Publications
145 results found
Song C, Wang Y, 2023, Simulating seismic multifrequency wavefields with the Fourier feature physics-informed neural network, GEOPHYSICAL JOURNAL INTERNATIONAL, Vol: 232, Pages: 1503-1514, ISSN: 0956-540X
Hao Y, Bell R, Rao Y, et al., 2023, Prediction of Permian karst reservoirs in the Yuanba gas field, northern Sichuan basin, China, Marine and Petroleum Geology, Vol: 154, Pages: 1-12, ISSN: 0264-8172
Karst reservoir has great hydrocarbon potential, however karst reservoir prediction is inhibited by the strong lateral and vertical heterogeneity of karstification which in turn results in recognition difficulty when geological and geophysical methods are used in isolation. Combined geological and geophysical methods, including core observation, thin section analysis, well log interpretation, seismic attributes and seismic inversion are applied to understand the depositional environment, types of karstification, the geophysical response and distribution of karst reservoir and the controls over and evolution model of karst reservoir in Permian Yuanba gas field, northern Sichuan Basin. The results show that there are four types of major seismic facies recognized in the study area, which correspond to platform margin reef, carbonate platform, platform margin inter-bay and platform margin slope. Karstification can be divided into three zones: the supergene karst zone, the vertical seepage zone and the horizontal underflow zone, among which the supergene karst zone have the strongest karstification. Karstification is highlighted with low seismic impedance, low Poisson's ratio, and high seismic attenuation on seismic inversion as well as micro scale paleo geomorphology recognized by trend surface analysis. By comparing the distribution of karstification with paleo geomorphology, fault distribution and gas contents, it can be observed that the karstification have a good matching relationship with these factors. The dominant type of karstification is epigenic karst, which is strongly influenced by depositional facies and paleo geomorphology. Fracture networks have contributed to karstification but are not the dominant factor of karst formation. The integration of geological and geophysical methods can predict karst reservoir with high accuracy within large area and can be applied to karst reservoir hydrocarbon exploration of similar geological setting.
Song C, Wang Y, Richardson A, et al., 2023, Weighted envelope correlation-based waveform inversion using automatic differentiation, IEEE Transactions on Geoscience and Remote Sensing, ISSN: 0196-2892
Yu Y, Luo Y, Cilliers J, et al., 2023, Numerical solution of the electric field and dielectrophoresis force of electrostatic traveling wave system, Micromachines, Vol: 14, Pages: 1347-1347, ISSN: 2072-666X
Electrostatic traveling wave (ETW) methods have shown promising performance in dust mitigation of solar panels, particle transport and separation in in situ space resource utilization, cell manipulation, and separation in biology. The ETW field distribution is required to analyze the forces applied to particles and to evaluate ETW design parameters. This study presents the numerical results of the ETW field distribution generated by a parallel electrode array using both the charge simulation method (CSM) and the boundary element method (BEM). A low accumulated error of the CSM is achieved by properly arranging the positions and numbers of contour points and fictitious charges. The BEM can avoid the inconvenience of the charge position required in the CSM. The numerical results show extremely close agreement between the CSM and BEM. For simplification, the method of images is introduced in the implementation of the CSM and BEM. Moreover, analytical formulas are obtained for the integral of Green’s function along boundary elements. For further validation, the results are cross-checked using the finite element method (FEM). It is found that discrepancies occur at the ends of the electrode array. Finally, analyses are provided of the electric field and dielectrophoretic (DEP) components. Emphasis is given to the regions close to the electrode surfaces. These results provide guidance for the fabrication of ETW systems for various applications.
