bluuebunny/crossref_metadata_2025 huggingface dataset:
MULTIPLE REFLEXIONEN IN NORDWESTDEUTSCHLAND*
Authors: Bortfeld Reinhard
Published: April 2006

Abstract

In N.W. Germany multiple reflections have been observed in numerous areas. They are not curiosities but represent true problems.

In many cases these multiples are recognizable by routine Δt analysis of the records. Sometimes the Δt anomalies are so great that multiples can be recognized without any computational work, merely by looking at the records. This is due to the great contrast between the interval velocities of the Tertiary and of the Upper Cretaceous. One example is discussed fully.

Most of the multiples are of the type AB (a multiple caused by reflections at two different reflectors A and B, and at the surface). It is also shown (by a rough estimate) that this type of multiple is theoretically the most probable. Finally, the interference between the two components of AB (one multiple being reflected first at A, then at B, and the other reflected first at B, then at A), and its appearance in constructed examples, are discussed.
ON THE EFFECT OF THE TANK WALL MATERIAL IN GEOELECTRICAL MODEL EXPERIMENTS
Authors: GOUDSWAARD W.
Published: April 2006

Abstract

The effect of the composition of the tank walls on apparent resistivity determinations made in model experiments has been investigated for the two extreme cases of an insulating and a perfectly conducting tank wall: The resulting errors have been determined both by calculation and by experiment.

Experiments are described which demonstrate that the magnitude of the effect can be considerably reduced by specially constructed tank walls.
MANGANESE ORE OF SOUTH‐INDIA AND ITS MAGNETIC PROPERTIES *)
Authors: BHIMASANKARAM V. L. S. , RAO B. S. R.
Published: April 2006

Abstract

The Kodur Manganese belt has been surveyed with a vertical magnetometer. It was generally observed that both high positive and negative anomalies were associated with some of the existing ore bodies. Other large manganese ore deposits gave little or no magnetic anomalies. Further it was observed that both types of manganese ore deposits giving rise to large and little magnetic anomalies, contained similar percentages of manganese and iron. In view of these discrepancies, an extensive study of the magnetic properties of these manganese ores was taken up. The results of these measurements showed that the susceptibilities of the manganese ore samples collected vary over a wide range.

It was observed that the high susceptibilities are associated with samples containing manganmagnetite and vredenburgite, whereas samples rich in psilomelane and pyrolusite possess low susceptibilities. From the chemical analysis, normative values of manganmagnetite and vredenburgite–with a general formula of (Mn.Fe)3O4– were calculated and a linear relationship could be established between these normative values and susceptibilities.
RICHTCHARAKTERISTIKEN VON GEOPHONGRUPPEN MIT BERÜCKSICHTIGUNG DER EINZELCHARAKTERISTIKEN*
Authors: SCHILLEMEIT JOST , CELMINŠ AIVARS
Published: April 2006

Abstract

The directional sensitivities of an array of geophones depend as much on the size of the array as on the directional sensitivities of the single geophones forming the array. In a former paper (Celminš 1956) the effect of the size of the array was investigated. In addition to this the influence of the directional sensitivities of the individual geophones on the sensitivities of an array of geophones is investigated here.

In δ 2 some general formulae for the directional sensitivities are derived. In addition the directional sensitivities of a single geophone according to P‐ and S‐waves are investigated (δ3 and δ4). In δ5 the'directional sensitivities for the most important cases of arrays of parallel geophones are computed. The results of the computation (shown in fig. 4 and 5) give an idea of the types of directional sensitivities which occur in the use of geophone arrays.
QUELQUES RECENTS ASPECTS DU FORAGE SISMIQUE*
Authors: DUFOUR J. , DEGORSE A.
Published: April 2006

