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80th EAGE Conference & Exhibition 2018 Workshop Programme
- Conference date: 10 Jun 2018 - 15 Jul 2018
- Location: Copenhagen , Denmark
- ISBN: 978-94-6282-257-3
- Published: 10 June 2018
1 - 20 of 99 results
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An accurate Eulerian travel-time computation: implication for slope tomography
Authors J.V. Virieux, S. Sambolian, P. Le Bouteiller, S. Operto, A. Ribodetti and B. TavakoliComputation of travel-times and its spatial derivatives is at the heart of many seismic imaging techniques. We shall discuss shortly the Lagrangian, semi-lagrangian and Eulerian approaches which have been investigated in the past. Eulerian approaches enjoy recent advances when considering anisotropic media with complex topographies while having the attractive regular sampling needed for slope tomography and migration workflow. While this Eulerian approach is quite efficient for firstarrival travel-time/slope tomography and has replaced ray tracing approach, it has not yet replaced standard ray tracing tools (in spite of its irregular sampling of the medium) in migration where multiple arrivals are important. An efficient and accurate discontinuous Galerkin method for solving the non-linear Eikonal partial differential equation providing travel-times might be an attractive proposition both for tomography and migration. Thanks to this Eulerian approach, data- and domainspace definitions involve only subsurface parameters such as velocity parameters and imaging point positions for slope tomography while the forward modeling has a computational complexity depending only on the acquisition design and not on the picking density. Still bottle-necks exist when considering multiple arrivals and their identification will help to find solutions in the future.
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Diffraction wavefront tomography - efficient automated velocity inversion for multi-fold and single-channel data
Authors A.B. Bauer, B.S. Schwarz and D.G. GajewskiSeismic multi-channel acquisition offers the benefits of high data redundancy and improved illumination. However, large-offset recordings are generally expensive to acquire. For the case of passive seismic data, no offsets are available. Diffractions provide superior illumination compared to reflections, but typically have low amplitudes. However, diffractions possess unique properties, which bear the potential to improve the lateral resolution of inversion results. We present wavefront tomography as an efficient and stable tool for velocity inversion of both single-channel and multichannel as well as passive seismic data. For the case of single-channel data, we suggest an approach that reveals the diffracted background in the data through automated adaptive subtraction of the dominant reflected wavefield. Based on local stacking and coherence evaluation, the recorded diffracted events are treated as passive source wavefields characterized in terms of local properties of wavefronts emerging at the registration surface. The subsequently obtained inversion results are in good agreement with fault zones known from the local geology. In an industrial multi-channel field data example, we carried out a joint inversion of reflections and diffractions and present a laterally well-resolved velocity model, which we validate with reverse-time depth-migrated (RTM) results.
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Multi-scale traveltime inversion: a robust method for velocity estimation in difficult geological context
Authors C. Barnes and M. ChararaA robust method for velocity estimation is presented. We regularize the traveltime inversion using a multi-scale approach, gradient conditioning or joint inversion using additional seismic datasets.
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Integrating Reflection-FWI in depth imaging velocity model building workflows
Authors C.R. Rivera, E. Bergounioux, D. Otriz-Rubio and F. AudebertReflection full waveform inversion (RFWI) is the next step for wave equation based model building techniques. In this work we will present ways to integrate our implementation of Reflection full waveform inversion in depth imaging workflows with examples. Our RFWI implementation is based on multi-parameter inversion where impedance and velocity are inverted in a sequential manner, thus allowing for focusing and repositioning of misplaced reflectors.
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Traveltime based reflection full waveform inversion
More LessIn this paper, we present a new method called traveltime based reflection full waveform inversion (TT-RFWI) that corrects the kinematic errors between the synthetic and real data. With the new objective function and gradient, the proposed method aims to avoid convergence to local minima with inaccurate initial model and in the meanwhile takes benefits of reflection data. The goal is to provide a deeper reliable low-wavenumber update with reflected energy while missing a good starting background model.
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Understanding resolution and sharpness in ray based tomography
Authors D.E. Nichols and Y. YouRay based tomography is still the workhorse for velocity model building. Recent advances have shown that we can build much higher resolution models than was previously understood. We will show that some of this uplift comes from better quality data, some comes from better constraints on the model, and some comes from improvements in the inversion process.
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Shaping the velocity model beyond the diving wave penetration
More LessFull-waveform inversion (FWI) usually utilizes diving and refracted waves to update the low-wavenumber/background components of the model; however, the update is often depth limited due to the limited offset range acquired. To extend conventional FWI beyond the limits of the transmitted energy, we must use reflection data. There are several ways of using the reflections to update the background model. Field data examples demonstrate that, even in a complex subsalt Gulf of Mexico setting, the background velocity model can be updated from shallow to deep water using conventional FWI followed by reflection-based FWI.
