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53rd EAEG Meeting
- Conference date: 26 May 1991 - 30 May 1991
- Location: Florence, Italy
- ISBN: 978-90-73781-03-0
- Published: 28 May 1991
1 - 50 of 315 results
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Interpolation beyond aliasing by (t,x)-domain PEFs
Authors J. F. Claerbout and D. NicholsA great many processes are limited by the simple statement of the spatial Nyquist requirement-that no wavelength be shorter than twice the sampling interval on the data wavefield. This condition forces costly expenditures in 3-D reflection data acquisition. The sirnple statement of the Nyquist requirement oversimplifies reallife. At the 1989 SEG meeting, S. Spitz showed astonishing 2-D interpolations that seem to violate the Nyquist requirement and so they give us a deeper understanding of it. The real Nyquist limitation is on the spectral bandwidth, not on the maximum frequency, and Spitz' results can be explained by saying that the bandwidth need not be contiguous. We often characterize data as "good" or "noisy" when we really mean it contains "few" or "many" plane wave events. For noisy data there is no escaping the simple form of the Nyquist limitation but with good data it seems we can.
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A semblance-guided median filter
Authors E. E. Reiter and M. N. ToksözWe describe and implement a slowness selective median filter based on information from a local set of traces. The filter is constructed in two steps, the first being an estimation of a preferred slowness and the second the selection of a median or trimmed mean value to replace the original data point. A symmetric window of traces is selected about each trace to be filtered and the filter repeatedly applied to each time point. The preferred slowness is determined by scanning a range of linear moveouts within the user specified slowness passband. Semblance is computed for each trial slowness and the preferred slowness selected from the peak semblance value.
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3D Reconstruction of irregularly sampled wave fields
Authors N. A. Kinneging, A. J. W. Duijndam and L. OnkiehongA complication in 3D marine acquisition is that streamer feathering causes a crossline distribution of the actual midpoints. In conventional processing the individual traces are gathered in bin sorts and stacked after NMO correction. The stacked traces are posted at the centre of the bin, thus causing a posting error. This approach has some disadvantages. Depending on the feathering conditions some bin sorts will be overpopulated, while others will be underpopulated producing inconsistent stacking responses. The binstack smears the data over the bin area and thus puts a limit on the resolution. On the other hand this latter effect may be considered as a kind of spatial anti-alias filter.
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The impact of processing on the APF.VO responses of a marine seismic dataset
Authors A. Mazzotti and G. RavagnanIt is weIl known that the diagnostic potential of seismic data may be severely dependent on the acquisition and processing procedures. This is certainly true for any kind of interpretation approach or inversion algorithm but it becomes of the utmost importance when we deal with prestack seismic data. Namely, the Amplitude Vs. Offset (AVO) and the cornbined Amplitude, Phase and Frequency Vs. Offset (APF.VO) analyses may be very sensitive to the previous acquisition and processing. The main purpose of this paper is to show the impact that processing procedures have on the APF.VO responses of reflected signals pertaining to an offshore seismic line. We focus on two separate targets that give rise to bright reflections on the stack section: a cineritic layer and a gas-sand bed.
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Integration of trend and detail
Authors N. P. van Dijk, G. J. M. Lörtzer and A. J. BerkhoutLinearized inversion of amplitude versus offset (AVO) from multi-offset data consists of weighted stacking. It yields the elastic parameters as traces in terms of bandlimited relative contrasts. (Smith and Gidlow 1987; Lörtzer and Berkhout 1989). The weighted stacking results are displayed as seismie traces. These traces may be considered as spiky relative contrasts convolved with the seismic wavelet.
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The signal coherence as a versatile diagnostic tool to improve seismic data processing effectiveness
Authors B. Boiardi and M. CardamoneThe increasingly large amount of seismic data involved in 20 and 30 seismic data processing projects requires the personal skill of the analyst to be assisted in the choose of algorithms and parameters. At the same time the increasing complication of nowadays exploration themes wants the seismic method to provide highly reliable and uniform results.
