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55th EAEG Meeting
- Conference date: 07 Jun 1993 - 11 Jun 1993
- Location: Stavanger, Norway
- ISBN: 978-94-6282-135-4
- Published: 08 June 1993
41 - 60 of 500 results
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Interpreting non-orthogonal split shear waves in multicomponent VSPs
Authors X. -Y. Li, S. Crampin and C. MacBethMany techniques for processing shear-wave splitting in VSP data assume orthogonality of the split shear-waves, and are consequently restricted to zero or near-offset VSPs and symmetry planes (Wintersteen and Meadows 1991; Zeng and MacBeth 1993; among others). Here, we derive equations for multicomponent seismic data (two or three sources recorded by 3C receivers) for non-orthogonal split shear-waves. The equations can be solved by the linear-transform technique (LTT) of Li and Crampin (1993) to determine the shear-wave polarizations in both zero- and offset VSPs . This method is particularly useful where orthogonal techniques often fail when deviation from orthogonality exceeds 5°, or the incidence angle exceeds 1.5°.
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Analysis of split-shear waves from near-offset VSP data using a neural network
Authors D. Hengchang and C. MacbethNeural networks provide a way of recognizing particular patterns and extracting their characteristic parameters. Here they are applied to the different patterns of shear-wave particle motion recorded by orthogonal horizontal geophones. It is postulated that the major component of this particle motion is from shear-wave splitting, and that it can be parameterized as the polarization direction of the leading shear-wave and the time-delay between split shear-waves. The network is trained initially to recognize patterns of shear-wave splitting with known parameters from synthetic seismograms. Once training has been accomplished, the network can now be used to recognize patterns which have unknown characteristics, but which still lie within or not far outside the experience of the network. It is hoped to use the network to rapidly quantity any patterns of shear-wave splitting and to analyse large sets of seismic data.
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A Comparison of two methods for measuring shear wave birefringence from VSP data - Parametric inversion and layer stripping
By J. J. WalshShear wave birefringence has been the subject of considerable study in recent years. A principal application is the determination of fracture orientation from shear wave splitting in multicomponent VSPs. This is accomplished by studying the polarization direction of the lesding shear wave -and the travel time delay between the two split shear waves, which may give a direct indication of the orientation of the anisotropy. Here, we examine two methods for detection and description of fractured zones from shear wave splitting: layer stripping and parametric inversion.
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Processing of single-source split shear waves for imaging
Authors D. R. Watts and M. BoulfoulShear wave splitting may be regarded as a nuisance in the production of a shear wave image. Splitting or diffraction effects in the near surface or the weathering layer will degrade stacks especially if there is a rapid variation in the change of polarization along the survey line. We present a technique that may utilize a single source of indeterminate polarization for shear wave imaging even for the case of splitting in the weathering layer.
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True-amplitude processing of P- and PS- (converted) - Wave data for AVO-analysis
Authors P. Krajewski, C. Krajewski and S. GrummtThe analysis of seismic reflection amplitudes for reservoir characterisation or, more general, for the lithological interpretation of reflection data has become a standard approach in exploration geophysics. However the nonuniqueness of the interpretation of amplitude anomalies in P-wave sections has shown the need for shear-wave velocity information to permit a reliable lithology discrimination. In the paper Processing of PS-reflection data applying a common conversion-point stacking technique by Tessmer et al. 1990 a field data set has been presented which has been generated using three conventional P-wave vibrators as source and in-line horizontal geophones as receivers. This technique of shear wave data acquisition is relatively simple and inexpensive compared to techniques using shear-wave vibrators, because it can be done simultaneously with the routine P-wave recording.
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AVO Versus shearwaves by mode conversion
Authors F. Nieuwland and R. MarschallThis paper describes the results of a field experiment which was conducted in the central part of Friesland - The Netherlands.
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Three component seismic experiment in Saudi Arabia
Authors D. J. Fyfe, B. E. Dent, P. G. Kelamis, K. H. Al-Mashouq and D. A. NietupskiIn 1991, Saudi Aramco conducted an experimental three-component seismic program, over a known oil field, using conventional P-wave vibrators and three component geophones. One of the main objectives of the experiment was to use the converted (P-S) energy to improve the structural and stratigraphic picture of the reservoir sands. We recorded usable P-S energy as expected, but the surprisingly strong, coherent, shear energy generated at or near the vibrators (S-S) gave us a clearer image of the reservoir interval than either the vertical component (P-P) stack or the P-S stack.
