AN APPLICATION OF DISTRIBUTED TEMPERATURE SENSING TO CHARACTERIZE FLOW IN A WELL COMPLEX DURING PUMPING

To better understand groundwater flow and heterogeneity in the complex regional hydrogeologic setting of the Nevada National Security Site, a fiber-optic distributed temperature sensor (DTS) was tested as a monitoring tool for groundwater flow in a deep well complex during pumping The fiber-optic cable was deployed in a piezometer adjacent to a sampling well, with a screened interval corresponding to the sampled completion in the sampling well. The sampling well was pumped at 34 gallons per minute for 25 hours, and temperature profiles in the piezometer were measured every minute at a vertical spatial resolution of 12.5 centimeter before, during, and after well pumping. Preliminary analysis has shown changes in the piezometer temperature profile indicative of changing vertical flows during pumping, which enables the tracing of incoming water towards the submersible pump in the main completion. The influence of pumping in the main completion can be seen across the 158 meter long screened interval, including a change from downward flow under ambient conditions to upward flow during pumping. Temperature profiles within the screened interval are examined in order to relate temperature changes to possible flow zones, which are typically structural discontinuities (e.g. faults and joints). This work demonstrates a potentially promising technique for examining vertical heterogeneity in hydrogeologic formations.