LTI-SIRT层析静校正方法研究和应用效果分析
摘要
近地表结构复杂地区的地震资料的处理和解释是当前陆地地震勘探的一个主要任务,地震层析成像是一种地层重建和速度反演的地震数据处理方法,利用初至波层析技术构建近地表速度场可以从本质上消除近地表时间的畸变。本文主要做了如下工作:
1、通过实验发现现有的正演算法不能适应复杂的介质速度分布模型以及较大的速度梯度变化;同时,在反演算法中,也存在着稳定性不高,对初始模型的依赖性较强等问题。通过比较,本次研究采用旅行时线性插值法(LTI, Linear Traveltime Interpolation) ,和迭代重建法(SIRT, Simultaneous Iterative Reconstruction Technique),实现了速度场的正演和反演。
2、在反演过程中,发现最大炮检距的选取范围对反演效果影响很大,深层误差会影响表层速度的反演精度;同时,最大炮检距太小,会导致覆盖近地表地层的射线不足,也会影响反演精度。研究发现最大炮检距可以根据炮间距,在初始模型上正演时射线走的深度以及想要的反演深度来确定。
3、为了验证层析反演算法的稳定性和收敛性,进行了理论模型实验;同时,引入了井深和随机误差。通过实验得出结论:①层析算法反演的速度模型趋势是正确的。②在测量和拾取准确的情况下,反演结果较好。③存在误差的情况下,模型收敛,效果略差。④模型反演中,井深比随机误差影响大。
4、在结合LTI和SIRT算法实现层析静校正的过程中,首先,建立了三种初始模型,选取了西部地区西秋的一条二维测线的地震资料,通过比较,速度突变型速度模型反演效果最好;其次,找出影响反演效果的原因,对速度场进行了插值和平滑,插值方法是反距离平方法,平滑分别采用一维平滑和二维平滑,通过比较,插值和平滑后,速度场反演精度有明显提高。
5、通过分析传统软件,它们通常采用等深和等高的方法提取等速面,这可能导致错误的静校正量,为了解决这一问题,改进了提取等速面的方法,使反演精度提高了。同时,为了消除等速面上的一些速度突变值,采用中值滤波和均值滤波的方法,平滑了等速面。
6、从应用层析静校正剖面图来看,有改进的地方,也有变差的地方,造成此结果的原因有待进一步深入研究。
本文通过速度模型和实际资料的反演结果表明,该方法能稳定、有效、快速地重建近地表的速度场分布,要很好地反演出此构造得依靠野外观测系统误差的减小,先验信息的利用,算法适应性高,参数的适当选择等。
The seismic data processing and interpretation for the near-surface structure of complicated region is a major task of seismic exploration on land .Seismic tomography is a seismic data processing methods which reconstructs statum and inverse velocity. The use of the first break tomography to build near-surface velocity field can eliminate distortion of the time-distance curves. In this paper, following jobs have been done:
1. The experiment shows that the existing ray tracing algorithm can not adapt to complicated velocity model as well as velocity model with large change in velocity gradient.At the same time, there are also some problems in the inversion algorithm ,such as low stability, the strong dependence of the initial model and so on. By comparison, this paper uses LTI(Linear Traveltime Interpolation), and SIRT(Simultaneous Iterative Reconstruction Technique) to realize the forward and inversion of the velocity field.
2. In the inversion process,the selection of the largest offset has great effect on the inversion because the error of the deep statum will affect the accuracy of the near-surface velocity inversion. But if the largest offset is too small,it will cause the rays are not enough to cover near surface which will also affect the accuracy of inversion.Largest offset can be determined by the depth of the ray traveling in initial model and the required invesion depth
3. In order to verify the stability and convergence of the tomographic inversion algorithm,theoretical model experiment is done,in which the depth error and randon error are introduced. The conclusions of the experiment are following:①tomography algorithm inversion trend is correct.②pick up in the accurate measurement and Inversion results is better with accurate measurement and pick-ups.③Error can lead to worse convergence of the velocity model.④In model inversion, the influence of the overall deviations is bigger than that of random error.
4. In the realization of LTI and SIRT algorithm, first of all,three kinds of initial model are built,and the seismic data of a two-dimensional survey line is selected. By comparison,the inverstion result of the model is better. Second,the reasons for the effect of velocity inversion are identified; Interpolation and smoothing technique are used to improved the accuracy.
5. Traditional softwares usually usd fixed depth to extract the isovelocity surface, this may lead to the wrong amount of static correction. In order to solve this problem, we improved the methods of extraction of isovelocity surface to improve the inversion accuracy . At the same time, in order to eliminate some of the velocity mutation of the isovelocity surface we use median filter and mean filter method to smooth the surface velocity
6. There is improvement, but also a place to show signs of deterioration in static Correction profiles.The result in this outcome is expecting further study.
