By employing the plane wave analysis method, the dispersion equations associated with compressional and shear waves using Santos's three-phase poroelastic theory were driven. Considering the reservoir pressure, the high frequency corrections and the coupling drag of two fluids in pores, the influences of frequency and gas saturation on the phase velocities and the inverse quality factors of four body waves predicted by Santos's theory were discussed in detail. The theoretical velocities of the fast compressional and shear waves were compared with the results of the low and high frequency experiments from open publications, respectively. The results showed that they are in good agreement in the low frequency case rather than in the high frequency case. In the latter case, several popular poroelastic models were considered and compared with the experimental data. In the models, the results of White's theory fit the experimental data, but the parameter b in White's model has a significant impact on the results. Under the framework of the linear viscoelasticity theory, the attenuation mechanism of Santos's model was extended, and the comparisons between the experimental and theoretical results were also made with respect to attenuation. For the case of water saturation less than 90%, the extended model makes good predictions of the inverse quality factor of shear wave. There is a significant difference between the experimental and theoretical results for the compressional wave, but the difference can be explained by the experimental data available. unsaturated porous media, poroelastic media, phase velocity, attenuation PACS: 43.20.Jr, 43.35.Cg, 91.60.LjPores of subsurface rocks or surface soil sometimes contain two types or more than two types of fluids such as water, gas and oil. In such situations, acoustic models of porous media saturated by more than one fluid should be established so that the models under consideration are more accordant to practice. Research results relating to the dynamic response of porous media filled up with two fluids have been applied extensively in geophysics, seismology, civil engineering, and in marine engineering. For the acoustic characteristics of porous materials, wave velocity and attenuation are two important properties that provide the information about lithology, pore fluids, saturation and the in situ conditions of rocks.Because of the universality of the existence of unsaturated porous media, which is one case of porous media containing two fluids, acoustic wave phenomena in such media have received a great deal of attention in recent years. Brandt [1] reported that in a water saturated quartz sand column, compressional wave velocity linearly decreases as the degree of water saturation decreases, and levels off at the saturation of 50%. Elliott and Wiley [2] performed ultrasonic laboratory experiments (700 kHz) for Ottawa rock samples and showed that in the range of 9%-85% water saturation, the velocity of compressional wave is unrelated to the saturation. They used Wyllie e...
Under the condition of simulated formation temperature and pressure, the compression and shear wave velocity of the tuffaceous conglomerates and rock-fragment sandstones of the reservoirs in K1t, k1n group of Cretaceous system in Tanan are measured. The effects of lithology, mineral content, density, porosity, shale content, and water saturation on the acoustic velocity of the athrogenic rock are studied. Within the limits of our observation, some rules are found: (1) the velocity of the fine tuffaceous conglomerates is remarkably greater than that of the tuffaceous rock-fragment sandstones with good physical property; (2) the compression velocity increases with fragment content, and decreases with quartz and feldspar content in the mud; (3) the compression velocity increases with density, especially, in tuffaceous rock-fragment sandstones, the velocity keeps a good relation with density in form of power function; (4) compression and shear wave velocity decreases with porosity and shale content, velocity of the tuffaceous rock-fragment sandstones keeps a good relation with porosity and shale content in form of negative linear function, but effects of shale content is only 1/5 to 1/10 of that of the porosity, hence can be neglected; (5) with porosity increases, compression wave velocity is relatively sensitive to fluid alternation, and the rang in which velocity varies keeps positive correlation with porosity. The result provides a foundation for the research of seismic and logging data evaluation approaches in athrogenic rock reservoirs, Haita basin.
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