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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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3.
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
4.
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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A particular methodology adapted to crystalline formations with a thin weathered zone was developed for a village hydrological project, in Benin. A combination of electrical profiles, Schlumberger and square arrays, was able to locate the most fractured zones in the basement. We present some results obtained from theoretical models as well as from field data. The suggested methodology uses both measurements of resistivity and anisotropy. Strong anisotropy and low resistivity indicate the most productive hydrogeological areas. 相似文献
6.
在3种非含岩成分造成的岩石原始电阻率各向异性标本(在采集和加工过程中，标本完整性遭 到破坏的标本)，和一种由含岩成分形成的 岩石原始电阻率各向异性标本上，布设多个电极，并将标本用水饱和. 然后用多电极组合法 ，将己布电极组合成不同方向、不同极距的电阻率各向异性测线. 采用单轴压缩、低围压 三 轴压缩和剪切3种加载方式，对标本进行动态电阻率变化实验. 观测标本电阻率随承载力的 变化. 实验结果表明∶对于岩石原始电阻率各向异性标本，在电阻率变化各向异性方面，与 岩石 原始电阻率各向同性标本相似，即∶裂隙和破碎带通过区域的测点，视电阻率变化各向异性 结果好，４种组合求得的４个各向异性主轴方向趋向一致，且与破碎带方向基本吻合；裂隙 和破碎带不经过区域的测点，４个视电阻率变化各向异性主轴方向不一致，或者根本求不出 各向异性解. 这后一种情况，在裂隙面平行测量面时，表现最为明显. 相似文献
7.
万全断裂是洋河盆地北缘断裂带组成断裂之一,控制沿线构造活动及地貌发育。断裂走向NE,倾向SE,在沟口处隐伏于第四纪覆盖层,采用电阻率成像和浅层地震联合勘探方法,获得该断裂隐伏段落综合物探异常,结合地质地貌调查,判定隐伏段落展布的具体位置、产状、活动特征及地下结构特征等。研究结果表明,万全断裂隐伏段落走向NE,倾向SE,倾角约75°,上断点埋深约20 m,20—240 m深度可见断裂破碎带（宽约10—20 m）物探异常特征及断裂两侧地层结构差异。该联合探测模式可有效探测复杂地质构造条件下的隐伏活动断裂,具有较强实用性,值得推广。 相似文献
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The suitability of VLF ground surveys in the investigation of shallow two-dimensional structures is analyzed. For such structures the polar formalism is derived, necessary in practice since the transmitters are generally not in the structural strike or profile. A simple vertical dike is considered to demonstrate the striking anisotropy which can be expected over such a structure, in particular the high apparent resistivity along the direction of a well-conducting dike and the low resistivity across it. The theory is then confronted with the practical example of an asymmetrical vertical dike resulting from a strike-slip fault. Modelling of the survey results is very successful and yields good confirmation of the polar behaviour. VLF ground surveys thus provide a quick and powerful tool for the study of geological accidents within about 100 m of the surface. 相似文献
9.
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
10.
The effectiveness of azimuthal apparent-resistivity measurements as a method for determining fracture strike orientations 总被引：2，自引：0，他引：2
J.P. Busby 《Geophysical Prospecting》2000,48(4):677-695
Azimuthal apparent-resistivity measurements are made for the purpose of determining the strike direction of subvertical fracture sets. Data are collected about a common centre, with an electrode array expanded along a sufficient number of azimuths to define the variation of apparent resistivity with orientation. The apparent resistivities for any one electrode spacing are then plotted in a polar diagram. If the data form an ellipse, this is often interpreted as reflecting aligned, subvertical fracturing. However, it is also possible for heterogeneity within the rockmass to manifest itself, at the scale of the measurement, as a variation of apparent resistivity with azimuth. It is recommended that the offset Wenner array is used for all measurements and that a parameter is introduced, the homogeneity index, which defines whether the variations due to homogeneous anisotropy, such as subvertical fracturing, are greater than those due to inhomogeneity. This simple parameter, which is the quotient of two standard deviations, is valid for both single-peaked and multiple-peaked ellipses. A four-stage scheme for the interpretation of azimuthal data is suggested and a consistent set of quantitative measures is recommended. These will allow data, collected by different workers over different lithologies, to be compared. There are a number of geological situations which can give rise to anisotropy within the rockmass and great care is needed when interpreting azimuthal data in terms of aligned fracturing. Numerical modelling of the response to a buried channel of a rotated offset Wenner array demonstrates that elliptical data are generated by such a linear feature. Depending on the location of the array with respect to the channel, these data are either indistinguishable from those generated by aligned fracturing, or can be recognized by application of the homogeneity index. In the case where the response can be identified as being due to a channel, diagnostic information can be derived on the location and strike of the channel. 相似文献
11.
