bluuebunny/crossref_metadata_2025_split huggingface dataset:
TRANSIENT FINITE INTEGRAL POINT SOURCE RESPONSE FROM A PLANAR ACOUSTIC INTERFACE: THE CAUSALITY APPROACH*
Authors: HUBRAL P. , TYGEL M. 
Published: April 2006

ABSTRACTPoint source reflection/transmission responses from planar interfaces based on the Sommerfeld‐Weyl integral are causal and are given in the form of a solution integral with an infinite integration limit. They can be simply transformed to integrals with a finite limit by an approach that takes into account causality as well as time‐symmetry aspects. To introduce the fundamental principles involved, the transformation is applied to the simple case of a point‐source response from a planar acoustic interface. For a point source above a planar interface separating an upper and lower acoustic half‐space of velocity c1and c2 the inhomogeneous plane waves in the Sommerfeld‐Weyl source representation do not contribute to the final result if c1≤c2 and only a limited spectrum of inhomogeneous plane waves comes into play if c1c2.
WAVE FIELD EXTRAPOLATION TECHNIQUES FOR INHOMOGENEOUS MEDIA WHICH INCLUDE CRITICAL ANGLE EVENTS.
Authors: WAPENAAR C. P. A. , BERKHOUT A. J. 
Published: April 2006

AbstractWave field extrapolation including critical angle events in modeling, migration and inversion can be handled with algorithms based on both the one‐way wave equations and the two‐way wave equation. It is shown that for 1‐D inhomogeneous media, critical angle events as well as multiple reflections may elegantly be included in pre‐stack modeling, pre‐stack migration and velocity inversion. For 2‐D and 3‐D inhomogeneous media a powerful pre‐stack migration scheme can be developed which includes critical angle events as well as multiple reflections. Finally, suggestions for practical applications are given.
QUANTITATIVE INTERPRETATION OF PULSE EM MEASUREMENTS OVER A WEATHERED KIMBERLITE DIATREME*
Authors: RAI S. S. , BHATTACHARYA B. B. 
Published: April 2006

AbstractThe application of pulse EM and MAXMIN II systems in search of a kimberlite diatremes under conducting cover has been demonstrated through a field example. The effectiveness of the PEM system in the search for conductive zones of economic importance and in discrimination against geologic noise such as overburden has been investigated. The transient observation has been transformed to equivalent half‐space resistivities at various times. The feasibility of mapping thin conducting overburden using the PEM system has been studied by inverting the transient measurement to the thin infinite horizontal sheet conductance. The PEM measurement is shown to be an economic and effective tool for shallow geoelectric mapping.
TESTING THE TRANSIEL METHOD IN MINERAL AND GEOTHERMAL EXPLORATION*
Authors: DUPRAT A. , ROUDOT M. , SPITZ S. 
Published: April 2006

ABSTRACTTransiel is the name given to a qualitative, time domain induced polarization (IP) method. The aim of the method is twofold: to locate and to distinguish between deep and shallow polarizable media. This discrimination is based on the data analysis, which distinguishes Transiel from the conventional IP methods.Two case histories are presented: one related to mineral prospecting and the other to geothermal exploration. The information supplied by Transiel on the deep polarizable layers is checked at each test site by an independent inversion of the recorded transients.At the mineral test site, the method correctly predicts the target location. In this particular survey, the maximum penetration depth of the method is 700 m. At the geothermal test site, a fair correlation is found between IP anomalies and the productive wells. Since the method's penetration depth does not exceed 500 m, we believe that the observed IP anomalies are related to reduction phenomena occurring in the overburden and leading to pyrite formation. We suppose that these phenomena are caused by thermochemical exchanges between the reservoir and the overburden above zones of high reservoir permeability.
SAMPLING AND MINIMUM PHASE FROM BOTH A CONTINUOUS AND DISCRETE POINT OF VIEW*
Authors: MITCHELL A.R. , STOKES W.D. 
Published: April 2006

AbstractExamples show that the sampling operation–i.e., the change from the continuous time domain to the discrete time domain–does not necessarily preserve the minimum‐phase property. Further examples can be constructed to show that the resampling operation on the discrete time domain does not necessarily preserve the minimum‐phase property. Finally it can be shown that the minimum‐phase property can be either created or destroyed by sampling or resampling.
SOLUTION OF THE VSP ONE‐DIMENSIONAL INVERSE PROBLEM*
Authors: MACE D. , LAILLY P. 
Published: April 2006

