ORCID Profile
0000-0002-4976-7988
Current Organisation
Imperial College London
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Publisher: Oxford University Press (OUP)
Date: 11-02-2004
Publisher: Wiley
Date: 04-03-2013
DOI: 10.1111/TER.12032
Publisher: Oxford University Press (OUP)
Date: 17-02-2004
Publisher: Oxford University Press (OUP)
Date: 23-10-2013
Publisher: Society of Exploration Geophysicists
Date: 21-01-2022
Abstract: Biot’s theory of poroelasticity describes seismic waves propagating through fluid-saturated porous media, so-called two-phase media. The classic Biot’s theory of poroelasticity considers the wave dissipation mechanism as being the friction of relative motion between the fluid in the pores and the solid rock skeleton. However, within the seismic frequency band, the friction has a major influence only on the slow P-wave and an insignificant influence on the fast P-wave. To represent the intrinsic viscoelasticity of the solid skeleton, we incorporate a generalized viscoelastic wave equation into Biot’s theory for the fluid-saturated porous media. The generalized equation that unifies the pure elastic and viscoelastic cases is constituted by a single viscoelastic parameter, presented as the fractional order of the wavefield derivative in the compact form of the wave equation. The generalized equation that includes the viscoelasticity appropriately describes the dissipation characteristics of the fast P-wave. Plane-wave analysis and numerical solutions of our wave equation reveal that (1) the viscoelasticity in the solid skeleton causes the energy attenuation on the fast P-wave and the slow P-wave at the same order of magnitude and (2) the generalized viscoelastic wave equation effectively describes the dissipation effect of the waves propagating through the fluid-saturated porous media.
Publisher: Society of Exploration Geophysicists
Date: 2020
Abstract: For fractured reservoirs with low permeability and low porosity, water injection is often needed during hydrocarbon production. We have developed methods to accurately simulate pore-pressure diffusion during water injection and to evaluate the diffusion flux from a complex fracture network. We proposed explicit scalar coefficients of the anisotropic diffusion instead of a diffusion tensor at each lattice, and we assigned these scalar coefficients in an elliptical form, with the major axis aligned with the fracture orientation. Based on these coefficients, we derived mathematical equations for calculating the flux of the pore-pressure diffusion in fracture networks. Numerical simulation of the anisotropic characteristic of diffusion with a prolonged water injection time revealed that although water injection affects pore-pressure distribution mainly along the in idual fractures during the early stage, it gradually affects the pore pressure of the media surrounding the fractures and changes the physical property of fractured media.
Publisher: Oxford University Press (OUP)
Date: 28-04-2011
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2019
Publisher: Oxford University Press (OUP)
Date: 25-02-2020
DOI: 10.1093/JGE/GXAA007
Abstract: This paper presents a case study on the prediction of hydrocarbon reservoirs within coal-bearing formations of the Upper Palaeozoic. The target reservoirs are low-permeability low-pressure tight-sandstone reservoirs in the Daniudi Gas Field, Ordos Basin, China. The prime difficulty in reservoir prediction is caused by the interbedding coal seams within the formations, which generate low-frequency strong- litude reflections in seismic profiles. To tackle this difficulty, first, we undertook a careful analysis regarding the stratigraphy and lithology of these coal-bearing formations within the study area. Then, we conducted a geostatistical inversion using 3D seismic data and obtained reservoir parameters including seismic impedance, gamma ray, porosity and density. Finally, we carried out a reservoir prediction in the coal-bearing formations, based on the reservoir parameters obtained from geostatistical inversion and combined with petrophysical analysis results. The prediction result is accurately matched with the actual gas-test data for the targeted four segments of the coal-bearing formations.
Publisher: Elsevier BV
Date: 02-2014
Publisher: Oxford University Press (OUP)
Date: 12-2015
Publisher: Springer Science and Business Media LLC
Date: 17-08-2017
DOI: 10.1038/S41598-017-09294-Y
Abstract: In seismic waveform tomography, or full-waveform inversion (FWI), one effective strategy used to reduce the computational cost is shot-encoding, which encodes all shots randomly and sums them into one super shot to significantly reduce the number of wavefield simulations in the inversion. However, this process will induce instability in the iterative inversion regardless of whether it uses a robust limited-memory BFGS (L-BFGS) algorithm. The restarted L-BFGS algorithm proposed here is both stable and efficient. This breakthrough ensures, for the first time, the applicability of advanced FWI methods to three-dimensional seismic field data. In a standard L-BFGS algorithm, if the shot-encoding remains unchanged, it will generate a crosstalk effect between different shots. This crosstalk effect can only be suppressed by employing sufficient randomness in the shot-encoding. Therefore, the implementation of the L-BFGS algorithm is restarted at every segment. Each segment consists of a number of iterations the first few iterations use an invariant encoding, while the remainder use random re-coding. This restarted L-BFGS algorithm balances the computational efficiency of shot-encoding, the convergence stability of the L-BFGS algorithm, and the inversion quality characteristic of random encoding in FWI.
Publisher: Society of Exploration Geophysicists
Date: 24-01-2022
Abstract: Seismic full-waveform inversion (FWI) needs a feasible starting model because otherwise it might converge to a local minimum and the inversion result might suffer from detrimental artifacts. We have built a feasible starting model from wells by applying dynamic time warping (DTW) localized rewarp and convolutional neural network (CNN) methods alternatively. We use the DTW localized rewarp method to extrapolate the velocities at well locations to the nonwell locations in the model space. Rewarping is conducted based on the local structural coherence, which is extracted from a migration image of an initial infeasible model. The extraction uses the DTW method. The purpose of velocity extrapolation is to provide sufficient training s les to train a CNN, which maps local spatial features on the migration image into the velocity quantities of each layer. Furthermore, we design an interactive workflow to reject inaccurate network predictions and to improve CNN prediction accuracy by incorporating the Monte Carlo dropout method. We have determined that our method is robust against kinematic incorrectness in the migration velocity model, and it is capable of producing a feasible FWI starting model.
Publisher: Society of Exploration Geophysicists
Date: 28-03-2022
Abstract: Surface-offset common-image gathers (CIGs) are an important data format for seismic velocity analysis. However, the reverse time migration (RTM) method, which is wavefield propagation based, does not directly produce surface-offset CIGs because it propagates waves from all the offsets together. Here, we implement the generation of surface-offset CIGs by synthesizing the backward wavefields using the forward wavefields at locations where source and receiver locations overlap. This method produces surface-offset CIGs with high accuracy and low cost when compared with those generated by backpropagating each trace separately. We adopt nonnegative least-squares filters for sparse linear deconvolution. The computational effectiveness of the proposed method increases for higher dimensions, higher-order stencils, and more complicated wave equations. The proposed method works stably on a realistic towed-streamer acquisition system with moderate geometric positioning errors between the locations of airguns and hydrophones.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2023
Publisher: Springer Science and Business Media LLC
Date: 12-06-2017
DOI: 10.1038/S41598-017-03578-Z
Abstract: Using a topography-dependent tomographic scheme, the seismic velocity structure of the Eastern Tibetan Plateau, including the uplifted Longmenshan (LMS) orogenic belt, is accurately imaged in spite of the extreme topographic relief in the LMS region and thick sedimentary covers in the neighbouring Sichuan Basin. The obtained image shows a high-resolution upper crustal structure on a 500 km-long profile that is perpendicular to the LMS. The image clearly shows that the crystalline basement was uplifted within the LMS orogenic belt, and that the neighbouring Songpan-Ganzi Terrane was covered by a thick flysch belt, with evidence of near-surface thrust faults caused by convergence between Eastern Tibet and the Sichuan Basin. The indication that the lower crust beneath the LMS was folded and pushed upwards and the upper crust was removed by exhumation, supports the concept of a lower crustal channel flow beneath Eastern Tibet. The image also reveals that the destructive Wenchuan earthquake of year 2008 occurred in the upper crust, directly at the structural discontinuity between Eastern Tibet Plateau and the Sichuan Basin.
Publisher: Society of Exploration Geophysicists
Date: 2020
Abstract: Seismic inversion of litude variation with offset (AVO) plays a key role in seismic interpretation and reservoir characterization. The AVO inversion should be a simultaneous inversion that inverts for three elastic parameters simultaneously: the P-wave impedance, S-wave impedance, and density. Using only seismic P-wave reflection data with a limited source-receiver offset range, the AVO simultaneous inversion can obtain two elastic parameters reliably, but it is difficult to invert for the third parameter, usually the density term. To address this difficulty in the AVO simultaneous inversion, we used a subspace inversion method in which we partitioned the elastic parameters into different subspaces. We parameterized each single elastic parameter with a truncated Fourier series and inverted for the Fourier coefficients. Because the Fourier coefficients of different wavenumber components have different sensitivities, we grouped the Fourier coefficients of low-, medium-, and high-wavenumber components into different subspaces. We further assigned different d ing factors to the Hessian matrix corresponding to different wavenumber components within each subspace. This inversion scheme is referred to as a multid ed subspace method. Synthetic and field seismic data ex les confirmed that the AVO simultaneous inversion with this multid ed subspace method is capable of producing reliable estimation of the three elastic parameters simultaneously.
