Intrinsic attenuation of the earth causes energy loss and phase distortion in seismic wave propagation.To obtain high-resolution imaging results,these negative effects must be considered during reverse time migration(...Intrinsic attenuation of the earth causes energy loss and phase distortion in seismic wave propagation.To obtain high-resolution imaging results,these negative effects must be considered during reverse time migration(RTM).We can easily implement attenuation-compensated RTM using the constant Q viscoacoustic wave equation with decoupled amplitude attenuation and phase dispersion terms.However,the nonphysical amplitude-compensation process will inevitably amplify the high-frequency noise in the wavefield in an exponential form,causing the numerical simulation to become unstable.This is due to the fact that the amplitude of the compensation grows exponentially with frequency.In order to achieve stable attenuation-compensated RTM,we modify the analytic expression of the attenuation compensation extrapolation operator and make it only compensate for amplitude loss within the effective frequency band.Based on this modified analytic formula,we then derive an explicit time-space domain attenuation compensation extrapolation operator.Finally,the implementation procedure of stable attenuation-compensated RTM is presented.In addition to being simple to implement,the newly proposed attenuation-compensated extrapolation operator is superior to the conventional low-pass filter in suppressing random noise,which will further improve the imaging resolution.We use two synthetic and one land seismic datasets to verify the stability and effectiveness of the proposed attenuationcompensated RTM in improving imaging resolution in viscous media.展开更多
Amplitude versus offset analysis is a fundamental tool for determining the physical properties of reservoirs but generally hampered by the blurred common image gathers(CIGs).The blurring can be optimally corrected usi...Amplitude versus offset analysis is a fundamental tool for determining the physical properties of reservoirs but generally hampered by the blurred common image gathers(CIGs).The blurring can be optimally corrected using the blockwise least-squares prestack time migration(BLS-PSTM),where common-offset migrated sections are divided into a series of blocks related to the explicit offsetdependent Hessian matrix and the following inverse filtering is iteratively applied to invert the corresponding reflectivity.However,calculating the Hessian matrix is slow.We present a fast BLS-PSTM via accelerating Hessian calculation with dip-angle Fresnel zone(DFZ).DFZ is closely related to optimal migration aperture,which significantly attenuates migration swings and reduces the computational cost of PSTM.Specifically,our fast BLS-PSTM is implemented as a two-stage process.First,we limit the aperture for any imaging point with an approximated the projected Fresnel zone before calculating the Hessian matrix.Then,we determine whether a seismic trace contributes to the imaging point via DFZ during calculating the Hessian matrix.Numerical tests on synthetic and field data validate the distinct speedup with higher-quality CIGs compared to BLS-PSTM.展开更多
The large storage requirement is a critical issue in cross-correlation imaging-condition based reverse time migration(RTM),because it requires the operation of the source and receiver wavefields at the same time.The b...The large storage requirement is a critical issue in cross-correlation imaging-condition based reverse time migration(RTM),because it requires the operation of the source and receiver wavefields at the same time.The boundary value method(BVM),based on the finite difference method(FDM),can be used to reconstruct the source wavefield in the reverse time propagation in the same way as the receiver wavefield,which can reduce the storage burden of the RTM data.Considering that the FDM cannot well handle models with discontinuous material properties and rough interfaces,we develop a source wavefield reconstruction strategy based on the finite element method(FEM),using proper orthogonal decomposition(POD)to enhance computational efficiency.In this method,we divide the whole time period into several segments,and construct the POD basis functions to get a reduced order model(ROM)for the source wavefield reconstruction in each segment.We show the corresponding quantitative analysis of the storage requirement of the POD-FEM.Numerical tests on the homogeneous model show the effectiveness of the proposed method,while the layered model and part of the Marmousi model tests indicate that the POD-FEM can keep an excellent balance between computational efficiency and memory usage compared with the full-stored method(FSM)and the BVM,and can be effectively applied in imaging.展开更多