In this paper, theoretical models and actual data inversion results show that the method can reconstruct near-surface distribution of the velocity field stably, effectively and rapidly . To perform well in this anti-structure, it is necessary to rely on errors reduction of field observation system ,use of first examination of information , the high adaptivity of the algorithm, and the appropriate choice of parameters.
1、通过实验发现现有的正演算法不能适应复杂的介质速度分布模型以及较大的速度梯度变化;同时,在反演算法中,也存在着稳定性不高,对初始模型的依赖性较强等问题。通过比较,本次研究采用旅行时线性插值法(LTI, Linear Traveltime Interpolation) ,和迭代重建法(SIRT, Simultaneous Iterative Reconstruction Technique),实现了速度场的正演和反演。
2、在反演过程中,发现最大炮检距的选取范围对反演效果影响很大,深层误差会影响表层速度的反演精度;同时,最大炮检距太小,会导致覆盖近地表地层的射线不足,也会影响反演精度。研究发现最大炮检距可以根据炮间距,在初始模型上正演时射线走的深度以及想要的反演深度来确定。
3、为了验证层析反演算法的稳定性和收敛性,进行了理论模型实验;同时,引入了井深和随机误差。通过实验得出结论:①层析算法反演的速度模型趋势是正确的。②在测量和拾取准确的情况下,反演结果较好。③存在误差的情况下,模型收敛,效果略差。④模型反演中,井深比随机误差影响大。
4、在结合LTI和SIRT算法实现层析静校正的过程中,首先,建立了三种初始模型,选取了西部地区西秋的一条二维测线的地震资料,通过比较,速度突变型速度模型反演效果最好;其次,找出影响反演效果的原因,对速度场进行了插值和平滑,插值方法是反距离平方法,平滑分别采用一维平滑和二维平滑,通过比较,插值和平滑后,速度场反演精度有明显提高。
5、通过分析传统软件,它们通常采用等深和等高的方法提取等速面,这可能导致错误的静校正量,为了解决这一问题,改进了提取等速面的方法,使反演精度提高了。同时,为了消除等速面上的一些速度突变值,采用中值滤波和均值滤波的方法,平滑了等速面。
6、从应用层析静校正剖面图来看,有改进的地方,也有变差的地方,造成此结果的原因有待进一步深入研究。
本文通过速度模型和实际资料的反演结果表明,该方法能稳定、有效、快速地重建近地表的速度场分布,要很好地反演出此构造得依靠野外观测系统误差的减小,先验信息的利用,算法适应性高,参数的适当选择等。
The seismic data processing and interpretation for the near-surface structure of complicated region is a major task of seismic exploration on land .Seismic tomography is a seismic data processing methods which reconstructs statum and inverse velocity. The use of the first break tomography to build near-surface velocity field can eliminate distortion of the time-distance curves. In this paper, following jobs have been done:
1. The experiment shows that the existing ray tracing algorithm can not adapt to complicated velocity model as well as velocity model with large change in velocity gradient.At the same time, there are also some problems in the inversion algorithm ,such as low stability, the strong dependence of the initial model and so on. By comparison, this paper uses LTI(Linear Traveltime Interpolation), and SIRT(Simultaneous Iterative Reconstruction Technique) to realize the forward and inversion of the velocity field.
2. In the inversion process,the selection of the largest offset has great effect on the inversion because the error of the deep statum will affect the accuracy of the near-surface velocity inversion. But if the largest offset is too small,it will cause the rays are not enough to cover near surface which will also affect the accuracy of inversion.Largest offset can be determined by the depth of the ray traveling in initial model and the required invesion depth
3. In order to verify the stability and convergence of the tomographic inversion algorithm,theoretical model experiment is done,in which the depth error and randon error are introduced. The conclusions of the experiment are following:①tomography algorithm inversion trend is correct.②pick up in the accurate measurement and Inversion results is better with accurate measurement and pick-ups.③Error can lead to worse convergence of the velocity model.④In model inversion, the influence of the overall deviations is bigger than that of random error.
4. In the realization of LTI and SIRT algorithm, first of all,three kinds of initial model are built,and the seismic data of a two-dimensional survey line is selected. By comparison,the inverstion result of the model is better. Second,the reasons for the effect of velocity inversion are identified; Interpolation and smoothing technique are used to improved the accuracy.
5. Traditional softwares usually usd fixed depth to extract the isovelocity surface, this may lead to the wrong amount of static correction. In order to solve this problem, we improved the methods of extraction of isovelocity surface to improve the inversion accuracy . At the same time, in order to eliminate some of the velocity mutation of the isovelocity surface we use median filter and mean filter method to smooth the surface velocity
6. There is improvement, but also a place to show signs of deterioration in static Correction profiles.The result in this outcome is expecting further study.