Publisher: Society of Exploration Geophysicists
Date: 09-1995
DOI: 10.1190/1.1443884
Abstract: For the purposes of seismic propagation, a slip fault may be regarded as a surface across which the displacement caused by a seismic wave is discontinuous while the stress traction remains continuous. The simplest assumption is that this slip and the stress traction are linearly related. Such a linear slip interface condition is easily modeled when the fault is parallel to the finite‐difference grid, but is more difficult to do for arbitrary nonplanar fault surfaces. To handle such situations we introduce equivalent medium theory to model material behavior in the cells of the finite‐ difference grid intersected by the fault. Virtually identical results were obtained from modeling the fault by (1) an explicit slip interface condition (fault parallel to the grid) and (2) using the equivalent medium theory when the finite‐difference grid was rotated relative to the fault and receiver array. No additional computation time is needed except for the preprocessing required to find the relevant cells and their associated moduli. The formulation is sufficiently general to include faults in and between arbitrary anisotropic materials with slip properties that vary as a function of position.
Publisher: Wiley
Date: 28-08-2002
Publisher: Society of Exploration Geophysicists
Date: 11-1999
DOI: 10.1190/1.1444698
Abstract: To efficiently invert seismic litudes for elastic parameters, pseudoquartic approximations to the Zoeppritz equations are derived to calculate P-P-wave reflection and transmission coefficients as a function of the ray parameter p. These explicit expressions have a compact form in which the coefficients of the p 2 and p 4 terms are given in terms of the vertical slownesses. The litude coefficients are also represented as a quadratic function of the elastic contrasts at an interface and are compared to the linear approximation used in conventional litude variation with offset (AVO) analysis, which can invert for only two elastic parameters. Numerical analysis with the second‐order approximation shows that the condition number of the Fréchet matrix for three elastic parameters is improved significantly from using a linear approximation. Therefore, those quadratic approximations can be used directly with litude information to estimate not only two but three parameters: P-wave velocity contrast, S-wave velocity contrast, and the ratio of S-wave and P-wave velocities at an interface.
Publisher: Oxford University Press (OUP)
Date: 30-12-2016
DOI: 10.1093/GJI/GGV514
Publisher: Society of Exploration Geophysicists
Date: 11-2012
Abstract: The seismic frequency spectrum provides a useful source of information for reservoir characterization. For a seismic profile presented in the time-space domain, a vector of the frequency spectrum can be generated at every s ling point. Because the spectrum vectors at different time-space locations have different variation features, I attempt for the first time to exploit the variation pattern of the frequency spectrum for reservoir characterization, and test this innovative technology in prediction of coalbed methane (CBM) reservoirs. The prediction process implicitly takes account of the CBM reservoir factors (such as viscosity, elasticity, cleat system, wave interference within a coal seam, etc.) that affect the frequency spectrum, but strong litudes in seismic reflections do not necessarily show any influence in clustering analysis of spectral variation patterns. By calibrating these variation patterns quantitatively with CBM productions in well locations, we are able to characterize the spatial distribution of potential reservoirs.
Publisher: Society of Exploration Geophysicists
Date: 07-2012
Abstract: Theoretical evaluation of the elastic impedance (EI) and the ray impedance (RI) reveals that RI has a more reliable value range and is less sensitive to noise than EI. We devised a new measurement [Formula: see text] to estimate the ray impedance from elastic impedance derived by existing techniques. The recovered [Formula: see text] was expressed in the form of a normalization of EI. It solved the range variability problem of EI and had the same interpretation capability as RI. In addition, reflection coefficients represented by [Formula: see text] showed good agreement with the Zeoppritz equation even at postcritical angle of incidence. Tests of these three attributes (RI, [Formula: see text], and EI) were performed on the log data of three different types of reservoir: a typical Class III marine gas-sand, a Class I tight gas-sand, and a Class II oil-bearing sand in thin sand-mud interbedded layers. Although the crossplots of EI against acoustic impedance (AI) showed visually similar characteristics for a gas-sand as that of RI, based on the linear/quadratic discrimination analysis, RI appeared to be more applicable than EI for characterizing gas sands, especially tight gas sands. [Formula: see text], estimated from EI, had a comparable value range to the AI, and retained the interpretation ability of the original RI. Application on real seismic data showed that existing EI inversion results could be improved straightforwardly by means of the introduced transformation.
Publisher: Society of Exploration Geophysicists
Date: 12-04-2023
Abstract: Seismic–well tying is an important technique for correlating well-logging curves in depth with seismic traces in time. An appropriate seismic–well tying technique must account for two types of nonstationarity: the nonstationary time errors in the synthetic seismic trace caused by the inaccurate time–depth relationship established based on sonic-logging velocity and the nonstationary seismic signals due to the time-varying wavelets during wave propagation. The nonstationary problems related to the time–depth relationship and the time-varying wavelets are interrelated in seismic-well tying procedure. We implemented a nonstationary seismic–well tying method by iteratively updating the time-depth relationship and estimating the time-varying wavelets. From the estimated time-varying wavelets, we also estimated a Q-value by assuming that the subsurface medium has a constant Q at depth and used the constant Q to constrain the variation of the seismic wavelet during propagation. Then, we used the improved time–depth relationship and time-varying wavelets with the Q constraint for further iterations. In the iterative procedure, we quantified the accuracy of the seismic–well tying result using the correlation coefficient between the synthetic and the true seismic trace in each iteration and evaluated the reliability using the normalized mean-square errors among the wavelets estimated in different iterations.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 05-2018
Publisher: Oxford University Press (OUP)
Date: 09-12-2015
Publisher: American Geophysical Union (AGU)
Date: 13-03-2009
DOI: 10.1029/2008JB005916
Publisher: Oxford University Press (OUP)
Date: 04-2022
DOI: 10.1093/JGE/GXAC016
Abstract: In seismic wave simulation, solving the wave equation in the frequency domain requires calculating the inverse of the impedance matrix. The total cost strictly depends on the number of frequency components that are considered, if using a finite-difference method. For the applications such as seismic imaging and inversion, high-frequency information is always required and thus the wave simulation is always a challenging task as it demands tremendous computational cost for obtaining dispersion-free high-frequency wavefields for large subsurface models. This paper demonstrates that a data-driven machine learning method, called the Fourier neural operator (FNO), is capable of predicting high-frequency wavefields, based on a limited number of low-frequency components. As the FNO method is for the first time applied to seismic wavefield extrapolation, the experiment reveals three attractive features with FNO: high efficiency, high accuracy and, importantly, the predicted high-frequency wavefields are dispersion free.
Publisher: Society of Exploration Geophysicists
Date: 07-2015
Abstract: We have developed a case study of crosshole seismic tomography with a cross-firing geometry in which seismic sources were placed in two vertical boreholes alternatingly and receiver arrays were placed in another vertical borehole. There are two crosshole seismic data sets in a conventional sense. These two data sets are used jointly in seismic tomography. Because the local sediment is dominated by periodic, flat, thin layers, there is seismic anisotropy with different velocities in the vertical and horizontal directions. The vertical transverse isotropy anisotropic effect is taken into account in inversion processing, which consists of three stages in sequence. First, isotropic traveltime tomography is used for estimating the maximum horizontal velocity. Then, anisotropic traveltime tomography is used to invert for the anisotropic parameter, which is the normalized difference between the maximum horizontal velocity and the maximum vertical velocity. Finally, anisotropic waveform tomography is implemented to refine the maximum horizontal velocity. The cross-firing acquisition geometry significantly improves the ray coverage and results in a relatively even distribution of the ray density in the study area between two boreholes. Consequently, joint inversion of two crosshole seismic data sets improves the resolution and increases the reliability of the velocity model reconstructed by tomography.
Publisher: Oxford University Press (OUP)
Date: 12-08-2004
Publisher: Oxford University Press (OUP)
Date: 03-11-2015
DOI: 10.1093/GJI/GGU384
Abstract: The Ricker wavelet has been widely used in the analysis of seismic data, as its asymmetrical litude spectrum can represent the attenuation feature of seismic wave propagation through viscoelastic homogeneous media. However, the frequency band of the Ricker wavelet is not analytically determined yet. The determination of the frequency band leads to an inverse exponential equation. To solve this equation analytically a special function, the Lambert W function, is needed. The latter provides a closed and elegant expression of the frequency band of the Ricker wavelet, which is a s le application of the Lambert W function in geophysics and there have been other applications in various scientific and engineering fields in the past decade. Moreover, the Lambert W function is a variation of the Ricker wavelet litude spectrum. Since the Ricker wavelet is the second derivative of a Gaussian function and its spectrum is a single-valued smooth curve, numerical evaluation of the Lambert W function can be implemented by a stable interpolation procedure, followed by a recursive computation for high precision.
Publisher: Elsevier BV
Date: 02-2023
Publisher: Springer Science and Business Media LLC
Date: 18-06-2022
DOI: 10.1007/S00024-022-03083-Z
Abstract: The viscoelasticity of the subsurface media varies spatially, and such viscoelasticity can be represented concisely by a wave equation in the form of fractional temporal derivative (FTD). We have developed a strategy for simulating seismic waves propagating through a heterogeneous viscoelastic model. The FTD is transferred to fractional spatial derivatives (FSDs), and the FSDs are implemented through the fast Fourier transform (FFT), for improving the computational efficiency. However, the FFT implementation is not rigorously applicable to the heterogeneous model. In this paper, we have reformulated the FSD wave equation by introducing a spatial-position dependent filter. This spatial filter corrects the errors that are caused by the assumption of non-heterogeneity in the FFT implementation. This formulation appropriately represents the viscoelastic effect in seismic wave propagation, leading to the improvement on the accuracy of numerical simulation.
