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78th EAGE Conference and Exhibition 2016
- Conference date: May 30, 2016 - June 2, 2016
- Location: Online
- Published: 30 May 2016
1001 - 1034 of 1034 results
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The Håpet Dome in the Norwegian Barents Sea, Structural Evolution and Morphometry of Salt Basins
Authors R.W. Dellmour, E. Stueland, S. Lindstrom, G. Tari and S. PurkisSummaryDuring Upper Carboniferous to Upper Permian the vast Barents Sea Platform between Timan-Pechora and Spitsbergen was host to an environment stimulating a variety of reef morphology and inter-reef facies development. Salt ponds and basins of variable dimensions and morphometry are scattered over the platform, competing with the adjacent reefs. The present study focuses on the area of the Håpet Dome in the eastern Bjarmeland Platform, where the shape and outline of salt ponds and basins are defined by a fractal pattern. The salt basins in the Håpet area have been classified into Macro, Meso and Mini salt-basins. The structural evolution of the Håpet Dome can be timely separated into an earlier extension during Upper Triassic and a later collapse phase during Late Cretaceous to Tertiary.
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Salt Tectonics Offshore Morocco - New Insights from Numerical Modelling and 2D Seismic Interpretation
Authors L. M. Pichel, M. Huuse, E. Finch and J. RedfernSummarySalt tectonics is known to be an important control on the structural configuration of many continental margins. It is a critical mechanism that influences syn-deformational sedimentation and depositional style and has a significant impact on potential reservoir distribution, fluid migration pathways and trap formation.
This study adopts an integrated seismic stratigraphic interpretation and forward modelling approach, using a Discrete-Element Technique, to study salt-related deformation with the aim of characterizing and modelling salt tectonics and associated sedimentation on the Offshore Agadir Basin of Morocco, an area of recent renewed exploration interest.This margin is highly structured following remobilisation of underlying Triassic syn-rift salt, and interpretation of a regional 2D seismic grid has allowed the identification of at least three different structural styles: 1) a southern area with upright tear-drop diapirs and adjacent minibasins, 2) a central area dominated by large allochthonous salt tongues and sheets, and 3) a northern section with well-defined extensional, transitional and contractional domains of salt tectonics due to the lower volume of salt that is affected by paleovolcanoes. The integration of seismic interpretation with numerical modelling affords a better understanding of the margin evolution, especially of how the complex allochthonous salt features developed and their effects to sedimentation patterns.
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Mathematical Fidelity and Open Source Libraries for Large Scale Simulation and Optimization
By W. SymesSummaryOptimization algorithms used to solve inverse problems in geoscience have abstract mathematical descriptions – many of them (Conjugate Gradient iteration, Newton’s method,…) are so–called matrix free algorithms, that is, they manipulate their mathematical objects (vectors, functions) without reference to their internal details. Similarly, time-stepping algorithms for dynamical simulation may be described in terms of update rules for dynamical states, without reference to the internal structure of these states or the precise action of the rules. Both of these algorithmic settings provide opportunities for creation of reusable open source code bases, applying to many different tasks. Not only do such libraries save programmer effort and reduce the incidence of errors, but also they could potentially make possible comparison of inversion techniques by providing common implementations for common components. This paper lays out some examples of features that computational types should inherit from their mathematical models, and some solutions to the programming problems that arise in implementing such types.
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SES3D - An Open-source Package for Seismic Waveform Modelling and Inversion
Authors A. Gokhberg, S. Simutė and A. FichtnerSummaryWe present SES3D, an open-source HPC software package for seismic forward modelling and full-waveform inversion. SES3D is based on a time-domain spectral-element discretisation of the 3D seismic wave equation for anisotropic, visco-elastic media and operates in the natural spherical coordinate system. In our research we aimed at constructing lean, robust, and portable software capable of running on a wide range of modern high-performance computing platforms and accessible for seismologists working in both academic and industrial environments. We address all major performance aspects, which include data-parallel computations, data transfers between distributed computational nodes, and parallel bulk I/O. SES3D can be applied to a wide range of forward and inverse modelling problems on local to continental scales. The application areas include full-waveform inversion, seismic source inversion, forward modelling studies, and sensitivity analysis.
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PyGIMLi - An Open Source Python Library for Inversion and Modelling in Geophysics
Authors C. Rücker, T. Günther and F. WagnerSummaryPyGIMLi - A Python Library for Inversion and Modelling in Geophysics is a versatile open-source tool for modelling and inversion of various geophysical methods, based on finite element modelling and inversion frameworks that allow flexible regularization strategies, time-lapse processing and petrophysical or structural coupling of multi-physical data sets.