ABSTRACTThe acoustical impedance distribution of the substratum, or equivalently, the reflection coefficient sequence, is determined from VSP data. This nonlinear inverse problem is solved by a least‐squares method.As the wavelet is unknown, the impedance distribution and the Neumann boundary condition (which characterizes the excitation of the medium) are simultaneously identified.The inversion method is applied to synthetic and field VSP's; the result is satisfactory, even when strong noise corrupts the data, provided that a suitable constraint on the impedance distribution is introduced in order to ensure the stability of the inverse problem.The reliability of the inversion result in the case of field VSP, is confirmed. Some ways in which this result may be used are illustrated (calibration of the seismic surface data, multiple identification, prediction ahead of the bit).
STATISTICAL MULTIVARIATE ANALYSIS OF AIRBORNE GEOPHYSICAL DATA ON THE SE BORDER OF THE CENTRAL LAPLAND GREENSTONE COMPLEX*
Authors: LANNE E. 
Published: April 2006

ABSTRACTStatistical multivariate methods for the integrated processing of airborne geophysical data were tested. The data consisted of magnetic, electromagnetic and gamma radiation measurements, to which cluster analysis, principal components analysis and discriminant analysis were applied. Also, auxiliary variables were derived from the original ones and their value was tested. Although the frequency distributions of the data do not favour statistical analysis, the practical results are acceptable. Principal component analyses show geological and technical aspects that are difficult to obtain from the original observations. In cluster analyses, the sources of measured fields control the grouping of variables. Discriminant analysis was applied to the automatic identification of rocks by geophysical data. The rocks investigated are metasediments and metavolcanics, some magnetic and others conductive. When all available geophysical data were included, correct identifications were made in more than 60% of cases. In particular, gamma ray observations were found to improve the discrimination of non‐magnetic and non‐conductive rocks. The geophysical similarity of rocks studied by cluster analysis depends on electrical and magnetic properties as well as on their origin; the content of radioactive elements in turn is related to the origin.
NONLINEAR COMPLEX RESISTIVITY OF SOME NICKEL SULPHIDES FROM WESTERN AUSTRALIA*
Authors: HALL S.H. , OLHOEFT G.R. 
Published: April 2006

ABSTRACTThe electrochemical transfer characteristics of nickel sulphides from six West Australian localities are examined by the nonlinear complex resistivity (nlcr) method. Ores are classified on the basis of their state of oxidation (supergene, transition zone and primary ores) in an equivalent mine water electrolyte; evidence is found for a systematic change of electrical response with oxidation that is symptomatic of electrochemical reactions varying from diffusion to charge‐transfer controlled processes. The analysis is based on the assumption that the Randies’ circuit is an effective model of a rock's electrical response in its natural electrolyte. Both complex impedance plane graphs and computer inversion are used to study the model. Harmonic distortion is a useful aid in this interpretation.
SIGNAL‐TO‐NOISE RATIO ENHANCEMENT IN MULTICHANNEL SEISMIC DATA VIA THE KARHUNEN‐LOÉVE TRANSFORM*
Authors: JONES I.F. , LEVY S. 
Published: April 2006

ABSTRACTThe Karhunen‐Loéve transform, which optimally extracts coherent information from multichannel input data in a least‐squares sense, is used for two specific problems in seismic data processing.The first is the enhancement of stacked seismic sections by a reconstruction procedure which increases the signal‐to‐noise ratio by removing from the data that information which is incoherent trace‐to‐trace. The technique is demonstrated on synthetic data examples and works well on real data. The Karhunen‐Loéve transform is useful for data compression for the transmission and storage of stacked seismic data.The second problem is the suppression of multiples in CMP or CDP gathers. After moveout correction with the velocity associated with the multiples, the gather is reconstructed using the Karhunen‐Loéve procedure, and the information associated with the multiples omitted. Examples of this technique for synthetic and real data are presented.
TOPOGRAPHIC REDUCTION OF GRAVITY MEASUREMENTS BY NUMERICAL INTEGRATION OF BOUNDARY INTEGRALS*
Authors: GRANSER H. 
Published: April 2006

