Strong low-frequency energy beneath a hydrocarbon reservoir is called a seismic low-frequency shadow and can be used as a hydrocarbon indicator （Tarter et al., 1979） bu the physical mechanism of the observed low-fre...Strong low-frequency energy beneath a hydrocarbon reservoir is called a seismic low-frequency shadow and can be used as a hydrocarbon indicator （Tarter et al., 1979） bu the physical mechanism of the observed low-frequency shadow is still unclear. To stud） the mechanism, we performed seismic numerical simulation of geological models with a hydrocarbon-bearing zone using the 2-D diffusive-viscous wave equation which car effectively model the characteristics of velocity dispersion and transform the seismic dat~ centered in a target layer slice within a time window to the time-frequency domain by usinl time-frequency signal analysis and sort the frequency gathers to common frequency cubes. Then, we observe the characteristics of the seismic low-frequency shadow in the common frequency cubes. The numerical simulations reveal that the main mechanism of seismic lowfrequency shadows is attributed to high attenuation of the medium to high seismic frequency components caused by absorption in the hydrocarbon-filled reservoir. Results from a practical example of seismic low-frequency shadows show that it is possible to identify the reservoir by the low-frequency shadow with high S/N seismic data.展开更多
Soft matters are observed anomalous viscosity behaviors often characterized by a power law frequency dependent attenuation in acoustic wave propagation. Recent decades have witnessed a fast growing research on develop...Soft matters are observed anomalous viscosity behaviors often characterized by a power law frequency dependent attenuation in acoustic wave propagation. Recent decades have witnessed a fast growing research on developing various models for such anomalous viscosity behaviors among which one of the present authors proposed the modified Szabo＇s wave equation via the positive fractional derivative. The purpose of this study is to apply the modified Szabo＇s wave equation to simulate a recent ultrasonic imaging technique called the clinical amplitude- velocity reconstruction imaging （CARI） of breast tumors which are of typical soft tissue matters. Investigations have been made on the effects of the size and position of tumors on the quality of ultrasonic medical imaging. It is observed from numerical results that the sound pressure along the reflecting line, which indicates the detection results, varies obviously with sizes and lateral positions of tumors, but remains almost the same for different axial positions.展开更多
First, two tanh-coth type solutions of a class of nonlinear wave equation are derived by using a simplified modified extended tanh-function method. Then, further analysis to some tanh-coth type solutions of nonlinear ...First, two tanh-coth type solutions of a class of nonlinear wave equation are derived by using a simplified modified extended tanh-function method. Then, further analysis to some tanh-coth type solutions of nonlinear evolution equations are given. The results show that when balance number m is one or two, the tanh-eoth type solutions obtained by the modified extended tanh-funetion method can be obtained by using the hyperbolic-function method.展开更多
The conventional pseudo-acoustic wave equations（PWEs） in vertical transversely isotropic（VTI）media may generate SV-wave artifacts and propagation instabilities when anisotropy parameters cannot satisfy the pseudo-...The conventional pseudo-acoustic wave equations（PWEs） in vertical transversely isotropic（VTI）media may generate SV-wave artifacts and propagation instabilities when anisotropy parameters cannot satisfy the pseudo-acoustic assumption. One solution to these issues is to use pure acoustic anisotropic wave equations, which can produce stable and pure P-wave responses without any SVwave pollutions. The commonly used pure acoustic wave equations（PAWEs） in VTI media are mainly derived from the decoupled P-SV dispersion relation based on first-order Taylor-series expansion（TE）, thus they will suffer from accuracy loss in strongly anisotropic media. In this paper, we adopt arbitrary-order TE to expand the square root term in Alkhalifah＇s accurate acoustic VTI dispersion relation and solve the corresponding PAWE using the normalized pseudoanalytical method（NPAM） based on optimized pseudodifferential operator. Our analysis of phase velocity errors indicates that the accuracy of our new expression is perfectly acceptable for majority anisotropy parameters. The effectiveness of our proposed scheme also can be demonstrated by several numerical examples and reverse-time migration（RTM） result.展开更多
基金supported by the National Hi-tech Research and Development Program of China (863 Program) (Grant No. 2006AA0AA 02 - 2).