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Seismic Data Analysis in Julia
Authors K.A. Stanton, M.D. Sacchi and N. KazemiSummaryA new programming language for scientific computing has undergone rapid development since 2012. The language is named Julia– perhaps a reference to the beautiful fractal patterns of the Julia set. Julia is a high level programming language with an extensive library of mathematical functions that is easy to code and share with others. However, unlike other high level languages it offers C-like performance. It is an open source language with a large community of users and developers with a built-in package manager. The Signal Analysis and Imaging Group (SAIG) has recently released a seismic data processing package named Seismic.jl that contains utilities for reading and manipulating seismic data. We believe Julia is a great new language for research and teaching in the geosciences.
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Eight Strategies for Revolutionizing the Open Geoscience Ecosystem
By M HallSummaryThe open source geoscience software scene is reasonably healthy. A quick survey of the core projects — Madagascar, OpendTect, SU, and so on — suggests that they continue to progress their technology, and their user bases are growing. There’s also progress on the fringe, with new experiments in open source software, new open access content from the SEG and others, and new activity around open collaboration. But at its core, our science has a long, long way to go: reproducibility is simply not yet valued in geoscience. For example, Geophysics publishes the source code for only about two papers every year, which is less than 1%.
This paper reviews some of the fringe activities that I am aware of or involved in, highlighting those that seem to have good traction. Rather than just listing them, I segment them into eight themes. Each theme suggests a strategy for cementing and accelerating the progress that the open source community has made. As we face months, perhaps years, of reduced economic activity in the petroleum industry, it remains possible that what is undoubtedly a threat to the commercial software industry, can be an opportunity for the progress of geoscience.
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Tectono-sedimentary Evolution of the Eastern KopetDagh Fold and Thrust Belt, North Eastern Iran
Authors R. Noemani Rad, G. Gharabeigli and B. SoleimanySummaryThe Amu Darya Basin is a highly productive petroleum province in Turkmenistan and Uzbekistan, extending southward to Iran and Afghanistan. The Eastern KopetDagh region considered as an important hydrocarbon province seated in NE of Iran and southern part of the Amu-Darya Basin. The Late Triassic-Jurassic extensional tectonic produced a domino-type half-graben/tilted-block system, with more than 9 km thickness of the syn to post-rift sediments (Late Triassic- Present Day), as measured in the giant Gonbadly-Khangiran gas fields. The Gonbadly and Khangiran structures were formed by Paleocene-Present Day oblique inversions of the Jurassic half grabens above the Mid Jurassic Kashafrud Formation, which is the main detachment in this region.
The sequence stratigraphy of the Mid-Jurassic Kashafrud Formation, derived from the marginal fault scarps, depends on the balance between uplift and erosion rates in the basin margins. The attribute study and unsupervised sequence stratigraphy represent Northeastward channel-lobe systems in Low Stand System Tracts, associated levees and overbank areas on the slope to the basin floor fans. The result of this research leads to explore a sort of complex (structural and stratigraphic) traps in the syn-rift sediments as a new potential hydrocarbon system in KopetDagh basin.
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Joint Inversion Using Multi-objective Global Optimization Methods
Authors P.G. Lelièvre, R. Bijani and C.G. FarquharsonSummaryThe standard deterministic approach to joint inversion is to combine the multiple objectives (data misfits, regularization and joint coupling terms) into a weighted sum (aggregate) and minimize using a descent-based method. This approach has some disadvantages: appropriate weights must be determined for the aggregate, the use of local optimization requires that the objective functions be differentiable and well behaved, and there is the potential for entrapment in local minima. Pareto Multi-Objective Global Optimization (PMOGO) algorithms can overcome these issues. Also, PMOGO algorithms generate a suite of solutions representing the best compromises between the multiple objectives. We have implemented a PMOGO genetic algorithm and applied it to three classes of inverse problems: standard mesh-based problems for which the physical property values in each mesh cell are treated as continuous variables; mesh-based problems in which the cells can only take discrete physical property values corresponding to known or assumed rock units (a lithological inversion); and a fundamentally different type of inversion for which a model comprises wireframe surfaces representing contacts between rock units (essentially a geometry inversion). Joint inversion is greatly simplified for the latter two classes because no additional mathematical coupling measure is required in the objective function.
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Optimized Sequence of Single-domain and Joint Inversions Using Quantitative Integration Systems (QUIS)
Authors P. Dell’Aversana, G. Bernasconi and F. ChiappaSummaryIn this paper we discuss a “systemic approach” for integrating multidisciplinary geophysical data. We apply a Bayesian inversion algorithm to perform a sequence of single domain and joint inversions of seismic and electromagnetic data. We show how this integration workflow allows accurate estimations of porosity and fluid saturation. We extend this approach also to gravity data combining cooperative modeling, single domain inversion and joint inversion for integrating real multidisciplinary data sets in the Barents Sea.
