Predicting long-term well performance from short-term well tests in the Piedmont.

摘要

A reliable estimate of the physically sustainable discharge of a well is a fundamental aspect affecting management of water resources, but there are surprisingly few analyses describing on how to make such an estimate. Current available methods include either an empirical or a quantitative approach. The empirical method is based on holding the head or flow rate constant in order to maintain a target drawdown for as long as possible. The second method involves conducting a constant rate test to calculate the properties of the aquifer, T and S, and extrapolate the drawdown using a type curve (i.e. Theis analysis).;To improve well performance prediction, we have been using the effects of streams on short-term hydraulic well tests to predict long-term performance during pumping. An analysis was developed to calculate the long-term steady state specific capacity of a well using early-time information from a constant-rate test. The analysis first considers a homogeneous confined aquifer with a well fully penetrating the aquifer. A more detailed analysis considers a variable strength of interaction between a stream and a well extends the versatility of this method to a wide range of conditions.;The analysis is evaluated numerically to explore effects from typical Piedmont geometries not included in the analysis. Evaluating the analytical solution with numerical models allowed the characterization of different Piedmont geometries to determine the effectiveness of the analysis. Numerical models were allowed to reach steady state conditions, and the analysis was compared to the numerical results.;The analysis was then evaluated with two field examples from well tests in the Piedmont of South Carolina. The results show that the analysis successfully predicts the long term performance of wells within a few percent of the actual observed steady state specific capacities.