基于波动方程正演的地震观测系统设计
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摘要
常规地震观测系统设计方法基于地下水平层状介质及共中心点(CMP)覆盖的假设,通常不能适应复杂构造情况。基于射线的地震波照明分析方法存在高频近似和射线理论本身的缺陷,在复杂目标区的精度很低。本文从波动方程正演出发,提出了一种面向目标的地震观测系统设计方法,该法基于地质—地球物理模型,采用双程声波方程交错网格高阶有限差分法计算地震波照明度。文中针对冀中地区复杂断块模型进行了面向目标的地震观测系统优化设计,并重点探讨了检波器排列间距对成像质量的影响,得出以下认识:①复杂断块构造引起地震波传播能量的非均匀分布,局部目标成像质量优劣与目标体上的照明度强弱存在一一对应的关系。②在震源相同、检波器排列间距不同时,双向照明强度变化很明显,依此可以确定针对目的层段的最佳检波器间距。③对同一倾斜界面CRP点而言,沿倾斜方向随着CRP点的不同,不同位置炮点的双向照明强弱的变化规律不同;水平目标层面震源照明和倾斜目标层面震源照明的地表接收能量分布不同,能量强弱与偏移成像结果一致,由此可以确定地面最佳炮点或检波点分布范围。④道间距、排列长度的变化对地震波成像振幅和分辨率有明显影响;利用点扩散函数(或分辨函数)可以评价地震成像质量和分辨率,还可确定最佳检波器间距、排列长度等采集参数。实践表明,文中方法用于面向目标的地震观测系统优化设计是可行的。
The conventional design of seismic geometry is on the basis of hypotheses of underground horizontal layered medium and common-mid-point(CMP)coverage,which is not suitable for the complex structural situations.The analytic approach of ray-based seismic wave illumination has shortcomings of high-frequency approximation and ray theory itself,and has lower precision in the area of complex targets.Starting from wave equation forward simulation,the paper presented the design method of target-oriented seismic geometry,which is based on geologic-geophysical model,using staggering grid high-order finite-difference algorithm of two-way acoustic wave equation to compute the illumination of seismic waves.Faced with complex fault block model in Jizhong area,the paper carried out optimum design of target-oriented seismic geometry,discussed with the emphasis on the influence of geophone interval on imaging quality and got the following knowledge:①there is one-to-one relationship between the imaging quality of local target and the strength of illumination on the target since the complex fault-block structure caused non-uniform distribution of propagation energy of seismic waves;②the strength variation of two-way illumination is distinctive for same source and different receiver interval at the same time,from which the optimum target-oriented receiver interval can be determined;③for the CRP on same incline interface,the variation raw of strength of two-way illumination at different shot points with different CRP in incline direction is different,the energy distribution received from horizontal target and incline target illuminated by source is different on surface,but the strength of energy and imaging result of migration are consistent,from which the optimum distributing range of shot and receiver points can be determined;④the variation of group interval and spread length have clear influence on the imaging amplitude and resolution of seismic waves;using point-expansion function(or resolution function)can evaluate the seismic imaging quality and resolution,and also can determine such acquisition parameters as the optimum receiver interval and spread length.The practice showed that the method in the paper is feasible for optimized target-oriented design of seismic geometry.
The conventional design of seismic geometry is on the basis of hypotheses of underground horizontal layered medium and common-mid-point(CMP)coverage,which is not suitable for the complex structural situations.The analytic approach of ray-based seismic wave illumination has shortcomings of high-frequency approximation and ray theory itself,and has lower precision in the area of complex targets.Starting from wave equation forward simulation,the paper presented the design method of target-oriented seismic geometry,which is based on geologic-geophysical model,using staggering grid high-order finite-difference algorithm of two-way acoustic wave equation to compute the illumination of seismic waves.Faced with complex fault block model in Jizhong area,the paper carried out optimum design of target-oriented seismic geometry,discussed with the emphasis on the influence of geophone interval on imaging quality and got the following knowledge:①there is one-to-one relationship between the imaging quality of local target and the strength of illumination on the target since the complex fault-block structure caused non-uniform distribution of propagation energy of seismic waves;②the strength variation of two-way illumination is distinctive for same source and different receiver interval at the same time,from which the optimum target-oriented receiver interval can be determined;③for the CRP on same incline interface,the variation raw of strength of two-way illumination at different shot points with different CRP in incline direction is different,the energy distribution received from horizontal target and incline target illuminated by source is different on surface,but the strength of energy and imaging result of migration are consistent,from which the optimum distributing range of shot and receiver points can be determined;④the variation of group interval and spread length have clear influence on the imaging amplitude and resolution of seismic waves;using point-expansion function(or resolution function)can evaluate the seismic imaging quality and resolution,and also can determine such acquisition parameters as the optimum receiver interval and spread length.The practice showed that the method in the paper is feasible for optimized target-oriented design of seismic geometry.
