bluuebunny/crossref_metadata_2025 huggingface dataset:
SIMULTANEOUS GAMMA‐RAY AND NEUTRON LOGGING
Authors: Swift Gilbert
Published: October 2002

Newly developed instrumentation for Radioactivity Well Logging is described whereby two curves, the Gamma‐Ray Curve and the Neutron Curve, are made simultaneously, together with a record of the casing collar positions, on one upward passage of the logging instrument. A functional description of all of the system elements is provided, showing how the resulting log is continuously drawn in the surface vehicle on a multi‐pen recorder, with consequent saving in rig‐time and elimination of possible depth discrepancy between curves, which may exist where successive runs are required. The application of radioactivity logs to production problems is briefly discussed.
AN APPLICATION OF PUNCHED CARD METHODS IN GEOPHYSICAL INTERPRETATION
Authors: Sharpe Joseph A. , Fullerton Paul W.
Published: October 2002

There is a large class of problems in geophysical interpretation which is solved by the integral over a plane surface of the product of an observed field value or an assumed surface density of some characteristic property F by a weighting function W, [Formula: see text][Formula: see text] Use of a trigonal coordinate system and substitution of finite sums for the infinite integrals leads to a particularly useful form of adequate practical accuracy, for calculation by punched card methods. The geophysical interpretation problems to which this attack applies will be listed, and an illustration will be given of the calculation of the second vertical derivative of magnetic total intensity by employment of the widely available I.B.M. punched card machines.
REFLECTION SEISMOGRAPH PROSPECTING—HOW IT STARTED
Authors: Schriever William
Published: October 2002

Imagine the calamity that would be caused by a complete lack of the essential products supplied by our petroleum industry! Millions of automobiles and trucks would stay in their garages; farm tractors would not move over the fields, and the production of food would all but cease; our tremendous earth‐moving machines would not disturb a single clod; busses would not take on passengers; many municipalities would be without water, heat, and electric power; crack trains, both passenger and freight, would not move; many industrial plants would have to close for lack of heat, power, and light; ocean liners would stay in their harbors; air transportation would not exist; our Army would be immobilized and our Naval vessels would stay at anchor.
THE SEISMIC HISTORY OF SOUTHEASTERN NEW MEXICO
Authors: Innes Arland I.
Published: October 2002

Seismic exploration in southeastern New Mexico was initiated early in 1928 by the Amerada Petroleum Corporation and the Gulf Oil Company. In the period 1928–1931, refraction profiling was exclusively used to detail Hobbs and to locate the Monument structure. The 1932–1935 period was dominated by correlation refractions. Detailed shooting outlined the Monument structure. During the period 1934–1950, reflection profiling was successfully used and is credited with locating the Knowles, Bagley, Hightower, Cross Roads, Denton, Bough, and Saunders oil fields. The presentation of data includes reproductions of seismic records and structure maps.
GULF COAST SURFACE WAVES
Authors: Howell Lynn G. , Neuenschwander E. F. , Pierson A. L.
Published: October 2002

Surface wave recordings were made with the following: a three‐component velocity seismometer, a long‐period displacement seismometer, six dynamic seismometers, an air‐actuated condenser microphone, and a vertical strain seismometer. Wave trains were recorded similar to those obtained by B. F. Howell in California. We have divided the surface waves into two trains instead of three. The early train seems to have properties of the M‐2 wave of Sezawa; the late train seems to be a Rayleigh wave. An air‐coupled wave is shown to be associated with the M‐2 wave. In the group velocity dispersion curve of the Rayleigh wave, the short‐period branch was found as predicted by theory as well as the usually observed long‐period branch. By making certain assumptions, the thickness of the top layer appears to be about 50 feet according to the theoretical curves of Kanai.
VELOCITY MEASUREMENTS IN NEAR‐SURFACE FORMATIONS
Authors: White J. E. , Sengbush R. L.
Published: October 2002

Procedures are described for measuring various seismic velocities at shallow depths in the earth, and examples of the resulting logs are presented. Velocities in Austin chalk and Eagle Ford shale show that these formations are not isotropic, and velocities in loose sand are seen to increase smoothly with depth except for an abrupt increase in compressional speed at the water table. Elastic constants for chalk and shale are computed. A discussion is given of the literature dealing with a packing of spheres as a model for loose sand, and an approximate theory is presented which includes tangential forces between spheres.
VELOCITY FUNCTIONS IN SEISMIC PROSPECTING
Authors: Kaufman H.
Published: October 2002

An account of the mathematical properties of velocity functions used in the seismic method of geophysical prospecting is presented. Basic equations are given for deriving various quantities of interest associated with a particular velocity function, such as average velocity as a function of depth, average velocity as a function of vertical travel time, parametric equations for displacement, depth, travel time, etc. In Part I the relations are based on a given instantaneous‐velocity—depth function. Part II contains a similar analysis based on a given instantaneous‐velocity—vertical‐time function. The results are incorporated in Tables I and II.
PROPAGATION OF RADIO WAVES OVER A STRATIFIED GROUND
Authors: Wait James R.
Published: October 2002

