Zohdy方法在三维电阻率测深数据反演中的应用

三维电阻率测深数据采用Zohdy方法近似反演,正演计算采用有限单元法,反演初始模型由测量视电阻率数据给出,通过比较实测视电阻率值和预测模型计算的视电阻率值对数差来修改模型网格电阻率.为了解决任意电极距测深数据的反演,采用大、小双网格剖分,大网格反映地下电性分布情况,小网格用于实际有限元正演计算.文章对加5%随机噪声的模型理论视电阻率测深断面数据和实测视电阻率测深断面数据进行反演.结果表明该反演方法需要的内存小、计算量少,并能够取得很好的反演效果.     

电偶源频率电磁测深中比值视电阻率和阻抗相位的联合反演

本文论述了电偶源频率电磁测深中,利用比值视电阻率和相应阻抗相位进行联合反演的必要性和可能的应用前景及具体实施方法。理论模型和实际观测资料的反演试验表明这一联合反演是可行和有效的,且明显地优于视电阻率和阻抗相位的单参量反演。     

电偶源频率电磁测深中比值视电阻率和阻抗相位的联合反演

本文论述了电偶源频率电磁测深中，利用比值视电阻率和相应阻抗相位进行联合反演的必要性和可能的应用前景及具体实施方法。理论模型和实际观测资料的反演试验表明这一联合反演是可行和有效的，且明显地优于视电阻率和阻抗相位的单参量反演。     

频率测深中单分量视电阻率—相位联合反演

讨论了电偶源频率电磁测深相位定义的某些问题,阐述了由作者定义的一套单分量比值视电阻率所相应相位的优点。研究了电偶源频率电磁测深中三种单分量视电阻率—相位联合反演的实施方法,并论述了其实际应用效果。     

电偶源频率电磁测深二维层状模型参数化反演

本文在大地电磁测深松弛（ｒａｐｉｄ）反演理论方法的基础上，探讨了电偶源频率电磁测深（赤道装置）阻抗视电阻率的二维反演问题。由二维层状模型反演目标函数的近似简化出发。将全剖面的二维反演约化为沿剖面各测点的逐一测点一维反演，从而构制了一个简易可行的二维层状模型参数化反演方案。反演试验表明，这一反演方法是实用和有效的     

时域激电单极-偶极、偶极-单极排列测深法二维地电断面成像

介绍了不对称测深法装置的测深原理;在吉林某地进行了激电测深勘探,结果显示:正向单极-偶极和反向偶极-单极采集的视电阻率、视充电率原始数据在拟断面图的分布特征,和大地电磁测深原始数据受到的静态效应类似,视电阻率、视充电率受局部地形和电磁噪声的影响,在拟断面图中呈假的带状异常。正向单极-偶极、反向偶极-单极装置获取的视电阻率、视充电率数据也可分别进行二维反演,但联合单极-偶极/偶极-单极装置测深二维反演地质结果最好,具有采集的数据量大、激电信号强 、穿透深度大、勘探精度高等优点,根据视电阻率、视充电率二维反演在地电断面成像技术,能够准确确定电性异常体的空间分布,为钻探验证电异常提供准确的地球物理依据。     

电阻率测深一维反演的曲线对比法

本文对佐迪的电测深自动解释方法进行了改进，采用新的方法建立初始反演模型。将电测深实测曲线转变为纵向电导——深度曲线，由ｄＨ／ｄｓ得出电阻率——深度的初始反演模型。通过把初始反演模型得到的视电阻率曲线与真实地电模型的视电阻率曲线进行对比，来校正初始反演模型电阻率，校正后的反演模型的视电阻率曲线与真实模型的视电阻率曲线拟合程度有所提高。如此反复进行多次校正，获得与其实地电模型更接近的最终反演结果。模型试验和实际例子表明，该方法的反演拟合误差一般均小于１％，模型试验可达到０．１％。     

直流电阻率测深曲线解释中的直接反演法

本文根据在电导率随深度变化梯度不大的情况下，ＤａｒＺａｒｒｏｕｋ曲线与视电阻率曲线基本重合这一性质，通过各种变换，在电阻率测深中导出了一种可与大地电磁测深中Ｂｏ－ｓｔｉｃｋ反演方法相比美的直接反演方法，将视电阻率随极距变化曲线转换为电阻率随深度变化曲线。     

