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76th EAGE Conference and Exhibition - Workshops
- Conference date: 16 Jun 2014 - 19 Jun 2014
- Location: Amsterdam, Netherlands
- ISBN: 978-90-73834-90-3
- Published: 16 June 2014
41 - 60 of 142 results
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Joining Diverse 3D Geometries in PSTM
Authors S. Ziramov, M. Urosevic, J. Kinkela, A. Dzunic and M. PenneyUnique set of 4 overlapped 3D hard rock seismic surveys was processed jointly after successful merging. All four data sets had significant differences in design parameters so that nominal bin size, fold, source/receiver spacing, source line/receiver line interval, azimuthal and offset distribution were quite diverse. Hence the main objective became to attenuate strong footprint caused these geometrical differences. To do so we firstly utilised unique CMP binning followed by surface consistent processing and relative amplitude preservation. Excellent PSTM results were subsequently achieved by appropriate operations performed in the offset planes and by zeroing all the extrapolated migration artefacts. This comprehensive approach resulted in amplitude consistent, fully merged 3D seismic cube with continuous reflectors across entire area which made interpretation reliable and provided assistance to the drilling program.
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Deep Shear Wave Imaging Using Cross-dipole Wireline Data
Authors T.W. Geerits and A. PrzebindowskaDuring the last three decades significant developments have occurred in the design and application of borehole acoustic measurements. Where during the first decade the main focus has been on slowness analysis and its applications (E.g., porosity, synthetic seismogram, etc.), the last two decades have resulted in more advanced applications: -permeability estimation from Stoneley waves; -intrinsic/stress-induced anisotropy from flexural waves; -and most recently, imaging away from the wellbore. The latter application has great promise in imaging fine structural features away from the wellbore, particularly in hard rock (I.e., less attenuation) and it is complementary to conventional surface seismic. Whereas the seismic method has an imaging resolution of order 10^1 m and a depth of investigation of order 10^3 m, the borehole acoustic method has an imaging resolution of order 10^-1 m and a depth of investigation of order 10^1 m. Furthermore, although the borehole acoustic method has been developed for and applied to mainly wireline configurations, it is considered to have an even greater value in a Logging While Drilling (LWD) setting as a result of its geosteering potential. The cross-dipole acoustic measurement principles, theory and processing steps will be explained in conjunction with two case studies.
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The Application of Borehole Hydrophone Arrays in Hardrock Environments
Authors A.J. Greenwood, M. Urosevic, J.C. Dupuis and A. KepicThe geometry of a VSP survey allows us to understand the characteristics of both the transmitted and reflected wavefields. As such, VSP is an “in-field seismic laboratory”, necessary for understanding the origin of seismic events. VSP enables calibration of surface reflection images and the survey can be designed to produce an image around the borehole at a much higher resolution than the surface reflection method. The main drawback of the method with respect to the mining community is the high logistic cost. Hence the main objective of the research presented here is to look into alternative ways of implementing VSP surveys that are cost effective, readily implementable in slim holes and pose lower risk to equipment in unstable uncased mineral exploration boreholes. As shown in this work, these objectives have been met using a borehole hydrophone array. Presented are two field trials in the Agnew-Wiluna and Kambalda regions of Western Australia. The results of these field experiments demonstrate that a borehole hydrophone array is capable of imaging structure in a complex geologic environment. These results, however, are not easily achieved because of the high sensitivity of hydrophones to acoustic modes in the borehole and the passive coupling to the formation.
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Fracture Detection via Beam Imaging and Image Spectrum Analysis
Authors M. Protasov, V.A. Tcheverda and G.V. ReshetovaAn approach to seismic imaging of fractures by multicomponent surface data is presented and discussed. It is based on a specific imaging procedure, which consists in a weighted summation of multicomponent multishot/multioffset data. These weights are computed by tracing a specially chosen Gaussian beams. In order to get image of fractures these beams are taken in a way forming so called selective images (Pozdnyakov and Tcheverda, 2006; Protasov and Tcheverda, 2011). Their geometry provides suppression of regularly reflected waves and, thus, emphasizes the presence of small-scale heterogeneities that give rise to diffracted/scattered waves. Additionally spectral removal is applied for more essential suppression of regular reflections footprint. Numerical experiments with synthetic data set computed for the typical seismogeological model of Yurubcheno-Tokhomskoye area are presented and discussed.
