USGS Publications Warehouse

Abstract

In May 1980, the University of Minnesota began a project to evaluate the feasibility of storing heated water (150 degree Celsius) in the deep Franconia-Ironton-Galesville aquifer (180 to 240 meters below land surface) and later recovering it for space heating. High-temperature water from the University's steam-generation facilities supplied heated water for injection. The Aquifer Thermal- Energy Storage system is a doublet-well design in which the injection/withdrawal wells are spaced approximately 250 meters apart. Water was pumped from one of the wells through a heat exchanger, where heat was added or removed. This water was then injected back into the aquifer through another well. Four short-term test cycles were completed. Each cycle consisted of approximately equal durations of injection, and withdrawal. Equal rates of injection and withdrawal, ranging from 17.7 to 18.4 liters per second, were maintained for each short-term test cycle. Injection temperatures ranged from 88.5 to 117.9 degrees Celsius. A three-dimensional, anisotropic, noniso- thermal ground-water flow and thermal-energy- transport model was constructed to simulate the four short-term test cycles. The only model properties varied during model calibration were longitudinal and transverse thermal dispersivities. The model was calibrated by comparing model-computed results to (1) field-recorded temperatures at selected locations, in four observation wells; (2) field- recorded temperatures at the production well; and (3) calculated aquifer-thermal efficiences. Model- computed withdrawal-water temperaturs were within an average of about 3 percent of measured values and model-computed aquifer-thermal efficiencies were within an average of about 5 percent of calculated values for the short-term test cycles. These data indicate that the model accurately simulated thermal-energy storage.