瞬变电磁法三维延拓成像中的信息提取技术研究
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摘要
地球物理研究中有很多不适定问题,解决起来有很大困难,电磁法勘探中这种现象尤为突出。在瞬变电磁法中传统上是用经典的电阻率公式算出地下电阻率分布情况。但要得到地下电性分界面则很难从中区分,因为传统成像图中的电阻率分布是渐变的。如果换成对电性界面表现更好形象的波动方程,并在此过程中移植地震勘探中的诸多成熟技术,则会大大提高分辨能力,进而对提高勘探精度有很大帮助。
如今在瞬变电磁场中,学术界已寻找到一个数学上的处理办法,即利用现有瞬变电磁场变换成“波场”。在已解决波场逆变换问题的基础之上,将原满足扩散方程的瞬变电磁场变换为波场来处理。运用克希霍夫积分,将虚拟地震波场由地面向地下反向逆时偏移成像。把波场分析的原理用于对瞬变电磁场的解释,就形成了瞬变电磁偏移方法。从波场角度看,它拓展和丰富了瞬变电磁场的内涵,以前用常规解释方法处理实测资料无法提取的信息,在利用上述方法对地下目标体直接成像后,变得更加容易得到。
在此过程中,扩散场刚转化为波场后,为使得波形在“强”“弱”反射面的振幅有可比性,需要求取均衡系数以方便后期成像处理;为抵消大地滤波作用,对电性界面精确定位,可以通过对虚拟波场的离散数据求取反褶积,以达到“锐化”反射面的效果;然后,同样基于为得到良好成像效果之目的,利用多点平滑处理波形。如此,在延拓成像中即可更精确的确定界面深度。取得的一些结论,将为在瞬变电磁法中正确合理地引入地震处理解释方法提供重要的理论依据,和实验参照。
There're many of ill-posedness problems in geophysical research, for that, we can hardly handle them most of the time, especially in the electromagnetic exploration method. Tranditionally, the data of resistivity under groud are usually calculated with the classical resistivity formula in the field of TEM. At the same time, to get the depth of interface of the resistivity are not easy, because the data are gradual changed at the chart of resistivity profile. It will be inproved on the sharpness of ' separation and be great helped on exploration precision, if it can be change to the form that could expressed by wave equation ,which have the power to show the interface, since for doing that, lots of mature technology belonged to seismic exploration will be introduced into TEM.
Nowadays, a math treatment has been found in academe group that is to transform to wave field from the TEM data. Base on the wave field inverse transformation problem, which has been solved, in TEM, we can turn diffusion to wave for better deal with. The seismic wave field is migrated imaging from earth surface to underground opposite to general, with Kirchhoff integral method, in doing this, migration method will be made in TEM if we use the wave field analysis principle. In the view of the wave field that extends the connotation of TEM electromagnetic field, and makes the information unfold that was covered before. We are able to get the signal more easily when imaging directly.
After getting the wave field from diffuse field, to balance two kinds of plane of reflection, both strong and weak, the equilibrium coefficient's computing is needed that's for post treatment. The deconvolution should be calculated with virtual wave field discrete data, for reaction the interface accurately, as the effect of earth filter. After that for the sake of the same purpose, multiple point smoothing should be use in our wave shape, just for better outcome. The conclusions we get are going to be provided to theoretical basis and experimental reference, for that seismic data processing utilizing to TEM reasonably.
如今在瞬变电磁场中,学术界已寻找到一个数学上的处理办法,即利用现有瞬变电磁场变换成“波场”。在已解决波场逆变换问题的基础之上,将原满足扩散方程的瞬变电磁场变换为波场来处理。运用克希霍夫积分,将虚拟地震波场由地面向地下反向逆时偏移成像。把波场分析的原理用于对瞬变电磁场的解释,就形成了瞬变电磁偏移方法。从波场角度看,它拓展和丰富了瞬变电磁场的内涵,以前用常规解释方法处理实测资料无法提取的信息,在利用上述方法对地下目标体直接成像后,变得更加容易得到。
在此过程中,扩散场刚转化为波场后,为使得波形在“强”“弱”反射面的振幅有可比性,需要求取均衡系数以方便后期成像处理;为抵消大地滤波作用,对电性界面精确定位,可以通过对虚拟波场的离散数据求取反褶积,以达到“锐化”反射面的效果;然后,同样基于为得到良好成像效果之目的,利用多点平滑处理波形。如此,在延拓成像中即可更精确的确定界面深度。取得的一些结论,将为在瞬变电磁法中正确合理地引入地震处理解释方法提供重要的理论依据,和实验参照。
There're many of ill-posedness problems in geophysical research, for that, we can hardly handle them most of the time, especially in the electromagnetic exploration method. Tranditionally, the data of resistivity under groud are usually calculated with the classical resistivity formula in the field of TEM. At the same time, to get the depth of interface of the resistivity are not easy, because the data are gradual changed at the chart of resistivity profile. It will be inproved on the sharpness of ' separation and be great helped on exploration precision, if it can be change to the form that could expressed by wave equation ,which have the power to show the interface, since for doing that, lots of mature technology belonged to seismic exploration will be introduced into TEM.
