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72nd EAGE Conference and Exhibition incorporating SPE EUROPEC 2010
- Conference date: 14 Jun 2010 - 17 Jun 2010
- Location: Barcelona, Spain
- ISBN: 978-90-73781-86-3
- Published: 14 June 2010
61 - 80 of 797 results
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Using High–density OBC Seismic to Optimise the Andrew Satellites Development
Authors L. Padmos, D. Davies, M. Davies and J. McGarritySuccessful development of the Andrew satellite fields (Central North Sea) will depend strongly on the ability to place development wells in an optimal position in the poorly imaged, subtle structures. Towed-streamer seismic quality is poor at the Palaeocene reservoir level due to the presence of anomalously fast Eocene sand channels in the overburden. In order to achieve a step change in data quality, a 140 km2 high shot density, wide-azimuth Ocean Bottom Cable (OBC) seismic survey has been acquired over Kinnoull, Kidd and Farragon. The survey was acquired between December 2008 and July 2009, and the processed P/Z product was on the workstation in December 2009. The new high-density OBC data has been very successful in improving the imaging below the Eocene channels. Signal to Noise and resolution have been improved, resulting in reservoir reflections that can be interpreted with a lot more confidence. The OBC data has also allowed a better estimation of the zero offset and gradient AVO products. The improved seismic quality will play an important role in optimising well trajectories and help de-risk upside development options.
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5D Data Reconstruction Using the Anti-leakage Fourier Transform
By G. Poole LtdWide-azimuth datasets allow us to incorporate more dimensions into data regularisation. Using a multi-dimensional Fourier transform that handles irregular data we can either output traces on a regular grid or interpolate additional source and receiver lines. This allows us to fill holes more effectively and regularise in the offset and azimuth directions whilst preserving amplitude variation with offset and azimuth (AVO and AVAz). We show how the anti-leakage Fourier transform can be used with four spatial dimensions and use OBC and land data examples to highlight improvement in continuity and accurate reconstruction of missing data.
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Can We Correct for Azimuthal Variations of Residual Moveout in Land WAZ Context Using Depth Non-linear Slope Tomography?
Authors S. Zimine, G. Lambaré, P. Guillaume, J. P. Montel, J. P. Touré, N. Deladerrière, X. Zhang, A. Prescott, D. Lecerf, S. Navion, J. L. Boelle, A. Belmokhtar and A. LadmekHigh-density wide azimuth (WAZ) land surface acquisitions have demonstrated superior imaging capabilities. However, processing of such data exhibits several challenges related to the traditionally poor S/N ratio of land recording and the necessity of reconciling the kinematics of the various azimuths. We present an imaging case history involving WAZ non-linear slope tomography. Based on kinematic invariants, velocity model update is performed both in depth and time from the same picking. Our dense automated dip and residual move-out picking is done on an initial pre-stack time migrated (PreSTM) dataset after application of a structurally consistent filtering that greatly improves the S/N ratio. Our case study demonstrates that non-linear slope tomography in the depth domain greatly improves the imaging of the structures when compared to the initial PreSTM result. Even if tomography in the time domain significantly enhances imaging, it cannot successfully honour the kinematics of the various azimuths within the constraints of time imaging assumptions. On the contrary, WAZ non-linear slope tomography in the depth domain offers an efficient way to reconcile these kinematics, thus promoting the use of depth imaging when processing high-density WAZ data, even in the context of mild geological complexity.
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Analysis Methodology for Azimuthal Anisotropy
Authors K. Bishop, A. Osadchuk and M. StanleyHere is a prescription for the implementation of a data-driven analysis procedure for determining accurate horizontal anisotropic velocity parameters. The high resolution method is simple and fast and can be quickly applied to 3D surveys. Wide and multiple azimuth datasets are making it clear that azimuthal anisotropy is more prevalent than most imagers realize. In many regions, significant horizontal stress can deform the rock or pore matrix or cause fracturing that result in directionally dependent horizontal velocity or horizontal transverse isotropy (HTI). This method extends the parameterization accuracy by defining an elliptical gradient technique. The normally occurring abundant spatial sampling of data provides sufficient statistics for computing a gradient surfaces and finding the minimum to solve for the anisotropy parameters.
