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76th EAGE Conference and Exhibition - Workshops
- Conference date: 16 Jun 2014 - 19 Jun 2014
- Location: Amsterdam, Netherlands
- ISBN: 978-90-73834-90-3
- Published: 16 June 2014
101 - 120 of 142 results
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Simultaneous CRS Parameters Search Based on a Non-linear Conjugate Gradient Method with Preconditioning
By S. DellMulti-parameter methods, e.g., Common-Reflection-Surface (CRS) stacking, have become popular because they exploit increased data fold compared to conventional CMP processing, resulting in an improved signal-to-noise ratio and, thus, enhanced images. However, these methods require additional effort since they incorporate more stacking parameters than CMP processing. The simultaneous brute-force search for all parameters is still not common because the increase in computer performance is countered by an increasing amount of acquired data (the amount grows faster than Moore’s law). An optimization method can therefore serve as an alternative to the global (brute-force) approach since it reduces the number of evaluations of the coherence functional (e.g., semblance) significantly. I propose to use a non-linear conjugate gradient method to estimate the CRS attributes. The method utilizes the secant method, the Polak-Ribière formula, and preconditioning. I applied this approach to a complex marine dataset which led to more focused stack results than using the traditional pragmatic CRS attribute search.
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Effective CRS Workflow for Prestack Data Regridding, Regularization, and Depth Imaging
Authors G. Eisenberg-Klein, H. Trappe, H. Endres and J. PruessmannThe common-reflection-surface (CRS) technique provides an effective workflow for seismic data preparation and imaging in large areas of regional studies. In a case study from the North Sea, the multi-parameter stacking technique is used to combine and homogenize vintage seismic data in time domain, and to accelerate the model building cycle in depth imaging. CRS time processing may directly start from input data acquired at diverse natural binning grids, and provide the regularisation and interpolation to a uniform output grid in one step. The regular CRS gathers show an almost complete CMP-offset coverage and a high signal to-noise ratio, and thus enhance the resolution of prestack migration in time and depth. Depth model building departs from the CRS attributes which provide the initial model via CRS tomography, and benefits in the model update by residual moveout analysis from the enhanced signal-to-noise ratio in the prestack data.
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MultiFocusing Imaging for Seismic Data with Irregular Acquisition Design in Densely Populated Areas
Authors N. Elhaj, S. Rutherford, D. Gish, M. Rauch-Davies, K. Deev and D. PelmanAcquiring seismic 3D data in highly populated areas is very difficult. The design of such surveys is usually highly irregular and the processing of these data challenging. The MultiFocusing (MF) imaging technology, which belongs to the group of multi-parameter processing (MPP) methods, does not require a regular acquisition design and is especially suitable for such scenarios. We will illustrate this imaging technology and show MF data regularization results utilizing an irregular 3D dataset acquired in a populated area in the USA. A 3D dataset that was acquired with a highly irregular design over a densely populated area was processed with a conventional processing sequence and with the multi-dimensional MF methodology. The MF data regularization was crucial for this dataset for subsequent prestack time and depth imagining. The first MF dataset had a 110ft x 110ft binning. Further testing showed that a binning of 55ft x 55ft produced the best results for horizon mapping and was used for the final PSTM delivery. For additional attribute work, the 110ft x 110ft binning was more suitable as it showed a higher frequency content.
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CRS Offset-azimuth Regularisation of Wide-azimuth Seismic Data for Optimized Imaging and Amplitude Studies
Authors J. Pruessmann and G. Eisenberg-KleinWide azimuth (WAZ) marine seismic data commonly provide an enhanced but varying coverage in azimuth-offset domain, which decreases towards crossline azimuths and near-offsets. The variable offset-azimuth illumination of WAZ data is commonly exploited in prestack depth migration in order to resolve complex subsurface structures, but often leads to amplitude footprints due to the variation, that disturb AVO and AVAZ analyses. An interpolation in azimuth-offset domain based on the CRS technique may largely reduce these footprints, and effectively precondition the data for amplitude studies. The CRS, or Common Reflection Surface method is essentially a multi-parameter stacking method that is used here to regularize and interpolate the data in one step. A regular coverage in CMP-offset-azimuth is thus achieved in most part of the data. Subsequent azimuth-dependent prestack time migration provides high resolution images at low migration noise, with strongly reduced footprints and well-preserved amplitude trends as a basis for subsequent amplitude studies.