Publisher: American Geophysical Union (AGU)
Date: 05-09-2009
DOI: 10.1029/2009GL039580
Publisher: Society of Exploration Geophysicists
Date: 2003
DOI: 10.1190/1.1543220
Abstract: An expanded multichannel matching (EMCM) filter is proposed for the adaptive subtraction in seismic multiple attenuation. For a normal multichannel matching filter where an original seismic trace is matched by a group of multiple‐model traces, the lateral coherency of adjacent traces is likely to be exploited to discriminate the overlapped multiple and primary reflections. In the proposed EMCM filter, a seismic trace is matched by not only a group of the ordinary multiple‐model traces but also their adjoints generated mathematically. The adjoints of a multiple‐model trace include its first derivative, its Hilbert transform, and the derivative of the Hilbert transform. The convolutional coefficients associated with the normal multichannel filter can be represented as a 2D operator in the time‐space domain. This 2D operator is expanded with an additional spatial dimension in the EMCM filter to improve the robustness of the adaptive subtraction. The multiple‐model traces are generated using moveout equations to afford efficiency in the multiple attenuation application.
Publisher: Springer Science and Business Media LLC
Date: 02-08-2013
Abstract: In 2001 and 2002, fatal myocarditis resulted in the sudden deaths of four, two adult and two juvenile, orang utans out of a cohort of 26 in the Singapore Zoological Gardens. Of the four orang utans that underwent post-mortem examination, virus isolation was performed from the tissue homogenates of the heart and lung obtained from the two juvenile orang utans in Vero cell cultures. The tissue culture fluid was examined using electron microscopy. Reverse transcription and polymerase chain reaction with Encephalomyocarditis virus (EMCV)-specific primers targeting the gene regions of VP3/VP1 and 3D polymerase (3Dpol) confirmed the virus genus and species. The two EMCV isolates were sequenced and phylogenetic analyses of the virus genes performed. Serological testing on other animal species in the Singapore Zoological Gardens was also conducted. Electron microscopy of the two EMCV isolates, designated Sing-M100-02 and Sing-M105-02, revealed spherical viral particles of about 20 to 30 nm, consistent with the size and morphology of members belonging to the family Picornaviridae . In addition, infected-Vero cells showed positive immunoflorescence staining with antiserum to EMCV. Sequencing of the viral genome showed that the two EMCV isolates were 99.9% identical at the nucleotide level, indicating a similar source of origin. When compared with existing EMCV sequences in the VP1 and 3Dpol gene regions, the nucleotide ergence were at a maximum of 38.8% and 23.6% respectively, while the amino acid ergence were at a maximum of 33.9% and 11.3% respectively. Phylogenetic analyses of VP1 and 3Dpol genes further grouped the Sing-M100-02 and Sing-M105-02 isolates to themselves, away from existing EMCV lineages. This strongly suggested that Sing-M100-02 and Sing-M105-02 isolates are highly ergent variants of EMCV. Apart from the two deceased orang utans, a serological survey conducted among other zoo animals showed that a number of other animal species had neutralizing antibodies to Sing-M105-02 isolate, indicating that the EMCV variant has a relatively wide host range. The etiological agent responsible for the fatal myocarditis cases among two of the four orang utans in the Singapore Zoological Gardens was a highly ergent variant of EMCV. This is the first report of an EMCV infection in Singapore and South East Asia.
Publisher: Society of Exploration Geophysicists
Date: 2023
Abstract: The anisotropic full-waveform inversion (FWI) is a seismic inverse problem for multiple parameters, which aims to simultaneously reconstruct the vertical velocity and the anisotropic parameters of the earth’s subsurface. This multiparameter inverse problem suffers from two issues. First, the objective function of the data fitting is less sensitive to the anisotropic parameters. Second, the crosstalk effect among the different parameters worsens the model update in the iterative inversion. We have developed a method that statistically regularizes the anisotropic FWI using Wasserstein adversarial networks, by penalizing the Wasserstein distance between the distribution of the current model parameters and that of the parameters at the borehole locations. The regularizer can mitigate the issues of anisotropic FWI with multiple parameters and therefore it also can be applied to other inverse problems with multiple parameters.
Publisher: Society of Exploration Geophysicists
Date: 09-2011
Abstract: The relationship between the seismic data and the reservoir properties can be modeled by using statistical approaches, such as regression and artificial neural networks (ANN) however, another nonlinear regression method, known as the group method of data handling (GMDH), has been proven to perform better than regular statistical methods. GMDH is a supervised machine learning tool that automatically self-organizes (synthesizes) the models. Although it is self-organized, like unsupervised ANN, it learns from the ex les introduced similar to the supervised ANN. We apply the GMDH algorithm to seismic attributes to predict reservoir porosity. GMDH can automatically determine the best network structure, as well as the number of nodes, thus gauging sensitivity of the input without overtraining the data. Moreover, GMDH predicted porosity has better resolution than that predicted using ANN.
Publisher: Elsevier BV
Date: 03-2006
DOI: 10.1016/J.WATRES.2006.01.017
Abstract: The Pd/Sn-modified activated carbon fiber (ACF) electrodes were successfully prepared by the impregnation of Pd2+ and Sn2+ ions onto ACF, and their electrocatalytic reduction capacity for nitrate ions in water was evaluated in a batch experiment. The electrode was characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), X-ray photoelectron spectrum (XPS) and temperature programmed reduction (TPR). The capacity for nitrate reduction depending on Sn content on the electrode and the pH of electrolyte was discussed at length. The results showed that at an applied current density of 1.11 mA cm(-2), nitrate ions in water (solution volume: 400 mL) were reduced from 110 to 3.4 mg L(-1) after 240 min with consecutive change of intermediate nitrite. Ammonium ions and nitrogen were formed as the main final products. The amount of other possible gaseous products (including NO and N2O) was trace. With the increase of Sn content on the Pd/Sn-modified ACF electrode, the activity for nitrate reduction went up to reach a maximum (at Pd/Sn = 4) and then decreased, while the selectivity to N2 was depressed. Higher pH value of electrolyte exhibited more suppression effect on the reduction of nitrite than that of nitrate. However, no significant influence on the final ammonia formation was observed. Additionally, Cu ion in water was found to cover the active sites of the electrode to make the electrode deactivated.
Publisher: Oxford University Press (OUP)
Date: 20-05-2005
Publisher: Oxford University Press (OUP)
Date: 07-09-2019
DOI: 10.1093/GJI/GGZ387
Abstract: When seismic waves propagate through viscoelastic media, the viscoelastic response can be presented as a fractional-order derivative of the strain. This fractional order $\\beta $ controlling the degree of viscoelasticity of subsurface media is referred to as the viscoelastic parameter. However, the viscoelasticity is conventionally quantified by the quality factor Q, and there is a gap between the viscoelastic parameter $\\beta $ and the Q factor. Here this paper bridges the gap by establishing a relationship between these two parameters. An exact Q model is derived analytically based on the viscoelastic parameter $\\beta $. Since the exact Q model is frequency dependent, a constant-Q model which is frequency independent is proposed under a small-dissipation assumption. This constant-Q model is applicable to seismic data with a narrow frequency band and is consistent with Kolsky's attenuation model. Furthermore, an inverse function of the constant-Q model is presented for evaluating the viscoelastic parameter $\\beta $ from any given Q factor. Thus, the viscoelastic parameter $\\beta $ has an intuitive physical meaning that is directly linked to the Q factor.
Publisher: Springer International Publishing
Date: 2020
Publisher: Elsevier BV
Date: 11-2007
Publisher: American Geophysical Union (AGU)
Date: 09-2004
DOI: 10.1029/2004GL020572
Publisher: The Royal Society
Date: 09-2022
Abstract: For a non-stationary seismic signal, time–frequency analysis methods often include a time window function that serves as a weighting function and by which the signal is multiplied to form a segment. The time window function often has the highest weighting coefficient for the central s le of the signal segment. For the rest of the segment, there is no adequate representation in the frequency spectrum. Here, I propose to use multiple orthogonal window functions to properly represent the local spectral property in the time–frequency plane and recover the information lost due to time windowing before applying the Fourier transform. First, I propose to construct multiple window functions directly using a stack of Gaussian functions. The weighted average spectrum of the multiple window functions has a flat passband, which is better than the conventional multiple windows. Taking advantage of the linearity of the Fourier transform, we can apply each window to the analytic signal to generate the instantaneous autocorrelation accordingly and form an averaged instantaneous autocorrelation by a weighted sum before performing the Fourier transform to generate the Wigner–Ville distribution (WVD). This multi-window WVD method successfully represents the local spectrum of the non-stationary seismic signal in the time–frequency plane.
Publisher: Society of Exploration Geophysicists
Date: 1997
DOI: 10.1190/1.1444134
Abstract: The τ‐p transformation of reflection seismic data excited by a point source requires a cylindrical slant stack, which includes compensation for the phase shift and geometrical spreading associated with cylindrical geometry. Using a simple test model, we review and compare the different computational methods used for the cylindrical slant stack. The two major method types are the Bessel‐Fourier transform (BFT) method and a set of methods (TD2D, TDX, TDTC and TDTS) based on time‐domain convolution. The stack integral in each of these approaches can be separated into two parts, with the part corresponding to the contribution of incoming waves being negligible for large ray parameter p. Neglecting the latter term for large p generally avoid a major problem caused by aliasing between time and space domains. The TDTS method introduced here has the advantage of being expressed in terms of a conventional 2-D slant stack (weighted by offset x) plus a correction term. This formulation facilitates a quantitative comparison of the 3-D cylindrical slant stack with a 2-D slant stack. The TDTS method compares favorably with the TD2D method, in which the cylindrical slant stack is expressed as a weighted integral of the 2-D slant stacks. TDTS avoids the singular weighting function needed in the integral for the TD2D method, and therefore has less problems with numerical noise. For all of the methods considered, the accuracy of the map transformation is limited by the spatial and temporal resolution of the test data set. Some corrections to previously published methods are also provided.
