bluuebunny/crossref_metadata_2025 huggingface dataset:
THE ELECTROMAGNETIC FIELD DUE TO INDUCED CURRENTS IN A CONDUCTIVE SLAB OF FINITE DIMENSIONS
Authors: Belluigi A.
Published: October 2002

In conformity with what the author (1949a) presented briefly, the theory is developed of the electromagnetic eddy fields relative to a plane, thin, conducting slab with its plane perpendicular to the horizontal ground. The mineral slab is subjected to an alternating inducing magnetic field, paralleling the surface of the ground. After discussing the problem of the finite slab, the special case is considered of a semi‐infinite slab (Peters & Bardeen, 1930), e.g., the mineralized vein type, using existing formulas. With adequate development they can be used in the construction of theoretical graphs of the electromagnetic effects of the slab in which eddy currents are produced. The limiting dimensions, both of the dyke (first case of the finite slab), and the vein (second of the semi‐infinite slab case), act noticeably upon the measurable electromagnetic effect, and the influence diagrams characterize the slab‐shaped, conducting mineral. Therefore some fundamental characteristics on the surface and at depth of the slab and its extension in depth (thickness) can be deduced. The present paper consists of two sections, namely, (A) The theory of the finite, plane, and thin slab (dyke) and corresponding general formulas of magnetic influence. (B) A discussion of the special case of the semi‐infinite slab, or mineralized vein and of Peters‐Bardeen’s (1930) integral formulas, and their integration and illustration by means of graphs.
ELASTIC WAVE VELOCITIES IN ROCKS AT HIGH PRESSURES AND TEMPERATURES
Authors: Hughes D. S. , Cross J. H.
Published: October 2002

The variation in dilatational and rotational velocities in rock samples with pressure and temperature has been studied. The measurements were taken at pressures from 1 bar (atmospheric) to 5,000 bars, and temperatures of 25°C. to 200°C. for all samples and up to 300°C. for two samples. We can thus reach a pressure equivalent to some 18 km or 60,000 feet of burial but our highest available temperature probably at most corresponds to no more than 8–9 km. The measured rotational velocities check very well with independent measurements. Laboratory measurements of the dilatational velocity are not available for comparison. From the measured dilatational and rotational velocities, the elastic moduli and Poisson’s ratio may be computed. Values of Poisson’s ratio are tabulated for all samples. In general, highly quartzitic rocks have low values 0.13–0.20 whereas the majority of rocks have values in the range 0.26–0.33. The effect of interstitial water has been investigated in one sandstone and one limestone. The sandstone shows an increase in velocity at low pressure and a decrease at high pressure whereas the limestone shows the opposite effect.
A SEISMIC WAVE GUIDE PHENOMENON
Authors: Burg K. E. , Ewing Maurice , Press Frank , Stulken E. J.
Published: October 2002

On one particular prospect in shallow water repetitive patterns appeared on short spread seismograms in such prevalence as to jeopardize identification of desired reflections. It is demonstrated that under favorable conditions, less restrictive than thought necessary heretofore, a layer of water comprises an effective wave guide for seismic energy propagation. Reinforcement fronts formed by multiple reflection of sound in water can develop into a set of waves completely overshadowing other seismic arrivals. With but minor modifications conventional wave guide theory applies. Examples from the prospect are presented to illustrate various reinforcement patterns. Observed frequency characteristics, group velocity, and phase velocity magnitudes are investigated for normal modes of propagation.
UP‐HOLE TIMES
Authors: Woods J. P.
Published: October 2002

The up‐hole travel time for the seismic impulse from a dynamite explosion is usually taken to depend only on charge depth and formation velocity. In practice, the measured travel time is influenced by charge size, by filter setting, by instrument sensitivity, and by previous history of the shot hole. In some areas, there occur anomalous up‐hole times which are difficult to explain.
A NOMOGRAM FOR THE COMPUTATION OF TIDAL DEVIATIONS OF THE VERTICAL
Authors: Malone A. B.
Published: October 2002

It is possible to adapt a nomogram, devised by Thomas A. Elkins for the computation of tidal variations in the vertical component of the earth’s gravitational field, to the computation of tidal deviations of the vertical. The nomogram is explained and illustrated and a worked example given.
FREQUENCY ANALYSIS OF SEISMIC WAVES
Authors: Jakosky J. Jay , Jakosky John J.
Published: October 2002

This paper contains a brief description of the general factors governing choice of recording media; a description of the instrumentation employed in wave analysis studies; a review of some of the factors involved in the generation of seismic waves and their propagation; and a few examples of wave separation to illustrate some of the points discussed and their application to seismic exploration. The results of these studies demonstrate that instrumentation of this type is of advantage in those areas where frequency discrimination can improve the signal/interference ratio.
THE APPLICATION OF THE REFLECTION SEISMOGRAPH TO NEAR‐SURFACE EXPLORATION
Authors: Allen C. F. , Lombardi L. V. , Wells W. M.
Published: October 2002

