共查询到20条相似文献，搜索用时 15 毫秒
1.
G. M. HABBERJAM 《Geophysical Prospecting》1972,20(2):249-266
An account is given of the use of the square array technique in investigating the surface effects of rotational anisotropy when the axes of anisotropy are inclined to the surface. It is shown that, as with other arrays, two anisotropy parameters and n can be derived by varying the array orientation. On the basis of these considerations, the effects of such anisotropy on the values of the mean apparent resistivity and azimuthal inhomogeneity ratio normally obtained in square array measurements is reviewed. Particular attention is paid to the variation of resistivity with orientation and it is noted that, in areas of moderate anisotropy, this variation is lower for the square than for the Schlumberger array. In addition to this advantage, the azimuthal inhomogeneity ratio obtained from square array measurements may be used to indicate the severity of anisotropy in an area and two field examples of this use are given. Where anisotropy is severe, gross variations of apparent resistivity with orientation are obtained with either square or collinear arrays. In these circumstances, the use of crossed measurements is considered and the particular stability of the crossed square array demonstrated. 相似文献
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Youcef Meheni Roger Guérin Yves Benderitter Alain Tabbagh 《Journal of Applied Geophysics》1996,34(4):255-269
Resistivity prospecting is the main tool used to investigate the shallow structure of the ground. A series of new techniques for determining the 2-D and 3-D geometry of the ground is now finding increasing use, but the light and simple Wenner prospecting technique remains a practical and efficient tool for rapidly mapping lateral variations in resistivity. When the resistivity changes are smooth, 1-D modelling can be used to interpret the data, and the criteria governing this approximation can be defined from synthetic data generated by a 3-D slab-model. For a Wenner array, two quadripole configurations can be used, Normal and Dipole-Dipole. For these two configurations the width of the transition zone, the apparent anisotropy effect and the precision of the resistivity values recovered from 1-D inversion differ. However the simultaneous inversion of both sets of data gives better results than for either configuration by itself. Two examples illustrate that in geological contexts where the thickness of the weathered zone causes the changes in the apparent resistivity value, this parameter can be recovered from 1-D inversion. 相似文献
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This study focuses on the factors that may affect the feasibility of performing elliptical anisotropy analysis on azimuthal PP- and PS-wave data in HTI media, with the aim of using the modeling results as guidance in real seismic data application. Our results reveal that there is an offset limitation for both PP- and PS-waves in elliptical anisotropy fitting, and that PS-waves show a wider applicable offset range and larger observable azimuthal anisotropy than PP-waves. The major axis of the elliptical fit to the amplitudes of the R-component is perpendicular to the fracture strike, which is opposite to that in PP-wave analysis. The azimuthal interval travel time of PS-waves shows a nearly elliptical distribution and the major axis of the fit ellipse is perpendicular to the fracture strike, which is same as that in PP-wave analysis. For data within the applicable offset range, the anisotropic magnitude obtained from amplitude and travel time attributes of PP- and PS-waves exhibits a dependence on fracture density, and the major to minor axis ratio of the fit ellipse may be used to infer the relative distribution of fracture densities. 相似文献
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为研究井周裂缝发育特征,本文提出一种新型方位侧向测井方法,利用三维有限元法,模拟裂缝的方位侧向测井响应.结果显示,深浅侧向电阻率幅度差异受裂缝倾角的控制,低角度缝为负差异,高角度缝为正差异;倾斜裂缝张开度的增大使测井响应值减小,方位电阻率差异增大;井周方位电阻率可反映裂缝方位产状,单一缝或裂缝密度较小时,沿裂缝走向的方位电阻率小,沿裂缝倾向的方位电阻率大;裂缝发育地层的测井响应显示宏观各向异性特征,但方位电阻率的差异显示发生反转现象,即沿裂缝走向/层理方向的方位电阻率大,沿裂缝倾向/垂直层理方向的方位电阻率小;对方位电阻率测井响应进行井周成像,直观显示了裂缝的产状和发育特征. 相似文献
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A. Apparao G.S. Srinivas V. Subrahmanya Sarma P.J. Thomas M.S. Joshi P. Rajendra Prasad 《Geophysical Prospecting》2000,48(5):797-813
We define the apparent frequency effect in induced polarization (IP) as the relative difference between apparent resistivities measured using DC excitation on the one hand and high‐frequency excitation (when the IP effect vanishes) on the other. Assuming a given threshold for the minimum detectable anomaly in the apparent frequency effect, the depth of detection of a target by IP can be defined as that depth below which the target response is lower than the threshold for a given electrode array. Physical modelling shows that for the various arrays, the depth of detection of a highly conducting and volume polarizable target agrees closely with the depth of detection of an infinitely conducting and non‐polarized body of the same shape and size. The greatest depth of detection is obtained with a two‐electrode array, followed by a three‐electrode array, while the smallest depth of detection is obtained with a Wenner array when the array spread is in‐line (i.e. perpendicular to the strike direction). The depth of detection with a Wenner array improves considerably and is almost equal to that of a two‐electrode array when the array spread is broadside (i.e. along the strike direction). 相似文献