电测深法视电阻率对介质电阻率偏导数的计算

在前人工作基础上,对电测深法一维正演解析解递推电阻率转换函数求偏导,给出了电测深法视电阻率对介质电阻率偏导数的解析计算方法;根据Seigel体激发极化理论,采用视电阻率对介质电阻率偏导数矩阵的线性组合,计算出了电测深法的视极化率,其结果与"等效电阻率法"计算视极化率最大相对误差小于1.1%。在一次正演计算过程中就可以同时得到视电阻率、视极化率以及视电阻率对介质电阻率的偏导数矩阵,提高了计算效率,也为后续的多层地电模型电测深法数据优化反演计算提供了关键性技术。     

TEM全区视电阻率在煤田采空区注浆效果检测的应用

文章分析总结了前人各类求取回线源瞬变电磁全区视电阻率的方法。首先介绍一维层状介质中心回线瞬变电磁测深法的全区视电阻率定义,研究总结常用的全区视电阻率数值计算方法,介绍了隐函数的反函数求解问题,并对比两种反演方法,对典型地电断面模型进行正演模拟。最后将全区视电阻率及反演运用到煤矿采空区注浆效果验证中,取得较好效果。     

Effects of galvanic distortions on magnetotelluric data: Interpretation and its correction using deep electrical data

The non-inductive galvanic disturbances due to surficial bodies, lying smaller than high frequency skin depth, cause serious interpretational errors in magnetotelluric data. These frequency independent distortions result in a quasi-static shift between the apparent resistivity curves known as static shift. Two-dimensional modelling studies, for the effects of surficial bodies on magnetotelluric interpretation, show that the transverse electric (TE) mode apparent resistivity curves are hardly affected compared to the transverse magnetic (TM) mode curves, facilitating the correction by using a curve shifting method to match low frequency asymptotes. But in the case of field data the problem is rather complicated because of the random distribution of geometry and conductivity of near surface inhomogeneities. Here we present the use of deep resistivity sounding (DRS) data to constrain MT static shift. Direct current sensitivity studies show that the behaviour of MT static shift can be estimated using DC resistivity measurements close to the MT sounding station to appreciable depths. The distorted data set is corrected using the MT response for DRS model and further subject to joint inversion with DRS data. Joint inversion leads to better estimation of MT parameters compared to the separate inversion of data sets.     

A numerical comparison of enhancing horizontal resolution (EHR) technique utilizing 2D resistivity imaging

The effectiveness of inversion apparent resistivity data to determine accurately the true resistivity distribution over 2D structures has been investigated using a common inversion scheme based on smoothness-constrained nonlinear least-squares optimization with enhancing horizontal resolution (EHR) technique by numerical simulation. The theoretical model generates in RES2DMOD software at specific distance and depth using Wenner, Wenner–Schlumberger, and pole–dipole arrays were inverted. The inversion model was compared with the original 2D model in RES2DINV software. The study model includes horizontal layering, vertical resolution, and horizontal two layers with different resistivity. Also, the response to variations in data density of these arrays was investigated. The study shows the best array suitable to be used in the survey was chosen for real data acquisition at the actual site. Subsequently, the results from borehole were used to verify the results of 2D resistivity imaging method with and without EHR technique. Saturated zone (0–40 Ω-m) was found scattered at the depth of 10–20 m. The borehole is located at 63 m at 2D resistivity imaging survey which shows at depth 10–20 m is sandy silt. Highly weathered sandstone was found at 6 m depth with resistivity value of 800 Ω-m and SPT N value of 20. The bedrock was found at 27 m depth with resistivity value of 3,000 Ω-m and SPT N value of 50. The application of 2D resistivity imaging with EHR technique indicate the ability of the proposed approach in terms of density, depth, and resistivity value of anomalous and layer in a computationally and numerically efficient manner and to exhibit good performance in the data inversion.     

