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EAEG/SEG Summer Workshop - Construction of 3-D Macro Velocity-Depth Models
- Conference date: 24 Jul 1994 - 27 Jul 1994
- Location: Noordwijkerhout, Netherlands
- ISBN: 978-94-6282-131-6
- Published: 24 July 1994
21 - 34 of 34 results
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Representation and Visualization of 3D Velocity-Depths Models
Authors F. Daube, O. Hagenes, H. Bernth and P. FarmerBuilding velocity-depth models for structural imaging requires combining information about layer boundaries and interval velocities in a geologically consistent manner. This requires working with seismic data and modelobjects in a single environment and is best done on an interactive workstation. The complexity of a software system designed to support such an activity increases dramatically when moving from 2-D to 3-D velocity-depth models. We present a system for 3-D interactive velocity-depth model building and visualization.
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Generating a 3D Velocity Model - the GOCAD Approach
Authors R. Cognot, P. Lavest, F. Bosquet and J. L. MalletBoth of the Overthrust and the Salt Dome (SEG/EAEG) models have been built synthetically from a set of cross sections, into a set of surfaces, then converted into 3D velocity grids. In both cases, the GOCAD software has been intensively used for these operations, and the goal of this presentation is to focuse mainly on the grid generation step, more specifically taking the example of the Overthrust model. It must be said that the methods that will be discussed here are very general, and has also been with success to the salt dome model.
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Building the SEG/EAEG Overthrust Velocity Macro Model
Authors J-C. Lecomte, E. Campbell and J. LetouzeyThrust zones are areas in the crust that give extreme imaging and interpretation problems to reflection seismologists. This article presents the development of a 3D overthrust model that will be used by geophysicists to construct synthetic seismograms in order to test and improve the validity of the seismic imaging processes.
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Velocity Model Building for 3D Pre-Stack Depth Migration - a Case Study
Authors D. Hinkley, R. Ho and S. LeeIn this case study we used three different velocity estimation methods, SIVA/RAYMAP (Sierrat tm) velocity analysis package, focusing analysis, and residual velocity analysis, to build velocity models for 3D prestack depth migration. The first two methods are more interpretation oriented than the last one. The imaging results from 3D Kirchhoff prestack depth migration from these three different models are discussed in this paper.
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Construction of 3D Velocity-Depth Models
Authors N. R. Hill and J. L. ToldiThree-dimensional velocity-depth models are playing an increasingly important role in our seismic data processing and interpretation. In addition to being critical input for 3D depth migrations, the models are becoming an integral part of our structural interpretations of complex prospects. Even when working with 2D seismic data, a 3D model enforces consistency across interpretations of individual lines. This talk presents our methods of constructing and refining velocity models for a series of examples ranging in complexity from a simple four-Iayer model for West Africa, to a more intricate faulted model for West Africa, to a complex Thrust Belt model. All of these examples begin with 2D analysis and then advance to fully 3D model building.
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3D Structural Inversion via GOCAD
Authors S. Kapotas and P. GuillaumeIssues of accurate structural interpretation along with more accurate reservoir characterization have led the oil industry to acquire more and more 3D data over more complex geological regions. This type of strategy imposes the need of a method that wiIl allow us to estimate velocity and depth variations for these types of environments which in turn can provide a model for seismic imaging.
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A 3D Velocity Modelling Strategy that Includes Structural Geology
By A. DownieThe structural features of a 3D subsurface velocity model must be defined not only to support seismic modeling, seismic processing and geologic interpretation but also to support the kinematic history of the subsurface structure. A strategy for implementing a 3D velocity model is presented. The key feature of our strategy is that, in addition to being topologically correct, the model is also supported by the principles of structural geology.
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Efficient Generation and Verification of 3D Velocity Models - UK Southern Gas Basin
Authors I. G. Mitchell, J. M. Reilly and D. L. HinkleyThe need for robust 3D model-building technology and methodology to support 3D prestack imaging is weIl recognised within the seismic processing industry. What has received relatively less attention is a) development of techniques which maximise the value of the conventional 3D processing sequence; and b) critical evaluation of the performance of the ray trace algorithms which generate the traveltime tables for the prestack migration "engines". Enhancements in these two areas are considered essential components in the creation of an economically viabIe 3D pre-stack processing product. In this paper we present a case history which specifically examines these issues.
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Estimation of Velocity-Depth Model for Structural Targets - a Case History from the North Sea
Authors O. Yilmaz, P. Farmer, A. Pieprzak and B. GodfreyThree-dimensional seismic data from the North Sea were analyzed to remove the deleterious effect of the Zechstein diapiric formation on imaging the underlying Permian sands of Rotliegendes. This Required accurrate imaging of the overburden and delineating the geometry of the halite and anhydride-dolomite units in the Zechstein formation.
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Performance and Validation of the 3D Acoustic Modelling Code for the EAEG & SEG 3D Modelling Project
Authors J. Brac, L. Anne, A. Bamberger and P. DuclosThe EAEG&SEG 3D Modeling Committee decided (Progress Report in Leading Edge and First Break of February, 1994) the main features of the 3D modeling code for the project. A finite difference method was selected in order to model complex structures and a one-parameter acoustic wave equation was accepted
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Easy-to-Use Modelling - 3D Ray Field Propagation in Open Ray Models
By K. AstebølRay modelling has proven useful in a wide range of seismic applications, including survey planning, velocity inversion. map migration. synthetic seismogram generation, model-based stacking, and pre- and post-stack depth migration. Still, the spreading of modelling-based techniques relies very much on how easy modelling is to use. If modelling requires lots of special interpretation and preparation and very specialized skill to make useful results, the application is limited to the rare, special cases. On the other hand, if modelling in large can do with data made in standard processing and interpretation, and easy-to-use, efficient, and robust ray calculation is available, ray-based modelling applications may flourish. Simple ray-based applications, like map migration, may even become part of the standard, routine tools.
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Seismic Evaluation of the Overthrust Model
Authors J. Brac, C. Naville, S. Serbutoviez and L. AnneAs mentioned in the companion paper "3D Seismic Modeling on the Overthrust Model", it is essential to check the relevance of the overthrust 3D model with respect to its geophysical objectives before starting intensive computations. The critical decisions concern the choice of the source frequency (15 Hz main frequency), the mesh size (25m), the velocity range & distribution, and the acquisition parameters, which determine the computational cost. These choices take into account the geological constraints, the geophysical objectives and the current limits of computer technology (hardware and software). The choice of the numerical modeling parameters has been carefully studied and is presented in another paper concerning the validation of the 3D acoustic modeling software.
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The 3D SEG Salt Model - Dreams and Reality
More LessWave-equation modeling of 3-D seismic data in non-trivial geologic models is a non-trivial computational problem. While ray-tracing and other simple methods offer advantages in speed and/or simplicity, we are drawn toward using as complete a physical description of wave phenomena as we can aspire to. Typically this means full wave equation finite-difference or finite-element methods. If we are interested in P-wave or "acoustic" data, we have the choice of modeling a zero-offset section directly, or modeling shot records which would simulate a typical field experiment; one can also model other experiments, hypothetical or real, such as plane wave or conical wave sources. From the point of view ofthe numerical simulation, the goal is to get as many wavelengths of some specified frequency into the computational model as possible.
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