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56th EAEG Meeting
- Conference date: 06 Jun 1994 - 10 Jun 1994
- Location: Vienna, Austria
- ISBN: 978-90-73781-05-4
- Published: 10 June 1994
1 - 20 of 537 results
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A Discussion on the depth of dynamite source
Authors H. Amano, K. Watanabe and T. OtsukaThe dynamite has been used as the seismic source in many surveys. It has been reported that the amplitude and signature of seismic waves generated with the dynamite are affected not only by the charge size but also by the depth of the energy source (e.g., Winkel, 1989). The depth of the dynamite source is usually selected based only on the preliminary shots which are examined as one of the field tests. The amplitude and signature variation with the source depth is considered to be mainly dependent on the difference of the surrounding conditions of the energy source. In the field of civil engineering, the "soil test" has been caried out as a conventional method to investigate the condition of the ground. In this paper, we discuss the relationship between the result of soil test and the signature of seismic waves generated with the dynamite.
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Computerized refraction seismic analysis (RSA) and its application to static correction calculation
Authors R. K. Fruhwirth, A. Kogler and R. SchmoellerThe refraction seismic method was introduced into geophysics in 1920 by L .Mintrop. The Orchid salt dome was the first oil field discovered 1924 by this method. The success of the seismic method in petroleum exploration and the financial background of this branche encourages the development of more and more detailed analysis methods in both, the reflection and refraction seismic method. The rather simple RSA methods using critical distance or intercept time are nowadays in the era of computerization replaced by more sophisticated methods like the Wave Front Method, the Plus Minus Method or the Generalized Reciprocal Method.
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Dual source vibroseis acquisition for 2D survey by using conventional and E-code sweeps
Authors R. Servodio and L. BertelliAGIP has successfully transferred in the 2D acquisition the Dual source Vibroseis technique to achieve high resolution, low cost, vibroseis 2D data, following the fruitful experiences carried out in 3D acquisition (L. Bertelli, R. Servodio, 1991 and L. De Luchi, R. Marshall, H. Werner, 1987). As well known the aim of the dual source technique is to improve field efficiency by increasing the production and reducing the survey duration and costs. As a matter of fact the application of the dual source methodology in our 2D survey allowed a cost saving of about 40% of the final acquisition costs without smearing final data quality.
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Measuring the performance of deployed geophones
Authors R. A. Brook, M. L. Abrams, P. E. Carrol, G. D. Fisseler and D. F. KratochvilOver the last three years there has been a significant improvement in the precision of seismic acquisition systems. The Instantaneous Floating Point amplifier a standard in the exploration industry for over 25 years, has been succeeded by the 24-bit converter. The introduction of high performance geophones with reduced harmonic distortion has continued to improve data precision.
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Testing a new kind of explosive for seismic acquisition in hard ground
Authors P. Fink, E. Herndler, A. Kogler and Ch. SchmidAustrian alpine hydrocarbon exploration was motivated by exploration successes within Triassic dolomites under the Vienna Basin as those dolomites are also present in the overthrusts of the Northern Calcarous Alps (Wessely 1988).
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Recording reliability in seismic exploration as influenced by geophone-ground coupling
Authors P. W. Maxwell, H. A. K. Edelmann and K. FaberThe large amount of information carried by the seismic signal can only be brought into play for seismic interpretation if geophones are able to follow the movement of the ground faithfully. This means that the bandwidth of the transfer function of the geophone and the ground must be as large as possible. Latest developments in data acquisition instruments open new perspectives towards larger bandwidths.
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Correction of nonlinear and phase distortions of vibroseismic signals
Authors M. B. Shneerson, K. L. Mitchel and A. P. ZhukovSeismic signals excited by vibrational sources are subjected to nonlinear and phase distortions decreasing effectiveness of vibrational seismic prospecting. The distortion intensity is the largest at low frequencies due to the fact that relative movements of vibrator baseplate exceed by far the magnitude of ground elastic deformation.
