Simulating Flow and Transport Uncertainty Associated with Water Supply Well Modification Based Upon Well Profiling and Pumping Test Data

Typical approaches for improving water quality from water supply wells include treating water at the wellhead and installing new wells. A potential alternative and more economical approach for improving pumped water quality is to hydraulically modify the existing wells. Zones of higher contaminant concentrations are blocked off in order to improve water quality while giving up some production capacity. This approach requires profiling data for both flow and water quality along the screened interval(s) of the well.   

 

In order to plan the hydraulic modification of a well, the hydraulics inside the wellbore and in the area immediately surrounding the well must be understood. The physics considered differ from classical well hydraulics in that 1) vertical averaging cannot be employed and 2) the details of flow inside the well must be addressed.  Models are increasingly being used to evaluate the level at which the hydraulics are actually understood.  Early efforts to simulate well hydraulics in this fashion involved the use of many parameters that required estimation from a relatively small amount of field data. We extend these previous attempts by presenting a method that results in a parameterization scheme more amenable to model calibration.

 

Our approach uses a combination of field data derived from well profiling (flow, quality and head), as well as constant and step discharge testing, to develop a minimum set of parameters necessary to calibrate a flow and transport model for the wellbore. We present the results of nonlinear regression parameter estimates of effective hydraulic conductivity values associated with the wellbore.  Initial estimates of uncertainty associated with predictions of flow and transport for hydraulically modified wells are also presented using linearization techniques.