Conventional seismic exploration method based on post-stack data usually fails to identify the distribution of fractured and caved carbonate reservoirs in the Tarim Basin,so the rich pre-stack information should be ap...Conventional seismic exploration method based on post-stack data usually fails to identify the distribution of fractured and caved carbonate reservoirs in the Tarim Basin,so the rich pre-stack information should be applied to the prediction of carbonate reservoirs.Amplitude-preserved seismic data processing is the foundation.In this paper,according to the feature of desert seismic data （including weak reflection,fast attenuation of high frequency components,strong coherent noises,low S/N and resolution）,a set of amplitude-preserved processing techniques is applied and a reasonable processing flow is formed to obtain the high quality data.After implementing a set of pre-stack amplitude-preserved processing,we test and define the kernel parameters of amplitude-preserved Kirchhoff PSTM （pre-stack time migration） and subsequent gathers processing,in order to obtain the amplitude-preserved gathers used to the isotropic pre-stack inversion for the identification of caved reservoirs.The AVO characteristics of obtained gathers fit well with the synthetic gathers from logging data,and it proves that the processing above is amplitudepreserved.The azimuthal processing techniques,including azimuth division and binning enlargement,are implemented for amplitude-preserved azimuthal gathers with the uniform fold.They can be used in the anisotropic inversion to detect effective fractures.The processing techniques and flows are applied to the field seismic data,and are proved available for providing the amplitude-preserved gathers for carbonate reservoir prediction in the Tarim Basin.展开更多
本实验以鲜肉和传统冰箱冻结(-18℃,36 h)为对照,探究低频交变磁场辅助冻结(low-frequency alternating magnetic field assisted freezing,LF-MFF)、-18℃条件下处理不同时间(12、24、36 h和48 h)对猪肉品质的影响,分析不同条件冻结处...本实验以鲜肉和传统冰箱冻结(-18℃,36 h)为对照,探究低频交变磁场辅助冻结(low-frequency alternating magnetic field assisted freezing,LF-MFF)、-18℃条件下处理不同时间(12、24、36 h和48 h)对猪肉品质的影响,分析不同条件冻结处理后肉样冻结速率、保水性、嫩度、色泽、pH值等理化特性、水分迁移及流变特性的变化。结果表明:与传统冰箱冻结相比,在3 mT低频交变磁场处理条件下,肉样的冻结速率更快,猪肉的品质得到明显改善(P<0.05);所有冻结方式处理中,LF-MFF 36~48 h可提高样品的保水性、色泽和嫩度(P<0.05),维持了更好的理化品质;低场核磁共振(low field nuclear magnetic resonance,LF-NMR)结果显示,与冰箱冻结相比,LF-MFF 36~48 h后显著提高了样品不易流动水的比例,降低了自由水比例(P<0.05);动态流变结果也表明,LF-MFF 36~48 h后样品G’值较高,蛋白质变性程度较低,形成了较好的黏弹性蛋白凝胶。Pearson相关性分析表明,不同冻结处理后猪肉理化特性与水分迁移的变化具有较强的相关性。因此LF-MFF 36~48 h可作为最佳的猪肉冻结条件,可较好地维持猪肉理化特性,降低水分子的迁移率,延缓蛋白变性,改善冻结猪肉的品质。展开更多
基金supported by the Marine S&T Fund of Shandong Province for Pilot National Laboratory for Marine Science and Technology(Qingdao)(No.2021QNLM020001)the Major Scientific and Technological Projects of Shandong Energy Group(No.SNKJ2022A06-R23)the Major Scientific and Technological Projects of CNPC(No.ZD2019-183-003).
文摘Intrinsic attenuation of the earth causes energy loss and phase distortion in seismic wave propagation.To obtain high-resolution imaging results,these negative effects must be considered during reverse time migration(RTM).We can easily implement attenuation-compensated RTM using the constant Q viscoacoustic wave equation with decoupled amplitude attenuation and phase dispersion terms.However,the nonphysical amplitude-compensation process will inevitably amplify the high-frequency noise in the wavefield in an exponential form,causing the numerical simulation to become unstable.This is due to the fact that the amplitude of the compensation grows exponentially with frequency.In order to achieve stable attenuation-compensated RTM,we modify the analytic expression of the attenuation compensation extrapolation operator and make it only compensate for amplitude loss within the effective frequency band.Based on this modified analytic formula,we then derive an explicit time-space domain attenuation compensation extrapolation operator.Finally,the implementation procedure of stable attenuation-compensated RTM is presented.In addition to being simple to implement,the newly proposed attenuation-compensated extrapolation operator is superior to the conventional low-pass filter in suppressing random noise,which will further improve the imaging resolution.We use two synthetic and one land seismic datasets to verify the stability and effectiveness of the proposed attenuationcompensated RTM in improving imaging resolution in viscous media.