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The wave equation stack
By R. SilvaIt is generally known that common midpoint (CMP) stacking and Kirchhoff migration are similar operations. This similarity arises from the fact that they both perform summation over hyperbolic trajectories defined by two-way travel times. Since migration can be considered as a shifting of energy with respect to the midpoint axis, stacking can be described in terms of shifting energy with respect to the offset axis.
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New perspectives in inverse VSP method by using explosives in the open hole
Authors P. C. Layotte, C. Naville and P. FroidevauxA borehole seismic experiment was carried out in the southeast part of France in the Balazuc-1 well belonging to the B.R.G.M.'s scientific project G.P.F. (Géologie Profonde de la France: Deep Geology of France). This experiment was supported by the ARTEP* association.
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The influence of acquisition system; coupling environment and sensor type on VSP image quality
Authors K. J. Dodds, T. Spencer, G. Ballantyne and R. BuntThe influence of the acquisition system type and its coupling environment on the quality of a VSP reflector signature is a source of conjecture prior to any VSP survey. We present a case history data set that involves variations of both acquisition system and environment including two different types of sensors and evaluate the differences evident in both the raw data and final processed image.
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Secondary shear waves generated from source boreholes
Authors J. A. Meredith, M. N. Toksöz and C. H. ChengIn cross weIl tomography experiments there are two types of sources commonly used. The most common are point sources, such as the airgun or dynamite, and axial sources. In general, the point sources generate tube waves which travel up and down the borehole and these tube waves contain more than 99% of the energy generated by the source (Winbow, 1989). AdditionaIly, point and radial sources also generate shear waves (Heelan, 1953, Lee and Balch, 1982). Axial sources do not generate tube waves (Winbow, 1989; Meredith, 1990) and therefore will not be discussed in this abstract.
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Acquisition and processing of VSP data obtained in horitzontal wells drilled from floating platforms
Authors S. A. Petersen and R. HeggernesWithin the last couple of years the use of horizontal wells for oil production purposes has increased. Clearly this new acquisition environment has an impact on the logging tools and deployment methods employed and on the post-survey dataprocessing. This is also the case for the Vertical Seismie Profiling (VSP) method. In the following the problems met in collecting and processing VSP data from floating platforms are discussed for an example from the central part of the North Sea.
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Multicomponent VSP radon transform for transversely isotropic media
By J. E. GaiserShear-wave particle motion directions measured in vertical seismie profiles (VSP) are very sensitive to anisotropic properties of the medium; however, in the case of compressional waves this is not true (Crampin 1981). Analyzing polarization diagrams (holograms) to measure these directions can be inaccurate because individual 3-component geophones are subject to interference from ambient noise and ot her coherent signals. An alternative is to investigate polarization characteristics along wavefronts using multicomponent Radon transforms.
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VSP Noise suppression through spectral equalisation
By P. B. DillonSpectral equalisation or spectral balancing is the suppression of seismic noise through power-spectral processing only, the phase spectra remaining unchanged. Tufekcic et al (1981) demonstrated a multichannel scheme in which the power spectra were spatially smoothed, over a large number of traces. Coppens and Mari (1984) showed that selectively weighting the power spectrum over the useful frequency band also gave good results. Both these schemes target the distortion introduced by surface-seismic ground roll. Ground roll is usually characterised by high-amplitude narrow-band spectral interference. That is, the noise is non-Gaussian. Since the character of VSP noise is very of ten non- Gaussian, it would seem that spectral equalisation should solve some of the noise problems experienced in the borehole environment.
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VSP and acoustic logging. Case history on the Cere La Ronde structure
Authors J. L. Mari and F. VerdierThe comparison of seismic data recorded at very different frequencies (a few hundred Hz for VSP and a few ten KHz for acoustic logging) and of dipmeter information can help for the interpretation of seismic anomalies. The VSP can have a lateral investigation of several ten or even hundred meters and a 1 to 10 meters vertical resolution. The acoustic logging used in reflected or diffracted modes has a vertical resolution of a few ten centimeters an 1 to 20 meters lateral investigation.