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Diffraction Imaging in Hard Rock Environments
Authors K.V. Tertyshnikov, R. Pevzner, A. Bóna, F. Alonaizi and B. GurevichHard rock seismic exploration normally has to deal with rather complex geological environments. These types of environments are usually characterized by a large number of local heterogeneities. The seismic data from such environments often have a poor signal to noise ratio because of the complexity of hard rock geology. In such situations, the processing algorithms that are capable of handling data with a low signal/noise ratio and are able to image geological discontinuities and subvertical structures are essential. Herein we present a modification of the 3D Kirchhoff post-stack migration algorithm and diffraction imaging. The modification utilizes coherency attributes obtained by the diffraction imaging algorithm in 3D to weight or steer the main Kirchhoff summation. We applied diffraction techniques to a number of 3D seismic datasets from different hard rock mine sites.
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Surface Wave Dispersion Analysis - From Local 1D Models to Tomography
Authors L.V. Socco, P. Bergamo and F. GarofaloThe analysis of surface wave dispersion represents an important exploration method at different scales. The basic scheme of the method is mainly based on 1D assumption, but laterally varying sites can be resolved if an opportune processing and inversion strategy is applied. Spatially constrained inversion (SCI), joint inversion with P-wave travel times and tomography represent possible techniques to apply to retrieve 2D models.
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Past, Present, and Future of Seismic Interferometry
By R. SniederI give an overview of the long history in of seismic interferometry, starting with Einstein's work in 1906 on Brownian motion, through developments in physics in the 1950's to the surge in seismic interferometry in 2000's. I indicate the possibilities and limitations of the method, and pose a number of challenges.
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Probing Near Surface Shear Velocity Structure from Ambient Noise and Surface Wave Array Tomography
More LessAmbient noise tomography has provided essential constraints on crustal and uppermost mantle (isotropic and anisotropic) shear velocity structure in global seismology. Recent studies demonstrate that high frequency (e.g., ~ 1 Hz) surface waves between receivers at short distances can be successfully retrieved from ambient noise cross-correlation and then be used for tomography of near surface shear velocity structures. This approach provides important information for strong ground motion prediction in urban area and near surface structure characterization in oil and gas fields. Here we first give a brief overview about the methodology of ambient noise tomography in global seismology. Then we focus on some recent developments on recovering near surface shear velocity structure using ambient noise tomography. We propose a new one-step iterative surface wave tomography approach that directly inverts all path-dependent dispersion data for 3-D shear wave speeds, in which we perform surface-wave ray tracing at each period using the fast marching method and update ray paths for the next step tomographic inversion. The proposed approach is more efficient than the traditional two-step surface wave tomography and provides a consistent framework for future joint surface wave and body wave travel time tomography.
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Near-surface Full Waveform Inversion Using Surface Waves and Reflected Waves
Authors I. Masoni, W. Zhou, R. Brossier, L. Métivier, S. Operto and J.M. VirieuxWe investigate the capacity of extracting near-surface shear-wave velocity by considering dispersive surface waves and non-dispersive reflected waves. We show that indeed the full waveform fitting of these waves requires a dedicated approach by using lateral spatial and frequential coherence for surface waves and by explicitely introduces the fitting of reflected waves in the inversion formulation. On a simple example as a two-layers model, lateral variations of the velocity are reconstructed while the low-wavenumber content of the velocity could be improved through reflection waves. Combining these two sources of information on the shear-wave velocity could improve our shear-wave velocity imaging in the near-surface context.
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Challenges for 2-D elastic Full Aaveform Inversion of Shallow-seismic Rayleigh Waves
Authors L. Groos, M. Schäfer, S. Butzer, T. Forbriger and T. BohlenShallow-seismic Rayleigh waves are attractive for geotechnical site investigations. They exhibit a high signal to noise ratio in field data recordings and have a high sensitivity to the S-wave velocity, an important lithological and geotechnical parameter to characterize the very shallow subsurface. In recent years we studied the applicability of the two-dimensional elastic FWI method using numerous synthetic reconstruction tests and two field data examples. Some important challenges are reported here: (1) the accurate correction of the geometrical spreading, (2) the estimation of the source wavelet, (3) the importance of an-elastic attenuation in the forward simulations. We found that Important pre-processing steps for the application of 2-D elastic FWI to shallow-seismic field data are the 3D to 2D correction of geometrical spreading and the estimation of a priori Q-values that must be used as a passive medium parameter during the FWI. Furthermore, a source-wavelet correction filter should be applied during the FWI process. Smooth initial models obtained from the analysis of the first arrivals of body waves are important and seem to be sufficient. Our field data examples indicate that FWI is able to resolve lateral variations of S-wave velocities in the very shallow subsurface.
