Step-drawdown test for identifying aquifer and well loss parameters in a partially penetrating well with irregular (non-linear increasing) pumping rates

Abstract

A step-drawdown test with an increasing pumping rate at each step in a fully penetrating well is a typical procedure for estimating aquifer parameters and well losses. However, partially penetrating wells in closed aquifers have also been adopted mainly due to economic constraints with a stepwise increase in the pumping rate. In this study, a new empirical method is proposed based on the stepwise drawdown defined by irregular pumping rates in a partially penetrating well. The method was validated by fitting drawdown data from classical works. The characteristics of the drawdowns and well losses were discussed for varying pumping scenarios. The results indicate that the new empirical method interprets previous works more accurately for a fully penetrating well and also effectively estimates the aquifer and well loss parameters. A new coefficient, the pumping rate-varying index α, was introduced to indicate the pumping rate difference (ΔQ) between the two steps. As such, a negative pumping rate difference would decrease the well-loss and result in a negative α. In addition, the effect of the ratio of the well’s screen length to aquifer thickness demonstrates that a longer screen would cause a larger well loss. Finally, the proposed empirical method was applied to a fieldwork conducted in Xiangyang city, central China, to investigate the aquifer and well loss parameters using the particle swarm optimization (PSO) method.