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72nd EAGE Conference and Exhibition - Workshops and Fieldtrips
- Conference date: 14 Jun 2010 - 17 Jun 2010
- Location: Barcelona, Spain
- ISBN: 978-90-73781-87-0
- Published: 13 June 2010
1 - 20 of 105 results
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Integrated interactive framework for the prestack interpretation arena
Authors O. Kvamme Leirfall, S. -K. Foss, A. Osen, M. Rhodes and Ø. SkjævelandCreating an arena for interactive collaboration between geology and geophysics has for some time been identified as a field for strengthening seismic exploration. The set objective was always to release the synergies of combining these two fields of expertise. The challenges faced in providing an arena capable of true interactivity have historically limited the options for real time processing. Over the last few years there have been several publications on interactive migration, indicating that interactive processing is scalable within the current standards of production high performance computing (HPC) configurations. In this article we will present a scalable framework of visualization and interactive processing only limited to available combined memory of a HPC installation and high-speed interconnect. This in addition to interpretation software and visualization capabilities, define the hardware of an interactive prestack interpretation arena
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Optimizing interpretation knowledge with full azimuth information and data in a common canvas
More LessPre stack seismic data structures are a result of a systematic and formulated reconstruction of the recorded seismic wavefield. Seismic processing and imaging specialists spend most of their time generating, refining, analyzing, and inverting these pre stack data structures in order to attenuate noise, build velocity models, image the subsurface structure, search for direct hydrocarbon indicators and derive elastic properties. Seismic interpreters, on the other hand, spend most or all of their time performing operations on the stacked image. While modern interpretation systems are rich in data mining, visualization, and extraction procedures, these operations, and the information extracted from them, are limited to the dimensionality of the data and the loss of information suffered during the stacking process. To overcome these deficiencies, approximations in the form of limited dimensional stacks over acquisition offset or subsurface angle are frequently used as part of the interpretation process.
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Pre-Stack Pro: Scaleable Pre-Stack Computing on the Interpretation Desktop
Authors B. Shea and F. -J. Pfreundtrated by in-house and contract processors, and are forced to rely on stacking to reduce data volumes to “interpretable” dimensions. Pre-Stack Pro, a new breed of software application, harnesses several high-performance computing (HPC) technologies to bring large-scale pre-stack computing to the interpreter’s desktop. By fully exploiting parallelism throughout the system, we simplify pre-stack analysis and deliver a system whose throughput scales efficiently with total hardware investment.
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Waveform inversion from a poor starting model – using a residual ‘drip-feed’ strategy
Authors N. K. Shah, M. R. Warner, L. Guasch, I. Stekl and A. P. UmplebyWe present a new waveform inversion scheme designed to avert the need for an accurate starting
model and low frequency content in the data – a necessary key step in making the technique work on
a much wider range of exploration datasets and targets than it currently can. The scheme operates by
preceding the inversion of the field data by inversion of intermediate target datasets – synthesised out
of the curl-free (irrotational) part of the phase mismatch at the lowest useable frequency. We
demonstrate its effectiveness over the corresponding conventional approach by inverting data from the
Marmousi model with a 1-D starting model and minimum frequency of 5Hz.
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Building anisotropic models for depth imaging: from imaging parameters to Earth model
Authors A. Bakulin, O. Zdraveva, M. Woodward, K. Osypov, P. Fowler, D. Nichols and Y. LiuVelocity model is the bridge that links our data with our images of the subsurface. Therefore our images can only be as good as our velocity models. Moving to “difficult oil” in sub-salt, sub-basalt and generally deeper targets, we can no longer afford the compromises of simplistic models we did in the past. Doing that leads to poor or no image areas. To fully leverage potential of new data types (wide azimuth, long offsets), we have to put a realistic complexity into our models. To address these challenges industry moved into using anisotropic earth models as a new standard (vertical and tilted transverse isotropy or VTI and TTI). Incorporating anisotropy increases our ability to fit the data and image every single piece of it. However growing expectations requires not only focusing the image but also accurately positioning seismic images for drilling. While this is achievable with anisotropic models, it only occurs when geology and data from boreholes are intimately incorporated into velocity model building from the very start.
