How Petroleum Geoscientists Can Contribute to Geothermal Energy

In the latter part of 2024, ThinkOnward hired me for “Project Travertine”, a regional assessment of the geothermal potential of the United States. Having spent around 20 years working across petroleum exploration and development projects worldwide, I was tasked to leverage and adapt oil and gas workflows to assess the subsurface potential, and bring a “thinking and doing” geological perspective to prospective terranes and plays to highlight “sweet spots” for geothermal development.

There is extensive commentary and optimism on the significant potential of geothermal energy in the public domain, especially for Enhanced Geothermal Systems (EGS) utilising existing oil field practice and technology to move from purely convective to conductive systems (Fig. 1). But to meet the current U.S. Department of Energy’s “commercial lift off’ ambition of 2-5 GW across four to six states (Fig. 2), with up to $25 billion in investment by 2030, what will it take to achieve this, and how can petroleum geoscientists contribute (U.S. Department of Energy 2024)? Ultimately, it comes down to finding, describing, and testing the right subsurface opportunities that can deliver value.

Figure 1: Enhanced Geothermal Systems (EGS) favorability of the United States. Temperatures above 150°C and depths below 3 km are considered more favorable. After Roberts, 2009 (NREL).

Figure 2: Potential impact of 5GW of geothermal power production

Subsurface Characterization Subsurface characterization for geothermal energy development contains many critical elements that require integration and screening to mitigate risk and uncertainty. Petroleum geoscience skills are a good match for identifying and assessing viable geothermal resources:

• Many existing approaches to geothermal exploration workflows are based on limited subsurface criteria, and provide an unconstrained choice, where you can pick almost anywhere and drill deep enough to find geothermal resources. Establishing pragmatic screening criteria, with a key focus on risk, uncertainty, and cost consciousness is needed to define geologically, technically, and economically feasible areas.

• Petroleum geoscientists are adept at thinking in 3D and integrating multimodal datasets, identifying favorable subsurface formations and geometries using gravity and magnetic data, seismic surveys (Fig. 3), petrophysical well logs, and geological modeling.

• Geoscientists are skilled at analyzing and interpreting core samples and well data to determine rock properties (e.g., porosity, thermal conductivity), which dictate how efficiently heat can be extracted.

• In geothermal energy exploration, they can apply these techniques to locate heat- bearing reservoirs/hosts, characterize stress regimes, and assess existing or predicted fracture networks (e.g., especially in EGS where monolithic rock is fractured to provide a permeable heat matrix).

• Geoscientists also assess the depth, temperature, flow, and pressure of geothermal resources—skills honed from drilling petroleum wells apply directly to geothermal drilling targets.

• Understanding subsurface fluid geochemistry is a crucial crossover skill, as analyzing mineral-rich and corrosive brines—whether in geothermal systems or oil fields—helps predict scaling and corrosion of infrastructure in contact with the fluids and environmental impacts, ensuring efficiency and safety.

• Geoscientists are good at integrating data sets in multiple software platforms like Petrel, ArcGIS, and Leapfrog.

Figure 3: Uninterpreted and interpreted 2D seismic line through the FORGE Fallon site in Northern Nevada. The target EGS host units are Cenozoic granitic intrusive bodies and associated volcanics (Siler et al., 2019). Many geothermal prospects today are identified primarily using gravity and magnetic data, which do not offer the vertical resolution and precision of modern seismic imaging. However, valuable insights can be gained by incorporating legacy and modern onshore oil and gas seismic and well data—datasets that are well understood by petroleum geoscientists

Resource Assessment Estimating the extent, size, heat content, and sustainability of a geothermal reservoir mirrors evaluating oil and gas play and prospect resources/reserves:

• Play-based exploration and frontier exploration approaches can be adapted to determine favorable regions and characterise the resource density in geothermal systems. These approaches are based upon establishing key subsurface characteristics and stacking them to develop an understanding of where the areas with most/all of the desired characteristics are located, or to highlight what data or work needs to be done to change the understanding of certain areas.

• Petroleum geologists use their knowledge of fluid dynamics and thermodynamics to model how much energy a geothermal system can produce over time, factoring in variables like recharge rates, reservoir/host sweep, and heat flow.

