摘要
地震波场在本质上是三维矢量波场,而单分量记录仅能记录到三维矢量波场的部分投影。因此地震波偏振分析的目的就是提取地震波场的空间偏振特性和特征参数,并利用得到的特性和参数将单分量记录的标量波场还原成矢量波场。
对于VSP来说地震波偏振分析还有一些特殊用途:首先可以用来进行井下检波器水平定位;其次,可以帮助我们识别并分离VSP的复杂波场。
本文对VSP偏振特性进行了分析,详细介绍了偏振分析基本理论和波场分离合成理论,另外着重介绍了几种时变偏振分析方法,包括Cho和Spencer估算混合波场中各种波极化方向法和协方差矩阵分析法,另外还提出一种传统能量准则解析法的改进算法:基于FK滤波的时变能量准则解析法。
利用编程环境,完成了VSP水平定向偏振合成处理模块,并实现了Cho和Spencer估算混合波场中各种波极化方向法、协方差矩阵分析法和基于FK滤波的时变能量准则解析法算法,完成了三分量合成处理模块。通过理论和实际资料测试,取得了较好的效果,并对三种方法的优劣性及实用性进行了分析,其结果表明:
①传统的时不变VSP三分量合成处理方法,如能量准则解析法,在检波器水平定位方面有较好的应用效果。但在偏振合成方面则存在较大误差。
②Cho和Spencer估算混合波场中各种波极化方向法属于谱分析偏振分析法,对模型和实际资料测试的结果表明,该方法对处理模型数据和实际记录均有较好的应用效果。
③协方差矩阵分析法在处理模型数据时效果较好,但是在实际资料的应用存在一定问题,主要是时窗内波场复杂的情况下,该方法会受到干扰而无法精确计算偏振角,另外时窗选取对于协方差矩阵分析法的合成效果也有较大影响。
④基于FK滤波的时变能量准则解析法属于解析信号偏振分析法,利用人机交互式处理方法,使用灵活,但受人为因素影响较大。
For three components seismic detection,each single component record is just a projection of three-dimension vector wave-field.With the wave-field's essence is three-dimension and vector,the polarization analysis of wave-field is purpose to extract characteristic of space polarization,and to get vector wave-filed from the record of single component detector.
There are some significant and special usages which focus on VSP:Fist,geophone horizontal location of VSP needs polarization analysis.Then,facing on complex wave-field of VSP,polarization analysis could make great help in wave-field recognition and separation.
The thesis content is mainly as follows:the characteristic analysis of VSP polarization, including the basic theory of polarization analysis and wave-field synthesis of three components VSP seismic,and emphatically introduce some time-shift methods,including Estimation of polarization in mixed wave-fields by Cho and Spencer,Covariance matrix analytical method and Time-shift energy criterion analytical method based on FK filter.
With the programming tools,we produce VSP geophone horizontal location processing module,and accomplish time-shift synthesis of three-component seismic processing module with three methods mentioned above.The theoretical data and practical data is applied to test processing module with satisfactory results.The difference of results between different methods have been analyzed,and the practicality and superiority-inferiority of different methods are demonstrated.
The testify result of theoretical data and practical data show that:
①Traditional time-invariance VSP three-component synthesize method,as energy criterion analytical method,could get good results in geophone horizontal location.But in polarization aspect,there are more errors.
②The method of estimation of polarization in mixed wave-fields by Cho and Spencer which is belongs to spectral matrix analysis method.The satisfactory result for theoretical data and practical data demonstrate the correctness and efficiency of this method.
③Covariance matrix analytical method is proper in dealing with theoretical data,but for practical data,the process result will be more unreliable.Cause the complex wave-field will make the polarization angle computed by this method inaccuracy.And the range of time-windows have great impact on the computing result.
④Time-shift energy criterion analytical method based on FK filter use human-computer interaction system which make the process more flexible,but the subjective factor will make influence on the result.
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