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Ray versus full wave velocity model building: status and challenges
By G. LambaréWhile full wave based velocity model building approaches have earned their stripes during the last decade, ray based approaches remain the working horse in industry. I review here first the successes and the limitations of both families of approaches. If it appears that ray based approaches suffer of limitations in complex media, others of their characteristics like the picking (often seen as a weakness) or the computation of Fréchet derivatives may also appear in practice as decisive advantages. I believe that these are points on which we should challenge and even inspire full wave approaches. By the end rather than opposing ray based and full wave approaches I review the various trends in terms of the combination of the tools and concepts which appear from my point of view as the most promising.
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Machine Learning and Wave Equation Inversion of Skeletonized Data
More LessWe compare the full waveform inversion (FWI), skeletonized wave equation inversion (SWI), and supervised Machine Learning (ML) algorithms with one another. For velocity inversion the advantage of SWI over FWI is it is more robust and has less of a tendency in getting stuck at local minima. This is because SWI only needs to explain the kinematic information in the seismograms, which is less demanding than FWI’s difficult task of explaining all of the wiggles in every arrival. The disadvantage of SWI is that it provides a tomogram with theoretically less resolution than the ideal FWI tomogram. In this case, the SWI tomogram can be used as an excellent starting model for FWI. SWI is similar to supervised Machine Learning in that both use skeletonized representations of the original data. Simpler input data lead to simpler misfit functions characterized by quicker convergence to useful solutions. I show how a hybrid ML+SWI method and the implicit function theorem can be used to extract almost any skeletal feature in the data and invert it using the wave equation. This assumes that the skeletal data are sensitive to variations in the model parameter of interest.
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Examples of asymptotic analysis for understanding and building seismic wave-equation imaging tools
Authors H.J. Chauris, T. Zhou, E. Cocher and Y. LiMigration velocity analysis aims at determining an optimal velocity macro-model to focus energy in the subsurface. The replacement of the adjoint operator by the inverse operator in the extended subsurface offset domain offers a more robust velocity analysis approach. In order to better understand the non-linear relationship between the data and the velocity macro-model, we review here the behaviour of different wave-equation based operators through an asymptotic analysis. It is a very useful tool for interpreting and even building some imaging algorithms. In particular, we establish a mapping between the data and the subsurface image domains. This mapping offers new possibilities to better understand how velocity analysis behaves.
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The evolution of tomography and FWI: an example of high resolution velocity estimation using refraction and reflection FWI
Authors I.F. Jones, J. Singh, P. Cox, M. Warner, C. Hawke, D. Harger and S. GreenwoodThe primary objective of this project was to improve the understanding of the internal structure of the Viscata and Fortuna reservoirs, and this objective was met via clearer internal imaging of these reservoir intervals and the overlying gas-charged sediments. The underlying geophysical challenge was the presence of extensive, but small-scale low-velocity gas pockets, which gave rise to significant and cumulative image distortion at target level. This distortion had not been resolved in a vintage 2013 broadband preSDM project, as the velocity model was not sufficiently well resolved. But in the initial commercial phase of this project, high-resolution non-parametric tomography using improved broadband deghosted data enabled us to achieve the stated objectives. The follow-on work, considered here, deals with the use of full waveform inversion, to see if we could further delineate small-scale velocity anomalies, associated with the highly compartmentalized reservoir units.
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Nonlinear slope tomography: a versatile data- and challenge-driven velocity model building technique
Authors T. Allemand, P. Guillaume, F. Gamar, G. Lambaré, O. Leblanc, J. Messud and J.P. MontelMost recent depth seismic imaging studies involve both full-wave and ray-based methods as the resolution of complex ill-posed problems often require a wide range of tools. Also ray based methods suffer from well-known drawbacks, they will provide accurate results in most of the cases. Moreover, relying on nonlinear slope tomography, a challenge-driven approach can be designed for each problem by incorporating prior or external information as needed. Here we propose to show such examples of the challenge-driven approach.
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Borrowing insight from travel-time reflection tomography to solve the depth reflectivity-velocity coupling issue of RFWI.
Authors R. Baina and R. ValensiThe reflectivity-velocity coupling is one of the major reason of the slow convergence of the conventional Reflection Full Waveform Inversion (RFWI) approach. In this communication, we start by reviewing the travel-time reflection tomography (RT) and the different ways of accounting for the depth-velocity coupling. Then, we draw the connection between the inverse problem of the RFWI approach and the inverse problem of RT. From this analogy, we see that the conventional RFWI does not fully account for the reflectivity-velocity coupling effects. To overcome this issue, we propose to reformulate the conventional RFWI problem into a Reflectivity-Velocity Consistent Waveform Inversion (RVCWI) method. Finally, with a numerical example, we compare the performances of the conventional RFWI and the RVCWI approaches. This numerical experiment confirms us the very slow convergence rate of the conventional RFWI approach and the much faster convergence rate obtained with the RVCWI approach .
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Migration Velocity Analysis with a second-order Gauss-Newton scheme: a 2D real data example
Authors R. Soubaras and B. GratacosWe present the application of a Migration Velocity Analysis with a second-order Gauss-Newton update scheme (Soubaras and Gratacos (2017)) on a real 2D dataset. This second order scheme includes a deconvolution of the gradient by the Hessian, which removes the “gradient artefacts” on the velocity gradient and produces an extended reflectivity which is a least-squares migration rather than a migration. Starting with a crude initial velocity model (linear gradient from the water bottom) and leaving the velocity unconstrained, we obtained a detailed velocity model which is consistent with the geology, as well as flattened gathers.
