components during the time domain extrapolation.We use this method in reverse time migration and separate both the source and receiver wavefield.And the imaging noise and signal can be separated after applying the imaging condition to the separated wavefield.The wavefield propagation direction is usually defined by temporal and spatial Fourier transform.In the Fourier domain,the wavefield propagation direction is defined by the sign of frequency and spatial wavenumber.In order to efficiently apply the wavefield separation imagingcondition in reverse time migration,we extend the analytical time signal into the wavefield and call it analytical time wavefield.Since the analytical time wavefield contains only the positive frequency component,the wavefield propagation direction can be defined by the sign of spatial wavenumber.To avoid the I/O cost in generating the analytical wavefield at every imaging point,we propose an analytical wavefield propagation equation based on the linear relation between the source term and wavefield in wave equation.We solve the proposed equation by finite difference method.Then we separate the source and receiver wavefield into their up and down going components and apply the imaging condition to the separated wavefield. Four imaging components（i.e.,imaging component from up going source and down going receiver wavefield,imaging component from down going source and down going receiver wavefield,imaging component from down going source and up going receiver wavefield and imaging component from up going source and up going receiver wavefield）are effectively separated.Then the imaging noise and signal are separated.We use the syncline model and real data to test the proposed method.Numerical example on syncline model shows that the proposed method can effectively separate imaging component from down going source and up going receiver wavefield,imaging component from up going source and down going receiver wavefield,imaging component from down going source and down going receiver wavefield and imaging component from up going source and up going receiver wavefield.When the migration velocity is not accurate,the correlation imaging condition and equivalent wavefield separation imaging condition would generate imaging artifact in central area of the syncline.And the proposed method can eliminate the artifact.Numerical example on real data shows that this method can generate imaging result free from low frequency noise.Wavefield separation imaging condition can effectively separate the imaging noise and signal in reverse time migration and enhance the imaging quality.The proposed analytical wavefield extrapolation method can separate the source and receiver wavefield into their up and down going components.The imaging noise can be suppressed by applying the imaging condition to the separated wavefield.We want to further use this method to generate common angle imaging gather in reverse time migration and provide input data for AVA and migration velocity inversion.
出处
《地球物理学报》
SCIE
EI
CAS
CSCD
北大核心
2015年第8期2886-2895,共10页
Chinese Journal of Geophysics
基金
973项目(2011CB201002)
国家自然科学基金(41374117)
国家重大专项(2011ZX05005-005-008HZ
2011ZX05006-002
2011ZX05023)资助
关键词
解析时间波场外推
波场分解
噪音消除
逆时深度偏移
Analytical time wavefield extrapolation
Wavefield separation
Noise elimination
Reverse time migration
