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61st EAGE Conference and Exhibition
- Conference date: 07 Jun 1999 - 11 Jun 1999
- Location: Helsinki, Finland
- ISBN: 978-90-73781-10-8
- Published: 07 June 1999
1 - 20 of 502 results
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Seismic Velocity Structure at the Gas Hydrate Reflector - Indonesia and Pakistan
Authors C. Gavrila, J. Sheiman and J. RyanThis paper describes the experimental processing of foor seismic lines, in which we attempted to learn more about the transition to and from a phase in which gas is trapped in the foren of a methane hydrate . The gas hydrate phase occurs in a temperature/pressure regime that is typically found a few hundred metres below a deep water seafloor . The transition is expressed as a so-called Bottom Simulating Reflector (BSR) ; so named because its structure mimics that of the seafloor rather than follówing the local bedding direction. Indeed reflections associated with bedding planes often cross through the BSR . In addition to the BSR, we looked for changes in seismic interval velocity, amplitude and AVO effects in the neighbourhood of the BSR. All of these help us to glean information about the nature of the gas hydrate, its generation and the hydrate / free-gas transition .
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The Effect of Acquisition Direction on Pre-Sdm Imaging
Authors I. F. Jones, H. Baud, B. Henry, A. Strachan, J. Kommedal and M. GainskiA production 3D preSDM p roject .from the southern North Sea using several vintages of input data was run using a velocity-depth model common to the whole area , with goud fnal results . The expected progress ive improvement from postSTM to postSDM to preSDM was demonstrated for the target horizons.
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Depth Imaging in the Heide-Buesum Transition Zone Area
Authors J. Navarro, J. Thiessen, H. -J. Zoch, H. Janie and K. FischerThe recent Heide -Busum TZ 3D survey from RWE-DEA AG and Wintershall AG presented unusual challenges for depth imaging . Seismic data had to be acquired offshore; in the transition zone and on land . The three datasets were combined with proper source designature and phase matching. The acquisition also made use of the patch technique, resulting in ve ry irregular fold and offset distribution . A new type of normalization, by fold density as a function of offset, is presented that corrects some of these problems .
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Mapping Sub-Basalt Reflectors Using Model-Based Analysis
Authors L. Sønneland, J. O. Hansen, B. Tjøstheim, B. Larssen and S. JåsundThe continental break-up of the Northern European plate and the Greenland plate during the Paleocene age was associated with transient, massive volcanism. This resulted in that volcanic rocks such as basalts covered a significant part of land-surface and sea-beds of Paleocene age. It is well known that the main hydrocarbon reservoirs in Europe are in sedimentary layers of older age than Paleocene. As a consequence many sedimentary sequences of highest hydrocarbon potential are overlaid by lava-deltas.
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Seismic Imaging Surveys at the Apso Hrl
More LessBorehole seismic imaging surveys have been undertaken over a range ofdifferent scales at the Aspo Hard Rock Laboratory (HRL) to address a number of different objectives. In this paper two of those objectives, that encompass the end members of the range of scales are presented and discussed.
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Algorithmic Approaches to Psdm for Imaging Beneath Salt Structures - An Example from the Uk Sns
Authors C. Docherty, M. Sugrue and A. StrongAreas of structural complexity that include strong lateral velocity contrasts prove considerable obstacles for imaging and are best addressed by pre-stack depth migration (PSDM) . However, the ability of PSDM schemes to tackle such problems is varied and much depends on the approach to initial velocity model building. An excellent testing area for PSDM is provided by a steep (and/or fault) sided salt diapir piercing its overburden. We outline the fundamental differences between two PSDM schemes from separate contractors and present their success on imaging a 2D data set over a prospect underlying salt in Southern North Sea Block 48/3b.
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Sub-Basalt Imaging Improvements - West Hebrides
More LessStandard seismic processing and controlled stacking of mode converted energy has proven successful in sub-basalt imaging (most recently Emsley et al., 1998; Longshaw et al., 1998). There is however, widespread scepticism about the nature of the imaged reflectors (sub-basalt primary vs. multiple). In this paper, we present new results from migration of long-offset data (12.5 km) that were acquired in 1996 by Phillips Petroleum over Tertiary flood basalt in the Rockall Trough, NW of the Hebrides.
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Enhanced Composite 3D Cube Derived from Multi-Azimuth 3D Marine Acquisitions
Authors H. Houllevigue, H. Delesalle and E. De BazelaireIn Seismic imaging, the influence of the angle between the acquisition azimuth and the main axis of geological structures has been well known for a long time (Levin 1971). Many analytical studies have been undertaken but rather few on real cases (Bullwinkle 1993). This azimuthal sensitivity is enhanced in complex tectonic, leading to complex rays trajectories.
