Analysis and Application of Step-Drawdown Test

Abstract

A review of the theory behind the step-drawdown test shows that the analytical method developed by Rorabaugh should be routinely used to discriminate among various types of flow and to determine more accurately flow parameters. The usual analysis for one selected time after the beginning of each step should be supplemented by a consideration of test results as a whole to assure the derived flow equations satisfactorily describe all observed drawdowns. Drawdown trends should be extrapolated by projecting the trends evident toward the end of each step and not by assuming slopes to be proportional to pumping rates. In extrapolating, the time origin for each step should be taken as the beginning of that step. In deriving well efficiency, the time for which it applies should be stated and it is recommended that some standard time should be adopted for this purpose. A number of illustrative examples from Alberta, Canada, and other areas are presented.