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Results
Efficient reverse time migration method in tilted transversely isotropic media based on a pure pseudoacoustic wave equation
Han, Jiale (China University of Petroleum (East China)) | Huang, Jianping (China University of Petroleum (East China)) | Shen, Yi (China University of Petroleum (East China)) | Yang, Jidong (China University of Petroleum (East China)) | Mu, Xinru (China University of Petroleum (East China)) | Chen, Liang (China University of Petroleum (East China))
ABSTRACT In general, velocity anisotropy in shale media has been widely observed in laboratory and field work, which means that disregarding this characteristic can lead to inaccurate imaging locations when data are imaged with reverse time migration (RTM). Wavefields simulated with the conventional coupled pseudoacoustic wave equation may introduce S-wave noise and this equation is only valid in transversely isotropic media (). Certain decoupled qP-wave equations require the use of the pseudospectral method, which makes them computationally inefficient. To address these issues, we develop a new pure qP acoustic wave equation based on the acoustic assumption, which can be solved more efficiently using the finite-difference (FD) method. This equation can also be used in the forward-modeling process of RTM in tilted transversely isotropic (TTI) media. First, we perform a Taylor expansion of the root term in the pure qP-wave dispersion relation. This leads to an anisotropic dispersion relation that is decomposed into an elliptical anisotropic background factor and a circular correction factor. Second, we obtain the pure qP-wave equation in TTI media without a pseudodifferential operator. The new equation can be efficiently solved using FD methods and can be applied to RTM in TTI media with strong anisotropy. Our method indicates greater tolerance to numerical errors and is better suited for strong anisotropy, as compared with previously published methods. Numerical examples indicate the high kinematic and phase accuracy of our pure qP-wave equation along with its stability in TTI media characterized by (). By using a sag model and an overthrust TTI model, we determine the efficiency and accuracy of our TTI RTM.
- Asia > China > Shanxi > Ordos Basin > Changqing Field (0.99)
- Asia > China > Shaanxi > Ordos Basin > Changqing Field (0.99)
- Asia > China > Ningxia > Ordos Basin > Changqing Field (0.99)
- (2 more...)
GAN-enhanced directional seismic wavefield decomposition and its application in reverse-time migration
Sun, Jiaxing (China University of Petroleum (East China)) | Yang, Jidong (China University of Petroleum (East China)) | Huang, Jianping (China University of Petroleum (East China)) | Yu, Youcai (China University of Petroleum (East China)) | Tian, Yiwei (China University of Petroleum (East China)) | Qin, Shanyuan (China University of Petroleum (East China))
Reverse time migration (RTM) is an accurate method for imaging complex geologic structures without imposing any dip limitations. However, a large amount of high-amplitude, low-frequency noise, which is mainly generated by the crosscorrelation of source and receiver wavefields propagating in the same directions, seriously contaminates the image quality. The causal imaging condition with separated up- and downgoing wavefields is an effective approach to reduce these low-frequency artifacts. Explicit up- and downgoing wavefield decomposition based on the Hilbert transform is computationally expensive due to additional wavefield extrapolation and storage for the imaginary parts. Directionally propagating wavefield has distinctive kinematic patterns such as traveltime and wavefront curvature, which provides us an opportunity to implement the wavefield decomposition using the statistical neural network method. Using extrapolated wavefields as the input and the decomposed up-, down-, left- and rightgoing wavefields as the labeled data, we train a pair of generative adversarial networks to predict directional wavefields. The training datasets are generated using seismic full-waveform modeling and explicit wavefield decomposition based on the Hilbert transform. Then, the decomposed directional wavefields are incorporated into a novel imaging condition that depends on subsurface dip angles to compute the reflectivity perpendicular to reflectors. Numerical experiments demonstrate that the proposed method can produce accurate directional wavefield decomposition results and high-quality reflectivity images without low-wavenumber artifacts.
