Publications Details

The BRIDGE Project - Hidden Systems Reconnaissance in Western Nevada

Schwering, Paul C.; Lowry, Thomas S.; Hinz, Nicholas; Matson, Gabe; Sabin, Andrew; Blake, Kelly; Zimmerman, Jade; Sewell, Steven; Cumming, William

The Basin & Range Investigations for Developing Geothermal Energy (BRIDGE) Project kicked off in the Autumn of 2021. The Department of Energy Geothermal Technologies Office (GTO) funded BRIDGE as part of a broader GTO initiative to advance the identification and development of hidden, or “blind”, geothermal energy resources in the Basin and Range Province (Basin & Range) of the western USA. The BRIDGE Team is a collaboration being led by Sandia National Laboratories (Sandia) with partners from Geologica Geothermal Group, the US Navy Geothermal Program Office, and others that will contribute to various stages of the project. The focus of this project is on Western Nevada with areas of interest, identified chiefly from the prior Nevada Play Fairway Analysis (PFA) study, located primarily in Churchill and Mineral Counties including lands managed by the Department of Defense (DOD). The first stage of BRIDGE is focused on reconnaissance of PFA targets that are suspected or known to be associated with hidden geothermal resources on DOD and surrounding lands. Helicopter-borne transient electromagnetism (HTEM) surveying is being used in a novel conceptual approach for optimizing shallow and deep well targeting in Basin & Range geothermal exploration. This reconnaissance phase is part of the overall BRIDGE workflow: 1. Assess the pre-survey likelihood of geothermal systems in the study area based on PFA reviews and a reanalysis of existing information to constrain subsurface temperature, structure, hydrology, and thermal manifestations. 2. Design and execute HTEM resistivity surveying to image the depth to the low resistivity and low permeability clay cap, within which a thermally conductive (linear) temperature gradient could be targeted for drilling, and potentially image the underlying higher resistivity associated with shallow aquifers hosting outflows from deeper geothermal systems. 3. Drill temperature gradient (TG) wells that penetrate a thick enough section of the clay cap detected by HTEM surveying to provide a linear thermal gradient that could be reliably extrapolated to the base of the cap. 4. In areas where the TG wells detected a prospective temperature gradient but where the HTEM survey did not penetrate to the base of the cap, conduct surface magnetotelluric (MT) resistivity surveys to image the base of the cap to identify the depth to which the linear TG well gradient could be reliably extrapolated. 5. On the most prospective target(s), drill at least one testable slim hole well to discover the resource associated with the interpreted geothermal reservoir upflow source. The first stage of the project and the second stage HTEM survey have been completed. Preliminary results are being analyzed with respect to potential TG targets and plans for followup surveys, geophysical joint inversion, conceptual model development, and interpretation.