Elastic Moduli and Seismic Wave Attenuation in Dry and Saturated Rock. Volume 2.Modulus Dispersion and Attenuation

摘要

Four different laboratory techniques were used to determine Young's modulus andextensional wave attenuation as a function of frequency for the same rock specimen while minimizing variations in other important parameters. The data were then pieced together and compared over a net frequency bandwidth ranging from .01 to 1,000,000 Hz. Specimens of Sierra White granite and Berea sandstone were analyzed in dry and water saturated states. Dispersion in moduli and attenuation in the dry samples are negligible. Frequency dependent attenuation and modulus dispersion are clearly evident in the saturated samples and attributed to flow of pore fluid, unconfined sample boundaries and sample dimensions. A cyclic loading technique was used to examine the effects of strain amplitude and water saturation at constant frequency. The modulus and attenuation determined from hysteresis loops are strain amplitude dependent in both dry and saturated states. As strain amplitudes are increased above 5 x .000001, the modulus continually drops while attenuation increases. A significant reduction in modulus is observed in the saturated samples that is attributed to a reduction in surface energy at the fluid/rock interface and an unconfined sample radial boundary.