叠前逆时偏移假象去除方法
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摘要
叠前逆时偏移(RTM)求解全波动方程进行波场延拓,可以精确描述地震波的传播,在陡倾界面和复杂构造成像方面具有显著优势.但在实际应用中,互相关成像条件会带来低波数高振幅的假象.本文分析了假象产生的原因,实现并比较了Laplace滤波、坡印廷矢量法和上下、左右行波分解这三种假象压制方法,针对不同的计算平台分析其优劣.数值试验表明,坡印廷矢量法当波场简单时较为有效;而上下、左右行波分解法和Laplace滤波可以应对较复杂的波场.就去假象结果而言,使用波场分解成像条件并施加Laplace滤波效果最佳;然而就计算效率而言,CPU平台应用波场分解成像条件只增加少量的计算量,但GPU平台的实现则需要对数据的读写付出较大的代价.因此,综合考虑,对于CPU平台上述两种方案的组合为最佳策略;而基于GPU平台的逆时偏移采用Laplace滤波去噪仍然是目前最经济的选择.Marmousi模型和SEG/HESS VTI模型试验验证了上述结论.
Prestack reverse time migration(RTM) solves full wave-equation for wavefield extrapolation so that propagation of seismic wave can be described precisely.It shows great advantage in imaging dip reflectors and complex structures.However,traditional cross-correlation imaging condition brings low-wavenumber and high-amplitude artifacts in its application.In this paper,we analyze the cause of the artifacts,then implement and make close comparisons among three methods on CPU and GPU platform respectively:namely Laplace filtering,Poynting vector and wavefield decomposition.Numerical test shows that Poynting vector works well only when the wavefield is simple.But Laplace filtering and wavefield decomposition can handle complex wavefield.Wavefield decomposition imaging condition plus Laplace filtering achieves satisfactory results but brings additional computational cost,especially on GPU platform.So considering efficiency and quality of the image,that combination is currently the best choice for CPU platform.But simply applying Laplace filter remains the most economical way of removing artifacts for GPU platform.Finally,we conduct numerical examples of Marmousi and SEG/HESS model to validate the conclusion above.
Prestack reverse time migration(RTM) solves full wave-equation for wavefield extrapolation so that propagation of seismic wave can be described precisely.It shows great advantage in imaging dip reflectors and complex structures.However,traditional cross-correlation imaging condition brings low-wavenumber and high-amplitude artifacts in its application.In this paper,we analyze the cause of the artifacts,then implement and make close comparisons among three methods on CPU and GPU platform respectively:namely Laplace filtering,Poynting vector and wavefield decomposition.Numerical test shows that Poynting vector works well only when the wavefield is simple.But Laplace filtering and wavefield decomposition can handle complex wavefield.Wavefield decomposition imaging condition plus Laplace filtering achieves satisfactory results but brings additional computational cost,especially on GPU platform.So considering efficiency and quality of the image,that combination is currently the best choice for CPU platform.But simply applying Laplace filter remains the most economical way of removing artifacts for GPU platform.Finally,we conduct numerical examples of Marmousi and SEG/HESS model to validate the conclusion above.
引文
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[2]McMechan G A.Migration by extrapolation of time-dependentboundary values.Geophysical Prospecting,1983,31:413-420.
[3]Baysal E,Kosloff D D,John W C Sherwood.Reverse timemigration.Geophysics,1983,48(11):1514-1524.
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[7]Sun R,McMechan G A,Lee C S,et al.Prestack scalarreverse-time depth migration of 3D elastic seismic data.Geophysics,2006,71(5),S199-S207.
[8]Zhang Y,Zhang H Z.A stable TTI reverse time migrationand its implementation.79th Annual International Meeting,SEG Expanded Abstracts,2009:2794-2798.
[9]Jin S,Jiang F,Ren Y.Comparison of isotropic,VTI and TTIreverse time migration:an experiment on BP anisotropicbenchmark dataset.80th Annual International Meeting,SEGExpanded Abstracts,2010:3198-3202.
