Volumetric Approach to type Curves in leaky Aquifers

Abstract

A nonequilibrium formula in terms of the depression cone volume is used to predict the drawdown variations in a fully penetrating large diameter well discharging from a leaky aquifer. The derivation of the formula is based on the continuity and Darcy laws. Sets of type curves are presented to find the aquifer and aquitard hydraulic properties. The asymptotic curves, as the leakage diminishes to zero, approximate the type curves for large diameter wells in confined aquifers. Leaky aquifer type curves for drawdowns in the producing well have three distinctive portions. The initial portion is a straightline and it reflects the effect of the well storage. It does not provide any relevant information about either the aquifer or the semipervious layer hydraulic properties. The second portion is a transition from the well storage effect to the complete leakage effect only. The last portion is a horizontal line corresponding to the steady state flow due to leakagev. In fact, the second portion is the most significant one from the aquifer parameters determination point of view. Comparison of these type curves with the point source solution indicates that the deviations are larger for small times but large leakages. However, for large times and small leakages, these deviations reduce to practically acceptable limits.