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Two-Dimensional Textures and Prediction-Error Filters
Authors J. Claerbout and M. BrownFor many years it has been true that our most powerful signal-analysis techniques are in one-dimensional space, while our most important applications are in multi-dimensional space. The helical coordinate system introduced by Claerbout (Geophysics, 1998, vol 63, no 5) makes a giant step towards overcoming this difficulty. Figure 1 shows how convolution in two dimensions is equivalent to that in one dimension.
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MSVE - a Novel Approach to Statistical Estimation of Primaries Superimposed on Incoherent Multiples
Authors G. A. Ryzhikov and M. S. BiryulinaThe problem of attenuation of multiples is of permanent interest for theoreticians as well as for practical geophysicists (e.g. [1]). Classical approaches to suppression of multiples exploit a well-seen self-repetition of wave-forms, resulting in a rather high correlation of primaries and respective multiples (coherent-, or waveform preserved-, reverberations).
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Prediction and Subtraction of Multiples from Complex Water-Bottom
More LessThe main differences between our scheme for prediction and subtraction of multiples from complex water-bottom and other wave-equation approaches (see references) are the following : 1) By applying the adaptive subtraction of the predicted multiples in the tau-p domain, we take into account the angle-dependency of the reflection coefficients from the water-bottom ; 2) We do not split the subtraction procedure into two steps - first subtraction of the 'pure' multiples and receiver-side peg-legs, then subtraction of source-side peg-legs.
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A Comparison of the Feedback and Inverse Scattering Internal Multiple Attenuation Methods
Authors D. J. Verschuur, K. H. Matson, A. J. Berkhout, A. B. Weglein, C. Y. Young and H. JakubowiczMethods for removal of free-surface and internal multiples have been developed From both a feedback model approach and inverse scattering theory.
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Integration of OBS Data and Surface Data for OBS Multiple Removal
Authors D. J. Verschuur and E. I. NeumannThe surface-related multiple elimination method, based on the work of Berkhout (1982) and described as a data adaptive procedure by Verschuur et al. (1992), has already been applied successfully to several marine and land datasets, as shown by e.g. Verschuur and Werkhout (1997), Verschuur et al. (1995) and Kelamis and Verschuur (1996).
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Multiple Attenuation of Multicomponent Ocean-Bottom Data According to an Elastic Model
By R. SoubarasIn multicomponent ocean-bottom acquisitions, hydrophone data is acquired together with vertical and horizontal geophone data. The pressure and vertical velocity measurements are contaminated by ghosts and peg-leg multiples and must be merged for water-lager multiple attenuation. In this paper, a method is presented for water-lager multiple attenuation which takes into account nonvertical propagation and the elastic nature of the water-bottom without requiring the subsurface elastic parameters to be known, nor the measurements to be well calibrated.
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Elastic Waves in Three-Phase Poroelastic Media
Authors A. Bakulin and L. MolotkovReal rocks are often multiphase. Two-phase porous rocks consisting of skeleton and fluid are well described by Biot model.
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The Effects of Porosity - Pore-Fluid and Mineralogy on VpNs in Carbonate Rocks
Authors S. Assefa, C. McCann, J. Sothcott, T. Astin and S. JohnstadCarbonates are important hydrocarbon reservoir rocks. They have complex textures and petrophysical (porosity and permeability) properties.
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Wave Refraction with a Porous Plate in Liquid - Comparison of Biot's and Bisq Theories
More LessA comparison of the theoretical results for wave refraction by a porous plate immersed in a liquid with the experimental ones is made both for Biot's and BISQ models of porous medium. BISQ model is found to be more adequate to the experiment from the viewpoint of fast pressure wave attenuation, but less adequate from the viewpoint of slow pressure wave generation than Biot's model.
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Acoustic Velocities in Partially Saturated Sandstones Versus Effective Stress
Authors A. Khaksar and C. GriffithsThe influence of saturation by water, gas, and mixtures thereof on velocities and elastic moduli of reservoir rocks is of considerable interest in exploration seismology.
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Modelling Rock Behaviour with Linear Slip Deformation Theory
More LessThe dynamic elastic properties of rock are defined in terms of linear slip deformation theory, which is based on infinitesimal motion across weak planes being linearly related to the traction on those planes. The linear parameters governing slip on these planes though are highly non-linear functions of static stress state, and as such the theory provides a way to predict, based on a very limited set of measurements, the acoustic behavior of dry granular rock as a function of static stress.
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Detecting Fractures in the Unsaturated Zone from Acoustic Properties
Authors R. Horobin, C. McCann and M. PriceThe presence of fractures in a rock usually have the effect of reducing the acoustic velocity and increasing the attenuation (Peacock et. al., 1994; Groenenboom and Foktrema, 1998).
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