Acoustics Response of Granular Porous Media with Wettability Changes

Summary Quantifying the acoustic response to different levels of pore surface wettability of rocks has great potential in geophysical applications, such as remotely monitoring the displacing oil efficiency for enhanced oil recovery. However, acoustic signatures of wettability changes in porous rocks are poorly understood. To generate a favourable experimental condition for wettability acoustic monitoring, we approach this issue by ultrasonic experiments with partially saturated glass-bead packings before and after chemical treatment that increases contact angles and improves the water–bead coupling. The measurements under hydrophilic and weakly hydrophilic conditions show that the hydrophilic bead packings result in higher velocity and lower attenuation of coherent waves. Interestingly, a series of incoherent high-frequency waves with wave speeds exceeding those of the coherent waves are observed once reaching a critical saturation. We interpret the observed coherent and incoherent waves in terms of the wettability-dependent ability by liquid bridges that create a force chain across neighboring beads.