A low-cost model for slug tests in a confined aquifer with skin-zone effect

While the effect of small-scale skin has been extensively investigated, numerical models incorporating the effect require expensive computational cost due to fine spatial discretization of the skin and have not been widely available. This study develops a new model for slug tests at a partially-penetrating well in a two-zone confined aquifer of skin and formation zones. A new basic formulation defines transient flow in the skin with an additional skin factor reflecting the skin storage effect. The formulation assumes horizontal flow in the skin with excluding the vertical skin hydraulic conductivity. The analytical solution and finite element solution of the model are developed. The analytical expression relating the skin factor to the skin specific storage is derived. Results suggest the formulation is a useful alternative to conventional flow equation for the skin in achieving coarse spatial discretization and low computational cost. The present solution agrees well with the field head data obtained from Butler (2019). To conclude, this study presents theoretical advance and efficient simulation in modeling of well hydraulics.