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77th EAGE Conference and Exhibition 2015
- Conference date: June 1-4, 2015
- Location: Madrid, Spain
- Published: 01 June 2015
61 - 80 of 980 results
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Attenuation of Seismic Noise in Microseismic Monitoring from Surface Acquisition
Authors M.J. Chmiel, P. Roux and T. BardainnePresented hereafter, is a method to first characterize and then attenuate seismic noise. Microseismic studies are often contaminated by surface noise sources that can make identification of the subsurface microseismic signal troubleseome. The method is a fast, automatic, signal-preserving means to suppress seismic noise whose source is located at the earth’s surface. We need no a priori information to use this technique. The work-flow steps are: (1) calculate the Fourier transform for a given time window, (2) determine the Cross-Spectral Density Matrix (CSDM) for each frequency, (3) perform the Singular Value Decomposition on the CSDM, (4) remove the eigenvalues that correspond to the most energetic noise sources at the surface: create a projected signal, (5) recreate the signal in the time domain from the projector. Final results show that application of the presented algorithm to microseismic data significantly attenuates recorded seismic noise, up to 2.4 times its original level.
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Secondary Porosity, Image Log and Nuclear Magnetic Resonance Log Definition
Authors C. Smith and M. KozlowskiCarbonate reservoirs offer difficult challenges to evaluation due to the frequent incidence of secondary porosity features in the form of fractures and vugs. Image logs are useful to help identify the presence of these features, but they do not quantify their contribution to permeability or to production. Nuclear Magnetic Resonance (NMR) logs provide characterization of the unaltered formation along with an evaluation of the contribution to porosity and permeability of the secondary porosity features. Even very difficult portions of the formation can now be characterized and potential production predicted. This paper compares the results from image logs and NMR logs in different carbonate reservoirs. The increased value of the asset created by the enhanced porosity and permeability from secondary porosity can now be considered when contemplating completion attempts in complex carbonates.
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Multi-objective Geostistical History Matching
Authors J.C. Carneiro, A.S. Amílcar Soares and L. AzevedoVectorial Multi-Objective and Stochastic History Matching techniques produce good results and are able to quickly find several local minima, however, they entail a very large computational cost where hundreds to thousands of fluid flow simulations are needed in each iteration. The current work proposes a Geostatistically based Multi-Objective approach where the computational cost is drastically lowered. A simple synthetic case study is presented with promising results.
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Seismic Driven Carbonates Reservoir Characterization Process
Authors M. Zen, N. Rodriguez Morillas, C. Pellan, T. Ait-Ettajer, L. Fontanelli and B. O'ConnellCarbonate reservoir characterization is still poorly understood in terms of hydrocarbon exploration and production. The integrated seismic study including interpretation, seismic attributes from an elastic seismic inversion and detailed sequence stratigraphic analysis has led to construct a predictive and innovative input in order to generate a more precise carbonate reservoir model.
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Velocity Analysis of Simultaneous-source Data Using Similarity-weighted Semblance
More LessDirect imaging of simultaneous-source data, without the need of deblending, requires a precise subsurface velocity model. In this paper, we focus on velocity analysis of simultaneous-source data using the NMO based velocity picking approach. We demonstrate that it is possible to obtain a precise velocity model directly from the blended data in the common-midpoint (CMP) domain. More specifically, the similarity-weighted semblance can help us to obtain much better velocity spectrum with higher resolution and higher reliability. We use both synthetic and field data examples to demonstrate the performance of the proposed approach.
