The Research Of Reservoir Prediction Method Based On Dispersion And Attenuation Characteristics Of Fluid-bearing Fractured Porous Media

The fluid flow in the fractured porous rock will happen when the seismic wave passes through the fluid-bearing fractured porous media and then produce the energy loss,which gives rise to velocity dispersion and attenuation.We can make full use of the inherent dispersion and attenuation characteristics of the reservoir for reservoir delineation and fluid identification.Therefore,mining the mechanism of dispersion and attenuation of fluid-bearing fractured porous media is of great importance to understand the frequency-dependent seismic response of hydrocarbon reservoirs,which can provide theoretical support for reservoir prediction.Based on the theory of dispersion and attenuation of fluid-bearing fractured porous media,this paper aims at exploring the relationship between dispersion and attenuation and reservoir elastic parameters and mining frequency-dependent attributes associated with the fluid-bearing fractured porous media from field seismic data for reservoir prediction.The main contents of this paper are as follows:(1)Considering the influence of reservoir wettability,capillary parameter and fluid saturation,the calculation method of equivalent bulk modulus and equivalent fluid viscosity of multiphase immiscible fluids is proposed.The method is suitable for the case of the combined saturation for any fluid type and it lays a theoretical foundation for the dispersion and attenuation analysis of a fractured porous media saturated with multiphase immiscible fluids.(2)Based on Chapman's theory,the effects of reservoir wettability and capillary parameter on dispersion and attenuation can be explored through the calculation method of equivalent bulk modulus and equivalent fluid viscosity of multiphase immiscible fluids.Then,we analyze the dispersion and attenuation of the fractured porous media saturated with multiphase immiscible fluids and further understand the mechanism of dispersion and attenuation when a porous media saturated with multiphase immiscible fluids.Moreover,the seismic responses of the fractured porous rock saturated with multiphase immiscible fluids are analyzed by forwarding modeling and explored the relationship between fluid type,saturation and seismic responses,which provides an effective basis for establishing the more clear mechanism of reservoir prediction and fluid identification.(3)Based on frequency-dependent AVO(FDAVO)inversion,we propose an optimal inversion scheme to pursue the optimal dispersion factor.The dispersion factor obtained by the optimal scheme can highlight the dispersion anomaly of the fluid-bearing reservoir to the maximum extent and suppress the background interference of the elastic layers.The workflow is applied to field seismic data to delineate the high-saturation reservoirs.The results show that the optimal dispersion parameter can accurately delineate the location and spatial distribution of hydrocarbon-saturated reservoirs and realize the quantitative prediction of high gas saturation reservoirs.The study can reduce the nonuniqueness of the prediction and improve prediction accuracy.(4)Based on the effective medium model of fractured porous rock,a new fluid indicator that is closely related to the fluid parameters is introduced through the relationship between elastic parameters and stiffness parameters.By simplifying the stiffness parameters and perturbing the approximated stiffness parameters,and make use of the relationship between scattering potentials and reflection coefficients,we derive a frequency-dependent P-P reflection coefficient.Then,a new dispersion fluid factor obtained by the reflection coefficient has a strong sensitivity to the fluid-bearing reservoirs,which can suppresses the abnormal interference unrelated to the reservoir.The new dispersion fluid factor can be used for the high-accuracy reservoir delineation and fluid identification.(5)Based on the asymptotic representation for the frequency-dependent reflections in the fluid-saturated pore-elastic media,we derive a novel equation of reservoir energy density and present a practical numerical implement method for calculating the reservoir energy density using the low-frequency seismic data.Then,we propose an effective workflow to determine the optimal frequency,which can maximize the energy density anomalies of fluid-saturated reservoirs and improve the reservoir delineation accuracy.Synthetic and field data tests demonstrate that the energy density attribute shows excellent imaging quality for fluid-saturated reservoirs and can accurately delineate the location and spatial distribution of hydrocarbon-saturated reservoirs,and is less affected by the noises and the background interferences of elastic layers.The methodology provides a new approach to extract the information related to the properties of reservoir energy and provides a new way to further mine the low-frequency information related to hydrocarbon reservoirs from seismic signals.