The propagation of vertically polarized radio waves over a horizontally stratified medium is investigated. A general expression for the “wave tilt” is derived for the case of any number of layers with arbitrary properties in each layer. Numerical calculations are carried out for the special case of only two layers which show that the conductivity and dielectric constant variations of the lower layers will affect the magnitude and phase of the wave tilt.
INDUCED POLARIZATION: A METHOD OF GEOPHYSICAL PROSPECTING
Authors: Bleil D. F.
Published: October 2002

Laboratory experiments have shown certain fundamental relationships concerning the induction of a polarization potential on a metallic body in an electrolyte. The potential induced is a linear function of the potential drop across the body in the energizing field up to a saturation potential of 1.2 volts. Diffusion of ions and chemical action are the predominant factors which determine the rate of growth or decay of the polarization potential. Polarization occurs only at the boundaries of electrically conducting minerals. The results of the laboratory experiments provide an explanation of the induced polarization potential of a homogeneous, uniformly mineralized earth. This potential falls off as 1/r from a point electrode. Induced polarization susceptibility is defined and a method of analyzing field data is described. Field measurements over two mineralized zones (pyrrhotite and magnetite) substantiate the theory as developed.
ON THE THEORY OF HEAD WAVES
Authors: Heelan Patrick A.
Published: October 2002

When a combined longitudinal and transverse disturbance, diverging from a localized source, strikes a plane boundary between two solid elastic media, several systems of head waves and second‐order boundary waves are generated, each associated with grazing incidence of one or the other of the reflected or refracted waves. Associated with grazing incidence of [Formula: see text], the refracted P‐wave, is the head wave system comprising [Formula: see text] (the “refracted wave” of seismic prospectors), and [Formula: see text] (a transverse head wave) in the upper medium, and [Formula: see text] (a transverse head wave) in the lower medium. There is no boundary wave in the lower medium. These three waves, with the second‐order term of [Formula: see text] (the first‐order term is zero on the boundary) satisfy conditions of continuity of stress and displacement at the boundary. Moreover, the energy of the three head waves is derived completely from the second‐order component of [Formula: see text], which possesses a component of energy flow normal to the boundary. The amplitudes of [Formula: see text] [Formula: see text] and [Formula: see text] are calculated for certain cases.
A CONTRIBUTION TO THE COMPUTATION OF THE “SECOND DERIVATIVE” FROM GRAVITY DATA
Authors: Rosenbach Otto
Published: October 2002

The theory and practical application of the second derivative method of gravity interpretation have been discussed by Elkins (1951) in a very interesting paper based partly on an earlier paper by Peters (1949). In this paper, Elkins shows how the second derivative may be computed at the center of a series of concentric circles using the arithmetic means of the gravity values, assumed to be continuous, around each circle. A method is here proposed which does not use a continuum of gravity values but instead requires only a series development. The approximation formulas needed for the routine calculations can be derived by a method different from that of Elkins and the least squares adjustments he used can be dispensed with. Two hypothetical examples using the formulas derived by the series method are given and the results are compared with those computed by Elkins’ formula.
SEISMIC RECORDING ON MAGNETIC TAPE
Authors: Loper G. B. , Pittman R. R.
Published: October 2002

A system of recording and reproducing exploration seismograms on magnetic tape is described. Geophones and amplifiers with broad‐band response, approximately 4–300 cps, are used to channel the seismic signals to a 13‐track tape recorder. The magnetic tape is 1 inch wide. One of the tracks is used to record a time reference signal. Each broad‐band recording is formed into an endless loop and played back in repeating fashion. The signals are fed through a flexible system of filtering and mixing, then examined on the screen of a 12‐trace cathode‐ray oscilloscope. The sweep of the oscilloscope is synchronized with the loop and, by varying the sweep speed, the entire record, or an expanded portion thereof, is held stationary on the screen. Conventional paper records of the modified record as reproduced on the screen are finally made with a regular seismic camera. Played‐back records with variations of filtering and mixing are shown in order to illustrate the potential usefulness of the technique.
MICROLATEROLOG VERSUS MICROLOG FOR FORMATION FACTOR CALCULATIONS
Authors: Smith Harold D. , Blum Harold A.
Published: October 2002

A comparison of the MicroLaterolog and MicroLog for determining formation resistivity factors indicates that the MicroLaterolog is significantly more accurate. Data supporting this conclusion are presented comparing measured formation resistivity factors from cores with calculated values from the MicroLaterolog and MicroLog in both hard‐ and soft‐rock country. The use of the MicroLaterolog for quantitative electric log interpretation will increase the value of electric logging as an exploration tool.
REFLECTION QUALITY, A FOURTH DIMENSION
Authors: Rummerfield Ben F.
Published: October 2002