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3D kinematic inversion from a set of line profiles
More Less2-D interval velocity analysis is inaccurate in the case of tree-dimensional structures. This is demonstrated on the isotropic two-Iayered model where two reflecting interfaces have conflicted dip azimuths (Figure 1). We consider the profile Y=5km. The stacked section (Figure 2) is obtained from CMP gathers calculated by 3-D ray tracing. Interval velocity analysis along this profile is carried out by the 2-D coherency inversion (Landa et al.,1989). This analysis provides a high coherency (normalized semblance is about 0.8) for both reflection horizons on the CMP gathers.
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Velocity analysis with tomographic inversion on shot record migration
More LessPrestack time migration can still be a suitable alternative to image complex structures with moderate lateral velocity variations and it is less sensitive to the knowledge of the migration-velocity model than prestack depth migration.
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Advanced 3D macro-model estimation: The Sistre Project
By J. L. GuizouGetting a reliable depth image of the subsurface requires the identification of the main geological bodies beneath the surface of the earth, the estimation of the wave propagation velocities through these bodies, and an accurate positioning in depth of the interfaces which separate the geological layers. The exploration industry needs in the field of macro-model estimation have recently evolved from the conventional 2D framework towards the more attractive 3D framework. As a consequence, our geophysical industry must he prepared to offer reliable tools which make it possible to estimate structurally complex 3D geological bodies from seismic data. Several authors have reported methods to carry out three-dirnensional macro-model estimation using ray-tracing techniques and traveltime inversion techniques (Fawcett (1983), Chiu and Stewart (1987), and Guiziou and Haas (1988) ). However, these methods are limited to layer-cake-type subsurface models.
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A review of surface consistent imaging and DMO for irregular topography
Authors A. N. Ellis, R. A. Bale and P. W. KitchensideIn the processing of land data, static time corrections are used for improving velocity analyses, the enhancement of stacked sections and correcting for long-wavelength structural distortion due to irregular topography. Staties can be split into three categories, namely short-, medium- and long-wavelength, where medium wavelengths are of the order of one spread length. However static corrections are only valid when ray paths are verticaI near the surface. Therefore when the ray paths deviate from the verticaI, owing to steeply dipping reflectors or high velocities in the near surface (such as in permafrost environments), they must be replaced by more accurate wave-equation techniques.
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Impedance inversion using constant-offset reflection seismic data
Authors D. Wang, A. B. Weglein and T. J. UlrychAperture migration (aperture-compensated migration inversion) [1,2] inverts the zero-offset reflectivity from prestack reflection seismic data correctly. This method accommodates the incident angle of the wave, the reflector's dip and the actual receiver apert ure and is superior to conventional migration methods.
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Computation of true-amplitude reflections from offset data
Authors J. Schleicher, M. Tygel and P. HurbalCompressional primary seismic non-zero offset reflections as, e.g., common-midpoint or common-offset reflections are frequently used in seismic parameter estimation and imaging. Seismic migration procedures oper- . ating on such data are currently employed with increasing success. However, the dynamic aspects of wavefield migration methods still pose basic unsolved problems. One of the the questions is how the observed amplitudes can provide a measure of angle-dependent reflection coefficients.
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Estimation of elastic parameters from AVO effects in t-p domain
Authors J. Helgesen and M. LandrøThe objective of AVO techniques is to extract elastic layer parameters and lithological characteristics of subsurface layers from seismic measurements. Many of the works reported in this field has been of qualitative nature, e.g. using AVO techniques to distinguish between hydrocarbonrelated and lithology-related bright spots.
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A contribution on the study of the production mechanism of solfide mineralization self potential
Authors G. A. Skianis and T. PapadopoulosThe production mechanism of sulphide mineralisation self potential is still open to question. The majority of geophysicists support basically the dipole model. According to this model electrochemical reactions take pIace in the system of the mineralized body and the surrounding medium and as a resuIt an excess of negative and positive charges (of the same magnitude) are formed at the upper and lower part of the ore body, respectively. Thus an electrical field (geobattery) is formed the potential of which can be measured at ground surface. There have been proposed various models to describe the electrochemical reactions which take place in and around the dipole (Sato-Mooney 1960, Habashi 1966, Thornber 1975, Bolviken 1979, Sivenas-Beales 1982.).
