耦合势有限体积法高效模拟各向异性地层中海洋可控源的三维电磁响应

本文基于电场矢势与标势分解的耦合势有限体积法研究建立一套各向异性地层中海洋可控源电磁法的三维响应的高效数值模拟技术.首先引入电场的矢势和标势,将电场分解为无散场和无旋场之和,Maxwell方程转换为关于矢势与标势的混合Helmholtz方程,克服低感应数问题.在此基础上,借助Yee氏交错网格和有限体积法以及非均质单元中等效电导率公式,建立混合Helmholtz方程的离散方程.并采用直接法求解器PARDISO求解离散方程,有效保证在大的求解空间中仍然能够获得电磁场稳定可靠的数值解.此外,在数值模拟中利用差异场技术,克服源的奇异性问题,尽可能提高近场的计算精度.与解析解的对比证明了该算法的有效性.数值模拟结果表明,海洋可控源电磁法沿测线方向的电场,对油气藏的纵向电阻率敏感,对横向电阻率不敏感;对油气藏上方的覆盖层的纵向电阻率和横向电阻率都敏感.     

基于高精度自适应hp-FEM的随钻电阻率测井电场数值模拟

采用高精度自适应hp有限元(FEM)算法对随钻电阻率测井电场分布情况进行模拟,能够根据地层模型的实际情况和误差指示自动选择合适的细化方式和计算策略,不需要对整个求解域进行计算就能使有用信号呈指数速率准确地收敛到其真值附近.计算结果显示,获得的接收线圈感应电动势的相位差和幅度比曲线和地层分层情况吻合较好,有助于实际随钻电阻率测井资料的解释.     

用改进的传输线算法计算水平层状横向同性地层中海洋可控源电磁响应

利用二维Fourier变换与电磁场分解技术将层状横向同性地层中Maxwell方程转化成两个独立的关于横磁(TM)波和横电(TE)波的传输线方程; 借助传输线理论与叠加原理, 仅利用电流源传输线Green函数得到TM波和TE波的解, 改进传输线算法, 建立横向同性地层中频率-波数域电流源电场和磁场并矢Green函数的新算法与新的解析表达式, 提高海洋可控源电磁响应数值模拟效率. 在此基础上, 利用传输线Green函数的基本解以及边界条件, 推导出广义反射系数与振幅递推公式, 得到各个地层中传输线Green函数的解析解; 然后利用Fourier逆变换与Bessel公式将海洋可控源电磁响应表示为Sommerfeld形式的积分, 借助三次样条插值与Lommel积分公式快速计算其数值解. 通过数值模拟结果考察工作频率以及地层各向异性电阻率变化等对海洋电磁响应的影响. 关键词： 传输线法 横向同性地层 海洋可控源电磁 Sommerfeld积分     

圆弧片状声源向地层中辐射声场的有限差分模拟

提出了一种可用于随钻声波测井的非对称的圆弧片状声源,旨在发展一种能够在钻井过程中精确确定反射体位置的三维反射声波远探测方法。研究了在复杂的井孔条件(钻铤偏心、各向异性和不规则井孔形状)下,该声源向地层中辐射的声场的特征,进一步分析了不同井况条件对三维随钻远探测声波测井的影响。数值模拟结果表明,在圆形井孔、钻铤居中条件下,无论快速地层还是慢速地层,圆弧片状声源均能够向地层中定向辐射声波信号,其辐射指向性图主瓣3 dB角宽窄,旁瓣级低,方位分辨率较高,适用于随钻三维反射成像测井;井壁粗糙程度、地层各向异性等因素对声场特征影响不大,说明该方法适用于粗糙井壁和各向异性地层情况;钻铤偏心和井壁一侧的破坏对辐射声场的影响较大。对本文的模型而言,在破坏深度小于3 cm或者偏心距离小于2 cm时,声场仍有较好的方位特征,该方法仍然适用。而当破坏深度大于6 cm,声场指向性图出现多个幅值较大的角瓣,可能无法利用其确定反射体的方位。本文的研究结果为三维随钻反射声波仪的设计和研发提供了必备的理论基础。      

