The Experts below are selected from a list of 129 Experts worldwide ranked by ideXlab platform
Paul Sava - One of the best experts on this subject based on the ideXlab platform.
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3D angle decomposition for elastic reverse time migration
GEOPHYSICS, 2017Co-Authors: Yuting Duan, Paul SavaAbstract:ABSTRACTWe have developed three approaches for 3D angle decomposition using elastic reverse time migration. The first approach uses time- and Space-Lag common-image point gathers computed from elastic wavefields. This method facilitates computing angle gathers at sparse and possibly irregularly distributed points in the image. The second approach transforms extended time-Lag images to the angle domain using slant stacks along 4D surfaces, instead of using slant stacks along 2D straight lines. The third approach transforms Space-Lag common-image gathers to the angle domain. The three proposed methods solve a system of equations that handles dipping reflectors, and they yield angle gathers that are more accurate compared with those obtained via alternative existing methods. We have developed our methods using 2D and 3D synthetic and field data examples and found that they provide accurate opening and azimuth angles and they can handle steeply dipping reflectors and converted wave modes.
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Wide-azimuth angle gathers for anisotropic wave-equation migration
Geophysical Prospecting, 2012Co-Authors: Paul Sava, Tariq AlkhalifahAbstract:Extended common-image-point gathers (CIP) constructed by wide-azimuth TI wave-equation migration contain all the necessary information for angle decomposition as a function of the reflection and azimuth angles at selected locations in the subsurface. The aperture and azimuth angles are derived from the extended images using analytic relations between the Space- and time-Lag extensions using information which is already available at the time of migration, i.e. the anisotropic model parameters. CIPs are cheap to compute because they can be distributed in the image at the most relevant positions, as indicated by the geologic structure. If the reflector dip is known at the CIP locations, then the computational cost can be reduced by evaluating only two components of the Space-Lag vector. The transformation from extended images to angle gathers is a planar Radon transform which depends on the local medium parameters. This transformation allows us to separate all illumination directions for a given experiment, or between different experiments. We do not need to decompose the reconstructed wavefields or to choose the most energetic directions for decomposition. Applications of the method include illumination studies in complex areas where ray-based methods fail, and assuming that the subsurface illumination is sufficiently dense, the study of amplitude variation with aperture and azimuth angles.
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Wide-azimuth Angle-domain Imaging For Anisotropic Reverse-time Migration
SEG Technical Program Expanded Abstracts 2011, 2011Co-Authors: Paul Sava, Tariq AlkhalifahAbstract:Extended common-image-point gathers (CIP) constructed by wide-azimuth TI wave-equation migration contain all the necessary information for angle decomposition as a function of the reflection and azimuth angles at selected locations in the subsurface. The reflection and azimuth angles are derived from the extended images using analytic relations between the Space-Lag and time-Lag extensions. This post-imaging decomposition requires only information which is already available at the time of migration, i.e. the model parameters and the tilt angles of the TI medium. The transformation amounts to a linear Radon transform applied to the CIPs obtained after the application of the extended imaging condition. If information about the reflector dip is available at the CIP locations, then only two components of the Space-Lag vectors are required, thus reducing computational cost and increasing the affordability of the method. This efficient angle decomposition method is suitable for wide-azimuth imaging in anisotropic media with arbitrary orientation of the symmetry plane.
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Wide-azimuth angle gathers for wave-equation migration
GEOPHYSICS, 2011Co-Authors: Paul Sava, Ioan VladAbstract:Extended common-image-point (CIP) gathers contain all of the necessary information for decomposition of reflectivity as a function of the reflection and azimuth angles at selected locations in the subsurface. This decomposition operates after the imaging condition applied to wavefields reconstructed by any type of wide-azimuth migration method, e.g., using downward continuation or time reversal. The reflection and azimuth angles are derived from the extended images using analytic relations between the Space-Lag and time-Lag extensions. The transformation amounts to a linear Radon transform applied to the CIPs obtained after applying the extended imaging condition. If information about the reflector dip is available at the CIP locations, then only two components of the Space-Lag vectors are required, thus reducing computational cost and increasing the affordability of the method. Applications of this method include the study of subsurface illumination in areas of complex geology where ray-based methods are...
