An Alternative Approach to Acquiring Permeability from Ultrasonic S‐Wave

This is the authors' abstract. We don't add key points for this paper.

Water interaction between fractures and rock matrix is one of the themes in hydrogeology. Accurate values of Darcy permeability ( k D ) of the matrix are desired for better quantification of the water interaction. In contrast to the traditional method using seepage experiments to measure k D of a rock, this study uses the technique of ultrasonic shear (S‐) wave for determining k D of the rock matrix. From the perspective of waves, Darcy seepage is driven by slow compressional (P‐) wave at very low frequencies, and k D is associated with slow P‐wave in the regime of low frequency. Similarly, there is another permeability associated with S‐wave, namely, S‐wave permeability ( k s ). The rock samples are Navajo sandstone and Berea sandstone. Data of the dry sandstones with water are entered into Biot theory for yielding saturated phase velocity ( V s ) and the quality factor due to viscous fluid ( Q s ). Then, ultrasonically measured V s and Q s are fitted with the use of the model output. For Navajo sandstone, low‐frequency k s appears to be 0.107–0.115 darcy, surprisingly close to k D of 0.1 darcy. For Berea sandstone, low‐frequency k s turns out to be 0.081 darcy, also consistent with k D of 0.075 darcy. The success robustly shows that Biot theory is applicable to S‐wave in isotropic rock free of fractures. More importantly, the comparability between low‐frequency k s and k D demonstrates that ultrasonic S‐wave is an alternative approach to acquiring k D of the matrix.