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Common-Refection-Surface (CRS) Stacking with Diffraction Moveouts of Varying Aperture
Authors J.H. Faccipieri, T.A. Coimbra, M. Tygel and L.J. GeliusA modified version of the CRS stacking method based on diffraction moveouts with different midpoint and half-offset apertures is shown to provide clean stacked sections of reflection and diffraction events. Moreover, as the CRS diffraction moveout depends on fewer parameters than its counterpart conventional reflection moveout, the proposed approach also benefits from less computation effort. Illustrative real-data examples are provide showing good potential of the proposed approach.
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Kirchhoff-type Pre-stack Time Migration Using the CRS Stacking Operator
By G. GarabitoThe Common Reflection Surface (CRS) stack method was developed to simulate ZO (zero-offset) staked sections from multi-coverage datasets. However, stacked data plus post-stack migration may loss quality in structural complex geological environments. In order to obtain high-quality images, in this work is presented an application of the CRS stacking operator for pre-stack time migration (PSTM). This new method called combines the classical Kirchhoff migration with the CRS operator, that is, for each sample point to be migrated with the Kirchhoff migration operator a beam-type stacking is performed of the locally coherent events using the CRS stacking operator. To test the reliability the CRS-beam PSTM is applied to expressively crooked seismic data. A comparison with the result of the Kirchhoff PSTM reveals that this new method produces improved image.
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3D Velocity Independent Diffraction Imaging
Authors E. Bonomi, G. Caddeo, C. Tomas and P. MarchettiThis paper shows a new approach for 3D time imaging, that is based on diffractions and does not need any informations about the subsurface
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A CRS-based Heterogeneity Attribute
Authors J.H. Faccipieri, T.A. Coimbra, L.J. Gelius and M. TygelAn attribute describing heterogeneity is proposed based on the diffracted-wave contribution. In areas of complex geology the amount of diffracted energy will increase relative the specular reflections. By use of the modified CRS technique, a reliable measure of the diffractions can be obtained. Proper scaling with the output from a conventional CRS stack gives a normalized measure of the complexity of the geology. The new attribute has possible use both in seismic texture analysis and as a weight factor employed to combine CRS based reflection- and diffraction-enhanced stacks. The potential of the heterogeneity attribute is demonstrated using seismic data from offshore Brazil.
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From Zero-offset to Common-offset with Diffractions
Authors B. Schwarz, C. Vanelle and D. GajewskiThe simulation of a zero-offset section leads to a first interpretable time image and is still one of the key processing steps. While recent works have indicated that common-offset stacking leads to improved resolution and illumination in complex settings, the zero-offset approximations are reasonably accurate, when lateral heterogeneity is moderate. Due to the increased dimensionality of the problem, the common-offset stack is computationally expensive, though. We suggest a hybrid scheme in which the zero-offset operators are locally refined by their common-offset counterparts. We show that for diffractions, the necessary connection between the attributes is achieved by simple geometrical reasoning. Synthetic examples indicate that due to the symmetry of raypaths, the zero-offset diffraction attributes can directly be used to perform a common-offset stack, promising a high potential for improved prestack separation and inversion.
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Gardner Continuation
By S.B. FomelI define Gardner continuation as a continuous seismic-data transformation, described by a special linear partial differential equation. Under the usual approximations of prestack time migration, Gardner continuation transforms prestack seismic reflection data to remove both the dependence of moveout velocities on dip and the non-hyperbolic dependence of reflection moveouts on reflector curvature. This provides a useful reversible preconditioner of seismic data for different seismic data processing tasks.