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Moveout analysis of wave-equation extended images
GEOPHYSICS, 2010Co-Authors: Tongning Yang, Paul SavaAbstract:Conventionalvelocityanalysisappliedtoimagesproducedby wave-equationmigrationwithacrosscorrelationimagingconditionusesmoveoutinformationfromSpaceLagsorfocusinginformationfromtimeLag.However,morerobustvelocity-estimation methodscanbedesignedtosimultaneouslytakeadvantageofthe semblanceandfocusinginformationprovidedbymigratedimages. Such a velocity estimation requires characterization of the moveout surfaces defined jointly for Space- and time-Lags extended images. The analytic solutions to the moveout surfaces can be derived by solving the system of equations representing the shifted source and receiver wavefields. The superposition of the surfaces from many experiments shots is equivalent to the envelope for the family of the individual surface. The envelope forms a shape that can be characterized as a cone in the extended Space of depth, Space Lag, and time Lag. When imaged with the correct velocity, the apex of the cone is located at the correct reflectiondepthandatzeroSpaceandtimeLags.Whenimagedwith the incorrect velocity, the apex of the cone shifts in the depth direction and along the time-Lag axis. The characteristics of the cones are directly related to the quality of the velocity model. Thus, their analysis provides a rich source of information for velocity model-building. Synthetic examples verify the derived formulas characterizing the moveout surfaces. The analytic formulas match the numeric experiments well, demonstrating the accuracy of the formulas. Based on information provided by the extended imaging condition, future application for velocity updates can benefit from the robustness of the depth-focusing analysisandofthehighresolutionofthesemblanceanalysis.
Tariq Alkhalifah - One of the best experts on this subject based on the ideXlab platform.
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Image-domain wavefield tomography for VTI mediaVTI wavefield tomography
GEOPHYSICS, 2019Co-Authors: Antoine Guitton, Ilya Tsvankin, Tariq AlkhalifahAbstract:Processing algorithms for transversely isotropic (TI) media are widely used in depth imaging and typically bring substantial improvements in reflector focusing and positioning. Here, we develop acoustic image-domain tomography (IDT) for reconstructing VTI (TI with a vertical symmetry axis) models from P-wave reflection data. The modeling operator yields an integral wave-equation solution, which is based on a separable dispersion relation and contains only P-waves. The zero-dip NMO velocity ([Formula: see text]) and anellipticity parameter [Formula: see text] are updated by focusing energy in Space-Lag images obtained by least-squares reverse-time migration (LSRTM). Application of LSRTM helps mitigate aperture- and illumination-induced artifacts in Space-Lag gathers and improve the robustness of [Formula: see text]-estimation. The impact of the trade-off between [Formula: see text] and [Formula: see text] is reduced by a three-stage inversion algorithm that gradually relaxes the constraints on the spatial variation of [Formula: see text]. Assuming that the depth profile of the Thomsen parameter [Formula: see text] is known at two or more borehole locations, we employ image-guided interpolation to constrain the depth scale of the parameter fields and of the migrated image. Image-guided smoothing is also applied to the IDT gradients to facilitate convergence towards geologically plausible models. The algorithm is tested on synthetic reflection and borehole data from the structurally complicated elastic VTI Marmousi-II model. Although the initial velocity field is purely isotropic and substantially distorted, all three relevant parameters ([Formula: see text], [Formula: see text], and [Formula: see text]) are estimated with sufficient accuracy. The algorithm is also applied to a line from a 3D ocean-bottom-node data set acquired in the Gulf of Mexico.