The quality of seismic reflection results has a direct relation to newer petroleum provinces in the North American continent. An approach is suggested whereby a seismic study of changes of physical characteristics of subsurface reflecting horizons and/or reservoir beds can be attempted. The changes in the quality of deeper reflecting horizons in relation to a persistent shallow or “control” horizon may be able to add a fourth dimension to present seismic interpretations. It is possible that every record may become important from the viewpoint of evaluating petroleum possibilities and not merely those records “on structure.”
A RESEARCH LIBRARY IN THE GEOPHYSICAL FIELD
Authors: Macelwane James B.
Published: October 2002

The author points out the problem arising from the rapid accumulation of geophysical data in large amounts in the various companies. Much of this material is obsolete or is such that making it available to the research worker would entail no loss to the owners. The author suggests that a library, suitably staffed with competent scientists, might be set up, in a centrally‐located institution, where the material might be made available to the proper workers. This library might also be equipped with vaults for such data as the owners wish to be kept confidential for an indefinite period of time, and in that way, function also as a depository as well as a working library.
THE AMOUNT AND DISTRIBUTION OF SEISMIC AND GRAVITY EXPLORATION IN THE GULF COAST THROUGH 1936
Authors: Rosaire E. E. , Ransone K.
Published: October 2002

Maps are presented to show the accumulated density of exploration by the reflection seismograph and the torsion balance for one hundred fourteen counties and parishes comprising the Gulf Coasts of Texas and Louisiana. The conclusion is drawn that the conspicuous overruns of exploration for these two methods indicated by this survey are a natural consequence of complete surveys for this area by these companies exploring on a coastwide scale. These coastwide coverages represent prospect discovery by the method in question, and are considered to be good practice in view of the probable introduction of new methods of higher finding power.
RECENT DEVELOPMENTS IN EXPLOSIVES FOR SEISMOGRAPH PROSPECTING
Authors: Farren W. R. , White H. H.
Published: October 2002

In the early days of prospecting with the seismograph in this country, more attention was devoted to the development of instruments than to the explosives which provided the impulses they recorded.
DEVELOPMENTS OF ESSENTIAL CHARACTERISTICS IN ELECTRIC BLASTING CAPS FOR SEISMOGRAPH PROSPECTING
Authors: Rolland G. F. , White H. H.
Published: October 2002

The exacting requirements of seismograph prospecting call for two essential characteristics in electric blasting caps; uniformity and safety. The degree of uniformity demanded has required new standards in the manufacture of electric blasting caps, and a great deal of research has been carried on to this end.
THE INTERPRETATION OF GEOPHYSICAL DATA
Authors: Blau Ludwig W.
Published: October 2002

Geophysical data result from measurements of physical properties. The geophysicist postulates certain possible physical causes of the observed effects. The geologist reasons from observed geologic effects to geologic causes. The difficulties confronting the interpretation of physical effects as reflected in geophysical data in terms of geologic causes are pointed out. The author takes the position that geophysical data must be worked up independently. A competent geophysicist‐geologist may combine geophysical and geologic information in the preparation of a report which will then, and only when this procedure is followed, include all present knowledge of the area under investigation. The requirement that geophysical data be immediately translatable into geologic language and furnish material for drawing geologic contour maps is shown to be incompatible with the nature of geophysical data. Attention is drawn to the changing geophysical scene and to the tendency to use geophysical methods after they have ceased to be adequate for the solution of prospecting problems. It is suggested that geology can aid geophysics principally through library reconnaissance and advance surface mapping. Geophysics has become a serious competitor of geology in the search for oil, and the geophysic‐geological ecotone has advanced steadily into geologic territory.
PROBABILITY DISTRIBUTION OF REFLECTIONS ON SEISMIC RECORDS
Authors: Massé Lucien
Published: October 2002

A modification of the theory of radar information is proposed for the analysis of noisy seismic records by means of the cross‐correlation function. The method is applied to a synthetic record, and the amount of information provided by the method is evaluated by means of Shannon’s formula.
MUTUAL ELECTROMAGNETIC COUPLING OF LOOPS OVER A HOMOGENEOUS GROUND
Authors: Wait James R.
Published: October 2002

Computations are presented for the mutual impedance between small wire loops situated on or over a semi‐infinite conductor. The results have application to electromagnetic methods of geophysical exploration.
MINIMUM VARIANCE IN GRAVITY ANALYSIS PART II: TWO‐DIMENSIONAL
Authors: Brown William Fuller
Published: October 2002

The principles developed in Part 1 apply whether the data points are located on a line or distributed over a plane. The practical calculation problem, however, is more complicated in two dimensions than in one. There are two steps: (1) deciding what terms to keep in the polynomial approximation; (2) estimating second vertical derivatives and the like on the basis of the chosen approximation. For (1) we can use two‐dimensional orthogonal polynomials; but complete tables of them would be bulky, and therefore several alternative procedures are outlined. For (2) we can easily derive “best” estimation formulas by the minimum‐variance method; but these usually involve many‐digit multipliers, and therefore “near‐best” coefficients, with fewer digits, are also derived. The specific problems solved here start with uncorrelated data at points of a square grid. In practice, data are taken at irregularly distributed stations: then the minimum‐variance principle and orthogonalization still apply, but the calculations are more complex, and grid values computed from the station values are correlated.
CROSSROADS OF GEOPHYSICS
Authors: Lyons Paul L.
Published: October 2002

