Laboratory Permeability Errors from Annular Wall Flow
- Tetsu K. Tokunaga
Laboratory saturated hydraulic conductivity measurement errors introduced by permeameter fluid flow within gaps between sample cores and permeameter walls are estimated through a simple model that idealizes gap flow as occurring within a smooth annulus. The inner annulus boundary fluid velocity is matched to the Darcy velocity within the sample core. The ratio of flow within the annulus to that within the core, QRap/Qcore, is shown to have both cubic and linear dependence on the gap width. QRap/Qcore is also shown to be inversely dependent on both the core permeability and the permeameter radius. Although the model is very idealized, the strong possibility of overestimating permeabilities in laboratory cores is demonstrated. Related concerns include flow in fractured porous media, and potential errors in interpreting solute travel times in laboratory columns and field lysimeters.
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