The geophysical approach to very shallow exploration problems has been limited, in the main, to electrical, magnetic, electromagnetic, and refraction methods. The reflection seismograph, with its clear advantages of decreased ambiguity and increased resolving power, can be applied to many of these problems. In the fall of 1951, a Stanford Research Institute crew conducted an experimental reflection survey in Minnesota, mapping with correlation spreads the glacial drift‐bedrock interface along seventy miles of line. The interface varied from a few hundred to several hundred feet in depth below surface, and control core holes showed the seismic profile to be essentially correct, where checked. Over‐all velocities, determined by shooting core holes, varied from 3,800 feet per second to 5,500 feet per second. Special instrumentation included a high speed camera and a filter peaked at 100 cps. All shots were fired in the air. The method has obvious applications to mining, engineering, and ground‐water problems, and to difficult weathering problems involving thick alluvial, eolian, or glacial debris.
THE INADEQUACY OF THE STANDARD SEISMIC TECHNIQUES FOR SHALLOW SURVEYING
Authors: Evison F. F.
Published: October 2002

The seismic method in geophysics has been very thoroughly applied to prospecting for oil, but the techniques developed are not well suited to shallow surveying. A typical shallow survey is described to illustrate some of the shortcomings of the standard seismic techniques in this sphere. A full critique reveals both practical and fundamental limitations, the origin of most of which may be traced to the explosive source. Published data on the form of the explosive impulse suggest that it is inherently unsuitable for shallow surveying. The electromechanical source promises to overcome this difficulty by providing an impulse having any desired frequency and duration.
NOTE ON WAVE‐GUIDE PROPAGATION OVER A SHALLOW SALT DOME
Authors: Howell Lynn G. , Kean C. H.
Published: October 2002

This note shows evidence of a duct or wave‐guide type of wave propagation over a shallow salt dome located in the Gulf Coast.
BASIC THEORY OF THE MAGNETO‐TELLURIC METHOD OF GEOPHYSICAL PROSPECTING
Authors: Cagniard Louis
Published: October 2002

From Ampere’s Law (for a homogeneous earth) and from Maxwell’s equations using the concept of Hertz vectors (for a multilayered earth), solutions are obtained for the horizontal components of the electric and magnetic fields at the surface due to telluric currents in the earth. The ratio of these horizontal components, together with their relative phases, is diagnostic of the structure and true resistivities of subsurface strata. The ratios of certain other pairs of electromagnetic elements are similarly diagnostic. Normally, a magneto‐telluric sounding is represented by curves of the apparent resistivity and the phase difference at a given station plotted as functions of the period of the various telluric current components. Specific formulae are derived for the resistivities, depths to interfaces, etc. in both the two‐ and three‐layer problems. For two sections which are geometrically similar and whose corresponding resistivities differ only by a linear factor, the phase relationships are the same and the apparent resistivities differ by the same proportionality constant which relates the corresponding true resistivities. This “principle of similitude” greatly simplifies the representation of a master set of curves, such as is given for use in geologic interpretation. In addition to the usual advantages offered by the use of telluric currents (no need for current sources or long cables, greater depths of investigation, etc.), the magneto‐telluric method of prospecting resolves the effects of individual beds better than do conventional resistivity methods. It seems to be an ideal tool for the initial investigation of large sedimentary basins with potential petroleum reserves.
WAVELET CONTRACTION, WAVELET EXPANSION, AND THE CONTROL OF SEISMIC RESOLUTION
Authors: Ricker Norman
Published: October 2002

The general problem of seismic resolution is discussed. A seismogram, free from distortions, is an elaborate wavelet complex, and the analysis of a seismogram consists in breaking it down into its wavelet components. Distortions introduced by conventional seismographs are discussed and the conditions to be imposed upon seismic apparatus for distortionless wavelet transmission are set down. Three distortionless systems are possible: flat response; the wavelet contractor; and the wavelet expander. Wavelet contraction is discussed, whereby the individual wavelets which go to make up the seismogram may be contracted to a lesser breadth without altering the relative arrival times of the wavelet centers. Laboratory studies of the wavelet contractor are described and examples of wavelet contraction and the resolution of wavelet complexes are given. A description of the wavelet contracting seismograph used in the evaluation of the device in the field is given and results of the evaluation program are discussed. The wavelet contractor delineates subsurface formations with greater precision than does the conventional seismograph and it is able to carry pinchouts and truncations farther than is possible with conventional seismographs.
PROBLEM AREAS FOR THE SEISMOLOGIST
Authors: Conklin Glenn M.
Published: October 2002

This paper describes interpretative problems encountered in four widely scattered areas: Southern Florida; Beaver County, Oklahoma; the Plainview Basin of the Texas Panhandle; and Hancock County, Mississippi. Secondary refraction recordings offer problems, because refractions from deep beds are distorted and obscured by energy from shallow beds. The energy associated with the shallow refractors appears as multiples and is sustained for long periods of time. In Beaver County, Oklahoma, extreme variations in velocity cause distortion of reflections and introduce apparent dips which are erroneous. This velocity variation is thought to be due to differential salt solution from the Blaine‐Cimarron interval. In the Plainview Basin of the Texas Panhandle and in Hancock County, Mississippi, multiple reflections are troublesome. These reflections are discussed and records and cross‐sections illustrate these events. Some suggestions for the treatment of these problems are advanced.
THE MICROLOG CONTINUOUS DIPMETER
Authors: de Chambrier Pierre
Published: October 2002

