131 results found
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
<jats:p> 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. </jats:p>
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
<jats:title>Abstract</jats:title> <jats:p>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.</jats:p>
Guo X, Shi Y, Wang W, et al., 2022, Suppressing Migration Noise in VSP Reverse Time Migration by Multiple Stacking Estimation, GEOPHYSICS, Pages: 1-96, ISSN: 0016-8033
<jats:p> Reverse-time migration (RTM) has advantages of imaging steep dip structures but may inevitably produce migration swings when applied to vertical seismic profiles (VSP). These artifacts are often 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 multi-fold data while the noise is usually generated by a smaller subset of the data. A VSP RTM processing flow is proposed 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 stacking number. Then, the noise is suppressed by attenuating the imaging information of other dip angles. The EHTWD (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 multi wave 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 examples show that the presented method can significantly reduce migration noise and improve the image quality of VSP RTM. </jats:p>
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
<jats:p> 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. </jats:p>
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
<jats:p> 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 samples 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. </jats:p>
OMalley CPB, Roberts GG, Mannion PD, et al., 2022, Scale-Dependent Coherence of Terrestrial Vertebrate Biodiversity with Environment
<jats:title>Abstract</jats:title><jats:p>Disentangling contributions from environmental variables is crucial for explaining global biodiversity patterns. We use wavelet power spectra to separate wavelength-dependent trends across Earth’s surface. Spectra reveal scale- and location-dependent coherence between species richness and topography (<jats:italic>E</jats:italic>), annual precipitation (<jats:italic>P<jats:sub>n</jats:sub></jats:italic>), temperature (<jats:italic>T<jats:sub>m</jats:sub></jats:italic>) and temperature range (Δ<jats:italic>T</jats:italic>). > 97% of richness of carnivorans, bats, songbirds, hummingbirds and amphibians resides at wavelengths ≳ 10<jats:sup>3</jats:sup> km. 30–69% is generated at scales ≳ 10<jats:sup>4</jats:sup> km. At these scales, richness across the Americas is anti-correlated with <jats:italic>E</jats:italic> and Δ<jats:italic>T</jats:italic>, and positively correlated with <jats:italic>P<jats:sub>n</jats:sub></jats:italic> and <jats:italic>T<jats:sub>m</jats:sub></jats:italic>. Carnivoran richness is incoherent with Δ<jats:italic>T</jats:italic>, suggesting insensitivity to temperature seasonality. Conversely, amphibian richness is anti-correlated with Δ<jats:italic>T</jats:italic> at large scales. At scales ≲ 10<jats:sup>3</jats:sup> km, richness is highest within the tropics. Terrestrial plateaux exhibit coherence between carnivoran richness and <jats:italic>E</jats:italic> at scales ~ 10<jats:sup>3</jats:sup> km, reflecting contributions of orogeny/epeirogeny to biodiversity. Similar findings result from transects across other continents. Scale-dependent sensitivities of vertebrate populations to climate are revealed.</jats:p>
Alsalmi H, Wang Y, 2021, Mask filtering to the Wigner-Ville distribution, GEOPHYSICS, Vol: 86, Pages: V489-V496, ISSN: 0016-8033
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
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
Xie X, Wu K, Wang Y, et al., 2021, FREQUENCY ANALYZING BASED HYDROCARBON PROSPECTS CHARACTERIZATION OF PALAEOGENE HIGH AMPLITUDE SEISMIC ANOMALIES IN BOHAI OILFIELD, Pages: 2652-2656
High amplitude seismic anomalies are found to be commonly distributed within Paleogene strata in Liaodong Depression, Bohai Oilfield, which may be associated with the presence of hydrocarbon. In this paper, we have attempted to reveal the formation mechanism and then characterize the hydrocarbon prospects as well as spatial distribution of such bright spots. The research starts by rock physics analyzing of the drilled wells and forward modeling, which shows that gas sand with relatively low impedance and gravel sand with relatively high impedance both manifest as strong amplitude reflections. However, spectrum analysis demonstrates the differences between them in dominant frequency and bandwidth, and the result is further confirmed by spectral decomposition. The hydrocarbon-associated seismic anomalies are therefore distinguished from those “false bright spots” caused by other geologic factors through low-pass filtering based peak energy sum, which is then followed by frequency attenuation gradient (FAG) analysis for more accurate distribution of favorable areas and further risk mitigation.
Izadian S, Aghazade K, Amini N, et al., 2021, FINITE-DIFFERENCE FREQUENCY-DOMAIN MODELLING OF ACOUSTIC WAVE IN VTI MEDIA THROUGH PLANE WAVE INTERPOLATION, Pages: 3243-3247
We present a new finite difference scheme for the frequency-domain quasi-acoustic wave equations for vertical transversely isotropic (VTI) media. Compared to the optimized scheme, the proposed one enhances the overall performance and accuracy of the frequency domain solution as it significantly reduces the numerical dispersion error without any amount of extra cost. It improves upon the discretization rule of 4 grid points per minimum wavelength and reduces it to 2.5. The numerical examples of wave propagation in homogeneous and highly heterogenous models prove the validity and precision of the proposed scheme.