The shothole drilling industry has had new developments and its evolution is tied to several causes. First, more and more difficult and varied formations have to be drilled. Second, new procedures have to be used in desert regions recently open to prospecting. Finally, modifications of the seismic methods themselves (multiplication of the charges, shallow holes, etc.) lead the driller to use more economical and lighter tools. In this paper the following types of drilling equipment are described: the Mouton Delmag for spudding through pebbles and loose gravels; a mud mixing water truck and an extensible mast used for drilling multiple medium depth holes through caving sands; a compressed air‐drill for regions where the water supply is practically nil; rock drills, such as a Wagon‐Jack and the Warsop hammer, for multiple shallow holes in various formations.
AMMONIUM NITRATE: ECONOMY BLASTING AGENT FOR OIL EXPLORATION*
Authors: HALL T. O. , MARTIN J.
Published: April 2006

Abstract

Major savings for operators of seismic parties have been achieved by the use of prilled ammonium nitrate as a substitute for gelatin dynamite in areas where shot holes are dry. Pound for pound, the prills appear to have the same energy yield as 60% gelatin dynamite, and some improvement of records has been noted where prills are used. Safety problems are less with ammonium nitrate than with dynamite, and the development of efficient field handling techniques prevents the loss of production.
THE FIELD OF A D. C. ELEMENT, APPLIED TO GONDUCTIVELY ENERGIZED PENCILFORMED ORE BODIES
Authors: OVERHOLT K. J.
Published: April 2006

Abstract

The electric and magnetic field of a direct‐current element, embedded in a space consisting of two halfspaces differing in conductivity and permeability, is given in a form suitable for integration along a cable. From these formulae is obtained the field when one end of a D.C. cable is grounded in a highly conducting, pencilformed ore body, considered as a line electrode with uniform current leakage. Numerical examples are given for a horizontal line electrode. The formulae should be useful as a first approximation to the A.C. case. The validity of this is shortly discussed.
DESIGN CONSIDERATIONS OF A BORE‐HOLE GRAVIMETER
Authors: DOLBEAR D. W. N.
Published: April 2006

Abstract

Due weight must be given to three factors (1) its purpose, (2) the limitations imposed by nature, industry and environment, (3) the effect of errors in auxiliary measurements. Together the last two factors give an estimate of the accuracy which can be achieved. If this is sufficient for the instrument to fulfil its purpose design and construction can proceed. If it is not, a detailed survey of the last two factors is necessary in order to estimate the research effort that will be required when directed into the most effective channels. If the project is considered worth the effort it can proceed. These factors are discussed in relation to a borehole gravimeter. It is shown that the purpose will be served only if the accuracy is comparable with the best surface gravimeters. Borehole versions of some surface instruments are considered and it is concluded that none is suitable without considerable modifications. A successful borehole gravimeter is likely to be a completely new instrument.
OPTICAL ANALOGUE OF GRAVITY AND MAGNETIC FIELDS
Authors: ROY AMALENDU
Published: April 2006

Abstract

Gravity anomalies due to given mass distributions have been determined by model optical experiments, which utilise the fact that both the light intensity and the gravitational field due to point sources obey the Inverse Square law. The technique is somewhat different from that used by Gerrard et al (1957), and the results seem to be more accurate (maximum discrepancy 2 percent). The applicability of the anology for the determination of magnetostatic fields is also pointed out.
THE RESPONSE OF VELOCITY‐SENSITIVE WELL GEOPHONES *
Authors: DENNISON A. T.
Published: April 2006

Abstract

The factors affecting the response of a velocity‐sensitive well geophone are discussed and it is shown that the geophone movement in response to a seismic pulse is primarily due to the pressure difference between its ends. Several practical examples are calculated to show that the first arrival waveform recorded by a geophone depends on the distance from an interface and that these changes in recorded waveform may give errors of up to 3 msec in well‐velocity surveys. These errors may be minimised by using pressure geophones or by avoiding measurements at geological interfaces.
SYMPOSIUM ON SYNTHETIC SEISMOGRAMS*
Authors: DENNISON A. T.
Published: April 2006