Some of the methods used at the present time for determining the angle and the azimuth of the dip in the formations traversed by a borehole are based on correlations between three curves recording certain electrical characteristics of the formations, such as SP or resistivity, along the wall of the borehole in three equally spaced azimuths. With the conventional equipment used for the application of these methods, the measurements are made over separate intervals of depth. In the present paper, a new improved instrument called the MicroLog Continuous Dipmeter is described, wherein the three curves used for the determination of the dip are obtained with three MicroLog devices and wherein these three curves—as well as the orientation of the instrument and the inclination of the borehole—are simultaneously and continuously recorded. It is shown that with the help of this instrument more numerous dip determinations can be made in a given well with a higher accuracy and a greater recording speed. The paper is illustrated with field examples.
EXPLORATION HISTORY (PRIOR TO THE COTTON VALLEY DISCOVERY) OF THE RUSTON FIELD, LINCOLN PARISH, LOUISIANA
Authors: Walker J. Ryan
Published: October 2002

The first exploration in the Ruston field area that indicated the presence of a structural feature was a reconnaissance surface survey by the Arkansas‐Louisiana Gas Company in 1931. This paper, with maps, describes the surface work and the subsequent reflection seismograph surveys conducted by Arkansas‐Louisiana Gas Company in the area prior to the discovery of gas in the Cotton Valley formation. A comparison of the results of the surface and seismic work is made with the structure as revealed by present subsurface control.
SEISMIC MODEL STUDY OF REFRACTIONS FROM A LAYER OF FINITE THICKNESS
Authors: Press Frank , Oliver Jack , Ewing Maurice
Published: October 2002

Two dimensional model experiments on refractions from layers of finite thickness are described. Refractions can be unreliable for velocity and depth determinations when they occur with wavelengths which are large compared to the layer thickness. Discrepancies reported between refraction velocities and borehole velocities can be partially accounted for in this manner. Even simple two‐ and three‐layer models can show such effects as misleading second arrivals, echeloning of travel time curves, masked layers, and selective absorption in the overburden.
REVIEW OF PATTERN SHOOTING
Authors: McKay A. E.
Published: October 2002

Patterns of shot holes and patterns of seismometers are now standard technique in many areas currently being surveyed by the seismograph. This paper reviews some of these pattern arrangements and shows comparison records in a number of areas such as New Mexico, West Texas, western Oklahoma, Mississippi, and Florida. Although pattern shooting is definitely proven as a useful technique, it is not to be construed as a cure‐all for difficult shooting areas.
GEOPHYSICAL HISTORY OF THE GOOD FIELD, BORDEN COUNTY, TEXAS
Authors: McCarver Holland C.
Published: October 2002

The Good oil field, located in the southwestern part of Borden County, Texas, became a reef oil producer in April, 1949. The discovery well was drilled subsequent to a seismic program along a suspected reef trend. The discovery was made without benefit of reef reflections, and was based only on maps showing Permian draping. This technique offers interesting comparisons between seismic and subsurface data.
PERFORMANCE OF RESONANT SEISMOMETERS
Authors: Donn William L. , Ewing Maurice , Press Frank
Published: October 2002

A group of resonant vertical seismometers, each tuned to cover a part of the spectrum of microseism frequencies, has been operated for about one year. These instruments (a) clearly distinguish between simultaneous microseisms from two separate sources; (b) show an improved signal‐to‐noise ratio for microseisms from a single storm, permitting earlier detection of storm onsets; (c) show clearly the increase in period of frontal microseisms as cold fronts move seaward from the east coast of North America; (d) record only the envelope of the oscillations, which greatly facilitates measurement of intensity as a function of time; and (e) appear to be very useful tools in continued attempts at hurricane location by means of microseism amplitude studies. The performance of the instruments is demonstrated by seven case histories in which microseismic readings of seismometers tuned to different frequencies are related to the meteorological conditions which are apparently responsible for the microseismic activity.
GEOPHYSICS AS A SCIENCE
Authors: Gutenberg B.
Published: October 2002

“Geophysics” means “Physics of the Earth.” While in physics one tries to eliminate the effects of the gravitational, electric, and magnetic fields of the earth, in geophysics these fields, their properties and effects, and the structure and properties of parts of the earth are studied.
THREE‐DIMENSIONAL SEISMIC MODEL STUDIES
Authors: Levin F. K. , Hibbard H. C.
Published: October 2002

Elastic wave propagation in a two‐layer section has been studied with a solid two‐bed model and records resembling seismograms obtained for the four possible source‐detector configurations. Numerous events are identified. Among these, the shear waves are found to be surprisingly prominent. The amplitude of the ground roll falls off approximately as [Formula: see text] This is the amplitude‐range dependence expected for a surface wave. The ability of two in‐line detectors to reduce surface waves has been demonstrated.
THE MECHANISM OF GENERATION OF LONG WAVES FROM EXPLOSIONS
Authors: Dix C. Hewitt
Published: October 2002

