Oscillatory Slug-Test Data Sets: A Comparison of Two Methods

Abstract

Slug tests performed in high transmissivity aquifers may exhibit underdamped inertial oscillatory behavior. Analytical methods for oscillatory data have been developed, but are mathematically intimidating. Spreadsheet modeling is helpful because ready adjustments to the equations required to match the well-response data are quickly applied. A simplified presentation of the Kipp method for the practicing hydrogeologist is presented along with a spreadsheet model. A file containing the type curves is available over the Internet at www.mtech.edu from the Geological Engineering home page. Examples from southwestern Montana showing a variety of damping responses and well completions are presented to show how to perform the analysis. Sixteen well responses were modeled using the van der Kamp and Kipp methods, and the outcomes were compared using the two methods with oscillatory responses. Generally, there is good agreement between the methods. Screened wells tend to show more uniform oscillatory behavior, although open-hole completions can be analyzed with success. Other practical field applications and observations are presented. The theory describing inertial effects has been constrained to confined aquifers, although all aquifers exhibit elastic behavior during the initial disturbance from pumping or instantaneous slug removal.