The mechanisms of S-wave attenuation in grainstones

Abstract

Abstract The dominant mechanism of P-wave attenuation in fluid-saturated rock is well known to be the pore-scale squirt. However, the S-wave does not change the average fluid pressure in a pore and the pore volume stays unchanged. As such, the S-wave has a mechanism of attenuation distinctively different from the P-wave. This paper attempts to resolve the mechanisms of S-wave attenuation in fluid-saturated grainstones. The first mechanism is the viscous boundary layer in a fracture, the second is fluid acceleration plus a real-number permeability and the third mechanism is fluid acceleration plus a complex-number permeability (which arises from the viscous boundary layer). D'Euville limestone and Berea sandstone are used as illustrative examples. Ultrasonic velocity and the quality factor due to pore fluid (Qs) are compared between the three models and measurement. The results indicate that fluid acceleration plus the viscous boundary layer is the mechanism of S-wave attenuation in the water-saturated grainstones. In addition, the third model reveals a novel convex in the curve of Qs in the frequency range of 107–108 Hz.