bluuebunny/crossref_metadata_2025_split huggingface dataset:
A SEMI‐DIRECT METHOD OF INTERPRETING RESISTIVITY OBSERVATIONS*
Authors: KOEFOED O. 
Published: April 2006

ABSTRACTIn this paper a method of interpreting resistivity observations is proposed which consists of two steps. The first of these steps is to approximate the observed resistivity curve by a sum of two‐layer resistivity curves—which are asymptotic to the observed curve—decreased by a constant value. Experience shows that this approximation usually can be made to be reasonably close. In cases where the residue is too large to be neglected, this residue can be accounted for by the addition of the effect of a pair of fictitious current poles of equal and opposite strength.The approximation by asymptotic two‐layer curves could then be translated either into a distribution of fictitious current poles on the vertical through the current electrode, or into the kernel function in the integral expression for the apparent resistivity. Experience shows, however, that the distribution of fictitious poles derived from the approximation by asymptotic two‐layer curves, may deviate very strongly from the actual distribution of image poles. The error in the kernel function, on the other hand, is shown to be of the same order of magnitude as the relative error in the apparent resistivity. The kernel function is therefore used in the proposed method as an intermediary for determining the resistivity stratification.From the approximated kernel function some information can be obtained directly on the resistivity stratification in the subsurface. This information, however, is sometimes incomplete and often not very accurate. The step from the approximated kernel function to the resistivity stratification is therefore essentially indirect, i.e. the approximated kernel function is compared with kernel functions computed for different resistivity stratifications. The advantage of this method over comparison of the observed resistivity curve itself with theoretical resistivity curves is that the computation of the kernel function, starting from the resistivity stratification, can be done far more quickly than that of the resistivity curve. The kernel function for any number of resistivity layers is a quotient, of which both thé numerator and the denominator contain only terms which, when plotted on monologarithmic graph paper, are straight lines. This property of the kernel function makes it possible to compute e.g. the kernel function for a three‐layer case in about a quarter of an hour.
DIRECT METHODS OF INTERPRETING RESISTIVITY OBSERVATIONS*
Authors: KOEFOED O. 
Published: April 2006

ABSTRACTIn this paper direct interpretation methods of resistivity observations are discussed, which use the kernel function in the integral expression for the potential as an intermediary step. This kernel function can be expressed in the form of an integral expression, involving in the integrand a Bessel function and the apparent resistivity. This expression is the basis for the determination of the kernel function from the apparent resistivity curve. The integral can be determined directly; this method of computation, however, although practically feasible, is rather time consuming. Another method of computation is to approximate to the resistivity curve by a sum of a small number of two‐layer curves which are asymptotic to the observed resistivity curve. This method, which was described in a previous paper by the present author, is briefly restated. A more general method is to approximate to the observed resistivity curve by a sum of functions of other types; the choice of such functions is only restricted by the requirement that the contribution to the kernel function corresponding to them should be easily computable. Two different types of functions, that satisfy this condition, are discussed. The standard curves required for the application of the method are presented. An example of application of the method is given.The problem of determining the resistivity stratification from the kernel function has been solved by Pekeris in 1940. The method of Pekeris is briefly restated.
PROSPECTING FOR NON‐METALLIC MINERALS BY INDUCED POLARIZATION*
Authors: ŠUMI F. 
Published: April 2006

ABSTRACTThe method of induced polarization finds more and more application in the prospection of metallic ore deposits. It is very useful also in the determination of non‐metallic minerals and underground water flows.In the case when an electrical current flows accross the interface between metallic and electrolytic phases the causes of the induced polarization are well known and have often been discussed. In the case of non‐metallic minerals and rocks the polarization is mainly caused by the membrane potential, since the polyelectrolytic clay material, having the capacity of ion‐exchange in micells, acts as a semipermeable membrane.Practical examples of exploration for non‐metallic mineral by the induced polarization method are discussed. Some kaolin deposits have been revealed. The depth and the extent of a clay layer, impervious to water, are determined in the bottom of a future storage lake of an hydroelectric power‐plant. The underground water flows in the Karst region are traced.
THEORETICAL ANALYSIS OF APPARENT RESISTIVITY OVER A DYKE OF ARBITRARY SHAPE*
Authors: NAIDU PRABAKAR 
Published: April 2006