Cagniard’s method is applied to the numerical calculation of the vertical displacement due to a point source in a semi‐infinite elastic solid medium at three points on a vertical line through the source. The source is a step in the scalar displacement potential. From these calculated responses the response for any physically possible spherically symmetric source can be computed by application of the Duhamel integral. Clear evidence of backward transmission of transverse wave energy is found along the vertical axis through the source. This, together with the energy of the longitudinal waves, also transmitted backwards, accounts for the mechanism by which energy is held near the source and near the free surface long enough to account for the generation of long period surface waves. This mechanism of generation of long period surface waves is not restricted to the free surface case. Any good reflector, which also generates secondary transverse waves from longitudinal primary waves, will serve the purpose. It is suggested that this gives a clue to the mechanism of the formation of “ground roll” in many practical cases.
THE STRUCTURE OF THE NOISE BACKGROUND OF A SEISMOGRAM
Authors: Horton C. W.
Published: October 2002

It is postulated that the noise background of a typical seismogram is the result of the arrival at random times of a large number of small reflections which are reflected from small scatterers distributed throughout the earth. It is shown on the basis of this assumption that if one knows the shape of a typical reflection, one can calculate the statistical parameters of the seismogram trace. Conversely, if one has the experimental autocorrelation function, the shape of the individual reflections can be determined. This analysis has been applied to a vertical spread of three geophones located 10, 75, and 125 feet below the surface. The shapes of the individual reflections were determined for the two deeper geophones. These curves show that the disturbances detected by the deeper geophone have a significantly smaller dominant frequency.
ATMOSPHERIC ELECTRICITY AND GEOPHYSICAL OPERATIONS
Authors: Fordham Glenn W.
Published: October 2002

The safety hazards of lightning to seismic crews using explosives are well known. Lightning is a result of high potential gradients in the atmosphere. These high gradients, which accompany stormy weather, can be detected by measuring the corona‐discharge current from a sharp metal point called a point collector. Oscillograms of point‐collector currents taken during thunderstorms may be a definite aid to field personnel in determining when lightning is imminent. Many more data are needed. It is hoped that others in the industry will take similar measurements and pool the data thus obtained.
IN SUPPORT OF THE AMERICAN GEOLOGICAL INSTITUTE
Authors: Longwell Chester R.
Published: October 2002

Last year the number of member societies in the American Geological Institute was increased to 13 by admission of the Association of Geology Teachers. The youthful AGI, therefore, reminds us of our country at an early stage, when 13 independent colonies came to realize the advantage of standing together. What exactly is the AGI, and what are the prospects that it will improve the status of all earth science?
THE COMPOSITION OF REFLECTIONS
Authors: Woods J. P.
Published: October 2002

When the traces on a seismic reflection record all show about the same deflection at about the same time, the line‐up is marked and called a seismic reflection. An important fact is forgotten. The fact is that the reflection seen on the record is nearly always a composite of the various reflections caused by a set of closely spaced reflecting layers. When the arrangement of the layers in the set changes, then the various reflections add together in a different way, and the character of the composite reflection seen on the record changes. A series of artificial seismic records have been made to show this composition of reflections. The records were made by connecting a standard reflection seismograph to an acoustic model. The model was a three hundred foot length of steel pipe with input and output transducers at one end. Records were made for a wedge, a pinch‐out, a complex of thin layers, a sand bar, layers corresponding to well resistivity logs, and a regular layer system.
A COMPARISON OF ADDITIVE AND MULTIPLICATIVE COMPOUNDING
Authors: Dyk Karl
Published: October 2002

Additive and multiplicative compounding of seismometer outputs are compared. In the equations developed for multiplicative compounding some terms involve products of signal and noise, and an arbitrary division of these terms between signal and noise is made to facilitate handling. Under the assumptions made it is developed that for low signal‐to‐noise ratios (less than 0.8) additive compounding provides a greater improvement in signal‐to‐noise ratio than does multiplicative compounding unless large numbers of units are compounded.
PROSPECTING FOR CHROMITE WITH GRAVIMETER AND MAGNETOMETER OVER RUGGED TOPOGRAPHY IN EAST TURKEY
Authors: Yüngül Sulhi
Published: October 2002

From 1952 to 1954 gravity and magnetic surveys were made in Turkey over the concessions of the Eastern Chromite Works to discover new chromite reserves in a region of rugged topography and complicated geology. As a result of these surveys a new chromite ore body of 250,000 tons was discovered at the bottom of an open cut beneath a thin horizontal sheet of chromite. It is shown that gravity prospecting is a more promising technique for locating relatively large chromite masses, even over rugged topography, than might have been expected. The terrain corrections, which constitute the major part of the computations, must be simplified and it is important that the correct surface densities be employed. In addition, difficulties arizing from the high and variable magnetic susceptibilities in serpentines must be surmounted. The mass of chromite estimated from the gravity results agrees well with the amount found by subsequent drilling.
UNUSUAL REFLECTION EVENTS IN OFFSHORE SEISMIC WORK
Authors: Ellis L. G. , Winterhalter A. C.
Published: October 2002