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Beyond conventional 3D - 3D Undershoot
Authors W. Apel, H. -J. Koch, Th. Krey, L. Florchinger and R. MarschallIn the year 1968 the first 2D - undershoots (lines 62A, 64) were acquired in the concession Rotenburg - Wedehof for DEUTSCHE TEXACO AG. The acquisition geometry was as follows: - ∆g = 25m on top of dome and 50m at each side, 24 channels, fold = 6
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Extending the macro model by incorporating fine-layering propagation effects
Authors R. E. Slot and C. P. A. WapenaarIn seismic migration the elimination of propagation effects from the seismic data plays a major role. A wave propagating through the earth will encounter 'large contrast' boundaries which are separated by sequences of thin layers with smaller contrasts. Usually the propagation effects are quantified by a macro model, which accounts for the large contrast boundaries but suffices with the average velocities -(and densities) of the thin-layering between these boundaries. Hence, the angle-dependent dispersion effects due to internal multiple scattering in finely layered media, which have been studied extensively (O'Doherty and Anstey, 1971 ; Burridge and Chang, 1989; Herrmann and Wapenaar, 1992), are neglected in a macro model. We investigate the possibility of replacing a finely layered medium by a homogeneous, anisotropic, 'effective' medium with anelastic losces, thus mimicking the angle-dependent dispersion effects, and allowing for these effects to be incorporated in a 2-D or 3-D extended macro model for true amplitude migration.
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The generalized primary representation of 3D seismic data from highly heterogeneous media
More LessIn seismic modeling as well as in seismic imaging it is common use to ignore the rapid spatial variations of the medium parameters at a scale much smaller than the seismic wavelength. In particular, for 2-D or 3-D heterogeneous media the following approach is frequently used: - Replace the true medium by a 'macro model' that contains piecewise smoothly varying medium parameters and a 'contrast model' that is a spatially band-lirnited of the difference between the true medium and the macro model. - Formulate an implicit integral equation for the wave field in which the macro model describes the 'propagation effects' (in terms of Green's functions) and in which the contrast model describes the 'scattering effects'. - Solve this equation iteratively. This yields an explicit integral representation of the wave field that is non-linear in the contrast parameters.
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Limitations of elastic wave rayleigh scattering by an inclusion
Authors R. Gritto, V. A. Korneev and L. R. JohnsenScattering of seismic waves is a fundamental process in the propagation of waves through the Earth. In recent years, numerous authors have turned to the theory of scattering to describe the complicated nature of seismograms that occur in various places, believed to be caused by inhomogeneities and sequences of layering within the structure of the Earth. Recently, Korneev and Johnson (1993a, 1993b) derived a solution for the scattering of an elastic P wave by a spherical inclusion of arbitrary contrast and developed asymptotic solutions for this problem.
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Reflection points and surface points
By F. K. LevinThe reflection point on the plane - x sin θ + z cos θ = D (1) and the corresponding midpoint of a surface spread are connected by the relation - (x´p - xc cos θ) / X cos Ф cos θ = (yp - y,) / X sin Ф = X cos Ф / 4(D-xc sin θ). (2) In equation (1), D is the depth to the reflector measured perpendicular to the reflector from the origin and θ is the dip angle. In equation (2), X is the source-to-receiver separation and Ф is the profile direction measured from the x axis. The center of the spread is at (xc, yc, 0) is a coordinate system with the z axis perpendicular to the surface. The reflection point is (x´p, yp, D) in a coordinate system with the z axis perpendicular to the reflector.
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Finite difference modelling of faults and fractures
Authors R. T. Coates and M. SchoenbergA fault or fracture can be modelled as a surface across which stress traction is assumed to be continuous, yet displacement is allowed to be discontinuous. The simplest model that accounts for the effect of such a surface on seismic waves takes the traction vector and the displacement discontinuity vector to be linearly related by a `fracture compliance matrix'.
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Building complex geologic models by recursively merging the parts
Authors W. Wiggins and U. AlbertinA geologic model of an exploration target is usually complex, containing spatially variant velocities, and surfaces across which the lithology may be discontinuous. These complex features are not revealed en masse, but are discovered individually as seismic imaging uncovers them. For example, a salt structure is usually imaged first with a sediment-only model, then with the top-of-salt added, then with the bottom-of-salt added. Correspondingly , a geologic modeling facility should accommodate this piecemeal addition of detail to the model.