Efficient reverse time migration method in TTI media based on a pure pseudo-acoustic wave equation
Han, Jiale (China University of Petroleum (East China)) | Huang, Jianping (China University of Petroleum (East China)) | Shen, Yi (China University of Petroleum (East China)) | Yang, Jidong (China University of Petroleum (East China)) | Mu, Xinru (China University of Petroleum (East China)) | Chen, Liang (China University of Petroleum (East China))
In general, velocity anisotropy in shale media has been widely observed in lab and field work, which means that disregarding this characteristic can lead to inaccurate imaging locations when data are imaged with reverse time migration (RTM). Wavefields simulated with the conventional coupled pseudo-acoustic wave equation may introduce shear wave noise and this equation is only valid in transversely isotropic media (TI, ). Certain decoupled qP-wave equations require the use of the pseudo-spectral method, which makes them computationally inefficient. To address these issues, we propose a new pure qP acoustic wave equation based on the acoustic assumption, which can be solved more efficiently using the finite difference method. This equation can also be used in the forward modeling process of RTM in tilted transverse isotropic (TTI) media. First, we perform a Taylor expansion of the root term in the pure qP-wave dispersion relation. This leads to an anisotropic dispersion relation that is decomposed into an elliptical anisotropic background factor and a circular correction factor. Second, we obtain the pure qP-wave equation in TTI media without a pseudo-differential operator. The new equation can be efficiently solved using finite difference methods and can be applied to RTM in TTI media with strong anisotropy. The proposed method shows greater tolerance to numerical errors and is better suited for strong anisotropy, as compared to previously published methods. Numerical examples show the high kinematic and phase accuracy of the proposed pure qP-wave equation along with its stability in TTI media characterized by (). By utilizing a sag model and an overthrust TTI model, we demonstrate the efficiency and accuracy of the proposed TTI RTM.
- Asia > China > Shanxi > Ordos Basin > Changqing Field (0.99)
- Asia > China > Shaanxi > Ordos Basin > Changqing Field (0.99)
- Asia > China > Ningxia > Ordos Basin > Changqing Field (0.99)
- (2 more...)
A simple and high-efficiency viscoacoustic reverse time migration calculated by finite difference
Mu, Xinru (China University of Petroleum (East China), Pilot National Laboratory for Marine Science and Technology (Qingdao)) | Huang, Jianping (China University of Petroleum (East China), Pilot National Laboratory for Marine Science and Technology (Qingdao))
ABSTRACT The viscoacoustic wave equation with decoupled amplitude attenuation and phase dispersion terms is convenient for implementing reverse time migration (RTM) in attenuating media. However, the traditional viscoacoustic wave equations are expressed by the fractional Laplacian, which requires computationally expensive fast Fourier transforms to perform numerical solutions. This is not conducive for commercial applications with seismic data in terabyte, particularly in three dimensions. Based on the memory-variable-represented viscoacoustic wave equation, the new dispersion- and dissipation-dominated wavefield extrapolation operators that can be solved using the economical finite-difference method (FDM) are developed. In numerical simulation, the staggered-grid FDM is used to solve the temporal and spatial derivatives. The computational efficiency analysis indicates that, compared to the traditional viscoacoustic wave equation, the new viscoacoustic wave equation has an efficiency improvement of approximately more than two times. The accuracy of simulations of amplitude attenuation and phase dispersion is evaluated in viscoacoustic media with varying Q values. The proposed viscoacoustic wave equation is also extended to Q-compensated RTM. Two synthetic tests and one field data test indicate that the Q-compensated RTM can produce high-resolution images by correcting phase dispersion and compensating amplitude loss.
The viscoacoustic wave equation with decoupled amplitude attenuation and phase dispersion terms is convenient for implementing reverse time migration (RTM) in attenuating media. However, the traditional viscoacoustic waves are expressed by the fractional Laplacian, which requires computationally expensive fast Fourier transforms to perform numerical solutions. This is not conducive for commercial applications with seismic data in terabyte, particularly in 3D. Based on the memory-variable-represented viscoacoustic wave equation, we develop new dispersion-dominated and dissipation-dominated wavefield extrapolation operators that can be solved using the economic finite difference method (FDM). In numerical simulation, the staggered grid FDM is used to solve the temporal and spatial derivatives. The computational efficiency analysis shows that, compared to the traditional viscoacoustic wave equation, the new viscoacoustic wave equation has an efficiency improvement of approximately more than two times. The accuracy of simulations of amplitude attenuation and phase dispersion is evaluated in viscoacoustic media with varying Q values. We also extend the proposed viscoacoustic wave equations to Q-compensated RTM. Two synthetic tests and one field data test show that the Q-compensated RTM can produce high-resolution images by correcting phase dispersion and compensating amplitude loss.
Hierarchical wave-mode separation in the poroelastic medium using eigenform analysis
Tian, Yiwei (China University of Petroleum) | Yang, Jidong (China University of Petroleum) | Li, Zhenchun (China University of Petroleum) | Huang, Jianping (China University of Petroleum) | Qin, Shanyuan (China University of Petroleum)
ABSTRACT In the elastic medium, the scalar and vector P- and S-waves decomposition has been extensively studied and some strategies can be extended to the poroelastic medium to extract P- and S-wavefields. However, there are three propagation modes in the poroelastic medium in Biot’s theory, namely, a fast P wave, a slow P wave, and an S wave. Because the propagation characteristic of a slow P wave is different from that of a fast P wave and S wave, the wavefield separation methods in the elastic medium cannot be directly applied to the poroelastic medium to produce a complete wave-mode separation. Based on the eigenform analysis, we have developed a hierarchical wavefield decomposition method to completely separate S waves and fast and slow P waves in the poroelastic medium. Using the Helmholtz decomposition, we first compute scalar and vector potential wavefields to separate P and S waves. Then, a cross-product operator is proposed to decompose fast and slow P waves based on their different polarization directions. To produce correct amplitudes and phases, we apply another cross-product operator and an amplitude correction term to the separated wavefields. Three numerical examples demonstrate that our method can produce accurate fast P-wave, slow P-wave, and S-wave separation results, and the decomposed fast and slow P waves have the same phases and amplitudes as the P-wave potential wavefields.