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Challenges of depth model building for Tilted TI media
Authors P. M. Bakker and A. StopinOver the last years, Shell has accepted anisotropic velocity model building and pre-stack depth migration as the norm for their seismic imaging. This has reduced the number of sidetracks to be drilled as a consequence of sub-optimal imaging or positioning, which is a clear demonstration of the impact of including anisotropy in the model building cycle. While VTI is a commonly accepted working model, with a workflow that is conceptually clear, this is less obvious for Tilted TI. Tilted TI might be the preferred model at the flanks of salt bodies and minibasins, where the sediments are strongly dipping. We shall demonstrate such a real data case in the Gulf of Mexico, where the application of Tilted TI simultaneously explained mis-ties of well markers and sub-optimal focusing of dipping reflectors. Mis-ties and residual moveout were in conflict for a VTI model. Modelling experiments confirm that this can be the case if the subsurface is Tilted TI, indeed. We shall also see that availability of Wide-Azimuth data should be helpful in recognizing Tilted TI in the subsurface. Usually, anellipticity causes only subtle effects in focusing, considering the trade-off between Eta and moveout-related velocity. For the Gulf of Mexico, one generally finds Eta to be small. Therefore, model building is frequently restricted to vertically elliptic models, at least in the initial phase. Reflection tomography with such a model will flatten residual moveout already to a large extent. If, subsequently, a tilt angle is introduced in such a model, this has effect on the well-ties as well as on the residual moveout in the common image gathers. A method is discussed to fit well-markers in such a situation, aiming at preservation of moveout.
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Migration velocity analysis using a transversely isotropic medium with tilt normal to the reflector dip
Authors T. Alkhalifah and P. SavaA transversely isotropic model in which the tilt is constrained to be normal to the dip (DTI model) allows for simplifications in the imaging and velocity model building efforts as compared to a general TTI model. Though this model, in some cases, can not be represented physically like in the case of conflicting dips, it handles all dips with the assumption of symmetry axis normal to the dip. It provides a process in which areas that meet this feature is handled properly. We use efficient downward continuation algorithms that utilizes the reflection features of such a model. For lateral inhomogeneity, phase shift migration can be easily extended to approximately handle lateral inhomogeneity, because unlike the general TTI case the DTI model reduces to VTI for zero dip. We also equip these continuation algorithms with tools that expose inaccuracies in the velocity. We test this model on synthetic data of general TTI nature and show its resilience even couping with complex models like the recently released anisotropic BP model.
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Extended common-image-point gathers for anisotropic wave-equation migration
Authors P. Sava and T. AlkhalifahIn regions characterized by complex subsurface structure, wave-equation depth migration is a powerful tool for accurately imaging the earth’s interior. The quality of the final image greatly depends on the quality of the model which includes anisotropy parameters (Gray et al., 2001). In particular, it is important to construct subsurface velocity models using techniques that are consistent with the methods used for imaging. Generally speaking, there are two possible strategies for velocity estimation from surface seismic data in the context of wavefield-based imaging (Sava et al., 2010). One possibility is to formulate an objective function in the data space, prior to migration, by matching the recorded data with simulated data. Techniques in this category are known by the name of waveform inversion. Another possibility is to formulate an objective function in the image space, after migration, by measuring and correcting image features that indicate model inaccuracies. Techniques in this category are known as wave-equation migration velocity analysis (MVA).
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Extended common-image-point gathers for anisotropic imaging with blended sources
More LessIn regions characterized by complex geology, the accuracy of imaging is controlled by the quality of the Earth model used to simulate wave propagation in the subsurface (Gray et al., 2001). Thus, accurate model building is a critical prerequisite for imaging of the interior of the Earth. This requirement is even more stringent in regions characterized by strong anisotropy. Furthermore, it is important to construct subsurface velocity models using techniques that are consistent with the methods used for imaging. As reported in the recent literature, in the context of wavefield-based imaging, there are two main strategies that can be used for velocity estimation from surface seismic data. Those methods can be separated into two groups: data space methods, which operate by matching the recorded data with simulated data, and image space methods, which operate by correcting image features that indicate model inaccuracies (Sava et al., 2010).
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Imaging of VTI media from wide-aperture data by frequency-domain full-waveform inversion
Authors Y. Gholami, A. Ribodetti, R. Brossier, S. Operto and J. VirieuxSeismic imaging of anisotropic media is one of the most challenging problem in exploration geophysics because of the possible coupling between the different anisotropic parameters. In this study, we develop a frequency-domain full-waveform inversion (FWI) method for imaging 2D visco-elastic VTI media from wide-aperture data. The forward problem relies on a finite-element discontinuous Galerkin method on unstructured triangular meshes that allows for accurate seismic modeling in complex media with reflectors of arbitrary shape. The inversion relies on a quasi-Newton algorithm which allows for proper scaling of misfit-function gradients associated with different parameter classes. The model parameters are either the P and S wave speeds on the symmetry axis and the Thomsen’s parameters ! and ", or the stiffness coefficients c11, c33, c13 and c44. We first present a review of the diffraction patterns of each anisotropic parameter classes to assess the best parameterization of the inverse problem. Second, we present some preliminaries examples of FWI with simple synthetic model. Results highlight the coupling between the parameters and the difficulty of imaging the ! parameter from surface data.