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Ray field segment computation - An efficient and flexible wave propagation technique
By K. AstebolThere is an increasing interest in integration of ray-based wave propagation in different seismic procedures. This calls for efficient and robust ray modelling techniques. with flexibility to be integrated in a wide variety of applications. Traditionally, the ray calculation techniques have focused on the calculation of single rays. The two common techniques, ray shooting and ray bending, both basically search for a single ray between one shot and one receiver, and the search is repeated to simulate surveys. A more recent approach, the wavefront construction [1],[2], scans time step by time step through the rayfield, the entire field composed by the rays. Arrivals are recorded as the wavefront passes receivers. Ray modelling works on a geometrical model of the subsurface. It is assumed that the model consists of continuons, smooth velocity fields, separated by continuous and smooth interfaces. There are no restrictions on model geometry.
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Event-oriented velocity estimation based on pre-stack data in time or depth domain
Authors E. Iversen and H. GjoystdalIn this paper a new method of the reflection tomographic kind is described, with the purpose of estimating an improved macro-velocity field for pre-stack depth migration. We have implemented an event-oriented local approach of the `layer-stripping' type, in which the event representation is referring to the unmigrated time domain. Each event is defined in terms of a few characteristic parameters, depending on the sorting criterion applied to the seismic data.
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Seismic processing with consistant modules
Authors M. T. Taner and E. BaysalDigital processing of seismic data had its commercial beginring in early 1960's. Processing steps were gradually developed to inciude more sophisticated and computationally more expensive processes as computer capabilities were expanded. Reviewing the last two decades of processing steps we have seen that while some new processes were added to the stream, most of the processes were kept the same. In fact there were a number of processes which were left over from analog days. They are still in use in the field and as part of the processing sequence. Since the laws of evolution dictates that everything must change with time, we expect to have some evolutionary if not revolutionary changes in the seismic exploration technology. In order to have an overall realistic view of the processing sequence, we have to start from the objectives and work al/ the way back to the field data specifications.
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Detailed reservoir description by integration of well and 3D seismic data
Authors R. Allred, E. Poggiagliolmi and K. E. SvelaTemporal and lateral resolution of seismic data is principally determined bv the shape and duration of the propagating wavelet. Its accurate estimation and the ability to change its shape are both of paramount importance to achieve the maximum resolution afforded by the available bandwidth. An integrated multi-line, multi-well wavelet estimation and shaping procedure was performed at Heidrun field, located offshore Norway and operated by Conoco Norway, Inc. The procedure, a proprietary technique known as space adaptive wavelet processing, involves borehole analysis, extraction of wavelets at well locations and performs implicit spectral inversion to condition the seismic pulse to a common, broad band, zero phase wavelet.
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3D AVO Processing - Evolution of a processing sequence
Authors I. F. Jones, V. Mandanche, S. Campbell and S. LancasterThe use of seismic amplitudes has long been recognized as an important aid in the location of hydrocarbons. More recently, this has been extended to include the study of the variations of amplitude as the shot-receiver offset is changed.
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Zero-phasing marine data using one-parameter phase filters and kurtosis maximization
Authors G. Cambois and N. D. HargreavesA.purely empirical approach that has been used to the seismic and well data is to apply a set of trial phase rotations to the seismic data. With certain provisos on data requirements and available bandwidth such an approach can be automated by using a maximum kurtosis criterion to select the desired phase correction (White, 1986). Whilst there is no apparent theoretical reason why phase rotations alone should be sufficient to zero-phase processed seismic data, this very simple procedure can be surprisingly effective in many cases. In this paper we explore the physical justification for such a one-parameter phase-scan in terms of the nature of the error arising out of conventional deconvolution processing. We derive another set of one-parameter phase filters that are physically more meaningful and also allow zero-phasing of marine data through kurtosis maximization.
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