bluuebunny/crossref_metadata_2025_split huggingface dataset:
AN INTERACTION MODEL FOR ELASTIC WAVE PROPAGATION IN TWO‐PHASE MEDIA*
Authors: KUSTER G. T. 
Published: April 2006

AbstractThe effect of interactions among spherical inclusions on the effective propagation of long wavelength elastic waves in a two‐phase medium is investigated theoretically. Interactions are taken into account in an average sense via a generalized self‐consistent scheme. Bounds on the effective elastic moduli are obtained by overestimating and neglecting contributions of neighbouring inclusions. An intermediate model is proposed, which introduces the effect of interactions into the effective properties without requiring more information about the geometry of the medium than the relative volumes of the constituents.
TIME MIGRATION—SOME RAY THEORETICAL ASPECTS*
Authors: HUBRAL P. 
Published: April 2006

AbstractUsing an elementary theory of migration one can consider a reflecting horizon as a continuum of scattering centres for seismic waves. Reflections arising at interfaces can thus be looked upon as the sum of energy scattered by interface points. The energy from one point is distributed among signals upon its reflection time surface. This surface is usually well approximated by a hyperboloid in the vicinity of its apex. Migration aims at focusing the scattered energy of each depth point into an image point upon the reflection time surface. To ensure a complete migration the image must be vertical above the depth point. This is difficult to achieve for subsurface interfaces which fall below laterally in‐homogeneous velocity media. Migration is hence frequently performed for these interfaces as well by the Kirchhoff summation method which systematically sums signals into the apex of the approximation hyperboloid even though the Kirchhoff integral is in this case not strictly valid. For a multilayered subsurface isovelocity layer model with interfaces of a generally curved nature this can only provide a complete migration for the uppermost interface. Still there are various advantages gained by having a process which sums signals consistently into the minimum of the reflection time surface. The position of the time surface minimum is the place where a ray from the depth point emerges vertically to the surface. The Kirchhoff migration, if applied to media with laterally inhomogeneous velocity, must necessarily be followed by a further time‐to‐depth migration if the true depth structure is to be recovered. Primary normal reflections and their respective migrated reflections have a complementary relationship to each other. Normal reflections relate to rays normal to the reflector and migrated reflections relate to rays normal to the free surface. Ray modeling is performed to indicate a new approach for simulating seismic reflections. Commonly occuring situations are investigated from which lessons can be learned which are of immediate value for those concerned with interpreting time migrated reflections. The concept of the ‘image ray’ is introduced.
CORRELATION BETWEEN SEISMIC REFLECTION AMPLITUDE AND WELL PRODUCTIVITY – A CASE STUDY *
Authors: Hun F. 
Published: April 2006

AbstractThe results of specific processing of seismic sections on an actual oil field have proved that it is possible to find a link between a seismic parameter (amplitude of a reflecting horizon) and petrophysical characteristics of a reservoir whose changes modify well productivity.A good correlation appears between the values of good oil productivity and the weakness of the amplitudes of one horizon close to the oil producing layers.
SIGNATURE AND AMPLITUDE OF LINEAR AIRGUN ARRAYS *
Authors: NOOTEBOOM J. J. 
Published: April 2006

SummaryDuring the last few years many airgun arrays have been designed with the objective of generating a short signature of high amplitude. For linear arrays of non‐interacting airguns two rules have been derived that may help in the design or evaluation of airgun arrays. To achieve a short pressure pulse, the total available air volume has to be distributed over the individual guns in such a way that the tail of the signal, owing to the added bubble signals, becomes as flat as possible.When we think of ordering airguns according to volume, this flat signal tail can be achieved by designing the volumes such that the difference in bubble times of two adjacent guns is proportional to their volume to the power 2/3.The amplitude expected from a linear array of non‐interacting airguns is limited by the physical length of the array.A graph of measured values tends to confirm this relation.No relation has been found between the total volume of an array and its amplitude.The graph also detects inefficient use of available array length of existing arrays.
RADAR DETECTION OF BOREHOLES IN ADVANCE OF MINING*
Authors: TARANTOLO P. J. , UNTERBERGER R. R. 
Published: April 2006

