Abstract
Equations were derived that facilitate prediction of both the onset of non-Darcy flow in a porous medium, and the viscous and inertia force fractions of the hydraulic gradient, dp/ds, after non-Darcy flow has begun. The equations are based on measurements of hydraulic gradients dp/ds and corresponding fluxes q carried out with a permeameter in both the Darcy and non-Darcy flow regions on 0.8-mm to 1.4-mm and 0.4-mm to 0.6-mm glass beads and sand. Hydraulic resistivities r were calculated from dp/ds and q. The value of r(q) was found to be linear in the non-Darcy region. This linearity was used to determine the value of a non-Darcy flow parameter e. Its value was found to be 0.7 for glass beads and 0.9 for sand. At the onset of non-Darcy flow, 94.7% and 5.3% of dp/ds were used in viscous and inertia force flow, respectively. Calculations require knowledge of both the intrinsic permeability and e for the porous stratum under consideration. A value of e=0.9 is suggested for materials found in the field.
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