New Simplified Models of Single-Well Push-Pull Tests With Mixing Effect

AbstractWhen using singlewell pushpull (SWPP) tests to characterize in situ aquifer related to reactive transport, approximate analytical solutions were preferred to determine the aquifer dispersivity and other parameters, due to its computational efficiency. Simplified models were proposed in this study to estimate the retardation factor for a SWPP test with a reactive tracer, where the dispersivity had to be determined firstly using a SWPP test with a conservative tracer. Here, we find that previous models associated with SWPP tests contain an untested assumption when dealing with solute transport in the wellbore, probably causing great errors when interpreting the test data. This assumption states that the wellbore mixing effect is negligible in both injection and extraction phases, where the mixing effect refers to the mixing process between the native wellbore water and solute introduced into the wellbore. In this study, new approximate analytical solutions of the SWPP test are proposed for a fully penetrating well and a pointsource well by specifically considering the wellbore mixing effect. The new models of this study are tested by semianalytical solutions in Laplace domain and finite difference solutions. Results indicate that the new models perform substantially better than previous models of ignoring the wellbore mixing effect, which should not be overlooked when interpreting SWPP test data.

New Simplified Models of Single-Well Push-Pull Tests With Mixing Effect Academic Article