AbstractBoreholes present a potential hazard to mining in rock salt mines. The only rock salt mine in England was almost lost when they mined into an unknown borehole open to an aquifer. Rock salt is a good transmitter of VHF radar waves, so a good method of detecting boreholes is by using radar probing. This paper investigates theoretically the detection of a borehole in advance of mining using two different radar systems, Bravo II and Charlie II. Bravo II has a peak power of 20 kW at 230 MHz and Charlie II has 3 W at 440 MHz. The borehole detectability depends critically on the radar wave attenuation in salt, which is characterized by its loss tangent, tan δ. The backscattering cross section σ of the borehole is also important. These parameters are related in the radar signal‐to‐noise equation which determines the signal‐to‐noise ratio (S/N) for a given range in salt to the borehole. Theoretically, in salt with a tan δ of 10‐3, Charlie II can detect (S/N= 3 dB) a 12.7 cm borehole 225 m in advance of mining while Bravo II, using only 100 W, can detect the same borehole 680 m ahead. These values are with the antenna E field parallel to the axis of the borehole. Theory shows this antenna orientation to be optimum for maximum detection probability. For salt with a tan δ of 2 × 10‐5, the smallest value measured for salt, Bravo II can detect the borehole up to 15.3 km using maximum power of 20 kW.
SEISMIC FACIES ANALYSIS CONCEPTS *
Authors: ROKSANDIĆ M. M. 
Published: April 2006

AbstractSeismic facies analysis makes use of different seismic parameters in order to get other than structural information. A review is given of possibilities and usefulness of seismic facies analysis in oil exploration.A seismic facies unit can be defined as a sedimentary unit which is different from adjacent units in its seismic characteristics. Parameters that should be taken into consideration in the seismic facies analysis are as follows: reflection amplitude, dominant reflection frequency, reflection polarity, interval velocity, reflection continuity, reflection configuration, abundance of reflections, geometry of seismic facies unit, and relationship with other units.Interpretation of seismic facies data may be either direct or indirect. The purpose of the direct interpretation is to find out geological causes responsible for the seismic signature of a seismic facies unit. So, the direct interpretation may be aimed at predicting lithology, fluid content, porosity, relative age, overpressured shales, type of stratification, geometry of the geological body corresponding to the seismic facies unit and its geological setting. The indirect interpretation is intended to reach some conclusions on depositional processes and environments, sediment transport direction, and some aspects of geological evolution (transgression, regression, subsidence, uplift, erosion).The results of the seismic facies analysis may be shown on seismic facies cross‐sections and seismic facies maps. Depending on the available seismic data and geological conditions in the area under consideration, the seismic facies maps may be of different types such as general seismic facies maps showing distribution of different seismic facies units, sand‐shale ratio maps, direction of cross‐bedding and paleo‐transport maps etc.Several kinds of seismic facies units and their geological interpretation are discussed as examples of seismic facies analysis.
PROCEDES DE FILTRAGE ET DE FOCALISATION DE CHAMP POUR LA DETECTION ELECTROMAGNETIQUE DES CARRIERES SOUTERRAINES *
Authors: DUBUS J. P. , CLICQUE D. , BAUDET J. , GABILLARD R. 
Published: April 2006

AbstractThe electromagnetic surface detection of underground quarries by classical methods becomes difficult when they are situated at depths greater than ten meters and when the thickness and conductivity of the superficial layers are irregular.The problem is tackled in two stages: at first using successive approximations, characteristics of the miscellaneous layers of a stratified medium are identified, and the quarries are then detected by observation of the conductivity changes of one of the lower layers. Computer interpretation, however, is necessary.The chances of detection of the quarries are considerably improved by a field localization method developed by us: computer interpretation is eliminated. The new aspect is an auxiliary transmitter which annuls the currents induced by the principal transmitter in the uppermost—generally more conductive—layers.The theoretical and experimental results show that the probability of detection of the quarries by this method are four times as high as by the classical one.
HARMONIC INVERSION OF AN AEROMAGNETIC ANOMALY FROM A REMANENTLY MAGNETIZED PRECAMBRIAN SCHIST BELT (KARNATAKA, INDIA) *
Authors: MISHRA D. C. 
Published: April 2006

