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 Volume 18, Issue 1, 1970
Geophysical Prospecting  Volume 18, Issue 1, 1970
Volume 18, Issue 1, 1970


INTERPRÉTATION DIRECTE DES COURBES DE SONDAGE ÉLECTRIQUE ET LE PROBLÈME DE DIFFÉRENTS DISPOSITIFS DE MESURE *
More LessABSTRACTDirect interpretation methods of resistivity curves are discussed, which use the kernel function of the apparent resistivity. This function results from the consideration of the problem of diverse electrodes configurations.
Several expressions for the determination of the kernel function of the potential from the kernel function of the apparent resistivity are given.



ON OBTAINING A FAMILY OF BODIES WITH IDENTICAL EXTERIOR FIELDS‐METHOD OF BUBBLING *
Authors D. ZIDAROV and ZH. ZHELEVABSTRACTSome 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.



REMARQUES SUR L'INTERPRETATION DES SONDAGES DE POLARISATION PROVOQUEE ESSAI DE THEORIE QUANTITATIVE *
Authors PHAM VAN NGOC, J. ROUSSEL and Et D. TOURNIERABSTRACTThe transient phenomena associated with induced polarization are very complex and it is necessary to have both a proper understanding of the physical processes and a good supply of mathematical aids in order to make any advance in the quantitative interpretation of I.P. surveys.
The analogy between the classical electrical sounding method and the induced polarization sounding method has led a number of workers to interpret the results of the latter like the results of the former. To clarify this idea, it seems very interesting to calculate a mathematical model in order to know the form of the anomaly that can be probably expected.
The case of a thin horizontal polarizable layer, with the same uniform and isotropic conductibility as the homogeneous background, has been studied in this paper.
The result of the calculation for the case of a single current electrode and a single potential electrode is given. From these data, the theoretical curve of IP sounding using the Wenner electrode array is computed.
The master curve is compared with experimental curves obtained on scale models. A good correlation between these curves is noticed. In addition, it can be concluded that the mathematical model is proving the validity of the experiments on interpretation scale models.



FIXED SOURCE SYSTEM IN A CONDUCTIVE ENVIRONMENT *
More LessABSTRACTMeasuring systems with a fixed source fed with alternating current at sound frequency are used almost exclusively at the present time for a quick search for conductive zones in an environment with a high specific electrical resistivity. Owing to this fact it is useful to measure in a gradient configuration, i.e. to compare the quantities of the corresponding parameters of the field in two relatively close points oriented in the direction of the assumed change of the field. In this way we can obtain a suppression of the impact of the wider environment, since, in principle, we record the first derivative, i.e. the amount of the change only.
The present article points out some possibilities of the application of the system with a fixed source in non‐magnetic environment with arbitrary resistivity.



UNE METHODE D'ANALYSE FINE DES PROFILS AEROMAGNETIQUES *
By HENRI NAUDYABSTRACTA method to analyse aeromagnetic profiles is proposed: several horizontal (width‐) and vertical (amplitude‐) parameters are deduced from the anomalies. These parameters are then compared with diagrams drawn on a logarithmic scale. The comparison yields depth and magnetization of the causative bodies.
The method lends itself equally well to a quick estimate and to a thorough interpretation, depending on the number of parameters deduced and on the number of diagrams. It can be applied also to the anomalies of the total field and its vertical gradient.



SIGNAL ET BRUIT EN MAGNETOTELLURIQUE *
Authors L. CHAIZE and M. LAVERGNEABSTRACTConventional processes of extracting magnetotelluric signals from noisy records are reviewed: instrument noises and noises that are generated close to the detectors can be eliminated by the usual auto‐ and crosscorrelation processes. Identification of coherent noises, such as pulses due to field sources that are not uniform over at least 100 km in oil exploration or 1000 km in crustal studies, is much more tedious.
The 5 components Hx, Hy, Hz, Ex, Ey, of the magnetotelluric field have been recorded in many areas in France at different periods of the year, (a) in non‐uniform field sources in the vicinity of electric railways and of 50 cycle power lines, and (b) in areas of strong inhomogeneity at depth on the flanks of steep structures and near the sea shore.
Means for detecting non‐uniformity are reviewed. Measuring the vertical component of magnetic pulses is a good way of estimating field uniformity: if H vertical/H horizontal <10%, the uniform field assumption is valid, and the classical restitution formulas can be used; if H vertical/H horizontal > 10%, uniformity can not be assumed and there is some difficulty in deciding whether non‐uniformity is due to the field source or to anisotropy or inhomogeneities at depth. Several ways to solve this difficulty are described.
The reliability of calculation of actual resistivity at various depths is examined as a function of the precision of apparent resistivity measurements.



AN ELEGANT, UNIVERSAL NOMENCLATURE FOR ELECTROMAGNETIC MOVING SOURCE‐RECEIVER DIPOLE CONFIGURATIONS *
More LessABSTRACTThe transmitter and receiver coils and the line joining them in an electromagnetic moving source‐receiver system can, in principle, have an infinity of mutual orientations. Let the direction of a survey line (traverse direction) be x and let the vertical plane through it be the x‐z plane and let the z‐axis be a line in this plane perpendicular to the z‐axis, then the y‐axis of an orthogonal coordinate system is automatically determined. A definite coordinate system, dependent on the mutual coil orientation alone, and independent of the spatial direction of the survey line or alterations in it, is thus associated with each point. The geometry of a moving source‐receiver configuration is uniquely defined by specifying (i) the direction cosines a, b, c of the transmitter coil axis T, (2) the direction cosines d, e, f of the line L joining the transmitter and the receiver coils and (3) the direction cosines g, h, i of the receiver coil axis R. Hence a set of indices conveniently written as T a, b, c L d, e, f R g, h, i describes the geometry and also enables “reconstruction” of the system uniquely and without the risk of confusion inherent in such incomplete descriptions as “vertical coil system”, “horizontal coil system” etc. Degeneracy arises if the traverse direction is vertical. How this is overcome is described in the paper. To the above indices may be appended the indices T, the distance between T and R and v, the frequency.
For example, the most common “horizontal coplanar coil system” has the indices T 001 L 100 R 001. An airborne wing‐tip system with coil axes in the flight direction is specified by T 100 L 010 R 100. Other examples are given in the paper. Maps and data sheets of moving source‐receiver systems should be marked with the appropriate set of indices.



EMPIRICAL INVESTIGATION OF SOME FACTORS AFFECTING ELASTIC WAVE VELOCITIES IN CARBONATE ROCKS *
By W. JANKOWSKYABSTRACTContinuous 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
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 *
More LessABSTRACTThe 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.



THE CORRELATION OF SEISMIC VELOCITIES WITH FORMATIONS IN THE SOUTH‐WEST OF SCOTLAND *
By JEREMY HALLABSTRaCTIn seismic studies being carried out to elucidate the structure at depth of the Midland Valley rift and the Tertiary igneous province in the West of Scotland, a lack of deep boreholes makes the collection of velocity data imperative for identification of seismic events and for determinations of depth. Three methods are used to investigate the correlation of seismic velocities and geological formations. The results show as strong a dependence of velocity on method of measurement as on lithology and the wide spread of values within a given formation makes the attribution of discrete velocity ranges to specific formations impossible. Changes of velocity are more significant than absolute values. The variations in both are discussed.



BOOK REVIEWS
Book review in this Article:
H. Wöhlbier, R. H. Wöhlbier, F. H. Wöhlbier, H. Baston, Worldwide Directory of Mineral Industries Education and Research.

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Volume 72 (2023  2024)

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Volume 27 (1979)

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Volume 18 (1970)

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Volume 1 (1953)