ABSTRACTA numerical method for calculating the topographic reduction of gravity measurements is developed which follows the approximation of the topography by a single valued function. The method involves the conversion of the volume integral for the gravity effect into a two‐dimensional definite integral. The definite integral is partly solved by explicit, and partly by numerical, integration, using the Gauss‐Legendre quadrature formula. This method is well suited to calculating the topographic reduction of 50 to approximately 1000 m from the station–especially for microgravimetric surveys in areas of steeply sloping terrain. To test the method in practice it was applied in an area of rough relief in Keban (East Turkey).
PHASE ERRORS OF FINITE‐DIFFERENCE MIGRATION*
Authors: BEAUMONT C. M. , BOYCE J. F. , SILVA R. 
Published: April 2006

AbstractA quantitative analysis of the various approximations to the scalar wave equation used in seismic migration can be obtained by a study of the resulting phase errors. In the space‐time domain the effects of different modes of parameter optimization are displayed. In the space‐frequency domain the spatial derivatives may be expanded as a linear filter operator whose coefficients are determined by requiring that the resulting phase shifts agree with those that arise from planar wave solutions of the exact wave equation over a range of angles and frequencies.
TRACE INTERPOLATION IN SEISMIC DATA PROCESSING *
Authors: BARDAN V. 
Published: April 2006

AbstractTrace interpolation of spatially aliased seismic data is used to improve the quality of multi‐trace processing, especially that of migration. We consider non‐rectangular sampling lattices. After stating the real sampling requirements for (two‐dimensional or 3‐D) digitized signals, the paper explains geometrically the effect of migration and of the 2‐D dip filtering upon the aliased events, as well as our ability to interpolate traces from undersampled seismic data.
JOINT INTERPRETATION OF GRAVITY AND MAGNETIC DATA OVER AXIAL SYMMETRIC BODIES WITH APPLICATION TO THE DARNLEY BAY ANOMALY, NWT CANADA*
Authors: CHAVEZ R.E. , BAILEY R.C. , GARLAND G.D. 
Published: April 2006

ABSTRACTA method is presented for determining bounds of the properties of axial symmetric bodies from a finite number of gravity and magnetic observations based on Parker's theory of ideal bodies. Bounds on the density contrast and the intensity of magnetization are calculated as a function of depth to the top of the anomalous source, restricting the range of smallest possible solutions to fit the data.The model studied is approximated by an array of vertical annuli cylinders, each of uniform density and magnetization. Linear programming algorithms based on the ideal body theory were used to calculate the distribution of these parameters within the body.Simultaneous inversion of gravity and magnetic data is performed assuming a constant ratio between the density contrast and the intensity of magnetization and that a common body is responsible for both observed fields. The parameter k(|J|/δp) provides information about the rock type of the structure.Interpretation of gravity and aeromagnetic data from Darnley Bay, NWT, Canada, indicated the presence of a shallow ultrabasic intrusion.
INTERPRETATION OF TRANSIENT EM COMMON‐LOOP ANOMALIES BY RESPONSE CHARACTERISTICS*
Authors: OGILVY R.D. 
Published: April 2006

ABSTRACTTheoretically exact type curves for a semi‐infinite thin conductor are presented for various dip, angles, depth of burial and conductance. The study shows that the common‐loop response shape is sensitive to small changes in conductor dip, but is affected more subtly by comparable strike variations. For large sheet conductors a decrease in the strike angle results in a broadening but unlike that for a finite plate there is no reduction in peak amplitude. For dipping conductors, response asymmetry and the direction and magnitude of peak amplitude displacement can be used to assess the disposition and quality of the conductor. A generalized interpretation scheme is proposed, based on dimensionless response characteristics and normalized decay curves, to facilitate the rapid in‐field determination of conductor dip, conductance and depth of burial, for any time regime.
VERTICAL HETEROGENEITY AND MOVEOUT IN THE ONE‐DIMENSIONAL MEDIUM*
Authors: VETTER W.J. 
Published: April 2006