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Local probabilistic inversion of seismic AVO data
Authors H.J. Hansen and A.F. JakobsenThe drive towards extracting ever increasing amounts of information from seismic data has in the recent years increased the focus on the treatment and analysis of the associated uncertainties and lead to the utilization of additional information directly in the quantitative analysis of seismic data. In this context, a probabilistic framework for this quantitative analysis has a number of benefits, among these a rigorous treatment of the seismic data uncertainties, and a flexible setup for adding complementary information directly into the quantitative analysis. The following presents an approximate probabilistic method for inversion of seismic AVO data and real data examples illustrate its applicability.
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Grain-grain contacts evaluation in carbonate reservoirs
Authors J.A. Soares, R.L.C. Coura, N.M. Oliveira, L.C. Medeiros, J.J. Silva, L. Landau and A.P. Martins NetaThis work investigate the reasons for the high dispersion seen between elastic velocities and porosity of carbonate rock samples from Brazil. It is based on conventional lab petrophysical measurements, digital x-ray micro tomography image analysis and well logs usage. This gives a multiscale data integration, since micrometers from x-ray images, to metric scale from well logs. A new approach to predict elastic velocities of carbonate rocks from macro and micro porosity, as well as a quality index for grain-grain contacts was proposed. Multivariate regression functions determined for carbonates from Sergipe-Alagoas Basin, were applied to well logs of Santos Basin, which showed that the predominance of micro pores is associated to a higher values of the quality index of grain-grain contacts and to a lower values of elastic velocities. However, it is recommended to generate regression functions for rocks from the own Santos Basin, applying the proposed integrated method of laboratorial, microCT and well log investigation.
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Interpretation Benefits from a Flexible Multi-Physics Joint Inversion Approach
Authors P.L. Smilde, C. Mueller, M.H. Kringer and S. PetersenThe properties of a multi-physics joint inversion application are discussed, that takes into account the information from several geophysical methods, from well and laboratory data and from geological concepts to return a much more reliable interpretation of the model space. It facilitates to merge all these sources of information and the knowledge and capabilities of usually several expert groups in a well-balanced way. A practical approach is described, that helps to solve usual problems for such setups, like the optimal selection of common or compatible parametrizations, the flexible definition of well-delimiting, but non-conflicting boundary conditions, and satisfactory relative weighting of the diverse contributions. Furthermore, it is possible to incorporate forward modelling computations at each of the partners’ sites into the joint inversion framework. To this purpose a most suitable integration method of several suggested ones can be implemented. A practical realization based on these concepts has already proven its feasibility and is available to be extended with additional methods.
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Nonlinear 3D FE-Stability analysis of suction pile
Authors R. Schlegel, R. Lampert, S. Eckardt, K. Rognlien and F. HalvorsenSuction piles are used to anchor off-shore constructions (e.g., oil platforms) in the sea ground. For the implementation, an under-pressure is created inside the device. The task is to make sure that the suction pile does not fail due to buckling of the friction skirt. The consideration of possible imperfections in the friction skirt as well as the interaction of the suction pile with the surrounding sea ground is particularly important for this verification. State of the art to calculate the maximum possible suction presser before collapse was to use radial springs with non-linear stiffness to characterize the surrounding soil’s supporting effect. This new approach, using 3D Finite Element Simulation with highly non-linear material behavior representing the soil results in significantly increased working loads and economically improved design or installation options. To further validate the suction pressure capacity obtained with the new methodology, a verification with a series of simulation using different spring stiffnesses was carried out. Based on this, it is concluded that the results obtained by the new methodology are not only economically more valuable but rather also more physically correct.
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Lidar and UAV for Rock Mass Geomechanical Characterisation - Support to fracture studies of outcrop analogues
By A. TamburiniFracture studies of outcrop analogues represent a powerful tool in reservoir characterization. Outcrop analogues provide a valuable support in defining conceptual models to extrapolate borehole data outside the well control, trying to take into account reservoir heterogeneity
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The Use of Remote Sensing Products for Enhancing the Environment Protection and of Offshore Operations Safety
By M. FragosoOffshore operations at sea are often risky because very complex activities are performed in harsh environmental conditions. This combination of factors increases the potential for incidents that might cause harm to people, environment and assets. To be prepared for such problems, the knowledge of present and future states of the ocean is key. To reach this goal, a combination of technologies comprising in situ data collection, models and visualization tools is required to make sense of all the pieces of information and provide valuable guidance for decision makers. In this sense, satellite communications and remote sensing plays an essential and transverse role. Either for sending real-time environmental data collected in situ (e.g. drifters, floats, moored buoys), connecting equipment to their base stations (AUVs, ASVs) or for collecting ocean data through sensors onboard satellites (Sea Surface Temperature, Ocean Color, Sea Surface Height, wind and pollution detection)
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