基金supported by the National Key Research and Development Program of China under Grant 2018YFA0702501NSFC under Grant 41974126,Grant 41674116,and Grant 42004101the Project funded by the China Postdoctoral Science Foundation under Grant 2020M680516
文摘Amplitude versus offset analysis is a fundamental tool for determining the physical properties of reservoirs but generally hampered by the blurred common image gathers(CIGs).The blurring can be optimally corrected using the blockwise least-squares prestack time migration(BLS-PSTM),where common-offset migrated sections are divided into a series of blocks related to the explicit offsetdependent Hessian matrix and the following inverse filtering is iteratively applied to invert the corresponding reflectivity.However,calculating the Hessian matrix is slow.We present a fast BLS-PSTM via accelerating Hessian calculation with dip-angle Fresnel zone(DFZ).DFZ is closely related to optimal migration aperture,which significantly attenuates migration swings and reduces the computational cost of PSTM.Specifically,our fast BLS-PSTM is implemented as a two-stage process.First,we limit the aperture for any imaging point with an approximated the projected Fresnel zone before calculating the Hessian matrix.Then,we determine whether a seismic trace contributes to the imaging point via DFZ during calculating the Hessian matrix.Numerical tests on synthetic and field data validate the distinct speedup with higher-quality CIGs compared to BLS-PSTM.
基金This work was supported by Natural Science Basic Research Program of Shaanxi(Program No.2023-JC-YB-269)the National Natural Science Foundation of China(Grant No.41974122).
文摘The large storage requirement is a critical issue in cross-correlation imaging-condition based reverse time migration(RTM),because it requires the operation of the source and receiver wavefields at the same time.The boundary value method(BVM),based on the finite difference method(FDM),can be used to reconstruct the source wavefield in the reverse time propagation in the same way as the receiver wavefield,which can reduce the storage burden of the RTM data.Considering that the FDM cannot well handle models with discontinuous material properties and rough interfaces,we develop a source wavefield reconstruction strategy based on the finite element method(FEM),using proper orthogonal decomposition(POD)to enhance computational efficiency.In this method,we divide the whole time period into several segments,and construct the POD basis functions to get a reduced order model(ROM)for the source wavefield reconstruction in each segment.We show the corresponding quantitative analysis of the storage requirement of the POD-FEM.Numerical tests on the homogeneous model show the effectiveness of the proposed method,while the layered model and part of the Marmousi model tests indicate that the POD-FEM can keep an excellent balance between computational efficiency and memory usage compared with the full-stored method(FSM)and the BVM,and can be effectively applied in imaging.
基金financially supported by National Basic Research Program of China(No.2011CB201100)
文摘Conventional seismic exploration method based on post-stack data usually fails to identify the distribution of fractured and caved carbonate reservoirs in the Tarim Basin,so the rich pre-stack information should be applied to the prediction of carbonate reservoirs.Amplitude-preserved seismic data processing is the foundation.In this paper,according to the feature of desert seismic data （including weak reflection,fast attenuation of high frequency components,strong coherent noises,low S/N and resolution）,a set of amplitude-preserved processing techniques is applied and a reasonable processing flow is formed to obtain the high quality data.After implementing a set of pre-stack amplitude-preserved processing,we test and define the kernel parameters of amplitude-preserved Kirchhoff PSTM （pre-stack time migration） and subsequent gathers processing,in order to obtain the amplitude-preserved gathers used to the isotropic pre-stack inversion for the identification of caved reservoirs.The AVO characteristics of obtained gathers fit well with the synthetic gathers from logging data,and it proves that the processing above is amplitudepreserved.The azimuthal processing techniques,including azimuth division and binning enlargement,are implemented for amplitude-preserved azimuthal gathers with the uniform fold.They can be used in the anisotropic inversion to detect effective fractures.The processing techniques and flows are applied to the field seismic data,and are proved available for providing the amplitude-preserved gathers for carbonate reservoir prediction in the Tarim Basin.