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Surface-wave Analyses in Unconsolidated Granular Models with Increasing Degrees of Complexity
Authors L. Bodet, P. Bergamo, A. Dhemaied, R. Martin, R. Mourgues, S. Pasquet, F. Rejiba, L.V. Socco and V. TournatUsing micrometric glass beads, we build small scale physical models with increasing degrees of complexity in order to address theoretical and methodological issues of seismic methods (velocity gradients, lateral variations, pore overpressure, etc.). We simulate seismic records at the surface of the laboratory models thanks to a mechanical source and a laser-Doppler vibrometer. From recorded seismograms, we are able to invert surface-wave dispersion for one or two-dimensional velocity structures. These experiments are for instance used as benchmarks for processing and inversion techniques, enable the validation of numerical methods, or make it possible to study issues related to pore fluids.
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Near-surface Modelling from Surface and Guided Waves and Its Applications
Authors D. Boiero, C. Strobbia, A. Zarkhidze, E. Wiarda and P. VermeerSurface and guided waves are effective sources of information for near-surface characterization. They constitute a large part of the recorded energy and, with proper acquisition, analysis, and inversion, can be used to model the near surface with surprisingly high resolution. In this role, they can be used for correcting short- to long-wavelength perturbations, building velocity models, and optimizing coherent noise-filtering workflows.
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The Interpacific Project - A Cooperative Exercise for Assessing Reliability and Accuracy of Seismic Methods
Authors F. Hollender, P.Y. Bard, C. Cornou, B.R. Cox, S. Foti, F. Garofalo, M. Ohrnberger and D. SiciliaThe InterPacific (Intercomparison of methods for site parameter and velocity profile characterization) project aims to assess the reliability/variability of seismic site characterization methods (borehole and surface wave methods) used for estimating shear wave velocity (Vs) profiles and corresponding lumped parameters (e.g., Vs,30). The ultimate goal of the project is to determine procedures that can be used for the construction of consistent ground models for seismic studies. Three sites have been selected in France and Italy for the implementation of the project. They are representative of different geological conditions relevant for the evaluation of seismic site response effects: a stiff rock outcrop, a deep soft deposit, and an intermediate case with thick stiff soils and large bedrock depth.
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Deriving P-wave Near-surface Models from Exploration Data
Authors E.J. van Dedem, F. Ernst and J. ShorterAdequate handling of the near surface is crucial for proper imaging of land data, especially for complex overburdens. Recently we introduced modal elastic inversion (Ernst 2013): approximate FWI which inverts P-guided waves to near-surface P-velocity models. We will present two case studies of modal elastic inversion of P-guided waves to obtain near-surface velocity models. The results show that this inversion approach can give realistic results not only for modern high-end densely sampled surveys, but also for sparse legacy dynamite surveys.
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Effects of the Trace Interval on Surface Wave Dispersion and Inversion
Authors T.J. Gong, H.L. Chen, X.D. Li, Y.Q. Ye, J. Liu, H.J. Zhang, C.Z. Ni, G.D. Ding and B.J. LiangIt is the trace interval that determines the spatial frequency property of one shot gather. As the trace interval increases, spatial aliasing emerges and data quality deteoriates. Aliased surface waves in the dispersion energy map have false higher-mode dispersion curves, or low velocity noise, and have missing or pronged dispersion energy trends at certain frequency ranges. Qualitatively, large spacing causes a severe aliasing that smears the dispersion plot, yielding it unusable. As long as spatial aliasing is not dominant, the surface waves can be used to invert the corresponding subsurface structure. We present a synthetic example to test the effectiveness of the high resolution linear Radon transform (HRLRT) and the least squares Radon transform (LSRT), which are used to calculate dispersion curves. Since the HRLRT typically affords a better low frequency response, we use it to map the field example. Effects caused by different spatial intervals in dispersion maps of synthetic and field examples are also shown. A genetic algorithm is used in the inversion to determine the subsurface structure, and these results are then compared with a nearby borehole test. The agreement between the test and the model shows the promising prospect of the surface wave methods.