I am of the opinion that geophysics, after twenty‐five years of modern geophysical exploration, faces a crossroads. On our present road, which exploration geophysics has traversed in a generation, we have established a wonderful record for geophysics in the United States which has also been extended into the far places of the earth. Exploration geophysics originated in the old world, but it found its home in the United States. In the United States we can best examine its record. We have a fairly good record of its applications in this country.
NOISE ANALYSIS AND MULTIPLE SEISMOMETER THEORY
Authors: Smith Mark K.
Published: October 2002

The purpose of this paper is to present a general theory and some techniques for analyzing, estimating, and displaying the characteristics of wave noise, random noise, and reflection signal, in a form convenient for designing and evaluating multiple seismometer arrays and filters. Modifications of the characteristics resulting from weathering and elevation variations, and modifications of the array responses resulting from variations in plant and seismometer spacing are discussed. Criteria for the design of arrays are presented along with a multiple seismometer nomogram based on a specific set of criteria.
THE DETERMINATION OF THE LONG DIMENSION OF CONDUCTING ORE BODIES
Authors: Clark A. R.
Published: October 2002

A solution of Laplace’s equation in prolate spheroidal coordinates has been used to show that the resistivity profile obtained, when one current electrode is in the conducting body, may be used to obtain an estimate of the extent of the body along the long axis. The theoretical and experimental curves from a dipping conductor are compared.
LETTER TO THE EDITOR
Authors: Slichter Louis B.
Published: October 2002

In 1948 modeling programs for the study of electromagnetic prospecting systems, and for the study of problems in the propagation of elastic waves in inhomogeneous media were initiated at the Institute of Geophysics, University of California, under the support of a group of oil and mining companies.
OBSERVATION OF THE VERTICAL GRADIENT OF GRAVITY IN THE FIELD
Authors: Thyssen‐Bornemisza Stephen , Stackler W. F.
Published: October 2002

Field observations of the anomalous vertical gravity gradient were made at Houston, Texas, and over the Turner Valley structure near Calgary, Alberta, Canada. The results obtained are encouraging, but the precision of the measurements was to some extent reduced by vibrations generated in transporting the gravimeter up and down the tripod, as well as by gusts of wind.
ELEMENTARY APPROXIMATIONS IN AEROMAGNETIC INTERPRETATION
Authors: Smellie D. W.
Published: October 2002

Total magnetic intensity anomaly expressions are derived for four simple sources: the point pole’ line of poles, point dipole and line of dipoles. Type curves are presented for the point pole and dipole. For all cases, factors are calculated which may be multiplied into the half‐maximum distances on the anomaly profiles to yield depth estimates. These methods serve as a first approximation in the interpretation of aeromagnetic data, but their limitations must be kept in mind. Two examples of the application of the methods are given.
HEAT FLOW IN WEST TEXAS AND EASTERN NEW MEXICO
Authors: Herrin Eugene , Clark Sydney P.
Published: October 2002

Geothermal gradients are examined in West Texas and eastern New Mexico, and it is found that the gradients in the salt section of the Permian Salado formation are nearly uniform throughout the region. The values range from 7.70 to 9.00°C/km. Measured values of the thermal conductivity of rock salt are reviewed, and it is concluded that this quantity is most likely to be about [Formula: see text] cal/cm sec °C., with an estimated uncertainty of ten percent. From these figures, the heat flow is found to be [Formula: see text] in this region.
INDEX OF WELLS SHOT FOR VELOCITY (Fifth Supplement)
Authors: Gaither V. U.
Published: October 2002

This is the fifth supplement to the original Index published in the October 1944 issue of Geophysics, the first supplement appearing in the October 1946 issue, the second in the January 1949 issue, the third in the January 1951 issue, a combination of the four separate lists was published in booklet form in 1953 and the fourth supplement appeared in the January 1956 issue of Geophysics. Information is listed on 759 velocity surveys, most of which were shot in the years 1955 and 1956. Corrections and additional information on 7 previously indexed surveys are tabulated.
GEOPHYSICAL ACTIVITY IN 1955
Authors: Patrick Homer G.
Published: October 2002

In accordance with the indicated trend of geophysical activity reported by Dr. Sigmund Hammer in the Interim Report to Midyear the world‐wide exploratory effort in search of petroleum was increased in 1955 over that of the previous year. It is to be understood that the information concerning world‐wide or global activities is incomplete as there are still some parts of the world from which no statistical data are available. An average of 1119 geophysical crews of all types were reported as actively engaged in exploratory work during 1955. This is an increase of 83 crews over the number reported in 1954, and it is slightly higher than the previous record high of 1105 crews in 1953.
GEOPHYSICS—FULL PARTNER
Authors: Davis Morgan J.
Published: October 2002