AbstractThe conventional methods of magnetic interpretation consider in general the induced magnetization only. However, in a computer oriented inverse method, the direction of magnetization can be taken as arbitrary. Following this procedure, this study aims to present a realistic interpretation of an aeromagnetic anomaly from Chitaldrug Schist belt (Mysore, India) assuming a three‐dimensional configuration of the causative source possessing remanent magnetization. It further provides the direction of remanent magnetization of the source rock as obtained from the analysis of the magnetic anomaly. The total intensity map obtained delineates the surface and sub‐surface structures in the region and provides informations regarding the characteristics of primordial crust.
ATTENUATION OF COHERENT NOISE IN MARINE SEISMIC EXPLORATION USING VERY LONG ARRAYS *
Authors: URSIN B. 
Published: April 2006

AbstractThe use of arrays to separate primary reflections from unwanted coherent seismic events is common practice in land seismic surveys. Very long source and receiver arrays have been used recently to reduce the effects of waterbottom multiples on marine seismic data.The source array consists of five uniformly spaced identical subarrays, each with five different airguns, where the distance between the subarrays may vary from 20 m56 m. The volume of each subarray is 10.3 1 (630 cu.in.) which gives a total volume of the array of 51.5 1 (3150 cu.in.) operated at a pressure of 14 MPa (2000 psi). In order to have a flexible receiver system it was decided to implement the extended receiver array in data processing by computing a weighted sum of two to five traces. The hydrophone cable consists of fifty‐four channels with a group length of 50 m.Data shot with the superlong airgun array are processed by a combination of standard techniques and special procedures. In particular, the quality of the stack section is improved by using a weighted stack. The stack weights are computed by a program which takes into account the primary‐to‐multiple ratio.Comparisons with conventional data show significant improvements in data quality obtained by using the superlong airgun array. Examples show that the waterbottom multiples have been strongly attenuated and the deep seismic events have been enhanced.The combined array response function for dipping events is given in an appendix.
A FREQUENCY DOMAIN APPROACH TO TWO‐DIMENSIONAL MIGRATION *
Authors: BOLONDI G. , ROCCA F. , SAVELLI S. 
Published: April 2006

AbstractThe problem of the propagation of acoustic waves in a two‐dimensional layered medium can be easily solved in the frequency domain if the Dix approximation is used, i.e. when only the primary reflections are considered. The migrated data at a depth z are obtained by convolving the time section with a proper two‐dimensional operator dependent on z. The same result can be obtained by multiplying their two‐dimensional spectra and summing for all the values of the temporal frequency.The aspect of the operator in the time‐space domain has the classic hyperbolic structure together with the prescribed temporal and spatial decay.The main advantages of the frequency domain approach consist in the noticeable computer time savings and in the better approximation. On the other hand lateral velocity variations are very difficult to be taken into account. This can be done if a space variant filter is used in the time‐space domain.To reduce computer time, this filter has to be recursive; the problem has been solved by Claerbout by transforming the hyperbolic partial differential equation into a parabolic one, and using the latter to generate the recursion operator.In the presentation a method is given for the generation of recursive filters with a better phase characteristics that have a pulse response with the requested hyperbolic shape instead of the parabocli one. This allows a better migration of steeper dips.
EQUATIONS D'ONDE ET MODELES *
Authors: HEMON CH. 
Published: April 2006

AbstractThe method of finite differences is applied to the computation of multi‐dimensional synthetic seismograms. This paper gives a study of the mathematical and numerical formulations of the problem, the boundary conditions, the convergence conditions and how to simulate the source in both one solid or a liquid. It is shown that the numerical formulation chosen is valid both for direct and inverse problems (i.e. for modeling and migration). This formulation makes it possible to use the normal incidence reflection coefficients for P and S waves, whether they travel horizontally or vertically. The examples shown have been chosen on purpose in order to be easily interpreted. They do not give a full idea of the possibilities of the algorithm which allows to consider non‐planar interfaces, except close to the vertical axis.
A “PROCESSING DENSITY’TO CALCULATE MARINE BOUGUER GRAVITY FREE OF TOPOGRAPHIC VARIATIONS IN CASE OF UNKNOWN BOTTOM DENSITY *
Authors: MALZAC J. , ROUSSEAU A. 
Published: April 2006

