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- Volume 32, Issue 6, 2014
First Break - Volume 32, Issue 6, 2014
Volume 32, Issue 6, 2014
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Multi-Focusing imaging and regularization of an irregular 3D dataset in an urban environment
Authors Nicole Elhaj, Steven Rutherford, Dan Gish, Marianne Rauch-Davies, Danil Pelman and Kostya DeevNicole Elhaj, Steven Rutherford, Dan Gish, Marianne Rauch-Davies, Danil Pelman and Kostya Deev present a technique that provides coherent stacking of seismic data and enhanced pre-stack gathers. Increasing the fold for a coherent summation of the traces reduces random noise and increases the signal-to-noise ratio. The Multi-Focusing (MF) technology is based on multi-parameter and the correction formula is accurate, even for heterogeneous subsurface and strongly curved reflectors. A multi-parameter approximation for the actual traveltime surfaces, three parameters in 2D and eight parameters in the 3D case, are being utilized. These parameters are connected to emergence angles for the normal waves and radii of curvature for fundamental wavefronts, namely normal incident point and normal waves. When stacking reflection events with a larger number of seismic traces that can span many CMP gathers, the signal-to-noise ratio is enhanced and by simultaneously scanning for the parameters, negative effects are avoided and artifacts minimized.
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Experiencing the full bandwidth of energy from exploration to production with the art of BroadSeis
Authors Jo Firth, Idar Horstad and Menne SchakelJo Firth, Idar Horstad and Menne Schakel present the latest developments in BroadSeis broadband technology. The exceptionally broad bandwidth of more than 6 octaves delivered by BroadSeis variable-depth streamers, in combination with a BroadSource multi-level broadband source and advanced imaging algorithms, not only provides unprecedented information about the subsurface, it also produces stunning images. In particular, the additional high signal-to-noise ratios at low frequencies, down to 2.5 Hz, provide extra ‘texture’ as these provide an envelope to the seismic signal which shapes the larger-scale impedance variations, to deliver clear distinction between stratigraphic packages (see Figure 1). This full bandwidth has been exploited in many areas of the world to reduce exploration risk, improve development plans and maximize return on investment.
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Image-guided tomography: structure conforming inversion for complex overburden
Authors Guy Hilburn, Yang He, Francis Sherril, Taejong Kim and Zengjia YanGuy Hilburn, Yang He, Francis Sherrill, Taejong Kim and Zengjia Yan present a highresolution tomography method which flattens gathers reliably and quickly, while yielding geologically plausible velocity models. Traditional methods of updating velocity models by seismic tomography rely on a number of assumptions and simplifications. In many situations, these may either increase the amount of time or number of tomographic iterations required to flatten events in migration gathers, or even make gathers worse. In other cases, the velocity models obtained with these techniques may turn out to be physically unlikely, as they do not rely on prior geological knowledge. We have developed a high-resolution tomography method called image-guided tomography (IGT), which is composed of two key ingredients: inversion preconditioned by image-guided interpolation (IGI) and an offset-dependent residual moveout (RMO) picking technique. IGT flattens gathers more reliably and quickly than traditional methods, while yielding more geologically plausible velocity models.
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Applying a new synchronous inversion of seismograms using maximum likelihood method and stochastic refinements to study ultra-thin oil-saturated reservoirs
More LessSeismic inversion makes use of single or multi-dimensional seismic trace data to derive elastic properties from seismic amplitude data. These elastic properties are subsequently used to make inferences about seismic lithology, lithologic properties, and the presence of fluids. Most implementations of seismic inversions operate on limited stacked subsets of the seismic data. Common inputs to inversion methods include angle stacks, offset stacks, or multiple stacks of time-lapsed data. The implementation in this paper makes use of a synchronous pre-stack inversion based on the maximum likelihood algorithm (Anat Canning and Alex Malkin, 2009). The PMLI inversion is applicable to time and depth angle or offset seismograms. It is a full pre-stack inversion, which inverts each and every trace of an offset or angle gather and returns elastic properties. The PMLI inversion can also invert partial angular or offset sums, which can be created in any processing system. As a complete pre-stack inversion, PMLI provides higher accuracy and noise immunity as observed in the output results of Pw and Sw impedances, density, Vp/Vs, Poisson’s ratio, Lambda Rho (LR) and Mu Rho (MR). PMLI also incorporates a necessary and effective preprocessing step, which is performed on-the-fly as part of the inversion process. Because the PMLI method operates on gathers, it is easily and efficiently parallelized for multi-core and multi-node clusters and for shared memory architectures.
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High-fidelity complete wavefield velocity model building and imaging in shallow water environments – A North Sea case study
Accurate sub-surface image reconstruction from prestack depth migration of surface seismic wavefields requires precise knowledge of the local propagation velocities between the recording location and the image location at depth. Such velocity information has traditionally been derived by tomographically inverting residual moveout information of common image gathers, which have been computed using an initial velocity field. This methodology proves to be challenging in shallow water environments, particularly when strong and rapid velocity variations in the very shallow overburden need to be recovered, while moveout information from reflected arrivals is very sparse or not available.