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In areas where steep dips are encountered conventional practice in resistivity work has involved orienting arrays favourably in relation to the geological strike. In concealed conditions, however, the geological strike may not be known; moreover, strike may change with depth. Considerable advantage is to be gained, in such circumstances, by the use of crossed square arrays in that these yield orientationally insensitive resistivity measurements and also allow strike determinations and measurements of the effective vertical anisotropy. Two traverses of crossed square array observations are presented, together with one deeper sounding. The results show that, in favourable circumstances, reliable data on concealed strike directions can be obtained, and that the anisotropy findings greatly assist the subsequent interpretation. Model results pertinent to the field material are presented and discussed. 相似文献
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The anisotropy of Pg-wave velocity in the area of the central External Dinarides is measured by using arrival time data as reported by local and regional seismological stations. The observed velocity varies between 5.73 km/s (in the ESE-WNWdirection) and 6.20 km/s (in the SSW-NNE direction), indicating azimuthal anisotropy with symmetry axis azimuths of 23°±n 90°. These closely match the orientation of the principal stress axes in the region, as revealed by analyses of available fault-plane solutions. The observed anisotropy may be modelled by assuming a system of vertical/subvertical cracks in the upper crust, aligned under the influence of the regional tectonic stress field. 相似文献
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A simple unified equation of apparent resistivity for a general four-electrode array is developed. The main idea is the analytical integration of the Stefanescu expression for potential over a layered earth by writing an exponential approximation for the kernel function. Finally a matrix equation is developed to estimate the kernel function from observed apparent resistivity values. The general equation automatically reduces to the particular configuration once the electrode separations are modified suitably. Examples for Schlumberger and Wenner configurations are numerically calculated to estimate the precision of the method. Good results in a short execution time are obtained, irrespective of the shape of the apparent resistivity curve. Finally, the full interpretation of one theoretical resistivity curve and two field resistivity curves is demonstrated. The more stable ridge-regression estimation method is used in the identification of layer parameters from the kernel function. 相似文献
11.
Wm. MANSFIELD ADAMS 《Geophysical Prospecting》1970,18(Z1):728-737
In order to locate relatively optimum sites for drilling exploratory holes for fresh water, an electrical resistivity survey was conducted along the new Mahukona-Kawaihae Road on the west flank of the Kohala Mountain. Two resistivity soundings made at the same stations, using the Schlumberger electrode configuration, determined an a spacing of 275 feet for horizontal profiling with the Wenner array. The correlation coefficient of the elevation to profile data was 0.41. A procedure for removing elevation effect from observed apparent resistivity was developed. Based on the reduced resistivity profile, four relatively optimum sites for additional exploration, such as by drilling, are specified. There is no specific interpretation of the data that can definitely indicate the occurrence of large underground reservoirs of fresh water anywhere along the profile. This is because the interpretation of horizontal profiling data is essentially relative and not absolute. 相似文献
