Unsteady Drawdown at a Partially Penetrating Well in a Transversely Isotropic Artesian Aquifer

The work described in this paper investigates the effect of aquifer anisotropy on the unsteady drawdown at the face of a partially penetrating well, which is pumped at a constant rate. The aquifer is confined between two parallel aquicludes, and its hydraulic conductivity is assumed to be transversely isotropic. Based on a parametric study of the drawdown equation, it is concluded that the variation in drawdown depends on which of the principal permeabilities is held constant, as well as the ratio between them. For constant radial permeability, the rate of increase of drawdown with time is independent of the permeability ratio; furthermore, unless the well penetration is very small, aquifer anisotropy is of little consequence for permeability ratios close to unity. For constant vertical permeability, well penetration has practically no influence on the drawdown for lower permeability ratios. The effect of aquifer anisotropy increases from a negligible value for a fully penetrating well to a maximum for wells which just tap the aquifer.