Gao F, Wang Y, 2023, Seismic waveform tomography for 3D impedance model with salt structure, Pure and Applied Geophysics, Vol: 180, Pages: 2577-2587, ISSN: 0033-4553
Conventional impedance inversion from post-stack zero-offset seismic data is usually based on the convolution model, and wave-equation based inversion is rarely used, although it is capable to precisely describe seismic wave propagation and invert impedance model with higher resolution. That is because there are more than one physical parameters involved in the conventional wave equation, making impedance inversion complicated. In this study, a one-dimensional (1D) wave equation, containing only the impedance parameter, is adopted and applied for the inversion of 1D impedance model by seismic waveform tomography. However, for a three-dimensional (3D) model, direct application of the 1D waveform tomography may lead to lateral discontinuities. Therefore, we propose to utilize a truncated Fourier series to parameterize the 3D impedance model, and then invert for the Fourier coefficients. With this parameterization scheme, the large- and small-scale components of the impedance model can be reconstructed stepwise by gradually increasing the number of Fourier coefficients. To efficiently and effectively invert the coefficients for the 3D model with salt structure, we propose a joint strategy, in which the low-frequency seismic data is used to invert for the Fourier coefficients representing the large-scale components of the model, while the high-frequency seismic data is applied to invert for the Fourier coefficients representing the small-scale components of the model. Tests on a 3D impedance model with salt structure result in models with high resolution and good spatial continuity, proving the feasibility and stability of the impedance inversion procedure.
O'Malley CPB, Roberts GG, Mannion PD, et al., 2023, Coherence of terrestrial vertebrate species richness with external drivers across scales and taxonomic groups, Global Ecology and Biogeography, Vol: 32, Pages: 1285-1301, ISSN: 1466-822X
Aim: Understanding connections between environment and biodiversity is crucial for conservation, identifying causes of ecosystem stress, and predicting population responses to changing environments. Explaining biodiversity requires an under-standing of how species richness and environment covary across scales. Here, we identify scales and locations at which biodiversity is generated and correlates with environment.Location: Full latitudinal range per continent.Time Period: Present day.Major Taxa Studied: Terrestrial vertebrates: all mammals, carnivorans, bats, song-birds, hummingbirds, amphibians.Methods: 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 (ΔT).Results: >97% of species richness of taxa studied is generated at large scales, that is, wavelengths ≳103 km, with 30%–69% generated at scales ≳104 km. At these scales, richness tends to be highly coherent and anti-correlated with E and ΔT, and positively correlated with Pn and Tm. Coherence between carnivoran richness and ΔT is low across scales, implying insensitivity to seasonal temperature variations. Conversely, amphibian richness is strongly anti-correlated with ΔT at large scales. At scales ≲103 km, examined taxa, except carnivorans, show highest richness within the trop-ics. Terrestrial plateaux exhibit high coherence between carnivorans and E at scales ∼103 km, consistent with contribution of large-scale tectonic processes to biodiver-sity. 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.Main Conclusions: Sensitivities of ma
Yu Y, Cilliers J, Hadler K, et al., 2023, The motion of small particles in electrostatic travelling waves for transport and separation, Powder Technology, Vol: 425, Pages: 1-16, ISSN: 0032-5910
Electrostatic travelling waves can be used to transport small particles across a surface. This technology has received particular attention for dust mitigation on solar panels and for manipulating small particles on the Moon as part of in-situ resource utilization processes. Electrostatic travelling wave systems have no moving parts and are particularly well suited to low humidity environments. Here, we analyse the motion of small particles with the aim of exploiting differences in motion and velocity to separate particles by size. We investigate the effects of voltage, frequency, particle size and charge, wavelength and initial conditions on the properties of particle motion, such as particle velocity, levitation height and motion mode. We calculate the electrostatic fields using accurate boundary conditions based on the Fourier expansion method, which shows more detail near the surface of electrodes. We solve the equations of motion using the implicit Runge-Kutta method, and measure the particle charge with a free fall system. We show that the numerical results have a good agreement with the analytical results of a particle moving in a certain mode. We have observed three modes of motion with a high-speed camera, and these results provide guidance for the development of electrostatic travelling wave systems for various applications.
Gao F, Rao Y, Zhu T, et al., 2023, 3D seismic inversion by model parameterization with Fourier coefficients, IEEE Transactions on Geoscience and Remote Sensing, Vol: 61, Pages: 1-16, ISSN: 0196-2892
In seismic inversion, the subsurface model can be parameterized by a truncated Fourier series, and the inversion problem is then the inversion of the Fourier coefficients. To improve the efficiency of the evaluation of the Fourier coefficients and the reconstruction of the model from the inverted coefficients, we propose to use the efficient implementation of the fast Fourier transform (FFT) to speed up these two calculations. By using the FFT pair, the computation time for 3D subsurface models with realistic size could be reduced by two to three orders of magnitude compared to conventional methods. When this model parameterization scheme is applied to seismic impedance inversion, we proposed two strategies to further improve the efficiency. One is to invert the Fourier coefficients from small-valued numbers to large-valued numbers, and the other is to divide the seismic data into subgroups and use part of them for the inversion of the Fourier coefficients. Both strategies are helpful for efficient inversion of the Fourier coefficients from the seismic data. Moreover, thanks to this model parameterization scheme, the Fourier coefficients are inverted in a multi-trace manner, and the impedance model reconstructed from the inverted Fourier coefficients has good spatial continuity. The scheme is able to generate stable and continuous impedance models from the inversion of seismic data with missing traces, with affordable computation times.
