AN EXAMPLE OF THE APPLICATION OF THE RULES OF COMPOSITION IN RESISTIVITY INTERPRETATION*

The application of approximate rules, whereby apparent resistivity space sections for two dimensional structures can be composited from spaces derived for elementary features is extended to a complex example drawn from a field survey over a fluorite mineral vein. A quantitative solution for the observed resistivity space is presented and the computational sequence involved in matching the observed space is given in detail. The interpreted results are examined in relation to the known geology, supplemented by the results of excavation, and to model tests conducted using a tank analogue. The example also illustrates how successive compositions can be employed in estimating the form of resistivity space in a relatively complex situation.     

A NOTE ON THE USE OF NOMOGRAMS FOR APPARENT RESISTIVITY COMPUTATION*

Nomograms are presented for the purpose of rapid computation of the apparent resistivity functions from the field data for symmetrical and unsymmetrical linear electrode arrays.     

THE CONCEPT OF APPARENT RESISTIVITY IN LATEROLOG 7*

It appears that Doll (1951) and N. N. (1958, 1969, 1972) on the one hand, and Roy (1975) and Roy and Apparao (1976) on the other, used different formulas for computing the apparent resistivity for the Laterolog 7 sonde. This would partly explain the contra-dictory nature of LL7 results from these two groups of workers. The first group use a formula that relates the measured potential to a system of currents that are largely fictitious and non-existent in the ground at the time of measurement. The second group, on the other hand, employ a formula that combines the observed signal with the currents that actually exist in the ground and produce that signal. We believe that the second procedure is the right one.     

水平分层大地的交流视电阻率

本文给出了水平分层大地视电阻率的一种改进的定义,在这种改进了的视电阻率的远区曲线中,假极值效应有所压低,曲线的起伏度变得比原来的大,视电阻率的值也较接近于地层的真实电阻率.这些特性对于作出正确的判断都是有利的.     

水平分层大地的交流视电阻率

本文给出了水平分层大地视电阻率的一种改进的定义,在这种改进了的视电阻率的远区曲线中,假极值效应有所压低,曲线的起伏度变得比原来的大,视电阻率的值也较接近于地层的真实电阻率.这些特性对于作出正确的判断都是有利的.     

FINITE-DIFFERENCE EVALUATION OF APPARENT RESISTIVITY CURVES*

The problem of numerical evaluation of apparent resistivity curves is treated by finite difference modeling. The models proposed are set up in cylindrical coordinates and yield the potential field due to a point source located in a radially symmetric environment. The Schlumberger configuration, widely used for surface measurements, is emphasized. However, the treatment is equally applicable to other similar situations such as the computation of synthetic electric logs when the resistivity of the borehole fluid is different from that of the surrounding uniform or stratified medium. Moreover, the individual layers may not necessarily be isotropic. The medium under investigation is discretized by using a very coarse system of horizontal and vertical grid lines whose distance from the source increases logarithmically; consequently, the physical dimensions of the medium can be made “infinite” without affecting the numerical size of the model. Finer features such as a thin but anomalously resistive or conductive bed which would ordinarily be missed in coarse discretization are accurately taken into account, since the calculations are done in terms of the Dar Zarrouk parameters derived from the exact resistivity distribution of the model. This enables one to compute the potential field by inverting a small sparse matrix. When the medium comprises only a few layers, the efficiency of the finite-difference model is comparable to that of the known analytical methods; for more complicated structures, however, the finite-difference model becomes more efficient. The accuracy of finite-difference results is demonstrated by comparing them with the corresponding analytically obtained data.     

TRANSFORMATION OF SCHLUMBERGER APPARENT RESISTIVITY TO DIPOLE APPARENT RESISTIVITY OVER LAYERED EARTH BY THE APPLICATION OF DIGITAL LINEAR FILTERS *

A simple extension of our previous work in which digital filters were developed to transform dipole resistivity measurements over layered earth to Schlumberger ones leads us to the development of filters for transforming the latter to the former. As in the previous work we use a sampling interval of 1/6 In 10 in designing the filters that are both accurate and fast in operation.     

INVERSE FILTER COEFFICIENTS FOR THE COMPUTATION OF APPARENT RESISTIVITY STANDARD CURVES FOR A HORIZONTALLY STRATIFIED EARTH*

In this paper a fast method is developed for computing apparent resistivity curves for known layer configurations. The method is based on the application of a linear filter to determine the apparent resistivity curve from, the kernel function.     

AN APPROXIMATE METHOD OF RESISTIVITY SOUNDING INTERPRETATION*

An approximate method of interpretation of resistivity sounding is presented, which may be described as a very crude manner of application of the exact direct interpretation method. The accuracy of this method is fairly low, the errors being in the order of 25%. The method is very fast in application and well suited for application to multilayer cases. The main advantage of the method is that it is in close and clear relation to the exact theory.     

