SENSITIVITY OF DRAWDOWN TO PARAMETERS AND ITS INFLUENCE ON PARAMETER-ESTIMATION FOR PUMPING TESTS IN LARGE-DIAMETER WELLS

The sensitivity features of drawdown to aquifer parameters and their influence on parameter estimation and pumping-test design are investigated in terms of pumping tests conducted in a large-diameter well. It is concluded that the well storage reduces the sensitivities of drawdown to transmissivity and storativity, and increases the correlation between them. This leads to uncertainties in estimating the aquifer parameters, especially storativity. The most informative drawdowns in terms of parameter estimation change with time and space. This is instructive for pumping-test design in a large-diameter well. Both hypothetical and real examples are used to demonstrate key ideas.