Deep Energy Exploration & Production: Technology Trends in Scaling SHR Geothermal
Recent funding initiatives, such as a $20 million additional Series A fund for XGS Energy and the Biden-Harris Administration’s $60 million investment in three enhanced geothermal systems (EGS) projects (Chevron New Energies, Fervo Energy, and Mazama Energy), alongside the DOE’s geothermal commercial liftoff report, underscore the government’s commitment to advancing geothermal energy and investor interests. This focus is crucial as these projects and technologies pave the way towards the development of superhot rock (SHR) geothermal energy, aiming to make geothermal power cost-competitive and scalable.
In our previous blog post, we introduced SHR geothermal energy, discussing its potential economic viability due to its high temperatures and unique geographic characteristics. While the prospects are promising, significant challenges remain, prompting questions about the feasibility of pursuing geothermal 2.0 when the current “next-generation geothermal” technologies — enhanced geothermal systems (EGS) and advanced geothermal systems (AGS) — have yet to achieve widespread deployment. We concluded our last post by likening the current state of geothermal development to the early stages of the modern shale revolution. Just as it took over two decades to economically extract shale gas, EGS and AGS have been under development for many years, with commercial activities only recently gaining momentum. This highlights two critical points: geothermal projects are capital-intensive and have long development timelines. Delays in deployment will eventually strain the industry and supply chains, and complicate our efforts to achieve net-zero emissions, a challenge also faced by the nuclear energy sector.
Thus, it is imperative to outline the necessary steps to make geothermal energy cost-effective and competitive with future energy sources. It is worth recognizing that this is not a winner-takes-all scenario. In the near term, EGS and AGS systems will continue to be developed and refined as they are now. As we advance our ability to harness deeper geothermal resources, the role of SHR geothermal energy will gradually increase, complementing the existing systems and contributing to a diversified and resilient energy landscape.
In this blog post, we will explore emerging innovations and trends and highlight the innovators addressing these challenges. This is not an exhaustive list, but it will provide insights into the state-of-the-art across multiple disciplines, identifying gaps in knowledge and technology that require further research and investments. Within this multifaceted challenge for developing SHR, there are the following critical areas:
- Exploration, characterization, and modeling of SHR resources
- Drilling and completion of wells in high pressure and temperature conditions
- Reservoir creation and management
- Materials and tools for high pressure and temperature conditions
- Power conversion systems
Among these, we believe there are three key areas that should be of high focus to drive the development of SHR geothermal energy.
- Modeling and predictive capabilities
- Deep drilling and fracture stimulation
- Energy extraction & power generation
Modeling and Predictive Capabilities
Choosing the right location to develop geothermal energy is a function of risk and the readiness of technologies required to reach and extract thermal energy. Compared to conventional hydrothermal resources, SHR resources are ubiquitous, occurring at depths dependent on the local temperature gradient. This shifts the focus from locating resources for shallow to deep subsurface geological, geophysical, and geochemical parameters.
Adapting existing modeling packages to supercritical conditions would be the first step. Models would need to account for significant changes in fluid properties near the critical point, phase behavior, and the combined effects of conduction and convection heat transfer. Additionally, geochemical reactions like mineral dissolution and precipitation and mechanical behavior such as stress, strain, and fracture propagation within the reservoir should also be considered. A comprehensive understanding of the spatial and temporal variation of subsurface conditions would require not only these upgraded models but also lab data or field measurements. We are already seeing machine learning techniques being used for geothermal play fairway analysis (PFA), a method adapted from the oil and gas industry for regional- and local-scale geothermal resource identification and risk assessments, and expect further utilization of advanced computational methods to aid in the conceptual modeling, predicting, and well targeting.
Another key component to addressing risk in SHR development is the techno-economic models. Current models used in evaluating the commercial viability of geothermal production include GEOPHIRES and GETEM. These models predict the levelized cost of electricity (LCOE) given a user-defined geothermal resource and development concept. The missing pieces to presenting the cost and investment opportunity are accounting for parameter uncertainties and the capability to reverse predict, i.e. given a range of LCOE and defined geothermal resources and presenting various development solutions based on technology readiness levels of each component. This would require a larger library of technology models, even ones that are currently in their early stages of development but would present users with more options and bring awareness to early-stage technologies that could potentially be solutions to specific scenarios, such as SHR.
Related companies:
- Zanskar: using AI and advanced sensing techniques to drive down the risk and cost of geothermal development.
- Polpis Systems: techno-economic modeling and technology roadmap for SHR.
Deep Drilling and Fracture Stimulation
Conventional mechanical drilling technologies involve applying downward pressure on a cutting tool, which is then rotated to provide the necessary torque for gouging or scraping the rock surface. These technologies have been deployed for decades to reach depths of up to 10km and reach temperatures greater than 400 ℃. The deepest drilled holes attempted are the Kola Superdeep Borehole (12.26 km, 180 ℃) and the KTB borehole (9.10 km, 265 ℃) but these projects were not focused on mining thermal energy. Several (shallow) SHR drilling projects have been accomplished, such as the Venelle-2 well in Italy (2.90 km, 500 ℃) and IDDP-2 well in Iceland (4.65 km, 427 ℃).