ABSTRACT In exploration seismology, reflections have been extensively used for imaging and inversion to detect hydrocarbon and mine resources, which are generated from subsurface continuous impedance interfaces. When the interface is not continuous and its size reduces to less than half-wavelength, reflected wave becomes diffraction. Reflections and diffractions can be used to image subsurface targets, and the latter is helpful to resolve small-scale discontinuities, such as fault plane, pinch out, Karst caves, and salt edge. However, the amplitudes of diffractions are usually much weaker than that of reflections. This makes it difficult to directly identify and extract diffractions from unmigrated common-shot or common-middle-point gathers. Migrating seismic data into a subsurface location for different reflector dip angles yields a dip-angle-domain common-image gather (DACIG). One DACIG represents the migrated traces at a fixed lateral position for different reflector dips. The reflection and diffraction have different geometric characteristics in DACIG, which provides one opportunity to separate diffractions and reflections. In this study, we present an efficient and accurate diffraction separation and imaging method using a convolutional neural network (CNN). The training data set of DACIGs is generated using one pass of seismic modeling and migration for velocity models with and without artificial scatterers, respectively. Then, a simplified end-to-end CNN is trained to identify and extract reflections from the migrated DACIGs that contain reflections and diffractions. Next, two adaptive subtraction strategies are presented to compute the diffraction DACIGs and stacked images, respectively. Numerical experiments for synthetic and field data demonstrate that the proposed method can produce accurate reflection and diffraction separation results in DACIGs, and the stacked image has a good resolution for subsurface small-scale discontinuities.
- Geology > Structural Geology (0.66)
- Geology > Rock Type > Sedimentary Rock (0.54)
- Geophysics > Seismic Surveying > Seismic Processing > Seismic Migration (1.00)
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling > Seismic Inversion (0.46)
Modeling of pure visco-qP-wave propagation in attenuating tilted transversely isotropic media based on decoupled fractional Laplacians
Mu, Xinru (China University of Petroleum (East China), Pilot National Laboratory for Marine Science and Technology (Qingdao)) | Huang, Jianping (China University of Petroleum (East China), Pilot National Laboratory for Marine Science and Technology (Qingdao)) | Yang, Jidong (China University of Petroleum (East China), Pilot National Laboratory for Marine Science and Technology (Qingdao)) | Zhang, Jianfeng (CNOOC China Limited) | Wang, Zhiliang (CNOOC China Limited)
ABSTRACT The pseudoviscoacoustic anisotropic wave equation is widely used in the oil and gas industry for modeling wavefields in attenuating anisotropic media. Compared to the full viscoelastic anisotropic wave equation, it can greatly reduce the computational cost of wavefield modeling while maintaining the visco-qP-wave kinematics very well. However, even if we place the source in a thin isotropic layer, there will be some unwanted S-wave artifacts in the qP wavefield simulated by the pseudoviscoacoustic anisotropic wave equation due to the stepped approximation of inclined layer interfaces. Furthermore, the wavefield simulated by the pseudoviscoacoustic anisotropic wave equation may suffer from numerical instabilities when the anisotropy parameter epsilon is less than delta. To overcome these problems, we derive a pure-viscoacoustic tilted transversely isotropic (TTI) wave equation in media with anisotropy in velocity and attenuation based on the exact complex-valued phase velocity formula. The pure-viscoacoustic TTI wave equation has decoupled amplitude dissipation and phase dispersion terms, which is suitable for further reverse time migration with Q compensation. For numerical simulations, we adopt the second-order Taylor series expansion to replace the mixed-domain spatially variable fractional Laplacian operator, which guarantees the decoupling of the wavenumber from the space-related fractional order. Then, we use an efficient and stable hybrid finite-difference and pseudospectral method (HFDPSM) to solve the pure-viscoacoustic TTI wave equation. Numerical tests indicate that the simulation results of the newly derived pure-viscoacoustic TTI wave equation are stable, free from S-wave artifacts, and accurate. We further demonstrate that HFDPSM outperforms the pseudospectral method in terms of numerical simulation stability and computing efficiency.