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Geophysical Basin Modeling - Effective Stress, Temperature and Pore Pressure Uncertainty
Authors G. De Prisco, M.P. Corver, I. Brevik, H.K. Helgesen, D. Thanoon, R. Bacharach, K. Osypov, R.E.F. Pepper and T. HantschelThe predictive capability of a geo-simulator is strictly related to the quantification of uncertainties related to its inputs. This study addresses the problem of quantifying uncertainties for and from a geo-model system at basin length scales. The Logan prospect, deep water Gulf of Mexico, is used as an example to demonstrate our workflow. The effect of permeability, porosity and effective stress is shown in terms of uncertainties of pore pressure and porosity distribution. The basin modeling uncertainties, related to uncertainties of the input variable such as basal heat flow, thickness of the layers, among others affect directly the geo-simulator output. These uncertainties can be propagated into seismic velocity and anisotropic parameter derived from a rock model that has input from the geo-model. In this paper the review of stochastic geo-modeling is done while the application for rock physics modeling will be discussed in another paper.
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Shale Anisotropy Characterization in Heterogeneous Formations Using Multipole Sonic Data
Authors M. Ferla, J. Jocker, F. Pampuri and E. WielemakerHeterogeneity is a common phenomenon that needs to be taken into account when characterizing the elastic anisotropic properties of formations. This can be done successfully through a methodology involving careful binning of the velocity data on the basis of independent, petrophysical information, followed by an inversion process that is carried out on each bin individually. The resulting table of anisotropic parameters per bin can then be used to derive, among other results, correlations between formation petrophysical and anisotropic properties. A workflow was successfully applied to determine the elastic, transversely isotropic properties of heterogeneous sand-shale sequences. The results of the methodology have significant practical implications. One of these is that synthetics based on the anisotropy-corrected deviated well logs yield stronger and more apparent reflections, as well as a significantly different time-depth relation. Additional applications include the use of the inversion workflow results as inputs into anisotropic seismic velocity models and AVOs.
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Significance of Amplitude Variations in Shaley Mass-transport Deposits - A Petrophysical-geophysical Correlation
Authors T.M. Alves, K. Kurtev, G. Moore and M. StrasserFor this work were used three high-quality 3D seismic volumes from SE Japan and SE Brazil, together with borehole data from the Nankai Trough. We show that, on 3D seismic data, seismic texture is defined as a reflection amplitude pattern that is characterised by the magnitude and variation of neighbouring data in a seismic volume (Chopra and Marfurt, 2007). We show the importance of seismic amplitude variations to assess the seal competence and reservoir potential of MTDs.
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Geological Processes and Rock Physics Signatures of Upper Jurassic Organic-rich Shales, Norwegian Shelf
By P.A. AvsethIn this study we investigate the rock physics properties of Draupne/Spekk Fm organic rich shales offshore Norway. We attempt to understand the complex geologic processes of organic rich shales, and how these processes control the rock physics properties and seismic signatures of these rocks. With burial depth, there are many competing effects that impact the rock physics parameters of organic rich shales. The compaction itself will reduce porosities and stiffen the rock frame. The kerogen will gradually transform to hydrocarbons with increasing maturity. Using rock physics models we try to understand the effects of reducing TOC or kerogen volume, gas/oil expulsion, cracking and overpressure.
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Origin of Abnormal Pressures, Hydrodynamism and Pore Pressure Prediction
Authors J.J. Biteau, M.O. Spencer, B. Benazet and C. LongisCurrent Frontier exploration is bringing us to drill into increasingly highly pressured sedimentary intervals as well as hydrodynamic flows. In these Frontier contexts, lack of well calibrations & poor understanding of the pressure generating mechanisms lead to ever increasing uncertainties in our pore pressure prognoses. Total’s experience of all mechanisms of abnormal pressures shows that our in-house shale pressure modeling is quite accurate and reliable with conformity rates between the prognoses and results close to 100%. By taking a step back, it has been noticed that the greatest uncertainty lies within the reservoir pressures and that these are 100% linked to the understanding (or lack of) of the 3D geological model. All recent cases where the pressure results are significantly different from the prognosis are always linked to errors on the geological model used to estimate the reservoir pressures. Thankfully, Total’s philosophy for pre-drill pore pressure prognoses, follow-up while drilling and post-mortem analysis has allowed us to reach 100% of exploration objectives while keeping the highest safety standards & not put our operations at risk in case of non-compliance to the PPP modeling. We are putting great efforts to maintain this track record and striving to refine our methodologies.
