An important component of any CO_2 sequestration project is seismic monitoring for tracking changes in subsurface physical properties,such as velocity and density.Different reservoirs have different amplitude variatio...An important component of any CO_2 sequestration project is seismic monitoring for tracking changes in subsurface physical properties,such as velocity and density.Different reservoirs have different amplitude variation with offset(AVO) responses,which can define underground conditions. In the present paper we investigate walkaway vertical seismic profile(VSP) AVO response to CO_2 injection at the Ketzin site,the first European onshore CO_2 sequestration pilot study dealing with research on geological storage of CO_2.First,we performed rock physics analysis to evaluate the effect of injected CO_2 on seismic velocity using the Biot-Gassmann equation.On the basis of this model,the seismic response for different CO_2 injection saturation was studied using ray tracing modeling.We then created synthetic walkaway VSP data,which we then processed.In contrast,synthetic seismic traces were created from borehole data.Finally,we found that the amplitude of CO_2 injected sand layer with different gas saturations were increased with the offset when compared with the original brine target layer.This is the typical classⅢAVO anomaly for gas sand layer.The AVO responses matched the synthetic seismic traces very well.Therefore,walkaway VSP AVO response can monitor CO_2 distribution in the Ketzin area.展开更多
Multi-azimuth walkaway vertical seismic profiling is an established technique for the estimation of in situ slowness surfaces and inferring anisotropy parameters.Normally,this technique requires the assumption of late...Multi-azimuth walkaway vertical seismic profiling is an established technique for the estimation of in situ slowness surfaces and inferring anisotropy parameters.Normally,this technique requires the assumption of lateral homogeneity,which makes the horizontal slowness components at depths of downhole receivers equal to those measured at the surface.Any violations of this assumption,such as lateral heterogeneity or nonzero dip of intermediate interfaces,lead to distortions in reconstructed slowness surfaces and,consequently,to errors in estimated anisotropic parameters.In this work,we relax the assumption of lateral homogeneity and discuss how to correct vertical seismic profile data for weak lateral heterogeneity.We describe a procedure of downward continuation of recorded traveltimes that accounts for the presence of both vertical inhomogeneity and weak lateral heterogeneity,which produces correct slowness surfaces at depths of downhole receivers,noticing that sufficiently dense receiver coverage along a borehole is required to separate influences of vertical and lateral heterogeneity on measured traveltimes and obtain accurate estimates of the slowness surfaces.Once the slowness surfaces are found and a desired type of anisotropic model to be inverted is selected,the corresponding anisotropic parameters,providing the best fit to the estimated slownesses,can be obtained.We invert the slowness surfaces of P-waves for parameters of the simplest anisotropic model describing dipping fractures(transversely isotropic medium with a tilted symmetry axis).Five parameters of this model,namely,the P-wave velocity V0 in the direction of the symmetry axis,Thomsen's anisotropic coefficients e and d,the tilt n,and the azimuth b of the symmetry axis,can be estimated in a stable manner when maximum source offset is greater than half of receiver depth.展开更多
Since long ago, indirect study of the underground layers properties has been interesting to geologists.One method for this study was seismography which gained great interest besides other tools due to thedifferent ide...Since long ago, indirect study of the underground layers properties has been interesting to geologists.One method for this study was seismography which gained great interest besides other tools due to thedifferent identity of waves and energy attraction phenomena in different layers. Vertical seismic profiling(VSP) is considered as a valuable method in oil and gas exploration. This method is used to estimate therock properties in a well. In seismic operations elastic waves are sent down to the underground. Part ofthe waves’ energy is reflected after passing through the earth layers and are received by receivers on theground level. The received data determine the situation of the underneath layers after being processed,and one of the most important applications of seismic data is in the oil and gas exploration field. Qualityfactor is one of the most important seismic detectors that shows itself apparently in VSP data results. Themost substantial purpose of this study is to investigate the frequency content of the quality factor.展开更多
基金The European Commission,German Federal Ministry of Education and Research,German Federal Ministry of Economics and Technology as well as Research Institute and Industry are gratefully acknowledged for funding and supporting CO2 Storage by Injection into a Natural Storage Site CO2SINK(Project No.502599)
文摘An important component of any CO_2 sequestration project is seismic monitoring for tracking changes in subsurface physical properties,such as velocity and density.Different reservoirs have different amplitude variation with offset(AVO) responses,which can define underground conditions. In the present paper we investigate walkaway vertical seismic profile(VSP) AVO response to CO_2 injection at the Ketzin site,the first European onshore CO_2 sequestration pilot study dealing with research on geological storage of CO_2.First,we performed rock physics analysis to evaluate the effect of injected CO_2 on seismic velocity using the Biot-Gassmann equation.On the basis of this model,the seismic response for different CO_2 injection saturation was studied using ray tracing modeling.We then created synthetic walkaway VSP data,which we then processed.In contrast,synthetic seismic traces were created from borehole data.Finally,we found that the amplitude of CO_2 injected sand layer with different gas saturations were increased with the offset when compared with the original brine target layer.This is the typical classⅢAVO anomaly for gas sand layer.The AVO responses matched the synthetic seismic traces very well.Therefore,walkaway VSP AVO response can monitor CO_2 distribution in the Ketzin area.
文摘Multi-azimuth walkaway vertical seismic profiling is an established technique for the estimation of in situ slowness surfaces and inferring anisotropy parameters.Normally,this technique requires the assumption of lateral homogeneity,which makes the horizontal slowness components at depths of downhole receivers equal to those measured at the surface.Any violations of this assumption,such as lateral heterogeneity or nonzero dip of intermediate interfaces,lead to distortions in reconstructed slowness surfaces and,consequently,to errors in estimated anisotropic parameters.In this work,we relax the assumption of lateral homogeneity and discuss how to correct vertical seismic profile data for weak lateral heterogeneity.We describe a procedure of downward continuation of recorded traveltimes that accounts for the presence of both vertical inhomogeneity and weak lateral heterogeneity,which produces correct slowness surfaces at depths of downhole receivers,noticing that sufficiently dense receiver coverage along a borehole is required to separate influences of vertical and lateral heterogeneity on measured traveltimes and obtain accurate estimates of the slowness surfaces.Once the slowness surfaces are found and a desired type of anisotropic model to be inverted is selected,the corresponding anisotropic parameters,providing the best fit to the estimated slownesses,can be obtained.We invert the slowness surfaces of P-waves for parameters of the simplest anisotropic model describing dipping fractures(transversely isotropic medium with a tilted symmetry axis).Five parameters of this model,namely,the P-wave velocity V0 in the direction of the symmetry axis,Thomsen's anisotropic coefficients e and d,the tilt n,and the azimuth b of the symmetry axis,can be estimated in a stable manner when maximum source offset is greater than half of receiver depth.
文摘Since long ago, indirect study of the underground layers properties has been interesting to geologists.One method for this study was seismography which gained great interest besides other tools due to thedifferent identity of waves and energy attraction phenomena in different layers. Vertical seismic profiling(VSP) is considered as a valuable method in oil and gas exploration. This method is used to estimate therock properties in a well. In seismic operations elastic waves are sent down to the underground. Part ofthe waves’ energy is reflected after passing through the earth layers and are received by receivers on theground level. The received data determine the situation of the underneath layers after being processed,and one of the most important applications of seismic data is in the oil and gas exploration field. Qualityfactor is one of the most important seismic detectors that shows itself apparently in VSP data results. Themost substantial purpose of this study is to investigate the frequency content of the quality factor.
