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58th EAGE Conference and Exhibition
- Conference date: 03 Jun 1996 - 07 Jun 1996
- Location: Amsterdam, Netherlands
- ISBN: 978-90-73781-07-8
- Published: 04 June 1996
21 - 40 of 604 results
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Quick-look 3D prestack time migration
Authors R. Ferber, B. Sander and A. E. BerlinA major product of 3-D seismic data processing is the time migrated data cube. With conventional processing, this cube is generated by poststack time migration of the zero-offset cube, obtained by NMO-DMO stacking of multi-offset data. A major drawback of this processing sequence is, that migrated data can only be inspected at a very late stage of data processing and that there is no simple and efficient technique to derive the migration velocity field. In this presentation we show results of a recently developed 3-D prestack time migration technique to overcome this deficiency. Our method allows the generation of time migrated bin-gathers on a coarse grid within the 3-D survey, without a priori knowledge of a migration velocity field. These gathers hold an offset axis and a two-way travel-time axis, where the time is measured along the image ray. The migration velocities can then be estimated from the generated migrated data by conventional means, e.g. from semblance velocity spectra and multi velocityfunction stacks. The stack of the migrated data generates the proposed quick-look of the 3-D time migrated data set on the coarse grid. The estimated migration velocities are an additional product of this technique. They can be used to replace the smoothed dip-corrected stacking velocity field for the poststack migration of the zero-offset cube on the final grid.
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Can we afford the time for ´time´ processing?
Authors K. Hawkins, D. Evans, R. Laver, M. Vickers, N. Oliver and J. AndersonAnyone that is involved today with exploration for new gas reserves or production from fields about to come on stream in the Southern Gas Basin will be acutely aware of the recent dramatic drop in gas prices as a reward for their efforts. The situation is further aggravated by the fact that many of the remaining potential discoveries he in Carboniferous structures under complex overburdens and at considerable depth - in excess of four kilometers - which can make prospect definition uncertain and drilling cost high. In these situations the risk has to be defined as accurately as possible.
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Converted-wave (P-S) prestack migration and velocity analysis using equivalent offset migration
Authors J. C. Bancroft and S. WangA new approach for converted-wave prestack migration and velocity analysis is based on equivalent offset prestack migration using common scatter point (CSP) gathers (Bancroft et al. 1995, Wang et al. 1995). Each prestack migrated trace, gathers all input traces within the prestack migration aperture, and sorts them into offset bins based on an equivalent offset. The equivalent offset may be time varying, and is based on the offset of the scatter point from both the source and receiver.
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Steep dip Kirchoff migration for linear velocity gradients
Authors N. W. Martin, M. S. Donati and J. C. BancroftA non-hyperbolic Kirchhoff summation curve is introduced for 2-D post-stack time imaging of dips up 120° in a linear-with-depth (or constant gradient) velocity medium. It can be expressed as a 8th order polynomial equation whose coefficients are function of the half offset and velocity gradient.
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Some geophysical consequences of fractal scaling
More LessFractal models are being used to an increasing extent in the earth sciences to describe objects as diverse as cloud shapes or rock fractures (Korvin, 1992, is an excellent review of the topic.) Implicit in this is the belief that many natural phenomena have attributes that are unchanged over a wig range of scales. A photograph of a cliff face, for example, reveals a number of sedimentary layers; closer inspection reveals yet more layers. If the picture does not include the requisite rock hammer, or geology student, the scale of the object is unknown and in essence the image is scale free.
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The quantification of seismic data quality - (i) The method
Authors I. Scott, P. Armstrong and D. IresonEveryone would agree that it is essential to assess the quality of seismic data at each stage of the seismic process. Currently, this is generally based on subjective notions of quality which can only lead to a final product with unknown quality. There is obviously a need for an objective method to assess quality which can be used to improve the reliability and efficiency of acquisition and processing decisions.