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Multimodal Rayleigh Wave Dispersion Curve Picking and Inversion to Build Near Surface Shear Wave Velocity Models
More LessThe use of Rayleigh waves to invert for a near surface shear wave velocity model is attractive in converted wave processing, such as the application of receiver side statics correction and PS PSDM. We propose a differential evolution inversion scheme to invert Rayleigh wave dispersion curves, and we apply it on a field dataset with high density acquisition to obtain the underlying shear wave velocity structure. The joint use of a new misfit function, which allows multimodal inversion and reduces the risk of mode misinterpretations, combined with differential evolution inversion is highly likely to converge to the real shallow shear wave velocity structure. A semi-automatic picking method based on the quick thinning algorithm is introduced to extract the dispersion curves from frequency-phase velocity spectra. This greatly reduces the demand on manual labor and improves productivity.
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Surface Wave Analysis - Challenges for Application on an Ultra-shallow Structure Characterisation
Authors C.A. Pérez Solano, D. Donno, H. Chauris and G.P. DeiddaWe discuss several difficulties related to the application of Full Waveform Inversion using surface waves in the context of seismic data acquired on an ultra-shallow ground model (0 — 10 m depth). For instance, the choice of an accurate initial velocity model in the presence of very high velocity contrasts is complicated. The presence of surface waves increases local minima problems in the objective function, preventing from convergence towards the global minimum. For improving convergence, we propose to use an alternative functional, the windowed-Amplitude Waveform Inversion, which is similar to dispersion curve analysis but without any picking step. The source wavelet is iteratively estimated during the velocity model inversion. If previous examples have shown that this methodology is applicable in synthetic data sets, it is less obvious in real data sets as discussed here.
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Thickness Variations in Layered Subsurface Models - Effects on Simulated MASW
Authors S. Bignardi, G. Santarato and N. Abu ZeidSeismic surface wave methods allow to retrieve the shallow subsurface shear wave velocity. Among these, the “Multi-channel Analysis of Surface Waves” is to date one of the most widely adopted non-invasive active-source approaches in the professional world for the evaluation of the stiffness properties of the ground for geotechnical engineering purposes. The method utilizes the dispersive nature of surface waves by constructing the dispersion curve which is then inverted to obtain the shear wave velocity profile. Dispersion curves generation typically requires the transformation of the recorded seismograms into the frequency-velocity (f-V) domain. Commercially available inversion algorithms assume the subsurface model as a stack of homogeneous parallel layers, but unfortunately this may lead to misleading results if the actual soil profile is far from the assumed 1D geometry. We investigate the effects of lateral heterogeneities due to variations of layer thicknesses on the f-V spectrum to assess the limitations of the 1D approach and thus to judge the reliability of such surface waves interpretation
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Geological Setting of the Vaca Muerta Fm, Neuquen Basin - A World class Shale Play
Authors M. Di Benedetto, P. Biscayart, J. Zunino and J. SoldoThe Vaca MuertaFormation, the main proven source rock in the Neuquen basin, has become, in the last two years, a unit that promises an enormous potential as a Non-Conventional Shale Gas and Oil resource play. This unit shows a high geological complexity related, primarily, to its large size and extension. The aim of this work is to characterize the geological features of Vaca Muerta Fm., as an example of a shale play, in order to understand and define the productivity of this type of shale resources.
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Relationships among Porosity, Permeability and Seismic Velocity of Shales
By N.H. MondolThis study focuses on relationships among porosity, permeability and seismic velocity of shales. A total of thirty well characterized, brine-saturated (35000 ppm NaCl) synthetic shale of varying textural and mineralogical compositions were compacted mechanically both in triaxial and oedometer cells under controlled pore pressure and proper drained conditions. Results show that kaolinite dominated shales compact more but have higher permeability and seismic velocity compared to smectite dominated shales at same stress/depth. Permeability differs a maximum five orders of magnitude at the same porosity for different shales. For velocity-permeability relationship between kaolinite- and smectite-dominated shales, a maximum four orders of magnitude are observed. Velocity/porosity can therefore not be good proxy to estimate reliable permeability in shales. Comparison of experimental and published data show a good agreement and illustrated that a better understanding of mineralogical and textural relationships can be significantly improved to establish relationships among porosity, permeability and seismic velocity of shales. In addition to the existing database, the new experimental data (this study) can improve the calibration of fluid flow modeling, seismic and well-log interpretation and evolution of shale rock properties. The experimental results may also be of importance for structural design, slope stability analysis and waste disposal efforts.
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