Transient Flow to a Large‐Diameter Well in an Aquifer With Storative Semiconfining Layers

Abstract

The Hantush theory of leaky aquifers with storge in the semiconfining layers is combined with large‐diameter well theory to produce equations that can be used in the analysis of pumped‐well and observation well data for stratified formations. Included in the equations are storage in the pumped well and a linear resistance to flow at the sand face or well bore skin. Three cases proposed by Hantush are considered. These depend upon whether the upper boundary of the overlying semiconfining layer or the lower boundary of the underlying semiconfining layer are constant head or no‐flow boundaries. Laplace transform solutions, valid for the complete time domain, are given for each of the three cases for the hydraulic head in the pumped well, the aquifer, and each of the semiconfining layers. Type cures obtained by numerical inversion are selected to illustrate the effects of well bore storage, well bore skin, and leakage. Although several dimensionless parameters are involved, these parameters tend to influence the character of different portions of the type curves, suggesting that unique matches are possible. The type curves show that well bore storage in a large‐diameter well may completely obliterate effects of leakage derived from compressible storage in semiconfining layers. For the purposes of aquifer testing, it may be possible to reduce the magnitude of well bore storage in a large‐diameter well and thus reveal the presence of leaky semiconfining layers. This may help to prevent erroneous interpretation of the well test data and incorrect evaluation of the aquifer parameters.