ESTIMATING FORMATION PROPERTIES FROM EARLY-TIME RECOVERY IN WELLS SUBJECT TO TURBULENT HEAD LOSSES

A mathematical model is developed to interpret the early-time recoveri ng water level following the termination of pumping in wells subject t o turbulent head losses. The model assumes that turbulent head losses dissipate immediately when pumping ends. In wells subject to both bore hole storage and turbulent head losses, the early-time recovery exhibi ts a slope equal to 1/2 on log-log plots of the recovery versus time. This half-slope response should not be confused with the half-slope re sponse associated with a Linear flow regime during aquifer tests. The presence of a borehole skin due to formation damage or stimulation aro und the pumped well alters the early-time recovery in wells subject to turbulent head losses and gives the appearance of borehole storage, w here the recovery exhibits a unit slope on log-log plots of recovery v ersus time. Type curves can be used to estimate the formation storativ ity from the early-time recovery data. In wells that are suspected of having formation damage or stimulation, the type curves can be used to estimate the 'effective' radius of the pumped well, if an estimate of the formation storativity is available from observation wells or othe r information. Type curves for a homogeneous and isotropic dual-porosi ty aquifer are developed and applied to estimate formation properties and the effect of formation stimulation from a single-well test conduc ted in the Madison limestone near Rapid City, South Dakota. Published by Elsevier Science B.V.