Cai S, Fang F, Wang Y, 2023, Nonstationary seismic-well tying with time-varying wavelets, Geophysics, Vol: 88, Pages: M145-M155, ISSN: 0016-8033
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.
Zhao Z, Rao Y, Wang Y, 2023, The W transform with a chirp-modulated window, GEOPHYSICS, Vol: 88, Pages: V93-V100, ISSN: 0016-8033
A high-resolution time-frequency spectrum is desirable for processing and interpreting seismic data. The standard W transform is a method that effectively preserves the resolution in the low-frequency region of the time-frequency spectrum of non-stationary seismic signals. To further increase the energy concentration of the time-frequency spectrum estimated with the standard 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. Unlike the general linear chirplet transform, the chirp rate in the proposed algorithm 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 GPU computations. The application of the proposed algorithm to synthetic and field data shows that the frequency anomalies can be easily identified with the proposed algorithm.
Zhao Z, Rao Y, Wang Y, 2023, Structure-adapted Multichannel Matching Pursuit for Seismic Trace Decomposition, PURE AND APPLIED GEOPHYSICS, ISSN: 0033-4553
Xu Q, Wang Y, 2023, Determination of the viscoelastic parameters for the generalized viscoelastic wave equation, GEOPHYSICAL JOURNAL INTERNATIONAL, Vol: 233, Pages: 875-884, ISSN: 0956-540X
Yao J, Warner M, Wang Y, 2023, Regularization of anisotropic full-waveform inversion with multiple parameters by adversarial neural networks, Geophysics, Vol: 88, Pages: R95-R103, ISSN: 0016-8033
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.
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Wang G, Chen S, Wang Y, 2022, Direct inversion for the equivalent pore aspect ratio based on the theory of ellipsoid modelling, Geophysical Prospecting, ISSN: 0016-8025
<jats:title>Abstract</jats:title><jats:p>Pore aspect ratio, together with porosity, is a structural parameter that represents the geometric property of rock reservoirs. We have adopted the theory of ellipsoid modelling in material mechanics to derive the dry rock modulus. Based on this derivation, the Gassmann equation, which is a constitutional equation for a fully saturated rock model, can be linearized in terms of the pore structure parameters and the elastic parameters. We have established a relationship between the seismic reflection coefficient and the pore structure parameters, where the equivalent pore aspect ratio and porosity are two key parameters. Based on this relationship, the equivalent pore aspect ratio can be inverted directly from seismic reflection data instead of being converted from the intermediate parameters of conventional seismic inversion. Therefore, seismic inversion is a simultaneous inversion in which seven parameters are inverted: the elastic moduli (matrix bulk modulus and shear modulus, fluid bulk modulus), the densities (matrix and fluid densities) and the pore structure parameters (the equivalent pore aspect ratio and porosity). We applied this direct inversion scheme to a carbonate reservoir to predict the fracture development zone with low porosity and low aspect ratio.</jats:p>
Zhang H, Brito-Parada PR, Neethling SJ, et al., 2022, Yield stress of foam flow in porous media: The effect of bubble trapping, COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS, Vol: 655, ISSN: 0927-7757
Wang Y, 2022, Time–frequency Analysis of Seismic Signals, Publisher: Wiley, ISBN: 9781119892342
Time–frequency analysis of seismic signals aims to reveal the local properties of nonstationary signals. The local properties such as time-period, frequency, and spectral content are varying with time, and the time of a seismic signal is a proxy of geologic depth. Therefore, the time–frequency spectrum is composed of the frequency spectra that are generated by using the classic Fourier transform at different time positions. Different time–frequency analysis methods are distinguished in the construction of the local kernel prior to using the Fourier transform. Based on the difference in constructing the Fourier transform kernel, this book divides time–frequency analysis methods into two groups, the Gabor transform-type methods and the energy density distribution methods. This book provides a practical guide to geophysicists who attempt to generate geophysically meaningful time–frequency spectra, who attempt to process seismic data with time-dependent operations for the fidelity of nonstationary ...