文摘Strong low-frequency energy beneath a hydrocarbon reservoir is called a seismic low-frequency shadow and can be used as a hydrocarbon indicator （Tarter et al., 1979） bu the physical mechanism of the observed low-frequency shadow is still unclear. To stud） the mechanism, we performed seismic numerical simulation of geological models with a hydrocarbon-bearing zone using the 2-D diffusive-viscous wave equation which car effectively model the characteristics of velocity dispersion and transform the seismic dat~ centered in a target layer slice within a time window to the time-frequency domain by usinl time-frequency signal analysis and sort the frequency gathers to common frequency cubes. Then, we observe the characteristics of the seismic low-frequency shadow in the common frequency cubes. The numerical simulations reveal that the main mechanism of seismic lowfrequency shadows is attributed to high attenuation of the medium to high seismic frequency components caused by absorption in the hydrocarbon-filled reservoir. Results from a practical example of seismic low-frequency shadows show that it is possible to identify the reservoir by the low-frequency shadow with high S/N seismic data.
基金supported by National Basic Research Program of China (973 Project No. 2010CB832702)the National Science Funds for Distinguished Young Scholars (11125208)+2 种基金the R&D Special Fund for Public Welfare Industry (Hydrodynamics, Project No. 201101014)Wen Chen is grateful of the Alexander von Humboldt Foundation, Germany, for an Experienced Researcher fellowshipXiaodi Zhang would like to thank China Scholarship Council (CSC) for the financial support
文摘Soft matters are observed anomalous viscosity behaviors often characterized by a power law frequency dependent attenuation in acoustic wave propagation. Recent decades have witnessed a fast growing research on developing various models for such anomalous viscosity behaviors among which one of the present authors proposed the modified Szabo＇s wave equation via the positive fractional derivative. The purpose of this study is to apply the modified Szabo＇s wave equation to simulate a recent ultrasonic imaging technique called the clinical amplitude- velocity reconstruction imaging （CARI） of breast tumors which are of typical soft tissue matters. Investigations have been made on the effects of the size and position of tumors on the quality of ultrasonic medical imaging. It is observed from numerical results that the sound pressure along the reflecting line, which indicates the detection results, varies obviously with sizes and lateral positions of tumors, but remains almost the same for different axial positions.
基金Supported by the Natural Science Foundation of China under Grant No.11071209
文摘First, two tanh-coth type solutions of a class of nonlinear wave equation are derived by using a simplified modified extended tanh-function method. Then, further analysis to some tanh-coth type solutions of nonlinear evolution equations are given. The results show that when balance number m is one or two, the tanh-eoth type solutions obtained by the modified extended tanh-funetion method can be obtained by using the hyperbolic-function method.
基金supported by the National Natural Science Foundation of China (NSFC) under contract granted No. 41474110Research Foundation of China University of Petroleum-Beijing at Karamay under contract number RCYJ2018A-01-001
文摘The conventional pseudo-acoustic wave equations（PWEs） in vertical transversely isotropic（VTI）media may generate SV-wave artifacts and propagation instabilities when anisotropy parameters cannot satisfy the pseudo-acoustic assumption. One solution to these issues is to use pure acoustic anisotropic wave equations, which can produce stable and pure P-wave responses without any SVwave pollutions. The commonly used pure acoustic wave equations（PAWEs） in VTI media are mainly derived from the decoupled P-SV dispersion relation based on first-order Taylor-series expansion（TE）, thus they will suffer from accuracy loss in strongly anisotropic media. In this paper, we adopt arbitrary-order TE to expand the square root term in Alkhalifah＇s accurate acoustic VTI dispersion relation and solve the corresponding PAWE using the normalized pseudoanalytical method（NPAM） based on optimized pseudodifferential operator. Our analysis of phase velocity errors indicates that the accuracy of our new expression is perfectly acceptable for majority anisotropy parameters. The effectiveness of our proposed scheme also can be demonstrated by several numerical examples and reverse-time migration（RTM） result.