ABSTRACTSince the important contributions of Dürbaum and Dix, 30 years ago, velocity profile estimation procedures on horizontally layered and vertically heterogeneous media from seismic probing data have been based largely on hyperbolic moveout models and RMS and stacking velocity concepts. Re‐examination of the fundamentals reveals that quantitative velocity heterogeneity and canonical valocity profiles have been implicit factors for moveout modelling and for profile inversion in the use of the Dix procedure. Heterogeneity h is the ratio (and vRMS the geometric or harmonic mean) of the path‐average and time‐average velocities for a raypath or, in a more restricted sense, for the normal ray belonging to a velocity profile. The canonical profile for a given velocity profile or profile segment is a moveout‐equivalent monotonically increasing ramp‐like profile.The ramp or constant gradient in depth is the simplest velocity profile approximator which can explicitly accommodate velocity heterogeneity. A ramp model structure is detailed which facilitates moveout simulation and model parameter estimation, and the parametric effects are explored. The horizontal offset range is quantified for which this model can give good moveout approximations.
STUDIES OF ROADWAY MODES IN A COAL SEAM BY DISPERSION AND POLARIZATION ANALYSIS: A CASE HISTORY*
Authors: KRAJEWSKI P. , DRESEN L. , SCHOTT W. , RÜTER H. 
Published: April 2006

AbstractField data from two‐component in‐seam seismic measurements are used to study roadway modes and their interaction with reflected seam waves. Using the multiple‐filter technique to investigate the dispersion behaviour of the different waves, it can be shown that the roadway modes disperse very similarly to the related transmitted seam waves. However, because of the free surface of the coal face, the dispersion curves of the roadway modes show a velocity reduction and a slight shift to lower frequencies compared to those of the related transmitted seam waves. Polarization analysis using hodograms, rectilinearity and polarization angle confirms these results. The parameters found by polarization analysis can be used to design polarization filters which help to separate roadway modes and reflected events in the traveltime range of superposition in the presented field case.
HYBRID SEISMIC MODELLING: A TECHNIQUE TO COMBINE PHYSICAL AND COMPUTER METHODS FOR VERTICAL WAVE INCIDENCE*
Authors: MEISTER J. , DRESEN L. 
Published: April 2006

AbstractA hybrid seismic modelling technique has been developed to investigate complex geological phenomena. Those parts of a geological structure which are too complicated to be treated theoretically are studied by two‐dimensional physical models; other sections of the structure which can be treated theoretically, i.e., inhomogeneities in the vertical direction, are modelled by computer methods. A feedback process is used to combine the results of both physical and computer modelling.Horizontally layered coal‐seam models are presented to test the hybrid modelling technique for normal incidence. A comparison of the hybrid seismograms with pure synthetic seismograms shows an acceptable conformity for normal incidence. A hybrid zero‐offset section is shown to investigate a complex geological structure in the Ruhr coalfield in Germany.
MOVING SOURCE PROFILING (MSP)1
Authors: BRAUNER W. , DÜRSCHNER H. , KOOPMANN B. , MARSCHALL R. , PETERS K. 
Published: April 2006

ABSTRACTMoving source profiling is a modification of walk‐away vertical seismic profiling in which the source is moved along a line across a well while the signal is recorded in the well at a certain depth. The method was designed to better predict the target horizon below the drill bit and away from the well location. The method has several advantages in areas of complicated overburden.In overthrust regions, the receiver is placed below much of the complicated structure to minimize distortion of the reflected signal. The final seismic image is a depth presentation of the subsurface structure and stratigraphy based on wavefront calculations. This depth estimation is obtained without extensive processing of the recorded data. The final result is available within a few days and can help interpreters to decide if and where to sidetrack the well. The method is demonstrated using an example from the overthrust zone of the Lower Saxonian Basin and the Pompeckj's well in Northern Germany.
SEISMIC VIBRATOR MODELLING1
Authors: BAETEN G. J. M. , FOKKEMA J. T. , ZIOLKOWSKI A. M. 
Published: April 2006

