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78th EAGE Conference and Exhibition 2016
- Conference date: May 30, 2016 - June 2, 2016
- Location: Online
- Published: 30 May 2016
1021 - 1034 of 1034 results
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A Fast Iterative Solution of the Time-harmonic Wave Equation with MSSS-preconditioned IDR(s)
Authors M. Baumann and M.B. Van GijzenSummaryFor the Full Waveform Inversion in frequency-domain, the fast numerical solution of the time-harmonic wave equation is required. For large three-dimensional problems, the problem size exceeds several million of unknowns, and a short-recurrence Krylov method such as IDR(s) is used to solve linear systems of this size. Especially for high-frequency simulations, an efficient preconditioner needs to be applied in order to speed-up convergence.
In our presentation, we introduce a new preconditioner for the time-harmonic wave equation that exploits the hierarchical structure of the discretized problem. We use multilevel sequentially semiseparable (MSSS) matrix computations for the approximate inversion of the preconditioner. For large three-dimensional problems, we present a memory-efficient modification of the MSSS preconditioner that resembles the approximate solution of a sequence of two-dimensional problems. We conclude our presentation with numerical examples for the time-harmonic wave equation in both acoustic and elastic media, and in two and three spatial dimensions.
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Compact Finite Difference Schemes for the Acoustic Wave Equation
Authors L. Córdova, O. Rojas, B. Otero and J. CastilloSummaryIn this work, we implement and compare two fourth-order compact finite difference (CFD) methods to model the propagation of acoustic waves on a 1-D domain. The first scheme is based on standard implicit CFD constructed on nodal grids and must solve a couple of tridiagonal linear systems at each time iteration. The formulation of the second method uses the novel staggered mimetic CFD that explicitly approximate derivatives at cell center points. Mimetic FD operators inherit this name from the fact that some conservation properties fulfilled by the continuous divergence, gradient, and curl operators, are also satisfied by the discrete mimetic counterparts. Both CFD methods are combined to high-order Runge-Kutta schemes for time integration. In our current preliminary experiments, results show that the mimetic CFD scheme is slightly more accurate and shows similar fourth-order convergence than the nodal scheme. In this paper, we also compare the simulation times spent by the compact schemes to an explicit Leap-frog staggered solver. This comparison reflects the high computational efficiency of the mimetic CFD scheme, and along with its accurate results, suggests the potential of this method for multidimensional wave propagation problems.
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Simultaneous TV-regularized Time-lapse FWI with Application to Field Data
Authors M. Maharramov, B.L. Biondi and M. MeadowsSummaryWe present a field data application of the technique for reconstructing production-induced subsurface model changes from time-lapse seismic data using full-waveform inversion (FWI). The technique simultaneously inverts multiple survey vintages with total-variation (TV) regularization of the model differences. After describing the method, we discuss its application to the Gulf of Mexico, Genesis Field data. We resolve negative velocity changes associated with overburden dilation and demonstrate that the results are stable with respect to the amount of regularization and consistent with earlier estimates of time strain in the overburden. The estimated velocity anomalies are also consistent with the trajectory of three wells that are known to have failed.
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R-factor Recovery via Geertsma’s Pressure Inversion Assisted by Engineering Concepts
Authors M.Y. Wong and C. MacBethSummaryA technique is developed for a North Sea chalk reservoir to estimate the Hatchell-RØste R factors using a reservoir engineering constraint. This provides a way of defining the uncertainty on the R values, given the range of mechanical properties for the field of interest.
In our case study the average R for the reservoir and overburden appears to be in the range 7 to 22. R factors are also calculated for regions of pressure relaxation and drawdown identified in the field, and the results confirm the current understanding determined by laboratory experiment and previous studies that the magnitude varies as a function of strain polarity, with the asymmetry being at most a factor of three. These results are validated with full geomechanical modelling followed by time shift modelling, showing that the observed time shifts cannot be created unless this asymmetry is present
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Rock Physics and Integrated Geophysical Methods
More LessSummaryRock physics represents the background for integrating multidisciplinary geophysical data. In fact, some type of physical relationship is necessary for linking the different data and parameters in the seismic, gravity and electromagnetic domains. In this work, I discuss the different types of relationships and how these can be included in the objective functional of a Bayesian simultaneous joint inversion algorithm. Finally, I introduce the concept of Quantitative Integration System (QUIS). This is aimed at optimizing the integration workflow using a comprehensive software platform. It combines different types of modeling and inversion algorithms dealing with seismic and non-seismic domains, plus a library of rock physical relationships.
