Seismic Wave Velocity Attenuation And Dispersion In The Patchy Saturated Medium With Complex Pores And Cracks

The velocity dispersion and attenuation of seismic waves in fluid-containing porous media are of great significance in guiding the identification of oil and gas in complex reservoirs.This phenomenon is mainly caused by pore fluid flow at different scales,and has a close and complicated relationship with pore fluid properties(fluid type,saturation,etc.)and rock skeleton characteristics(porosity,bedrock modulus,etc.).Based on the consideration of the non-uniformity of fluid and framework in porous media,this paper constructs a variety of media containing pores and cracks.Then,we analyzed and studied the laws of seismic wave attenuation and dispersion in these models,as well as the changing laws of physical properties and fluid parameters that affect them.Finally,we derive the characteristic equations of reflection and transmission coefficients and analyze the response characteristics.These works have laid the foundation for seismic oil and gas identification in complex fluid-containing media.First of all,in this article,we constructed a patchy saturated medium with pores and cracks on the basis of considering the heterogeneity of the fluid and framework in the underground porous medium at different scales.The model includes both the microscale and mesoscale attenuation theories,and the dispersion velocity and attenuation factor of the seismic wave in the model are obtained by solving the equivalent modulus of the medium.This method overcomes the shortcomings that abnormal values will appear in the high frequency range and attenuation peaks of different scales can’t be separated.However,due to the intricacies of the underground medium,only considering the microscale and mesoscale attenuation theory cannot meet the needs of actual production materials.Therefore,we have established another doublescale model that includes both the microscale squirt flow and the macroscale global flow and obtained the dispersion velocity and attenuation factor of the seismic wave by solving the wave equation of the model under the Biot theory.For these two types of models,we have analyzed various factors that cause seismic wave attenuation and dispersion.Through these analyses,we found that,on the one hand,the stronger the non-uniformity of the fluid-containing porous medium,the greater the seismic wave attenuation.On the other hand,when there are multiple types of non-uniformity factors in the fluid-containing porous medium,the seismic wave attenuation curve Multiple peaks will appear,and the attenuation characteristics will become more complicated.On the basis of these two types of dual-scale models,we have coupled three different-scale mechanisms to establish a relatively unified three-scale seismic wave attenuation rock physics model.Under the Biot theory,the effects of inhomogeneous fluid,pore and crack structure,microscale squirt flow and mesoscale interlaminar flow on fluid pressure and elastic modulus are analyzed,and the wave equation of seismic wave in the three-scale model is obtained.Then,we solved the equation to obtain the corresponding seismic wave attenuation and dispersion curves,and analyzed the influence of different media parameters on the attenuation and dispersion curves.Finally,we deduced the characteristic equations of reflection and transmission coefficients of various polar waves at the interface when the model is covered with a uniform isotropic medium,and obtained three-dimensional curved surfaces of reflection and transmission coefficients that vary with frequency and incident angle.These works provide a theoretical basis for the construction of the AVO forward model and subsequent inversion and reservoir prediction.