Nowadays, a math treatment has been found in academe group that is to transform to wave field from the TEM data. Base on the wave field inverse transformation problem, which has been solved, in TEM, we can turn diffusion to wave for better deal with. The seismic wave field is migrated imaging from earth surface to underground opposite to general, with Kirchhoff integral method, in doing this, migration method will be made in TEM if we use the wave field analysis principle. In the view of the wave field that extends the connotation of TEM electromagnetic field, and makes the information unfold that was covered before. We are able to get the signal more easily when imaging directly.
After getting the wave field from diffuse field, to balance two kinds of plane of reflection, both strong and weak, the equilibrium coefficient's computing is needed that's for post treatment. The deconvolution should be calculated with virtual wave field discrete data, for reaction the interface accurately, as the effect of earth filter. After that for the sake of the same purpose, multiple point smoothing should be use in our wave shape, just for better outcome. The conclusions we get are going to be provided to theoretical basis and experimental reference, for that seismic data processing utilizing to TEM reasonably.
引文
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[8]薛国强.瞬变电磁法成像技术研究[D].西安:长安大学地测学院,2002,30-35
[9]李貅,郭文波,胡建平.瞬变电磁测深快速拟地震解释方法及应用效果[J].西安工程学院.2001.23(3):
[10]李貅.瞬变电磁虚拟波场的三维曲面延拓成像研究.[D]西安交通大学,2005:68-75,17-19.
[11]李蓉,胡天跃.时移地震资料处理中的互均衡技术[J].石油地球物理勘探,2004,39(4):424-427.
[12]金龙,陈小宏,刘其成.基于奇异值分解的时移地震互均衡方法[J].地球物理学进展,2005,6,20(2):294-297.
[13]丁伟.互均衡处理技术的分析与应用[J].石油地球物理勘探,2007,42(1):17-23.
[14]云美厚,丁伟,王开彦.互均衡处理技术不是万能的[J].中国地球物理,2006:136.
[15]张照明,刘政波,刘斌,等.应用MATLAB实现信号分析和处理[M].科学出版社,2006.
[16]封建湖,车钢明,聂玉峰.数值分析原理[M].科学出版社,2001.
[17]朴化荣.电磁测深法原理[M].北京:地质出版社,1990,1-10
[18]傅承义,陈运泰,祁贵仲.地球物理学基础[M].科学出版社,1985.
[19]Zhdanov M S,Li W D.2D finite-difference time domain electromagnetic migration.In:67th SEG EM2.1.1997,370-373
[20]WangTsili,Hohmann G W,A finite-diffrence,time-domain solution for three-dimensional electromagnetic modeling[J].Geophysic,1993,58(6):797-817
[21]A new approach to imaging with low frequency electromagnetic field[J]1993 Geophysics 780-796
[22]谭浩强,田淑清.FORTRAN语言——FROTRAN77结构化程序设计[M].清华大学出版社,1990.3.
[23]Alexander A.Kaufuman,George V.Kller,王建谋译,频率域和时间域电磁测深[M].北京:地质出版社,1983,20-26
[24]林君.电磁探测技术在工程与环境的应用现状[J].石油仪器.2000,14(3):167-177.
[25]翁爱华,陆东华,刘国兴.利用连分式定义瞬变电磁法全区视电阻率研究[J].煤田地质与勘探
[26]杨长福,林长佑,陈军营,王书明,张世中.三维瞬变电磁近似反演[J].2000,22(4):337-384
[27]华军,罗延钟.中心回线瞬变电磁法2.5维有限单元算法[J].地球物理学报.2003,46(6):65-70
[28]史明娟.瞬变电磁二、三维正演理论的发展[J].国外地质勘探技术,1996(2):1-4
[29]林君等.早期时间域电磁法—VETEM[J].国外地质勘查技术,1997,(6):1-5.
[30]李貅,薛国强,郭文波.瞬变电磁法拟地震成像研究进展[J].地球物理进展,2007 June 22(3):811-816
[31]Lee S,Memechan G A.Phase-field imaging;The electromagnetic equivalent of seismic migration[J].Geophysics,1987,52(5):678-693.
[32]Yutuka(1989) Yutuka,Sasaki.Application of phase-shift migration to magnetotelluric data.Presented at the 59th annual international SEG meeting,1989.
[33]Zhdannov M S,Frenkel M A.The solution of the inverse problems on the basis of the analytical continuation of the transient electromagnetic field in reverse time[J].J Geomag Geoelectr,1983,35:747-765.
[34]Zhdannov M S,Traynin P N.Resistivity imaging by time domain electromagnetic migration[J].Exploration Geophysics,1995,26:186-194.
[35]王家映.一维大地电磁资料的的直接反演法[J].地质科技情报,1987,(6):104-113.
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