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Numerical analysis of parameter sensitivity in 3D TTI tomography
More LessWe investigate the resolution of anisotropic model parameters in ray-based TTI reflection tomography. Our approach is to perform numerical experiments using 3D acoustic TTI finitedifference model data. In the first part of this presentation, we introduce a 3D TTI model that is used for this study. The size of this model is x=20 km, y=17.5 km and z=10 km. Some of the important features of the model are steeply dipping layers (dips up to 70 degrees) exhibiting relatively strong anisotropy with structurally conformable orientation of the anisotropic symmetry axis. The model also contains salt bodies that allow us to investigate the effects of TTI anisotropy in overburden sediments on the imaging of subsalt events.
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Gaining insights about imaging structural uncertainty: TTI 3-D synthetic case study
Authors K. Osypov, B. Nolte, U. Albertin, M. O‘Briain, Y. Yang, D. Nichols, M. Woodward and F. QiaoOsypov et al. (SEG 2008, EAGE 2010) introduced an uncertainty analysis method for anisotropic migration velocity analysis which generates model samples from the posterior distribution by using eigendecomposition of anisotropic tomography operators and null-space projection. A realistic synthetic model is an important object for validating the uncertainty method because the ground truth is known and various “what if” scenarios could be played. This study deals with analysis of set of such scenarios for the BP TTI 3-D model to gain insights about anisotropic velocity parameter estimation ambiguity and the scale dependency of uncertainty. This analysis was done by using TTI offset ray tracing of the model for an OBC mirror geometry.
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Azimuthal anisotropy? The time and depth imaging points of view: an imaging case history
The superior imaging capabilities of wide azimuth (WAZ) are now well established. Processing such acquisitions rquires adaptation of the processing workflows and tools. For example the recorded azimuthal information must be kept and the tools should be able to deal with the increased amount of data. Concerning the velocity model building, a question remains on the need of introducing azimuthal anisotropy. In this paper we address this point with a time and depth imaging case study for a high density wide azimuth (WAZ) land surface acquisition. We show on this dataset that azimuthally varying residual move-out observed on time migrated common image gathers (CIG) definitely disappears on the depth migrated CIGs (in both cases no azimuthal anisotropy is introduced in the velocity model). This illustration highlights the limits of the assumptions of time imaging, thuis promoting the use of depth imaging when processing high-density WAZ data, even in the context of mild geological complexity.
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Modeling overburden heterogeneity in terms of Vp and TI for PSDM, Williston Basin, U.S.A.
Authors G. M. Johnson and J. DorseyWe present a Williston Basin case study solution where using a new anisotropic depth migration velocity analysis work flow and available well data, Vp and TI parameters in the overburden are modeled and validated in sufficient detail to have a direct impact on the quality of the seismic image at depth. Comparison with isotropic modeling demonstrates the need for highly detailed spatial and vertical modeling of overburden TI heterogeneity prior to azimuthal attribute analysis and other reservoir characterization flows.
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TTI model interpretation when anisotropic migration velocity analysis is impossible: A case history from the Colombian Llanos Basin
Authors R. Vestrum and I. C. FlorezThe objective of the anisotropic depth imaging was to obtain a more accurate positioning of the events for an appropriate well trajectory. The original well location was determined from the isotropic depth migration, and it was clear from early in the drilling cycle that there were lateral-position errors on the seismic image. The TTI anisotropic depth migration project ran during drilling to refine the well trajectory. We used a collaborative, geologically constrained approach that integrates all available geologic information into the interpretation of the seismic velocity model. This area has interbedded siliciclastic rocks with high dips and vertical and lateral velocity contrasts, giving a considerable lateral movement in the images in depth when we correct for seismic anisotropy and lateral-velocity heterogeneity. The position of the structure and dips on the final depth image were confirmed by two wells drilled in the area.
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High resolution surveying - Historical perspectives - how and why we got here
By A. B. ReidHigh resolution and high sensitivity potential fields surveying has a long pedigree, going back to early recognition that sediments and hydrocarbon reduction effects could have observable magnetic signatures, and that very high resolution views of Basement geology could be obtained with close-spaced survey lines. Since then, close-spaced gravity and magnetic surveying has lived up to its early promise, and delineated sedimentary and basement structure with extraordinary effectiveness.
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HiRES airborne geophysical surveys in the UK: the Anglesey magnetic perspective
Authors D. Beamish and J. WhiteThis paper provides a comparison of vintage, UK national scale aeromagnetic data and modern, high resolution airborne data using a case study across the island of Anglesey, NW Wales. Deeper responses associated with magnetic basement are masked by a near-surface Palaeogene dyke swarm. In order to extract shallow and deeper basement features both data sets are processed in a consistent manner using azimuthal and spectral filtering procedures. A joint assessment is then carried out on the resolution capabilities of both data sets using established edge and depth location methodologies.