Publisher: Oxford University Press (OUP)
Date: 10-2015
DOI: 10.1093/GJI/GGV346
Publisher: Oxford University Press (OUP)
Date: 26-06-2020
DOI: 10.1093/JGE/GXAA029
Abstract: Seismic reflectivity inversion problem can be formulated using a basis-pursuit method, aiming to generate a sparse reflectivity series of the subsurface media. In the basis-pursuit method, the reflectivity series is composed by large amounts of even and odd dipoles, thus the size of the seismic response matrix is huge and the matrix operations involved in seismic inversion are very time-consuming. In order to accelerate the matrix computation, a basis-pursuit method-based seismic inversion algorithm is implemented on Graphics Processing Unit (GPU). In the basis-persuit inversion algorithm, the problem is imposed with a L1-norm model constraint for sparsity, and this L1-norm basis-pursuit inversion problem is reformulated using a linear programming method. The core problems in the inversion are large-scale linear systems, which are resolved by a parallelised conjugate gradient method. The performance of this fully parallelised implementation is evaluated and compared to the conventional serial coding. Specifically, the investigation using several field seismic data sets with different sizes indicates that GPU-based parallelisation can significantly reduce the computational time with an overall factor up to 145. This efficiency improvement demonstrates a great potential of the basis-pursuit inversion method in practical application to large-scale seismic reflectivity inversion problems.
Publisher: Oxford University Press (OUP)
Date: 12-1997
Publisher: Oxford University Press (OUP)
Date: 12-12-2008
Publisher: Oxford University Press (OUP)
Date: 26-08-2011
Publisher: Society of Exploration Geophysicists
Date: 1999
DOI: 10.1190/1.1444514
Abstract: Both traveltimes and litudes in reflection seismology are used jointly in an inversion to simultaneously invert for the interface geometry and the elastic parameters at the reflectors. The inverse problem has different physical dimensions in both data and model spaces. Practical approaches are proposed to tackle the dimensional difficulties. In using the joint inversion, which may properly take care of the structural effect, one potentially improves the estimates of the subsurface elastic parameters in the traditional analysis of litude variation with offset (AVO). Analysis of the elastic parameters estimated, using the ratio of s-wave to P-wave velocity contrasts and the deviation of this parameter from a normal background trend, promises to have application in AVO analysis. The inversion method is demonstrated by application to real data from the North Sea.
Publisher: Society of Exploration Geophysicists
Date: 09-2018
Abstract: We developed a case study of seismic resolution enhancement for shale-oil reservoirs in the Q Depression, China, featured by rhythmic bedding. We proposed an innovative method for resolution enhancement, called the full-band extension method. We implemented this method in three consecutive steps: wavelet extraction, filter construction, and data filtering. First, we extracted a constant-phase wavelet from the entire seismic data set. Then, we constructed the full-band extension filter in the frequency domain using the least-squares inversion method. Finally, we applied the band extension filter to the entire seismic data set. We determined that this full-band extension method, with a stretched frequency band from 7–70 to 2–90 Hz, may significantly enhance 3D seismic resolution and distinguish reflection events of rhythmite groups in shale-oil reservoirs.
Publisher: Oxford University Press (OUP)
Date: 02-12-2017
Publisher: Springer Science and Business Media LLC
Date: 12-2009
Publisher: Oxford University Press (OUP)
Date: 31-05-2019
DOI: 10.1093/JGE/GXZ023
Publisher: Society of Exploration Geophysicists
Date: 2014
Abstract: Seismic ray tracing with a path-bending method leads to a nonlinear system that has much stronger nonlinearity in anisotropic media than the counterpart in isotropic media. Any path perturbation causes changes to directional velocities, which depend not only upon the spatial position but also upon the local propagation direction in anisotropic media. To combat the high nonlinearity of the problem, the Newton-type iterative algorithm is modified by enforcing Fermat’s minimum-time principle as a constraint for the solution update, instead of conventional error minimization in the nonlinear system. As the algebraic problem is incorporated with the physical principle, it is able to stabilize the solution for such a highly nonlinear problem as ray tracing in realistically complicated anisotropic media. With this modified algorithm, two ray-tracing schemes are presented. The first scheme involves newly derived raypath equations, which are approximate for anisotropic media but the minimum-time constraint will ensure that the solution steadily converges to the true solution. The second scheme is based on the minimal variation principle. It is more efficient than the first one as it solves a tridiagonal system and does not need to compute the Jacobian and its inverse in each iteration. Even in this second scheme, Fermat’s minimum-time constraint is employed for the solution update, so as to guarantee a robust convergence of the iterative solution in anisotropic media.
Publisher: Elsevier BV
Date: 08-2005
Publisher: Springer Science and Business Media LLC
Date: 28-05-2019
Publisher: Society of Exploration Geophysicists
Date: 09-2003
DOI: 10.1190/1.1620637
Abstract: The spectrum of a discrete Fourier transform (DFT) is estimated by linear inversion, and used to produce desirable seismic traces with regular spatial s ling from an irregularly s led data set. The essence of such a wavefield reconstruction method is to solve the DFT inverse problem with a particular constraint which imposes a sparseness criterion on the least‐squares solution. A working definition for the sparseness constraint is presented to improve the stability and efficiency. Then a sparseness measurement is used to measure the relative sparseness of the two DFT spectra obtained from inversion with or without sparseness constraint. It is a pragmatic indicator about the magnitude of sparseness needed for wavefield reconstruction. For seismic trace regularization, an antialiasing condition must be fulfilled for the regularizing trace interval, whereas optimal trace coordinates in the output can be obtained by minimizing the distances between the newly generated traces and the original traces in the input. Application to real seismic data reveals the effectiveness of the technique and the significance of the sparseness constraint in the least‐squares solution.
Publisher: Oxford University Press (OUP)
Date: 09-03-2016
Publisher: Society of Exploration Geophysicists
Date: 09-2020
Abstract: The 3D seismic data in the prestack domain are contaminated by impulse noise. We have adopted a robust vector median filter (VMF) for attenuating the impulse noise from 3D seismic data cubes. The proposed filter has two attractive features. First, it is robust the vector median that is the output of the filter not only has a minimum distance to all input data vectors, but it also has a high similarity to the original data vector. Second, it is structure adaptive the filter is implemented following the local structure of coherent seismic events. The application of the robust and structure-adaptive VMF is demonstrated using an ex le data set acquired from an area with strong sedimentary rhythmites composed of steep-dipping thin layers. This robust filter significantly improves the signal-to-noise ratio of seismic data while preserving any discontinuity of reflections and maintaining the fidelity of litudes, which will facilitate the reservoir characterization that follows.
Publisher: Elsevier BV
Date: 08-2016
Publisher: Oxford University Press (OUP)
Date: 11-07-2011
Publisher: Wiley
Date: 2003
Publisher: Society of Exploration Geophysicists
Date: 2007
DOI: 10.1190/1.2387109
Abstract: A seismic trace may be decomposed into a series of wavelets that match their time-frequency signature by using a matching pursuit algorithm, an iterative procedure of wavelet selection among a large and redundant dictionary. For reflection seismic signals, the Morlet wavelet may be employed, because it can represent quantitatively the energy attenuation and velocity dispersion of acoustic waves propagating through porous media. The efficiency of an adaptive wavelet selection is improved by making first a preliminary estimate and then a localized refining search, whereas complex-trace attributes and derived analytical expressions are also used in various stages. For a constituent wavelet, the scale is an important adaptive parameter that controls the width of wavelet in time and the bandwidth of the frequency spectrum. After matching pursuit decomposition, deleting wavelets with either very small or very large scale values can suppress spikes and sinusoid functions effectively from the time-frequency spectrum. This time-frequency spectrum may be used in turn for lithological analysis—for instance, detection of a gas reservoir. Investigation shows that the low-frequency shadow associated with a carbonate gas reservoir still exists, even high-frequency litudes are compensated by inverse-[Formula: see text] filtering.
Publisher: Society of Exploration Geophysicists
Date: 07-2002
DOI: 10.1190/1.1500385
Abstract: Seismic trace interpolation is implemented as a 2‐D (x, y) spatial prediction, performed separately on each frequency (f) slice. This so‐called f‐x‐y domain trace interpolation method is based on the relation that the linear prediction (LP) operator estimated at a given frequency may be used to predict data at a higher frequency but a smaller trace spacing. The relationship originally given for thef‐x domain trace interpolation is successfully extended to the f‐x‐y domain. The extension is achieved by masking the data s les selectively from the input frequency slice to design the LP operators. Two interpolation algorithms using the full‐step and the fractional‐step predictions, respectively, are developed. Both methods use an all‐azimuth prediction in the x‐y domain, but the fractional‐step prediction method is computationally more efficient. While the interpolation method can be applied to a common‐offset cube of 3‐D seismic, it can also be applied to 2‐D seismic traces for prestack data processing. Synthetic and real data ex les demonstrate the capability of the interpolation method.
Publisher: Elsevier BV
Date: 02-2016
DOI: 10.1053/J.GASTRO.2015.10.048
Abstract: There have been increasing reports of food-borne zoonotic transmission of hepatitis E virus (HEV) genotype 3, which causes chronic infections in immunosuppressed patients. We performed phylogenetic analyses of the HEV sequence (partial and full-length) from 1 patient from the Middle East who underwent liver transplantation, and compared it with other orthohepevirus A sequences. We found the patient to be infected by camelid HEV. This patient regularly consumed camel meat and milk, therefore camelid HEV, which is genotype 7, might infect human beings. Our finding links consumption of camel-derived food products to post-transplantation hepatitis E, which, if detected at early stages, can be cured with antiviral therapy and reduced administration of immunosuppressive agents.
