The elastic moduli of four sandstone samples are measured at seismic （2-2000 Hz） and ultrasonic （1 MHz） frequencies and water- and glycerin-saturated conditions. We observe that the high-permeability samples under...The elastic moduli of four sandstone samples are measured at seismic （2-2000 Hz） and ultrasonic （1 MHz） frequencies and water- and glycerin-saturated conditions. We observe that the high-permeability samples under partially water-saturated conditions and the low-permeability samples under partially glycerin-saturated conditions show little dispersion at low frequencies （2-2000 Hz）. However, the high-permeability samples under partially glycerin-saturated conditions and the low-permeability samples under partially water-saturated conditions produce strong dispersion in the same frequency range （2-2000 Hz）. This suggests that fluid mobility largely controls the pore-fluid movement and pore pressure in a porous medium. High fluid mobility facilitates pore-pressure equilibration either between pores or between heterogeneous regions, resulting in a low-frequency domain where the Gassmann equations are valid. In contrast, low fluid mobility produces pressure gradients even at seismic frequencies, and thus dispersion. The latter shows a systematic shift to lower frequencies with decreasing mobility. Sandstone samples showed variations in Vp as a function of fluid saturation. We explore the applicability of the Gassmann model on sandstone rocks. Two theoretical bounds for the P-velocity are known, the Gassmann-Wood and Gassmann-Hill limits. The observations confirm the effect of wave-induced flow on the transition from the Gassmann-Wood to the Gassmann-Hill limit. With decreasing fluid mobility, the P-velocity at 2-2000 Hz moves from the Gassmann-Wood boundary to the Gassmann-Hill boundary. In addition,, we investigate the mechanisms responsible for this transition.展开更多
基金supported by 973 Program "Fundamental Study on the Geophysical Prospecting of the Deep-layered Oil and Gas Reservoirs"(No.2013CB228600)
文摘The elastic moduli of four sandstone samples are measured at seismic （2-2000 Hz） and ultrasonic （1 MHz） frequencies and water- and glycerin-saturated conditions. We observe that the high-permeability samples under partially water-saturated conditions and the low-permeability samples under partially glycerin-saturated conditions show little dispersion at low frequencies （2-2000 Hz）. However, the high-permeability samples under partially glycerin-saturated conditions and the low-permeability samples under partially water-saturated conditions produce strong dispersion in the same frequency range （2-2000 Hz）. This suggests that fluid mobility largely controls the pore-fluid movement and pore pressure in a porous medium. High fluid mobility facilitates pore-pressure equilibration either between pores or between heterogeneous regions, resulting in a low-frequency domain where the Gassmann equations are valid. In contrast, low fluid mobility produces pressure gradients even at seismic frequencies, and thus dispersion. The latter shows a systematic shift to lower frequencies with decreasing mobility. Sandstone samples showed variations in Vp as a function of fluid saturation. We explore the applicability of the Gassmann model on sandstone rocks. Two theoretical bounds for the P-velocity are known, the Gassmann-Wood and Gassmann-Hill limits. The observations confirm the effect of wave-induced flow on the transition from the Gassmann-Wood to the Gassmann-Hill limit. With decreasing fluid mobility, the P-velocity at 2-2000 Hz moves from the Gassmann-Wood boundary to the Gassmann-Hill boundary. In addition,, we investigate the mechanisms responsible for this transition.
