Recovery in Large Diameter Wells

A closed-form approximate analytical solution for recovery in fully penetrating large diameter wells tapping a confined aquifer is presented. The solutions are also applicable for unconfined flow under conditions of small drawndown. The analysis predicts exponential decreases of inflow rate, a transient logarithmic recovery response, and an asymptotic increase of comulative recovery with time. The solution is verified against the field recovery response in a wide range of geological aquifer formations, e.g., fissured rock, lateritic as well as sandy alluvial deposits. The predicted response and the actual field response for all the types of aquifers mentioned are found to match extremely well. The available theoretical time-recovery relationship for unconfined flow conditions approaches to the present theory of confined aquifer under smaller drawdown.