ABSTRACTThis paper deals with the apparent resistivity as observed on the surface due to a dyke of arbitrary shape. In order to give a closed analytical solution it has been necessary to assume that the dyke is either perfectly conductive or resistive relative to the enclosing medium. Furthermore we have considered an infinite line source instead of a conventional point current source; however a simple integral transform is given to transform the point‐source‐data into the line‐source‐data. So the present study is equally useful where line sources are inconvenient to handle. Besides considering the conventional method of electrical surveying (bipole method) where the source and sink are separated by a finite distance, we have considered a new variation (unipole method) where the source and sink are separated by an infinite distance, and the source is split into two separate sources each of half strength. A series of apparent resistivity curves for both methods are presented for different parameters of the dyke. The usefulness of these curves lies mainly in the fact that they may provide the necessary guide‐lines for semi‐quantitative interpretation of the observed data.
HORIZONTAL STACKING AND MULTICHANNEL FILTERING APPLIED TO COMMON DEPTH POINT SEISMIC DATA*
Authors: MEYERHOFF HENRY J. 
Published: April 2006

AbstractThe common depth point method of shooting in oil exploration provides a series of seismic traces which yield information about the substrata layers at one location. After normal moveout and static corrections have been applied, the traces are combined by horizontal stacking, or linear multichannel filtering, into a single record in which the primary reflections have been enhanced relative to the multiple reflections and random noise.The criterion used in optimum horizontal stacking is to maximize the signal to noise power ratio, where signal refers to the primary reflection sequence and noise includes the multiple reflections. It is shown when this criterion is equivalent to minimizing the mean square difference between the desired signal (primary reflection sequence) and the weighted horizontally stacked traces.If the seismic traces are combined by multichannel linear filtering, the primary reflection sequence will have undergone some phase and frequency distortion on the resulting record. The signal to noise power ratio then becomes less meaningful a criterion for designing the optimum linear multichannel filter, and the mean square criterion is adopted. In general, however, since more a priori information about the seismic traces is required to design the optimum linear multichannel filter than required for the optimum set of weights of the horizontal stacking process, the former will be an improvement over the latter. It becomes evident that optimum horizontal stacking is a restricted form of linear multichannel filtering.
A SURVEY OF HIGH RESOLUTION GEOMAGNETICS *
Authors: LANGAN LEE 
Published: April 2006

ABSTRACTThe development of optically pumped and monitored “atomic” magnetometers has allowed the application of greater resolution in geomagnetic measurements for exploration purposes. This paper presents a survey of instrumentation in use, the variety of exploration techniques that are being used in practice, and an estimate of their state of development.Alkali metals (rubidium and cesium) and helium have been used as active elements to obtain the magnetic‐field dependent Larmor frequency. Each of these instruments is capable of obtaining high resolution data (data with sensitivity numerically smaller than one‐tenth gamma). They have been adapted for airborne, land, and marine usage.Such sensitivity has enabled the rapid development of geomagnetic gradiometers, high sensitivity aeromagnetics, diurnally reduced ground surveys, broad‐band magneto‐telluric surveys, susceptibility measurements, and convenient magnetic search and location techniques. Outlines of each procedure and an example of its application are given.
SIGNIFICANCE AND IMPLICATIONS OF SHINGLING IN REFRACTION RECORDS *
Authors: CASSINIS R. , BORGONOVI L. 
Published: April 2006

AbstractThe occurrence of shingling in. long range refraction records often makes the task of the seismic interpreter heavier, especially when several refractors are encountered and the velocity contrasts are small.The explanation of the phenomenon given by the existing literature is examined and the theoretical results are compared with the observed data on field records.In field seismograms shingling must be separated from the effect of geological structures or lateral discontinuities.If an appropriate analysis of shingling is possible, this phenomenon can be related to the type of refracting layer, being a useful tool to a qualitative approach.On the other hand the implications of shingling are examined on the side of the geometrical interpretation
A THEORETICAL STUDY ON THE REDUCTION OF STATISTICAL PORE SYSTEM PARAMETERS TO MEASURABLE QUANTITIES*
Authors: SCHOPPER JÜRGEN R. 
Published: April 2006

AbstractAs shown previously [50], the relations between formation factor, permeability, and porosity can be expressed in statistical parameters of the microscopic pore system. A number of other macroscopically measurable quantities depend on those same parameters. Thus, by proper combination of these quantities, it should be possible to solve for those parameters, that cannot be retrieved by direct methods. In this article, the dependencies on these statistical parameters of the capillarity with imbibition and drainage, the irreducible water saturation, the flow dispersion with miscible displacement, and quantities that are directly observable at ground surfaces or thin sections, are preliminarily studied as a preparation for possible practical measurements.
PRINCIPLES OF DIGITAL WIENER FILTERING*
Authors: ROBINSON ENDERS A. , TREITEL SVEN 
Published: April 2006