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The quantification of seismic data quality - (ii) A case study
Authors L. Peardon, T. Birks and I. ScottThe Quantified Quality Assurance (QQA) methodology is a combination of statistical and deterministic analysis to quantify the quality of seismic data. This approach, described in detail in a companion paper by Scott, Armstrong and Ireson, 1996, is applicable to both acquisition and processing. In this paper, we describe an acquisition case study showing the use of the method in a 3D marine seismic survey.
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A Field case of data quality analysis
Authors B. C. Scheffers, E. C. C. Wildeboer Schut, J. A. C. Meekes and H. L. H. CoxTNO Institute of Applied Geoscience has developed a prototype Data Quality Analysis system that has been applied on several datasets. This paper presents the application on a high resolution seismic survey. The objective of this survey was to obtain a detailed image of the upper 50 to 400 m. For this, data with a wide frequency range up to 250 Hz is required. We encountered cases of very poor data quality without apparent evidence for a particular type of noise, or deficiency in the field operations. The aim of performing an analysis on quality aspects of the data is to enable us to anticipate on lateral variations at acquisition time.
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A Comparison of multi-dimensional wavelet compression methods
More LessMulti-dimensional, wavelet transform based, lossy compression of seismic data is increasingly being recognized as an effective means of substantially reducing seismic data volumes while maintaining the data integrity sufficient for many, if not all processing and interpretation applications. The benefit, or increase in compression ratio for a given quality level, gained by using a three dimensional (3D) compression method versus a two dimensional (2D) method is described quantitatively in terms of L1 and L2 norm error metrics. Conversely, the drawbacks incurred by using higher dimensional compression methods are illustrated in light of realistic operational environments.
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Analyzing and zerophazing seismic data using the wavelet transform
Authors S. Mansar and J. -M. RodriguezThe aim of any signal analysis method is to transform a signal into a new space where extraction of relevant information is possible. For instance, time structure information is obtained via the time sampling and the frequency structure information via the Fourier transform. When dealing with seismic signals and reservoir characterization, we need a description of the evolution of the frequency structure with time. The Continuous Wavelet Transform (CWT) [1] can achieve this purpose. An important condition for seismic signal analysis and reservoir characterization is the zero-phase condition. In this paper a CWT based method is derived for target ori ented zero-phasing.
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Coherence computations with eigenstructure
More LessSeismic coherence is a measure of similarity or dissimilarity between seismic traces. Varying between zero and one, zero indicates the greatest lack of similarity, while a value of one indicates total similarity, i.e., two identical traces. Coherence for more than two traces is defined similarly.
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Extraction of attributes from 3D seismic data
Authors P. Steeghs and G. G. DrijkoningenThe characterization of seismic data in terms of their spatial properties, such as horizon dip and azimuth, has greatly improved the interpretation of 3D seismic data (Hoetz and Watters 1091). In most cases the 3D seismic attributes are extracted at or between picked seismic horizons. In our paper we present an alternative method for 2D and 3D attribute extraction, that does not require the picking or tracking of horizons. We extend the relation between the 1D complex trace attributes and local spectra (Steeghs et al. 1995) to higher dimensions. Using the local 2D wavenumber-frequency spectrum we can extract dips and azimuths over time slices in 3D seismic data.
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Design, Manufacture and installation of a permanent seabed sensor network for seismic reservoir monitoring
Authors K. Roed, E. Dietrichson and D. IresonThe abstract of this presentation was made available at the Conference
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The dual-sensor ocean bottom cable method - Attributes, North Sea tests and recent advances
Authors F. J. Barr, J. Paffenholz and W. RabsonIncreasing numbers of 3-D seismic surveys are being conduct ed over producing fields to help improve hydrocarbon recovery. Existing fields are covered with oil-field equipment, including production well heads, pumps, and compressors. The amount of equipment and its areal distribution increases during the life of the field. Offshore, this equipment is installed on platforms that are dangerous obstacles for marine seismic vessels towing streamers.