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Recording and processing PSSP waves in the Barents Sea
Authors E. de Bazelaire, I. Gausland, O. E. Naess, H. Morizot and J. RavatSeismic profiles shot in Barents Sea cross a number of potential reef features, located between two reliable reflections at the top of Paleozoic and within the Paleozoic, 200 ms deeper. Conventional seismic work using P-waves is unable to separate porous from dry reefs, and all the more to assess the fluid contents.
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Rock properties - The missing link in exploitation and exploration
Authors C. H. Sondergeld and C. S. RaiRelationships between different physical properties of rock permit one to interpret log, seismic, magnetic and gravity data. One relies upon these correlations to infer subsurface properties. To map lithology, porosity, or permeability, for example, one must employ a technique which has sensitivity to the property of interest. These techniques generally produce a one, two, or three dimensional image of some attribute say vetocity or amplitude. Beyond a knowledge of the, physics behind a technique, one must establish the correlation between the attribute mapped and the property desired. In many circumstances these properties can not be linked to the attribute in an ab inito sense. Thus healthy empiricism is required to form the bridge. A case in point, the classical theories of Biot (1956a,b) and Gassmann (1951) require the definition of a porous frame modulus, this for obvious reasons can not be derived from first principles without a priori knowledge. However, once the modulus is defined, the theory permits one to conveniently calculate the influence of various saturants on velocity. Such information is extremely useful in modeling an AVO response, for example. The problems hampering such empiricism to date have been twofold: first, the cost on a per sample basis has been prohibitive and second, the core to be characterized has suffered irreversible degradation. GEM (Geophysical Evaluation Modules) has eliminated both these restrictions. Because GEM is portable, it can be brought to a well site or Gore facility and fresh samples can be characterized. Secondly, because of the high degree of automation and parallel processing concepts, the cost for a rather extensive suite of measurements has been reduced by an order of magnitude.
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The role of core measurements in seismic lithology prediction
By J. BartonCore measurements play an important role in lithology prediction from seismic data by: - Providing an accurate set of geophysical and petrophysical measurements about reservoir and caprock lithologies. - Allowing correlations between petrophysical and elastic parameters to be established. - Enabling key elastic parameters such as shear velocity, shear and bulk moduli to be determined for geophysical modelling. This paper describes how core measurements have helped evaluate and predict reservoir and caprock lithologies in the Paleocene section of Amoco operated fields in the UK Central Graben.
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Ultrasonic monitoring of hydraulic fracturing experiments
Authors M. Savic, M. J. Cockram and A. M. ZiolkowskiThis paper describes a state-of-the-art data acquisition system built at Delft University of Technology which allows rapid acquisition of reflection, pulse-echo and transmission records during hydraulic fracturing experiments on cement or rock samples. Recent experiments show that it is possible to observe clean acoustic signals from a hydraulic fracture that is very thin compared to the wavelength of the illuminating elastic waves. Imaging with reflected compressional signals produces a clean image of the fracture. The signals diffracted from the fracture tip carry important information about the position of the fracture.
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Water saturation - A critical review of computational procedures with a suggested approach
By M. H. KamelOne of the major petrophysical parameters that is of primary concern in the formation evaluation proces, particularly in shaly pay sand reservoirs, is the water saturation (SW). The purpose of this paper is first; to explain some of the concerned in-situ problems a log analysit comes across while choosing the most suitable equation to determine such parameter. Secondly; to propose a new approach to estimate the water saturation. Thirdly; to compare our new results with those obtained by other investigators. Finally, a field example taken from the northern part of the Gulf of Suez of Egypt will be used to illustrate the new approach .
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A global algorithm for pore pressure prediction
Authors D. Scott and L. ThomsenThe issue of subsurface pore-pressure prediction has a long history, and a long future. Despite a record of sonic success in prediction (in restricted contexts) via the "classical estimation algorithms", we regard the problem to be unsolved to date.
