基于快速推进迎风双线性插值法的三维地震波走时计算

三维地震波走时计算技术是三维地震反演、层析成像、偏移成像等诸多地震数据处理技术中非常重要的正演计算工具.为了获得精度高且兼顾效率的三维走时计算方法:首先,在常规双线性插值公式推导过程中,充分利用平面波双线性假设的结论,获得了二元极小值超越方程的解析解,进而推导出了准确的局部走时计算公式,同时构造性地证明了该计算公式满足地震波的传播规律和Eikonal方程;其次,引入迎风差分的基本思想,提出迎风双线性插值的局部走时计算策略,该计算策略能简化算法、提高效率且保证无条件稳定性;然后,将上述计算公式和迎风双线性插值策略与常规快速推进法中的窄带技术结合,获得了一种新的基于快速推进迎风双线性插值法的三维地震波走时计算方法;最后,通过精度和效率分析检验了新算法的精度、效率和正确性,并通过计算实例验证了算法在面对复杂介质时的稳定性和有效性.     

任意空间取向TI介质中长排列非双曲动校正公式优化(英文)

常规长排列非双曲动校正公式是在VTI介质中得到的,它不能满足任意空间取向TI(ATI)条件下的扩展.本文以VTI介质中非双曲动校正公式为基础,基于我们推导得出的ATI介质中精确四次时差系数解析解和NMO速度解析解,给出ATI介质中长排列优化的非双曲动校正公式.通过与各向异性射线追踪方法计算所得出的"精确走时"结果对比,研究表明优化后的非双曲动校正公式能精确地描述任意强弱、ATI介质中随测线方位变化的走时曲线,可以用来替代耗时、多偏移距、多方位的射线追踪方法正演拟合ATI介质中长偏移距反射走时,为利用非双曲时距的各向异性参数反演提供理论基础性认识。     

Biases and accuracy of, and an alternative to, discrete nonlinear filters

The biases and accuracy of the extended Kalman filter (EKF) and a second-order nonlinear filter (SONF) are discussed from the point of view of a frequentist; these are often derived by applying the relevant conditional quantities to the linear Kalman algorithm under the Bayesian framework. The EKF and the SONF are biased, although the SONF has been derived in the hope of improving first-order filters. Unfortunately the biases of the SONF may be magnified further, because the second-order terms of the relevant Bayesian conditional quantities have never been properly used to derive the SONF from the frequentist point of view. The variance–covariance matrix of the SONF given in the literature is proven to be incorrect up to the second-order approximation, and the correct one is derived. Finally, also from the point of view of a frequentist, an alternative, almost unbiased SONF is proposed, if the randomness of partials is neglected. Received: 12 July 1997 / Accepted: 5 October 1998     

Computation of qP-wave rays, traveltimes and slowness vectors in orthorhombic media

The eikonal equation is the equation of the phase slowness surface for isotropic and anisotropic media. In general anisotropic media, there is no simple explicit expression for the phase slowness surface. An approximate expression of the eikonal equation may be obtained in weakly anisotropic media. In orthorhombic media, the approximate eikonal equation of the qP wave is the sum of an ellipsoidal form and a more complicated term. The ellipsoidal form corresponds to what we call ellipsoidal anisotropy. Ray equations written in the Hamiltonian formulation are characteristics of the eikonal equation. Ray perturbation theory may be used to compute changes in ray paths and physical attributes (traveltime, polarization, amplitude) due to changes in the medium with respect to a reference medium. Examples obtained in homogeneous orthorhombic media show that a reference medium with ellipsoidal anisotropy is a better choice to develop the perturbation approach than an isotropic reference medium. Models with strong anisotropy can be considered. The comparison with results obtained by an exact ray program shows a relative traveltime error of less than 0.5 per cent for a model with relatively strong anisotropy. We propose a finite element approach in which the medium is divided into a set of elements with polynomial elastic parameter distributions. Inside each element, using a perturbation approach, analytical expressions for rays and traveltimes are obtained Ray tracing reduces to connecting these analytical solutions at the vertices of the cells.     

2D多尺度非线性地震速度成像

将遗传算法和单纯形算法相结合,得到了一种高效、健全的2D混合地震走时反演方法.把速度场划分为不同的空间尺度,定义网格节点上的速度作为待反演参数,采用双三次样条函数模型参数化,正问题采用有限差分走时计算方法,反问题采用多尺度混合反演方法.首先在较大的空间尺度内反演,然后减小空间尺度,将大尺度的反演结果作为次一级尺度反问题的初始模型,再进行混合反演,如此类推逐次逼近全局最优解.一个低速度异常体的数值模拟试验和抗走时扰动试验表明该方法是有效和健全的.我们将该方法应用到青藏高原东北缘阿尼玛卿缝合带东段上部地壳速度结构研究中,并与前人的成果进行了对比.     

一种二阶锥线性化方法在上限有限元中的应用研究

对于平面应变条件下岩土稳定性分析,基于线性规划的上限有限元需对常用的摩尔-库仑屈服准则形成的二阶锥约束进行线性化,直接地处理方法是以外接多边形替代锥体投影形成的圆域。为了提高线性化精度往往需直接增加外接多边形边数,从而造成线性规划模型中决策变量包含大量的塑性乘子变量,使计算难度大为增加甚至变得不可行。为此,引入Ben-Tal和Nemirovsky提出的一种二阶锥线性化方法,并将其嵌入到自编的上限有限元程序。经算例分析发现,该法与外接多边形线性化方法所获计算结果相互印证,且其通过适量的增加决策变量和等式约束数目,能保证摩尔-库仑屈服准则线性化精度,同时形成的线性规划规模更小,可望应用于基于线性规划模型的上限有限元中。     

测井资料解释煤成气层方法研究

本文在应用计算机对测井曲线进行分层的基础上,利用孔隙差异法、声波差值法、空间模量差比法和电阻率比值法逐层综合解释煤成气层,并对这几种方法在解释煤成气层时可能出现的问题进行了探讨．     

松辽盆地坳陷期湖盆层序地层研究

以横跨松辽盆地北部东西向大剖面为例,综合应用钻井岩芯、测井曲线、古生物和地震资料,进行松辽盆地北部坳陷期(早白垩世晚期—晚白垩世)湖盆层序地层学研究,共识别出2个二级层序界面和13个三级层序界面,划分出2个二级层序和13个三级层序。2个二级层序以姚家组底界不整合面为界,自下而上命名为SSI、SSII。