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73rd EAGE Conference and Exhibition incorporating SPE EUROPEC 2011
- Conference date: 23 May 2011 - 27 May 2011
- Location: Vienna, Austria
- ISBN: 978-90-73834-12-5
- Published: 23 May 2011
21 - 40 of 799 results
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Data Reconstruction via Sparse Bi-focal Transformation
Authors H. Kutscha and D. J. VerschuurIn most reconstruction algorithms information about the subsurface can not be utilised, even if such is available. Focal transformation is a way to effectively incorporate prior knowledge of the subsurface in seismic data reconstruction. The basis functions of this transformation are the focal operators. They can be understood as one-way propagation operators from certain effective depth levels in a prior velocity model. A sparseness constraint is used to penalize aliasing noise. By using several depth levels simultaneously the data can be described with less parameters in the transform domain. This results in a better signal to noise separation and, therefore, improved reconstruction. In addition, we introduce a smart choice of focal operators, based on data-driven operator updating where we follow closely the reflection events in the data. This allows an even stronger compression of the data in the focal domain.
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Parametric Matching Pursuit Methods to Reconstruct Seismic Data Acquired with Multichannel Sampling
Authors A. Ozbek, M. Vassallo, K. Ozdemir, D. J. van Manen, K. Eggenberger and J. O. A. RobertssonIn marine seismic data acquisition, multichannel sampling can occur in various scenarios, including over/under streamers, multicomponent streamer, and multicomponent ocean-bottom node. In these various multichannel sampling scenarios, each channel outputs samples of a filtered version of a seismic wavefield. These filters are different for each channel; the data are often coarsely and irregularly sampled. The objective is to reconstruct the unknown wavefield from the multichannel samples. In this paper, we discuss how parametric matching pursuit methods can be extended to solve such reconstruction problems. We give two examples based on data that a multicomponent streamer could record and show the form the reconstruction problem takes when two- and three-component data are available.
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Matching Pursuit Methods Applied to Multicomponent Marine Seismic Acquisition – The Issue of Crossline Aliasing
Authors M. Vassallo, A. Ozbek, K. Eggenberger, K. Ozdemir, D. J. van Manen and J. O. A. RobertssonIn this work we analyze the theoretical aspects of spatial aliasing in the crossline direction in marine seismic acquisition. We also explain the benefits of the additional measurements acquired by a multicomponent towed streamer, able to measure the three components of the particle velocity vector in addition to the pressure wavefield. We propose matching pursuit based techniques to reconstruct a 3D full bandwidth seismic wavefield on a fine receiver grid. The techniques that we describe process multicomponent seismic data; they calculate the desired 3D wavefield with satisfactory quality despite the severe aliasing that affects each of the individual input measurements in the crossline direction.
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Convergence Improvement and Noise Attenuation Considerations for POCS Reconstruction
Authors J. J. Gao, M. D. Sacchi and X. H. ChenIn recent years, a variety of algorithms for multidimensional seismic survey reconstruction have been proposed. Projection onto Convex Sets (POCS) seismic trace reconstruction appears to be an affective, uncomplicated and robust algorithm for the recovery of unrecorded seismic traces. Its slow convergence, however, could jeopardize its computational appeal. For this reason, we investigate the performance of POCS in terms of different threshold schedules. We show that a data driven threshold schedule leads to an efficient implementation of POCS where high-quality solutions can be obtained in a modest number of iterations (>30-40). In addition, we present a variant of POCS that permits concurrent reconstruction and denoising of seismic volumes. The latter is achieved by defining a weighted reinsertion trace strategy that alleviates the influence of the noisy traces in the final reconstruction of the seismic volume. We illustrate our findings with synthetic and real data examples.
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5D Seismic Volume Reconstruction Using HOSVD
Authors N. Kreimer and M. D. SacchiWe propose a tensor completion method to reconstruct sparse prestack data. An algorithm based on the High-Order SVD (HOSVD) is used to estimate a low rank decomposition of the seismic volume. The latter allows us to use rank-reduction of tensors to estimate missing traces and increase the SNR of the seismic volume. A real data set from the Western Canadian Sedimentary Basin is used to test the proposed algorithm.