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Electromagnetic and Seismoelectric Sensitivity Analysis Using Resolution Functions
Authors P.J. Maas, N. Grobbe, E.C. Slob and W.A. MulderFor multi-parameter problems, such as the seismoelectric system, sensitivity analysis through resolution functions is a low-cost, fast method of determining whether measured fields are sensitive to certain subsurface parameters. We define a seismoelectric resolution function for the inversion of a bulk density perturbation. The synthetic data and Green’s functions required to construct the resolution function are computed using the seismoelectric modelling code ESSEMOD. First, we consider the purely electromagnetic problem with a conductivity perturbation at a single point in an isotropic homogenous half-space. The result is nearly identical to a published result based on analytical Green’s functions. It correctly maps the position of the scatterer. Next, we perform an electromagnetic sensitivity analysis for the case of a layered background medium. Again, the resolution function is capable of correctly mapping the scatterer when it is above as well as below a layer of increased conductivity; although in the latter case with less resolution. Finally, we generate multi-component synthetic data with our forward modelling code and compute the seismoelectric resolution function for inversion of a bulk-density perturbation. We find that the seismoelectric system is sensitive to a perturbation in bulk density and that the position of the perturbation can be correctly recovered.
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Imposing Geological and Geomechanical Constraints on Time-lapse Time Strain Inversion
Authors J.A. Edgar and T.D. BlanchardProduction from hydrocarbon fields induces velocity changes and strains in the subsurface, which create time shifts between vintages of time-lapse seismic data. Recovering these time shifts can be useful for reservoir management, particularly through calibration of geomechanical models. These shifts can be estimated using non-linear inversion. However, such inversions are hampered by the limited bandwidth of seismic data and noise. Regularization is needed to obtain a suitable solution. We introduce a new constraint into a time-lapse non-linear inversion for time strain. A geologically consistent regularization scheme is imposed through the use of interpreted horizons as constraints. The horizons define layers within which coefficients of a function that describes the expected variation of time strain are inverted for. This decreases the reliance on classical damping parameters for noise suppression and reduces the size of the model space. The resulting time strain model depends on the function chosen to describe its expected variation and the layering scheme, both of which can be driven by geological and geomechanical understanding of the field. We show that this enables accurate recovery of the magnitude, shape and localization of time shift and time strain signals from beneath the reservoir, within the reservoir and throughout the overburden.
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Dating Fluid Migration in the Tarbert Reservoirs of the Greater Alwyn Area (North Sea, UK) - Impact on Reservoir Quality
Authors A. Ong, J.P. Girard and J. PirononIn the North Sea, areas with abnormal behavior and/or anomalously high reservoir quality preservation remain unexplained. The aim of this study is to understand processes responsible for the large variability in reservoir quality of the BRENT, observed in the Greater Alwyn Area. The tidal sandstones of the Tarbert Formation (Middle Jurassic) were investigated in two wells in the Forvie North and Jura condensate fields where it lies at depth of 3.5 km. Quantitative petrographic observations suggest that reservoir quality preservation is mainly controlled by retardation and/or inhibition of mechanical compaction due to less effective stress in Jura. P-V-T-X-t reconstruction of paleofluids migration history with modern fluid inclusions analytical procedure indicates earlier entrapment of hydrocarbon during the Eocene time (48 m.y.) in Jura, than in Forvie North (> 18 m.y.). The early hydrocarbon migration in Jura reservoir is associated with a significant fluid overpressure build-up that prevented the reservoir from extensive chemical compaction. In contrast, a later onset of hydrocarbon migration in Forvie North did not permit to inhibit efficiently mechanical and chemical compaction.
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Surface-related Multiple Elimination of Marine Data on GPU
More LessGPU has been performed in PSTM and RTM for years, and now further applied to multiple attenuation of marine data processing. Surface-related multiple elimination (SRME) algorithm can predict multiples but be burdened by strict requirement on data, we exploit the combination of DMO and DMO-1 method to reconstruct data to regular grid. The common offset gathers are utilized instead of common-source gathers and common-receiver gathers for GPU application. With the aid of GPU, the algorithm can get excellent results effectively.