R. K. FR
HLICH 《Geophysical Prospecting》1968,16(3):314-325
The theory of electrical dipole soundings proved that this method can produce resistivity measurements, which are comparable with those obtained by electrical soundings of the Wenner or Schlumberger type. Their main advantage is the use of short cable lengths, which is important if the depth of penetration should be large. A considerable disadvantage of the dipole method is the great sensitivity to lateral discontinuities. Though these have an influence on the Schlumberger arrangement as well, they can disturb a dipole sounding to such an extent than an interpretation based on a horizontal layer case is no more possible. There are six different dipole arrays, which differ from each other with respect to the angle enclosed by the two dipole orientations-the current dipole AB and the measuring dipole MN. The theoretical comparison of the dipole arrays with the Schlumberger array concerning their sensitivity to lateral discontinuities is a useful basis for the choice of the most suitable configuration. Considering geological subsurface conditions the right choice of a dipole array can give an optimal result, i.e. a dipole sounding for which the sensitivity to lateral discontinuities is as small as possible under the given circumstances. 相似文献
12.
Consideration is given to the use of a configuration of four electrodes set in a square array for resistivity measurements. It is found that, by passing current successively between different pairs of electrodes, an apparent resistivity can be determined which is both more sensitive to the position of the array centre and less dependent on orientation than the measures usually obtained with colinear arrays of electrodes. At the same time the observations made enable the degree of the departure of local conditions from conditions of lateral homogeneity to be assessed. Theoretical and practical examples of the use of this electrode system are given and the use of the system both as a tool in mapping and in depth investigations is considered. It is shown that provided electrode spacings are suitably arranged the results of a probe carried out using the square array can be interpreted by conventional methods. The system is shown to have particular advantages in the investigation of lateral resistivity variations and the reduced dependence on orientation makes possible the recasting of interpretation data in an orientationally invariant form with a consequent drastic reduction in the number of type curves required for a particular problem. 相似文献
13.
L. MALMQVIST 《Geophysical Prospecting》1978,26(1):97-121
The usefulness of IP-technique for different geophysical purposes is discussed on the basis of field examples. IP and resistivity results are not always correlated, and the IP-information may be unique in prospecting for very low grade sulphide mineralizations. The IP-technique seems to be useful sometimes in prospecting for disseminated Ni-Cu- mineralizations. A massive sulphide mineralization could be localized using IP. The disturbances from different kinds of geological objects other than prospecting targets generally are smaller in IP-work than in resistivity work. It was possible to discriminate between apparent resistivity anomalies caused by shear zones and by sulphide mineralizations by means of IP-measurements. The influence of magnetite on IP- measurements is briefly discussed. The relation between ground magnetic measurements ΔZ and the IP-parameter is in many areas weak and does not seriously influence the interpretation of the IP-measurements. A high correlation between ΔZ and IP-measurements has been found on a titaniferous iron ore. This ore body gives strong IP-anomalies indicating that it is a good IP-target. Finally, the application of small moving arrays in very detailed IP-measurements is found useful for detailed mapping of a mineralized zone under a thin overburden and for determination of the dip of mineralized zones. 相似文献
14.
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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When electric soundings are made over an irregular terrain, topographic effects can influence the values of apparent resistivity and lead to erroneous 1D interpretation. A 3D finite-element method has been applied to study the topographical effect of a slope on Schlumberger soundings parallel to the strike. When the resistivity survey is performed at the top of the slope, the apparent resistivity values can be two times higher than in the flat-earth case, depending on the angle (α) and height (H) of the slope, and on the distance (X) between the sounding and the slope top. The results are presented as nondimensional curves which can be used for evaluating topographic anomalies for any value of the parameters α, H and X. It is numerically shown that the topographic effects can be removed from measurements on horizontally layered structures with an irregular earth surface. Real measurements were performed in different geological conditions over an irregular terrain. The correction method based on the nondimensional curves has been applied to the data and has enabled the determination of the correct layered ground configuration using 1D interpretation. 相似文献
16.
