Searching for Answers Below the Surface: Hidden Systems Exploration Uncovers Geothermal Energy Potential

Geothermal resources exist on every continent. Numerous examples of these resources are visible and well-known; for example, 1.3 million people visit the geothermal spa, The Blue Lagoon, in Iceland every year. However, many geothermal resources are “hidden,” housed in permeable rock layers in Earth’s subsurface without any visible signs on the surface. Scientists and developers want to locate and tap into these resources to generate electricity from the geothermal energy.  

There’s just one challenge: If the resource is hidden, how do you know where to drill?  

With funding from the Geothermal Technologies Office, a research team from Sandia National Laboratories set out to answer just that question and provide the data needed to make future geothermal exploration easier. 

Working in Nevada’s Steptoe Valley, the research team sought efficient and cost-effective methods to characterize a stratigraphic hydrothermal resource, a specific type of hidden geothermal system characterized by sedimentary rocks, geothermal heat, and high porosity and permeability. Stratigraphic reservoirs offer significant potential to the geothermal industry: the expansiveness of certain sedimentary formations means they could have the potential to support multiple geothermal plants with a single characterization effort. This is more efficient and cost-effective compared to the typical one-characterization: one-plant ratio of other geothermal resources. Additionally, stratigraphic reservoirs have been historically associated with the oil and gas industry (O&G), so existing data from O&G production and exploration could be leveraged to geothermal projects—in fact, the stratigraphic resource at Steptoe Valley was first discovered during oil and gas exploration activities. 

The research team primarily used new and established geophysical imaging techniques to better visualize the subsurface and evaluate power capacity for geothermal energy at Steptoe Valley. Geophysical imaging is a non-invasive method for investigating the subsurface that results in 2D or 3D models. This technique offers cost-effective geological explorations with low environmental impact.  

Using geophysical imaging in combination with techniques and geophysical analysis, researchers enhanced understanding of the northern Steptoe Valley stratigraphic resource. The team found that geophysical imaging provided subsurface characterization sufficient for conceptual modeling and initial reservoir analyses. They also found that the method is most effective when coupled with geological and geochemical findings, such as those from surface and borehole studies. 

The project team has published their findings in multiple ways, a highlight being a StoryMap featuring graphs, maps, and images of Steptoe Valley. They have also published data and models from the project, ensuring open access to researchers, geothermal developers, and others, expanding opportunities to leverage geophysical imaging to “see” beneath Earth’s surface. 

By enhancing understanding of hidden geothermal systems and showcasing the effectiveness of geophysical imaging in research, GTO is enabling better and more cost-effective geothermal resource exploration and characterization. GTO’s website offers more information about research and opportunities in hydrothermal resources.