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A New approach to data acquistion processing and control for noisy geoelectric voltage recordings
Authors C. Satriano, V. Cuomo, V. Lapenna, M. Machiatto, D. Patella and C. SerioIn this paper we are concerned with the problem of picking out the useful signal from noisy voltage recordings in geoelectrical prospecting. The voltage time series, recorded at the measuring probes of the electrodic array is made up of the sum of a deterministic component, the response of medium to the energizing current, and a random noise component.
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Measurements of D.C. small signals masked by noises
By L. AlfanoThe measurement of a man made signal S, masked by natural noises of mean strenght N, is common to many geophysical methods; but the Author will take into account only the case of the geoelectrical D.C. current surveys about which he reached a sufficient experience. The problem arose when deep sounding where carried out by means of Dipole-Dipole arrays and with long distances between the two dipoles,up to twenty kilometers.
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Geoelectrical survey of structures closed in depth with two-dipping discontinuities
Authors E. Cardarelli and M. BernabiniIn a previous study presented to Geophisycal Prospecting we considered the case of bidimensional structures in which a conductive medium is between two resistive seminfinite media. The two dipping discontinuity surfaces were considered to be parallel (or divergent) planes (open structures).
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Interpretation of airborne geophysical measurements in sedimentary environments by image processing
Authors A. Gulyas, M. Bodrogt, R. Csatho, G. Y. Büttner and G. CsillacDetailed airborne EM, magnetic and radiometric mapping was carried out in the Transdanubian Central Range (Hungary) over an area of more than 240 km² in the past 3 years. The geology of the area is rather complicated. The Transdanubian Central Range is built up mostly Mesozoic and Tertiary sedimentary rocks, mafic volcanic rocks are also present. As the investigated geological objects are quite small e.g. bauxite lenses with a diameter of a few 10 m - the line spacing of the flying was 50 m.
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Analysis of D.C. logging through metal casing
Authors C. Schenkel and H. F. MorrisonThe measurement of formation resistivity through metal casing can aid in characterizing existing reservoirs for effective recovery of oil and gas, as well as geothermal heat, without the cost and time of drilling new wells. Measuring the resistivity of adjacent fonnations may be useful to locate oil that was missed during the original logging prior to insertion of the casing. The method is also useful to monitor changes in resistivity caused by subsurface processes such as injection or leakage of contaminants from a waste site, flooding operations for enhanced oil recovery, or extraction processes of geothennal production. Several patents have recently been issued which describe methods and devices that are capable of measuring formation resistivity through casing, (Kaufman, 1989; Vail, 1989a, 1989b; Gard et al., 1989). Currently, it is only known that Vail has developed and tested such a device, called Through-Casing Resistivity TooI (TCRT). Kaufman (1990) investigated the behavior of the potential and its derivatives for a borehole with casing based on models of an infinite-length conductive pipe in a homogeneous medium. Schenkel and Morrison (1990) presented numerical results for a point souree of current in or beyond the end of a fixed length of casing in a homogeneous half-space. This study has now been extended using a surface integral equation approach can calculate the potentials for various electrode configurations in the presence of a finite-length casing and a layered medium.
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First application of lP method in Iran to boundary detection of deeply buried salty and sweet water aquifers
Authors E. Yousefi and J. KimiaghalamThe induced polarization (commonly known as lP) method is one of the most effective tools in mineral exploration. As it is known the induced polarization is based on the electrochemical phenomenon of overvoltage, that is on the establishment and deection of double layers of electrical charge at the interface between ionic and electronic conducting materials when an electrical current is caused to pass across the interface (H.O. Seigel).