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Analytical solutions of vertical electrical soundings (VES) have mostly been applied to groundwater exploration and monitoring groundwater quality on terrains of fairly simple geology and geomorphology on which the electrode arrays are symmetrical (e.g. Schlumberger or Wenner configurations). The sounding interpretation assumes flat topography and horizontally stratified layers. Any deviations from these simple situations may be impossible to interpret analytically. The recently developed GEA-58 geoelectrical instrument can make continuous soundings along a profile with any colinear electrode configuration. This paper describes the use of finite-difference and finite-element methods to model complex earth resistivity distributions in 2D, in order to calculate apparent resistivity responses to any colinear current electrode distribution in terrains in which the earth resistivities do not vary along the strike. The numerical model results for simple situations are compared with the analytical solutions. In addition, a pseudo-depth section of apparent resistivities measured in the field with the GEA-58 is compared with the numerical solution of a real complex resistivity distribution along a cross-section. The model results show excellent agreement with the corresponding analytical and experimental data. 相似文献
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Because it is difficult to detect a strike fault, its physical properties are discussed in this paper. Using physical simulation, numerical modeling and the in situ data, the differences between the apparent resistivity of low resistivity model obtained by transverse profiling method （TPM） whose electrode array is vertical to the profile and those by longitudinal profiling method （LPM） whose electrode array is parallel to the profile are analyzed, respectively. Our results show that the former has much marked amplitudes of anomaly. Therefore, TPM can be used to detect a strike fault more effectively and locate it more precisely, and is expected to be a new approach for detecting a sliding fault. 相似文献
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Introduction The method of apparent resistivity with direct current (DC) measurement, adopted from geophysical exploration, is one of the most important precursory approaches in earthquake prediction, in which the geo-electric constitutive model is illustrated by the scalar theory Archies law and correspondingly a set of calculation methods for apparent resistivity of layered media has been established (QIAN, et al, 1985; YAO, 1989). But this is not consistent with the fact that in earthqu… 相似文献
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实际地层可能出现 2种电阻率的宏观各向异性 :微观的统计平均效应和裂缝走向等因素的构造效应。三分量感应测井方法可能是确定地层电阻率各向异性的最好方法 ,但是 ,该仪器目前在中国还没有应用。已有的数据一般是梯度和双感应曲线 ,梯度和双感应曲线单独使用都难以揭示各向异性 ,但是 ,将二者联合使用则有可能。在反演模型中考虑了电阻率各向异性的存在 ,给出了梯度和双感应曲线联合求地层电阻率各向异性的方法。通过直井水平层的二维人工模型表明 ,用感应方法可确定地层的水平电阻率和厚度。而梯度方法的视电阻率可以近似看作水平电阻率和纵向电阻率的几何平均值 ,梯度方法的视厚度是各向异性参数和真实厚度的乘积。因而不能用梯度方法单独确定各向异性参数和真实厚度 2个参数中的任何 1个。然而 ,联合梯度和双感应的方法则可能确定 3个参数 :各向异性参数 ,水平电阻率和地层厚度。人工数据的例子表明了这种联合的可行性 相似文献
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大地电磁法是广泛应用于深部地质结构探测、油气和矿产资源勘查等领域的一种地球物理方法.电性各向异性对电磁观测数据有很大影响,但介质各向异性参数对不同模式视电阻率的影响还较少有较为系统的研究.本文基于Maxwell方程组,推导了二维大地电磁场在任意各向异性介质中电场和磁场相互耦合的变分方程,结合有限单元法及并行计算编写了二维大地电磁任意各向异性正演程序,采用三角形网格剖分.验证程序正确性后,以倾斜板状体作为模型来研究三个主轴电阻率及三个旋转欧拉角和四种模式的视电阻率之间的关系.结果表明,主轴各向异性时,xy模式视电阻率几乎只受x方向电阻率影响,yx模式视电阻率主要受y方向电阻率影响,但同时也受z方向电阻率一定影响;三个欧拉角中只有倾角不为零时,yx模式视电阻率受倾角大小的影响较大,xy模式视电阻率几乎不受倾角的影响;只有走向角不为零时,四种模式的视电阻率同时受x、y两个主轴电阻率和走向角的大小的影响. 相似文献
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实际地层可能出现2种电阻率的宏观各向异性:微观的统计平均效应和裂缝走向等因素的构造效应.三分量感应测井方法可能是确定地层电阻率各向异性的最好方法,但是,该仪器目前在中国还没有应用.已有的数据一般是梯度和双感应曲线,梯度和双感应曲线单独使用都难以揭示各向异性,但是,将二者联合使用则有可能.在反演模型中考虑了电阻率各向异性的存在,给出了梯度和双感应曲线联合求地层电阻率各向异性的方法.通过直井水平层的二维人工模型表明,用感应方法可确定地层的水平电阻率和厚度.而梯度方法的视电阻率可以近似看作水平电阻率和纵向电阻率的几何平均值,梯度方法的视厚度是各向异性参数和真实厚度的乘积.因而不能用梯度方法单独确定各向异性参数和真实厚度2个参数中的任何1个.然而,联合梯度和双感应的方法则可能确定3个参数:各向异性参数,水平电阻率和地层厚度.人工数据的例子表明了这种联合的可行性. 相似文献
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2D电阻率成像技术近年来被广泛应用于工程、水文、环境和矿产等领域，在实际应用中它具有多种的装置类型，不同的装置类型对特定的地质情况有不同的应用效果.本文通过采用Wenner、Wenner-Schlumberger和dipole-dipole三种排列装置在一个水平和一个垂直模型上正演模拟和块反演，揭示了不同的排列装置在水平结构和垂直结构的异常响应，并对高阻体和低阻体进行了模拟.结果显示当采用Wenner,Wenner-Schlumberger和dipole-dipole数据采集技术时，不同的模型结构异常响应有明显的不同，三种排列类型对地下低阻体的分辨能力均高于高阻体，Wenner装置和dipole-dipole装置分别对水平层状结构和垂直结构有较好的分辨力，wenner-Schlumberger装置对水平层状结构有好的分辨力，对垂直结构有中等的分辨能力. 相似文献
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M. Schmutz P. Andrieux A. Bobachev J.P. Montoroi S. Nasri 《Journal of Applied Geophysics》2006,60(3-4):213-224
Azimuthal Resistivity Soundings (ARS), using the so-called “Arrow-type array” as proposed by Bolshakov et al. were carried out in Central Tunisia, together with azimuthal resistivity tomography, because of the known anisotropic behaviour of the nearly vertical formations.First, the developments designed by Bolshakov et al. are reviewed: they deal with the separation between the effects of anisotropy and of heterogeneities, the design of the Arrow-type array and the introduction of the azimuthal spectral analysis.Second, the main methodological results obtained near Gouazine Lake are presented: (1) the clear effect of a quasi-vertical contact and (2) the characterisation of the anisotropic substratum below a thin superficial layer in one site close to the axis of the valley: the strike direction (α = 50°N), and a rather high anisotropy coefficient (λ ≈ 4) are determined.And lastly two directions for further developments are suggested. 相似文献