Geothermal Energy: An Important Resource
Evaluation of a discrete-depth heat dissipation test for thermal characterization of the subsurface
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Published:March 01, 2016
Heat transfer in the subsurface can vary with depth due to variations in the thermal conductivity of the geologic medium as well as variations in groundwater flow velocity. However, traditional thermal response tests (TRTs) do not allow for evaluation of the depth variability of heat transfer. We investigate the potential for using discrete-depth heat dissipation tests in open, water-filled boreholes to evaluate variations in heat exchange rate with depth. Heat dissipation tests were initiated at target depths in a test well using an electrical resistance heater. Heat dissipation was monitored by measuring borehole water temperature through time using a fiber-optic distributed temperature sensing system. Temperature data were used to compare the thermal response at different depths in the borehole. To account for both the thermal conductivity of the geologic medium and the groundwater flow velocity, we used a numerical groundwater flow model (MODFLOW) and solute transport model (MT3DMS) to simulate heat dissipation tests. Simulation results indicate the measured response to a heat dissipation test in an open borehole is strongly dependent on the measurement location within the borehole; thus, data are ambiguous when the measurement location is uncontrolled. However, modeling results also indicate that the thermal response of a heat dissipation test as measured at the center of the borehole is sensitive to variations in thermal conductivity and groundwater flow velocity, suggesting that heat dissipation tests are a potentially useful method for characterizing depth variability in thermal properties if a centralized temperature measurement method is used to monitor the tests.
- characterization
- evaluation
- geothermal energy
- geothermal exploration
- geothermal wells
- heat capacity
- heat flow
- heat pumps
- heat sources
- heat transfer
- hydraulic conductivity
- mathematical models
- MODFLOW
- monitoring
- reservoir properties
- simulation
- specific heat
- thermal conductivity
- thermal waters
- United States
- Wisconsin
- south-central Wisconsin