A Study On Seismic Wave Dispersion And Attenuation Mechanism In Porous Media

Velocity dispersion and attenuation of seismic wave in porous media has become a research hotspot. The phenomenon is induced by pore fluid flow at different scales. Previous studies have tried to explain this mechanism by constructing various theoretical models of velocity dispersion and attenuation, none of which is able to account for the attenuation mechanism successfully. This thesis discusses pros and cons of some theoretical physical models, analyzes and improves the theoretical physical model in seismic frequency band, looks into attenuation mechanisms of seismic waves, carries out numerical simulation as well as experiment data tests, and finally obtains the seismic response characteristics of related reservoir through forward modeling.Most theoretical models consider a single mechanism of fluid motion. Despite of the same lithology of porous rocks, the differences in configuration and pore fluid distribution inside rocks also cause the differences in the applicability of theoretical models.Pressure gradient in heterogeneously distributed fluid was induced by longitudinal wave excitation in rock sample, generalizing pore fluid motion that changes rock’s elastic characteristics. This thesis analyzes theoretical model at macroscopic, microscopic and mesoscopic scale respectively.Predecessors puting forward Biot-Rayleigh(B-R) equation’s ignore the local fluid flow velocity field in inclusion, by fluid mass conservation equation, this thesis improves fluid field pattern inside and outside spherical inclusions with compressional excitation as well as kinetic energy equation and dissipation function of local fluid based on dual porosity model Biot-Rayleigh theory, derives the reformulated Biot-Rayleigh equations of elastic wave, and compares the example of different rocks and fluids with previous theory and experimental data, which demonstrates that the method in this thesis is right and practical.Pressure gradient in heterogeneously distributed fluid was induced by shear wave excitation in rock sample generalizing pore fluid motion. Aiming this problem of dynamic, there has been no domestic or foreign systematic study. This thesis tries on construction of constitutive equation related to shear force and pore fluid pressure, analyzes pore fluid distribution pattern under shear wave excitation, derives potential energy equation, kinetic energy equation and dissipative function under shear wave excitation, and finally derives shear wave equation in dual porosity media. Example of different rocks and fluids demonstrates that the method in this thesis is rational and applicable.Further base on the reformulated Biot-Rayleigh equations, this thesis considers the seismic wave dispersion and attenuation induced pore fluid flow, calculates the velocity of seismic wave in different frequency and saturation cases, constructs the forward modeling of AVO, studies the effects of reservoir fluid parameters on the seismic reflection amplitude, analyzes the seismic response characteristics of different frequencies, saturation and reservoir types. Based on seismic response direct detection of reservoir fluid provides the theory basis for the engineering application practice...