MULTIPLE DISTRIBUTED THERMAL PERTURBATION TESTS TO CHARACTERIZE VERTICAL HETEROGENEITIES IN A FRACTURED SYSTEM

To better understand the groundwater resources of southern Nye County, Nevada, a multi-part thermal perturbation sensing (DTPS) test was performed on a complex of three wells. These wells penetrate a complex fractured aquifer system, and characterizing the hydraulic properties and flow paths of the regional groundwater flow system has proven very difficult. The well complex comprised one pumping well and two observation wells, both located approximately 18 m from the pumping well. Fiber-optic cables and line heaters were deployed vertically to a depth of approximately 230 m in each of the monitoring wells. The initial DTPS test was done under unstressed conditions, and a subsequent test was done under stressed conditions, with the pumping well operating at a constant pumping rate and inducing significant drawdown. During each test, heat was injected into the water column through the line heater to induce a temperature change. After a steady, elevated temperature was reached, the heater was turned off and the vertical variations in dissipation of heat observed. In the unstressed test, areas of very slow dissipation are identified as low flow (primarily conduction) and areas of very fast dissipation are identified as flowing areas (primarily advection). Areas with median rates of heat dissipation have been harder to characterize. By changing the flow field in during the second stressed DTPS test, additional information is provided about these median areas, allowing us to better describe the vertical heterogeneities of the fractured formation.