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Generalized Multiparameter Joint Inversion Using Joint Total Variation - Application to MT, Seismic and Gravity Data
Authors D.M. Molodtsov and V.N. TroyanSummaryWe show that joint total variation can be efficiently used for simultaneous joint inversion of any number of geophysical methods, each sensitive to a different physical parameter of the subsurface. Joint total variation both provides structural coupling between different parameter domains and serves as a stabilizing functional in each domain, simplifying the objective function. Iteratively reweighted least squares scheme with Levenberg-Marquardt method results in decoupled linear systems for different domains, making computational complexity of joint inversion linear with respect to the number of domains and simplifying its software implementation. This approach is applied to 2-D joint inversion of MT impedance, seismic first-arrival traveltime and vertical component of gravitational field and its gradient. Results of the numerical experiment with synthetic data show efficiency of the approach and improvement of the inversion results over the single-domain inversions.
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Multi-physics Inversion for Reservoir Monitoring
Authors G.M. Hoversten, M. Commer, C. Schwarzbach and E. HaberSummaryIn this paper we consider the use of, time-domain electromagnetic, DC electrical and injection-production data in isolation and in combinations in order to investigate their potential for monitoring spatial fluid saturation changes within reservoirs undergoing enhanced oil recovery. We specifically consider two scenarios, a CO2 EOR within a relatively shallow reservoir, and a water flood within a deep carbonate reservoir. The recognition of the signal-enhancing role that electrically high conductivity steel well casings play makes the use of EM data possible in both these scenarios.
The work has demonstrated that reservoir fluid saturation changes from EOR processes produce observable changes in surface electric fields when surface-to-borehole (deep reservoirs), and surface-to-surface (shallow reservoirs) configurations are used and the steel well casings are accurately modeled. Coupled flow and TDEM data inversion can significantly improve estimate of fluid saturation levels and location compared to inversion of flow data only. The inversion of surface time-domain electric fields, including DC fields can resolve volumetric and resistivity differences that can distinguish between various water flood scenarios. Coupled flow and DC data can resolve the size and orientation of elongated fracture zones within limits that are considered a significant improvement over estimates made with traditional data.
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Insights on CO2 Migration Based on a Multi-physical Inverse Reservoir Modeling Framework
Authors F.M. Wagner, B. Wiese, C. Schmidt-Hattenberger and H. MaurerSummaryPermanent geophysical crosshole methods offer opportunities to provide spatiotemporal information on CO2 migration, since the physical properties change in regions affected by fluid substitution.
The direct and quantitative integration of geophysical methods in a reservoir modeling context is not straightforward and requires multi-physical process models coupled through petrophysical parameter transformations.
Based on an example from the Ketzin CO2 storage site, Germany, we present a hydrogeophysical modeling workflow, in which simulated CO2 distributions are transfered to changes in electrical properties used for geoelectrical forward modeling.
Simultaneous inversion of the electrical time-lapse response, reservoir pressure and CO2 arrival times has not been reported before and enables estimation of the permeability distribution.
The calibrated model captures the known migration direction of the CO2 and is able to explain the multi-physical calibration dataset.
The presented framework allows to integrate various types of observations into a single hydrogeophysical model leading to increased confidence in permeability parameterization and, in perspective, to improved predictive assessments of the storage reservoir.
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Addressing Current Challenges on Groundwater Model Structure through Effective Use of Geophysical Data
Authors T.N. Vilhelmsen, P.A. Marker, N. Foged, A.V. Christiansen, E. Auken and P. Bauer-GottweinSummaryWe wish to present a method for effective generation of structural models for groundwater flow simulations. The methodology is presented for two cases. A regional scale test, where geophysical data and borehole data is used for generating the regional scale hydrostratigraphy, and a local detailed case, where the same methodology is used to address the question of structural uncertainty.
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CO2 Capture and Storage - Developing industrial-scale CCS projects in Norway
By P. RingroseSummaryCO2 capture and storage (CCS) is an important part of the global solution for greenhouse gas control and was first implemented at an industrial scale at the Sleipner project in Norway in 1996. After reviewing the current state of progress with CCS projects, globally, we conclude that CCS is essential to achieving the 2oC warming scenario as stated in the Paris agreement. Industrial-scale CCS projects in Norway have been important vehicles for developing and demonstrating the many technologies involved in CCS. By reviewing this experience we identify key learnings and insights concerning: CO2 storage operations, testing of CO2 capture technologies, the value of geophysical imaging and monitoring data, and insights into storage capacity and injectivity performance.