In this paper, theoretical models and actual data inversion results show that the method can reconstruct near-surface distribution of the velocity field stably, effectively and rapidly . To perform well in this anti-structure, it is necessary to rely on errors reduction of field observation system ,use of first examination of information , the high adaptivity of the algorithm, and the appropriate choice of parameters.
引文
[1] Li JG, Yao Y, Rui YJ, et al. The research and application on static correction in complex surface area [J]. Geophysics,2008,(6): 227-230
[2] Mangue M, Perroud H, Rousset D First-arrival traveltimes inversion based on a minimal number of parameters in shallow cross-well GPR tomography [J]. Geophysics,2009,67(4): 278-287
[3] Mahapatra M, Mahapatra S Seismic diffraction tomography technique using very fast simulated annealing method for delineating small subsurface features [J]. Geophysics,2009,67(2): 125-129
[4] Takeuchi NA. low-velocity conduit throughout the mantle in the robust component of a tomography model [J]. Geophysical Research Letters,2009,36: L07306
[5] Clarke D, Townend J, Savage MK, et al .Seismicity in the Rotorua and Kawerau geothermal systems, Taupo Volcanic Zone, New Zealand, based on improved velocity models and cross-correlation measurements [J]. Journal of Volcanology and Geothermal Research,2009,180(1): 67-80
[6] Kanli AI.Initial velocity model construction of seismic tomography in near-surface applications , [J]. Journal of applied Geophysics,2009,67(1): 52-62
[7] Nakajima J, Hasegawa A.Existence of low-velocity zones under the source areas of the 2004 Chuetsu and 2007 Chuetsu-oki earthquakes inferred from travel-time tomography, [J]. Earth Planets and Space,2008,60(11): 1127-1130
[8] Osazuwa IB, Chinedu AD.Seismic refraction tomography imaging of high-permeability zones beneath an earthen dam, in Zaria area, Nigeria, [J]. Journal of applied Geophysics,2008,66(1-2): 44-58
[9] Negri S, Leucci G, Mazzone F.High resolution 3D ERT to help GPR data interpretation for researching archaeological items in a geologically complex subsurface. [J]. Journal of applied Geophysics,2008,65(3-4): 111-120
[10] Brauchler R, Cheng JT, Dietrich P, et al.An inversion strategy for hydraulic tomography: Coupling travel time and amplitude inversion, [J]. Journal of Hydrology,2007,345(3-4): 184-198
[11] Valenta J, Dohnal J.3D seismic travel time surveying a comparison of the time-term method and tomography (an example from an archaeological site), [J]. Journal of applied Geophysics,2007,63(1): 46-58
[12] Schneider Jr. W A, Ranzinger K A and Balch A H,et al.. A dynamic programming approach to first-arrival traveltime computation in mediawith arbitrarily distributed velocities. Geophysics,1992,57:39-50.
[13] Docherty P. Solving for the thickness and velocity of the weathering layerusing 2-D refraction tomography [J].Geophysics,1992,57(10): 1307-1308
[14] ZHU X, Mcmechan G A. Estimation of two-dimensionalseismic compressional-wave velocity distribution by itera-tive tomographic imaging [J].Internat J Imag SysTech,1999,1: 13-17.
[15]时磊,顾汉明,刘洪雷,无射线追踪法层析静校正及其应用[J].工程地球物理学报,2008,(05)
[16]杨为民,张云岗,刘原英,层析静校正技术在山地复杂地区三维地震勘探中的应用[J].中国煤田地质,2007,(02)
[17]王伟,廖大香,杜宏筠,层析静校正在泽口地区地震资料处理中的应用[J].石油天然气学报,2007,(03)
[18]林伯香,孙晶梅,徐颖,李博,几种常用静校正方法的讨论[J].石油物探,2006,(04)
[19]陈爱萍,梁波,邹文,初至波地震层析技术及其在四川复杂地区的应用[J].世界地质,2006,(04)
[20]李霞,张印堂,折射层析反演静校正在伊朗卡山地区的应用[J].勘探地球物理进展, 2006,(01)
[21]邹强,周熙襄,钟本善,交互的初至波反演及静校正[J].物探化探计算技术,2005,(01)
[22]张印堂,折射层析反演静校正及其在伊朗卡山地区的应用[J].油气地球物理,2005,(03)
[23]张建中,近地表介质地震初至波层析成像[J].厦门大学学报:自然科学版,2004,43(1): 63-66
