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《应用地球物理》2016,(1)
传统的复电阻率法二维正演是基于泊松方程完成的,而实际的频谱激电数据包括激电效应和电磁效应双重作用的影响,特别是频率较高时电磁效应甚至大于激电效应,因此只考虑激电效应的做法会降低反演结果的可靠性。本文的研究从麦克斯韦方程出发,引入Cole-Cole模型,同时考虑了激电效应和电磁效应,采用有限单元法实现了复电阻率法二维数值模拟。反演采用二维数据空间OCCAM方法,通过施加不同的模型光滑约束和参数界限约束,利用多排列电场数据同时反演Cole-Cole模型四个参数,既提高了反演的稳定性又降低了反演的多解性。为了提高计算效率,我们选用MPI实现了频谱激电二维正反演并行算法。通过理论模型的试算,对比串行程序和并行程序的计算结果和效率,验证了并行算法的稳定性、可靠性和高效性。 相似文献
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《地球物理学进展》2015,(3)
利用广义等效介质激电(GEMTIP)模型,本文提出了一种频率域中2.5维复电阻率有限体积正演计算方法.首先对GEMTIP的理论模型进行介绍,分析了不同参数影响下的视复电阻率响应变化特征.而后,详尽地推导了有限体积各控制容积所满足的离散方程式,利用预处理的广义极小残差算法(GMRES)求解线性方程组.通过与两相层状大地解析解进行对比,验证了数值算法的正确性.结合实际地质情况,构建若干典型多相态复合地电模型及简化斑岩型矿床模型进行试算,结果表明,GEMTIP模型是对Cole-Cole模型的一种扩展,其相关参量表征明确;在一定频段内计算所得场值异常分布明显,为岩、矿体的激电效应在宏观尺度上的近一步研究提供了新的途径. 相似文献
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进一步提高瞬变电磁法对地探测的解释精度,提出了回线源瞬变电磁成像原理及数值计算方法. 讨论了频率域中水平层状介质中瞬变电磁响应,得到一个以波阻抗为积分核的双重积分式;然后对水平层介质下电磁场的解进行上、下行波分离,得到含有以反射系数序列为未知的线性方程组,并给出了求取波阻抗和反射系数的数值解法：对实测磁场值进行域的变换,以均匀半空间下的等效波阻抗代替积分核函数,经过线性数字滤波后,在频率域求出等效波阻抗;把频率域中的波阻抗转换到时间域,以此为参数,构建方程组,在时间域用线性规划法求出反射系数序列. 最终以反射系数为参数进行成像. 对理论模型的数值计算结果表明,用本文提出的成像方法可以增强瞬变电磁法识别地下电性分界面的能力. 相似文献
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在给出真实模型和相应光滑背景模型的情况下,如何计算扰动模型(散射体)产生的散射波场是一个有实际意义的正演问题.在Gabor变换域描述散射体,且入射波场为短时宽带信号时,散射波场可以在频率域用高斯束或时间域用高斯波包描述.相对于波动方程方法,高斯束和高斯波包的计算效率更高;背景模型光滑时,高斯束和高斯波包方法的精度也接近波动方程方法.文中导出了声波假设下应用高斯束和高斯波包计算散射波的方法.测试分析了高斯波包的计算精度.给出了一般散射体的散射波模拟策略.同时针对一个理论模型完成了本文方法计算散射波的实验,实验结果表明高斯波包散射波计算方法是有效可行的. 相似文献
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由于激发极化效应的影响,时间域航空电磁晚期道信号经常会出现变号现象.基于电阻率的传统反演方法无法对变号数据进行正确反演,因此通常在数据处理中予以剔除.为深入了解极化介质的电磁扩散特征,认识航空瞬变电磁负响应的产生机理,本文研究时间域航空电磁系统的电磁扩散特征.我们以均匀极化、非极化半空间及层状介质模型为例,通过直接积分的方法求解频率域电场响应,并由欧姆定律得到电流响应,再经过汉克尔变换得到时间域电流响应.通过研究电流随时间在地下极化介质中的传播特征研究电磁扩散过程;通过对比不同激电参数对电磁扩散的影响,研究极化介质中感应电流与极化电流的扩散规律,从而合理地解释极化介质中负响应的产生机理.基于本文研究和分析结果,可加深对时间域航空电磁法中激电效应的认识. 相似文献
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地震波在地下含流体孔隙介质中传播时,会引起中观尺度的"局域流",进而产生地震波震电效应.基于Biot(1941)固结理论的准静态方程,在频率域中采用空间有限差分方法,正演模拟虚岩石物理岩样的地震波衰减和震电效应.与时间域虚岩石物理方法相比,该方法既可以直接求取任一频率下的地震波衰减和电势,便于应用于实际岩样的预测分析,也避免了讨论岩样外表面施加的力源函数表达式及时间剖分稳定性条件等问题.首先利用周期性层状介质模型验证了本文所描述方法的有效性,并进一步求取分析了周期性层状介质两种不同特征单元的渗流电流密度及电势,数值模拟结果表明由中观尺度"局域流"引起的震电效应电势振幅数量级在实验室测量范围之内,随后,分析研究了四种不同高渗介质占比值的地震衰减及震电效应特征.最后,将本文提出的震电效应数值计算方法推广至二维,并求取了二维斑块饱和模型的地震波衰减、速度频散、电势的振幅和相位角数值结果. 相似文献
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油气藏自身会产生激电效应,明确海洋可控源电磁场激电效应特征非常重要。本文基于自适应有限元方法实现了带激电效应的2.5D海洋可控源频率域电磁场正演。采用非结构化三角网格单元剖分地电模型,可以模拟任意起伏地形和复杂地电构造。利用Cole-Cole模型表述油气藏的激电效应,实现了考虑激电效应的海洋电磁复电阻率正演算法。将本文的计算结果与已发表的一维模型结果对比,检验了本文算法的正确性。最后,设计了不同的极化模型,针对不同的场源方位角、激电参数和地形,计算了的电磁场响应结果,分析了激电效应对海洋可控源电磁场的影响规律,结果表明油气藏的激电效应和海底地形对海洋可控源电磁场有一定的影响。 相似文献
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Jianping Xiang N.B. Jones Daizhan Cheng F.S. Schlindwein 《Geophysical Prospecting》2002,50(6):565-576
The problem of discrimination between a valid induced polarization (IP) response and electromagnetic (EM) coupling effects is considered and an effective solution is provided. First, a finite dimensional approximation to the Cole‐Cole model is investigated. Using the least‐squares approach, the parameters of the approximate model are obtained. Next, based on the analysis of overvoltage, a finite dimensional structure of the IP model is produced. Using this overvoltage‐based structure, a specific finite dimensional approximation of the Cole‐Cole model is proposed. Summarizing the analysis of the finite dimensional IP model, it is concluded