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Controlled-source Electromagnetic Modelling Studies – Utility of Auxiliary Potentials for Low-frequency Stabilization
Authors R. Streich, C. Schwarzbach, M. Becken and K. SpitzerWhen simulating controlled-source electromagnetic data at frequencies significantly lower than 1 Hz, standard formulations based, e.g., on the vector Helmholtz equation for the electric field, may fail to produce faithful results, because the term in the Helmholtz equation involving conductivity decays linearly with frequency. To stabilize low-frequency simulations, we introduce an auxiliary potential, constrained to be zero by boundary conditions, and explicitly enforce a divergence condition. We present an implementation of our stabilization technique within a finite-difference frequency-domain algorithm. The utility of the stabilized approach is demonstrated by showing synthetic data for frequencies as low as 0.001 Hz for a 3D model roughly mimicking the geometry of the CO2 sequestration pilot site in Ketzin, Germany. In these synthetic data, we observe that instability occurring primarily in the air for non-stabilized simulations disappears for stabilized computations. As expected, the auxiliary potential assumes near-zero values, but its amplitude increases with decreasing frequency due to numerical limitations. The amplitude characteristics of the auxiliary potential, and good accuracy of our synthetic data in comparison with 1D simulation results, suggest that the stabilization is usable down to frequencies at which electromagnetic fields can effectively be considered static.
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Exploiting the Airwave for Land CSEM Reservoir Monitoring
Authors M. Wirianto, W. A. Mulder and E. C. SlobDisplacement of oil by saline water leads to time-lapse differences in CSEM measurements. Because the time-lapse effect may be weak and difficult to observe, acquisition optimization plays an important role. Applying a horizontal dipole source on the surface creates a source-induced airwave component. We studied the effect of the airwave on time-lapse land CSEM measurements of resistivity changes after oil production by running numerical simulations for several configurations. Our study shows that the source-induced airwave is the predominant component in increasing the amplitude of the time-lapse fields, the difference between the recorded EM data before and after oil production. Moreover, the lateral extent of the depleted part of the oil reservoir is much better defined when the airwave is present.
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Using CSEM to Monitor the Production of a Complex 3D Gas Reservoir – A Synthetic Case Study
Authors D. L. Andreis and L. M. MacGregorThe marine CSEM method is currently being applied to the problem of detecting and characterizing hydrocarbons in a variety of settings for exploration purposes. Because of its physics it can on one hand, distinguish between fluids within formations. On the other hand, it can suffer from a poor resolution in positioning those bodies in the vertical plane. The purpose of this presentation is to highlight the possibilities and challenges the CSEM technique will have to face to successfully play a key role during monitoring phase of a hydrocarbon reservoir life cycle. This will be illustrated using synthetic data from a complex meandriform anticline channel charged with gas.
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Fast-track Marine CSEM Processing and 3D Inversion
Authors J. P. Morten and A. K. BjørkeWe present CSEM 3D inversion results where the receiver rotation angle relative to North is treated as a free parameter in the optimization. This allows us to omit receiver orientation estimation and data rotation pre-processing in the workflow. Moreover, the initial resistivity model is prepared independently from the CSEM data using available seismic and well log information. In this way, calibrated frequency domain data can be input directly to the anisotropic 3D inversion tool, with arbitrary initial values for the rotation angles. Synthetic data is generated using speed optimized modeling parameters. This demonstrates a fast-track 3D inversion workflow which can deliver a 3D inverted resistivity volume within few days after data has been uploaded from the vessel.