ABSTRACTThe theory of statistical communication provides an invaluable framework within which it is possible to formulate design criteria and actually obtain solutions for digital filters. These are then applicable in a wide range of geophysical problems. The basic model for the filtering process considered here consists of an input signal, a desired output signal, and an actual output signal. If one minimizes the energy or power existing in the difference between desired and actual filter outputs, it becomes possible to solve for the so‐called optimum, or least squares filter, commonly known as the “Wiener” filter. In this paper we derive from basic principles the theory leading to such filters. The analysis is carried out in the time domain in discrete form. We propose a model of a seismic trace in terms of a statistical communication system. This model trace is the sum of a signal time series plus a noise time series. If we assume that estimates of the signal shape and of the noise autocorrelation are available, we may calculate Wiener filters which will attenuate the noise and sharpen the signal. The net result of these operations can then in general be expected to increase seismic resolution. We show a few numerical examples to illustrate the model's applicability to situations one might find in practice.
NVESTIGATION OF TECTONICS BY GRAVITY DETAILING*
Authors: LINSSER HELMUT 
Published: April 2006

ABSTRACTMapping of fault patterns is an important part of geophysical exploration. A computerized digital template analysis method is described which tests gravity maps for the effects of faults by comparing measured gravity data with calculated master curves. The interpreted gravity data are incorporated in a tectonic map using geological symbols and units, for ready use by the geologists.Tectonics can be investigated by gravity detailing if the smallest undulations on the Bouguer map are taken into consideration. Up to now, residual and derivative gravity maps have explained gravity effects by assuming spherical bodies which are almost unknown in geology. The method discussed here uses tectonic elements, such as fault‐blocks and dikes as a basis of interpretation instead of the spherical bodies of the conventional interpretation methods.Gravity data can be easily and relatively cheaply obtained in the early phases of exploration by area wide spot coverage following lines of easy access such as roads, etc. Seismic studies, by contrast, have the disadvantage of being executed along predetermined profile lines. Only after sufficient detailing do seismic profiles permit‐if at all ‐an areal mapping of faults. Thus a tectonic map is obtained only at the end of a geophysical survey instead of being available prior to the planning of costly seismic profiles. The use of gravimetric data and their interpretation by the suggested method provides tectonic detail maps in the early phases of geophysical studies.In addition, this article discusses a general geophysical interpretation method, using the investigation of faults by gravity as an example. Applications of this method for different gravity and magnetics problems as well as for combined interpretations are outlined. Detailed case histories will be published in later articles.
NOUVELLE METHODE DE RESTITUTION D'UN HORIZON REFRAGTEUR PAR SISMIQUE REFRACTION*
Authors: PANCIROLI FRANCESCO A. , ARNAUD ET MAURICE L. 
Published: April 2006

ABSTRACTThe purpose of this report is to show a method of determining the top of a refractor departing from the times and slopes of the direct and inverse dromocrones. The method does not need topographical correction and can be applied without knowledge of the distance between the geophone and the shot point.These results having been obtained, the commonly accepted point of view is upset: instead of looking for two points on the surface corresponding to one point of the refractor, we try to etablish, starting with only one point from the surface, the two corresponding points from the top of the refractor.This method can be applied to isolated points and does not demand interpretative hypotheses of any kind, excluding the velocity evaluation of the overburden and of the refractor.The necessary calculations can be easily executed by means of a digital computer to which the dromocrone times and the distances between the geophones must be given. These calculations can also be executed by a person having no knowledge of refraction seismology.This report also examines the validity of the approximations involved in the method proposed.
DEFORMATION OF SEISMIC WAVELETS BY THIN LAYERS AND LAYERED BOUNDARIES*
Authors: MEISSNER R. , MEIXNER E. 
Published: April 2006

AbstractUsing plane wave theory and assuming a given input wavelet the shape of the reflected (or transmitted) wavelet from a layered boundary is derived. Several types of boundaries are considered, among them the weathered layer and a wedge shaped intermediate layer. Different angles of incidence and all internal multiples are taken into account. The examples shown in the figures can be used for a direct comparison between theoretical and observed shapes of reflected (or transmitted) wavelets from special boundaries.
GEOPHYSICAL STUDIES OF WATER LEAKAGES FROM RESERVOIRS*
Authors: OGILVY A. A. , AYED M. A. , BOGOSLOVSKY V. A. 
Published: April 2006