各向异性介质三维电磁响应模拟的Ho-GEBA算法

本文基于积分方程法研究并建立了一种模拟横向同性介质中任意各向异性异常 体三维电磁响应的高阶广义扩展Born近似(Ho-GEBA)算法. 首先利用逐次迭代技术给出积分方程的广义级数展开解, 为保证其收敛性, 引入一种各向异性条件下满足压缩映射的迭代算子. 然后利用异常体区域分解技术, 并结合扩展Born近似原理, 得到各向异性介质三维电磁响应的Ho-GEBA解. 为提高效率, 计算过程中采用并矢Green函数的解析表达式. 最后通过数值计算实例对比验证了本文算法的有效性. 关键词： 高阶广义扩展Born近似 积分方程 电磁模拟 解析Green函数     

利用积分方程法的各向异性地层频率测深三维模拟

应用一种新的积分方程算法对各向异性地层频率域电磁测深三维问题进行正演模拟.利用范数小于或等于1的修正Green算子得到各向异性地层中的新积分方程,由于满足压缩映射条件,该积分方程在任意参数条件下总是迭代收敛的.提出一种应用迭代法求解新积分方程的迭代初值优化选择方法,并通过具体算例对比说明该方法可使频率域电磁测深三维模拟的计算效率得到有效提高.最后应用所述算法对层状各向异性大地轴向频率测深视电阻率响应进行三维数值模拟,考察分析地层的各向异性对视电阻率响应特征的影响,得到一些重要结论.     

软地层随钻测井仪器偏心情况下低频四极子源 激发波场的数值分析*

为了探索测井仪器偏心对随钻低频四极子波场的影响,利用有限元法(多物理场耦合有限元软件包)对软地层井孔中随钻仪器偏心情况下低频四极子声源激发的波场进行了数值模拟。通过对随钻四极子测井波形的分析可知,当采用低频随钻四极子偏心声源激发时,测井波列中除传播速度与低速地层横波速度相当的地层四极子波模式外,还存在一个幅度非常低、传播速度略高于井孔流体中声速的模式波,该模式被对应钻铤弯曲波模式,且该模式波的幅度随着随钻四极子源偏离井孔中心距离的增大呈二次方规律增大,地层四极子模式波幅度呈三次方规律增加。     

用数值模式匹配算法高效仿真轴对称型散射体海洋可控源电磁响应

圆盘、球体以及球冠状体是地球物理研究中非常重要的一类散射类型.在海洋环境中,圆盘可以用于描述玄武岩基岩以及油气圈闭构造等电阻率异常体,而球冠可以近似描述某些基岩隆起或起伏地形等.这类散射体的一个重要特征是其电阻率空间分布具有轴对称性.如果能够针对这类形状的散射体研究建立一套有效的海洋可控源电磁数值模拟方法,对于认识复杂地层条件下海洋电磁响应的变化特征、研究建立相关的资料处理和解释方法具有非常重要的意义.本文根据电导率轴对称分布特征,设法用一个或多个不同半径、不同厚度的水平同心圆盘逼近这类轴对称电导率散射体,并将这些同心圆盘与海洋环境中的空气、海水、沉积层和基岩等背景介质结合,形成一个在水平方向电导率具有轴对称分布、在垂直方向又具有分层特征的水平层状非均质模型.在此基础上,应用数值模式匹配法研究水平电偶极子天线电磁场的数值模拟方法,给出位于对称轴上的水平发射天线电磁场在层状非均质地层中的半解析解,建立海洋可控源电磁响应高效算法.最后通过数值模拟结果对该算法进行检验并考察海洋可控源三维电磁响应特征.     