Publisher: Society of Exploration Geophysicists
Date: 30-09-2021
Abstract: The Wigner-Ville distribution (WVD) is a high-resolution time-frequency spectral analysis method for nonstationary signals yet, it suffers from cross-term interference among signal components. We proposed applying a masking filter directly to the WVD time-frequency spectrum to suppress the cross-term interference. Conventional methods for suppressing interference include the smoothed pseudo-WVD (SP-WVD) method, which incorporates smooth filtering in the time and frequency directions. We exploited the SP-WVD spectrum as a reference to design the masking filter thus, the mask-filtered WVD (MF-WVD) procedure is data-adaptive. The MF-WVD method preserves the high-resolution energy concentration in the spectrum portrayed by the standard WVD, while suppressing the cross-term interference cleanly as in the SP-WVD method. Applying the MF-WVD method to field 3D seismic data generates high-resolution spectral cubes for various frequencies, and these spectral cubes may be used intuitively for detecting reservoir-related characteristics.
Publisher: Oxford University Press (OUP)
Date: 04-1994
Publisher: Oxford University Press (OUP)
Date: 14-11-2011
Publisher: Oxford University Press (OUP)
Date: 04-05-2020
DOI: 10.1093/JGE/GXAA015
Abstract: Seismic facies analysis is of great significance for the detection of residual oil in a sand-shale interbed reservoir. In this study, we propose to predict spatial distribution of sand thickness over a reservoir, based on seismic facies analysis. The target reservoir is a thin sand-shale interbed layer, and the layer thickness varies between 2 and 10 m. The thickness of sand strata within the reservoir layer appears to have a fragmentary distribution in lateral space. Thin thickness and fragmentary distribution are two factors that cause difficulty in sand thickness prediction. To tackle this problem, this study adopted a three-stage strategy. First, the reservoir over the entire study area was classified into five different lithofacies, following sedimentary microfacies analysis against the characteristics of gamma-ray logging data, and the corresponding seismic responses were meticulously depicted. Then, exploiting these seismic responses, or seismic facies, the spatial distribution of the gamma-ray values was evaluated within the thin sand-shale interbed reservoir. Finally, the spatial distribution of the sand thickness was predicted according to the spatial distribution of the gamma-ray values. The prediction was conducted independently for each seismic facies, rather than in a non-discriminatory manner. Comparing the prediction to the actual evaluation derived from well-logging data demonstrated that the thickness distribution resulting from seismic data has a high accuracy, because of the facies-based analysis.
Publisher: Wiley
Date: 09-2001
Publisher: Oxford University Press (OUP)
Date: 04-2009
Publisher: Oxford University Press (OUP)
Date: 09-2006
Publisher: Oxford University Press (OUP)
Date: 03-08-2013
DOI: 10.1093/GJI/GGT278
Publisher: Society of Exploration Geophysicists
Date: 07-2014
Abstract: Vertical seismic profiling (VSP) provides a direct observation of seismic waveforms propagating to various depths within the earth’s subsurface. The [Formula: see text] analysis or attenuation ([Formula: see text]) analysis based on direct comparison between in idual waveforms at different depths, however, suffers from the problem of instability commonly due to fluctuations inherent in the frequency spectrum of each waveform. To improve the stability, we considered frequency and time variations and conducted [Formula: see text] analysis on an integrated observation. First, we transformed the time- (or depth-) frequency-domain spectrum to a 1D attenuation measurement with respect to a single variable, the product of time and frequency. Although this 1D measurement has a higher signal-to-noise ratio than the 2D spectrum in the time-frequency domain, it can also be used to further generate a stabilized compensation function. Then, we implemented two [Formula: see text]-analysis methods by data fitting (in a least-squares sense) to either the attenuation measurement or the data-driven gain function. These two methods are theoretically consistent and practically robust for conducting [Formula: see text] analysis on field VSP data.
Publisher: Society of Exploration Geophysicists
Date: 2020
Abstract: The Wigner-Ville distribution is a powerful technique for the time-frequency spectral analysis of nonstationary seismic data. However, the Wigner-Ville distribution suffers from cross-term interference between different wave components in seismic data. To mitigate cross-term interference, we have developed a multichannel maximum-entropy method (MEM) to modify the Wigner-Ville kernel. The method is related to the conventional maximum-entropy spectral analysis (MESA) algorithm because both algorithms use Burg’s reflection coefficients for the calculation of the prediction-error filter (PEF). The MESA algorithm works on the standard autocorrelation sequence, but it does not work for the Wigner-Ville kernel, which is an instantaneous autocorrelation sequence. Our multichannel MEM algorithm uses the PEF to modify any single Wigner-Ville kernel sequence by exploiting multiple Wigner-Ville kernel sequences simultaneously. This multichannel implementation is capable of robustly determining the reflection coefficient and a minimum-phased PEF for the Wigner-Ville kernel sequence. The Wigner-Ville distribution and the multichannel MEM algorithm in conjunction with each other in turn can produce a high-resolution time-frequency spectrum by mitigating the cross-term interferences and suppressing the spurious energy in the spectrum.
Publisher: Society of Exploration Geophysicists
Date: 05-2006
DOI: 10.1190/1.2192912
Abstract: A principal limitation on seismic resolution is the earth attenuation, or [Formula: see text]-effect, including the energy dissipation of high-frequency wave components and the velocity dispersion that distorts seismic wavelets. An inverse [Formula: see text]-filtering procedure attempts to remove the [Formula: see text]-effect to produce high-resolution seismic data, but some existing methods either reduce the S/N ratio, which limits spatial resolution, or generate an illusory high-resolution wavelet that contains no more subsurface information than the original low-resolution data. In this paper, seismic inverse [Formula: see text]-filtering is implemented in a stabilized manner to produce high-quality data in terms of resolution and S/N ratio. Stabilization is applied to only the litude compensation operator of a full inverse [Formula: see text]-filter because its phase operator is unconditionally stable, but the scheme neither lifies nor suppresses high frequencies at late times where the data contain mostly ambient noise. The latter property makes the process invertible, differentiating from some conventional stabilized inverse schemes that tend to suppress high frequencies at late times. The stabilized inverse [Formula: see text]-filter works for a general earth [Formula: see text]-model, variable with depth or traveltime, and is more accurate than a layered approach, which involves an approximation to the litude operator. Because the earth [Formula: see text]-model can now be defined accurately, instead of a constant-[Formula: see text] layered structure, the accuracy of the inverse [Formula: see text]-filter is much higher than for a layered approach, even when implemented in the Gabor transform domain. For the stabilization factor, an empirical relation is proposed to link it to a user-specified gain limit, as in an explicit gain-controlling scheme. Synthetic and real data exam-ples demonstrate that the stabilized inverse [Formula: see text]-filter corrects the wavelet distortion in terms of shape and timing, compensates for energy loss without boosting ambient noise, and produces desirable seismic images with high resolution and high S/N ratio.
Publisher: Oxford University Press (OUP)
Date: 10-02-2012
Publisher: Society of Exploration Geophysicists
Date: 03-2023
Abstract: A high-resolution time–frequency spectrum is desirable for processing and interpreting seismic data. The W transform is a method that effectively preserves the resolution in the low-frequency region of the time–frequency spectrum of nonstationary seismic signals. To further increase the energy concentration of the time–frequency spectrum estimated with the W transform, we propose to combine the W transform with a chirp-modulated window. The chirp rate in the chirp-modulated window can control the rotation of the window in the time–frequency plane to achieve a better match with the time–frequency spectrum. The chirp rate in the modified W transform can be directly determined with the estimated instantaneous frequency. It has been shown that the W transform with a chirp-modulated window maintains the resolution of the time–frequency spectrum and improves the energy concentration around the dominant frequency against noise. To speed up the computational process of the W transform with a chirp-modulated window, we formulate the transform as a matrix-vector multiplication, which can be accelerated by using graphics processing unit computations. The application of the modified algorithm to synthetic and field data indicates that the frequency anomalies can be easily identified with the modified W transform.
Publisher: Springer Science and Business Media LLC
Date: 05-2002
Publisher: Society of Exploration Geophysicists
Date: 07-2010
DOI: 10.1190/1.3462015
Abstract: The technique of matching pursuit can adaptively decompose a seismic trace into a series of wavelets. However, the solution is not unique and is also strongly affected by data noise. Multichannel matching pursuit (MCMP), exploiting lateral coherence as a constraint, might improve the uniqueness of the solution. It extracts a constituent wavelet that has an optimal correlation coefficient to neighboring traces, instead of to a single trace only. According to linearity theory, a wavelet shared by neighboring traces is the best match to the average of multiple traces, and therefore it might effectively suppress the data noise and stabilize the performance. It is found that the MCMP scheme greatly improves spatial continuity in decomposition and can generate a plausible time-frequency spectrum with high resolution for reservoir detection.