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Comparison of Marine TEM and FEM Techniques – Offshore West Africa
Authors L. D. Masnaghetti, M. Watts and G. CairnsMarine CSEM data acquired using a continuously-towed source and 50% duty cycle waveform were processed to give both time and frequency-domain responses from an array of receivers in water about 100m deep. 1 and 2.5D inversion gives results which are consistent with seismic data.
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The Value of CSEM Data in Exploration
Authors A. Buland, L. O. Løseth and T. RøstenA recent internal Statoil review of the CSEM performance in exploration shows a clear progress with time from the first early surveys to the more recent surveys. CSEM in hydrocarbon exploration has a short commercial history of less than ten years, and the progress can be explained by improvement during these years in acquisition, processing, interpretation techniques, experience, skills and tools. The economical value of CSEM data can be predicted for specific exploration settings using standard decision analysis. Based on performance tracking and review of the prediction strength, conservative estimates of the economical value of CSEM data can be more than 10 times above the typical costs for a CSEM survey and analysis.
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Scalable Solutions for Nonlinear Inverse Uncertainty Using Model Reduction, Constraint Mapping, and Sparse Sampling
Authors M. J. Tompkins and J. Fernandez MartinezWe present a general nonlinear inverse uncertainty estimation method that allows for the comprehensive search of model posterior space while maintaining computational efficiencies similar to deterministic inversions. Integral to this method is the combination of a parameter reduction technique, like Principal Component Analysis, a parameter bounds mapping routine, a sparse sampling scheme, and a forward solver. Parameter reduction, based on linearized model covariances, is used to reduce the model space by orders of magnitude. Parameter constraints are then mapped to this reduced space, using a linear programming scheme, defining a bounded posterior polytope. Sparse deterministic grids are employed to sample this feasible model region, while forward evaluations determine which model samples are equi-probable. The resulting ensemble represents the equivalent model space, consistent with Principal Components, that is used to infer uncertainty measures. The number of forward evaluations is determined adaptively and minimized by finding the sparsest sampling required for convergence of uncertainty measures. We demonstrate, with a surface electromagnetic example, that this method has the potential to reduce the nonlinear inverse uncertainty problem to a deterministic sampling problem in only a few dimensions, requiring limited forward solves, and resulting in an optimally sparse representation of the posterior model space.
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Sensitivity Study of Multi-sources Receivers CSEM Data for TI-anisotropy Medium using 2.5D Forward and Inversion Algorithm
Authors A. Abubakar, J. Liu, M. Li, T. M. Habashy and K. MacLennanOur study is to analyze the sensitivity of multicomponent electromagnetic fields to the reservoir conductivity. We assume the reservoir to be transverse isotropic (TI) and the field components include both electric and magnetic data. Several authors studied the 1D case and showed that the response from a TI-anisotropic thin resistive layer is dominated by the vertical conductivity, but to-date, anisotropy in a 2D model has not been adequately studied. In addition to the electric dipole sources, we also investigated the sensitivity of electric and magnetic fields due to magnetic dipole sources, which could provide complementary information on the reservoir conductivity.
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Seismic Imaging with Multiple Scattering
Authors A. J. Berkhout and D. J. VerschuurThis paper focuses on the promising concept of using multiple scattering in the migration process. This means that the input of the proposed migration algorithm consists of seismic data that includes (blended) multiples. It also means that both primary and multiple scattering contribute to the seismic image of the subsurface, utilizing the double illumination property.
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Angle-dependent Least-squares Imaging of Incoherent Wavefields
Authors D. J. Verschuur and A. J. BerkhoutIn traditional seismic acquisition, temporal overlap between the recordings of consecutive shots is avoided. In this paper we will investigate the proposal to abandon this acquisition constraint by introducing dense source distributions in an overlapping fashion (’blended acquisition’). The result is an improved source space with a favorable azimuth distribution. We will show that blended measurements can be directly used in an angle-dependent migration process with a multi-shift least-squares imaging condition, such that a densely sampled illumination is obtained in the ray parameter domain.