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Source signature estimation using plane wave decomposition
Authors V. Shtivelman and D. LoewenthalRecently a new deterministic technique for source signature estimation in one-dimensional models of media was introduced (Shtivelman and Loewenthal, 1988; Loewenthal and Shtivelman, 1989). The technique was developed for a general case of multilayered models with arbitrary locations of the source and two closely spaced receivers (provided the source is above the receivers) and can he applied to both marine and land data. The technique is based on the application of two sequential extrapolation processes and does not require explicit separation of the wave field into up and downgoing components. Lately, the method has been extended to the two-dirnensional problem (Loewenthal and Shtivelman, 1990).
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Multiple elimination via inversion velocity analysis and shifted hyperbolas
Authors G. Canadas, S. Desaunay and E. de BazelaireThe inversion processes introduced in the conventional velocity analysis yield better velocity stack gathers. Improved resolution means more accurate picking and better quality of the stacked signal. However, two problems are encountered when using these processes for multiple attenuation: 1) the high cost of inversion and 2) the construction of stacked traces from the inverted velocity-stack gather. Solutions are brought about by using shifted hyperbolas (de Bazelaire, 1988) and by implementing non-conventional stack methods.
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Wave equation multiple suppression using constrained cross equalization
By D. J. MonkA method for improving the attenuation of water layer multiple energy is suggested. The improvement is achieved using wave equation extrapolation to generate an initial model of the multiple energy, and then constraining the way the time variant wavelet is modified to fit the observed multiple energy. Reconciling the initial multiple model wavelet with the input data is a critical part of this process, and several techniques have been suggested previously by other authors. The approach used here is to fit time, amplitude and phase of the wavelets, by adapting the model trace using a weighted sum of four traces which can each be derived from the initial multiple model trace.
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Multiple suppression by multi-channel predictive deconvolution
Authors M. T. Taner, R. F. O‘Doherty and E. BaysalSince its inception deconvolution has become one of the standard tools of seismic data processing. It is used to suppress reverberations, wavelet shaping and suppression of short and long period multiples, most of the instances, all at the same time. Failure of single channel predictive deconvolution of suppressing multiples longer than 200 millisecond period led to developments of alternate methods, most of which involve with the multichannel processes. Prediction across the channels in the radial direction (Taner, 1980) and using slant stack traces (Alam and Austin, 1981) have been successful for sirnpler water bottom geometries. Of the multi-channel processes for general multiple suppression the ones using the wave equation continuation to predict the multiple arrival times (Morley, 1982; Wiggins, 1985) had a physical basis, hence more promise for success. The rest were various forms of multi-channel filters.
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Multichannel attenuation of high amplitude peg legs multiples. Example from the North Sea
More LessAstrong impedance contrast, such as the base of the Cretaceous in the North Sea, generates a train of high amplitude water bottom peg legs which can heavily obscure the underlying less energetic reflections, often of great petroleum interest. Attenuation of these peg legs, a prerequisite for defining the structural image, is a persistent and difficult problem in processing the seismic data.
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Multiple attenuation by predictive deconvolution in the p-t domain
More LessMany multiple attenuation or suppression methods depend on discrimination of the moveouts of reflections in unstacked data. Most of these methods, such as NMO stacks and f-k dip filters, are not very effective when primary and multiple reflections have similar moveouts and stacking velocities. Predictive deconvolution in the p-tau domain does not require such velocity discrimination. Land reflection seismic data from North Africa contains many strong multiples with essentially the same moveout as weak underlying primaries. Predictive deconvolution successfully attenuated these multiples and improved the interpretation of the subsurface.
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Deconvolution by the double-streamer experiments
Authors A. Matthies, H. Huck and M. TygelIn exploration seismics the geophysicist has to face two fundamental problems during data processing, namely the recovery of the source pulse, and thereafter the solution of the inversion problem, i.e. the extraction of the reflectivity series of the medium under investigation. This research adresses to both problems in a specific measurement configuration. We demonstrate the estimation of an arbitrary (i.e. mixed-delay) source wavelet and of the medium reflectivity from point-source seismograms obtained from a vertical double-streamer experiment. We assume the medium to be acoustic and horizontally stratified bounded or not bounded by a free surface above and a homogeneous acoustic half space below.