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Wide-azimuth angle gathers for anisotropic wave-equation migration
Geophysical Prospecting, 2012Co-Authors: Paul Sava, Tariq AlkhalifahAbstract:Extended common-image-point gathers (CIP) constructed by wide-azimuth TI wave-equation migration contain all the necessary information for angle decomposition as a function of the reflection and azimuth angles at selected locations in the subsurface. The aperture and azimuth angles are derived from the extended images using analytic relations between the Space- and time-Lag extensions using information which is already available at the time of migration, i.e. the anisotropic model parameters. CIPs are cheap to compute because they can be distributed in the image at the most relevant positions, as indicated by the geologic structure. If the reflector dip is known at the CIP locations, then the computational cost can be reduced by evaluating only two components of the Space-Lag vector. The transformation from extended images to angle gathers is a planar Radon transform which depends on the local medium parameters. This transformation allows us to separate all illumination directions for a given experiment, or between different experiments. We do not need to decompose the reconstructed wavefields or to choose the most energetic directions for decomposition. Applications of the method include illumination studies in complex areas where ray-based methods fail, and assuming that the subsurface illumination is sufficiently dense, the study of amplitude variation with aperture and azimuth angles.
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Wide-azimuth Angle-domain Imaging For Anisotropic Reverse-time Migration
SEG Technical Program Expanded Abstracts 2011, 2011Co-Authors: Paul Sava, Tariq AlkhalifahAbstract:Extended common-image-point gathers (CIP) constructed by wide-azimuth TI wave-equation migration contain all the necessary information for angle decomposition as a function of the reflection and azimuth angles at selected locations in the subsurface. The reflection and azimuth angles are derived from the extended images using analytic relations between the Space-Lag and time-Lag extensions. This post-imaging decomposition requires only information which is already available at the time of migration, i.e. the model parameters and the tilt angles of the TI medium. The transformation amounts to a linear Radon transform applied to the CIPs obtained after the application of the extended imaging condition. If information about the reflector dip is available at the CIP locations, then only two components of the Space-Lag vectors are required, thus reducing computational cost and increasing the affordability of the method. This efficient angle decomposition method is suitable for wide-azimuth imaging in anisotropic media with arbitrary orientation of the symmetry plane.
Hadi Mohammadi - One of the best experts on this subject based on the ideXlab platform.
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Nonlinear Dynamic Modeling of Urban Water Consumption Using Chaotic Approach (Case Study: City of Kelowna)
Water, 2020Co-Authors: Peyman Yousefi, Gregory Courtice, Gholamreza Naser, Hadi MohammadiAbstract:This study investigated urban water consumption complexity using chaos theory to improve forecasting performance to help optimize system management, reduce costs and improve reliability. The objectives of this study were to (1) investigate urban water distribution consumption complexity and its role in forecasting technique performance, (2) evaluate forecasting models by periodicity and lead time, and (3) propose a suitable forecasting technique based on operator applications and performance through various time scales. An urban consumption dataset obtained from the City of Kelowna (British Columbia, Canada) was used as a test case to forecast future consumption values using varying lead times under different temporal scales to identify models which may improve forecasting performance. Chaos theory techniques were employed to inform model optimization. This study attempted to address the paucity of studies on chaos theory applications in water consumption forecasting. This was accomplished by applying non-linear approximation, dynamic investigation, and phase Space reconstruction for input variables, to improve the accuracy in various periodicity and lead time. To reconstruct the phase Space, Lag time was calculated using average mutual information for daily resolution as 17 days to reconstruct the phase Space. The optimum embedding dimension and correlation exponent for the phase Space were 18 and 3.5, respectively. Comparing the results, the non-linear local approximation model provided the best performance. The forecasting horizon for the models was 122 days. Moreover, phase Space reconstruction improved the accuracy of the models for the different lead times. The findings of this study may improve forecasting performance and provide evidence to support further investigation of the chaotic behaviour of water consumption values over different time scales.
