Evaluation of Distributed Temperature Sensing Results at the West Point Military Campus

Abstract

We tested an exploratory 152-m geothermal borehole at a site in the United States Army Garrison, West Point, NY, as part of a Department of Energy (DOE) project to assess the site's geothermal potential. The test borehole site is located about 8.8 km southwest of the academic campus in the Hudson Highlands. The geology of these highlands comprises hard metamorphic rocks and shale, with igneous rock intrusions within a complex formation history and folding, as documented by borehole geophysics deployed at the site and cuttings examined during this field effort. A conventional thermal response test (C-TRT) at the site measured the composite thermal conductivity to be 2.82 W m-1 K-1. To explore the vertical variability in the composite C-TRT thermal conductivity result, we also deployed a value-added optical Sensornet Distributed Temperature Sensing (DTS) interrogator to measure the temperature time history along the borehole depth. We instrumented the borehole with two multimode fiberoptic cables: one inside a 3.8-cm-inside-diameter HDPE circulation pipe and another outside the circulation pipe. The results allow evaluation of thermal conductivity with depth and the relationships between those parameters and different rock types and layers in the formation. Our DTS results indicated thermal conductivity values ranging from 1.3 to 3.6 W m-1 K-1, both of which support the variability of thermal properties in metamorphized rocks and the range of values that depend on mineralogical content, dipping beds, faulting, and other features. These distributed results can guide the design of more efficient geothermal energy systems (e.g., optimal depth and spacing).