Advanced Instrumentation and Deployment Methods for High Resolution Shallow Temperature Measurements

Geothermal energy is a renewable, low-carbon resource for electricity production and direct-use applications that has the potential to play a major role in the transformation away from fossil fuel-based energy systems. DOE identifies as valuable technologies that reduce geological uncertainty related to locating, characterizing, and quantifying subsurface resources ahead of expensive exploratory drilling, thereby reducing financial risks in early-stage geothermal development and spurring the investments required to meet the 2050 GeoVision target. The direct relationship between heat flow and the energy density available for geothermal conversion makes the temperature gradient a fundamental quantity and high-value data type for geothermal exploration, especially where geothermal resources are blind (i.e. systems with no surface expression). The problem is current methods of evaluating geothermal heat flow are either biased to a few locations with relatively deep boreholes, or, when estimated using shallow surveys, are plagued by errors caused by interference from variations in ground surface heating. Blind geothermal resources are expected to be a large fraction of the available, unexplored geothermal resource base, and the lack of an exploration technique that can reliably identify heat flow anomalies from shallow measurements at scale is limiting the ability to identify these critical resources. In Phase I, we propose to develop and test a methodology to address this problem that uses shallow temperature measurements in combination with independent measurements of surface temperature to filter out from shallow survey data the climate-driven surface temperature signal. To enable this methodology, we need to develop instrumentation and a deployment method for a new type of shallow temperature survey that relies on a temperature sensor capable of high-precision measurements and high spatiotemporal sampling. We will test optical fiber-based temperature sensing technology for delivering high measurement precision and sampling with increased sensor endurance and a low power requirement that permits more effective surveying. We also propose to adapt an existing method to deploy our instrument to a significantly greater depth of interrogation than current shallow survey methods.