The advent of exploration geophysics in the United States was in late 1922 when torsion balances were brought over to the United States from Germany by both the Roxana (the predecessor of Shell) and the Amerada Petroleum Corporation. The first survey in the Gulf Coast of Texas was at Spindletop in December, 1922, under the direction of Donald C. Barton, who later and at the time of his death in 1939 was Humble’s chief research geologist. It was Donald Barton’s idea that the known shallow piercement‐type salt dome at Spindletop would furnish a testing ground for this new method. It should be recorded that an excellent anomaly was found in this survey. Discouraging results followed, however, as other known structures were found to give no significant anomaly, and in other instances where anomalous areas were outlined they were condemned by the drilling of exploratory wells. In March, 1924—about a year and a half later—however, an outstanding anomaly was found in the Nash area, Fort Bend County, Texas. In November of that same year dome material was found by the drill, and the discovery of the Nash Dome was a reality. It was not until January 3, 1926, though, that oil was found on the flank of the dome, and this is probably the first oil found as a result of the use of geophysical methods in the United States.
A NEW METHOD FOR INTERPRETATION OF AEROMAGNETIC MAPS: PSEUDO‐GRAVIMETRIC ANOMALIES
Authors: Baranov V.
Published: October 2002

The purpose of this paper is to describe a method of interpretation based on a transformation of the total magnetic intensity anomalies into simpler anomalies. The result of this transformation is the elimination of the distortion due to the obliquity of the normal magnetic field, so that the resulting anomalies will be located on the vertical of the disturbing magnetized bodies. The starting point of the theory is the well known relation between magnetic potential V and Newtonian potential U—relation which can be written: [Formula: see text] with: [Formula: see text] = magnetization, f = 66.7×10−9 u ⋅CGS, σ = assumed density of magnetized bodies. This relation may be considered as a partial differential equation. The boundary condition consists in the measured values of the total field T(P ) known at each point P at the datum plane. As T(P) is the derivative of a harmonic function V, we can determine this function everywhere above the datum plane. Solving then the partial differential equation, we find the Newtonian potential U and its vertical derivatives g, g′, g″⋯. Finally, we obtain these quantities as functionals of the measured magnetic anomaly T(P). For instance, one of the formula is [Formula: see text] where H(M, P) is the kernel of the transformation allowing the direct computation of g(M)—an anomalous field which will be called “pseudo‐gravimetric anomaly.” Of course, the pseudo‐gravimetric anomaly has all the usual properties of a gravimetric anomaly. The field of g(M) presents no distortion and the interpretation becomes as easy as that of a Bouguer anomaly map. To perform the actual routine calculations of this transformation, we start with the values of T taken on a rectangular or trigonal grid, as for the usual computation of the vertical derivatives. The use of punched‐card equipment speeds up considerably these calculations.
SEISMIC VELOCITY STUDY OF SYNTHETIC CORES
Authors: Murphy William O. , Berg Joseph W. , Cook Kenneth L.
Published: October 2002

The velocity of a longitudinal elastic wave through rock at room temperature and at atmospheric pressure depends upon the nature of the rock frame, the porosity of the rock, and the nature of the pore‐filling fluid. In the present investigation longitudinal elastic wave velocities were measured for sixty synthetic cores. The rock frame consisted of sorted quartz sand grains and cement, the percentage of cement varying from ten to fifty percent. The core porosities varied from 8.8 percent to 22 percent. The velocities were measured for dry air‐filled cores and for cores saturated with various liquids. These pore‐filling liquids were distilled water, ethyl alcohol, benzene, carbon tetrachloride, and chloroform. The measured velocities ranged from 2,360 feet per second to 14,710 feet per second. The wave velocity in liquid‐filled cores of 10 percent porosity was approximately twice the velocity for cores of 20 percent porosity, the same type of cement being used in both instances. For any given core, flooded with fluids of wave velocities ranging from 3,000 to 5,000 feet per second, the maximum observed variation in core velocity was around 20 percent. The experimental data fitted the empirical linear equation [Formula: see text] where [Formula: see text] of longitudinal elastic waves passing through the flooded core; [Formula: see text] of longitudinal elastic waves in passing through the saturating fluid. The constant k depends upon the porosity of the rock and the type of cement used. The constant, C, depends upon the nature of the rock frame.
TRANSIENT BEHAVIOR OF PATTERNS
Authors: White J. E.
Published: October 2002

A simple method is described for computing the waveform to be expected from a closely‐spaced pattern of shots or geophones when the individual signal is a pulse. Four strength distributions are compared, and the case of uniform strength along the pattern is discussed in detail. It is concluded that if the individual signal is a short pulse, such as a seismic reflection, then the performance of the pattern is quite comparable for the four source distributions considered.
THE NUMERICAL COMPUTATION OF CAGNIARD’S INTEGRALS
Authors: Dix C. H.
Published: October 2002