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Resolving Time Dependant Stress Variations through Analysis of Microseismicity Recorded During Hydraulic Fracturing
Authors A.M. Baig, T.I. Urbancic and E. von LunenHydraulic fracturing of shale reservoirs enhances productivity of reservoirs by propping open fractures in the reservoir. In order to map the extent of the successfully stimulated zones, microseismic monitoring is increasingly used; typical outputs of such monitoring efforts are the geometry of the microseismic event distribution. To relate these event distributions to production decline curves, geomechanical modelling of the injection using these event distributions as a constraint is frequently performed. However, a basic assumption of such efforts is that the stress regime under which the events are occurring is invariant. By using multiple-well recordings of microseismic events, the mechanisms of the microseismicity may be determined. These mechanisms are proportional to the strain rate (deformation) that is imparted to the medium at the point of rupture, and as such constrain the stress regime through the treatment. Observations indicate that the stress/strain conditions in the reservoir can be highly variable, implying that microseismicity needs to be coupled to geomechanical models at a more basic level, in that the dynamic stress regime controls both the occurrence of these events and the propagation of fluid and proppant in the reservoir.
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A Discontinuity Detection Strategy Based on Spectral Decomposition
More LessStructural and stratigraphic discontinuities developed in subsurface, such as channels, faults and fractures, usually contribute to the construction of traps and hydrocarbon reservoirs. Seismic attributes are usually used to characterize the reservoir features. For instance, coherence is an important attribute to measure waveform changes and delineate discontinuities, which allows interpreters to quickly visualize and map complex fault systems. Considering the multi-scale characteristic of seismic data, spectral decomposition is usually used to divide the multi-frequency seismic data to various uni-frequency data, thus to highlight certain scale of geologic structures. Due to attenuation, the dominant frequencies of seismic data usually decrease with depths. Then, extracting spectral components at dominant frequencies may provide more precise perspectives of primary scale of geologic structures. In this abstract, we develop a new strategy to perform discontinuity detection by combining dominant-frequency-optimized spectral decomposition and coherence calculation. Examples demonstrate that this new strategy can detects fault systems accurately, with high resolution and signal to noise ratio. In a word, the application of this new discontinuity detection strategy is an effective way to detect different-scale structural and stratigraphic discontinuity features.
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Pre-stack Reverse Time Migration Based on Layered Mapping Method for Irregular Surface
Authors Y.M. Qu, J.P. Huang, Z.C. Li and Q.Y. LiTraditional FD method has some difficulties in treating irregular surface, while mapping method can overcome the disadvantage by transform the irregular surface to horizontal surface. But in the meantime, the interface below the surface is transformed to more complex interface, resulting in the inaccurate of wave propagation and imaging. In this paper, a layered mapping method is proposed and is applied to elastic wave RTM. This method not only can overcome the effects of irregular surface but also the underground structure can not be destroyed. Wave field forward continuation, reverse time continuation and separation are completed in auxiliary system coordinate while imaging in Cartesian. Numerical examples of simple surface topography model and complex surface topography model show the correctness of the method proposed in the paper. After testing two extreme cases of inaccurate interface elevation we can find out that the imaging results using layered mapping RTM are much better than that using traditional mapping RTM.
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Jurassic Petroleum System in the Polish Lowlands (Central Poland) - Organic Geochemical and Numerical Modelling Approach
Authors P. Kosakowski, P. Wójcik-Tabol, A. Kowalski and J. ZacharskiThe study area comprising the cantral part of the Polish Lowlands, termed Mogilno-Łódź Synclinorium. This area could be important petroleum exploration target in Poland, especially for unconventional resources. In this paper, we evaluate organic source facies and the results of basin modelling in order to improve understanding of the regional petroleum system. Geochemical and petrographic analyses of potential source rocks were used in this study. Our investigations showed that the organic carbon contents is high – up to 7.5% wt% in the Upper Jurassic and even to 5.5 wt% in the Middle Jurassic strata. with nearly 50 mg of hydrocarbons/g rock. A large majority of the study area source rocks reached initial and main phase of „oil window”. Numerical modelling of generation of hydrocarbons indicates the source rocks entered the early mature phase in the early Cretaceous time, and mian phase of “oil window” in the late Cretaceous time. The generation was terminated as a result of post-Cretaceous inversion of the study area. The Jurassic source rocks do not show expulsion. The pore spaces are saturated by hydrocarbons generated, indicating possible presence of unconventional hydrocarbons accumulation in the analyzed rocks.