Ioan Vlad - One of the best experts on this subject based on the ideXlab platform.
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Efficient Wide-azimuth Angle Decomposition for Reverse-time Migration
73rd EAGE Conference and Exhibition incorporating SPE EUROPEC 2011, 2011Co-Authors: P. C. Sava, Ioan VladAbstract:Extended common-image-point-gathers (CIP) contain all the necessary information for decomposition of reflectivity as a function of the reflection and azimuth angles at selected locations in the subsurface. This decomposition operates after the imaging condition applied to wavefields reconstructed by any type of wide-azimuth migration method, e.g. using downward continuation or time reversal. The reflection and azimuth angles are derived from the extended images using analytic relations between the Space-Lag and time-Lag extensions. The transformation amounts to a linear Radon transform applied to the CIPs obtained after the application of the extended imaging condition. If information about the reflector dip is available at the CIP locations, then only two components of the Space-Lag vectors are required, thus reducing computational cost and increasing the affordability of the method. Applications of this method include the study of subsurface illumination in areas of complex geology where ray-based methods are not usable, and the study of amplitude variation with reflection and azimuth angles if the subsurface subsurface illumination is sufficiently dense. Migration velocity analysis could also be implemented in the angle domain, although an equivalent implementation in the extended domain is cheaper and more effective.
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Wide-azimuth angle gathers for wave-equation migration
GEOPHYSICS, 2011Co-Authors: Paul Sava, Ioan VladAbstract:Extended common-image-point (CIP) gathers contain all of the necessary information for decomposition of reflectivity as a function of the reflection and azimuth angles at selected locations in the subsurface. This decomposition operates after the imaging condition applied to wavefields reconstructed by any type of wide-azimuth migration method, e.g., using downward continuation or time reversal. The reflection and azimuth angles are derived from the extended images using analytic relations between the Space-Lag and time-Lag extensions. The transformation amounts to a linear Radon transform applied to the CIPs obtained after applying the extended imaging condition. If information about the reflector dip is available at the CIP locations, then only two components of the Space-Lag vectors are required, thus reducing computational cost and increasing the affordability of the method. Applications of this method include the study of subsurface illumination in areas of complex geology where ray-based methods are...
Peyman Yousefi - One of the best experts on this subject based on the ideXlab platform.
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Nonlinear Dynamic Modeling of Urban Water Consumption Using Chaotic Approach (Case Study: City of Kelowna)
Water, 2020Co-Authors: Peyman Yousefi, Gregory Courtice, Gholamreza Naser, Hadi MohammadiAbstract:This study investigated urban water consumption complexity using chaos theory to improve forecasting performance to help optimize system management, reduce costs and improve reliability. The objectives of this study were to (1) investigate urban water distribution consumption complexity and its role in forecasting technique performance, (2) evaluate forecasting models by periodicity and lead time, and (3) propose a suitable forecasting technique based on operator applications and performance through various time scales. An urban consumption dataset obtained from the City of Kelowna (British Columbia, Canada) was used as a test case to forecast future consumption values using varying lead times under different temporal scales to identify models which may improve forecasting performance. Chaos theory techniques were employed to inform model optimization. This study attempted to address the paucity of studies on chaos theory applications in water consumption forecasting. This was accomplished by applying non-linear approximation, dynamic investigation, and phase Space reconstruction for input variables, to improve the accuracy in various periodicity and lead time. To reconstruct the phase Space, Lag time was calculated using average mutual information for daily resolution as 17 days to reconstruct the phase Space. The optimum embedding dimension and correlation exponent for the phase Space were 18 and 3.5, respectively. Comparing the results, the non-linear local approximation model provided the best performance. The forecasting horizon for the models was 122 days. Moreover, phase Space reconstruction improved the accuracy of the models for the different lead times. The findings of this study may improve forecasting performance and provide evidence to support further investigation of the chaotic behaviour of water consumption values over different time scales.