| Elastic wave velocity dispersion and attenuation in fluid-saturated porous medium are of great significance for both theoretical research and practical application of seismic wave propagation. Elastic velocity dispersion and amplitude attenuation is mainly because of the heterogeneity of the medium, and this heterogeneity may be embodied in various different spatial scales. Therefore, this thesis is going to consider how inhomogeneous body—cracks at different spatial scales combined with fluid flow theory can influence the velocity dispersion and attenuation of elastic wave in fluidsaturated fractured porous medium.Based on long wavelength effective medium theory, this paper considered the influence of micro scale cracks on the effective elastic properties of rock firstly. Due to the characteristic frequency of the traditional theory of squirt flow is mainly constrained to sonic logging frequency domain, and the control factor of the characteristic frequency is crack's aspect ratio which is generally a constant value, we can use the rock physical experiment data to extract the rock pore structure characteristic parameters, and based on the which to extend squirt flow model. The extension of the quirt flow model reflects the quantitative relationship among rock elastic properties, fluid properties, pore structure, effective stress and the frequency. Secondly, considering the different seismic wave propagation characteristics of the rock containing fractures at different scales, we use White model to carry out a model to quantitatively characterize the rock containing mesoscopic cracks, which reflects the effect of the physical properties of the crack on the elastic wave passing through the rock. Finally, combining with the actual drilling core sample of tight sandstone reservoir, and the microscopic, mesoscopic fracture pore medium of seismic wave propagation theory, we analyzed the effects of micro size, medium size cracks on fluid velocity dispersion and attenuation in porous media respectively. In addition, this paper experimentally combined both scales of cracks to model how fluid flow affects elastic properties of porous media, and discussed the across scales crack velocity dispersion and attenuation characteristics of porous media.On the whole, through the research of this paper we found that the micro scale of fracture will widely influence the seismic wave in fluid-saturated porous medium, the influence of frequency range covers from conventional seismic exploration in low frequency band to the ultrasonic experiments of high frequency band. And mesoscopic fracture will influence the seismic wave propagation in lower frequency range more efficiently. Different scales of fracture on elastic wave velocity dispersion and attenuation have a cumulative effect. |
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