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Prestack Data Enhancement Using Local Traveltime Approximation
Authors V. Buzlukov, R. Baina and E. LandaThe quality of recorded seismic data depends on many factors such as complexity of the subsurface, strong noise level, the topography of the earth’s surface, near surface inhomogeneities etc. We propose to use a local common offset (CO) approximation for traveltime stacking surface description. It allows to approximate traveltimes of reflection events in the vicinity of arbitrary ray and thus arbitrary offset. We present the general workflow and the implementation of a signal enhancement scheme.
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3D Prestack Beam Migration with Compensation for Frequency Dependent Absorption and Dispersion
Authors Y. Xie, C. Notfors, J. Sun, K. Xin, A. Biswal and M. BalasubramaniamSpatial variations in the transmission properties of the overburden cause seismic amplitude attenuation, wavelet phase distortion and seismic resolution reduction on deeper horizons. This poses problems for the seismic interpretation, tying of migration images with well-log data and AVO analysis. We developed an efficient prestack beam Q migration approach to compensate for the frequency dependent dissipation effects in the migration process. A 3D tomographic amplitude inversion approach may be used for the estimation of absorption model. Examples show that the method can mitigate these frequency dependent dissipation effects caused by transmission anomalies and should be considered as one of the processes for amplitude preserving processing that is important for AVO analysis when transmission anomalies are present.
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Pure P-wave Propagators Versus Pseudo-acoustic Propagators for RTM in VTI Media
Authors X. Du, R. P. Fletcher and P. J. FowlerWe propose a new approach to obtain a pure P-wave propagator for vertical transversely isotropic (VTI) media. We compare it with existing “pseudo-acoustic” propagators as modeling kernels for prestack reverse time migration (RTM).
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Angle Gathers by Reverse-time Migration
Authors M. Vyas, E. Mobley, D. Nichols and J. PerdomoOne of the ways to compute angle gathers for reverse-time migration (RTM) is through time lags. Algorithm for the transformation of time lags to angles has been proposed previously by other authors. However, the proposed workflow requires a dip field and is increasingly inaccurate in areas with conflicting dips and for dips greater than 60-degrees. In this paper we propose methods to overcome the dip limitation and to do the angle transformation without explicitly using the dip field. The angle gathers thus obtained can be used for migration velocity analysis or to improve the image quality through stack. We use a synthetic 2D model to compare results obtained using our proposed methods and the conventional workflow. Finally, we show RTM angle gathers for SEAM model using our methods.
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Kirchhoff Beam Q Migration
Authors J. Liu and G. PalacharlaWe developed a Kirchhoff beam Q migration method that combines the advantages of beam migration and Q migration to correctly handle both multi-arrivals and amplitude/frequency restoration. The method was successfully applied to a 2-D synthetic data set and produced images that are superior to those from single-arrival Kirchhoff Q migration or Kirchhoff beam migration without Q compensation.
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Impact of TTI Anisotropy on Elastic and Acoustic Reverse Time Migration
Authors R. Lu, P. Traynin, J. E. Anderson and T. DickensIn this study, we use synthetic seismic data to demonstrate the impact of proper anisotropic parameterization as well as the choice of elastic migration algorithm on the output image. We synthesize an elastic dataset using a 2D TTI elastic model based on the SEAM 3D model. Then we migrate this dataset using isotropic acoustic RTM, VTI acoustic RTM, TTI acoustic RTM, and TTI elastic RTM algorithms, respectively. Image quality improves progressively as we use more realistic models as well as more accurate elastic wave-propagation engine. Upgrading from TTI acoustic RTM to TTI elastic RTM results in better delineation of the salt boundary and better sediment termination against faults and salt. These differences result from the fundamental limitations of migrating elastic data using acoustic RTM and result from the proper positioning of converted waves.
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