Li Guangquan, Li Xiang, Liu Kui
Department of Geophysics, Yunnan University, Kunming, Yunnan 650504, China.
J Acoust Soc Am. 2024 Aug 1;156(2):891-897. doi: 10.1121/10.0028192.
Unconsolidated porous media are distinct from consolidated porous rocks in the negligible bulk and shear moduli. This paper is motivated by resolving the control mechanism of P-wave attenuation in the media (represented by Toyoura sands and glass beads) saturated with water. The first model is Biot theory in which longitudinal friction (arising from velocity difference between the two phases) is quantified using dynamic permeability as a function of frequency. The first model simulates phase velocity (Vp) and the ultrasonically measured quality factor (Qp) well. A second model is the transverse squirt model in which squirt is induced by pressure differential between contact of grains (COG) and the main pore space. The second model outputs unrealistic Vp and Qp. The results reveal that P-wave attenuation in unconsolidated porous media (saturated with water) is governed by longitudinal friction rather than intrapore squirt. Remarkably, low-frequency dynamic permeability is much smaller than Darcy permeability, indicating that ultrasonic P-wave is surprisingly capable of indirectly detecting the very narrow gap at COG.
非固结多孔介质与固结多孔岩石不同，其体积模量和剪切模量可忽略不计。本文旨在解决水饱和介质（以丰浦砂和玻璃珠为代表）中纵波衰减的控制机制问题。第一个模型是毕奥理论，其中纵向摩擦力（由两相之间的速度差引起）通过作为频率函数的动态渗透率来量化。第一个模型能很好地模拟相速度（Vp）和超声测量的品质因数（Qp）。第二个模型是横向喷射模型，其中喷射是由颗粒接触点（COG）与主要孔隙空间之间的压差引起的。第二个模型输出的Vp和Qp不切实际。结果表明，非固结多孔介质（水饱和）中的纵波衰减受纵向摩擦力而非孔隙内喷射的控制。值得注意的是，低频动态渗透率远小于达西渗透率，这表明超声纵波能够惊人地间接检测到颗粒接触点处非常狭窄的间隙。