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Minimizing Ellipsoidal Norm Seismic Data Interpolation with Radon Spectrum Constraints
Authors X. Wang, H. Z. Wang, D. H. Zhou and L. X. TianA data adaptive interpolation is designed under the Radon spectrum constraints for spatially aliased seismic data. The inverse process is formed through constructing an ellipsoidal norm, which can make full use of the information about the Fourier spectrum of the data. The ellipsoidal norm can enhance the relative distribution of the Fourier spectrum and is computed with the help of Radon spectrum. Radon spectrum can helpfully concentrate the energy distribution of the Fourier spectrum. Correspondingly, the aliasing components in the Fourier spectrum can be relatively attenuated. The solution of the interpolation inverse problem is sparser and the inverse process becomes more stable. The numerical examples show the effectiveness of the method. The method is applicable to 2D and 3D seismic survey data recorded sparsely in a horizontal plane. The most common pre-stack applications of the algorithm are common-mid-point and half-offset domain interpolation.
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Fast Generalized Fourier Interpolation of Nonstationary Seismic Records
Authors M. Naghizadeh and K. A. InnanenWe propose a fast and efficient method for the interpolation of nonstationary seismic data. The method uses the fast generalized Fourier transform FGFT to identify the space-wavenumber evolution of nonstationary spatial signals at each temporal frequency. The nonredundant nature of FGFT renders a big computational advantage to this interpolation method. A least-squares fitting scheme is used next to retrieve the optimal FGFT coefficients representative of the ideal interpolated data. For randomly sampled data on a regular grid, we seek a sparse representation of FGFT coefficients to retrieve the missing samples. A synthetic seismic data example was used to examine the performance of the method.
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How to Obtain a Seamless Dataset for a Pre-stack Multi-survey Merge Using 5D Data Reconstruction?
Authors J. L. Rivault and A. MotagallyPre-stack merging multi-survey datasets is often challenging in terms of processing effort as well as time and human resources. It is problematic not only due to issues arising from survey matching (due to differences in sources and receivers characteristics) but also from variations in sampling, which may relate to acquisition azimuth, bin size, shot/receiver line spacing. For such datasets, it is important to regularise the sampling of the data in order to harmonise fold and minimise migration artefacts. In this paper we demonstrate the use of 5D data reconstruction for the benefit of multi-survey merging by mapping all the different surveys to a single acquisition design. The result is a dataset with a single acquisition configuration which has a constant fold and a significantly reduced level of migration noise. It also allows the preservation of azimuthal information by migrating in the COV domain. Its shows that 5D data reconstruction fully preserves the original seismic aspect allowing to easily migrate pre-stack multi-survey vintages in a single pass, which reduces the work of the geophysicist.
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Determination of Shear-wave Velocity in Seabed from Dispersion Data of Love Waves
Authors H. Dong, G. Ke and K. DuffautEstimation of the shear (S-) wave velocity or shear strength in the seabed is of importance for geotechnical applications, characterization of subsurface, seismic exploration studies and geohazard investigation. S-wave velocities in the sediment can be estimated by invert the dispersion data of seismic interface waves, which will be considered in this study. Numerical study shows that Love wave sensitivity and inversion stability in linearized inversion is higher than that of the Rayleigh wave and the inversion of Love wave dispersion curve provides a more accurate results. However, in conventional underwater seismic experiments only Scholte wave can be generated. In a testing experiment S-wave sources were used and both Scholte wave and Love wave were generated and recorded. In this study the dispersion of Love waves are analyzed using three time-frequency analysis methods. The S-wave velocities are estimated by inverting the dispersion data. The inversion results show the maximum penetration depth of the estimates is around 25 m in the seafloor, where the estimated S-wave velocity is around 220m/s. This approach provides an alternate and supplementary means to estimate the seismic velocity structure that is valuable in both seafloor geotechnical engineering and the static correction in seismic exploration using reflection methods.
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PZ Summation of 3D WAZ OBS Receiver Gathers
Authors P. Hugonnet, J. L. Boelle, P. Herrmann, F. Prat and A. LaframPZ summation is a typical processing flow for 2-Component Ocean Bottom Seismic (OBS) data, which takes advantage of the simultaneous recording of the pressure and vertical velocity wavefields to separate the up-going and down-going wavefields and to attenuate the water bottom receiver-side peg-legs. However, practical implementations are often either monochannel/1D or designed for 2D receiver gathers, while modern acquisition geometries often lead to 3D, wide-azimuth (WAZ), densely sampled receiver gathers. Such 3D gathers can be processed in the tau-px-py domain with a monochannel algorithm. In this paper we extend the method to directly process 3D gathers, without the need for tau-px-py transforms. Some current implementations also attenuate the source-side multiples, but they rely on a first order approximation for the amplitudes and on the 1D geology (horizontally layered medium) assumption. By introducing a simultaneous 3D predictive deconvolution operator in the peg-leg attenuation formulation, we remove the first order approximation and we improve the attenuation in the case of deviations from the 1D assumption.