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Rock Physics Analysis and Fluid Contact Modeling in Vøring Basin, Norwegian Sea
Authors M. Gonzalez Fernandez, P. Lukito and C. CobosA rock physics analysis project was conducted to better understand the flat spot seismic response observed in the Vøring basin, Norwegian Sea, Norway. Flat spots could be considered as the best direct hydrocarbon indicator (DHI), however understanding their existent characteristics on the wells and circumstances under which they have a recognizable expression on the seismic data, could help to reduce risk for the exploration efforts currently being undertaken in this area. This study included a complete rock physics analysis and detailed prestack forward modeling to understand the effect of fluid, porosity and seismic resolution variations on fluid contact seismic reflections. From the modeling we generated a complete catalog of the expected fluid contact responses for various scenarios. To fully understand the specific characteristics of flat spots in this area, more than looking for standard responses such as flatness, associate “bright spot”, positive amplitude and tuning effects at the ends of the contact, we need to model fluid thickness, rock properties and seismic vertical resolution. This is mandatory for DHI prospect evaluation in the studied area.
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An Outcrop-based Detailed Geological Model to Test Automated Interpretation of Seismic Inversion Results
Authors R. Feng, S. Sharma, S.M. Luthi and A. GisolfPreviously, Tetyukhina et al. (2014) developed a geological and petrophysical model based on the Book Cliffs outcrops that contained eight lithotypes. For reservoir modelling purposes, this model is judged to be too coarse because in the same lithotype it contains reservoir and non-reservoir lithologies. Hence, a new and more detailed geological model has been built based on the principles of sequence stratigraphy and with more emphasis on the reservoir-quality lithologies. Full elastic seismic data has been simulated based on a petrophysical model based on empirical rock-physical relationships. In order to improve the Full Waveform Inversion result, an additional scheme is proposed where the unconstrained seismic inversion result is automatically interpreted in terms of a scenario that represents prior geological information. In this way, thin layers, present in the prior model, can be interpreted from a bandlimited seismic inversion result if they are consistent with the data.
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3D Source Designature Using Source-receiver Symmetry in the Shot Tau-px-py Domain
More LessWhile sufficient for many deep water datasets, vertical source designature in shallow water environments can lead to unsatisfactory levels of ringing and amplitude striping, particularly on outer streamers where the assumption of a vertical farfield signature is least accurate. In this paper we modify the tau-px-py Radon equations to introduce a 3D directional designature algorithm. Assuming source-receiver propagation symmetry, a 3D source re-signature operation is introduced and solved with an iteratively re-weighted least squares solver. The results of the strategy lead to improved spatial consistency and a reduction in the level of amplitude striping in the output data. Data examples from a real-world dual-level source project with variable-depth streamers from the North Sea are shown.
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Two-grid Stochastic Full Waveform Inversion of 2D Marine Seismic Data
Authors A. Tognarelli, E.M. Stucchi, N. Bienati, A. Sajeva, M. Aleardi and A. MazzottiWe apply stochastic Full Waveform Inversion (FWI) to 2D marine seismic data to estimate the macro-model velocity field which can be a suitable input for subsequent local (gradient based) FWI. Genetic Algorithms are used as the global optimization method. Our two-grid representation of the subsurface, made of a coarse grid for the inversion and of a fine grid for the modeling, allows us to reduce the number of unknowns to an acceptable number for the given computer resources and to perform a stable and reliable finite difference modeling. Thus, notwithstanding the known high computational costs that characterize global inversion methods, we are able to reconstruct a smooth, low wavenumber, acoustic velocity model of the subsurface. The reliability of the estimated velocity macro-model is checked through the inspection of prestack depth migrated gathers and through the superposition of observed and modeled seismograms. The method we propose is less affected by the risk of being trapped in local minima of the misfit functional than gradient based FWI methods, and can be a viable alternative to estimate proper starting models for gradient based full waveform inversions.