Abstract

This paper is intended as a basic introduction to synthetic seismogram techniques. Their principles, uses and limitations are discussed and the relative advantages of the different methods are compared.
ATTACKING THE PROBLEMS OF THE SYNTHETIC SEISMOGRAM
Authors: ANSTEY N. A.
Published: April 2006

Abstract

The four problems considered are the definition and simulation of the filtering effects which occur in the earth between the explosive and the case of the geophone, the problem of errors in the time scale of the synthetic record, the simulation of multiple reflection effects, and the difficulty of finding a representative comparison trace on the field record. A partial solution to the first of these is offered by Siran, examples of whose operation are presented. A method of assessing allowable errors in the time scale is discussed. Multiple reflections may be introduced by the preparation of multiple‐corrected reflection‐coefficient logs on a digital computer such as the IBM 709. The particular problems of multiple reflections from the base of the weathered layer (including “ghost” reflections) are discussed. The preparation of a “composite” trace is shown to be a partial solution to the problem of the comparison with the field record.
ON THE OCCURRENCE OF LOW RESISTIVITY GEOLOGICAL CONDUCTORS
Authors: BOSSCHART R. A.
Published: April 2006

Abstract

Laboratory investigation has shown that the resistivity of massive sulphide ores at specimen dimensions is of the order of 0–10 ohmcm. Several writers, on the basis of field results obtained with various electromagnetic methods, deny the possibility that natural orebodies could have correspondingly low resistivities. The question is of interest, since such conductors, because of their small imaginary response, would be undetectable by electromagnetic methods measuring only imaginary components or phase shifts.

In the present paper anomalies obtained with the Loop‐Frame electromagnetic method on massive sulphide bodies in different parts of Canada are discussed. It is shown, by means of model experiments, that the conductors all have very low resistivities which, where the effective thickness can be determined, appear to correspond to the order of magnitude of specimen resistivity. It is demonstrated that confusion of the total width of a conductor with its effective thickness may lead to erronous resistivity determinations.
QUELQUES EXEMPLES D'UTILISATION DES FILMS SYNTHETIQUES*
Authors: DELAPLANCHE J.
Published: April 2006

Abstract

The synthetic seismogram is a geophysical instrument. Examples taken from several areas are presented in order to define this tool and to show how it may be utilised in all stages of the prospection.

The synthetic seismogram translates the stratigraphic information obtained from exploration wells into seismic terms; it therefore deserves to be taken into consideration when choosing the methods to be employed for solving a given problem.

The synthetic seismogram enables one to know the limitations imposed by the reflecting power of the different subsurface layers. The knowledge of these limitations, combined with an understanding of the difficulties inherent in the surface conditions, helps to determine the frame in which the survey and the interpretation must be set.

During the actual survey the synthetic seismogram illuminates somehow the work of the seismologist. It is a reference base which defines the correlation criteria which permit him to analize the real traces and, at the same time, to increase their resolving power.

The methods of utilisation are examined both with respect to the field work (attempts to determine the technique to be used in any area by reference to the synthetic traces; determination of the volume control; choice of filters) and in the field of interpretation (identification and picking of reflections; analysis of the signals in order to obtain stratigraphic information from them; study of the character of reflections on a regional scale and density of the synthetic seismograms to be made in any region; re‐evaluation of the information contained in old seismic records).
WAVE‐FRONT DIAGRAMS FROM UPHOLE SHOOTING*
Authors: MEISSNER R.
Published: April 2006

Abstract

Uphole shooting during a reflection or refraction survey provides additional information about the velocities within the weathered layer if recorded with a complete spread of geophones on the surface. Wave‐front diagrams can be constructed which give a genuine picture of the wave paths in the subsurface. Their construction is based on the assumption that the travel time from a shot in the hole to a geophone on the surface is the same as that from a fictitious shot on the surface to a fictitious geophone in the subsurface.
LA RADIOMÉTRIE AÉROPORTÉE, OUTIL D'EXPLORATION GÉOLOGIQUE STRUCTURALE*
Authors: GIRET R.
Published: April 2006