Li J, Wang B, Han D, et al., 2021, INTELLIGENT SEISMIC DEBLENDING BASED DEEP LEARNING BASED U-NET, Pages: 742-746
Blended acquisition can help improve the acquisition efficiency or enhance the data density. However, blended seismic data which contains information of multiple sources, should first be separated for traditional seismic data processing steps. Thus, we propose a U-net based intelligent deblending algorithm, combined with the traditional iterative strategy in this abstract. The proposed method can obtain the optimal parameters through self-learning while it should be selected by trial and error in traditional method. We train and valid the U-net by using a set of synthetic data with labels, and then parts of field data with labels are used to finetuned it. Finally, the finetuned U-net is used for intelligent deblending of the left field data. The deblending performance is promising compared with the curvelet transform based thresholding method, which demonstrates the validity of the proposed intelligent deblending algorithm in deblending accuracy, stability and efficiency.
Zhao Z, Wang Y, Chen J, 2021, TOPOGRAPHY-DEPENDENT FREQUENCY-DOMAIN FINITE-DIFFERENCE VISCO-ELASTIC WAVEFIELD SIMULATION, Pages: 2442-2446
In this research, we carried out topography-dependent frequency-domain finite-difference viscoelastic seismic wavefield simulation. Frequency-domain seismic wave equation in the curvilinear coordinate is obtained using the mapping relationship between the Cartesian coordinate to the curvilinear coordinate. By converting real-valued velocity to complex-valued velocity, attenuation effect is implemented to frequency-domain seismic wave equation. Numerical examples in the topography model verified the validity of the proposed algorithm.
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
Duarte EF, da Costa CAN, de Araujo JM, et al., 2020, Seismic shot-encoding schemes for waveform inversion, JOURNAL OF GEOPHYSICS AND ENGINEERING, Vol: 17, Pages: 906-913, ISSN: 1742-2132
Wang Y, Liu X, Gao F, et al., 2020, Robust vector median filtering with a structure-adaptive implementation, GEOPHYSICS, Vol: 85, Pages: V407-V414, ISSN: 0016-8033
Li H, Gao R, Wang Y, 2020, Predicting the thickness of sand strata in a sand-shale interbed reservoir based on seismic facies analysis, JOURNAL OF GEOPHYSICS AND ENGINEERING, Vol: 17, Pages: 592-601, ISSN: 1742-2132
Wang R, Wang Y, Rao Y, 2020, Seismic reflectivity inversion using an L1-norm basis-pursuit method and GPU parallelisation, JOURNAL OF GEOPHYSICS AND ENGINEERING, Vol: 17, Pages: 776-782, ISSN: 1742-2132
Wang Y, Rao Y, 2020, Seismic, Waveform Modeling and Tomography, Encyclopedia of Solid Earth Geophysics, 2nd edition, Editors: Gupta, Publisher: Springer, Cham, ISBN: 978-3-030-10475-7
Tomography. A seismic inversion method to produce slicing image of the internal structures of an object, by recording seismic wavefield propagating through and scattered-refracted-reflected back from the object and observing the difference in the effects on the wave energy impinging on those structures.
He F, Rao Y, Wang W, et al., 2020, Prediction of hydrocarbon reservoirs within coal-bearing formations, JOURNAL OF GEOPHYSICS AND ENGINEERING, Vol: 17, Pages: 484-492, ISSN: 1742-2132
Gao F, Wang Y, 2020, Radiation pattern analyses for seismic multi-parameter inversion of HTI anisotropic media, JOURNAL OF GEOPHYSICS AND ENGINEERING, Vol: 17, Pages: 65-75, ISSN: 1742-2132
Wang Y, Rao Y, Xu D, 2020, Multichannel maximum-entropy method for the Wigner-Ville distribution, GEOPHYSICS, Vol: 85, Pages: V25-V31, ISSN: 0016-8033
Liu J, Wang Y, 2020, Seismic simultaneous inversion using a multidamped subspace method, GEOPHYSICS, Vol: 85, Pages: R1-R10, ISSN: 0016-8033
Rao Y, Wang Y, 2020, Pore-pressure diffusion during water injection in fractured media, GEOPHYSICS, Vol: 85, Pages: MR51-MR56, ISSN: 0016-8033
Wang Y, 2019, A constant-Q model for general viscoelastic media, GEOPHYSICAL JOURNAL INTERNATIONAL, Vol: 219, Pages: 1562-1567, ISSN: 0956-540X
Liu Y, Xu T, Wang Y, et al., 2019, An efficient source wavefield reconstruction scheme using single boundary layer values for the spectral element method, EARTH AND PLANETARY PHYSICS, Vol: 3, Pages: 342-357, ISSN: 2096-3955
Shi Y, Zhang W, Wang Y, 2019, Seismic elastic RTM with vector-wavefield decomposition, JOURNAL OF GEOPHYSICS AND ENGINEERING, Vol: 16, Pages: 509-524, ISSN: 1742-2132
He C, Dong S, Wang Y, 2019, Lithospheric delamination and upwelling asthenosphere in the Longmenshan area: insight from teleseismic P-wave tomography, SCIENTIFIC REPORTS, Vol: 9, ISSN: 2045-2322
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