CSAMT一维全频视电阻率反演

本文采用全频率视电阻率反演,使用2~(-3)~2~(13)Hz频率,并且不做近区和过渡区校正,直接用卡尼亚视电阻率作为反演参数。正演采用虚界面法计算有限长导线在水平层状介质的电磁场分量,反演采用有限内存拟牛顿法。数值模拟采用三层模型和实测数据进行反演,得到了符合地下电性变化的反演模型结果,证实了CSAMT一维全频视电阻率反演具有可实施性。     

Combining TEM/resistivity joint inversion and magnetic data for groundwater exploration: application to the northeastern part of Greater Cairo,Egypt

This paper presents the combination of two complementary methods, magnetic and joint inversion of resistivity/TEM data, as an effective approach to characterize groundwater reservoirs. Twenty stations of transient electromagnetic (TEM) and vertical electrical soundings (VES) were measured and interpreted using a joint inversion technique to evaluate the subsurface low resistivity zones connected to the groundwater reservoir. A complementary survey including 871 land magnetic stations was carried out at the same area to detect the upper surface of the basaltic sheet, which represents the bottom of the Miocene aquifer in the study area. The geological log from one borehole drilled in the zone was used to partially calibrate the calculated models. The results revealed that the study area consists of five different geological units with ages ranging from Paleogene (Oligocene) to Quaternary. The methodology provides good results at a very low cost when compared with drilling boreholes.     

大地电磁测深数据TE与TM极化模式的对比

在大地电磁测深工作中,由于实际地下介质的非均匀性,所得到实测资料的TE、TM极化模式视电阻率曲线有很大差异,给正确认识和判断实际地质结构带来困难。通过建立简单地堑、地垒及断层模型,并进行正反演,总结了这些模型条件下TE、TM极化模式的响应规律,为大地电磁测深数据的定性分析和解释提供了依据。     

A novel and generalized approach in the inversion of geoelectrical resistivity data using Artificial Neural Networks (ANN)

The non-linear apparent resistivity problem in the subsurface study of the earth takes into account the model parameters in terms of resistivity and thickness of individual subsurface layers using the trained synthetic data by means of Artificial Neural Networks (ANN). Here we used a single layer feed-forward neural network with fast back propagation learning algorithm. So on proper training of back propagation networks it tends to give the resistivity and thickness of the subsurface layer model of the field resistivity data with reference to the synthetic data trained in the appropriate network. During training, the weights and biases of the network are iteratively adjusted to make network performance function level more efficient. On adequate training, errors are minimized and the best result is obtained using the artificial neural networks. The network is trained with more number of VES data and this trained network is demonstrated by the field data. The accuracy of inversion depends upon the number of data trained. In this novel and specially designed algorithm, the interpretation of the vertical electrical sounding has been done successfully with the more accurate layer model.     

反演技术在解决煤层顶板岩性应用中的几个重要环节

淮南矿区煤层为石炭二叠纪煤层,13-1煤属下石盒子组,煤层全区稳定,平均厚度为3．5m。由于该区视电阻率曲线在砂岩及煤层反映为高电阻率,而泥岩电阻率相对平缓,针对这个特点,利用约束稀疏脉冲反演方法,结合地震数据,重构富含顶底板砂泥岩信息的波阻抗曲线,得到了联井波阻抗剖面及煤层顶板属性切片图,该成果图可清晰反映13—1煤层及顶板以上10m范围内的砂、泥分布。通过该实例的应用,对如何建立地质模型、重构波阻抗的方法、子波估算方法及稀疏脉冲反演中的A值的选择等几个重要环节进行了剖析。     

直流电阻率测深中二维与三维反演结果的对比与分析

直流电阻率测深中,用二维反演程序对三维地质体进行了反演,并与三维反演结果进行对比和分析。首先,对比二维和三维最小二乘反演在正演模拟算法和先验信息的确定方法;然后,对若干比较典型的模型进行反演实例对比。由于二维程序反演仅考虑单个剖面的电阻率信息,无论是在异常位置、形态及电阻率特性上,其反演精度都比较低;三维电阻率反演综合了多个测深剖面的电阻率信息,其结果与实际模型吻合得非常好。