Abstract

This paper gives the results of an airborne radiometric survey flown in France over an area of 1,700 km2 at 150 m. above ground, with parallel north‐south profiles 1 kilometre apart. Besides uranium indications discovered or recovered, this survey shows a close correlation between isorad and geological maps. The southern granitic zone is more radioactive than the northern gneissic one, with a constant step on the boundary. In the northern zone granitic intrusions have high radioactivity, and isorad contours are right on the boundaries of the main granitic units. In addition, the radiometric map shows the connections between these batholith roots and probable new satellite outcrops not shown on the geological map. Such a radiometric map is a help towards completing the geological map, and gives indications regarding probable structural connections between different granites.

The detailed survey of an anomaly discovered during the previous reconnaissance survey is given as another example. It was flown twice, with an aircraft at 75 m elevation with profiles 250 m apart, and with a helicopter at 35 m elevation with profiles 50 m apart. In this area of the main Marche fault, granulites in the south and gneisses in the north have low radioactivity, and the central shearing zone also. But, on both sides of this shearing zone, two crushed areas have high radioactivity, and uranium indications. The geological survey of the northern crushed gneisses area shows small granitic intrusions linked with the radioactive anomalies. These intrusions were unknown until they were discovered with the help of this map. Some mineral indications are connected with them.
EARTH TILTS AND THE FLOW OF OIL WELLS*
Authors: TOMASCHEK R. K. A.
Published: April 2006

Abstract

It has been discovered that certain flowing oilwells in the Eakring area (Nottinghamshire, England), which have not otherwise been disturbed, show distinct annual variations in the flow of total fluid. There appears to be a definite connection between these variations and the seasonal movements of the earth's crustal layers as evidenced by observations of the tilts of the earth's surface. The investigation has been extended further to show that a similar relation exists between the earth tilts and the production of a whole oilfield which has not been disturbed unduly by outside influences.

A correlation has also been established between the earth tilt observations and the periodicity of shallow earthquakes.
SOME EXAMPLES OF THE APPLICATION OF ISOSTASY*
Authors: DE BRUYN J. W.
Published: April 2006

Abstract

It is pointed out that the isostatic correction of regional Bouguer isogam maps is necessary for their interpretation. The work involved in the computation of the necessary isostatic reductions is greatly reduced when isostatic iso‐correction line maps are made.
THE APPLICATION OF ELECTRONIC COMPUTERS TO THE CALCULATION OF EFFECTIVE MAGNETISATION
Authors: VOGEL ANDREAS
Published: April 2006

The normal procedure in calculating the effective induced magnetisation of bodies is to introduce the demagnetisation factor. The theory of calculating the demagnetisation factor is however restricted to bodies of 2nd degree surface lying in a homogeneous field i.e. homogeneously magnetised bodies. All other bodies have to be approximated.

Here, the method is based on iterative calculation of magnetisation fields, which makes it possible to calculate the effective magnetisation of any bodies, when the distribution of the inducing field and susceptibility are known.
A LABORATORY STUDY OF STREAMING POTENTIALS*
Authors: AHMAD MOID UDDIN
Published: April 2006

The magnitude of the streaming potential due to the passage of a liquid through a porous medium is examined, under conditions similar to those found in an aquifer under the action of a pumping well. Three models simulate flow in channels, conduits, and unconfined aquifers for several grain sizes of sands and for several resistivities of fluids. The ratio of the streaming potential to the pressure difference is constant for a selected sand and fluid, decreases as grain size increases, is essentially independent of the geometry of the flow, increases slightly as the permeability decreases, and decreases as the salt concentration increases. Extremely low streaming potentials can be expected near a pumping well.
PROPRIETES DE FILTRAGE DES FORMULES UTILISEES POUR LA TRANSFORMATION DES CARTES GRAVIMETRIQUES*
Authors: NAUDY HENRI
Published: April 2006

