FIELD-TEST RESULTS OF AQUIFER THERMAL-ENERGY STORAGE AT ST-PAUL, MINNESOTA

A field-test facility (FTF) for aquifer thermal energy storage (ATES) was designed, constructed, and operated to study the feasibility of mo derately high-temperature thermal energy storage in a confined aquifer . The FTF was designed to inject and recover heat at a rate of 5 MW (t hermal) using a well doublet spaced at 255 m, operating at a maximum w ater temperature of 150-degrees-C. The wells were completed in the Fra nconia-Ironton-Galesville confined aquifer at a depth of 1822-44 m, wh ich has static water levels about 55 m below the ground surface. A ser ies of four short-term and three long-term cycles showed the technical feasibility of ATES in a confined aquifer at temperatures above 100-d egrees-C and clarified the groundwater chemistry and thermal interacti ons of the heated water with the aquifer and its confining beds. From 46% to 67% of the energy added to the injected water was recovered dur ing a cycle. A summary of representative results and findings (with pa rticular emphasis on the final cycle) is provided. A bibliography of p roject reports and papers is also given.