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[15]李博,刘红伟,刘国峰等.地震叠前逆时偏移算法的CPU/GPU实施对策.地球物理学报.2010,53(12):2938-2943Li B,Liu H W,Liu G F.Computational strategy of seismicpre-stack reverse time migration on CPU/GPU.Chinese J.Geophys.(in Chinese),2010,53(12):2938-2943.
[16]Claerbout J F.Toward a unified theory of reflector mapping.Geophysics,1971,36(3):467-481.
[17]Youn O K,Zhou H.Depth imaging with multiples.Geophysics,2001,66(1):246-255.
[18]Guitton A,Kaelin B.Least-square Attenuation of ReverseTime Migration Artifacts.76th Annual InternationalMeeting,SEG Expanded Abstracts,2006.2348-2352.
[19]Fletcher R F,Fowler P,Kitchenside P,Suppressing artifactsin prestack reverse time migration.75th Annual InternationalMeeting,SEG Expanded Abstracts,2005.2049-2053.
[20]Xie X B,Wu R S.A depth migration method based on thefull-wave reverse-time calculation and local one-waypropagation.76th Annual International Meeting,SEGExpanded Abstracts,2006:2333-2337.
[21]Yan R,Xie X-B,A new angle-domain imaging condition forprestack reverse-time migration.79th Annual InternationalMeeting,SEG Expanded Abstracts,2009:2784-2788.
[22]Yoon K,Marfurt K J,Reverse-time migration using thePoynting vector.Exploration Geophysics,2006,37,102-107.
[23]Liu F,Zhang G,Morton S A,et al.Reverse-time migrationusing one-way wavefield imaging condition.77th AnnualInternational Meeting,SEG Expanded Abstracts,2007:2170-2174.
[24]Isabeelle L.Resolution and illumination analyses in PSDM:A ray-based approach.The Leading Edge,2008,27(5):650-663.
[25]Zhang Y,Sun J,Gray S.Reverse-time migration:amplitudeand implementation issues.77th Annual InternationalMeeting,SEG Expanded Abstracts,2007:2145-2149.
[26]Hu L,McMechan G A.Wave-field transformations of verticalseismic profiles.Geophysics,52(3):307-321.
[27]Fletcher R,Du X,Fowler P J.A new pseudo-acoustic waveequation for TI media.78th Annual International Meeting,SEG Expanded Abstracts,2008:2082-2085.
[28]Thomsen L.Weak elastic anisotropy.Geophysics,1986,51(10):1954-1966.
[2]McMechan G A.Migration by extrapolation of time-dependentboundary values.Geophysical Prospecting,1983,31:413-420.
[3]Baysal E,Kosloff D D,John W C Sherwood.Reverse timemigration.Geophysics,1983,48(11):1514-1524.
[4]Loewenthal D,Mufti R I.Reversed time migration in thespatial frequency domain.Geophysics,1983,48(5):627-635.
[5]Alkhalifah T.An acoustic wave equation for anisotropic media.Geophysics,2000,65(4):1239-1250.
[6]Fowler P J,Du X,Fletcher R P.Coupled equations for reversetime migration in transversely isotropic media.Geophysics,2010,75(1):S11-S22.
[7]Sun R,McMechan G A,Lee C S,et al.Prestack scalarreverse-time depth migration of 3D elastic seismic data.Geophysics,2006,71(5),S199-S207.
[8]Zhang Y,Zhang H Z.A stable TTI reverse time migrationand its implementation.79th Annual International Meeting,SEG Expanded Abstracts,2009:2794-2798.
[9]Jin S,Jiang F,Ren Y.Comparison of isotropic,VTI and TTIreverse time migration:an experiment on BP anisotropicbenchmark dataset.80th Annual International Meeting,SEGExpanded Abstracts,2010:3198-3202.
[10]张会星,宁书年.弹性波叠前逆时偏移.中国矿业大学学报,2002,31(5):371-375.Zhang H X,Ning S N.Pre-Stack Reverse Time Migration ofElastic Wave Equation.Journal of China University ofMining&Technology(in Chinese),2002,31(5):371-375.
