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- Volume 25, Issue 3, 2007
First Break - Volume 25, Issue 3, 2007
Volume 25, Issue 3, 2007
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Automated delineation of geological elements from 3D seismic data through analysis of multichannel, volumetric spectral decomposition data
Authors J. Henderson, S.J. Purves and C. LeppardJonathan Henderson,Stephen J Purves,and Chris Leppard describe some innovative volumetric spectral decomposition techniques designed to optimize the amount of geological information obtainable from seismic data sets. The spectral content of recorded seismic data is dependent on the acoustic properties of the earth along the propagation path. Variations in spectral content occur due to variations in bed thickness/tuning effects, the nature of the interface between different layers (fining/coarsening sequences) and changes in pore-fill, in particular the presence of gas. Although in most instances insufficient information is available to isolate why a particular change in the received frequency spectrum has occurred, significant insights can be gained from examining the spatial variation of the response at different frequencies. This has led to substantial interest in spectral decomposition as a seismic interpretation tool for both stratigraphic analysis (Partyka et al., 1999, Marfurt and Kirlin 2001, Johann et al., 2003) and for hydrocarbon detection (Castagna et al., 2003). In general, application of spectral decomposition to interpretation of 3D seismic data has involved extraction of data associated with 2D planes or horizons or producing 3D data sets that show the response at a single frequency. To realize the full potential of spectral decomposition, techniques are required that allow the 3D spatial variation in response at different frequencies to be analyzed and the results of the analysis to be used for 3D delineation of geological elements (GeoBodies).
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Advances in quantitative model-assisted seismic interpretation
Authors H. Gjøystdal, A. Drottning, I. Lecomte and M. BranstonHåvar Gjøystdal, Åsmund Drottning, Isabelle Lecomte, and Mike Branston* of NORSAR Innovation, introduce a modelling concept that aims to provide users with the tools to make a quantitative interpretation of their seismic data. Today’s seismic interpretation and attribute analysis is performed at many levels in the E&P cycle – from structural horizon picking in early exploration, to advanced 4D reservoir studies during petroleum production. In many cases the interpretation process is simply a systematic collection of seismic attributes (e.g. horizon/attribute tracking) without any direct relation to a particular model behind. In more advanced interpretation, it can be very fruitful to relate the interpretation to a well-defined geo-model representation. We have developed a new software tool (SeisRoX) based on the idea that such a geo-model should always exist. In this context, the geo-model is defined as a spatial representation of geophysical and geological properties in a certain volume of the subsurface, containing sufficient information to allow a simulation of the seismic response of that model which includes external constraints, such as survey geometry and source signature. The seismic response will usually have different meanings depending on its intended use. It could, for example, be calculated traveltimes or simulations of seismic data in prestack or poststack domains. Seismic response is a simulated migrated seismic cube, or seismic attributes deduced from such a cube as this is the usual working domain for most interpreters.
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Scalable desktop solutions transform the oil and gas industry
By Y. NirYoav Nir of visualization company Barco reports on how hybrid display technology can produce a cost effective, collaborative visualization experience which enhances the geoscientist’s analysis toolkit and ultimately improves the bottom line for E&P companies. The oil and gas industry is evolving. Facing limited natural resources, greater demand, and stiff international competition, companies must examine their research procedures to achieve maximum efficiency and productivity. In particular, they must re-evaluate the way they analyze information. Unprecedented streams of data are available today from desktop software, satellite feeds, sophisticated computer applications, and other inputs. Oil and gas companies have a vast array of information resources at their disposal, but they lack the ability to fully understand the dynamics and interrelationships of all these resources in a unified context. To the extent that they are successful at managing, manipulating, and mining this multi-faceted information, they tend to do so in isolated ‘silos.’