A number of unusual reflections were recorded during a reflection seismograph survey by the Sun Oil Company in the Gulf of Mexico. These reflections are such as to indicate horizontal travel paths. A limited amount of work was done to try to determine the nature of the reflecting sources. Although conclusive evidence as to their exact nature was not obtained, this work indicates the sources are associated with rather small areas of the Gulf floor. Sonic depth finder recordings over some of these areas can be interpreted as indicating they are small silt filled depressions.
COMMENTS ON PAPER, “RESISTIVITY OF SANDSTONES AS RELATED TO THE GEOMETRY OF THEIR INTERSTITIAL WATER” BY F. M. PERKINS, JR., J. S. OSOBA AND K. H. RIBE
Authors: Wyllie M. R. J. , de Witte A. J.
Published: October 2002

The experimental data presented in the above paper are of interest and value. Nevertheless, it is of some importance to note a basic claim made by the authors; namely, that they can measure the tortuosities of porous media experimentally. This claim, we believe, cannot be substantiated. We shall demonstrate below why we think the claim is unjustified. It is necessary first to point out that the paper under discussion is based on the reasoning presented originally by Winsauer, Shearin, Masson and Williams. Thus what is said of the present paper applies with equal strength to the earlier work.
RESISTIVITY STUDIES OF METALLIFEROUS SYNTHETIC CORES
Authors: Mandel Peter , Berg Joseph W. , Cook Kenneth L.
Published: October 2002

The observed resistivities of synthetic cores comprising disseminated test lead particles, quartz sand grains, and commercial cement (25% by volume) and saturated with NaCl solutions are apparently best represented by a relationship similar to that of an electrically parallel circuit. The empirical relationship that best approximated the experimental data is: [Formula: see text], where [Formula: see text], is the observed resistivity of the core; [Formula: see text] is the resistivity of the lead; [Formula: see text] is the formation factor that the core would have if none of the solid materials were conductive; [Formula: see text] is the resistivity of the saturating conductive fluid; and α is a parameter dependent upon the fractional volume of the fluid [Formula: see text], the fractional volume of lead [Formula: see text], and other factors. These experiments indicate that α can be approximated as follows: [Formula: see text], where C and K are “constants” for these particular experimental conditions. It was found that the observed resistivity varies markedly with changes in either lead content or the fractional volume of saturating conductive fluid. At low values of the fractional volume of lead, the current conduction through the cores is largely electrolytic, and the observed resistivity is strongly influenced by changes in the fractional volume of the saturating fluid. When the fractional volume of the saturating fluid is maintained relatively constant and the lead content is increased, the observed resistivity decreases because some of the current is conducted through the lead particles by electronic conduction.
ELECTRICAL RECORDER FOR SEISMIC DATA
Authors: Hadley C. F. , Eisler J. D.
Published: October 2002

A method of making multitrace seismic records using electrically sensitive paper is described. The record is immediately available for use without any type of processing. A disk carrying wire brushes on its periphery is revolved with its axis parallel to the direction of the motion of the electrical paper. The paper is pulled under the scanning disk and is shaped so that brushes remain in contact with it. Short electrical pulses are fed to the brushes to produce a number of traces composed of closely spaced dots. The position of the dots is determined by the time of occurrence of the pulses. This time is a function of the amplitude of the seismic signal. Timing lines are placed on the record by feeding a series of dots to all brushes. Provision is made to count down and emphasize the fifth and tenth timing lines. A system of multiplexing is used to employ each brush on many traces and thus reduce the rotational speed of the rotating disk. This recorder has proved its usefulness in reproduction of magnetically recorded seismic data.
PROPAGATION OF AN ELECTRIC PULSE THROUGH A HOMOGENEOUS AND ISOTROPIC MEDIUM
Authors: Bhattacharyya Bimal Krishna
Published: October 2002

The paper discusses the propagation of a step‐function pulse in a medium characterized by the three electric constants, permittivity ε, permeability μ and conductivity σ. The effect of the displacement current on the propagation is fully taken into account. Expressions of electric and magnetic fields are determined. It is shown that the time of travel of the pulse and the initial and final values of any one of the non‐vanishing field components (all of which can be measured) fully specify the values of conductivity and permittivity of the medium.
DEEP‐HOLE GEOPHONE STUDIES
Authors: Levin Franklyn K. , Lynn Ralph D.
Published: October 2002

Seismic surveys have been made in eight widely separated wells with two types of wall‐coupled geophones. These geophones accurately detected and reproduced elastic waves traveling in the earth. Both direct (initial) pulses from shots and reflection events were studied. The complexity introduced into the initial pulses by secondary reflections varied from well to well. Amplitude decayed as the negative 2.4 power of travel time. Pulse‐broadening caused by selective absorption of high frequencies was found. Different wells showed amounts of broadening ranging from nearly complete to that indicating little absorption of high seismic frequencies. Reflections from interfaces below the geophone were traced to their origin in the earth. At three wells, the same reflections were found on surface seismograms giving an identification of surface‐detected reflections and of reflector depth. Multiple reflections were distinguished from direct reflections and were found to mask the latter at four wells. In one case, multiple reflections were identified with events on surface records. Reflection coefficients found for direct reflections averaged 0.36. Accurate velocity surveys of the wells resulted from this work.
INTERRELATIONSHIPS BETWEEN MAGNETIC ANOMALY COMPONENTS
Authors: Affleck James
Published: October 2002

