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摘要
Despite the intensive research on characteristics of the attenuation and dispersion of seismic waves in the porous medium, there is no explicit understanding for the physical mechanisms in such media containing different kinds of cracks. This work attempted to deduce seismic wave equations for the porous medium containing two kinds of cracks including the coin-shaped and pinchout-shaped cracks utilizing the analysis of the pressure of fluids in the cracks. @@@ When the stress is imposed on the porous medium containing two kinds of cracks, the fluid flux flowing out from the cracks can be calculated by the conservation equation of mass and the Stokes equation. The seismic equations for this medium can be derived using the Biot equation and the fluid pressure influenced by the flow from the cracks. The high and low frequency limits of modulus can be figured out when the frequency approaches infinite great and zero. @@@ From the analysis of seismic wave attenuation and dispersion in the porous medium containing two kinds of cracks and the relationship with the parameters of crack and permeability, the following knowledge can be gained, (1) When the microscopic "squirt-flow" is only considered, there are two peaks of seismic wave attenuation, one for the coin-shaped crack and the other for pinchout-shaped cracks. The velocity of the high frequency limit is approaching the Gassmann value. (2) The seismic wave attenuation has three peaks, of which two are accounted for different cracks and the other is for the Biot flow in the context of Biot theory. The different seismic wave attenuations and dispersions can be achieved in the porous medium containing different kinds of cracks. The dispersion velocity of slow P-waves is little influenced by the "squirt-flow" of different kinds of cracks. (3) With the increase of permeability, the frequency of peak of attenuation of seismic waves caused by macroscopic "Biot flow" turns into the lower frequency band, while the amplitude of attenuation is constant. The frequency peak of attenuation of seismic waves is moving to the high frequency band with the crack aspect ratio getting greater. The attenuation of seismic waves caused by Biot theory is not impacted. Increasing fluid viscosity, the frequency peak of attenuation induced by microscopic "squirt flow" is shifting into the lower frequency band, contrary to that is caused by macroscopic "Biot flow". @@@ When it involves different causes such as, the porous shapes and the heterogeneous scales, the attenuation characteristics (the frequency peak and amplitude) vary correspondingly. The attenuation of seismic waves can exhibit the multi-peaks when two or more causes are accounted. The different parameters of the porous medium containing mixed cracks can influence the attenuation by many kinds of ways. The parameters like the permeability and crack aspect ratio and fluid viscosity can all control the frequency band where the effect occurs.
- 出版日期2015-4
- 单位中国石油大学（北京）