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Report on EAGE Vienna 2006 workshop on marine multi-azimuth seismic
Authors P. Fontana and T. SummersThe EAGE conference in Vienna, June 2006 was the venue for a workshop on one of the most interesting developments in seismic technology in recent years. The subject was multiazimuth and wide azimuth seismic surveying in the marine environment, with emphasis on its application in deepwater environments. The timing of this workshop was particularly appropriate with the introduction, since 2004, of several new technologies and methodologies to image below complex overburden in major deepwater oil and gas provinces. The workshop brought together a range of presenters from E&P companies and seismic contractors to present the state of play in the technology and discuss challenges for the future. It was the first of several sessions on the subject in 2006. The EAGE workshop was followed by the SEG/EAGE Summer Research Workshop on subsalt imaging and a special session on multi-azimuth and wide azimuth seismic at the SEG convention in October. Below is a summary of the EAGE Multi-Azimuth workshop as an introduction to the papers in this special edition of First Break. The perspectives provided in the two authors’ keynote papers as coordinators of the workshop form the basis of this article.
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Experience with towed streamer multi-azimuth processing and acquisition
Authors C. Page, R. Van Borselen, E. Fromyr, J. Keggin, T. Manning and W. RietveldMulti-azimuth towed streamer acquisition is a technique whereby conventional marine 3D seismic surveys are acquired in several distinct acquisition directions and then combined in some way to produce an improved image. The method as described here has produced some impressive comparisons in the literature, e.g., Keggin et al. (2006), Page et al. (2006), and is drawing increasing interest especially for areas of poor signalto-noise ratio. Over the years that this method has been pioneered, some standard acquisition and processing procedures have been established which will be discussed here with examples from BP’s six azimuth Raven survey from the Nile Delta, courtesy BP Egypt.
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Multi-azimuth 3D provides robust improvements in Nile Delta seismic imaging
Authors J. Keggin, M. Benson, W. Rietveld, T. Manning, P. Cook and C. PageSince gas was first discovered in the Nile Delta in the late 60s, most exploration programmes have focussed on shallow Pliocene reservoirs, where gas can clearly be seen as bright events on excellent quality seismic data and where exploration success has been very high. The petroleum geology of the deeper pre-Pliocene section is fundamentally no different to that seen in the Pliocene, where potential reservoirs consist of sand prone channel systems originating from the Nile. Why then, have we been deterred from exploring in the deeper section? The problem is two fold: 1. Deeper burial and harder rocks mean that reservoir sands and hydrocarbons will be less visible on our seismic data. 2. Pre-Pliocene seismic quality is highly variable and often very poor. (Figure 1) Poor imaging being the result of wavefield distortion though the Messinian anhydrite layer, attenuation, and the presence of complex multiple diffraction noise.
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Multi-azimuth towed streamer 3D seismic in the Nile Delta, Egypt – processing solutions
Authors W. Rietveld, T. Manning, M. Benson, J. Keggin, A. Burke and A. HalimMulti-azimuth or wide azimuth seismic is not a new technology, and has been with us for many years in the form of land, and ocean bottom surveys. The literature is rich with examples of how high-fold multi-azimuth data can produce stunning improvements over their single azimuth 3D equivalents (Rogno et al., 1999, Keggin et al., 2002, Gaus and Hegna, 2003, Arntsen and Thompson, 2003, Riou et al., 2005, Manley et al., 2006, Michell et al., 2006). We know from theory and case histories that multi-azimuth data will lead to improved signal to noise, improved multiple attenuation and improved illumination. However, because of approximations in current processing technology, the processing of multi-azimuth data will leave errors in the final imaged results. Simple stacking of the data, though surprisingly robust makes assumptions about data consistency between surveys and will likely not result in the most optimal image. This paper shows how multi-azimuth (MAZ) towed streamer data is processed in the Nile Delta, looks at some of the issues highlighted above and discusses the initial processing sequence to improve the combined subsurface image.
