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 i nfluence on parameter estimation and pumping-test design are investiga ted in terms of pumping tests conducted in a large-diameter well. It i s concluded that the well storage reduces the sensitivities of drawdow n to transmissivity and storativity, and increases the correlation bet ween them. This leads to uncertainties in estimating the aquifer param eters, especially storativity. The most informative drawdowns in terms of parameter estimation change with time and space. This is instructi ve for pumping-test design in a large-diameter well. Both hypothetical and real examples are used to demonstrate key ideas.