关键词: 超声波速度, 速度频散, 静水压力, 流体饱和岩石, Biot理论频散, “局部流”模型频散

Abstract: The quantitative relation among Biot's theoretical dispersion, local fluid dispersion and total dispersion are presented under laboratory ultrasonic frequency. Large gap exists between Biot's theoretical dispersion and total dispersion when the hydrostatic pressure is low, Biot's theoretical dispersion can not explain the real dispersion in experiments very well. Using the local fluid model (including Biot's dispersion) can perform well to explain the experimental results. As the hydrostatic pressure increases total dispersion and local dispersion decrease. Especially, under high pressure, Biot's theoretical dispersion is comparable to total dispersion. The dominant dispersion mechanism is able to transform in high - porosity samples with increasing pressure. The close of low aspect ratio cracks with increasing pressure is the fundamental reason to form those experimental results above, because difference of pore stiffness is the base on which the local fluid exists. The effect on velocity dispersion of pore fluid is also examined. As the viscosity of pore fluid increases, total dispersion and local fluid dispersion increase significantly.

Key words: ultrasonic velocity, velocity dispersion, hydrostatic pressure, fluid saturated rock, Biot's theoretical dispersion, local fluid dispersion