Publisher: Oxford University Press (OUP)
Date: 23-03-2007
Publisher: Earth and Planetary Physics
Date: 2019
DOI: 10.26464/EPP2019035
Publisher: Public Library of Science (PLoS)
Date: 24-05-2018
Publisher: Wiley
Date: 14-11-2016
Publisher: Oxford University Press (OUP)
Date: 04-2021
DOI: 10.1093/JGE/GXAB015
Abstract: Least-squares reverse-time migration (RTM) works with an inverse operation, rather than an adjoint operation in a conventional RTM, and thus produces an image with a higher resolution and more balanced litude than the conventional RTM image. However, least-squares RTM introduces two side effects: sidelobes around reflectors and high-wavenumber migration artifacts. These side effects are caused mainly by the limited bandwidth of seismic data, the limited coverage of receiver arrays and the inaccuracy of the modeling kernel. To mitigate these side effects and to further boost resolution, we employed two sparsity constraints in the least-squares inversion operation, namely the Cauchy and L1-norm constraints. For solving the Cauchy-constrained least-squares RTM, we used a preconditioned nonlinear conjugate-gradient method. For solving the L1-norm constrained least-squares RTM, we modified the iterative soft thresholding method. While adopting these two solution methods, the Cauchy-constrained least-squares RTM converged faster than the L1-norm constrained least-squares RTM. Application ex les with synthetic data and laboratory modeling data demonstrated that the constrained least-squares RTM methods can mitigate the side effects and promote image resolution.
Publisher: Elsevier BV
Date: 12-2014
Publisher: Society of Exploration Geophysicists
Date: 2008
DOI: 10.1190/1.2806924
Abstract: An inverse-[Formula: see text] filtered migration algorithm performs seismic migration and inverse-[Formula: see text] filtering simultaneously, in which the latter compensates for the litudes and corrects the phase distortions resulting from the earth attenuation effect. However, the litudes of high-frequency components grow rapidly in the extrapolation procedure, so numerical instability is a concern when including the inverse-[Formula: see text] filter in the migration. The instability for each frequency component is independent of data and is affected only by migration models. The stabilization problem may be treated separately from the wavefield-extrapolation scheme. The proposed strategy is to construct supersedent of attenuation coefficients, based on given velocity and [Formula: see text] models, before performing wavefield extrapolation in the space-frequency domain. This stabilized algorithm for inverse-[Formula: see text] filtered migration is applicable to subsurface media with vertical and lateral variations in velocity and [Formula: see text] functions. It produces a seismic image with enhanced resolution and corrected timing, comparable to an ideal image without the earth attenuation effect.
Publisher: Society of Exploration Geophysicists
Date: 2021
Abstract: Time-frequency spectral analysis methods such as the S transform cannot appropriately present low-frequency anomalies in seismic traces because they generate a time-frequency spectrum with a low resolution in time at low frequencies. I have developed the W transform to improve the time resolution of the spectrum at low frequencies, for an effective detection of seismic anomalies related to hydrocarbon reservoirs in petroleum exploration and abnormal features in near-surface geophysics. The W transform has three features: (1) the spectral energy is concentrated around the dominant frequency of a seismic waveform, rather than being shifted toward higher frequencies by the S transform (2) the implementation is numerically stable because it avoids any potential frequency singularity in the S transform (3) the Gaussian window function is defined using a nonstationary frequency weight, rather than using a stationary frequency weight in the S transform, because the dominant frequency is a time-dependent function. Therefore, the time-frequency spectrum generated by the W transform appropriately represents seismic properties varying with geologic depth, and it has an improved time resolution at low frequencies that makes it suitable for characterizing reservoirs in petroleum geophysics and for detecting karsts in construction engineering.
Publisher: Oxford University Press (OUP)
Date: 07-11-2019
DOI: 10.1093/JGE/GXZ090
Abstract: In seismic waveform inversion, selecting an optimal multi-parameter group is a key step to derive an accurate subsurface model for characterising hydrocarbon reservoirs. There are three parameterizations for the horizontal transverse isotropic (HTI) media, and each parameterization consists of five parameters. The first parameterization (P-I) consists of two velocities and three anisotropy parameters, the second (P-II) consists of five elastic coefficients and the third (P-III) consists of five velocity parameters. The radiation patterns of these three parameterizations indicate a strong interference among five parameters. An effective inversion strategy is a two-stage scheme that first inverts for the velocities or velocity-related parameters and then inverts for all five parameters simultaneously. The inversion results clearly demonstrate that P-I is the best parameterization for seismic waveform inversion in HTI anisotropic media.
Publisher: Oxford University Press (OUP)
Date: 31-01-2014
Publisher: Elsevier BV
Date: 06-2009
Publisher: Society of Exploration Geophysicists
Date: 1997
DOI: 10.1190/1.1444134
Abstract: The τ‐p transformation of reflection seismic data excited by a point source requires a cylindrical slant stack, which includes compensation for the phase shift and geometrical spreading associated with cylindrical geometry. Using a simple test model, we review and compare the different computational methods used for the cylindrical slant stack. The two major method types are the Bessel‐Fourier transform (BFT) method and a set of methods (TD2D, TDX, TDTC and TDTS) based on time‐domain convolution. The stack integral in each of these approaches can be separated into two parts, with the part corresponding to the contribution of incoming waves being negligible for large ray parameter p. Neglecting the latter term for large p generally avoid a major problem caused by aliasing between time and space domains. The TDTS method introduced here has the advantage of being expressed in terms of a conventional 2-D slant stack (weighted by offset x) plus a correction term. This formulation facilitates a quantitative comparison of the 3-D cylindrical slant stack with a 2-D slant stack. The TDTS method compares favorably with the TD2D method, in which the cylindrical slant stack is expressed as a weighted integral of the 2-D slant stacks. TDTS avoids the singular weighting function needed in the integral for the TD2D method, and therefore has less problems with numerical noise. For all of the methods considered, the accuracy of the map transformation is limited by the spatial and temporal resolution of the test data set. Some corrections to previously published methods are also provided.
Publisher: Oxford University Press (OUP)
Date: 05-10-2004
Publisher: Society of Exploration Geophysicists
Date: 03-2004
DOI: 10.1190/1.1707074
Abstract: This paper introduces a fully data‐driven concept, multiple prediction through inversion (MPI), for surface‐related multiple attenuation (SMA). It builds the multiple model not by spatial convolution, as in a conventional SMA, but by updating the attenuated multiple wavefield in the previous iteration to generate a multiple prediction for the new iteration, as is usually the case in an iterative inverse problem. Because MPI does not use spatial convolution, it is able to minimize the edge effect that appears in conventional SMA multiple prediction and to eliminate the need to synthesize near‐offset traces, required by a conventional scheme, so that it can deal with a seismic data set with missing near‐offset traces. The MPI concept also eliminates the need for an explicit surface operator, which is required by conventional SMA and is comprised of the inverse source signature and other effects. This method accounts implicitly for the spatial variation of the surface operator in multiple‐model building and attempts to predict multiples which are not only accurate kinematically but are also accurate in phase and litude.
Publisher: Society of Exploration Geophysicists
Date: 2003
DOI: 10.1190/1.1543219
Abstract: Applying inverse Q filtering to surface seismic data may minimize the effect of dispersion and attenuation and hence improve the seismic resolution. In this case study, a stabilized inverse Q filter is applied to a land seismic data set, for which the prerequisite reliable earth Q function is estimated from the vertical seismic profile (VSP) downgoing wavefield. The paper focuses on the robust estimate of Q values from VSP data and on the quantitative evaluation of the effectiveness of the stabilized inverse Q filtering approach. The quantitative evaluation shows that inverse Q filtering may flatten the litude spectrum, strengthen the time‐variant litude, increase the spectral bandwidth, and improve the signal‐to‐noise (S/N) ratio. A parameter measuring the resolution enhancement is defined as a function of the changes in the bandwidth and the S/N ratio. The stabilized inverse Q filtering algorithm, which may provide a stable solution for compensating the high‐frequency wave components lost through attenuation, has positive changes in both the bandwidth and the S/N ratio, and thereby enhances the resolution of the final processed seismic data.
Publisher: Oxford University Press (OUP)
Date: 24-12-2017
DOI: 10.1093/GJI/GGW485
Publisher: Society of Exploration Geophysicists
Date: 03-2014
Abstract: The Ricker wavelet is theoretically a solution of the Stokes differential equation, which takes into account the effect of Newtonian viscosity, and is applicable to seismic waves propagated through viscoelastic homogeneous media. In this paper, we defined the time-domain breadth and the frequency-domain bandwidth of the Ricker wavelet and developed quantities analytically in terms of the Lambert [Formula: see text] function. We determined that the central frequency, the geometric center of the frequency band, is close to the mean frequency statistically evaluated using the power spectrum, rather than the litude spectrum used in some of the published literature. We also proved that the standard deviation from the mean frequency is not, as suggested by the literature, the half-bandwidth of the frequency spectrum of the Ricker wavelet. Moreover, we established mathematically the relationships between the theoretical frequencies (the central frequency and the half-bandwidth) and the numerical measurements (the mean frequency and its standard deviation) and produced each of these frequency quantities analytically in terms of the peak frequency of the Ricker wavelet.
Publisher: Springer Science and Business Media LLC
Date: 11-12-2019
Publisher: Oxford University Press (OUP)
Date: 05-10-2007
Publisher: Oxford University Press (OUP)
Date: 30-09-2010
Publisher: Society of Exploration Geophysicists
Date: 09-2017
Abstract: Seismic characterization of carbonate reservoirs is a challenging task for geophysicists because of their special depositional environment and complex interior structures. We developed a case study of the seismic characterization of a karstified carbonate reservoir in the Tarim Basin, western China. The characterization procedure is sequential and includes fault and fracture detection, seismic facies classification, seismic impedance inversion, and lithofacies classification. We presented a dip-steered coherence algorithm for detecting faults and karst fractures in the carbonate reservoir. Incorporating the dip information improves the performance and robustness. We applied normalized seismic segments, rather than the litude values, as the input to seismic facies classification, so as to reduce the impact of strong litudes, such as karst fractures, and to enable the analysis of weak litudes in the background strata. For the impedance inversion, we adopted a Fourier integral method for fast simulation in the stochastic inversion in this karstified carbonate reservoir. The algorithm honors the lateral variation based on the seismic trace similarity, instead of the lateral variogram that is commonly used in stochastic inversion. We conducted lithofacies classification, in which we used seismic coherence as a prior knowledge, so as to honor the fracture-associated local lithofacies with dolomitization and to distinguish it from limestone without dolomitization. Based on reservoir characterization described above, we determined three drilling wells for potential oil/gas exploration.