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A Recipe for predicting the effective elastic properties of shales
Authors B. E. Hornby, L. M. Schwartz and J. A. HudsonSuccessful imaging of subsurface features in the earth depends on a knowledge of the behavior of the wave propagation through overlying strata. Shales make up about 75 percent of most sedimentary basins and most often overlie hydrocarbon hearing reservoirs. The elastic properties of shales are anisotropic (e.g. Jones and Wang, 1981 ; White et al., 1983; Bareik, 1984; Miller and Chapman, 1991). This anisotropy of shales must be taken into account, both for structural imaging of subsurface features and for more advanced inversions such as amplitude variation with offset (AVO) analysis of hydrocarbon-hearing reservoirs sealed by shale cap rocks.
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Slow wave in oil-saturated water
Authors G. M. Goloshubin, P. V. Krauklis, L. A. Molotkov and H. B. HelleBiot's theory (1956) predicts that wave propagation in a saturated porous medium involves three types of waves: two compressional waves and one shear wave. The two compressional waves are known as the fast P wave and the slow P wave. The slow P wave is the consequence of the fluid-solid coupling. Plona (1980) observed a compressional slow wave in a porous medium at ultrasonic frequencies. According to Biot's theory this wave attenuates very quickly and the attenuation is higher for low frequencies than for high frequencies. Thus, Biot's theory predicts that the low frequency slow waves cannot be observed at some distance from its origin. We discus the possibility of slow wave observation in an oilsaturated layer at seismic frequencies using experimental data and the theoretical solution.
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Effect of local inclusions on the attenuation of seismic waves in fluid-saturated rocks
Authors B. Gurevich, A. P. Sadovnichaja, S. A. Shapiro and S. L. LopatnikovInvestigations of a complex reservoir structure by VSP and cross-borehole soundings require the construction of a theory that can make predictions of seismic parameters for complex reservoir rock. In this paper we construct such a theory for a reservoir rock which can be considered as a fluid-saturated porous continuum containing randomly distributed inclusions. The host medium is assumed to behave in accordance with the low-frequency version of the Biot theory, and the effect of inhomogeneities is studied using the scattering theory.
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Unification of traveltime tomography methods
More LessTraveltime tomography methods can be divided info two general classes: 1) methods which back-project travel time residuals along raypaths, and 2) methods which back-project traveltime residuals along wavepaths. In this paper 1 present a general formula for the back-projection of travel time residuals and, for special cases, show that it reduces to the back-projection term in wave-equation traveltime inversion (or WT in Luo and Schaster, 1991), wavepath eikonal traveltime inversion (WET in Schaster, 1991), ray tracing tomography (RT), and the Woodward-Rocca (WR in Woodward and Rocca. 1988) method. This unification provides for an understanding of the differences and similarities among these traveltime tomography methods.
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The Rytov approximation aids the resolution of the broad velocity components in non-linear waveform inversion
By C. StorkThe bare of non-linear waveform inversion based on the Bom scattering model has been the need of a close starting model -- particularly for the broad components of the velocity field. Without a close starting model the method is susceptible to failure by getting stuck in a local minima (Tarantola, 1990 & Gauthier et al, 1986).
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2.5D Acoustic full-wave frequency-domain inversion
Authors Z. M. Song, P. R. Williamson and M. H. WorthingtonSeveral approaches to frequency domain inversion and imaging have been developed over the last decade (e.g. Devaney, 1984; Pratt, 1989). These methods have typically been developed for 2D geometries and are accordingly limited by the implicit assumption of line sources. Song and Williamson(1992) presented a method of extending the work of Pratt(1989) to 2.5D, in which sources can be represented in 3D while medium properties vary in 2D. This in principle allows direct comparison of calculated and real data gathered in effectively 2D media.
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Hybrid traveltime and waveform inversion of real crosswell seismic data
Authors C. Zhou, W. Cai, Y. Lou, G. T. Schuster and S. HassanzadehLuo and Schuster (1990) presented a hybrid wave equation traveltime+ waveform inversion (WTW) method to reconstruct 2-D velocity structure from crosswell seismic data. The key idea is to reconstruct the smooth component of the velocity field by first inverting first arrival traveltimes (Luo and Schuster, 1991), and then reconstivct the short wavelength components by waveform inversion. Using synthetic tests, they showed that WTW inversion was as robust as traveltime tomography and provided the high resolution of waveform inversion. In this paper, we apply the WTW method to a synthetic fault model, and also present the first application of WTW inversion to real crosswell seismic data.
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