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3D Elastic Full Waveform Inversion of Teleseismic Data for High-resolution Ospheric Imaging
Authors S. Beller, V. Monteiller, S. Operto, G. Nolet, L. Combe, L. Métivier, J. Virieux, T. Nissen-Meyer, A. Paul and L. ZhaoWe present a 3D time-domain target-oriented elastic full-waveform inversion method well-adapted to the reconstruction of lithospheric images from passive teleseismic data. In teleseismic configurations, sources no longer correspond to point sources embedded in the lithospheric target but rather correspond to a nearly plane wavefronts generated by distant Earthquake incoming from the outside of the targeted medium. To save computation time and apply FWI in the lithospheric target, we follow a two steps strategy based on grid-injection technics. First, wavefields generated by earthquake are propagated in axisymmetric global Earth model with AxiSEM to be stored on the target boundaries. Then, these wawefields are injected within the lithospheric medium and propagated with a spectral element method. We efficiently compute the gradient of the misfit function with the adjoint-state method in time domain. We assess the feasibility of the method on two synthetic models: a cubic inclusion and a realistic lithospheric model representative of the Western Alps. Preliminary results suggest that, despite a weak number of sources and a a coarse aperture illumination, our FWI implementation succeed in reconstructing the initial model thanks to the contribution of both forward and backward scattering regimes.
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A Geologically Constrained Basis for Global Inversion of CSEM Data Using a Dynamic Number of Parameters
Authors O.J. Skrede, J.P. Morten and L. BomanIn this paper, we introduce a new parameterization of the model space, where the basis is constrained on a priori information about the geology. The parameterization is able to represent complex model structures using only a few parameters, which can significantly reduce the computational complexity of the inversion problem. This facilitates a global inversion approach, and we consider a simulated annealing optimization. In order to facilitate the search for a minimum-parameter representation, we extended the inversion to be able to optimize for a dynamically varying number of variables. We demonstrate the method by inversion of marine CSEM data from the Troll West Oil Province. The algorithm is able to recover a resistivity profile which agrees with well log data from the area. The dimensionality of the parameter space is reduced by more than an order of magnitude using our approach compared to a layer-based discretization of the resistivity. The physically feasible models obtained are attributed to the constrained basis which makes the inversion very robust.
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CSEM Monitoring of Reservoir Oil-saturation Using a Novel Borehole-to-surface Configuration
Authors K. Tietze, O. Ritter, P. Veeken and B. VerboomTo optimize enhanced oil recovery techniques it is essential to know the spatial propagation of the injected fluids in the subsurface. We investigate the applicability of controlled-source electromagnetic (CSEM) methods to monitor fluid movement in a German oilfield (Bockstedt). Injected brines have much lower electrical resistivity than oil within the reservoir. 3D modelling suggests CSEM is sensitive to resistivity changes at reservoir depths, but only if sensors/transmitters are positioned closer to the reservoir, e.g. using observation wells. In particular, the vertical electric field component in shallow boreholes and/or use of alternative source configurations consisting of combinations of vertical and horizontal dipoles are promising. In spring 2014, a borehole CSEM survey (4 transmitters, 25 MT stations) was conducted across the oil field using a new horizontal-vertical source. The current was injected via the steel-casing of a 1.3 km deep abandoned oil-well. Redeployment tests of transmitters demonstrate high repeatability of CSEM measurements. First comparison of recordings from conventional and the new borehole transmitters indicate differing current distribution in the subsurface. Results of the new source configuration are in general agreement with predictions by numerical simulations.
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