VTI介质转换波保幅叠前时间偏移方法研究

发布时间：2018-05-07 22:19

本文选题：VTI介质 + 转换波　；参考：《长安大学》2015年博士论文

【摘要】：在地震资料处理中,地震成像作为一个工具正发挥着越来越重要的作用。在具有一定周期的复杂数据处理流程中,偏移成像是最后一个环节,它的目的是为地球科学家提供适合于解释的地球内部清晰图像。近年来转换波地震.勘探技术有了.迅猛发展,转换波偏移成像.方法技术成为研究.的重点课题。在地球介质中普遍存在各向异性,同时各向异性介质中的地震波偏移成像比在各向同性介质中更加复杂,因此研究复杂介质的转换波偏移成像方法显得尤为必要,叠前时间成像.实现的是真正共反射点道.集的叠加,偏移后数据.的信噪比有较大提高,同时还可以.实现保持振幅偏移,偏移成像.效果突出,所以叠前时间.偏移倍受关注。本文在VTI介质中研究了虚拟偏移距(POM-Pseudo-Offset Migration)的转换波叠前时间保幅成像方法。针对VTI介质,论文从偏移的基本概念和各向异性介质的基本原理出发,在前人研究的基础上,研究并实现了各向同性介质中两种求取转换波虚拟偏移距(POM)的方法以及它们的成像效果,在VTI介质中分别用二分法和弦截法求解虚拟偏移距,并将这两种偏移方法的成像结果进行对比分析。论文重点研究了VTI介质转换波POM叠前时间保幅偏移,给出了叠前时间偏移中保幅权函数的不同形式和转换波保幅偏移在时间域的共炮检距权函数的具体表达式,在抽取共转换散射点道集(CCSP)映射时将振幅用权函数来补偿以直接实现保幅,避免了相同时间点的累加现象,提高了运算效率。论文取得的主要研究成果有:(1)在各向同性介质中,分别用迭代法和极限法求解虚拟偏移距来抽取共转换散射点道集和保幅偏移成像,用倾斜模型验证了各向同性介质中使用这两种方法进行POM转换波叠前时间保幅偏移的正确性,并对比了它们的耗时,发现极限法的运算效率高于一般的迭代法,所以论文在各向同性介质中用极限方法抽取CCSP道集。对Marmousi模型试算的结果也表明了在各向同性介质中POM方法进行叠前时间保幅成像的有效性。(2)在VTI介质中,由于转换波时距曲线方程的复杂性,较难推导出如各向同性介质中求虚拟偏移距的公式,所以针对VTI介质转换波的时距曲线方程,推导了VTI介质中求射线参数的数学迭代表达式,论文分别用二分法和弦截法求解射线参数,进而求解虚拟偏移距,因为这两种迭代算法避免求导数,简化了求虚拟偏移距的步骤。(3)在VTI介质中,通过单一的散射点模型对比分析了各向同性介质和VTI介质中的CCSP道集,结果表明散射点模型的旅行时按照双曲线分布,符合共转换散射点道集的映射规律,收敛性好。对倾斜模型分别使用弦截法和二分法求解虚拟偏移距,对比了这两种方法的计算耗时,结果表明弦截法比二分法收敛速度快,可提高计算效率,最终的成像效果也说明了用这两种方法抽取CCSP道集的正确性。用两平层模型验证了各向异性参数会影响CCSP道集的结果以及最终的成像效果,所以各向异性参数在实际计算中是不容忽视的。通过用倾斜模型验证虚拟偏移距间隔和偏移孔径对成像效果的影响,表明在进行叠前时间偏移时,选取合适的虚拟偏移距间隔和偏移孔径是至关重要的。使用单层VTI介质模型,发现构建准确的速度函数相当关键。(4)在VTI介质中,对单层的凹陷模型、凸起模型、断层模型和多层组合模型等进行偏移成像,验证了POM的方法的准确性,并且对比分析了在各向同性介质和VTI介质中的成像效果,最后将该方法运用到实际资料中,取得了较好的偏移成像效果。说明在VTI介质中使用POM转换波保幅叠前时间偏移方法有一定优越性。
[Abstract]:In seismic data processing, seismic imaging is playing a more and more important role as a tool. In a complex data processing process with a certain period, migration imaging is the last link. Its purpose is to provide the earth scientists with a clear image of the interior of the earth. In recent years, the converted wave earthquake and exploration technology have been used. There is a rapid development, converted wave migration imaging. Method technology has become the focus of research. Anisotropy exists in the earth medium, and seismic wave migration imaging in anisotropic media is more complex than in isotropic medium. Therefore, it is necessary to study the transfer wave migration imaging method of complex medium. It realizes the real common reflection point channel. The superposition of the set, the offset data and the signal to noise ratio are greatly improved. At the same time, it is possible to maintain the amplitude offset and offset imaging. The effect is outstanding, so the prestack time. The offset is paid attention. In this paper, the conversion wave of the virtual offset distance (POM-Pseudo-Offset Migration) is studied in the VTI medium. Based on the basic concepts of migration and the basic principle of anisotropic media, based on the basic concepts of the VTI medium and the basic principle of anisotropic media, two methods for obtaining the virtual offset (POM) of converted waves in isotropic media and their imaging results are studied and implemented in the isotropic medium. The binary and chord in VTI medium are used respectively. The section method solves the virtual offset and compares the imaging results of the two migration methods. The paper focuses on the POM prestack time shift shift of VTI medium converted wave, and gives the different forms of the amplitude preserving function in the prestack time migration and the specific expression of the total offset weight function of the conversion wave preserving amplitude offset in the time domain. The weight function is used to compensate the amplitude by