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Inversion of Time-lapse Gravity Data for Reservoir Modeling
Authors Y. Li, J. Capriotti and R. KrahenbuhlSummaryCompared to other geophysical methods for monitoring subsurface dynamic systems, time-lapse gravity has one important advantage in that the measurements are directly sensitive to the variations in density, which is solely related to the amount of mass changes per volume. In oil and gas reservoirs, such changes are primarily due to fluid movement and substitutions. Thus, while seismic method provides unparalleled structural resolution, time-lapse gravity method has the potential for characterizing the “content” that is the fluid saturation within “containers” delineated by seismic images. There have been significant advances in instrumentation, data acquisition, and quantitative interpretation in time-lapse gravity methods. As a result, we may be on the threshold of a new phase in the application of this method. This paper will focus on the quantitative interpretation techniques for time-lapse gravity data through different inversions and the associated applications in characterizing both the static and dynamic properties of the reservoirs. In particular, we will present and review inversion techniques for recovering time-lapse density distribution in reservoir and joint inversion methods of time-lapse gravity data with production data for imaging the permeability and saturation distribution in reservoirs.
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Obtaining the Depth of Potential Field Sources
More LessSummaryLinear least-squares inversion is a powerful tool which, when applied to potential field data, can yield important insights into the nature of the subsurface geology. Unfortunately, most geophysical problems are non-linear, and the use of linear inversion has several consequences. At best, it now becomes necessary to iterate the inverse process to reach the optimum solution. At worst, the inverse process can diverge to infinity or become stuck in a local minimum of the misfit surface. Noise problems usually prevent second derivative (Hessian) or higher terms being used in the inversion.
This abstract shows how to solve a particular non-linear inverse problem, the depth of one or more potential field sources, in the frequency domain without the need to iterate. The method is applicable to magnetic or gravity data, and can be used with any forward model type (dyke, contact, sphere, arbitrary collection of two or three dimensional bodies, etc).
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Optimising Surface Mapping of Elongated Geological Features from Full Tensor Gravity Gradiometry
Authors D.J. FitzGerald, H. Holstein and H. J. GibsonSummaryThis inversion technique maps zones of influence of isolated elongated geological features. The outcomes are not too technically complex, and we demonstrate a practical application of how to use all of the observed tensor components to extract maximum signal content. The method is based on the physics of isolated sources. As previously discussed (2014), these cluster derived regions form a good starting point to determine dip estimates.
The time to solve the clustering is not significant (say 5 minutes), and so this technique should find general application. It does depend upon an estimation of an optimum near surface rock density, so that a terrain correction can flatten the response to sub-surface sources. This method is a useful a-priori method for mapping geology and not the other way round, i.e., no prior geological knowledge is required to infer sub-surface geology. The method is a joint inversion of all the measured gravity gradient tensor components, combined with clustering methods.
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Layer Constrained Composite Modelling and Inversion of Gravity Data
Authors V. Vandone, F. Chiappa, P. Marchetti, G. Bernasconi and P. Dell’AversanaSummaryThe inversion process for gravity interpretation has to treat the intrinsic ambiguities of the gravimetric data; for this reason, the possible investigated models need to be constrained in order to recover the uniqueness of the inversion process.
In this work, a novel approach to gravimetric inversion is presented. Geometric information on the existing structures, derived from other geophysical studies, are introduced in the form of interfaces and geobodies. In this way, independent regions are defines and discontinuities of the model are introduced. Furthermore, due to the integral nature of gravimetric method, it was possible to develop a composite forward modelling. A flexible geological-driven forward and inversion machine has been therefore created, allowing the automatic introduction of the geometric information and the a priori calibration, which is based on specific geological interpretation. The inversion is driven by logarithmic barriers, in order to keep inversion parameter inside physical range.