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Seismic methodologies for a 3 components sea floor geophone experiment on a potential flat spot in the Vøring Basin
Authors M. Brink, P. Y. Granger, M. Manin and S. SpitzThe usefulness of shear waves to obtain physical properties in relation to lithology is well known. Indeed, shear waves are less sensitive to pore fluid changes than compressional waves. At the same frequency, S waves achieve higher vertical and lateral resolutions than P waves. The advantages of S waves methodology have been demonstrated in land seismic. In the last years the industry has shown a growing interest in acquiring S waves at the bottom of the sea. Valuable information in a blind area for P waves caused by a gas chimney have already been obtained from such a 3 components acquisition (Berg et al., 1994). In this paper we present an experiment made to confirm the interpretation of a potential flat spot detected by surface acquisition.
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P- and S-wave separation for ocean bottom seismic recordings
Authors M. S. Donati and R. R. StewartThe quest for a more detailed and confident description of the subsurface has led to the rise of three-component (3- C) seismic surveying. Considerable effort is currently being expended to make and use converted-wave (P-to-S reflection) seismic sections from these 3-C recordings. Most of the effort to date has been with land recordings. However, with the advent of the SUMC (subsea seismic) survey and its very promising early results (Berg et al., 1994), more attention is focusing on the marine 3-C case. A fundamental aspect of deciphering 3-C records from the ocean bottom is to understand how seismic waves interact with a geophone at a fluid-solid interface. This paper reviews the basic theory of the geophone response at the water bottom and proposes a new filter to separate P and S waves so recorded. The separation filter is based on the methods of Dankbaar (1985). The separated waves (pure P and S) are then further processed into their respective sections.
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An Improved method for determining water bottom reflectivities from dual-sensor ocean bottom cable data
Authors J. Paffenholz and F. J. BarrThe primary goal of the Dual-Sensor technology is the elimination of the receiver ghost response which corrupts single hydrophone ocean-bottom cable data. The Dual-Sensor data allow separation of the wavefield into up- and downward traveling components. Therefore, elimination of the surface reflected energy is straightforward and is achieved by simple summation of the pressure and velocity signals. If however a suitably scaled velocity trace is used in the summation, both the up- and the downward traveling parts of the wavefield trapped in the water layer can be eliminated (Barr and Sanders, 1989; Barr, 1989). The scaling factor is a function of the oceanbottom reflectivity. Here we describe a method to derive the ocean-bottom reflectivity from production seismic data. The method eliminates the need for a separate calibration survey and is stable in the presence of random and shot-generated noise.
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Ghost attenuation in dual-sensor cable data
Authors L. L. Canales and M. L. BellBottom cable acquisition has become in use because it permits very sophisticated geometries. Particularly it permits placing the receivers very close to platforms or other obstacles. The bottom cable presents new problems, particularly the ghost produced by reverberations in the water column above the cable. One solution to this problem has been introduced by F.J. Barr et. al. (1990). A dual sensor bottom cable is used, one sensor records pressure and the other records vertical velocity displacement. The two sensors have the ghost notches at different frequencies so that the properly scaled sum produces a high signal to noise trace that is free of the ghost.
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Multiple attenuation on multicomponent sea floor data modelling
Authors A. Osen, L. Amundsen and A. ReitanFor several years, new technologies for recording seismic data directly on the sea floor have been evolving. Bottom cables for recording 3-D surveys near obstacles in shallow water were introduced in the mid-80's. Barr and Sanders (1989) designed a water-bottom cable with pressure and vertical velocity detectors to attenuate water-column reverberations. Berg et al. (1994) developed a concept for directly recording three-component particle velocity data along with pressure data on the sea floor. Recently, seismic contractors have licensed acquisition technologies for acquiring multicomponent sea floor data.
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Integrated 3D acquisition and processing techniques in heavily obstructed areas - the Belayim Field case history
Authors G. La Bella, D. Calcagni, G. Ronchitelli and I. MohamedThe sub-salt sequence in the Gulf of Suez (Egypt) is worldwide renown as one of the most difficult to be correctly imaged on seismic sections, due to the very strong multiple effects that almost completely mask the target seismic response.
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