偶极随钻声波测井声压和径向位移响应的差异*

声波测井仪接收到的电信号通常是多个压电片响应的叠加,它主要是由声压还是径向位移响应转化而来,或是两种响应兼有目前未有定论。该文通过实轴积分法和复变函数法计算并对比分析随钻声波测井的声压和径向位移场,发现这两种响应特性有着显著的差异。首先,软地层的偶极随钻测井时,声压信号包含钻铤波和舒尔特波两个波群,而径向位移信号仅有钻铤波波群;其次,单极声源情况下,声压和径向位移信号的钻铤波能量分别集中在钻铤内、外壁,而偶极情况恰好相反,可见,钻铤按照单极情况的分析结果进行刻槽后,高频时的拖尾现象会影响偶极信号中舒尔特波对横波速度的反演。因此,阐明两类信号的差异对横波速度的反演和钻铤波的压制都具有重要意义。     

MC模拟在随钻方位伽马成像正演中的应用

蒙特卡罗模拟是放射性测井一种重要的数值模拟方法,利用通用程序MCNP可方便地建立各种地层模型,为放射性测井研究提供了简便有效的方法。借助于蒙特卡罗方法建立随钻条件下地层模型,正演模拟随钻方位伽马成像特征。结果表明,随钻方位伽马成像图呈现正弦线特征,利用成像图可准确反演井眼相对倾角和放射性地层厚度;井眼相对倾角越大,放射性地层厚度越厚,成像图的正弦线高度值及在井轴方向上的展布高度值越大;井眼尺寸对利用成像图求取井眼相对倾角没有影响,但对计算放射性地层厚度有影响,仪器偏心对利用成像图求取井眼相对倾角和放射性地层厚度都有较大影响,若伽马计数满足测井计数统计性,可忽略井眼流体对成像图的影响。     

Generalized collar waves in acoustic logging while drilling

Tool waves, also named collar waves, propagating along the drill collars in acoustic logging while drilling(ALWD),strongly interfere with the needed P- and S-waves of a penetrated formation, which is a key issue in picking up formation P- and S-wave velocities. Previous studies on physical insulation for the collar waves designed on the collar between the source and the receiver sections did not bring to a satisfactory solution. In this paper, we investigate the propagation features of collar waves in different models. It is confirmed that there exists an indirect collar wave in the synthetic full waves due to the coupling between the drill collar and the borehole, even there is a perfect isolator between the source and the receiver.The direct collar waves propagating all along the tool and the indirect ones produced by echoes from the borehole wall are summarized as the generalized collar waves. Further analyses show that the indirect collar waves could be relatively strong in the full wave data. This is why the collar waves cannot be eliminated with satisfactory effect in many cases by designing the physical isolators carved on the tool.     

Study of wave propagation in various kinds of plasmas using adapted simulation methods,with illustrations on possible future applications

The understanding of wave propagation in turbulent magnetized plasmas can be rather complex, particularly if they are inhomogeneous and time-dependent. Simulation can be a useful tool for wave propagation studies, provided that the “model” equations take into account the characteristics of the medium relevant for the studied problem and that the numerical scheme including boundary conditions is stable and accurate enough. The choices for the model equations and the corresponding schemes are analyzed and discussed as a function of various parameters, such as the order of the numerical scheme and the number of grid points per wavelength. A quick review of the up-to-date numerical developments is given on the sheath boundary conditions and on the perfect matching layer in anisotropic media. Possible developments of plasma diagnostics conclude this state-of-the-art of simulations of electromagnetic waves in plasmas.     

随钻声波测井隔声体刻槽影响的数值模拟研究*

针对随钻声波测井中钻铤波干扰以及刻槽后散射波问题,该文 利用时域有限差分法模拟钻铤波在随钻隔声体中的传播规律,首先考察在无限大流体中钻铤波在凹槽分界面处的散射特征,利用波场快照直观显示了钻铤波会有一部分能量在刻槽的固液界面转化为斯通利波。同时在有地层时分别对比了均匀内刻槽和外刻槽对钻铤波的衰减效果,发现在选择均匀内刻槽还是外刻槽时结果不仅与频率范围有关,而且与刻槽的深度也有关系。最后对比了槽宽较大的均匀凹槽隔声体和槽宽较小的渐变凹槽隔声体。可以得出结论,在设计随钻隔声体时,在10 kHz以下选择均匀外刻槽方式相对于内刻槽隔声效果会更好。随着刻槽槽深增加,外刻槽在10 kHz以下相比于内刻槽隔声性能优势更加明显。渐变刻槽在满足衰减钻铤波幅度要求的同时,散射波对后续地层波和斯通利波影响也更小。     