视电阻率法的地形改正

文本提出用理论计算来消除复杂地形对视电阻率影响的方法。借助数学公式解析单元地形的线源畸变电场和点源畸变电场,计算并编制出量板,再将单元地形的视电阻率畸变曲线组合迭加,就能近似地取得复杂地形的改正曲线。文中举出实例,阐明了这种地形改正方法的应用和效果。     

视电阻率法的地形改正

文本提出用理论计算来消除复杂地形对视电阻率影响的方法。借助数学公式解析单元地形的线源畸变电场和点源畸变电场,计算并编制出量板,再将单元地形的视电阻率畸变曲线组合迭加,就能近似地取得复杂地形的改正曲线。文中举出实例,阐明了这种地形改正方法的应用和效果。     

多层地电断面视电阻率的高精度计算

目前地电的方法在我国已应用到地震预报的研究中,为了了解与地下力学场变化相联系的地电变化,需要了解台址下勘探体积内的电阻率分层情况,从而正确地认识各种影响因素对地电阻率的作用。     

多层地电断面视电阻率的高精度计算

目前地电的方法在我国已应用到地震预报的研究中,为了了解与地下力学场变化相联系的地电变化,需要了解台址下勘探体积内的电阻率分层情况,从而正确地认识各种影响因素对地电阻率的作用。     

椭球体电阻率和形状对其视电阻率异常的影响

在勘探地球物理学中,研究矿体电阻率和形状对其视电阻率异常值的影响具有实际意义。本文简要介绍椭球体电阻率和形状对矿顶上方视电阻率异常值大小的作用规律,并得出结论:视电阻率异常饱和极限值出现的快慢与矿体形状有密切关系;视电阻率异常值随矿体截面几何形状的变化非为单调增加或减小的简单关系,而是当有某个最佳几     

椭球体电阻率和形状对其视电阻率异常的影响

在勘探地球物理学中,研究矿体电阻率和形状对其视电阻率异常值的影响具有实际意义。本文简要介绍椭球体电阻率和形状对矿顶上方视电阻率异常值大小的作用规律,并得出结论:视电阻率异常饱和极限值出现的快慢与矿体形状有密切关系;视电阻率异常值随矿体截面几何形状的变化非为单调增加或减小的简单关系,而是当有某个最佳几     

视电阻率年变的定量计算

本文定量分析地温、地下水位变化对视电阻率的影响。首先建立与地温、地下水位变化相应的地电断面,这种断面的电性不是分层均匀的,然后用有限单元法计算视电阻率。计算结果表明,对与临沂地电台相近的地电断面,地下水位的变化对视电阻年变的影响大于地温年变的影响,前者约为后者的两倍。基岩对年变大小有强烈的控制作用,基岩浅,年变明显,基岩深,年变大为减弱。     

A NUMERICAL METHOD OF CALCULATING THE KERNEL FUNCTION FROM SCHLUMBERGER APPARENT RESISTIVITY DATA*

A method to calculate the resistivity transform of Schlumberger VES curves has been developed. It consists in approximating the field apparent resistivity data by utilizing a linear combination of simple functions, which must satisfy the following requirements: (i) they must be suitable for fitting the resistivity data; (ii) once the fitting function has been obtained they allow the kernel to be determined in an analytic way. The fitting operation is carried out by the least mean squares method, which also accomplishes a useful smoothing of the field curve (and therefore a partial noise filtering). It gives the possibility of assigning different weights to the apparent resistivity values to be approximated according to their different reliability. For several examples (theoretical resistivity curves in order to estimate the precision of the method and with field data to verify the practicality) yield good results with short execution time independent of shape the apparent resistivity curve.     

时间域瞬变电磁法中心方式全程视电阻率的数值计算

给出了一种时间域瞬变电磁法视电阻率的数值计算方法，利用该方法可以容易地求出中心方式的全程视电阻率. 根据中心方式磁场垂直分量时间变化率Bz/T的核函数Y′(Z)的表现特征，以参数Z把整个瞬变过程分为早期阶段（Z>1.6）、早期到晚期的转折点（Z=1.6）和晚期阶段（Z<1.6）. 首先分别得到早期视电阻率和晚期视电阻率的精确值，然后通过转折点构成一条完整的全程视电阻率曲线. 虽然磁场垂直分量Bz的核函数Y(Z)是参数Z的单值函数，但同样存在一个从早期到晚期的转折点Z=1.6，转换点两边仍然可以得到一条早期曲线和一条晚期曲线. 在数值计算中，当迭代步长ΔZ<0.005Z时，视电阻率的相对误差小于0.5髎. 理论模型和实际数据计算表明，与早期和晚期近似值比较，全程视电阻率具有更高的精度和分辨率.     

THEORY FOR THE BIPOLE-DIPOLE METHOD OF RESISTIVITY SOUNDING*

A theory for the bipole-dipole method of resistivity sounding is developed. Bipole-dipole apparent resistivities are related to Schlumberger apparent resistivities at two spacings. The theory can also be used to compute exact dipole-dipole apparent resistivity curves providing an improvement over the existing techniques which involve far field approximations. A comparison of bipole-dipole and dipole-dipole systems reveals the similarity between the two. However, the resolution of the bipole-dipole system depends on the azimuth angle. The flexibility of the theoretical expressions lead to a generalized field scheme independent of the bipolar or dipolar nature of the current source.