The numerical calculations may be made in such a manner as to make clear the influence of various factors on the results. This is done for the buried source and receiver in a semi‐infinite elastic medium. The process is to alter the path of integration so that with increasing time one increases the integration path length. Thus the total field unfolds as we carry out the integration. The work is done graphically. The path is mapped by an electrolytic tank technique suitably modified from that used by electric network synthesis workers. The integrand is separated into a product of two terms, one independent of time and position and one dependent on time and position. The independent term can be mapped on a conducting sheet for one Poisson ratio. The dependent term may be mapped for each time and position. A function multiplier and integrator are needed. The method is most accurate when the horizontal distance of the receiver is not very large compared with the sum of the depths of the source and receiver. The method is alterable to include the domain of difficult direct application. Every aspect of the methods herein described may be extended in the practical sense to the more general case treated by Cagniard. This is, in fact, the main justification for this study of an old problem.
ATTENUATION OF SHEAR AND COMPRESSIONAL WAVES IN PIERRE SHALE
Authors: McDonal F. J. , Angona F. A. , Mills R. L. , Sengbush R. L. , Van Nostrand R. G. , White J. E.
Published: October 2002

Attenuation measurements were made near Limon, Colorado, where the Pierre shale is unusually uniform from depths of less than 100 ft to approximately 4,000 ft. Particle velocity wave forms were measured at distances up to 750 ft from explosive and mechanical sources. Explosives gave a well‐defined compressional pulse which was observed along vertical and horizontal travel paths. A weight dropped on the bottom of a borehole gave a horizontally‐traveling shear wave with vertical particle motion. In each case, signals from three‐component clusters of geophones rigidly clamped in boreholes were amplified by a calibrated, wide‐band system and recorded oscillographically. The frequency content of each wave form was obtained by Fourier analysis, and attenuation as a function of frequency was computed from these spectra. For vertically‐traveling compressional waves, an average of 6 determinations over the frequency range of 50–450 cps gives α=0.12 f. For horizontally‐traveling shear waves with vertical motion in the frequency range 20–125 cps, the results are expressed by α=1.0 f. In each case attenuation is expressed in decibels per 1,000 ft of travel and f is frequency in cps. These measurements indicate, therefore, that the Pierre shale does not behave as a visco‐elastic material.
NUMERICAL RESISTIVITY ANALYSIS: HORIZONTAL LAYERS
Authors: Vozoff Keeva
Published: October 2002

The direct numerical solution of resistivity data for the case of horizontal layering is presented as the solution of a set of nonlinear algebraic equations. Two specific methods, Newton and Steepest Descent, were set up for three‐layer analyses on a digital computer. These were applied to field data and to data derived theoretically for three‐ and four‐layer cases. The case of a thin second layer was found to display a special kind of indeterminacy. It was found that the analyses do not and cannot theoretically be expected to yield the actual values of resistivity and thickness for these thin layers, but, rather, a good value for their ratio (conductive layer) or product (resistive layer) can be obtained. The question of ultimate resolubility of this type of information in the presence of measurement error is discussed quantitatively. It was found that, as the resistivity of the third (lowermost) layer increases, it becomes increasingly difficult to detect a thin, resistive second layer. When the second layer is not thin relative to the first, the resistivities and thicknesses are determined with reasonable accuracy. These solutions do not appear to be unique, but alternate solutions differ sufficiently for the true solution to be easily distinguished.
TERRAIN CORRECTIONS FOR AN INCLINED PLANE IN GRAVITY COMPUTATIONS
Authors: Sandberg C. H.
Published: October 2002

In many instances an inclined‐plane approximation represents more accurately the terrain near a gravity station than does the conventional block‐cylinder approximation. Combinations of the terrain effect of inclined planes through various terrain zones, as represented in the accompanying tables, can be used to approximate easily and quickly such familiar land forms as valleys, ridges, and hillsides.
GETTING THE MOST OUT OF PRESENT SEISMIC INSTRUMENTS
Authors: Hammond Joseph W. , Hawkins James E.
Published: October 2002

Much of the present seismic work is being carried out in areas where results are difficult to obtain. The paper outlines the requirements for seismic instruments for these operations. The particular characteristics desired for specific problems are illustrated, and the instrument factors that affect these characteristics are outlined. Examples of the effect of instrument adjustment are shown. The attainment of optimum results with present equipment under diversified field conditions may require modifications according to area, in shooting techniques, geophones, amplifiers, galvanometers, recording, and record presentation. The discussion of the advantages of magnetic recording assumes that the best field techniques have been applied.
A COMPARISON OF WELL VELOCITY METHODS IN SOUTH TEXAS
Authors: Wood A. B.
Published: October 2002

This velocity study is limited to data from one well in South Texas. Two short‐interval velocity logging methods compared with conventional seismic geophone data show large discrepancies. The Shell short‐interval velocity log agrees within close limits to the conventional seismic data except for the lower 4,000 ft. The indicated delay times for the upper 2,000 ft of this 4,000‐ft interval are short by 6.5 percent, and indicated delay times for the lower 2,000 ft are short by 4.0 percent. The Schlumberger Sonic Velocity Log, limited in this survey to the bottom 4,200 ft of hole, indicated delay times larger than the seismic time by more than 5 percent. There is a difference of approximately 9 percent between the two velocity logs, even though the tools were of similar dimensions. The spacing between detectors was three feet, and the distance from transmitter to near receiver was four feet for the Shell tool and three feet for the Schlumberger tool. An analysis of the basic data is necessary to resolve these discrepancies. There is no check on the Sonic data in its present form, but a thorough study of the Shell Oscillogram log and conventional seismic data for errors fails to explain the 6.5‐percent and 4‐percent discrepancies in the Shell short‐interval velocity data. The conclusion must be drawn that these discrepancies are real. This survey demonstrates the necessity to check short‐interval velocity logging with conventional seismic shots to maintain acceptable seismic well velocity standards.
UNIQUE DETERMINATION OF CONDUCTIVITY, SUSCEPTIBILITY, SIZE, AND DEPTH IN MULTIFREQUENCY ELECTROMAGNETIC EXPLORATION
Authors: Ward Stanley H.
Published: October 2002