Publisher: American Geophysical Union (AGU)
Date: 11-2004
DOI: 10.1029/2004GL020525
Publisher: Oxford University Press (OUP)
Date: 29-07-2016
Publisher: Oxford University Press (OUP)
Date: 11-10-2022
DOI: 10.1093/GJI/GGAC399
Abstract: To simulate seismic wavefields with a frequency-domain wave equation, conventional numerical methods must solve the equation sequentially to obtain the wavefields for different frequencies. The monofrequency equation has the form of a Helmholtz equation. When solving the Helmholtz equation for seismic wavefields with multiple frequencies, a physics-informed neural network (PINN) can be used. However, the PINN suffers from the problem of spectral bias when approximating high-frequency components. We propose to simulate seismic multifrequency wavefields using a PINN with an embedded Fourier feature. The input to the Fourier feature PINN for simulating multifrequency wavefields is 4-D, namely the horizontal and vertical spatial coordinates of the model, the horizontal position of the source, and the frequency, and the output is multifrequency wavefields at arbitrary source positions. While an effective Fourier feature initialization strategy can lead to optimal convergence in training this network, the Fourier feature PINN simulates multifrequency wavefields with reasonable efficiency and accuracy.
Publisher: Society of Exploration Geophysicists
Date: 23-06-2022
Abstract: Reverse time migration (RTM) has advantages of imaging steep dip structures but may inevitably produce migration swings when applied to vertical seismic profiles (VSPs). These artifacts often are not suppressed by stacking over shots. The noise is mainly generated from the limited coverage of VSP acquisition geometry, which leads to uneven superposition. The noise is processed by the imaging condition and then overlaps with the real layers, generating artificial images with different dip angles that are difficult to distinguish. The difference is that the real layers can be enhanced by the redundancy of multifold data, whereas the noise is usually generated by a smaller subset of the data. A VSP RTM processing flow is developed to suppress this type of noise. This method constructs the dip angle gather and estimates the redundancy of the coverage in the dip domain. In the stratigraphic dip domain, the false structure and the real structure are located at different dip angles. The real dip is determined by identifying the center of the stacking number. Then, the noise is suppressed by attenuating the imaging information of the other dip angles. The efficient wavefield decomposition method based on Hilbert transform-based instantaneous wavenumber method is adopted to determine the wave propagation direction. Compared with the Poynting vector method and the instantaneous wavenumber method, this approach alleviates the influence of multiwave arrivals and is suitable for complex media, ensuring the accuracy of image decomposition. The whole process is data-driven and does not require prior information. Theoretical and field ex les indicate that this method can significantly reduce migration noise and improve the image quality of VSP RTM.
Publisher: Elsevier BV
Date: 12-2022
Publisher: Society of Exploration Geophysicists
Date: 2015
Abstract: Reverse time migration (RTM) has shown increasing advantages in handling seismic images of complex subsurface media, but it has not been used widely in 3D seismic data due to the large storage and computation requirements. Our prime objective was to develop an RTM strategy that was applicable to 3D vertical seismic profiling (VSP) data. The strategy consists of two aspects: storage saving and calculation acceleration. First, we determined the use of the random boundary condition (RBC) to save the storage in wavefield simulation. An absorbing boundary such as the perfect matching layer boundary is often used in RTM, but it has a high memory demand for storing the source wavefield. RBC is a nonabsorbing boundary and only stores the source wavefield at the two maximum time steps, then repropagates the source wavefield backwards at every time step, and hence, it significantly reduces the memory requirement. Second, we examined the use of the graphic processing unit (GPU) parallelization technique to accelerate the computation. RBC needs to simulate the source wavefield twice and doubles the computation. Thus, it is very necessary to realize the RTM algorithm by GPU, especially for a 3D VSP data set. GPU and central processing unit (CPU) collaborated parallel implementation can greatly reduce the computation time, where the CPU performs serial code, and the GPU performs parallel code. Because RBC does not need the same huge amount of storage as an absorbing boundary, RTM becomes practically applicable for 3D VSP imaging.
Publisher: Oxford University Press (OUP)
Date: 11-1995
Publisher: Elsevier BV
Date: 08-2023
Publisher: Springer Science and Business Media LLC
Date: 15-02-2018
DOI: 10.1038/S41598-018-20992-Z
Abstract: The contrast of elastic properties across a subsurface interface imposes a dominant influence on the seismic wavefield, which includes transmitted and reflected waves from the interface. Therefore, for an accurate waveform simulation, it is necessary to have an accurate representation of the subsurface interfaces within the numerical model. Accordingly, body-fitted gridding is used to partition subsurface models so that the grids coincide well with both the irregular surface and fluctuating interfaces of the Earth. However, non-rectangular meshes inevitably exist across fluctuating interfaces. This non-orthogonality degrades the accuracy of the waveform simulation when using a conventional finite-difference method. Here, we find that a summation-by-parts (SBP) finite-difference method can be used for models with non-rectangular meshes across fluctuating interfaces, and can achieve desirable simulation accuracy. The acute angle of non-rectangular meshes can be relaxed to as low as 47°. The cell size rate of change between neighbouring grids can be relaxed to as much as 30%. Because the non-orthogonality of grids has a much smaller impact on the waveform simulation accuracy, the model discretisation can be relatively flexible for fitting fluctuating boundaries within any complex problem. Consequently, seismic waveform inversion can explicitly include fluctuating interfaces within a subsurface velocity model.
Publisher: Oxford University Press (OUP)
Date: 02-2021
DOI: 10.1093/JGE/GXAA068
Abstract: An absorbing boundary condition is necessary in seismic wave simulation for eliminating the unwanted artificial reflections from model boundaries. Existing boundary condition methods often have a trade-off between numerical accuracy and computational efficiency. We proposed a local absorbing boundary condition for frequency-domain finite-difference modelling. The proposed method benefits from exact local plane-wave solution of the acoustic wave equation along predefined directions that effectively reduces the dispersion in other directions. This method has three features: simplicity, accuracy and efficiency. Numerical simulation demonstrated that the proposed method has higher efficiency than the conventional methods such as the second-order absorbing boundary condition and the perfectly matched layer (PML) method. Meanwhile, the proposed method shared the same low-cost feature as the first-order absorbing boundary condition method.
Publisher: Wiley
Date: 11-2002
Publisher: Society of Exploration Geophysicists
Date: 03-2007
DOI: 10.1190/1.2408379
Abstract: Wave-equation-based multiple attenuation seismic methods may be ided into the two distinct phases of multiple modeling and multiple subtraction. These two are interrelated and must be optimized in order to produce an optimal final result. The multiple prediction through inversion (MPI) scheme updates the multiple model iteratively, as we usually do in a linearized inverse problem. The scheme models the multiple wavefield without an explicit knowledge of surface and subsurface structures or of the source signature both are generally unknown in seismic surveys. However, compared to a conventional surface-related multiple attenuation method, the accuracy of the multiple model is improved both kinematically and dynamically. It is because the MPI scheme implicitly takes account of the spatial variation of the surface reflectivity, the source signature, the detector patterns and receiver ghosts, and other effects included in the so-called surface operator. When the MPI scheme is used in the first phase it also significantly reduces the nonlinearity of the problem in the second phase that involves attenuating multiples without removing or altering primaries. The effectiveness of the MPI scheme is demonstrated by ex les involving real marine seismic data.
Publisher: Oxford University Press (OUP)
Date: 08-12-2023
DOI: 10.1093/GJI/GGAC488
Abstract: The viscoelasticity of subsurface media is succinctly represented in the generalized wave equation by a fractional time derivative. This generalized viscoelastic wave equation is characterized by the viscoelastic parameter and the viscoelastic velocity, but these parameters are not well formulated and therefore unfavourable for seismic implementation. Here, we prove that the generalized wave equation is causal and stable by deriving the rate-of-relaxation function. Causality and stability are two necessary conditions for the applicability of the wave equation in seismic simulations. On this basis, we determine the physical parameters for the application of the generalized wave equation. First, we formulate the relationship between the viscoelastic parameter and the constant Q model. The proposed frequency-independent relation agrees with the theoretical solution and fits the field data. Then, we formulate the viscoelastic velocity in terms of the reference velocity and the viscoelastic parameter. These two formulations adequately represent the viscoelastic effect in seismic wave propagation and lead to an improvement in the accuracy of the numerical simulation of the generalized viscoelastic wave equation.