Results show that geometric information put very strong constraints to density inversion. Furthermore, the composite forward modelling makes the algorithm more powerful with respect to standard approaches. The logarithmic barriers play a fundamental role in solving the intrinsic gravimetric ambiguity inside a geophysical domain.
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Progress in Defining Deeper Realistic Geology Using AEM 2.5D Joint Inversion
Authors J. Silic, R. Paterson, H.J. Gibson and D.J. FitzGeraldSummaryIncluding interpretations from airborne geophysical surveys to build geological models continues to improve outcomes for deriving more realistic geological representations. It is now highly practical for AEM data to be both forward modelled and inverted using 2.5D numerical approximations. In this paper we present one such code for performing these workflows: a finite element method that assumes a 2D Geological source and 3D electrical source. This is provided that the geo-electrical cross-section is relatively constant along a strike length that exceeds the AEM system footprint. Lines that exceed 30 kilometres can now be modelled and inverted on a standard laptop computer.
- The AEM inversion technique presented is usefully capable of defining detailed geometry for synclines, anticlines and deeply dipping beds.
- AEM 2.5D Inversion appears to match realistic geology trends to depths of up to 1 km and hence is cost-effective compared detailed drilling.
- Experience shows it’s best to use a half-space starting model, slightly adapted to the gross resistivity characteristics of the observed signal.
- Fully geologically-constrained inversion attempts to find the compromise between the observed geophysical signal, and the interpreted sections.
- Rock properties in the form of estimated and inferred resistivities for each formation, play an integral part in this AEM inversion workflow.
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Inversion of Public Domain Gravity Gradient Data in the Gulf of Mexico
Authors I.N. MacLeod, G. Connard and A. JohnsonSummaryThis study examines the outcome from a simple regional inversion of the satellite derived vertical gravity gradient data. The calculated density distribution is compared along four modelled gravity profiles to show that this approach, using public domain data sets and limited constraints for the inversion, can produce a useful starting model for any basin of interest anywhere on earth.
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Achieving High System Availability in Wireless Seismic Networks through Network Automation
Authors M.K. Lambert and A.K. ElderSummaryWe will discuss how multiple new techniques have been integrated to enable the deployment of a highly automated, radio-based, seismic recording and collection system that can operate efficiently at very high channel counts. The goal in developing this system is to make it effectively self-sustaining, so that it will consistently deliver both high System Availability and high Data Availability. System Availability is the percentage of time that a system can meet the requirements of the mission. Data Availability is the percentage of time that the majority of the seismic data and the related QC data are available to the Observer in real-time, where these data can be used to positively affect the quality of the seismic survey being recorded.
As onshore seismic crews grow to hundreds of thousands of deployed channels, it becomes a requirement that the operation of the recording system becomes effectively automated, where the Observer does not have to manage the minute-by-minute actions required to keep the system operating efficiently. Simultaneously, the Observer needs to monitor and manage the performance of the system in real-time and to easily and efficiently make local and global adjustments to the system operation to ensure optimal data quality and productivity.
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Using Robotic Flying Nodes for Seabed Seismic Data
Authors A Holloway and D. GrantSummaryFlying nodes, a type of self-propelled robotic node, provide an alternative to ROV placed and cabled deployed nodes for the acquisition of ocean bottom seismic (OBS) data. The prime motivation for the development of such a system is to increase the efficiency at which the sensors can be deployed and recovered from the seabed, therefore reducing the overall cost of acquiring ocean bottom seismic (OBS) data.
This paper provides a brief description of the concept, looks at the benefits that using flying nodes could bring to the acquisition of OBS and some of the application areas for flying nodes. The paper then looks at the challenges of developing such a system and how technological developments in other fields are helping to solve some of these challenges.
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Salt Is a Heavy Fluid
By D.G. QuirkSummaryThe aim of this presentation is to describe and explain the most common halokinetic structures resulting from heavy, viscous salt reacting to gravity and overburden faults based on seismic observations and simple physical models. These examples are meant to help workshop participants when interpreting their own data.
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