[11]杜启振,秦童.横向各向同性介质弹性波多分量叠前逆时偏移.地球物理学报,2009,52(3):801-807.Du Q-Z,Qin Tong.Multicomponent prestack reverse-timemigration of elastic waves in transverse isotropic medium.Chinese J.of Geophys.(in Chinese),2009,52(3):801-807.
[12]何兵寿,张晓明,张会星.非零井源距VSP多分量地震资料逆时偏移.山东科技大学学报.2010,29(2):1-7.He B S,Zhang X M,Zhang H X.Reverse-Time Migration ofVSP Multi-Component Seismic Data with non-Zero Offset.Journal of Shandong University of Science and Technology(in Chinese),2010,29(2):1-7.
[13]刘红伟,刘洪,邹振等.地震叠前逆时偏移中的去噪与存储.地球物理学报.2010,53(9):2171-2180.Liu H W,Liu H,Zou Z,Cui Y F.The problems of denoiseand storage in seismic reverse time migration.Chinese J.Geophys.(in Chinese),2010,53(9):2171-2180.
[14]刘红伟,李博,刘洪等.地震叠前逆时偏移高阶有限差分算法及GPU实现.地球物理学报.2010,53(7):1725-1733.Liu H W,Li B,Liu H,et al.The algorithm of high orderfinite difference pre-stack reverse time migration and GPUimplementation.Chinese J.Geophys.(in Chinese),2010,53(7):1725-1733
[15]李博,刘红伟,刘国峰等.地震叠前逆时偏移算法的CPU/GPU实施对策.地球物理学报.2010,53(12):2938-2943Li B,Liu H W,Liu G F.Computational strategy of seismicpre-stack reverse time migration on CPU/GPU.Chinese J.Geophys.(in Chinese),2010,53(12):2938-2943.
[16]Claerbout J F.Toward a unified theory of reflector mapping.Geophysics,1971,36(3):467-481.
[17]Youn O K,Zhou H.Depth imaging with multiples.Geophysics,2001,66(1):246-255.
[18]Guitton A,Kaelin B.Least-square Attenuation of ReverseTime Migration Artifacts.76th Annual InternationalMeeting,SEG Expanded Abstracts,2006.2348-2352.
[19]Fletcher R F,Fowler P,Kitchenside P,Suppressing artifactsin prestack reverse time migration.75th Annual InternationalMeeting,SEG Expanded Abstracts,2005.2049-2053.
[20]Xie X B,Wu R S.A depth migration method based on thefull-wave reverse-time calculation and local one-waypropagation.76th Annual International Meeting,SEGExpanded Abstracts,2006:2333-2337.
[21]Yan R,Xie X-B,A new angle-domain imaging condition forprestack reverse-time migration.79th Annual InternationalMeeting,SEG Expanded Abstracts,2009:2784-2788.
[22]Yoon K,Marfurt K J,Reverse-time migration using thePoynting vector.Exploration Geophysics,2006,37,102-107.
[23]Liu F,Zhang G,Morton S A,et al.Reverse-time migrationusing one-way wavefield imaging condition.77th AnnualInternational Meeting,SEG Expanded Abstracts,2007:2170-2174.
[24]Isabeelle L.Resolution and illumination analyses in PSDM:A ray-based approach.The Leading Edge,2008,27(5):650-663.
[25]Zhang Y,Sun J,Gray S.Reverse-time migration:amplitudeand implementation issues.77th Annual InternationalMeeting,SEG Expanded Abstracts,2007:2145-2149.
[26]Hu L,McMechan G A.Wave-field transformations of verticalseismic profiles.Geophysics,52(3):307-321.
[27]Fletcher R,Du X,Fowler P J.A new pseudo-acoustic waveequation for TI media.78th Annual International Meeting,SEG Expanded Abstracts,2008:2082-2085.
[28]Thomsen L.Weak elastic anisotropy.Geophysics,1986,51(10):1954-1966.
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