Velocities of seismic waves in porous rocks
- Massachusetts Inst. of Tech., Cambridge
Velocities of seismic compressional and shear waves in porous rocks under different saturation conditions are calculated theoretically and compared with laboratory data. For theoretical formulations, the rocks are represented by a solid matrix and pores of spherical and oblate spheroidal shapes. The effect of confining pressure on velocities is calculated by taking into account pore closing and saturant compressibilities. The theoretical calculations show that with all other parameters fixed, thin pores (small aspect ratios) have much greater effects on elastic moduli and velocities than rounded pores at the same concentration. The properties of the saturating fluid (gas, oil, or water) have greater effects on the compressional velocities than on shear velocities. The velocities of compressional waves are higher when the rock is saturated with water than when it is dry or gas-saturated. For shear waves the behavior is generally opposite, with shear velocities higher in the dry or gas-saturated case than in the water-saturated case. Compressional and shear velocities measured as a function of pressure in laboratory samples of granite, limestone, and sandstone, under dry and water-saturated states, are fitted with theoretical curves and pore shape spectra which fit the data are calculated. A spectrum of pore shapes ranging from spheres to very fine cracks (aspect ratios 1 to 10/sup -5/) is required to fit the data. Theoretical velocities calculated using these models fit the measured velocities in water-saturated and frozen rocks, as well as the compressional velocities in partially saturated rocks.
- OSTI ID:
- 7339084
- Journal Information:
- Geophysics; (United States), Vol. 41:4
- Country of Publication:
- United States
- Language:
- English
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