The relationships between the various magnetic anomaly components are developed from fundamental theory. A symbolism is introduced which permits expression of the relationships in algebraic form. These techniques have been found useful in predicting anomaly shapes for any magnetic latitude and in simplifying calculations of aeromagnetic or other component intensity anomalies for rock masses. Two examples of the application are shown.
SEISMIC MODEL EXPERIMENTS WITH SHEAR WAVES
Authors: Evans J. F.
Published: October 2002

The experimental study of shear waves in the earth has been limited by the difficulty of producing them in sufficient strength. However, sensitive piezoelectric shear plates can now be made which enable experimentation with shear waves using small‐scale seismic models. Seismic model experiments serve to demonstrate the simplicity of SH‐shear wave reflections in a single homogeneous layer, the production of SH waves by an impulsive horizontal thrust, and the development of relatively high amplitude Love waves in a low‐velocity surface layer. The results of these model experiments with shear waves are in general agreement with and confirm theory. They also agree with the results of field experiments in the scattered cases for which comparison is available.
THE RESPONSE OF SEISMOMETERS IN SERIES AND PARALLEL CONNECTIONS
Authors: Seriff A. J.
Published: October 2002

Two similar seismometers connected in series with a load exhibit two independent or “normal” modes of motion. In the first mode the two coils move so that the voltages generated are almost equal and in phase, producing a large current in the circuit and considerable damping of the motion. This is the mode normally considered in designing the external damping circuit for series seismometers. In the second mode the coils move nearly 180° out of phase, produce a relatively small current in the circuit, and, consequently, experience very little damping in addition to their open circuit damping. Strong initial excitation of this mode can produce a sustained oscillation damaging to later parts of the seismic record. The usual mathematical description of this system, i.e., two harmonic oscillators coupled through their damping terms, readily yields approximate expressions for the size and damping of the load current in the case of nearly identical seismometers with little internal damping. For example, two such seismometers connected to a load producing large damping for the first mode will exhibit a damping of only [Formula: see text] in the second mode. Here [Formula: see text] and [Formula: see text] are the angular frequencies of the two separate seismometers, ω is the average angular frequency, and f is the fraction of critical damping for the first mode. Two seismometers connected in parallel can have considerable electromagnetic damping in both modes of oscillation. For n seismometers in series, there are n−1 modes which may be poorly damped. The frequencies of these modes are distributed so that one lies between each adjacent pair of the original uncoupled frequencies. The damping in each mode is of the order of [Formula: see text]. The steady‐state characteristic can be readily examined using the seismometer equivalent circuits. The result is strongly dependent on the mode of excitation. For example, if two similar seismometers are connected in series but only one is excited, the frequency characteristic shows both a maximum near the rms of the two seismometer frequencies and a minimum at the frequency of the seismometer not excited.
THE ELECTROSEISMIC EFFECT
Authors: Martner S. T. , Sparks N. R.
Published: October 2002

The electroseismic effect manifests itself as an electrical potential generated in the subsurface by the passage of seismic waves. It can be detected at the surface of the ground with electrode pairs. The time of occurrence of the voltage clearly distinguishes the effect from either the ionization potential produced at the time of explosion or the seismic electric effect produced coincident with the arrival of seismic waves at the surface of the ground. Evidence is presented which associates the electroseismic effect with the base of the weathered layer and demonstrates its characteristics in several areas and at various distances from the shotpoint. Its immediate utility appears to be that of determining the travel time through the weathered layer at the shotpoint.
DISCUSSION ON: LATERAL VELOCITY VARIATIONS NEAR BOREHOLES
Authors: Kaarsberg E.
Published: October 2002

The discrepancies between regular geophone‐type logs or surveys and continuous velocity surveys have been noted ever since the latter came into use. Hick’s speculations as to the cause of these discrepancies in terms of compositional and structural changes in the rock surrounding the borehole are, therefore, welcome. His description of the actual mechanism of alteration of shale velocity due to shale damage is, however, brief, and some additional and/or alternative causes, which could be considered, are given below.
SEISMIC VELOCITY DATA FROM TRINIDAD, B.W.I., AND COMPARISON WITH THE CARIBBEAN AREA
Authors: Higgins G. E.
Published: October 2002

The results of the velocity surveys made on four deep (±10,000 ft) wells in Trinidad are reported, together with summaries of the lithologic and stratigraphic data recorded by the wells. An unusual velocity inversion of 5,000 ft/sec between 2,500 and 5,000 ft depth is reported in one well, Moruga 15. The recorded data from the well surveys and from refraction surveys shot near the metamorphosed Northern Ranges in Trinidad are compared with published data reported by Worzel, Ewing, et al. in their refraction surveys within the Caribbean Sea, the Venezuelan waters near Trinidad, and Barbados. Comparison is also made with the results of refraction surveys in British and Dutch Guiana.
THE CORRECTION OF SEISMIC TIME MAPS FOR LATERAL VARIATION IN VELOCITY BENEATH THE LOW VELOCITY LAYER
Authors: Acheson C. H.
Published: October 2002