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An equivalent source approach to the removal of cultural noise from HRAM survey data: examples from Midland region of central Ireland and Haynesville, Louisiana, United States
Authors A. Salem, K. Lei, C. Green, D. Fairhead and G. StanleyHigh-resolution aeromagnetic surveys are commonly flown close to the ground surface (~80m) and sample the magnetic field at about 10m spacing. Such surveys are thus susceptible to magnetic anomalies resulting from populated and/or industrial areas (rigs, pipelines etc). These anomalies are generally called “cultural noise” and need to be removed from the survey data if one wishes to carry out accurate microlevelling to identify and interpret subtle anomalies resulting from subsurface geological structures. Conventional algorithms of cultural noise removal tend to be based on Fast Fourier Transform (FFT) operations either on their own or together with identification and removal of cultural noise signals, using either manually or nonlinear filters methods. These algorithms can have difficulty interpolating across the profile edited sections (i.e., data gaps where cultural noise has been removed) and can introduce artificial anomalies. For these reasons, we have developed a semiautomated method that both identifies sections of profile data containing cultural noise and use the equivalent source approach to recover the magnetic responses of subtle geological anomalies and interpolate their field across the cultural noise gaps in the profile. Theoretical examples of combined subtle magnetic anomalies and cultural noise are used to test the effectiveness of the proposed method, which is shown to provide results that are closer to the original magnetic data without the cultural noise. We demonstrate the practical utility of the approach using highresolution aeromagnetic data from Ireland and United States.
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Aeromagnetic mapping of Norway and adjacent ocean areas - from the Quaternary to the Precambrian
Authors O. Olesen, M. Brönner, J. Ebbing, L. Gernigon, J. Koziel, T. Lauritsen, R. Myklebust and S. UsovAeromagnetic surveys have in the past mainly been used for mapping depths to magnetic basement and igneous units in sedimentary basins. NGU has since 1994 acquired high-resolution aeromagnetic surveys and has also revealed the existence of significant magnetic anomalies arising from sedimentary layers. We have recognized that susceptibility measurements on core samples, hand specimens and in situ on bedrock exposures are essential for the interpretation of these anomalies. Petrophysical data (magnetic susceptibility and remanence) of 40.000 rock samples from the Norwegian mainland and offshore wells and drill holes have been acquired in order to constrain the interpretation of the aeromagnetic data. Sub-cropping Late Paleozoic to Tertiary sedimentary units along the Trøndelag-Nordland coast produce a very distinct anomaly pattern. The asymmetry of the anomalies, with a steep gradient and a negative anomaly to the east and a more gentle gradient to the west, relate the anomalies to a
strata gently dipping westward. The susceptibility measurements on Sintef’s cores indicate that these coast-parallel anomalies are caused by 1) alternating beds of sandstone and claystone/siltstone/mudstone [mean suscept. 0.00013 and 0.00025 SI], 2) siderite-cemented sedimentary rocks [mean suscept. 0.00135 SI], and 3) sedimentary units containing detrital Fe-Tioxides [suscept. 0.00100-0.01000 SI]. Negative anomalies are caused by low-magnetic gypsum, anhydrite, salt or coal [mean suscept. 0.00007 SI]. Recent aeromagnetic surveys in the Barents Sea have also revealed distinct negative magnetic anomalies clearly associated with salt diapirs.
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Full tensor magnetic gradiometry processing and interpretation developments
Authors D. Fitzgerald, H. Holstein and S. LettsIn recent years, Anglo/De Beers have championed the development of a Full Tensor Magnetic gradient (FTGM) signal instrument from IPHT. Multiple surveys of this quantity have been made in Southern Africa. With the advent of this new potential field full tensor
gradient instrumentation, new methods have been developed to de-noise and process these curvature gradients. Traditional Fourier domain and minimum least squares residual of the linear differential tensor relationships have been adapted. This leads to levelling, gridding and grid filtering innovations. The result is a full tensor grid representation of the curvature gradients that is coherent and compliant with the physics at all points in the grid. All of the observed data is thus honoured in the Tensor grid. Isolating the signal and then refining it to be sure there are no distortions have dominated efforts to date. Superior anomaly interpretation regarding the full magnetic history and inferences can then be made. A survey from the Groblersdal Platinum mine is shown in the context of the structural geology interpretation. In particular, the dolerite dykes and faults are seen. The Hornfels footwall contact is very strong. The phase map traces the Platreef contact. The Upper Zone magnetites are more pervasive and fine layered structure is revealed there. None of the granites can be seen. A 3D geology model is in preparation. The observed FTG signal will be compared to the predicted thin-body responses from the model. There is more directly inferable structural geology in this tensor signal than can be found in a conventional TMI signal.
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