The response of a conductive, magnetic sphere in a uniform, alternating magnetic field is a function of the conductivity, permeability, and radius of the sphere and of the frequency of the alternations. Over one range of frequencies, eddy‐current density in any given sphere and secondary magnetic fields of the sphere are relatively constant and high. Over a much lower range of frequencies eddy currents are negligible, but the secondary magnetic fields may be of large constant amplitude but of polarity reversed to that of the higher frequency range. At some intermediate frequency the secondary magnetic fields will be entirely quadrature with respect to the inducing field. Utilization of this peculiar frequency dependence and of the geometry of the secondary magnetic fields permits unique determination of the conductivity, permeability, radius, and depth to the center of a buried sphere. The procedure for obtaining these variables is described in this article. As an added feature, it is shown that by completing a gravity survey as well as an electromagnetic survey over a dense, magnetic, conductive spherical ore body, it is possible to determine the above variables, plus density, uniquely. Precise identification of the material of the sphere is seen as a possible result of the application of this technique.
SOUND SPEED AND ABSORPTION STUDIES OF MARINE SEDIMENTS BY A RESONANCE METHOD
Authors: Shumway George
Published: October 2002

Laboratory measurements of compressional sound speed, and absorption, have been made on 111 unconsolidated marine sediment samples, ranging from shallow water sands to deep‐sea clays. In addition, determinations were made of porosity, wet density, and grain size distributions. Frequencies between 20 kc/sec and 37 kc/sec were used for the acoustic studies. Sound speed values at room temperature range from 1.474 km/sec for a red medium clay to 1.785 km/sec for a medium sand. More than one‐third of the values are lower than the value for sea water alone. Variations in the speed of sound in unconsolidated sediments as found in nature are caused by the following factors, in order of importance: (1) porosity, because of the great difference in compressibility of water and mineral grains; (2) the factor which produces rigidity, which appears to be related to the abundance of coarse grains; (3) pressure; (4) temperature; (5) compressibility of the grain aggregate, determined from compressibilities of individual minerals. Sound absorption measurements ranged from 0.5 db/m for a medium clay (28.4 kc/sec) to about 20 db/m for silts and fine sands (between 30 and 37 kc/sec). An absorption maximum occurs for sediments of intermediate porosity (0.45–0.6) and intermediate grain size (0.031 mm–0.25 mm). The expression [Formula: see text], where α is the linear absorption coefficient, M is a frequency‐dependent factor related to the sediment volume fraction of grains in mutual contact, and [Formula: see text] is a computable total acoustically effective grain surface area, predicts the absorption values and the absorption maximum. Absorption measurements at more than one frequency between 20 kc/sec and 37 kc/sec were obtained for 65 samples. Assuming that absorption is directly proportional to frequency raised to a power n, the data yield an average value of n equal to 1.79, with a standard deviation of 0.98.
A COMPREHENSIVE SYSTEM OF AUTOMATIC COMPUTATION IN MAGNETIC AND GRAVITY INTERPRETATION
Authors: Henderson Roland G.
Published: October 2002

In the interpretation of magnetic and gravity anomalies, downward continuation of fields and calculation of first and second vertical derivatives of fields have been recognized as effective means for bringing into focus the latent diagnostic features of the data. A comprehensive system has been devised for the calculation of any or all of these derived fields on modern electronic digital computing equipment. The integral for analytic continuation above the plane is used with a Lagrange extrapolation polynomial to derive a general determinantal expression from which the field at depth and the various derivatives on the surface and at depth can be obtained. It is shown that the general formula includes as special cases some of the formulas appearing in the literature. The process involves a “once for all depths” summing of grid values on a system of concentric circles about each point followed by application of the appropriate one or more of the 19 sets of coefficients derived for the purpose. Theoretical and observed multilevel data are used to illustrate the processes and to discuss the errors. The coefficients can be used for less extensive computations on a desk calculator.
BASEMENT MAPPING WITH AEROMAGNETIC DATA—BLIND RIVER BASIN
Authors: Steenland Nelson C. , Brod Robert J.
Published: October 2002