• Geologists can help screen for areas where temperatures are above 150°C or 302°F (ideally 200°C to 300°C or 392°F to 572°F). These high-temperature resources are most efficient in generating geothermal electricity. At this range, dry steam or flash steam power plants can be used. Dry steam plants (where steam directly drives turbines) and single/double-flash plants (where high-pressure fluid is flashed into steam) achieve efficiencies of 15-20% or higher, depending on the setup and turbine design. The sweet spot for maximizing efficiency and output tends to be around 200- 250°C (392-482°F), allowing robust steam production without excessive equipment strain.

• Geothermal electrical capacity resource density estimates for high-temperature resources range from 0.67 MW/Km3 (Augustine 2016) to 9.1 MW/Km3 (Norbeck et al., 2024). The biggest drivers of extractable energy are recovery factor and plant efficiency. Optimizing development requires a comprehensive understanding of the subsurface, which a geoscientist can provide.

Drilling Optimization and Leveraging Existing Technology Petroleum Geologists are well versed in planning and executing wells in conventional and unconventional settings. Equipment and practices can be adapted to drill EGS wells or target deep sedimentary basins:

• Geothermal wells often require depths and conditions similar to oil and gas wells—sometimes 2-5 km deep, with high temperatures and pressures. Petroleum geologists collaborate with engineers to select suitable sites, design drilling plans, and mitigate risks like blowouts or corrosive fluids, drawing on their experience with hydrocarbon extraction (Figs. 4 and 5).

• Petroleum geologists can also help repurpose depleted oil wells for geothermal use, a growing trend in places like Texas or the North Sea, where old petroleum infrastructure could get a second life tapping subsurface heat.

Figure 4: Section through the Fervo and FORGE EGS projects in Southern Utah (Horne et al., 2025). Note EGS wells are drilled in a deviated manner to maximise contact with desired thermal zones similar to horizontal wells for unconventional oil and gas wells.

• Companies, with the help of geologists, are adapting existing petroleum drilling techniques, tools, and materials to develop their sites, including in the U.S.. The emphasis is on drilling wells efficiently and quickly to reduce costs (e.g., Fercho et al. 2025, Horne et al., 2025).

Figure 5: Transect through wells drilled at the Fervo Cape Project in Utah (Fercho et al., 2025). Wells are drilled in deviated paths and “wine racked” to maximise the heat window and aid production and Formation recharge.

Understanding value drivers, project cycle times, and access at scale are key crossovers between petroleum and geothermal systems exploitation:

• Ultimately, sufficient extractable resources (heat) over time dictates the long-term value of an opportunity.

• Using Fervo Energy’s Cape project in Utah as an example, the project aims to deliver a total capacity of 400 MW over +10 years (Figs., 4 and 5). This is at a reported development cost of up to $2 billion, of which around $500 million is currently funded.

• Meeting the DOE ambition of +2 GW by 2030 will take a lot of additional investment, with a potential lower rate of return than oil and gas developments may provide. Access to geothermal leases will dictate the ability to scale. Companies like Ormat have been active in recent federal sales. In states like Texas, where much of the land is private, repurposing hydrocarbon wells may make commercial development challenging.

Where Next? Petroleum geoscientists clearly play a role in finding geothermal resources, assessing their potential, and developing them efficiently. The ability of the industry to scale, especially in EGS, has yet to be proven. Currently, few long-term employment opportunities exist for the large number of petroleum geoscientists and engineers now facing a shrinking oil industry. ThinkOnward offers an on-demand geoscience resource for companies looking to gain a rapid and immediately useful understanding of petroleum and geothermal resources in worldwide settings.

Key takeaways:

• Petroleum geoscientists possess valuable transferable skills for geothermal energy development, particularly in 3D subsurface characterization, resource assessment, and drilling optimization.

• The geothermal sector has significant growth potential, supported by DOE ambitions of 2-5 GW across 4-6 states with up to $25 billion in investment by 2030. High-temperature resources (above 150°C, ideally 200-300°C) represent the most efficient targets for geothermal electricity generation. Adapting petroleum industry workflows, technologies, and commercial approaches can accelerate geothermal development, as demonstrated by companies like Fervo Energy.

• Commercial viability remains a common concern, as geothermal projects often require significant upfront investment and may offer slower financial returns than conventional oil and gas developments. However, note that this comparison may be misaligned with the priorities of sectors like data centers, where investment decisions are guided by energy reliability, sustainability commitments, and predictable long- term costs.

• Access to geothermal leases and land rights will be a determining factor in the industry's ability to scale, particularly in states with predominantly private land ownership.

• While the geothermal industry offers promising opportunities for petroleum professionals facing a contracting oil industry, the scale of employment transition currently remains limited.