Abstract 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.
This work was supported by 973 Program “Fundamental Study on the Geophysical Prospecting of the Deep-layered Oil and Gas Reservoirs” (No. 2013CB228600).
Cite this article:
. Velocity dispersion and fluid substitution in sandstone under partially saturated conditions[J]. APPLIED GEOPHYSICS, 2018, 15(2): 188-196.
Adam, L., and Otheim, T., 2013, Elastic laboratory measurements and modeling of saturated basalts: Journal of Geophysical Research: Solid Earth, 118, 840-851.
Adelinet, M., Fortin, J., Guéguen Y., Schubnel A., and Geoffroy, L., 2010, Frequency and fluid effects on elastic properties of basalt: Experimental investigations: Geophysical Research Letters, 37, L02303.
Batzle, M. L., Han, D., and Hofmann, R., 2006, Fluid mobility and frequency-dependent seismic velocity-Direct measurements: Geophysics, 71(1), N1-N9.
Berryman, J. G., and Wang H. F., 2000, Elastic wave propagation and attenuation in a double-porosity, dual-permeability medium: International Journal of Rock Mechanics and Mineral Science, 37, 63-78.
Biot, M. A., 1956, Theory of propagation of elastic waves in a fluid-saturated porous solid: II-Higher frequency range: Journal of the Acoustic Society of America, 28, 179-191.
David, E. C., and Zimmerman, R. W., 2012, Pore structure model for elastic wave velocities in fluid-saturated sandstones: Journal of Geophysical Research, 117, B07210.
Deng, J., Zhou, H., Wang, H., Zhao, J., and Wang, S., 2015, The influence of pore structure in reservoir sandstone on dispersion properties of elastic waves: Chinese Journal of Geophysics, 58, 3389-3400.
Dutta, N. C., and Ode, H., 1979, Attenuation and dispersion of compressional waves in fluid-filled porous rocks with partial gas saturation White model: Part II: Results: Geophysics, 44, 1789-1805.
Gary, M., and Tapan, M., 1998, Bounds on low-frequency seismic velocities in partially saturated rocks: Geophysics, 63, 918-924.
Lucet, N., Rasolofosaon, P. N. J., and Zinszner, 1991, Sonic properties of rocks under confining pressure using the resonant bar technique: J. Acoust. Soc. Am., 89(3), 980-990.
Mavko, G., and Jizba, D., 1991, Estimating grain-scale fluid defects on velocity dispersion in rocks: Geophysics, 56, 1940-1949.
Mavko, G., Mukerji, T., and Dvorkin, J., 2009, The rock physics handbook: Tools for seismic analysis of porous media: Cambridge University Press.
Maxim, L., and Julianna, T. -S., 2009, Direct laboratory observation of patchy saturation and its effects on ultrasonic velocities: The Leading Edge, 24-27.
Mikhaltsevitch, V., Lebedev, M., and Gurevich, B., 2014, A laboratory study of low-frequency wave dispersion and attenuation in water-saturated sandstones: The Leading Edge, 33, 616-622.
Müller, T. M., Gurevich, B., and Lebedev, M., 2010, Seismic wave attenuation and dispersion resulting from wave-induced flow in porous rocks—A review: Geophysics, 75(5), 75A-147A.
Pimienta, L., Fortin J., and Guéguen, Y., 2015a, Bulk modulus dispersion and attenuation in sandstones: Geophysics, 80(2), D111-D127.
Spencer, J. W., and Shine, J., 2016, Seismic wave attenuation and modulus dispersion in sandstones: Geophysics, 81(3), D219-D239.
Wang, S. X., Zhao, J. G., Li, Z. H., et al., 2012, Differential Acoustic Resonance Spectroscopy for the acoustic measurement of small and irregular samples in the low frequency range: Journal of Geophysical Research, 117(B6), B06203.
White, J. E., 1975, Computed seismic speeds and attenuation in rocks with partial gas saturation: Geophysics, 40, 224-232.
Yin, H., Wang, S., Zhao, J., Ma, X., Zhao, L., and Cui, Y., 2016, A laboratory study of dispersion and pressure effects in partially saturated tight sandstone at seismic frequencies: 86th Annual International Meeting, SEG, Expanded Abstracts, 3236-3240.
Zhao, J., Tang, G. Y., Deng, J. X., Tong, X. L., and Wang, S. X., 2013, Determination of rock acoustic properties at low frequency: A differential acoustical resonance spectroscopy device and its estimation technique: Geophysical Research Letters, 40, 2975-2982.
Zhao, J. G., Wang, S. X., Tong, X. L., Yin, H. J., Yuan, D. J., Ma, X. Y., Deng, J. X., and Xiong, B., 2015, Geophysical Journal International, 202, 1775-1791.