1971 / 2019-08-30 21:51:58

Models of single-well push-pull test with mixing effect in the wellbore

12、水文地质与水科学 > 专题7：地下水模拟与不确定性分析

The mechanism of solute transport around the wellbore was found to play an important role in
the single-well push-pull (SWPP) test, but it was grossly overlooked in previous studies. For instance, the
mixing effect of injected tracer with water in the wellbore was ignored in analyzing both injection and
extraction phases of SWPP. In this study, new models were developed by including such a mixing effect in the
wellbore. Two types of boundary conditions at the wellbore were considered: the resident concentration
continuity and the flux concentration continuity. To test the assumptions used in the mathematical model,
the stochastic modeling, the numerical simulation, and the laboratory-controlled experiment were
executed. Results showed that the SWPP test was sensitive to the mixing effect in both injection and
extraction phases. A larger wellbore volume could result in a smaller concentration at the late stage of the
extraction phase. Flux concentration continuity was more reasonable in describing solute transport at the
wellbore-aquifer interface than resident concentration continuity, and the difference between them
decreased with decreasing radial dispersivity. The MODFLOW/MT3DMS package contained an invalid
assumption on the mixing effect for the SWPP test. Stochastic modeling demonstrated that the
homogeneous assumption was a good approximation for the reality when the variance of natural logarithm
of the autocorrelated hydraulic conductivity field was less than 0.25 (σ2lnK≤0:25). The laboratory-controlled
experiment showed that the radial advection-dispersion equation model of this study worked well for the
well-sorted sand aquifer