AbstractIn marine gravity interpretation, the density required for the Bouguer correction is not easily measured, and, therefore, one often uses either standard values or extrapolates density from a station or a profile to an entire survey. If the real density varies, this leads to inconsistencies. In this paper a method is proposed to eliminate as much as possible the gravimetrical effects of real density variations. The principle is to apply Nettleton's method to the whole space, but also to use a continuously variable density in the Bouguer gravity computation. It is possible to avoid affecting real gravity anomalies by using stations situated on suitable area elements the optimal size of which is determined by the program. The density that is obtained is called “processing density’ because it is not a real one, but rather the resultant of the densities affect on each station. Use of the method is demonstrated on an example from the southeastern part of Bay of Biscay.
COHERENCY WEIGHTING—AN EFFECTIVE APPROACH TO THE SUPPRESSION OF LONG LEG MULTIPLES*
Authors: BUTTKUS B. 
Published: April 2006

AbstractLong leg multiples can be suppressed by a method which provides an alternative to weighted common‐depth‐point stacking and multichannel stacking filtering. The suppression is achieved by coherency weighting whereby the time‐dependent weighting factor decreases as the semblance of the multiple reflections increases.The algorithm of the method is described. Its efficiency is discussed in relation to the input data and results of its application to marine seismic data are presented.For practical application, the stacking velocity of the multiples has to be known. As the process is based on stacking velocities, different types of multiples can be handled, for instance water‐bottom multiples or internal multiples. The parameter analysis shows that the degree of multiple suppression can easily be controlled by adapting the parameters of the procedure to the field conditions.During the suppression of multiples, the primaries are saved according to the moveout differences between the two. The non‐linear behaviour of the process causes signal suppression and distortion effects, which have to be corrected by AGC normalization and low‐pass filtering.Among the various applications available, only the suppression of long leg water‐bottom multiples is treated here. The results show that their suppression on the basis of moveout differences is efficient even when standard length streamers are used in regions with water depth of up to 1500 m and more, if the stacking velocity of the primaries is about 10 to 20% higher than that of the multiples. Even if those parts of the primaries which are masked by the multiples are suppressed in the individual common‐depth‐point gathers by the procedure, the remaining primaries in the AGV stacked section are largely uncovered by the multiple suppression.
TIME‐VARYING PREDICTION FILTERING BY MEANS OF UPDATING*
Authors: RISTOW D. , KOSBAHN B. 
Published: April 2006

AbstractIn contrast to the conventional deconvolution technique (Wiener‐Levinson), the spike‐, predictive‐, and gap‐deconvolution is realized with the help of an adaptive updating technique of the prediction operator. As the prediction operator will be updated from sample to sample, this procedure can be used for time variant deconvolution. Updating formulae discussed are the adaptive updating formula and the sequential algorithm for the sequential estimation technique. This updating technique is illustrated using both synthetic and real seismic data.
MINIMUM ENTROPY DECONVOLUTION WITH AN EXPONENTIAL TRANSFORMATION*
Authors: OOE M. , ULRYCH T. J. 
Published: April 2006

AbstractThe Minimum Entropy Deconvolution (MED) technique of Wiggins (1977) represents a breakthrough in deconvolution and will undoubtedly find wide application in many fields. MED does not require any phase assumptions about the disturbing function and seeks a deconvolved output which consists of the smallest number of large spikes consistent with the input data.The efficiency of MED is much improved when an exponential transformation is incorporated into the algorithm. This is particularly true when the input traces contain additive noise. In this case the noise suppression characteristics of MED are considerably enhanced by the transformation and the identification of smaller spikes is improved. This paper also presents a kurtosis criterion of simplicity rather than the varimax norm introduced by Wiggins. It appears that for a multiple trace input the kurtosis measure leads to improved results.
SYNTHETIC SEISMOGRAMS AT NON‐VERTICAL INCIDENCE*
Authors: DOUZE E. J. 
Published: April 2006