ABSTRACTThe wavefield in, and at the surface of, a homogeneous, isotropic, perfectly elastic half‐space, excited by a traction distribution at the surface of the medium is investigated. The emitted wavefield is a spatial convolution of the surface tractions and the spatial impulse response. The properties of the wavefield in the far‐field of the medium are derived and it is shown that the far‐field particle velocity is essentially equal to a weighted sum of the time derivative of the integrated surface tractions, that is, of the components of the ‘ground force’. The theory is valid for an arbitrary geometry and orientation of the surface tractions, and is independent of the boundary conditions at the surface of the medium.The surface tractions are related to a source that consists of a mass distribution with an arbitrary force distribution imposed upon it. A boundary condition is introduced that accounts for the mass load and the forces applied to it but neglects vibrations within the mass. The boundary condition follows from the equation of motion of the surface mass load.The theory is applied to the Vibroseis configuration, using a P‐wave vibrator model with a uniformly distributed force imposed on top of the baseplate, and assuming that horizontal surface traction components are absent. The distribution of displacement and stress directly underneath the baseplate of a single vibrator and an array of vibrators is investigated. Three different boundary conditions are used: (1) assuming uniform pressure, (2) assuming uniform displacement, (3) using the equation of motion of the baseplate as a boundary condition. The calculations of the distribution of stress and displacement over the plate for different elastic media and several frequencies of operation show that only the results obtained with the mixed boundary condition agree with measurements made in the field.The accuracy of three different phase‐feedback signals is compared using synthetic data. Baseplate velocity phase‐feedback leads to huge deviations in the determination of the far‐field wavelet; reaction mass acceleration phase‐feedback looks stable but neglects the differentiating earth filter; and phase‐feedback to a weighted sum of baseplate and reaction mass accelerations becomes unstable with increasing frequency. The instability can be overcome using measurements over the whole baseplate.The model can be extended to a lossy layered earth.
MULTIFREQUENCY INVERSION OF INDUCTION LOGS1
Authors: KUTH CH. , NEUBAUER F. M. 
Published: April 2006

ABSTRACTThe concept of multifrequency induction logging simulations in the frequency range of 10 kHz to 1 MHz, applied to two‐dimensional, axial symmetric model geometries, is presented. The scalar Helmholtz equation has been solved by a finite‐element procedure. The model domain has been discretisized under the condition that the discontinuities in conductivity are represented by the nodes of the adjacent triangular elements. The modification of the signal distribution by the skin effect is illustrated for several models. Several sets of induction logs have been calculated with particular consideration of the frequency‐dependent conductivities and permittivities.The improvement of a multifrequency inversion technique, based on standard least‐squares methods, is shown for a two‐layer model including borehole and invasion zones. Using this improved inversion technique we can state, as an additional inversion parameter, the frequency dependence of each inverted rock conductivity.
PRINCIPLES AND APPLICATION OF MAXIMUM KURTOSIS PHASE ESTIMATION1
Authors: LONGBOTTOM J. , WALDEN A. T. , WHITE R. E. 
Published: April 2006

ABSTRACTMethods of minimum entropy deconvolution (MED) try to take advantage of the non‐Gaussian distribution of primary reflectivities in the design of deconvolution operators. Of these, Wiggins’(1978) original method performs as well as any in practice. However, we present examples to show that it does not provide a reliable means of deconvolving seismic data: its operators are not stable and, instead of whitening the data, they often band‐pass filter it severely. The method could be more appropriately called maximum kurtosis deconvolution since the varimax norm it employs is really an estimate of kurtosis. Its poor performance is explained in terms of the relation between the kurtosis of a noisy band‐limited seismic trace and the kurtosis of the underlying reflectivity sequence, and between the estimation errors in a maximum kurtosis operator and the data and design parameters.The scheme put forward by Fourmann in 1984, whereby the data are corrected by the phase rotation that maximizes their kurtosis, is a more practical method. This preserves the main attraction of MED, its potential for phase control, and leaves trace whitening and noise control to proven conventional methods. The correction can be determined without actually applying a whole series of phase shifts to the data. The application of the method is illustrated by means of practical and synthetic examples, and summarized by rules derived from theory. In particular, the signal‐dominated bandwidth must exceed a threshold for the method to work at all and estimation of the phase correction requires a considerable amount of data.Kurtosis can estimate phase better than other norms that are misleadingly declared to be more efficient by theory based on full‐band, noise‐free data.