Design of electromagnetic cloaks and concentrators using form-invariant coordinate transformations of Maxwell’s equations

The technique of applying form-invariant, spatial coordinate transformations of Maxwell’s equations can facilitate the design of structures with unique electromagnetic or optical functionality. Here, we illustrate the transformation-optical approach in the designs of a square electromagnetic cloak and an omni-directional electromagnetic field concentrator. The transformation equations are described and the functionality of the devices is numerically confirmed by two-dimensional finite element simulations. The two devices presented demonstrate that the transformation optic approach leads to the specification of complex, anisotropic and inhomogeneous materials with well directed and distinct electromagnetic behavior.     

Electromagnetic modeling of inhomogeneous and anisotropic structures by volume integral equation methods

Given the application of inhomogeneous and anisotropic structures in different application areas, it is of critical importance to develop accurate and efficient modeling methods. Among various methods, volume integral equations (VIEs) using moment method are efficient solutions for electromagnetic modeling of inhomogeneous and anisotropic structures. In this paper, we investigate the solutions of the VIE method and augmented volume integral equation (A-VIE) method for solving inhomogeneous and anisotropic structures with arbitrary shapes. The moment method solutions are presented and curl-conforming bases are used to discretize the electric and magnetic field distributions inside the structures. When the structures contain inhomogeneous magnetic materials, A-VIE method is applied. Various numerical examples are shown to demonstrate the accuracy and efficiency of the algorithms.     

钻具遇卡声波检测理论与实验研究*

石油钻探过程中,钻具经常发生陷入泥沙中不能自由活动进而卡在井下的事故。本文提出使用单发双收声系来检测钻具遇卡的方法,首先使用有限差分模拟了钻具外为自由流体和泥沙两种介质时的钻铤波响应,通过对比远近接收器的钻铤波衰减,发现泥沙卡钻情况下的钻铤波衰减要明显大于自由钻具情况。随后建立了实验模型对理论结果进行了验证。理论模拟与实验结果均表明声波方法可用以检测钻具遇卡事故,从而确定卡钻的深度位置,为解卡钻作业提供解释依据。     

Nonaxisymmetric radiative transfer in inhomogeneous cylindrical media with anisotropic scattering

In this paper, the control volume finite element method (CVFEM) is applied for the first time to solve nonaxisymmetric radiative transfer in inhomogeneous, emitting, absorbing and anisotropic scattering cylindrical media. Mathematical formulations as well as numerical implementation are given and the final discretized equations are based on similar meshes used for convective and conductive heat transfer in computational fluid dynamic analysis. In order to test the efficiency of the developed method, four nonaxisymmetric problems have been examined. Also, the grid dependence and the false scattering of the CVFEM are investigated and compared with the finite volume method and the discrete ordinates interpolation method.     

Scattering from an elliptical cylindrical plasma for electromagnetic waves with wavelength much greater than the dimensions of the plasma cross-section

The distribution of the electric potential inside and outside a cold plasma column with elliptical cross-section when electromagnetic waves scatter from it are obtained. It is assumed that the wavelength of incident wave is much greater than the dimensions of the cross section of the plasma column. The electrical potential inside and outside a magnetized elliptical plasma column for an anisotropic scattering process are obtained. The graphs of the ratio of the electric field inside the plasma and the incident electric field versus the incident angle, the geometrical dimension of the elliptical plasma column and cyclotron frequency are presented separately. Finally, scattering of the same waves from an elliptical cylindrical inhomogeneous isotropic cold plasma is also investigated.