AbstractSynthetic seismograms are usually computed for reflections from vertical incidence of P waves for a horizontally layered medium. In actual practice the angle of incidence departs from the vertical, as receivers are usually located at some distance from the source. At angles other than the vertical, the conversion of P‐ to S‐wave energy and changes in the reflection coefficient affect the shape of the synthetic seismograms. The effect of non‐vertical incidence on synthetic seismograms is examined in this paper.Seismograms at non‐vertical incidence have been computed using the plane‐wave approach of Haskell (1953) for a layered medium. The use of plane waves is an approximation to the actual case of spherical wavefronts from a surface source.Using plane‐wave theory, the expected wave forms as a function of angle of incidence were computed numerically for several simple models. The results indicate that the synthetic seismograms do not change significantly for angles of incidence between o and 25 degrees. For larger angles the changes in the wave forms may be severe. The effect is more pronounced for high‐velocity layers than for low‐velocity layers.
THEORETICAL AND EXPERIMENTAL INVESTIGATIONS FOR CAVITY RESEARCH WITH GEOELECTRICAL RESISTIVITY METHODS*
Authors: MILITZER H. , RÖSLER R. , LÖSCH W. 
Published: April 2006

AbstractThe exact localization of subterranean cavities and the determination of their dimensions is very important for the planning of geotechnical and mining activities. It is a complicated geophysical task often at the limit of detection. Nevertheless geophysical investigation is the only alternative to a dense and expensive grid of boreholes. This report tests the usefulness of geoelectrical resistivity methods for cavity detection under some new aspects. The basis for evaluation was a theoretical analysis of different conventional and focussing measuring arrays and of special arrays for a geoelectrical research between two boreholes.The limit of detectability of a cylindrical cavity of defined cross‐section and depth was calculated for the different measuring arrays on the basis of computation of the apparent resistivity ρa. Furthermore, the influence of possible errors (current supply of the electrodes and the distance between the electrodes) is discussed for focussed systems.The second part of the article is directed at the behaviour of the apparent resistivity ρa, the disturbing potential δVd caused by the cavity and the normal potential δV0 of the measuring array all in relation to a homogeneous earth. Some new results are presented.In the last part of the article theoretical results are compared with some field measurements.
END CORRECTIONS IN POTENTIAL FIELD MODELING*
Authors: RASMUSSEN R. , PEDERSEN L. B. 
Published: April 2006

AbstractA general treatment of end corrections in gravity and magnetic modeling is presented. The well‐known 2‐D formulae of Talwani and Talwani and Heirtzler become slightly changed to represent a 2 1/2–D body, i.e. a body of polygonal cross section with the tails In the strike direction cut off.
THE STUDY OF THE GENESIS OF SURFACE WATERS BY OBSERVING THEIR ELECTRICAL RESISTIVITIES*
Authors: OGILVY A. A. , BERRY B. L. , KUZMINA E. N. 
Published: April 2006

AbstractSpecific electrical resistivity of natural waters contains information on their genesis. The authors propose to conduct mass and regime observations of this parameter in river and stream beds.The electrical resistivities in streams flowing from under a glacier reveal details formed at the same time as the glacier. Observations in the beds of big rivers show a gradual increase in water salinity overlain by reductions by inflowing glacial waters.The diurnal and annual trend of changes in the electrical conductivity of water associated with the change in the balance of glacial and ground waters has been established near to glaciers.Resistivity observations help to locate discharge sites of sub‐permafrost waters, for water.
AUTOMATIC DECONVOLUTION OF GRAVIMETRIC ANOMALIES*
Authors: BICHARA M. , LAKSHMANAN J. 
Published: April 2006

AbstractExisting techniques of deconvolution of gravity anomalies are principally based on upward and downward continuation of measured fields. It can be shown that a unique set of linear filters, depending only on geometrical parameters, relates density distribution at a given depth to gravity measured on the surface. A method to compute the filter coefficients is developed. Very accurate reconstitution of theoretical models of intricate shape, prove the validity of the linear relationship. One of these sets of linear filters is applied to a field case of underground quarries.