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High resolution processing of reflection data
Authors A. L. R. Rosa, T. J. Ulrych and W. S. LeaneyThe widespread occurrence of subtle trap accumulations offshore Brazil has led to the need for the development of a high resolution processing scheme that helps the delineation of these features. To be successful, a comprehensive wavelet processing technique should take into consideration the spectral properties of both the seismic pulse and the reflectivity function. In this paper we present such a technique, and we apply it to the processing of reflection data from the Campos basin offshore Brazil.
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Tutorial interpretive evaluation of migrated data
By O. YilmazIn practice, decisions with regard to migration include choice of migration strategies (2-D/3-D, poststack/prestack, time/depth), migration algorithms (integral, finite-difference, frequency-wavenumber) , parameters for a given algorithm (aperture width, depth step, stretch factor), factors related to input data (profile length, spatial sampling, noise), and most importantly, migration velocities (the weak link between seismic and geologic sections). By using a large number of field data examples, the problem of conflicting dips with different stacking velocities and that of strong lateral velocity variations associated with complex overburden structures will be discussed. Emphasis will be made on uncertainties in migration velocities and interpretive evaluation of the results we obtain from migration.
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True-amplitude finite-offset migration
Authors P. Hurbal, M. Tygel and J. SchleicherSeismic reflection data provide traveltimes and amplitudes of seismic waves. Current processing and interpretation are, however, almost totally based on traveltime measurements. This is easy to understand as traveltimes possess the robustness and stability attributes required to the implementation of most seismic data manipulations. Amplitudes of primary reflection arrivals are strongly related to angular dependent refiection coefficients and, if properly processed, may be of great interpretational value.
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Time migration imaging for complex overburden
Authors M. O. Marcoux, A. Downie and R. WesterbergLarge lateral velocity gradient in the overburden causes structural imaging by conventionally applied time migration to fail. Depth migration can image such structures correctly but depends on a modelling procedure which is more costly than time methods and which brings interpretation into the processing sequence at a relatively early stage. In this presentation, an extension to prestack time migration is used to image the well known Marmousi synthetic to gauge the effectiveness of the extended technique relative to prestack depth migration results.
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Migration to zero-offset in variable velocity media
More LessMigration to Zero-Offset (MZO) or Prestack Partial Migration (PSPM) transforms prestack data into zero-offset data and is equivalent in a constant velocity medium to the normal moveout correction (NMO) followed by the dip moveout correction (DMO) applied as a single step process. For media with lateral velocity variation or with sharp increase of velocity in depth the migration to zero-offset process cannot be split in NMO followed by DMO, but must be applied as a single process.
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Prestack frequency-wavenumber (f-k) migration in a transversely isotropic medium
Authors A. Gonzalez and W. LynnPrestack frequency-wavenumber (f-k) migration (Stolt, 1978) is an efficient way to do prestack time migration. This technique is also useful for migration velocity estimation, where it is expected to yield dipindependent velocities (Li et al, 1991). In practice, however, we often find that imaging velocities do exhibit dip-dependency. This is especially noticeable with fault-plane reflections which usually image best at velocities higher than those of surrounding flat events. In a companion paper (Lynn et al, 1991), it is shown that the dip dependency of migration velocities can be explained by assuming that waves have propagated in a transversely isotropic earth. Because anisotropy affects both processing and interpretation of seismic data, it is important to identify its presence and measure its strength. In this paper we develop the necessary modifications to prestack f-k migration that compensate for such media. Moreover, we find that the transverse-isotropy adjustment parameter can be used to estimate, in an average sense, the amount of transverse isotropy.
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A unified formulation of wave field decomposition: theory and examples
Authors P. Herrmann, C. P. A. Wapenaar and A. J. BerkhoutUsing a recording by multicomponent sources and receivers, it is possible to decompose the vector wave field (velocities and stresses) into its scalar components (P and S waves) at the source and receiver side. The fully decomposed data set can constitute the starting point of a new procedure to process multicomponent data, as has been described by Berkhout and Wapenaar (1990).