RESUME

Pour caractériser les anomalies de la carte initiate et de la carte transformeé, on définit des indices de netteté désingés respectivement par I0 et I et on étudie le rapport I/I0 pour diverses formules appliquées à trois anomalies typiques (sphère, anticlinal, faille). Les courbes obtenues permettent d'introduire, par analogie avec les circuits électriques, des notions telles que profondeur de coupure et pente.
VISCOELASTIC PROPERTIES OF THE STANDARD LINEAR SOLID*
Authors: MEIDAV TSVI
Published: April 2006

This study is an attempt to find a phenomenological model which will behave in a manner similar to that of common earth materials in regard to the dependence of attenuation and phase velocity on frequency.

An analysis of two commonly employed rheological models, Maxwell's and Kelvin‐Voigt's and their variants, is presented indicating that these models are too simple to conform phenomenologically to the behavior of rocks. It is shown that a linear combination of the Maxwell and Kelvin‐Voigt models, known as the standard linear solid, comes closer to giving an adequate description of the behavior of some earth materials, than either one of the two models.

A method of determining the viscoelastic constants of a solid is presented provided that its attenuation and dispersion curves are known. The viscoelastic constants (relaxation times and/or viscosity coefficients) of the solid are determined by superimposing the experimental curves on master curves, and reading the constants off the theoretical curves.

An analysis of published experimental data is presented, indicating that the present model is capable of accounting for at least some attenuation and dispersion phenomena.
GRATICULES FOR THE COMPLETE DETERMINATION OF THE MAGNETIC FIELD OF HOMOGENEOUSLY MAGNETIZED CYLINDRICAL BODIES WITH ARBITRARY CROSS SECTION AND FINITE LATERAL EXTENSION*
Authors: HELBIG KLAUS
Published: April 2006

Graticules are known for the calculation of the magnetic field of homogeneously magnetized “two‐dimensional” structures. For bodies whose lateral dimensions are comparable with the dimensions of the cross section and/or the distance between the point of observation and the structure, these graticules allow an approximative computation of the field in the plane of symmetry only. The degree of approximation can be improved by means of end corrections, but the amount of work involved increases rapidly. Moreover, even with end corrections the applicability of the graticules is still restricted to cases of rather simple geometry.

In this paper, a set of graticules is proposed which already incorporates all end corrections. The set consists of three graticules, and it can be shown that at any point of observation lying outside the body each graticule needs be applied once only in order to calculate any component of the magnetic field produced by a homogeneously magnetized cylinder of arbitrary cross section, finite lateral extension and arbitrary spatial orientation.

Curves and tables have been prepared, which allow the construction of the graticules under consideration. The application is illustrated by a hypothetical example. Possibilities for further improvements of the method are discussed.
ÜBER DIE DIMENSIONIERUNG UND DAS VERHALTEN VON REGELKREISEN IM SEISMISCHEN VERSTÄRKER*
Authors: WACHHOLZ HELMUT , WEISSENSTEINER KARL
Published: April 2006

The purpose of the automatic gain control in seismic amplifiers is to balance the slow decrease of the signal in such a manner that its energy does not exceed the capacity of the recording system. At the same time the interesting seismic content of the signal has to be preserved as undistortedly as possible. At first, the technical data of AGC circuits are calculated. The characteristic curves of circuits with one, two, and three time constants are computed. In circuits with two and more time constants an oscillating of the AGC is possible. In order to guarantee aperiodic operation, the ratio of the time constants must not fall below a certain value. As long as these technical conditions are complied with, the free choice of the largest time constant remains open and can be accommodated to the geophysical conditions.

From the endeavour to balance the slow decrease of the signal as well as possible, an upper limit for the choice of the time constants can be derived. A lower limit is obtained from the condition that the seismic content of the signal has to be preserved. The determinant time constant should lie between the two limits and differ from them as much as possible.