Lateral variation in velocity beneath the low velocity layer often causes time anomalies that obscure the true structural picture. A method of correction to a deep datum has been developed to minimize the spurious anomalies without affecting those caused by structure. This method makes use of the discovery that for any particular well in Western Canada, there exists a simple exponential relationship between time and depth so that the results of relatively shallow core hole velocity surveys can often be extrapolated to predict times to much greater depths. An example is given to show how this method was applied successfully to a particular problem area in Western Canada. It has since been used in several other places.
THE USE OF ACOUSTIC LOGS IN THE EVALUATION OF SANDSTONE RESERVOIRS
Authors: Pickett G. R.
Published: October 2002

It is shown that acoustic velocities in sandstones are primarily dependent on porosity, shaliness, and pressure differential between overburden and fluid pressures. Although there are undoubtedly other variables which have some effect on acoustic velocities in sandstones, usable porosity predictions can be made from acoustic borehole logs if measured velocities are corrected for effects of pressure differential and shaliness. A theoretical relation between acoustic velocity and pressure differential in a hexagonal packing of spheres has been empirically extended by correlation of laboratory measurements on cores with actual well‐bore measurements. A system of empirical relations among acoustic velocity, porosity, and self potential of sandstones is developed. Further, it appears that the resistivity of water in permeable rocks can be estimated from the velocity and resistivity of adjoining shales. When this is possible, the SP log can then be used to estimate the shaliness of a sandstone in order to correct velocities for porosity estimates.
MARINE SEEP DETECTION—A NEW RECONNAISSANCE EXPLORATION METHOD
Authors: Dunlap H. F. , Bradley J. S. , Moore T. F.
Published: October 2002

A number of major oil accumulations of the world are associated with oil or gas seeps. At the least, seeps prove the existence of mobile hydrocarbons in a basin. At the most, and when used with other geological and geophysical data, they can aid in locating exploratory wells. An effective and inexpensive instrumental technique for locating gas seeps has been developed for use in water‐covered areas. If a seep is present, some of the methane dissolves in the water as the gas bubbles rise to the surface. Currents spread this methane‐enriched water into a long plume. A boat samples the water continuously, operating over a grid laid out at right angles to the current. The gas dissolved in the water is broken out of solution, and trace concentrations of methane detected using an infrared analyzer. This equipment has detected seeps at distances as great as six miles. A novel system of locating using navigational radar is used in carrying out the survey. Several marine seeps surveys have been carried out using equipment mounted on various vessels ranging in size from a 14-ft outboard powered skiff to a coastwise freighter. Under most circumstances, the cost of the survey is a few cents per acre. In new basins, the method promises to be of considerable value in localizing areas of interest for more expensive exploration methods.
TWO‐DIMENSIONAL MODELING AND ITS APPLICATION TO SEISMIC PROBLEMS
Authors: Angona F. A.
Published: October 2002

Laboratory seismograms of a fault model demonstrate the mechanism for diffraction and clearly show the difference in amplitude decay and moveout between a reflection and a diffraction. The inverted order and the deflection to the side of reflected energy from a curved reflector with a buried focus is demonstrated. A comparison is made of seismograms from a simple fault model and from one combining a fault with curved reflectors leading to it. The curved surfaces increase the overlap of the reflected events and mask the fault. Modeling techniques, involving the control of the reflection coefficient between layers by thickness variations and the control of the propagation velocity through a layer by combining two or more materials into a laminated sheet, are demonstrated.
SUGGESTIONS FOR BETTER ELECTRIC LOG COMBINATIONS AND IMPROVED INTERPRETATIONS
Authors: Doll H. G. , Dumanoir J. L. , Martin Maurice
Published: October 2002

In modern electrical logging, several resistivity measuring devices are now available or are under development which cover a wide range of radial investigations. In order of increasing penetration, they include: a) The Proximity Log (a new tool for recording formation resistivity close to the wall of the hole). b) A new type of Laterolog having a shallow investigation and adapted for simultaneous recording with an Induction Log. c) An Induction Log appropriate for moderate invasion (e.g., the present 5FF40). d) A deep investigation Induction Log (e.g., the new 6FF40). All these devices have a high vertical resolution, and their readings are practically unaffected by the mud column. This paper deals essentially with the case of logging in fresh mud. A discussion is presented of the information which can be obtained on saturation, when combinations of respectively two, three, or four of the above listed devices are used. The general case where nothing is known about the depth of invasion is first considered: The combination of the Laterolog and deep investigation Induction Log, when compared with SP curve, permits visual recognition of most salt‐water‐bearing beds. With the addition of the Proximity Log, and medium investigation Induction Log, the effect of invasion can be estimated and the distinction of practically all water‐bearing and oil‐bearing beds is made possible. The possible presence of a low resistivity zone beyond the invaded zone can be detected and accounted for. The ratio [Formula: see text] can be determined, from which an estimation of saturation can be made. The value of [Formula: see text] can be furthermore derived, which gives another way of computing saturation if the formation factor can also be obtained, for example from the porosity given by a Sonic Log. In these combinations the 16 inch normal can be used instead of the Laterolog, when bed resistivities are not too high. In those regions where the depth of invasion is known from local experience, one or even two of the above devices can be omitted. The advantage of a logarithmic resistivity scale for a convenient and rapid visual interpretation of the logs is explained. Charts to be used in the above procedures are shown, and the discussion is illustrated with field examples.
RADIOACTIVITY LOGGING AND ITS FUTURE POTENTIAL
Authors: Mardock Edwin S.
Published: October 2002