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Airborne resistivity: mapping subsurface stratigraphy from the air
Authors Horace Snyder and Carl KincheloeElectrical resistivity is one of the fundamental physical properties of the subsurface Earth and, from the perspective of many explorationists, one of the most important. Conrad and Marcel Schlumberger, for whom the largest oilfield service company in the world is named, pioneered the concept of using downhole electrical measurements to map subsurface rock formations in 1926. Since then, resistivity measurements have been captured for almost every well drilled in the world as part of the standard well logging suite. The value added by the traditional oilfield resistivity measurement comes from the fact that hydrocarbon- rich reservoir rocks tend to be electrically resistive while water-filled zones are not. Powerful as this type of resistivity information is, one significant flaw exists with the logging technique – it requires a well to be drilled.
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4D seismic, 4D geomechanics and hydraulic stimulation in the low permeability South Arne chalk field
Authors O.V. Vejbæk, F.R. Mohamed and J.V. HerwangerGeomechanical models have many purposes in reservoir management. Applications include the prediction of reservoir compaction, subsidence and long-term well-bore integrity, optimization of drilling trajectories and mudweights, and the design of hydraulic stimulation and perforation campaigns. The basis for all geomechanical applications is an accurate knowledge of the subsurface stress state, pore pressure and the mechanical properties, which in combination form a geomechanical (or mechanical earth) model. To increase trust in their predictions, these models need to match data observations that are linked to the subsurface stress-state. In the initial phases of reservoir production, such observations typically include observations during drilling (e.g., loss of drilling mud allows estimation of an upper bound for pore pressure, and inflow events give a lower bound for pore pressure), observations of drilling-induced fractures and wellbore breakouts, as well as leak-off and formation integrity tests. During reservoir production wellbore failure in shear and compaction gives indications of production-induced localized strain. On a field-wide scale, time-lapse seismic time shifts in the overburden are now commonly ascribed to reservoir compaction and serve as a field-wide calibration method for geomechanical models. Reservoir compaction causes overburden elongation and an associated velocity slow-down (Hatchell and Bourne, 2005), and this causes an increase in two-way traveltime between base- and monitor survey, termed time-lapse time shift. This close link between observed time-lapse time shifts and the modelled reservoir compaction and overburden elongation is now being used as a field-wide calibration tool for geomechanical models (e.g., Staples et al., 2007; Herwanger and Koutsabeloulis, 2011).
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From rock physics to geophysical data integration: theory, applications and implications
More LessPaolo Dell’Aversana of Eni tells First Break about his new book that will raise the bar on integration of multi-disciplinary geophysical models. He will be speaking more about integration in geophysics during the EAGE Student Lecture Tour Europe in 2014-2015. The book, setting out his ideas on practical and theoretical aspects of integration will be available to buy at the EAGE bookshop at the Annual Meeting in Amsterdam.
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Seismic stratigraphy of the Lower Cretaceous Valhall Formation (Danish Graben, North Sea)
Authors Marie Vidalie, Frans van Buchem, Ingelise Schmidt and Anette UldallDetailed seismic stratigraphic analysis of a 3D seismic survey covering the southern part of the Danish Central Graben in the North Sea has revealed a complex stratigraphic basin infill pattern controlled by eustacy and local tectonics in the Lower Cretaceous Valhall Formation. The understanding of the stratigraphic architecture of this mudstone formation is critical for the development of the overlaying chalk reservoirs of the Tuxen and Sola Formations. The applied workflow included an application of flattening in order to approximate the Lower Cretaceous basin morphology, the attenuation of multiples generated by the overlying chalk deposits, a systematic use of both 2D transects and horizon slices in the analysis of the depositional geometries and the application of a Relative Geological Time (RGT) model interpretation technology. The results show an asymmetrical infill of the Lower Cretaceous consisting of westward prograding, mud-dominated clinoforms. The overall progradational pattern is clearly expressed in the most southern part of the basin by coast-parallel features interpreted as shelf margin breaks. The asymmetrical paleotopography, created by the muddy shelf of the Valhall Formation, formed subsequently the substratum for the deposition of the chalks of the Tuxen and Sola Formations, and controlled their facies distribution.
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Is curvature overrated?
More LessCurvature seismic attributes identify where fractures are more likely to occur, and offer a detailed view of structural features. They have no rivals for the first purpose, but for the second purpose they compete with discontinuity and other structural attributes. Many studies give the impression that curvature is superior to discontinuity for all purposes. However, for routine mapping of faults and channels, discontinuity is consistently more interpretable than curvature, whether derived from seismic data or their amplitudes. Amplitude change is often better as well. Curvature reveals finer detail than other attributes, but the significance is unclear.
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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)