鄂博梁山地近地表问题及其模型实验分析
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摘要
柴达木盆地鄂博梁地区山地具有典型山地特征 ,单斜高陡 ,高速地层出露地表 ,第四系松散沉积与之共存 ,近地表速度横向变化剧烈。为了研究该区山地地震勘探问题 ,必须研究复杂条件下地震波传播规律 ,分析复杂近地表地质结构对地下中深层反射地震波的影响。由于主要目的是研究近地表单斜高陡地层对地震波传播及其成像的影响 ,所以在制作数学模型和物理模型时简化了山地地形的起伏 ,简化了中深层复杂的地质构造。数学模拟和物理模拟采用了相同的模型以利于对比分析 ,实验采用了多次覆盖观测系统。实验结果表明 :①山地特殊的近地表结构会强烈改造中深层的反射 ,并对中深层反射成像产生强烈影响 ,认识这种作用 ,对山地地震资料采集方式、处理流程和解释模式都有重要作用 ;②近地表高陡构造会产生类似于折射波的干扰波 ,这种干扰波在单炮记录或叠加剖面上很容易被认为是有效波 ;③在近地表地质结构为高陡地层并且不存在浅层折射界面 (在山地常出现这种情况 )时 ,初至波不是折射波 ,建议山地资料处理中慎用折射波静校正。图 4参 2 1
Mountains in Eboliang region of Qaidam basin are characterized by monoclines of high velocity, which are coexisted with the Quaternary loosen deposits and by near surface velocity varying violently in cross. In order to study the seismic prospecting problems of this mountainous region, the traveling laws of seismic wave in complicated condition and the influence of the complicated near surface geological structure must be studied and analyzed. Either in mathematical modeling or physical modeling, it is necessary to simplify the realistic problem and to highlight principal contradiction. The purpose of this thesis is to study the influences of the complicated near surface, monoclinic, high, precipitous zone to seismic wave traveling and imaging, therefore the undulate of the mountainous region and the complicated geological structure of the middle and deep layers were simplified in mathematical and physical models. Same model parameters are used both in mathematical modeling and in physical modeling, in order to compare and analyze the results. In this experiment, multifold coverage geometry is adapted. The results of the modeling implies as follows:(1)The near surface structure of mountainous regions can violently reform the reflecting of the deep and middle layers, and influence the imaging of these layers. It is important for us to realize the influence and to improve the gathering mothod of mountainous seismic data, processing sequences and the modeling interpretation; (2)The near surface high and precipitous structure can produce noise similar to refracting wave; it is easy to take the noise as valid wave in singular shot record or stacked profile; and (3)When near surface geological structure is high and precipitous, and there is no shallower refracting surface (it is often in mountainous region). The first arrival is not refracted wave. Then it is suggested that the refracting static method should be applied carefully when processing seismic data from mountainous region.
Mountains in Eboliang region of Qaidam basin are characterized by monoclines of high velocity, which are coexisted with the Quaternary loosen deposits and by near surface velocity varying violently in cross. In order to study the seismic prospecting problems of this mountainous region, the traveling laws of seismic wave in complicated condition and the influence of the complicated near surface geological structure must be studied and analyzed. Either in mathematical modeling or physical modeling, it is necessary to simplify the realistic problem and to highlight principal contradiction. The purpose of this thesis is to study the influences of the complicated near surface, monoclinic, high, precipitous zone to seismic wave traveling and imaging, therefore the undulate of the mountainous region and the complicated geological structure of the middle and deep layers were simplified in mathematical and physical models. Same model parameters are used both in mathematical modeling and in physical modeling, in order to compare and analyze the results. In this experiment, multifold coverage geometry is adapted. The results of the modeling implies as follows:(1)The near surface structure of mountainous regions can violently reform the reflecting of the deep and middle layers, and influence the imaging of these layers. It is important for us to realize the influence and to improve the gathering mothod of mountainous seismic data, processing sequences and the modeling interpretation; (2)The near surface high and precipitous structure can produce noise similar to refracting wave; it is easy to take the noise as valid wave in singular shot record or stacked profile; and (3)When near surface geological structure is high and precipitous, and there is no shallower refracting surface (it is often in mountainous region). The first arrival is not refracted wave. Then it is suggested that the refracting static method should be applied carefully when processing seismic data from mountainous region.