Publisher: Cold Spring Harbor Laboratory
Date: 23-01-2022
DOI: 10.1101/2022.01.21.477239
Abstract: Understanding connections between environment and bio ersity is crucial for conservation, identifying causes of ecosystem stress, and predicting population responses to changing environments. Explaining bio ersity requires an understanding of how species richness and environment co-vary across scales. Here, we identify scales and locations at which bio ersity is generated and correlates with environment. Full latitudinal range per continent. Present-day. Terrestrial vertebrates: all mammals, carnivorans, bats, songbirds, humming-birds, hibians. We describe the use of wavelet power spectra, cross-power and coherence for identifying scale-dependent trends across Earth’s surface. Spectra reveal scale- and location-dependent coherence between species richness and topography ( E ), mean annual precipitation ( Pn ), temperature ( Tm ) and annual temperature range (∆ T ). 97% of species richness of taxa studied is generated at large scales, i.e. wavelengths 10 3 km, with 30–69% generated at scales 10 4 km. At these scales, richness tends to be highly coherent and anti-correlated with E and ∆ T , and positively correlated with Pn and Tm . Coherence between carnivoran richness and ∆ T is low across scales, implying insensitivity to seasonal temperature variations. Conversely, hibian richness is strongly anti-correlated with ∆ T at large scales. At scales 10 3 km, examined taxa, except carnivorans, show highest richness within the tropics. Terrestrial plateaux exhibit high coherence between carnivorans and E at scales ∼ 10 3 km, consistent with contribution of large-scale tectonic processes to bio ersity. Results are similar across different continents and for global latitudinal averages. Spectral admittance permits derivation of rules-of-thumb relating long-wavelength environmental and species richness trends. Sensitivities of mammal, bird and hibian populations to environment are highly scale-dependent. At large scales, carnivoran richness is largely independent of temperature and precipitation, whereas hibian richness correlates strongly with precipitation and temperature, and anti-correlates with temperature range. These results pave the way for spectral-based calibration of models that predict bio ersity response to climate change scenarios.
Publisher: Springer Science and Business Media LLC
Date: 06-05-2019
DOI: 10.1038/S41598-019-43476-0
Abstract: We apply teleseismic P-wave tomography to reconstruct the velocity structure of the Longmenshan area. Our results show possible large-scale delamination beneath the Songpan-Ganzi and Qiangtang terranes, which induced upwelling asthenosphere. Upwelling asthenosphere might have led to lower crust heating, facilitating eastward extrusion of the Songpan Ganzi terrane resulting in localized deformation and uplift along the Longmenshan orogenic belt. We suggest that the eastward extrusion of the Songpan-Ganzi terrane against the rigid lithospheric root of the Sichuan Basin results in stress accumulation and release, leading to large earthquakes in the Longmenshan area.
Publisher: Geological Society of London
Date: 2007
DOI: 10.1144/SP280.15
Publisher: Society of Exploration Geophysicists
Date: 05-2019
Abstract: The acoustic property and the P-wave velocity of partially saturated rocks depend not only on the water saturation but also on the pore-scale fluid distribution. Here, we analyzed the pore-scale fluid distribution using nuclear magnetic resonance (NMR) [Formula: see text] spectra, which present the variation of porosity components associated with NMR transverse relaxation time [Formula: see text]. Based on the [Formula: see text] spectra, we classified the pore-scale fluid distribution during water imbibition and drainage into three models: a low-saturation model, a patchy distribution model, and a uniform distribution model. We specifically assigned the low-saturation model to deal with the acoustic property of the rocks at the imbibition starting stage and the drainage final stage because cement softening has a nonnegligible effect. We studied the acoustic properties of sandstone rocks with various pore-scale fluid distributions, at the imbibition process and the drainage process. We confirmed that, once the variations in water saturation and pore-scale fluid distribution are taken into account, the P-wave velocity prediction matches well with the laboratory measurement of s les, representing nearly tight sandstone rocks that are partially saturated with distilled water.
Publisher: Springer Science and Business Media LLC
Date: 10-2000
DOI: 10.1007/PL00001052
Publisher: Society of Exploration Geophysicists
Date: 07-2009
DOI: 10.1190/1.3122408
Abstract: In seismic multiple attenuation, once the multiple models have been built, the effectiveness of the processing depends on the subtraction step. Usually the primary energy is partially attenuated during the adaptive subtraction if an [Formula: see text]-norm matching filter is used to solve a least-squares problem. The expanded multichannel matching (EMCM) filter generally is effective, but conservative parameters adopted to preserve the primary could lead to some remaining multiples. We have managed to improve the multiple attenuation result through an iterative application of the EMCM filter to accumulate the effect of subtraction. A Butterworth-type masking filter based on the multiple model can be used to preserve most of the primary energy prior to subtraction, and then subtraction can be performed on the remaining part to better suppress the multiples without affecting the primaries. Meanwhile, subtraction can be performed according to the orders of the multiples, as a single subtraction window usually covers different-order multiples with different litudes. Theoretical analyses, and synthetic and real seismic data set demonstrations, proved that a combination of these three strategies is effective in improving the adaptive subtraction during seismic multiple attenuation.
Publisher: Oxford University Press (OUP)
Date: 31-01-2019
DOI: 10.1093/JGE/GXY016
Publisher: Wiley
Date: 03-2011
DOI: 10.1111/J.1442-2018.2011.00586.X
Abstract: Patients living with end-stage renal disease experience different levels of physical and psychological disability that can impact on the type and level of social interaction in which they engage with others. The researchers concurrently collected and thematically analyzed the interview data that were generated from 21 participants who were undergoing hemodialysis in Iran. Four major themes were constructed from the analysis of the transcripts: living with fatigue changes in self-image patients' dependency on the device, place, and time of hemodialysis and hiding the disease. The results from this study showed that the patients who were living with hemodialysis in Iran experienced altered social interactions with others. The culture of Iran resulted in the participants trying to hide their disease from others, which led to social avoidance, thus reducing the participants' social interactions with others. It is recommended that nurses include a comprehensive assessment of the social interactions of persons who are receiving hemodialysis in their overall nursing assessment and that this is reviewed on a regular basis.
Publisher: Springer Netherlands
Date: 2011
Publisher: Oxford University Press (OUP)
Date: 13-01-2011
Publisher: Society of Exploration Geophysicists
Date: 09-2015
Abstract: The study of thin-bed seismic response is an important part in lithologic and methane reservoir modeling, critical for predicting their physical attributes and/or elastic parameters. The complex propagator matrix for the exact reflections and transmissions of thin beds limits their application in thin-bed inversion. Therefore, approximation formulas with a high accuracy and a relatively simple form are needed for thin-bed seismic analysis and inversion. We have derived thin-bed reflection and transmission coefficients, defined in terms of displacements, and approximated them to be in a quasi-Zoeppritz matrix form under the assumption that the middle layer has a very thin thickness. We have verified the approximation accuracy through numerical calculation and concluded that the errors in PP-wave reflection coefficients [Formula: see text] are generally smaller than 10% when the thin-bed thicknesses are smaller than one-eighth of the PP-wavelength. The PS-wave reflection coefficients [Formula: see text] have lower approximation accuracy than [Formula: see text] for the same ratios of thicknesses to their respective wavelengths, and the [Formula: see text] approximation is not acceptable for incident angles approaching the critical angles (when they exist) except in the case of extremely strong impedance difference. Errors in phase for the [Formula: see text] and [Formula: see text] approximation are less than 10% for the cases of thicknesses less than one-tenth of the wavelengths. As expected, a thinner middle layer and a weaker impedance difference would result in higher approximation accuracy.
Publisher: Oxford University Press (OUP)
Date: 13-08-2020
DOI: 10.1093/JGE/GXAA051
Abstract: A shot-encoding technique can be used in seismic waveform inversion to significantly reduce the computational cost by reducing the number of seismic simulations in the inversion procedure. Here we developed two alternative shot-encoding schemes to perform simultaneous-sources waveform inversion. The first scheme (I) encodes shot gathers with random-phase rotations applied to seismic traces. The second scheme (II) encodes shot gathers with random static time shifts. The well-known polarity encoding scheme (III) is just a special case of the random-phase rotation scheme. The second scheme is a variation of the conventional static shift encoding (IV), but the static time shifts in the second scheme are limited to one period of the dominant frequency. All encoded shot gathers are added up into a single super-shot gather for seismic waveform inversion. We perform the time-domain waveform inversion, using these shot-encoding schemes in conjunction with a restarted L-BFGS algorithm in the iterative inversion. The effectiveness and efficiency analyses demonstrate that the two shot-encoding schemes (I and II) proposed in this paper may improve the convergence of the iterative inversion, reduce the crosstalk effect among shots and consequently produce a subsurface velocity model with a high resolution.
Publisher: Springer Science and Business Media LLC
Date: 07-06-2018
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2023
Publisher: Oxford University Press (OUP)
Date: 11-06-2013
DOI: 10.1093/GJI/GGT190
Publisher: Centers for Disease Control and Prevention (CDC)
Date: 08-2009
Publisher: Oxford University Press (OUP)
Date: 07-2000
Publisher: Society of Exploration Geophysicists
Date: 03-2002
DOI: 10.1190/1.1468627
Abstract: Stability and efficiency are two issues of general concern in inverse Q filtering. This paper presents a stable, efficient approach to inverse Q filtering, based on the theory of wavefield downward continuation. It is implemented in a layered manner, assuming a depth‐dependent, layered‐earth Q model. For each in idual constant Q layer, the seismic wavefield recorded at the surface is first extrapolated down to the top of the current layer and a constant Q inverse filter is then applied to the current layer. When extrapolating within the overburden, instead of applying wavefield downward continuation directly, a reversed, upward continuation system is solved to obtain a stabilized solution. Within the current constant Q layer, the litude compensation operator, which is a 2‐D function of traveltime and frequency, is approximated optimally as the product of two 1‐D functions depending, respectively, on time and frequency. The constant Q inverse filter that compensates simultaneously for phase and litude effects is then implemented efficiently in the Fourier domain.
Publisher: Oxford University Press (OUP)
Date: 23-05-2016
Publisher: Oxford University Press (OUP)
Date: 22-08-2005
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Boon Huan Tan.