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Rock Physics Guided Velocity Modelling for Migration and Pore Pressure Prediction
Authors B. Deo, Y. Liu, K. Ramani, N.C. Dutta and J. DaiWe present a workflow using geology in conjunction with thermal history modelling and rock physics principles for velocity modelling and imaging is presented. A novel feature of this workflow is to use predicted pore pressure as a guide to improve the quality of Earth model. Thus, we are not only flattens the CIP gathers (a necessary imaging condition) but also limits the velocity field to its physically and geologically plausible range without well control.This has yielded both improved image and more accurate pore pressure.
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Geological and Rock Physics Constraints in Anisotropic Tomography
Authors M. Woodward, Y. Yang, K. Osypov, R. Bachrach, D. Nichols, O. Zdraveva, Y. Liu and A. FournierBecause anisotropic models are unconstrained by surface-seismic data alone, we must learn to incorporate other non-seismic measurements and knowledge into the model building process. For this purpose, we demonstrate the regularization of anisotropic tomography with a preconditioning method which smooths updates along geological dip and constrains cross-property correlations to follow the predictions of rock-physics for compacting shales. The method is applied to the Green Canyon area in the Gulf of Mexico.
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Tomographic Velocities - Challenges and Applications
Authors L. Vigée, M. Bader, A. Bénédini, C. Brillatz, D. Carotti, A. Cavalié, T. Coléou, P. Guillaume, G. Hénin, G. Lambaré, T. Le Ruyet, L. Lopes, A. Vasseur and N. VidalThe resolution of seismic imaging has long been characterized by a mid-frequency gap between the long vertical wavelength components that can be inferred from travel-time tomography and the short vertical wavelength components that can be inferred from seismic migration. The progress in tomography and in broadband acquisition now allows this mid-wavelength gap to be filled and even results in the overlapping between the resolution obtained from velocity model building and from seismic migration. Recent progress in tomographic approaches now provides vertical resolution up to 6 Hz, with in addition, a precise localization of the velocity contrasts. With a case study we discuss their benefits for reservoir characterization, where the missing frequencies are traditionally coming from a model interpolated/extrapolated from well log information. If the seismic inversion for reservoir characterization is not sensitive to the low-to-mid frequencies, this low-to-mid frequency modelling is critical for the estimation of absolute rock properties, and replacing a model extrapolated from sparse well information by actual measurements is of paramount importance.
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Importance of Cross-disciplinary Constraints in Anisotropic Model Building and Updating
Authors O.K. Zdraveva, M.J. Woodward, D. Nichols and K. OsypovOver the last decade of building anisotropic earth models for depth imaging, we developed many methods and techniques that make them geologically plausible and maintain consistency with geomechanics and rock-physics. In this paper, we demonstrate the importance of including of cross-disciplinary data in all stages of the anisotropic earth-model building workflow and discuss various methods and techniques for anisotropic parameter derivation and update. We illustrate them with successful examples from the Gulf of Mexico and offshore West Africa.
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TI Model Building through Geologically Regularized Tomography
Authors J. Panizzardi, N. Bienati and E. SpadavecchiaA vast number of case histories have demonstrated that anisotropy cannot be neglected in several fields of interest: among others, the creation of a reliable seismic image, AVO analysis, AVO modeling and pore pressure prediction. The standard industrial tool for velocity model building is grid tomography: it is therefore straightforward to be interested in the extension of the tomographic techniques to manage anisotropic parameters at the same accuracy of the velocity field. A regularized approach to anisotropic multi-parameter tomography is proposed, exploiting the knowledge of geological models and geological data to reduce the ambiguity in tomographic inversion and thus improve achievable resolution and reliability of anisotropic tomography. A depth-domain inversion technique, completely based on PSDM and on the classic CIG flattening principle, is proposed. It is based on a joint tomographic inversion of two anisotropic velocity volumes, which are able to properly account for the non-hyperbolic residual moveout of CIGs. The method is applied on a multi-azimuth dataset and on a marine dataset.
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