引文
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[12] WilliaASchneider.用折射模拟法解决静校正问题[A].SEG年会论文集[C].1994.
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[15]RobertBloor.Near surfacelayertravel timeinversion:Syntheticexample[J].GeophysicalProspecting,1996,44,197213.
[16] LuigiZanzi.Inversionofrefractedarrivals:Afew problems[J].GeophysicalProspecting1990,38,339364.
[17] EvgenyLanda.Determinationofashallowvelocity depthmodelfromseismicrefractiondatabycoherenceinversion[J].GeophysicalProspecting,1995,43,17190.
[18] LinesLR .Tutorialareviewofleast squaresinversionanditsappli cationtogeophysicalproblems[J].GeophysicalProspecting,1984,32,159168.
[19] KimBakOlsen.Astableandflexibleprocedurefortheinverse mo delingofseismicfirstarrivals[J].GeophysicalProspecting,1989,37,455465.
[20] IgorBelfer.Shallowvelocity depthmodelimagingbyrefractionto mography[J].GeophysicalProspecting,1996,44,859870.
[21] SurendraSighn.Aniterativemethodfordetaileddepthdetermina tionfromrefractiondataforanuneveninterface[J].GeophysicalProspecting,1976,26,303311.
[2] 渥·伊尔马滋.地震数据处理[M].北京:石油工业出版社,1994.
[3] 德力克帕尔默.折射地震学[M].北京:地质出版社,1989.
[4] 刘清林.地震初至波射线路径追踪[J].石油物探,1993.
[5] 刘清林.论地震初至波初至时间计算方法[J].地球物理学进展,1991,(3).
[6] 张荣忠.层析成像技术在静校正中的应用[J].国外油气勘探,1998,(4).
[7] 邓志文.敦煌盆地库姆塔格沙漠静校正方法[J].石油地球物理勘探,1998,(3).
[8] 许亚军.塔里木复杂地表区静校正问题的处理方法及效果[J].石油地球物理勘探,1996,(4).
[9] 杨贵明.塔里木盆地大沙漠静校正方法[J].石油地球物理勘探,1994,(3).
[10] 李章明.正交迭代静校正方法[J].石油地球物理勘探,1997,(1).
[11] GlynMJones.折射分析的射线反演法[A].SEG年会论文集[C].1993.
[12] WilliaASchneider.用折射模拟法解决静校正问题[A].SEG年会论文集[C].1994.
[13] OsephP .StefaniTurning raytomography[J].Geophysics,1994,60(6).
[14] AldoLVesnaver.RaytracingbasedonFermat’sprincipleinirregu largrids[J].GeophysicalProspecting,1996,44,741760.
[15]RobertBloor.Near surfacelayertravel timeinversion:Syntheticexample[J].GeophysicalProspecting,1996,44,197213.
[16] LuigiZanzi.Inversionofrefractedarrivals:Afew problems[J].GeophysicalProspecting1990,38,339364.
[17] EvgenyLanda.Determinationofashallowvelocity depthmodelfromseismicrefractiondatabycoherenceinversion[J].GeophysicalProspecting,1995,43,17190.
[18] LinesLR .Tutorialareviewofleast squaresinversionanditsappli cationtogeophysicalproblems[J].GeophysicalProspecting,1984,32,159168.
[19] KimBakOlsen.Astableandflexibleprocedurefortheinverse mo delingofseismicfirstarrivals[J].GeophysicalProspecting,1989,37,455465.
[20] IgorBelfer.Shallowvelocity depthmodelimagingbyrefractionto mography[J].GeophysicalProspecting,1996,44,859870.
[21] SurendraSighn.Aniterativemethodfordetaileddepthdetermina tionfromrefractiondataforanuneveninterface[J].GeophysicalProspecting,1976,26,303311.
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