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Enhanced Wavefield Separation of OBS Data
Authors E. Zabihi Naeini, L. Baboulaz and S. GrionIn ocean-bottom seismic (OBS) data processing, wavefield separation results are sometimes affected by high levels of noise on the vertical component Z, while the pressure component P is in general of good quality. Nonetheless, Z is needed to achieve complete pre-stack wavefield separation and also to drive processes such as mirror imaging and up-down deconvolution. To address the problem of noise on Z affecting wavefield separation results, we propose a new method which first estimates a multiple model from the downgoing wavefield in a least-squares fashion. Next, this multiple model is used as a measure of seismic signal coherency to calculate an enhanced upgoing wavefield with minimal noise degradation. We show the benefits of this new method on a real data example from the Caspian Sea.
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Velocity-based Wavelet Corrections for Domain Transformation
By J. E. GaiserIt is well established that similar vertical wavelength ranges must be preserved in multicomponent data and that wavelengths of P- and S-waves must match in order to sample reflectivity in an equivalent manner. Conversion of a wavefield to another time or depth domain is described by transformation functions that depend on average VP/VS ratios and velocity. Although these functions align corresponding stratigraphic events of different wavefields, they distort the seismic wavelet because global average velocity properties are independent of local interval properties that define wavelength. In this study we develop a theory of velocity-based wavelet corrections for domain transformations, which are expressed as functions of interval and average VP/VS and velocity, to match wavelength of multicomponent wavefields. We examine the effects for both land and marine data examples and find that land surveys are affected more than marine, and may require spectral broadening of the wavelet. Data from the Marcellus shale in northeast Pennsylvania, USA, shows significant bandwidth improvements for C-waves when wavelet corrections based on velocity match their wavelengths with P-waves. Application of these wavelet corrections should benefit registration fidelity, joint AVO/A (offset and azimuth) inversions and attribute analyses.
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Polarity Reversal Correction for Multicomponent Joint Elastic Reverse Time Migration
Authors Q. Z. Du, Y. T. Zhu, G. Fang and X. F. GongMulticomponent joint elastic reverse time migration is one of important parts in multicomponent seismic data processing. We analyse the implementation of elastic reverse time migration and the polarity reversal in PS and SP images. We present a method using Poynting vector to correct the polarity reversal in elastic reverse time migration. The polarity reversal correction using Poynting vector can be done with the imaging conditions at every time step of the elastic RTM. And the whole correction procedure can be carried out in common shot domain rather than angle domain, which is low cost and convenient. Examples show this method can accurately locate the normal incidence point and correct the polarity reversal for both simple and complex models.
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Using 2D–3C Seismic Data to Discriminate the Sandstone Reservoir in Guang’an Gas Field
More LessThis paper describes the interpretation of 2D-3C seismic survey acquired in the Guang’an Gas Field of Sichuan Basin, which is located at the southwest part of China. Estimating reservoir parameters from geophysical data is vitally important in hydrocarbon exploration and production. We present a joint-inversion algorithm to estimate reservoir parameters directly, using both PP and PS seismic amplitude variation with offset (AVO) data. Reservoir parameters are linked to geophysical parameters through a rock-properties model. The joint inversion method for PP and PS seismic data solves approximated linear expressions of PP and PS reflection coefficients simultaneously using simulated annealing algorithm. By combining the two independent measurements (PP and PS seismic data) together, we stabilize the system of equations for PP and PS seismic data separately, leading to more robust parameter estimation.
