Non-Darcian effect on slug test in a leaky confined aquifer
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2015 Elsevier B.V. Slug test has been commonly applied to determine the near-well aquifer properties because of its logistical and economic advantages over other aquifer tests. Instantaneously increasing or decreasing the water level inside a slug test well will generate a significant hydraulic gradient near the well screen-aquifer interface (particularly at early stage of slug test), which may result in near-well aquifer flow deviated from Darcian behavior. However, previous studies on slug test rarely considered non-Darcian flow process associated with the slug test. In this study, a transient model of slug test in a leaky confined aquifer was established considering non-Darcian horizontal flow in the aquifer, and Darcian and vertical flow in the aquitard. The non-Darcian flow in the aquifer was described by the Izbash (power-law) equation. A finite-difference solution was presented for solving the non-linear model of slug test, the accuracy of which was tested through comparison with a previous analytical solution. By analyzing the sensitivities of dimensionless aquitard leakance (. D), non-Darcian index (. n), and ratio of well screen radius versus well casing radius (. ) on the water level recovery (WLR) of slug test, one could conclude that the rate of WLR increased with the decrease of n for a given time. The WLR curve of Darcian flow (. n=. 1) was above the curves of non-Darcian flow, including fully developed turbulent flow. There was a deflection point for each WLR curve without the aquitard leakance in log-log scales, and the slope of the curve approached a constant after such a point. The effects of aquitard leakance on WLR for non-Darcian case appeared later than Darcian case. The normalized sensitivity coefficients of WLR with respect to n, D and were negative, and they were most sensitive to n and least to D.
