Characterizing the Geothermal Resource at the Detroit Arsenal

Abstract

As part of the Federal Geothermal Partnerships (FedGeo) initiative, the University of Wisconsin–Madison conducted in situ characterization of the low-temperature geothermal resource at the U.S. Army Garrison Detroit Arsenal to support techno-economic evaluation and borefield optimization. This study employed mud-rotary drilling, geophysical logging, and advanced monitoring techniques—including fiber-optic distributed temperature sensing (FO-DTS)—to assess thermal, physical, and hydrogeological properties along a 152-m test borehole. A conventional thermal response test (TRT) indicated a bulk thermal conductivity of 2.25 W·m⁻¹·K⁻¹, while the acquired FO-DTS data revealed significant variability in heat transfer, identifying high-conductivity formations such as the Birdsong Bay Limestone (67–78 m), Traverse Limestone (78–93 m), and cherty dolomite of the Dundee Group (140–152 m). Drilling performance demonstrated that a 152–168 m borehole can be advanced in a single workday using the mud-rotary drilling method. Completing the drilling in one workday optimizes the installation of the borehole, thus reducing contracting cost. Our testing results suggest that extending the borehole deeper to at least 168 m could increase thermal capacity by approximately 15% compared to a 152-m ground heat exchanger. These findings inform optimal borehole depth, spacing, and layout for geothermal borefields, which represent the most variable and costly component of ground heat exchange systems and thermal energy networks.