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Downward extrapolation of decomposed P and S wave fields
Authors G. Haime and C. P. A. WapenaarThe use of amplitude information in pre-stack seismic data to delineate and characterize reservoirs has shown a considerable growth in recent years. Therefore, in redatuming or prestack migration techniques it is required that the used extrapolation operator contains all the necessary characteristics to treat both the phase and amplitude information in a correct manner, even in cases where the medium is strongly inhomogeneous and/or anisotropic.
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Finite-difference prestack reverse time migration using P-SV wave equation
Authors M. A. B. Botelho and P. L. StoffaPrestack Reverse Time Migration (RTM) is performed using a first-order system of hyperbolic elastic equations of motion and constitutive laws expressed in terms of particle velocities and stresses. It is well known that the RTM procedure must contain three important steps, i.e., it must apply (a) the imaging condition, (b) the reverse time extrapolation and (c) the extraction of amplitudes from the seismic data in order to build the final images. Here the above mentioned steps are implemented using the same code, which is a two-dimensional explicit finite-difference scheme. It is of second-order accuracy in time and fourth-order accuracy in space.
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Extraction of accurate P- and S-wave velocities from fixed offset well seismic profiles, UK Central North Sea
Authors J. M. Reilly and M. IdreesThe acquisition and processing of both compressional and shear wave energy from Well Seismic Profiles (WSP) is an important source of data for the investigations of seismic Amplitude Versus Offset (AVO) and anisotropy. In the marine environment we are normally dependant upon the mode conversion of conventional compressional sources (air- or watergun) for the production of shear wave energy.
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Focusing P-SV converted waves
Authors P. Y. Granger, R. Garotta and F. BaixasWith the present state of the art in data processing, converted P-SV wave sections do not show as comprehensive and detailed an image as that obtained from compressional waves. This observation alone may explain why there are objections to the use of converted waves. Results are clearly disappointing because of inaccuracies in CRP gathering and the lack of dip moveout.
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The derivation of shear velocities from log and VSP data
Authors W. L. Nutt and K. DoddsA knowledge of formation Shear Velocities is essential for many state of the art computations in Petrophysics and Geophysics. In particular mechanical properties of formations can only be accurately predicted if the corresponding formation shear velocity is equally accurately known. The interpretation and prediction of Amplitude versus Offset dependence of seismic reflection strength, AVO, is also heavily dependent on the knowledge of formation shear velocities.
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3D Multicomponent seismic reservoir characterization of South Casper Creek field, Natrona Co.
Authors R. D. Benson and T. L. DavisThe South Casper Creek field provides a unique opportunity to study a reservoir in an established oil field. A large amount of geologie and geophysical data has been collected which include weIl logs, core analyses, multicomponent vertical seismic profiles, and 3-D multicomponent surface seismic data. Interpretation of these data have contributed to an improved understanding of the reservoir. The continuing objective of this work is to develop 3-D multicomponent seismic methods to better characterize reservoir heterogeneities.
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Using mode converted shear data to map conglomerates - A case history
Authors J. D. Boyd and M. P. HarrisonThe Carrot Creek field, of Alberta, Canada produces oil from sandstones and conglomerates of the Cardium formation, which is of Upper Cretaceous (Turonian) age. A strong impedance contrast between the conglomerates and surrounding shales has made it a successful target for seismic exploration, as a purely stratigraphic play.
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Advances in airborne gamma-ray system design for geophysical and environmental applications
Authors J. R. Cox, J. Masek and J. BartosekThe purpose of this paper is to acquaint current users of Gamma- Ray equipment with the latest technology in this specialised field. Wherever possible the inforrnation is presented with a bias to Airborne applications, but of course the techniques discussed are directly applicable to Ground or Borehole applications. The presentation tries to balance an accurate explanation of these methods, with time allotted, so out of necessity, a somewhat simplified description has been used where possible.
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