Anelasticity and dispersion in dry unconsolidated sands

Laboratory measurements reveal frame modulus dispersion and creeping behavior in room-dry samples of unconsolidated, quartzo-feldspathic Upper Miocene turbidites from the Wilmington Field, CA. A single standard linear solid model predicts both the dispersion and the creep response. Similar behavior is observed in Ottawa sand samples when mixed with wetted Montmorillonite. In this case the magnitude of dispersion and creep increase with increasing clay content. We suggest that the anelastic behavior of the Wilmington sands is due to the presence of micas and a small amount of clay. The transition frequency of 2×10−4Hz (i.e., between high and low frequency behavior) suggests that seismic, sonic, and ultrasonic measurements of rock moduli are quite similar in the absence of fluids. The static frame modulus should be used to model tectonic processes and long term production-related changes in oil-field environments.