Inversion of hydraulic parameters of high permeability confined aquifer based on slug test

To improve the accuracy of estimated hydraulic parameters such as hydraulic conductivity and specific storage in confined aquifers with high permeability, and provide a scientific explanation for the nonlinear oscillation phenomenon of test well water levels, this study established a slug test model that takes into account the skin and non-Darcy flow effects, as well as inertial force action. The skin effect was described by Robbin boundary conditions and the non-Darcy flow effect was explained by the Forchheimer equation; momentum balance equation expressed the inertial force action . The Laplace transform method was used to derive the analytical solution of this model. Then the impacts of three factors on estimating of hydraulic parameters were analyzed using field data. The results show that the influences of skin effect, non-Darcy flow effect, and inertia force action on the parameter estimation cannot be ignored. More specifically, the higher values of the dimensionless skin factor (S_w), the Forchheimer coefficient (γ), and the vertical distance (l) between the water level in the well and the top of the confined aquifer after instantaneous water injection, the slower rate of water level recovery. As the value of S_w increases, the amplitude of water level oscillation decreases, whereas the amplitudes of water level oscillation increase with larger values of γ and l. Ignoring the skin effect, non-Darcy flow effect or inertia force will lead to underestimating hydraulic conductivity and specific storage. The results can provide theoretical guidance and technical support for the inversion of hydraulic parameters in fractured confined aquifers.