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Rich azimuth marine seismic, a cost effective approach to better subsalt images
Authors M. Howard, C. Harding and D. StoughtonThere are many areas of complex velocity structure, such as subsalt areas in the Gulf of Mexico, where improvements in depth imaging and noise removal have given better images. However, with several subsalt discoveries, we found some areas where these images are inadequate for cost effective appraisal and development. There have been many cases (some published, for example, O’Connell et al., 1993) where a new seismic survey in a different orientation improves the image in some areas of complex structure, while the image in other areas is better on the original data. These examples suggested that source-receiver azimuth was an important part of the equation. In the spring of 2006, we acquired a rich azimuth survey over our Shenzi discovery (centered on Green Canyon block 653) that took substantially less effort (cost) than we originally imagined. We have presented results at both EAGE and SEG meetings (Howard et al., 2006). This paper documents for a larger audience the studies that led to the decision to conduct the survey and some of those results.
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Shot-based pre-processing solutions for wide azimuth towed streamer datasets
Authors P. Herrmann, G. Poole, A.L. Pica, S. Le Roy and R. TaylorWide azimuth towed streamer (WATS) acquisition has been shown to provide improved seismic imaging, especially in areas with complex 3D structures. By making use of additional source vessels shooting into the streamer array from large lateral offsets, a dataset is created with a large cross-line aperture, higher fold, and a broader offset-azimuth distribution than conventional (narrow azimuth) streamer datasets. The improved imaging provided by WATS acquisition geometry has been well illustrated as this method is being more widely adopted. An example which illustrates the superiority of WATS data for imaging was given by Michell et al. (2006). There, a straightforward depth migration of WATS data with limited pre-processing was shown to provide a significantly improved image compared to the results obtained with conventional streamer acquisition.
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Experiences with full-azimuth acquisition in ocean bottom seismic
Authors M. Thompson, B. Arntsen and L. AmundsenThe problem of collecting seismic data is rather like attending a football match, as described in the textbook ‘Introduction to petroleum seismology’ (Ikelle and Amundsen, 2005). Your view of the game depends not only on the lighting system of the stadium but also on where you are sitting. For example, a journalist may prefer to be in the stands where he or she will have a good view of the entire game, which is necessary for analyzing and reporting all of the moves and tactics. A photographer, however, may prefer to be near the touchline where he or she can immortalize the goals, even at the expense of not seeing the rest of the game. The ticket prices for these special positions may be more than that of a standard seat; but the extra cost will pay off handsomely. As in football matches, the view of the subsurface given by seismic data is determined by the location of the sound sources for ‘illuminating’ the area of interest, and the location and types of sensors that capture the ground motion caused by the passage of seismic waves.
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Volumes & issues
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Volume 42 (2024)
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Volume 41 (2023)
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Volume 40 (2022)
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Volume 39 (2021)
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Volume 38 (2020)
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Volume 37 (2019)
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Volume 36 (2018)
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Volume 35 (2017)
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Volume 34 (2016)
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Volume 33 (2015)
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Volume 32 (2014)
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Volume 31 (2013)
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Volume 30 (2012)
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Volume 29 (2011)
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Volume 28 (2010)
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Volume 27 (2009)
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Volume 26 (2008)
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Volume 25 (2007)
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Volume 24 (2006)
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Volume 23 (2005)
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Volume 22 (2004)
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Volume 21 (2003)
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Volume 20 (2002)
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Volume 19 (2001)
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Volume 18 (2000)
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Volume 17 (1999)
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Volume 16 (1998)
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Volume 15 (1997)
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Volume 14 (1996)
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Volume 13 (1995)
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Volume 12 (1994)
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Volume 11 (1993)
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Volume 10 (1992)
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Volume 9 (1991)
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Volume 8 (1990)
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Volume 7 (1989)
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Volume 6 (1988)
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Volume 5 (1987)
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Volume 4 (1986)
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Volume 3 (1985)
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Volume 2 (1984)
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Volume 1 (1983)