Type Curve Analysis of Inertial Effects in the Response of a Well to a Slug Test

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Abstract
The water level response to a slug or bailer test in a well completed in a confined aquifer has been evaluated taking into account well‐bore storage and inertial effects of the water column in the well. The response range, from overdamped with negligible inertial effects to damped oscillation, was covered employing numerical inversions of the Laplace‐transform solution. By scaling the time with respect to the undamped natural period of the well‐aquifer system and by using the damping parameter for a second‐order damped, inertial‐elastic system, a set of type curves was constructed that enables water level response data from a slug or bailer test to be analyzed under conditions where the inertial parameter is large. Values of transmissivity and effective static water column length can be determined when an estimate of storage coefficient is available. The numerical solution and resulting type curves cover the transition range between the limiting cases of negligible inertial effects and of damped oscillation that have been treated by others. Two examples of slug test analysis show that precise results depend on accurate measurements of water level displacement (±1% of initial value).