AbstractConsiderable water leakages from reservoirs make it difficult to attain the planned storage capacity. In some cases water leakages give rise to suffusion followed by catastrophes. Until recently methods for locating water leakages were extremely imperfect. Geophysical methods offer good prospects in this direction. For solving these problems, it is effective to use streaming potential measurements, water flow rate observations and thermometry.Laboratory experiments were carried out in connection with the fact that water leakages from reservoirs are characterized by negative anomalies of natural currents; the more filtration discharge, the higher these anomalies are. As a result, the relationship governing the intensity of streaming potential and sand granulometric composition, electrolyte concentrations and other factors were revealed. To determine the velocity of water flowing to leakage sites, a special device, based on the relationship between the temperature of a heated body and its resistance, is applied. This device simultaneously makes it possible to measure the water medium temperature.Observations at reservoir sites were effected by moving along the reservoir non‐polarizable potential electrodes and water velocity devices. Recordings were carried out automatically by the recording device of the logging apparatus. Under the conditions of ice cover on water surfaces, measurements were made through separate points by digging holes in the ice cover.Practical field observations were carried out at reservoir sites located in regions where fissured massive rocks as well as loose sediments predominate. In the first case field experiments were carried out in alpine reservoirs, in Armenia. The major water leakages were found to be concentrated on the right bank of the reservoir. In this connection it was not only possible to locate water leakage sites, but also to evaluate their relative intensity. These data were used for planning antifiltration measures. In the second case water leakages from a reservoir located in Uzbekistan in the submontane part of the Pamirs were studied. Streaming potential anomalies and high benthonic flow rates made it possible to discover high filtrations in the base and walls of the dam.Further perfection of these methods should not only permit the determination of water leakage sites and their relative intensity, but also filtration discharges in absolute units.
ON OBTAINING A FAMILY OF BODIES WITH IDENTICAL EXTERIOR FIELDS‐METHOD OF BUBBLING *
Authors: ZIDAROV D. , ZHELEV ZH. 
Published: April 2006

ABSTRACTSome of the theoretical bases of the bubbling method (different terms of an equipotential family can be approximately obtained using this method) are considered. A few examples for application of this method are given (a programme for a digital computer is used), showing its efficacy at solving problems from the exploration geophysics.
EMPIRICAL INVESTIGATION OF SOME FACTORS AFFECTING ELASTIC WAVE VELOCITIES IN CARBONATE ROCKS *
Authors: JANKOWSKY W. 
Published: April 2006

ABSTRACTContinuous velocity log data from the Upper Cretaceous section of about 65 wells from NW. Germany have been studied in order to find some factors which affect the behaviour of elastic wave velocities in carbonate rocks. It could be assumed for these particular rocks that the velocities they exhibit may be subject predominantly to their state of compaction and their lithology (shale‐carbonate ratio).Considering the behaviour of the VL‐curve, several types could be distinguished: The basic type r for which the shale‐carbonate ratio remains almost invariable over a large depth range (as suggested i.a. by a constant degree of radiation in the accompanying Gamma Ray log) discloses a clear relationship between interval velocity (measured as travel time per meter) and overburden pressure.Velocity profiles of log type r and also “peak” velocities from “pure” limestones, plotted versus depth indicate an increase rate almost identical to that of Jurassic shales.It is shown that the lithologic constant
image
can be extracted from the Velocity Log data and then used for mapping fades changes in an area with sufficient well control.In certain cases it is even possible to determine the rate of uplifting (or the original maximum burial position) for a carbonate rock which has an anomalous high velocity in respect to its present depth.
REMARKS ON THE USE OF THE MAGNETIC GRADIOMETER IN OIL EXPLORATION *
Authors: LINSSER HELMUT 
Published: April 2006

ABSTRACTThe principle of optical pumping allows the design of magnetometers with high sensitivity. When mapping the field of the total magnetic force, it is no longer possible to make full use of the accuracy of the instruments because the accuracy of the reduction of the diurnal variation is limited. By simultaneously recording with two instruments in different altitudes, the vertical gradient can be measured which doe's not depend on the time variation of the magnetic field. Therefore, the gradiometer seems to be a more adequate tool for oil exploration than the magnetometer.It is investigated in this article whether the results of this gradiometer or the measurements of the total magnetic field by the high sensitive magnetometer are more useful in oil exploration. The article comes to the conclusion that for most problems of oil exploration the total magnetic field is a more valuable unit than the vertical gradient measured directly by the gradiometer. The total magnetic field allows a better investigation of the tectonics than the vertical gradient. The apparent advantages of the gradiometer claimed by its supporters are mainly based on inconsistent mathematical concepts.
SUR LA CORRELATION EXISTANT ENTRE POROSITE ET FAGTEUR DE FORMATION DANS LES SEDIMENTS NON CONSOLIDES*
Authors: ACCERBONI E. 
Published: April 2006

AbstractThe relationship between porosity and formation factor in unconsolidated homogeneous and anisotropic sediments without granule‐liquid interaction is investigated by introducing a parametric model that simulates a variable cellular structure.In this hypothesis, porosity φ and F‐factor are calculated for some fixed values of the parameter, solving numerically two integral expressions.From these calculations the form of the function φ=f(F), corresponding to the proposed model, has been deduced. This relation is in very good agreement with Archie's empirical law for unconsolidated sands which requires that F=φ‐‐1,3. Therefore it seems that the validity of Archie's law is theoretically confirmed for the unconsolidated sediments considered in this paper.