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

摘要： 给出在实验超声频率下储层砂岩样品“局部流”模型理论频散、Biot理论频散与实验总频散的定量关系。在低压情况下，实验总频散与Biot理论频散差异较大，Biot理论频散不足以解释实际频散结果；而作者所用“局部流”模型理论频散（已包括Biot理论频散）与实际结果符合较好；压力较高时，“局部流”模型频散以及总频散均会下降，这时Biot理论可以解释流体饱和速度变化。孔隙度较大样品在加压的过程中会出现主导频散机制的转换。造成以上现象的根本原因是，岩石中低面率塑性孔隙随压力的变化，而孔隙刚度的差异是“局部流”作用存在的基础。研究了不同孔隙流体对岩石速度频散的影响。流体粘度增加，实验总频散与“局部流”模型频散均有较大增加，而Biot理论频散变化不大。流体的粘度，以及岩石的渗透率在两种频散机制中所起的作用是相反的。

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