Use of cumulative volume of constant-head injection test to estimate aquifer parameters with skin effects: Field experiment and data analysis

Abstract

[1] In a silty sand aquifer, constant-head injection tests (CHITs) were performed for the determination of aquifer parameters. In a CHIT the test well is overflowed by the injection of surface water. The difference between the injection flow and the overflow measured by an automated system directly yields the cumulative volume Vw(t) that enters the aquifer. Therefore the method of using Vw(t) in determining the aquifer transmissivity and the storage coefficient is developed, where well skin effects are taken into account. The semilog plot of t/Vw(t) is useful in indicating whether well skin exists around the constant-head pumping well. If well skin is absent, the semilog plot of t/Vw(t) shows a straight line at large times, from which the transmissivity and the storage coefficient can be determined. If well skin exists, the semilog plot of t/Vw(t) exhibits two straight-line sections occurring at small and large times, respectively. Then only the transmissivity can be determined from the slope of the large-time straight line. In this event, aquifer drawdown/buildup observed at observation wells is needed for the determination of the storage coefficient. In fact, both the transmissivity and the storage coefficient can be determined with aquifer drawdown/buildup normalized with respect to Vw(t), regardless of well skin around the constant-head pumping well. Once T and S are known, the skin factor of the constant-head pumping well can be obtained from t/Vw(t).