A solution based on Tabarovskii's coupled pair of surface integral equations is given for the potential of a direct current flowing in an electrically anisotropic body and within the enclosing isotropic surroundings. The sources of the secondary potential exterior and interior to the body are fictitious surface charge distributions. The equations are solved numerically using point matching with pulse functions as subsectional basis functions. The model used in the applications is a long prism, excited by long line current electrodes aligned parallel to the strike. The strike length is set at a length sufficient to guarantee 2D behaviour of the model. Comparisons of computation results indicate that for the models, electrode arrays and numerical procedures applied, the solutions based on fictitious surface sources converge faster and behave more regularly than those based on real surface charges. When compared with previously published integral equation solutions, the present solution seems to be relatively efficient, even in the case of purely isotropic models. The model experiments also showed that at moderate resistivity contrasts, the anomaly shapes are strongly dependent on the directions of the principal axes of the body resistivity. However, when the external resistivity is more than 100 times that of the geometric mean of the principal resistivities in the body, with the principal resistivities differing from each other by at most one order of magnitude, the contribution of the anisotropy to the anomaly diminishes as a result of electrical saturation. 相似文献
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我们用自制仪器于1977年首次在西藏高原进行了大地电磁测量。本文给出了那曲、曲水、江孜、帕里、亚东5个测点的测量和反演结果。 5个测点均反映为五层地电模型。得到如下结果: 1.那曲、曲水、江孜、帕里及亚东前四层总厚度分别为:66、65、62、57、50公里; 2.各测点电性特征相似,均属低-高-低型; 3.各测点的地壳中均存在一低阻层,其埋深约为10-20公里; 4.以雅鲁藏布江为界,南北两地区电性层厚度变化程度有显著差异,北部平缓,南部较剧; 5.表面沉积层厚度在4公里左右。 相似文献
18.
F.D.Stacey 《地震学报》1984,6(1):1-7
本文是作者于1983年访华期间接受中国学术刊物的请求而撰写的.文中指出,地震应力在数量上相当小,因此它的效应一定很微妙,需要有灵敏的仪器去觉察它们.文中对压磁效应、波速比、应变、地倾斜、大地测量、电阻率、水氡和前震等各国常用的地震预报手段进行了评价,提出了建议.结论为,虽然注意到了 Brune[1](1979)关于在原理上地震可能是不可预报的强有力的论证,但作者并不那样悲观.认为地壳可能十分不均匀,它的状态可能是多变的,这就要求我们拥有大量数据.所以必须同时使用几种方法和大量的仪器进行观测.更多的注意力应放在:(1)地震波传播的各向异性和衰减,(2)多色激光测距,(3)改善构造磁学中的信噪比,(4)在电导率测量中使用可交替极性的供电极和较大面积的测量极网和(5)对前震和余震序列的统计学分析进行重新仔细检验. 相似文献
19.
M. W. ASTEN 《Geophysical Prospecting》1974,22(2):238-245
In a transversely electrically anisotropic rock mass of arbitrary dip, the potential distribution about an electrode at arbitrary depth is the sum of the whole-space potential about that electrode, plus the whole-space potential about a postulated image electrode displaced up-dip from the source position. Equipotential lines on the rock-air surface are ellipses, elongated parallel to strike, and with centers displaced up-dip from the surface projection of the electrode position. In metamorphosed rocks frequently encountered in mining geophysics, anisotropy is such that elongation is most marked in steeply dipping rocks, with displacement most evident in low to moderate dip. Graphs relating the anisotropy coefficient to displacement and elongation assist in separation of the anisotropy-related effects from those of a significant subsurface conductive body, particularly if surface resistivity sounding establishes the coefficient of anisotropy. 相似文献
20.
Water flooding disasters are one of the five natural coal-mining disasters that threaten the lives of coal miners. The main causes of this flooding are water-conducting fractured zones within coal seams. However, when resistivity methods are used to detect water-conducting fractured zones in coal seams, incorrect conclusions can be drawn because of electrical anisotropy within the water-conducting fractured zones. We present, in this paper, a new geo–electrical model based on the geology of water-conducting fractured zones in coal seams. Factors that influence electrical anisotropy were analyzed, including formation water resistivity, porosity, fracture density, and fracture surface roughness, pressure, and dip angle. Numerical simulation was used to evaluate the proposed electrical method. The results demonstrate a closed relationship between the shape of apparent resistivity and the strike and dip of a fracture. Hence, the findings of this paper provide a practical resistivity method for coal-mining production. 相似文献