A detailed aeromagnetic map at 1,700 ft of 16 sq mi of the uranium‐producing Blind River Basin of Ontario, Canada, shows anomalies interpreted to originate from shallow basic intrusives and deeper basement rocks. The identification of a major basement fault from a basement anomaly is described after demonstrating the isolation of these anomalies from the intrusive rocks on the basis of calculations of their depths. An aeromagnetic map computed upward to 2,630 ft and two second vertical derivative maps confirm the identification of the two categories of anomalies. Later drilling tends to confirm the existence of the fault. The entire study is considered applicable to much larger aeromagnetic surveys because all types of anomalies are present within this small area where they can easily be correlated with their origins.
COLLECTION AND PROCESSING OF DIGITIZED ACOUSTIC LOG DATA
Authors: Broding R. A. , Poole J. L.
Published: October 2002

The mathematical processes involved in making acoustic logs useful for the geophysicist or production analyst have prompted the handling of log data by digital means. Digital punched tape logs from retraced analog recordings as well as digital recordings made by punching tapes directly from the recording galvanometer signal obtained during a logging survey are being used as input to electronic computers. These computers can be programmed to perform the normal computations now used in data reduction. This process yields higher precision data and allows computational procedures to be performed that previously were considered burdensome or tedious. The technique is attractive in preparation of geophysical logs, synthetic seismograms, calculating effective porosities and saturations. However, the requirement of converting recorded digital data to be compatible with the input of different digital computers and to all the various formats for individual programs is a problem that will require standardization in formats. It is evident that the advantages to be realized in data reduction processes will require the log of the future to be recorded in digital as well as analog form.
AN ELECTRICAL RESISTIVITY SURVEY FOR GROUND WATER
Authors: Meidav Tsvi
Published: October 2002

An electrical resistivity survey was carried out in Grundy, Chariton, and Carroll Counties, Missouri, in connection with a ground water project of the Missouri Geological Survey. The aim of the project was to locate buried channels under the glacial cover. The resistivity data obtained was interpreted both empirically and quantitatively. The empirical method was found to be satisfactory wherever the uniformity of electrical properties was maintained by either the glacial cover or bedrock, and the resistivity contrast was high. The quantitative technique used most commonly in this study was Spicer’s (1956) modification of Hummel’s (1932) procedure, used in conjunction with standard two‐, three‐, and four‐layer master curves. The limitations of the quantitative methods of interpretation are indicated in a series of resistivity distribution curves.
INDEX OF WELLS SHOT FOR VELOCITY
Authors: Gaither V. U.
Published: October 2002

This is the ninth supplement to the original Index published in the 1944 issue of Geophysics Information is listed on 340 well velocity surveys not heretofore reported in any previous publication of the Index. Corrections and/or additional information on 5 previously listed surveys are also tabulated.
On: “LOG INTERPRETATION IN SANDSTONE RESERVOIRS,” BY M. R. J. WYLLIE, GEOPHYSICS, AUGUST 1960, pp. 748–778.
Authors: de Witte L.
Published: October 2002

In his article on log interpretation in sandstone reservoirs, under the heading: “The Determination of Resistivity Index,” Dr. Wyllie reviews the history and present status of the so called “shaly sand problem.”
THE ELECTRONIC COMPUTER AND GEOPHYSICS
Authors: Morrison L. S. , Watson Robert
Published: October 2002

With the advent of electronic computers a revolution in data handling has been brought about. As yet few people outside of scientific research or accounting fields are familiar enough with these computers to know how they can be applied in their particular type of work. Electronic computers consist of three basic elements: an operations register, a digital computer and a memory unit. The memory unit retains information in numeric form in locations that are identified by a coordinate system. Data stored in memory may be retrieved and processed in the digital computer and the results of the computation may be stored for later use. Computations are carried out in the binary or two‐digit number system. The operations register controls the operation of the digital computer and the memory unit and acts as a link between the intent of the programmer and the internal operation of the system. An object, given the proper code numbers describing its shape, size, color, etc., can be identified from other objects by comparison of code numbers. The speed and ability of electronic computers to compare and identify makesn possible the solution of very exacting problems that otherwise would be humanly next to impossible from time considerations. Electronic computers have been used in geophysical exploration to compute and contour derivative maps of gravity and magnetic data. They have been used to reduce gravity data to datum, compute interval and average velocities from velocity profile data and have been used to solve many non‐recurring problems.
ANOMALOUS EVENTS ON THE REFLECTION SEISMOGRAM
Authors: Seabrooke David S.
Published: October 2002

Anomalous events, i.e., events other than simple reflections, are becoming more and more evident with the advent of magnetic tape and the various types of display sections such as variable area, variable density, full trace, etc. Recognition of these events, such as multiple reflections, diffractions, etc., is of considerable importance if the interpreter is to make optimum use of his data. A knowledge of the characteristics of the anomalous events likely to be encountered aids in their identification. Simple parameters, viz., arrival time, apparent dip stepout and normal moveout, readily obtained from the reflection seismogram, may be used to enable the problem to be approached quantitatively. Under the general headings: direct, refracted, reflected, and diffracted energy, air waves, surface waves, ghost reflections, simple multiples, complex multiples, diffractions, reflected refractions and refracted reflections are discussed. An example of a simple analytical attempt to solve an unusual offshore multiple problem is briefly described.