Single-well push-pull test in transient Forchheimer flow field
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2017 Elsevier B.V. Using the single-well push-pull (SWPP) test to quantify in situ aquifer characteristics associated with solute transport (dispersion coefficient, geobiochemical reaction rates), the accuracy of parameter estimation was not only dependent on the solute transport models but also the groundwater flow models. However, many previous studies on the SWPP test were based on assumptions over-simplifying the flow field, namely, groundwater flow followed Darcy's law; flow was in the steady state during the entire test duration; the wellbore storage could be negligible. In this study, we have carefully examined such assumptions by developing a new finite-difference model of the SWPP test under the transient Forchheimer flow condition, considering the wellbore storage. The SWPP test included an injection phase, a chaser phase, a rest phase, and an extraction phase. The results showed that the concentration of the steady-state flow solution was greater than that of the transient flow solution at the beginning, and its peak value was also greater than that of the transient flow solution. The difference between the breakthrough curves (BTCs) of the transient flow SWPP model and the steady-state flow SWPP model was not negligible, and such a difference increased with the decreasing specific storage. We also found that BTCs were not sensitive to the inertial force coefficient, while they were sensitive to the wellbore storage. BTCs with different radius of the wellbore (rw) were clearly different from each other, and a larger rw resulted in a greater concentration at the well during the extraction phase.
