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
Hydroelastic effect of sloshing is studied through an experimental investigation. Different excitation frequencies are considered with low-fill-depth and large amplitude. Morlet wavelet transform is introduced to anal...Hydroelastic effect of sloshing is studied through an experimental investigation. Different excitation frequencies are considered with low-fill-depth and large amplitude. Morlet wavelet transform is introduced to analyze the free surface elevations and sloshing pressures. It focuses on variations and distributions of the wavelet energy in elastic tanks. The evolutions of theoretical and experimental wavelet spectra are discussed and the corresponding Fourier spectrums are compared. Afterwards, average values of the wavelet spectra are extracted to do a quantitative study at various points. From the wavelet analysis, sloshing energies are mainly distributed around the external excitation frequency and expanded to high frequencies under violent condition. In resonance, experimental wavelet energy of the elevation in elastic tanks is obviously less than that in the rigid one; for sloshing pressures, the elastic wavelet energy close to the rigid one and conspicuous impulse is observed. It recommends engineers to concern the primary natural frequency and impulsive peak pressures.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.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51609168 and 51239008)the Open Fund of State Key Laboratory of Coastal and Offshore Engineering(Grant No.LP1608)the National Key Basic Research Program of China(Grant No.2014CB046804)
文摘Hydroelastic effect of sloshing is studied through an experimental investigation. Different excitation frequencies are considered with low-fill-depth and large amplitude. Morlet wavelet transform is introduced to analyze the free surface elevations and sloshing pressures. It focuses on variations and distributions of the wavelet energy in elastic tanks. The evolutions of theoretical and experimental wavelet spectra are discussed and the corresponding Fourier spectrums are compared. Afterwards, average values of the wavelet spectra are extracted to do a quantitative study at various points. From the wavelet analysis, sloshing energies are mainly distributed around the external excitation frequency and expanded to high frequencies under violent condition. In resonance, experimental wavelet energy of the elevation in elastic tanks is obviously less than that in the rigid one; for sloshing pressures, the elastic wavelet energy close to the rigid one and conspicuous impulse is observed. It recommends engineers to concern the primary natural frequency and impulsive peak pressures.