extracting the amplitude of the common conversions scatter point channel set (CCSP), avoiding the accumulation of the same time points and improving the operation efficiency. The main research results obtained in this paper are as follows: (1) in isotropic media, the common conversion scattering is extracted by iterative method and limit method, respectively. Point set and amplitude preserving migration imaging are used to verify the correctness of the two methods in isotropic media using these two methods to protect the amplitude shift of the pre stack time in the isotropic medium, and compare their time consuming. It is found that the operation efficiency of the limit method is higher than that of the ordinary iterative method. So the paper uses the limit method to extract the CCSP channel in the isotropic medium. The results of the trial calculation of the Marmousi model also show the validity of the pre stack time preserving imaging of the POM method in the isotropic medium. (2) in the VTI medium, because of the complexity of the time distance curve equation of the converted wave, it is difficult to deduce the formula for finding the virtual offset in the isotropic medium, so the time distance curve of the converted wave of the VTI medium is so used. Linear equation, the mathematical iterative expressions for ray parameters in VTI medium are derived. The paper uses dichotomy and chord method to solve the ray parameters, and then solves the virtual offset, because these two iterative algorithms avoid the derivative and simplify the steps to find the virtual offset. (3) in the VTI medium, a single scattering point model is compared and analyzed. The results of CCSP channel set in isotropic medium and VTI medium show that the scattering point model is distributed according to the hyperbolic distribution and conforms to the mapping law of the converged scatter point channel set, and its convergence is good. The calculation time of the two methods is compared with the use of the string section method and the dichotomous method for the tilted model, and the results show the chord method. The rate of convergence is faster than the dichotomy, and the computational efficiency can be improved. The final imaging results also show the correctness of using these two methods to extract the CCSP set. The two flat layer model proves that the anisotropic parameters will affect the results of the CCSP set and the final imaging effect, so the anisotropic parameters can not be ignored in the actual calculation. The influence of the virtual offset interval and the offset aperture on the imaging effect is verified by the tilt model. It is shown that it is very important to select the appropriate virtual offset interval and the offset aperture in the prestack time migration. Using the single layer VTI medium model, it is found that the construction of accurate velocity function is the key. (4) in the VTI medium, the single layer is concave. The subsidence model, the convex model, the fault model and the multi-layer combination model are used for migration imaging. The accuracy of the POM method is verified, and the imaging results in the isotropic medium and the VTI medium are compared and analyzed. Finally, the method is applied to the actual data, and the better migration imaging results are obtained. It shows that the POM rotation is used in the VTI medium. The method of wave amplitude preserved prestack time migration has certain advantages.

【学位授予单位】：长安大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：P631.44

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