Study On Low-frequency Seismic Response Based On Dispersion-viscous Model

With the progress of petroleum exploration and development technology,the depth and precision of seismic exploration is increasing day by day.The form of oil and gas reservoir are increasingly complex and the exploration target has been shifted from simple structural reservoirs to the complex lithology reservoirs or lithologic-structural composite reservoirs.In this case,it's necessary to put forward a higher precision of reservoir prediction method and technology,and carry out a more in line with the seismic wave propagation theory under actual media.At the same time,the seismic wave propagation in the fluid reservoir result in energy attenuation,especially in the high frequency seismic signal.The low-frequency seismic information can propagate deeper than high-frequency under the real media,and the low-frequency seismic information contains a great deal of information what could characterize the fluid in the pores of the rock.Therefore,the potential significance and application value of low-frequency seismic reflection wave more and more subject to the attention of geophysicist and geophysical exploration industry.In this paper,we discussed the theory of seismic signal attenuation and the forming mechanism of low frequency in three aspects: the geometric attenuation,the physical attenuation,and the factors of affecting seismic wave attenuation.Then,we put forward the finite difference forward modeling of the diffusive-viscous wave equation based on the wave field continuation of the diffusive-viscous wave equation.Secondly,we analyzed the influence of the diffusive coefficient,the viscous coefficient in the wave function and the thickness of reservoir on the amplitude and frequency information of seismic signal,especially the influence of low-frequency signal,and studied low frequency response including amplitude,phase and frequency based on different diffusive-viscous model.Then studied the spectral decomposition method to extract low frequency information,this paper proposed a generalized S transform based on linear optimization Gaussian window function,which can improve the time resolution of low-frequency band without affecting the high-frequency time and frequency resolution.This method provided a powerful tool for reservoir prediction and fluid identification with low frequency.Finally,this paper applied seismic frequency information to identify the fluid and predict the oil reservoir,the specific methods are divided into two types: one is to use low frequency information directly indicate oil and gas directly,the other one is analyzing to related attributes which could reflect the sensitivity of reservoir fluid in low frequency.The ultimate goal is guiding the application of reservoir prediction with low frequency information,and improving the identification accuracy of oil and gas.