Effects of porosity and clay content on acoustic properties of sandstones and unconsolidated sediments
Ultrasonic compressional and shear velocities were measured in vacuum-dried and water-saturated states as functions of confining pressure for 80 sandstone samples whose porosities ranged from 2-30% and clay contents from zero to 50%. For shaly sandstones, both V/sub p/ and V/sub s/ were found to correlate linearly with porosity and approximated linearly with clay content at differential pressures higher than 10 MPa. Clays classified as bound- and matrix-clay are affected mainly by reducing shear modulus rather than bulk modulus. Velocities of shaly sandstones are significantly lower than those of clean sandstones because of the bound-clay effects. The effects of porosity and clay content were simulated using different bounds and porous models. The results reveal that even the simple velocity-porosity relation for clean sandstones cannot be modeled accurately. Using the ultrasonic velocity data and the Biot-Gassmann theory, velocity dispersions of water-saturated sandstones were estimated. The Biot dispersions, usually less than 1%, increase with increasing porosity and decreasing clay content. The apparent velocity dispersions of shaly sandstones range from 1 to 9%, and are dominated by non-Biot dispersion, which increases with decreasing porosity and increasing clay content. Porosities and V/sub p/ and V/sub s/ of saturated sand-clay mixtures with clay content by weight fraction ranged from 0 to 30% were measured at differential pressures up to 50 MPa. The study suggests that clay particles can be deformed plastically. Porosity decreases while velocities increase with increasing clay content. Shear velocity of saturated clay show much low value than that of pure sand.
- Research Organization:
- Stanford Univ., CA (USA)
- OSTI ID:
- 5477973
- Country of Publication:
- United States
- Language:
- English
Similar Records
Characterization of rock for constraining reservoir scale tomography at the Geysers geothermal field
Ultrasonic velocities in sands--Revisited
Related Subjects
580300* -- Mineralogy
Petrology
& Rock Mechanics-- (-1989)
CLAYS
COMPRESSION
CORRELATIONS
MATHEMATICAL MODELS
MECHANICAL PROPERTIES
POROSITY
PRESSURE DEPENDENCE
QUANTITY RATIO
ROCKS
SANDSTONES
SATURATION
SEDIMENTARY ROCKS
SHEAR PROPERTIES
SOUND WAVES
ULTRASONIC WAVES
VELOCITY
WATER SATURATION
WAVE PROPAGATION