引文
[1]Laurain R et al.Areview of3Dillumination studies.Journal of Seismic Exploration,2004(13):17～37
[2]Schneider W Aet al.Efficient and accurate modeling of3-D seismic illumination.Expanded Abstracts of69th SEG Mtg,1999,633～636
[3]Muerdter D et al.Understanding subsalt illumination through ray-tracing modeling,Part I:Simple2-Dsalt models.The Leading Edge,2001,20(6):726～728
[4]Muerdter D et al.Understanding subsalt illumination through ray-tracing modeling,Part II:Dipping salt bodies,salt peaks,and nonreciprocity of subsalt am-plitude response.The Leading Edge,2001,20(7):688～697
[5]Muerdter D et al.Understanding subsalt illumination through ray-tracing modeling,Part III:Salt ridges and furrows,and the impact of acquisition orienta-tion.The Leading Edge,2001,20(8):803～816
[6]Hoff mann J.Illumination,resolution,and image quali-ty of PP-and PS-waves for survey planning.The Leading Edge,2001,20(9):1008～1014
[7]Wu R S et al.Mapping directional illumination and acquisition-aperture efficacy by beamlet propagators.Expanded Abstracts of72nd SEG Mtg,2002,1352～1355
[8]Wu R S et al.Acquisition aperture correctionin angle-domain and true-amplitude imaging for wave equation migration.Expanded Abstracts of74th SEG Mtg,2004,937～940
[9]Xie X b et al.Three-dimentional illumination analysis using wave equation based propagato.Expanded Ab-stracts of73rd SEG Mtg,2003,989～992
[10]Xie X b et al.Wave-equation-based seismic illumina-tion analysis.Geophysics,2006,71(5):169～177
[11]Ost mo S et al.Seismic illumination fromfinite-differ-ence modeling.Expanded Abstracts of65th Confer-ence&Technical Exhibition,EAGE,2003,147
[12]Luo Met al.Comparison of illumination analysis u-sing one-way and full-wave propagators.Expanded Abstracts of74th SEG Mtg,2004,67～70
[13]牟永光等.三维复杂介质地震数值模拟.北京:石油工业出版社,2005
[14]Mcmechan G A.Migration by extrapolation of time-denpendent boundary values.Geophysical Prospec-ting,1983,31:413～420
[15]Yoon Ket al.3Dreverse-time migration using the a-coustic wave equation:An experience with the SEG/EAGE data set.The Leading Edge,2003,22:38～41
[16]Vernzeer V J O.Factors affecting spatial resolution.Expanded Abstracts of67th SEG Mtg,1997,27～30
[2]Schneider W Aet al.Efficient and accurate modeling of3-D seismic illumination.Expanded Abstracts of69th SEG Mtg,1999,633～636
[3]Muerdter D et al.Understanding subsalt illumination through ray-tracing modeling,Part I:Simple2-Dsalt models.The Leading Edge,2001,20(6):726～728
[4]Muerdter D et al.Understanding subsalt illumination through ray-tracing modeling,Part II:Dipping salt bodies,salt peaks,and nonreciprocity of subsalt am-plitude response.The Leading Edge,2001,20(7):688～697
[5]Muerdter D et al.Understanding subsalt illumination through ray-tracing modeling,Part III:Salt ridges and furrows,and the impact of acquisition orienta-tion.The Leading Edge,2001,20(8):803～816
[6]Hoff mann J.Illumination,resolution,and image quali-ty of PP-and PS-waves for survey planning.The Leading Edge,2001,20(9):1008～1014
[7]Wu R S et al.Mapping directional illumination and acquisition-aperture efficacy by beamlet propagators.Expanded Abstracts of72nd SEG Mtg,2002,1352～1355
[8]Wu R S et al.Acquisition aperture correctionin angle-domain and true-amplitude imaging for wave equation migration.Expanded Abstracts of74th SEG Mtg,2004,937～940
[9]Xie X b et al.Three-dimentional illumination analysis using wave equation based propagato.Expanded Ab-stracts of73rd SEG Mtg,2003,989～992
[10]Xie X b et al.Wave-equation-based seismic illumina-tion analysis.Geophysics,2006,71(5):169～177
[11]Ost mo S et al.Seismic illumination fromfinite-differ-ence modeling.Expanded Abstracts of65th Confer-ence&Technical Exhibition,EAGE,2003,147
[12]Luo Met al.Comparison of illumination analysis u-sing one-way and full-wave propagators.Expanded Abstracts of74th SEG Mtg,2004,67～70
[13]牟永光等.三维复杂介质地震数值模拟.北京:石油工业出版社,2005
[14]Mcmechan G A.Migration by extrapolation of time-denpendent boundary values.Geophysical Prospec-ting,1983,31:413～420
[15]Yoon Ket al.3Dreverse-time migration using the a-coustic wave equation:An experience with the SEG/EAGE data set.The Leading Edge,2003,22:38～41
[16]Vernzeer V J O.Factors affecting spatial resolution.Expanded Abstracts of67th SEG Mtg,1997,27～30
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