[24]李录明,罗省贤,复杂三维表层模型层析反演与静校正[J].石油地球物理勘探,2003,38(6):636-641
[25]李家康,余钦范,近地表速度的约束层析反演[J].石油地球物理勘探,2001,36(2): 137-140
[26]李录明,罗省贤,初至波表层模型层析反演[J].石油地球物理勘探,2000,35(5):559-564
[27]李福中,邢国栋,白旭明等,初至波层析反演静校正方法研究[J].石油地球物理勘探, 2000,35(6):710-718
[2] Mangue M, Perroud H, Rousset D First-arrival traveltimes inversion based on a minimal number of parameters in shallow cross-well GPR tomography [J]. Geophysics,2009,67(4): 278-287
[3] Mahapatra M, Mahapatra S Seismic diffraction tomography technique using very fast simulated annealing method for delineating small subsurface features [J]. Geophysics,2009,67(2): 125-129
[4] Takeuchi NA. low-velocity conduit throughout the mantle in the robust component of a tomography model [J]. Geophysical Research Letters,2009,36: L07306
[5] Clarke D, Townend J, Savage MK, et al .Seismicity in the Rotorua and Kawerau geothermal systems, Taupo Volcanic Zone, New Zealand, based on improved velocity models and cross-correlation measurements [J]. Journal of Volcanology and Geothermal Research,2009,180(1): 67-80
[6] Kanli AI.Initial velocity model construction of seismic tomography in near-surface applications , [J]. Journal of applied Geophysics,2009,67(1): 52-62
[7] Nakajima J, Hasegawa A.Existence of low-velocity zones under the source areas of the 2004 Chuetsu and 2007 Chuetsu-oki earthquakes inferred from travel-time tomography, [J]. Earth Planets and Space,2008,60(11): 1127-1130
[8] Osazuwa IB, Chinedu AD.Seismic refraction tomography imaging of high-permeability zones beneath an earthen dam, in Zaria area, Nigeria, [J]. Journal of applied Geophysics,2008,66(1-2): 44-58
[9] Negri S, Leucci G, Mazzone F.High resolution 3D ERT to help GPR data interpretation for researching archaeological items in a geologically complex subsurface. [J]. Journal of applied Geophysics,2008,65(3-4): 111-120
[10] Brauchler R, Cheng JT, Dietrich P, et al.An inversion strategy for hydraulic tomography: Coupling travel time and amplitude inversion, [J]. Journal of Hydrology,2007,345(3-4): 184-198
[11] Valenta J, Dohnal J.3D seismic travel time surveying a comparison of the time-term method and tomography (an example from an archaeological site), [J]. Journal of applied Geophysics,2007,63(1): 46-58
[12] Schneider Jr. W A, Ranzinger K A and Balch A H,et al.. A dynamic programming approach to first-arrival traveltime computation in mediawith arbitrarily distributed velocities. Geophysics,1992,57:39-50.
[13] Docherty P. Solving for the thickness and velocity of the weathering layerusing 2-D refraction tomography [J].Geophysics,1992,57(10): 1307-1308
[14] ZHU X, Mcmechan G A. Estimation of two-dimensionalseismic compressional-wave velocity distribution by itera-tive tomographic imaging [J].Internat J Imag SysTech,1999,1: 13-17.
[15]时磊,顾汉明,刘洪雷,无射线追踪法层析静校正及其应用[J].工程地球物理学报,2008,(05)
[16]杨为民,张云岗,刘原英,层析静校正技术在山地复杂地区三维地震勘探中的应用[J].中国煤田地质,2007,(02)
[17]王伟,廖大香,杜宏筠,层析静校正在泽口地区地震资料处理中的应用[J].石油天然气学报,2007,(03)
[18]林伯香,孙晶梅,徐颖,李博,几种常用静校正方法的讨论[J].石油物探,2006,(04)
[19]陈爱萍,梁波,邹文,初至波地震层析技术及其在四川复杂地区的应用[J].世界地质,2006,(04)
[20]李霞,张印堂,折射层析反演静校正在伊朗卡山地区的应用[J].勘探地球物理进展, 2006,(01)
[21]邹强,周熙襄,钟本善,交互的初至波反演及静校正[J].物探化探计算技术,2005,(01)
[22]张印堂,折射层析反演静校正及其在伊朗卡山地区的应用[J].油气地球物理,2005,(03)
[23]张建中,近地表介质地震初至波层析成像[J].厦门大学学报:自然科学版,2004,43(1): 63-66
[24]李录明,罗省贤,复杂三维表层模型层析反演与静校正[J].石油地球物理勘探,2003,38(6):636-641
[25]李家康,余钦范,近地表速度的约束层析反演[J].石油地球物理勘探,2001,36(2): 137-140
[26]李录明,罗省贤,初至波表层模型层析反演[J].石油地球物理勘探,2000,35(5):559-564
[27]李福中,邢国栋,白旭明等,初至波层析反演静校正方法研究[J].石油地球物理勘探, 2000,35(6):710-718
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