that the proposed IP model, which fits the field data much better than the traditional Cole‐Cole model, is essentially an RC‐circuit. From a circuit‐analysis point of view, it is well known that an electromagnetic effect can be described by an RL‐circuit. The simulation results on experimental data support this conception. According to this observation, a new method to discriminate between a valid IP response and EM coupling effects is proposed as follows: (i) use a special finite dimensional model for IP–EM systems; (ii) obtain the parameters for the model using a least‐squares approach; (iii) separate RC‐type terms and RL‐type terms – the first models the IP behaviour, the latter represents the EM part. Simulation on experimental data shows that the method is very simple and effective. 相似文献
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本文将LabVIEW与基于32位ARM单片机的数据采集电路结合,研究实现了一种高精度、多功能的双频激电信号采集系统.激电信号被采集系统接收后,经信号调理进入模数转换电路转换为数字信号,由USB接口送入基于LabVIEW软件平台的上位机中.上位机对该信号进行滤波选频、幅值测量、频谱分析、幅频率计算等处理,得到目标参数,同时还具有绘图、保存、查看等功能.本文就双频激电信号采集进行了阻容网络模拟实验,先用公式计算出理论视幅频率值,然后搭建电路进行实测.实验结果表明,该采集系统对双频激电信号采集的视幅频率测量误差小、精度高,具有良好的测量效果. 相似文献
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地电体对频率域电磁波激发源的响应为电磁感应和激电效应的综合响应.传统CSAMT法进行数据正反演时认为大地介质电阻率是与频率无关的实数,而实际上因为激电效应,地下可极化体的电阻率是一个与频率相关的复数.为推进二者总体响应研究,并扩展激电法的应用范围,同时提高电磁法勘探的精度,本文基于Dias模型,以复电阻率代替不考虑地电体极化效应的直流电阻率,对CSAMT场源一维层状模型进行了正演模拟,为提取CSAMT信号中所含激电信息提供理论基础.结果表明,考虑激电参数后,视电阻率及相位响应曲线出现明显异常（包括远场、过渡场、近场）;极化前后振幅比值异常峰值、相位差值异常峰值可直观体现激电异常;异常峰值与极化层层厚、埋深以及电阻率变化有连续的对应关系.认为从频率域电磁法信号中提取激电信息有乐观的前景. 相似文献
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Theoretical and experimental study of time domain-induced polarization in water-saturated sands 总被引：1，自引：0，他引：1
A theoretical model of spectral-induced polarization (IP) of sand is presented. In the proposed model, contacts of sand grains and intergrain solution-filled space are considered as electrical current passages of varying thickness, which differ in values of ion transport number. Ion-selective narrow passages are considered as active zones, large passages as passive. The proposed model describes spectral IP characteristics for the medium where the length of passive zones is much greater than the length of active ones. The model is called short narrow pores (SNP) model. The SNP model predicts a growth of IP time constant with increase of length of ion-selective zone. Both the time domain and frequency domain parameters are described. The parameters of Cole–Cole model corresponding to the SNP model were also found.The behaviour of model parameters is compared with experimental data obtained on natural and sieved sands using time domain technique. The natural sand spectra correspond neither to the simple SNP model nor simple Cole–Cole model with single time constant because the lengths of ion-selective zones vary, reflecting the grain-size distribution.The spectra of sieved sand compared with the theoretical SNP spectra reveal close correspondence between experimental data and theoretical parameters. For four sieved sands, both the theoretical and experimental data show that the time constant of the IP is proportional to the square of the average grain size. 相似文献
