Propagation Characteristics Of Elastic Waves In Porous Media Based On The Patchy-saturated Model

Based on the relationship between the parameters of the underground reservoir and the characteristics of the oil and gas distribution,research on the propagation characteristics of the elastic wave in the porous medium is playing an important role in the practical application of oil quality identification and the exploration of oil and gas.The patchy-saturated porous medium model can describe the attenuation and dispersion phenomena of the elastic wave in the seismic frequency band.However,there is no specific systematic study of the dispersion and attenuation characteristics of the two kinds of compression wave and the shear wave in partially saturated porous media to get a comprehensive grasp about propagation characteristics of elastic waves.In this paper,the mathematical model for wave propagation in partially saturated rocks is established based on the White's model of spherical gas pockets.The Biot's wave equation of completely saturated porous media is extended to the seismic wave equation of two-phase patchy saturated porous media,and the specific expression form of compression wave and shear wave is deduced.The propagation laws of the two types of compression wave and the shear wave in the saturated fluid medium of the rock are studied with the frequency,porosity,saturation and permeability of the sandstone samples and oil sandstone samples.The influence of the parameters of the porous media on the propagation characteristics of three kinds of elastic waves is systematically analyzed.Firstly,the mathematic model of spherical saturated porous media is established,and then the propagation equation of seismic wave in partially saturated porous medium is obtained.The specific wave equations of the P-wave and S-wave in the spherical patchy saturation model are deduced by the Helmholtz decomposition theory.We discuss the variation of the velocity and attenuation with frequency between the compression wave and shear waves.And then,it is verified to study the feasibility of the compression wave attenuation and dispersion characteristics based on the theoretical model,by comparing the attenuation and dispersion of the compression wave between the spherical patchy model and the Johnson model.Secondly,under the condition of different porosity,permeability,gas saturation and viscosity,the attenuation and dispersion characteristics of compression wave and shear wave in the sphere gas-water saturated porous media are studied by numerical simulation method.Furthermore,we analyze differences of the propagation characteristics between the compression wave and shear wave.Finally,we analyze the attenuation and dispersion of compression waves and shear wave in oil-water saturated porous media with different porosity,oil saturation,permeability and viscous coefficient,and have explored the effects of frequency and the parameters of the porous media.Then we compares the characteristics of oil-water saturated medium with that of gas-water saturated medium,to determine the attenuation and dispersion law of elastic wave in the oil and gas reservoir.The research results of this paper can provide a theoretical basis for improving the accuracy of fluid identification and oil-gas prediction.