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High-effort 3C 3D Seismic Survey in Northern Piceance Basin, Colorado, USA
Authors K. T. Lewallen, T. Johns and J. HeftiThe Upper Cretaceous Mesaverde Group in the Piceance Basin, northwest Colorado, USA, contains a large gas accumulation in a tight sand reservoir. Previous work using well log, borehole and surface seismic data demonstrated potential to utilize converted-wave images and attributes recorded on multicomponent data for fracture identification and lithology discrimination. A high-effort multicomponent 3D surface seismic survey was acquired that pushed the limits of available recording technologies. Preliminary processing results show PP images that overcome significant field noise issues and PS attributes consistent with previous assessments. The measured reservoir HTI attributes after layer stripping through the overburden indicate a principal axis direction of 130º and PS1 (fast) and PS2 (slow) traveltime delays between 10 and 40 ms consistent with pre-survey predictions. Processing and research continues to improve PP/PS images and attributes to support business decisions as well as to investigate the effects of fold, offset, azimuth and spatial sampling on data quality for future surveys in tight gas and other unconventional resource plays.
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3D-3C Geomechanical Study of In-situ Bitumen Recovery, Alberta, Canada
By K. Wikel3D converted wave data have been used in the past as an indicator of fractures and differential stress, although the emphasis has historically been on fractures. Recently, industry has been analyzing stress directions and stress changes based on the direction of fast converted mode (PS1) and the time lag between the fast and slow converted modes (PS1/PS2) in the near surface. In the compliant near surface of NE Alberta the data provided from converted wave seismic data rotated into fast and slow shear directions allows us to evaluate cap rock integrity and areas where the cap rock may deviate from the regional faulting regime. This information is extremely useful in discerning the cap rocks ability to maintain integrity during shallow high pressure bitumen and heavy oil recovery. In addition to this, the changes in PS1 direction and PS1/PS2 time lag with time can assist us in monitoring reservoir changes and recovery of bitumen. This paper is an overview of a case study from Petrobanks pilot THAI facility near Conklin, Alberta, and the results of a converted wave cap rock integrity study.
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Preserved-traveltime Smoothing
Authors V. Vinje, A. Stovas and D. ReynaudMost ray-based migration- and tomography methods require some degree of smoothness in the depth velocity models. A drawback of the conventional smoothing is errors in the traveltimes at the discontinuities of the velocity models. These errors are offset-dependent and they cause errors in both depth and RMO. Here we propose a new method, Preserved-Traveltime Smoothing (PTS) that preserves traveltimes (and hence depths) at these discontinuities. This is done by smoothing of composite anisotropic velocity parameters using a specific convolution filter.
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High Resolution Velocity Model for Imaging Complex Structures
More LessWith the improvement of automatic CIG picking tool, the accuracy of tomography is mainly limited by the model representation (e.g. model grid size) and the regularization of the inversion solver. In practice, a dense model grid with the grid size less than 20 meters and a 100 meters’ smoothing are applied to achieve high resolution velocity updates in some well-conditioned areas (e.g. shallow sediment areas). The small grid size and small model smoothing may cause inversion artefacts in poorly conditioned areas (deep part) and increase the computational cost dramatically. In this abstract, we introduce a non uniform grid, which has a dense sampling in shallow and a sparse sampling in deep to reduce the computing cost. Also we propose a scheme for smoothing along geological structures to stabilize the inversion. We demonstrate with a production example in the Gulf of Mexico that our high resolution tomography is able to improve the subsurface images.
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RTM and Kirchhoff Angle Domain Common-image Gathers for Migration Velocity Analysis
Authors J. P. Montel and G. LambaréAngle domain common image gathers are recommended in Kirchhoff and reverse time migration for velocity model building in complex area. For these both approaches there is a general agreement that the tomographic ray pairs are fully defined by the reflection and azimuth angle information and the reflection dip and that if the velocity model is correctly updated down to a given horizon, it is not necessary to shoot the tomographic ray pairs upwards through this horizon. We show here through examples and a theoretical analysis that these both statements have to be mitigated when the common image gathers exhibit a significant residual move out on. We also show how to accurately compute the tomographic ray pairs allowing then for an accurate angle domain migration velocity analysis.
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Automatic Migration Velocity Analysis Using Reverse Time Migration
Authors W. W. Weibull and B. ArntsenThe objective of this paper is to describe an automatic velocity analysis method based on Reverse Time Migration and Differential Semblance Optimization. The velocity analysis is based on the solution of a nonlinear least squares problem aiming at the focusing of offset domain common image point gathers constructed by Reverse Time Migration. Because the method is based on the solution of the two-way wave equation, it can deal with strong and sharp velocity contrasts both in a stable and accurate manner. It is therefore expected that this method will help improve seismic imaging over complex geological settings. We illustrate the method with a simple synthetic 2D seismic example.
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