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The induced polarization (IP) in rocks and minerals is of significance to the marine controlled-source electromagnetic (CSEM) field. We propose an adaptive finite-element algorithm for the 2.5D frequency-domain forward modeling of marine CSEM that considers the induced polarization. The geoelectrical model is discretized using an unstructured triangular elemental grid that accommodates the complex topography and geoelectrical structures. We use the Cole–Cole model to describe the IP and develop a complex resistivity forward modeling algorithm. We compare the simulation results with published 1D model results and subsequently calculate the electromagnetic field for variable azimuth sources, IP parameters, and topography. Finally, we analyze the IP effect on the marine CSEM field and show that IP of oil reservoirs and topography affects the marine CSEM electromagnetic field. 相似文献
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B. S. Svetov V. V. Ageev S. D. Karinskii O. A. Ageeva 《Izvestiya Physics of the Solid Earth》2013,49(6):836-843
In the first part of the paper, with some constraints, we find the analytical solution of the self-consistent problem of induced polarization (IP) for an electrokinetically polarized sphere. The stationary (on long time intervals) solution of the self-consistent problem is a set of the potential fields that are interconnected with each other: the exciting electric field, the extraneous hydrodynamical field (electroosmotic flow of a viscous incompressible fluid), and the resulting electromagnetic IP field. The extraneous field is the field of the osmotic flow of a charged liquid and the field of the charges that emerge due to the membrane effect in the narrowed segments of the pore channels. The calculations show that the IP fields derived by solving the self-consistent problem and by the Seigel-Komarov phenomenological approach are different. In the second part of the paper, by generalization of the obtained analytical solution, we formulate the self-consistent IP problem for isotropic σ-η media of arbitrary shape, which are bounded by a smooth surface. The problem can be solved by the numerical methods. 相似文献
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Indrajit G Roy 《Geophysical Prospecting》1999,47(4):527-550
Non-linear least-squares inversion operates iteratively by updating the model parameters in each step by a correction vector which is the solution of a set of normal equations. Inversion of geoelectrical data is an ill-posed problem. This and the ensuing suboptimality restrict the initial model to being in the near vicinity of the true model. The problem may be reduced by introducing damping into the system of equations. It is shown that an appropriate choice of the damping parameter obtained adaptively and the use of a conjugate-gradient algorithm to solve the normal equations make the 1D inversion scheme efficient and robust. The scheme uses an optimal damping parameter that is dependent on the noise in the data, in each iterative step. The changes in the damping and relative residual error with iteration number are illustrated. A comparison of its efficacy over the conventional Marquardt and simulated annealing methods, tested on Inman's model, is made. Inversion of induced polarization (IP) sounding is obtained by inverting twice (true and modified) DC apparent resistivity data. The inversion of IP data presented here is generic and can be applied to any of the IP observables, such as chargeability, frequency effect, phase, etc., as long as these observables are explicitly related to the DC apparent resistivity. The scheme is used successfully in inverting noise-free and noisy synthetic data and field data taken from the published literature. 相似文献