A Look Into Geothermal Discoveries Across the Western United States

Abstract

Historically, most conventional hydrothermal geothermal systems have been discovered by drilling in the vicinity of surface geothermal features (e.g., fumaroles, hot springs, or paleo-geothermal deposits) or discovered accidentally during drilling for fossil fuel, mineral, or water resources. In this paper we highlight key insights into the history of exploration across the contiguous western U.S. from a comprehensive dataset of wells and springs from various industry, academic, and public sources. Our analysis focuses on the extent to which the subsurface, particularly fault zones, has been explored. Notably, we find that less than 10% of the contiguous western U.S. has been sampled for subsurface temperatures, most of which are at shallow depths (0-20 m). Of this subsurface data, early stage geothermal exploration drilling has covered only about 0.4% of the contiguous western U.S. Additionally, fault zones remain largely unexplored, with two-thirds of Quaternary faults not restricted by protected land status lacking subsurface temperature data within a 1 km radius. This limited spatial coverage highlights significant gaps in the available data and underscores the need for targeted exploration efforts to identify and develop more resources. Throughout the history of geothermal discoveries in this region more blind and hidden sites have been found by accident than on purpose. Accidental discoveries, primarily from water wells and mining activities, account for half of all utility-scale geothermal resources, and the majority of all the blind or hidden discoveries. Estimates from previous studies at the USGS, Department of Energy, and Great Basin Center for Geothermal Energy indicate that blind or hidden geothermal systems are likely to comprise the majority of geothermal resources in the Great Basin and western U.S. This assertion is mainly corroborated by the historical rate of accidental discoveries, where historical water well drilling has accidentally discovered more than a third of known blind or hidden geothermal systems. Furthermore, because homesteading was ended in 1976 by the Federal Land Policy and Management Act, the rate of these accidental water well discoveries has slowed to a trickle. The industry’s dependency on accidental discoveries for blind resources means that the available developable pipeline is small and is not sufficiently growing. This paper highlights the need for a new era of targeted greenfield campaigns to increase the rate of blind discoveries and expand the industry’s development pipeline. Based on historical success rates, we estimate that drilling 100k new exploration holes could lead to more than 100 new blind or hidden geothermal discoveries.