A theoretical and experimental analysis of minipermeameter response including gas slippage and high velocity flow effects

Minipermeameters have been used in a wide variety of laboratory and field applications where localized measurements are needed to characterize the spatial distribution of permeability. The ability of the device to obtain a large quantity of cheap, rapid, nondestructive measurements is unsurpassed by conventional methods; however, to date there have been no attempts to mathematically model the response of the minipermeameter in flow patterns consistent with its applications. In this study, the authors introduce a geometrical factor which, when submitted into a modified form of Darcy's law, allows the computation of permeability from steady-state measurements of gas flow rate and injection pressure. This geometrical factor (G/sub o/), determined to be a function of injection tip-seal size and sample dimensions, is given for two basic flow geometries: (1) half-space flow as encountered in outcrop measurements and (2) unconfined core-plug flow for measurements taken on samples not held in a conventional Hassler-sleeve device. Examination of G/sub o/ factors for both flow patterns allows us to estimate the depth of investigation for typical tip-seal dimensions. Then, through experiment, they validate the geometrical factor approach for the unconfined core-plug flow geometry. These experiments reveal that, for certain ranges of sample permeability, the response ofmore » the minipermeameter is affected by gas-slippage and high-velocity gas flow. They demonstrate how to correct for these effects on an example of a highly detailed vertical sequence of measurements taken from a Page sandstone core.« less