Wang Y, 2022, Time-frequency domain local spectral analysis of seismic signals with multiple windows, PROCEEDINGS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES, Vol: 478, ISSN: 1364-5021
Yu Y, Cilliers J, Hadler K, et al., 2022, A review of particle transport and separation by electrostatic traveling wave methods, Journal of Electrostatics, Vol: 119, Pages: 1-16, ISSN: 0304-3886
The controlled movement of dry particles using non-mechanical means is desirable in a number of different applications, including solar panel dust mitigation, toner particle motion and in the handling and beneficiation of regolith for In-Situ Resource Utilization (ISRU). The electric curtain, the electrostatic traveling wave (ETW) and the electro-dynamic screen (EDS) are examples of techniques that can transport and separate particles with no moving parts nor fluid medium. This review paper brings together the research carried out on these techniques.We provide a comprehensive review on the particle movement mechanisms and the development and application of ETW methods, featuring a diverse range of hardware and circuitry, particulate material and process objectives. We focus on the evaluation of experimental development in the area of dust mitigation, particle transport and ISRU processes. We also detail the current knowledge about theory and modelling methods. Moreover, we provide a guide for possible improvement of the effectiveness of ETW devices, by outlining the limitations in application, theoretical understanding and potential research aspects.
Guo X, Shi Y, Wang W, et al., 2022, Suppressing migration noise in reverse time migration of vertical seismic profiles by multiple stacking estimation, GEOPHYSICS, Vol: 87, Pages: S223-S235, ISSN: 0016-8033
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Xu Q, Wang Y, 2022, Spatial filter for the pseudo-spectral implementation of fractional derivative wave equation, Pure and Applied Geophysics, Vol: 179, Pages: 2831-2840, ISSN: 0033-4553
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.
Yao J, Warner M, Wang Y, 2022, Generating surface-offset common-image gathers with backward wavefield synthesis, GEOPHYSICS, Vol: 87, Pages: S129-S135, ISSN: 0016-8033
Song C, Wang Y, 2022, High-frequency wavefield extrapolation using the Fourier neural operator, JOURNAL OF GEOPHYSICS AND ENGINEERING, Vol: 19, Pages: 269-282, ISSN: 1742-2132
Yao J, Wang Y, 2022, Building a full-waveform inversion starting model from wells with dynamic time warping and convolutional neural networks, GEOPHYSICS, Vol: 87, Pages: R223-R230, ISSN: 0016-8033
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Ni J, Gu H, Wang Y, 2022, Seismic wave equation formulated by generalized viscoelasticity in fluid-saturated porous media, GEOPHYSICS, Vol: 87, Pages: T111-T121, ISSN: 0016-8033
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Alsalmi H, Wang Y, 2021, Mask filtering to the Wigner-Ville distribution, GEOPHYSICS, Vol: 86, Pages: V489-V496, ISSN: 0016-8033
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Jamali J, Javaherian A, Wang Y, et al., 2021, The behavior of elastic moduli with fluid content in the VTI media, JOURNAL OF PETROLEUM SCIENCE AND ENGINEERING, Vol: 208, ISSN: 0920-4105
Wu D, Wang Y, Cao J, et al., 2021, Least-squares reverse-time migration with sparsity constraints, JOURNAL OF GEOPHYSICS AND ENGINEERING, Vol: 18, Pages: 304-316, ISSN: 1742-2132
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Izadian S, Aghazade K, Amini N, et al., 2021, Semi-exact local absorbing boundary condition for seismic wave simulation, JOURNAL OF GEOPHYSICS AND ENGINEERING, Vol: 18, Pages: 62-73, ISSN: 1742-2132
Wang Y, 2021, The W transform, GEOPHYSICS, Vol: 86, Pages: V31-V39, ISSN: 0016-8033
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Rosa DR, Santos JMC, Souza RM, et al., 2020, Comparing different approaches of time-lapse seismic inversion, JOURNAL OF GEOPHYSICS AND ENGINEERING, Vol: 17, Pages: 929-939, ISSN: 1742-2132
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