The quantitative application of radioactivity logs for the estimation of formation petrophysical properties is dependent on certain fundamental factors which are discussed. It is difficult to avoid “hybrid” combinations of processes; for example neutron‐neutron and neutron‐gamma effects together, however, it is believed that the future of quantitative application of neutron logs depends to a large extent on the development of single component logging processes. Positive location of the sonde within the borehole for all types of logs needs further development. These improvements plus future developments in gamma‐ray spectral logs, neutron‐gamma spectral logs, neutron activation logs, and neutron inelastic scattering logs promise a bright future for radioactivity logging.
PRODUCTION WELL LOGGING TECHNIQUES
Authors: Bryant Harvey L.
Published: October 2002

Production well logging techniques provide information necessary for efficient and economical well production. The various techniques are summarized and grouped into the three phases of well production. Temperature logs, radioactive tracer logs and velocity logs are used to obtain cement tops and indications of cement channeling in well completion work. In well repair work encroaching gas and water may be located by various neutron logging techniques, the temperature log, the flowing fluid density log, the gamma‐gamma log and the conductivity log. Well evaluation work, including fracture location, injectivity profiles and productivity profiles can be facilitated by use of radioactive tracer logs and the flowmeter log. Field examples are presented to demonstrate usage of the many logging techniques. Interesting applications of the flowing neutron log are shown including multiple gas‐oil contact location, gas “coning” and dual completion logging operations. Location of water entry by the flowing fluid density log and the conductivity log are illustrated. The “Humble” flowmeter is briefly discussed. Future development trends in the field of production well logging conclude the paper.
ELECTRICAL ANALOG APPROACH TO DIPMETER COMPUTATION
Authors: Braun T. H. , Wheatley G. Y.
Published: October 2002

An electrical analog instrument has been developed to calculate dip and strike from continuous dipmeter logs. The particular model described is designed specifically for the Schlumberger CDM-P, or Poteclinometer, logs and it can be used with hole deviations of up to 36 degrees. Every control on this instrument corresponds to one of the recorded parameters of the dipmeter log. It is thus easy to see the effect of any one parameter on the resolved dip and strike. The instrument is portable and can therefore be used at the well site, if necessary, to make on‐the‐spot decisions regarding further drilling operation after a dipmeter log has been run. No elaborate training in procedure is required. The rapidity with which the computations can be made also permits a larger number of levels to be computed. This frequently results in more accurate information and a considerable saving in computation expense.
TWO‐DIMENSIONAL SEISMIC MODELS WITH CONTINUOUSLY VARIABLE VELOCITY DEPTH AND DENSITY FUNCTIONS
Authors: Healy John H. , Press Frank
Published: October 2002

A method for fabricating two‐dimensional ultrasonic seismic models with variable velocity and density is described. The method is justified theoretically. It is tested by comparing the experimental and theoretical dispersion of Rayleigh waves in a model of a two‐layered earth crust.
NUMERICAL RESISTIVITY INTERPRETATION: GENERAL INHOMOGENEITY
Authors: Vozoff K.
Published: October 2002

A linear approximation is developed for the equation of conduction in a medium where resistivity is an arbitrary function of x, y, and z. This is applied by assuming the earth to be subdivided into small, homogeneous blocks of arbitrary resistivity. Under this approximation, the apparent resistivity is just the sum of the effects of the individual blocks. The equations are linear, and surface apparent resistivity data can be inverted to yield block resistivities. The quality of the approximation has been checked by comparison with model measurements in two situations: remote current source (telluric method), and local current source (resistivity method). It was found that the results are satisfactory provided that the proper type of expression is used for the effect of the resistivity contrast of each block.
HEAT FLOW IN PENNSYLVANIA AND WEST VIRGINIA
Authors: Joyner William B.
Published: October 2002

In order to obtain heat‐flow values for six wells in Pennsylvania and West Virginia a simple technique was developed for estimating thermal resistivities from well‐sample logs. This technique made use of average resistivity values for various categories of sedimentary rocks. The averages were calculated from available resistivity measurements on rock specimens, many of which did not come from the region in which the wells were located. The results indicate that, allowing for error in the estimates, the heat flow at the wells lies between 1.1 and [Formula: see text]. The problem of developing a more accurate technique for estimating resistivity is discussed. Such a technique would be valuable in extending our knowledge of the earth’s heat flow.
AN INTEGRATION TECHNIQUE FOR AIRBORNE GRAVITY GRADIENT MEASUREMENTS
Authors: Paterson Norman R.
Published: October 2002

For some purposes it may be desirable to work with the gravity force g rather than its vertical gradient g′. A simple method has been tested by which measurements of g′ on a plane surface can be integrated to produce values of g anywhere in space above the plane of measurement. The method appears to show promising results.