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Cost-effective Seismic Reflection Imaging Using Seismic Interferometry for Imaging of Enhanced Geothermal System - A Case Study in the Neuquén Basin
Authors Y. Nishitsuji, S. Minato, B. Boullenger, K. Wapenaar, M. Gomez and D. DraganovSummaryWe investigate the applicability of passive seismic interferometry using P-wave coda from local earthquakes for the purpose of retrieving reflections for imaging enhanced geothermal systems. For this, we use ambient-noise data recorded in the Neuquén basin, Argentina, where the Peteroa and Los Molles geothermal fields are present nearby. After retrieving reflections, we proceed to process them following a standard processing sequence to obtain images of the crustal structures. Examining crosscorrelation, crosscoherence, and multidimensional deconvolution approaches, we find that multidimensional deconvolution, based on the truncated singular-value decomposition scheme, gives us slightly better structural imaging than the other two approaches. Our results provide higher-resolution imaging of the crustal structures down to the lower boundary of the Moho in comparison with previous passive seismic imaging by receiver function and global-phase seismic interferometry in this region. We also interpret the deep basement thrust fault that has been indicated by active-seismic reflection profile and nearby exploration well. The method we propose could be used as a low-cost alternative to active-source acquisition for imaging and monitoring purposes of deeper geothermal reservoirs, e.g., in enhanced geothermal systems, where the target structures are down to 10 km depth.
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Mimetic Operators for Seismic Exploration
Authors J. de la Puente, O. Rojas, M. Ferrer and J. KormannSummaryMimetic operators are a kind of discrete operators which, on staggered grids, can accomplish “mimetic” properties analogous to their continuous counterparts. Furthermore, they can attain identical convergence order everywhere in the domain, including at or near the domain’s boundaries in non-periodic problems. This property makes mimetic finite difference (MFD) operators attractive whenever high-contrast interfaces or physical boundary conditions are present in our models. In the seismic case, the strongest boundary condition is the interface between Earth and air, the so-called free surface. This surface is typically represented as a traction-free boundary condition and, although it is of critical importance for achieving accurate results, due to its vicinity to the sources and receivers, it is still a problem for current FD implementations. Despite efforts in the past, few FD schemes have attained convergence of order beyond two in results involving the free surface. Here we summarize the properties of mimetic operators applied to the elastic wave equation, as well as the changes required in order to incorporate into current explicit staggered grid codes the mimetic approach of the free-surface condition
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A Fast 3-D Free-surface Topography Method for Acoustic Full-waveform Inversion
Authors M.J. Huiskes, R.E. Plessix and W.A. MulderSummaryWe propose a finite-difference scheme for the simulation of seismic waves interacting with 3-D free-surface topography. The intended application is velocity model building by acoustic full-waveform inversion (FWI). The scheme follows an immersed boundary approach for wave equations in the first-order stress-velocity formulation, discretized on a standard staggered grid. Our scheme employs modified 1-D stencils rather than a full 3-D field wavefield extension at the free surface. Although this decreases the accuracy, it improves the scheme’s simplicity and robustness. To avoid stability problems, points close to the zero-pressure boundary must be excluded. The scheme, and its adjoint, have been tested by tilted geometry tests and by comparison to a finite-element method. We present a first test result of full-waveform inversion with the new scheme.
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Simple and Accurate Operators Based on Taylor Expansion for 2D Elastic Seismogram Calculation under Geological Discontinuities with Regular Cartesian Grids
Authors N. Fuji, O. Ovcharenko, R. Martin and C. CuvilliezSummaryWe propose a set of local operators to deal with internal discontinuities that do not coincide with collocated Cartesian grids in 2D transversely isotropic media. We use globally optimally accurate operators in order to obtain high accuracy. We derive modified operators by extrapolating wavefields from nearby grid points to the discontinuous point, introducing boundary conditions; we then distribute those conditions to the nearby grid points. Numerical examples suggest that the operators improve the coherency of the wavefront. We would like to optimise the local operators to control all the error propagation during the modelling.
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Exact Boundary Conditions for Local Wave Field Modelling
Authors F. Broggini, M. Vasmel, J.O.A. Robertsson and D.J. van ManenSummaryWe present a new methodology for local wave field simulation after model updates using exact boundary conditions (EBC’s). The finite-difference time-domain (FDTD) solver can be applied to models of arbitrary complexity. We apply the local wave field modelling algorithm to a subset of the Sigsbee 2B model. We demonstrate that the wave field can be correctly modelled on a truncated domain and includes all (long-range) interactions with the surrounding domain. The proposed method, which is extendable to 3D and is also applicable to multiple disconnected truncated domains, could be advantageous for applications based on targeted iterative wave field recomputations, such as full waveform inversion (FWI).
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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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