SINGLE-WELL PUSH-PULL TEST FOR A PARTIALLY PENETRATING WELL IN A FLOW FIELD WITH A FINITE HYDRAULIC DIFFUSIVITY

The single-well push-pull (SWPP) test of a partially penetrating well is commonly used to quantify in situ aquifer characteristics. However, previous mathematic models of the SWPP test are often based on an over-simplified conceptual model, which includes the following assumptions such as 1) the hydraulic diffusivity is infinite or the media is incompressible, 2) vertical flow is negligible, 3) water flux is uniformly distributed along the well screen, 4) the wellbore storage could be negligible, and 5) dispersion coefficients only depend on the horizontal component of flow velocity. In this study, we will investigate the influence of such assumptions on the solute transport in the SWPP test by developing a new finite-difference numerical model under a flow field with a finite hydraulic diffusivity, considering the wellbore storage. Two types of the boundary conditions will be considered for the well screen: uniformly distributed flux boundary condition (UFBC) and uniformly distributed head boundary condition (UHBC). The dispersion coefficients are in a tensor form, not only depending on the horizontal flow, but also on the vertical flow. The SWPP test includes four operational phases: an injection phase, a chaser phase, a rest phase, and an extraction phase. The results show that the influence of the assumptions mentioned above may cause non-negligible errors when modeling the solute transport in the SWPP test and should not be overlooked. The difference between the UFBC and UHBC solutions is obvious in the early extraction stage, and becomes negligible at the late stage. Field application demonstrates that the estimated values of dispersivity are not unique, if only best-fitting the BTCs of the SWPP test. The time-drawdown data is necessary and should be collected during the SWPP test, which could help determine the hydraulic parameters of the aquifer, and improve the accuracy of the in situ aquifer characteristics associated with solute or geothermal transport.