Finally, the problem of the amplifier “squeezed” by energy pulses is touched.
INFLUENCE DE LA LARGEUR DU PAS D'ECHANTILLONNAGE DU CAROTTAGE CONTINU DE VITESSES SUR LES SISMOGRAMMES SYNTHETIQUES A MULTIPLES*
Authors: BOIS P. , HEMON CH. , MARESCHAL N.
Published: April 2006

Abstract

Attenuation caused by transmission is known to be the greater the closer the samples are taken together. As a result, the amplitudes of seismograms with multiple reflections can be expected to be negligible within a more or less brief time interval, as is the case for seismograms without multiple reflections with attenuation. This paper examines the process by which multiple reflections regenerate these greatly attenuated reflections. It is also ascertained that a sampling interval of one ms for continuous velocity logs is valid for any survey. For economic reasons, we recommend the selection of a larger interval without, however, overdoing things and thus losing too much information.
A SEMI‐DIRECT METHOD OF INTERPRETING RESISTIVITY OBSERVATIONS*
Authors: KOEFOED O.
Published: April 2006

In 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

In 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

The 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

This 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.
COLLECTION OF FORTRAN II PROGRAMS FOR FILTERING AND SPECTRAL ANALYSIS OF SINGLE CHANNEL TIME SERIES
Authors: ROBINSON ENDERS A.
Published: April 2006

This report gives a description of Fortran II programs for filtering and spectral analysis. All programs are tested.
HORIZONTAL STACKING AND MULTICHANNEL FILTERING APPLIED TO COMMON DEPTH POINT SEISMIC DATA*
Authors: MEYERHOFF HENRY J.
Published: April 2006

The 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

The 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.
A THEORETICAL STUDY ON THE REDUCTION OF STATISTICAL PORE SYSTEM PARAMETERS TO MEASURABLE QUANTITIES*
Authors: SCHOPPER JÜRGEN R.
Published: April 2006

As 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

The 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

Mapping 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

The 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

Abstract

Using 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

Abstract

Considerable 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

Some 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

Continuous 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

The 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

Abstract

The 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.
THE MAGNETIZATION OF THE MAGNETITE OREBODY NEAR CORTEGANA, SPAIN*
Authors: BADER K.
Published: April 2006

Abstract

The magnetic ground survey of ΔZ across the orebody near Cortegana suggests that the direction of the magnetization of the orebody deviates from the present earth field direction in that area. Magnetic measurements of more than 500 specimens of drilling cores of several vertical and one nearly horizontal drill holes showed that the magnetization of the orebody points essentially to the north in the direction of the inclination of the orebody and the banding of the ore. In the central part of the orebody with an average magnetite content of about 50 vol% the magnetization amounts to 0.35 Gauss, the remanent and induced component having the same order of magnitude. The outer parts of the orebody have a much smaller magnetization according to both the smaller magnetite content and greater inhomogeneity of the remanent magnetization, also partly due to their reversed magnetization which is brought about by the stray field of the central part of the orebody. As all drilling cores have been chemically analyzed with respect to their Fe content a logarithmic relationship could be established between the magnetite content, ranging from 25 to 80 vol%, and the susceptibility.
NOUVELLES APPLICATIONS DE LA THEORIE DES MILIEUX ALPHA HARMONIQUES A LA PROSPEGTION ELECTRIQUE EN COURANT CONTINU*
Authors: STEFANESCU SABBA
Published: April 2006

Abstract

The equation which determines the distribution of the stationary potential ϕ in isotropic heterogeneous conductive media with continuously varying local conductivity σ, takes the symmetrical form

image

if we choose as new variables

image

For certain grounds (half‐spaces) in which α is a harmonic function (Δα=ΔΨ= 0), it is possible to obtain by means of simple calculations the lines of equal apparent resistivity and the geoelectrical apparent cross‐sections for the usual devices of d.c. prospecting methods. Graphical examples are also given.