- Asia > China (0.46)
- North America > United States > Colorado (0.28)
- Geophysics > Seismic Surveying > Seismic Processing > Seismic Migration (1.00)
- Geophysics > Borehole Geophysics (1.00)
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling (0.92)
- North America > United States > Colorado > Piceance Basin > Williams Fork Formation (0.99)
- North America > United States > Colorado > Piceance Basin > Rulison Field > Mesaverde Formation (0.99)
Modeling viscoacoustic wave propagation using a new spatial variable-order fractional Laplacian wave equation
Mu, Xinru (China University of Petroleum (East China), Pilot National Laboratory for Marine Science and Technology (Qingdao)) | Huang, Jianping (China University of Petroleum (East China), Pilot National Laboratory for Marine Science and Technology (Qingdao)) | Wen, Lei (Yellow River Engineering Consulting Co., Ltd) | Zhuang, Subin (China University of Petroleum (East China), Pilot National Laboratory for Marine Science and Technology (Qingdao))
ABSTRACT We have developed a new time-domain viscoacoustic wave equation for simulating wave propagation in anelastic media. The new wave equation is derived by inserting the complex-valued phase velocity described by the Kjartansson attenuation model into the frequency-wavenumber domain acoustic wave equation. Our wave equation includes one second-order temporal derivative and two spatial variable-order fractional Laplacian operators. The two fractional Laplacian operators describe the phase dispersion and amplitude attenuation effects, respectively. To facilitate the numerical solution for our wave equation, we use the arbitrary-order Taylor series expansion (TSE) to approximate the mixed-domain fractional Laplacians and achieve the decoupling of the wavenumber and the fractional order. Then, our viscoacoustic wave equation can be directly solved using the pseudospectral method. We adopt a hybrid pseudospectral/finite-difference method (HPSFDM) to stably simulate wave propagation in arbitrarily complex media. We validate the high accuracy of our approximate dispersion term and approximate the dissipation term in comparison with the accurate dispersion term and accurate dissipation term. The accuracy of the numerical solutions is evaluated by comparison with the analytical solutions in homogeneous media. Theory analysis and simulation results indicate that our viscoacoustic wave equation has higher precision than the traditional fractional viscoacoustic wave equation in describing constant-Q attenuation. For a model with Q < 10, the calculation cost for solving the new wave equation with TSE HPSFDM is lower than that for solving the traditional fractional-order wave equation with TSE HPSFDM under the high numerical simulation precision. Furthermore, we examine the accuracy of HPSFDM in heterogeneous media using several numerical examples.
- Asia > China (0.46)
- North America (0.28)
- Geophysics > Seismic Surveying > Seismic Processing > Seismic Migration (1.00)
- Geophysics > Seismic Surveying > Seismic Modeling (1.00)
Viscoacoustic reverse time migration with a robust space-wavenumber domain attenuation compensation operator
Yang, Jidong (China University of Petroleum (East China)) | Huang, Jianping (China University of Petroleum (East China)) | Zhu, Hejun (The University of Texas at Dallas) | Li, Zhenchun (China University of Petroleum (East China)) | Dai, Nanxun (International Research and Development Center of BGP)
ABSTRACT Intrinsic attenuation gives rise to phase dispersion and amplitude loss during seismic wave propagation. Not correcting these effects in seismic imaging can result in inaccurate reflector locations, dimmed amplitudes, and degraded spatial resolution. In reverse time migration (RTM), attenuation compensation can be implemented by reversing the sign of the dissipation term and keeping the dispersion term unchanged for backward wavefield extrapolation. Although this Q-compensated RTM scheme can effectively correct attenuation effects, amplitude amplification during backpropagation might lead to numerical instabilities, especially for field data with strong high-frequency noise. To mitigate this problem, we have developed a robust space-wavenumber compensation operator and applied it to viscoacoustic RTM. By analyzing the dispersion-only and viscoacoustic Green’s functions, we obtain an analytical solution for the attenuation compensation operator in a homogeneous medium. Because it is a time-frequency operator, to apply it directly in viscoacoustic RTM requires access to the extrapolated wavefields within a certain time window. To avoid storing the wavefields and improve the computational efficiency, we use an approximated dispersion relation and convert the time-frequency operator to an equivalent space-wavenumber operator, which allows us to implement attenuation compensation on the fly during wavefield extrapolation. The hybrid-domain property of the operator enables us to account for the wavenumber-dependent compensation. A similar strategy also can be applied to the migrated images as a poststack processing approach, which is more efficient than the prestack compensation. Two synthetic and one land field data set examples demonstrate the feasibility and adaptability of our method.
- Asia > Middle East > Yemen (0.93)
- Asia > Middle East > Saudi Arabia (0.93)
- Africa > Sudan (0.93)
- (3 more...)