Deep drilling using mechanical drilling technology is cost prohibitive, with the mechanical rate of penetration affected by various factors such as geological formation strength and type as depth and temperature increases, pore pressure, and bit performance (wear, shortenedd life, low efficiency). In the context of SHR, horizontal wells or directional drilling along an isotherm is not strictly required, as drilling deeper will lead to higher temperatures and is preferable. To reach deeper and hotter SHR resources, new approaches have started to gain commercial traction. Instead of mechanical abrasion, it is possible to direct energy for drilling using energy sources such as electromagnetic waves or plasma. The main advantages here are that no mechanical systems could wear and break, and there is potentially no temperature/pressure limit.
mm-Wave: Quaise Energy is using gyrotrons to generate continuous, high-power (megawatt-scale) millimeter wave radiation and uses metallic waveguides to guide the electromagnetic wave downwards. When the beam reaches the bottom of the borehole, it not only vaporizes the rock and accomplishes the drilling action, but the beam also diverges after exiting the waveguide, effectively heating the walls of the hole and making it glassy, a process called vitrification, which can seal and strengthen borehole walls.
Plasma: GA Drilling is developing a different mechanism called plasma pulsed geo drilling, a process that uses high voltage impulses with short rise times to fracture rocks. This is a process based on electrical discharges formed between two electrodes separated by a dielectric liquid. The key here is to have steep pulses that operate in a region where the dielectric strength of water is stronger than that of the rock, allowing the discharge, or plasma channel, to be formed within the rock. The pressure in the plasma channel exceeds the tensile strength of the rock thereby breaking the rock.
Gravity hydraulic fracturing: This method uses a high-density fluid to induce downward fracture propagation under gravity forces. Hydraulic fracturing, or fracking, is a common method used to extract natural gas or oil by high-pressure injection of fluid into wellbore to create cracks. The key difference here is to use a fracturing fluid heavier than the surrounding rock, which allows gravity to aid or replace the need for injection by pumping. Although this method has only been modeled in research settings, Polpis Systems is aiming to induce a gravity-driven magma fracture that is effectively an “engineered fault” in the earth’s crust.
Energy Extraction & Power Generation
At superhot discharge temperatures exceeding 374 ℃ and pressures above 100 bar, turbines achieve significantly higher thermal energy conversion efficiencies. Utilizing existing technologies from subcritical to supercritical coal and gas-fired steam turbines, efficiencies are expected to range between 30% and 40%. Adapting power generation cycles that use supercritical water, commonly found in coal-fired and nuclear power plants, for SHR resources is possible. However, these systems face challenges due to fluid chemistry management, as the interaction between supercritical water and rock at SHR conditions can produce corrosive and metal-rich fluids, potentially damaging conventional turbine systems.
An alternative to water as the working fluid is carbon dioxide (CO2), which offers several benefits: it is non-explosive, non-flammable, non-toxic, and readily available at a low cost. CO2 reaches its critical point at 7.4 MPa and 31 ℃, making it easier to achieve supercritical conditions compared to water. In geothermal wells, supercritical CO2 (sCO2) reduces the need for external power sources to pump the working fluid because of the large buoyancy forces generated. These buoyancy forces arise from the significant density difference of sCO2 when it heats up upon reaching the production well, a phenomenon known as the thermosiphon effect. This effect is more pronounced in CO2 than in water due to the higher compressibility of sCO2.
The main advantage of the sCO2 power cycle is its high thermal efficiency at moderate temperatures, achieved through minimal compression work and the extensive recovery of heat from the turbine exhaust. In its supercritical state, CO2 is nearly twice as dense as steam, making it more energy-dense. This allows for smaller system components, such as turbines and pumps, which reduces the overall plant footprint and potentially lowers capital costs.
Sandia National Laboratories has developed a recuperated closed-loop Brayton cycle using sCO2 as the working fluid, heated up to 315 ℃. This system successfully delivered continuous power to the grid for 50 minutes. Future tests are planned to include a 1 MW-scale generator that will not require electrical power from the grid to heat the sCO2.
Another recent advancement occurred at the Supercritical Transformational Electric Power (STEP) Demo pilot plant at Southwest Research Institute. The team successfully test-fired the STEP plant, with their natural gas-powered turbine reaching speeds of 18,000 rpm and temperatures of 200 ℃. Future steps will involve increasing temperatures to 500 ℃ and eventually to 715 ℃, with the turbine operating at a full speed of 27,000 rpm to achieve a 10 MWe output.
Conclusion
Despite the significant challenges ahead, such as the need for substantial technological advancements and the capital-intensive nature of geothermal projects, the pursuit of SHR geothermal energy offers a promising pathway forward. Recent innovations and funding initiatives signal a strong commitment to advancing geothermal energy.
That being said, it is notable that the DOE has left supercritical geothermal technology off of its earthshot targets for achieving commercial liftoff. Instead, the DOE’s geothermal technologies office has adopted a “learning by doing” cost reduction methodology that forecasts an unsubsidized LCOE of $45/Mwh by 2035. There are two problems with this that create opportunities for technologists and entrepreneurs. The first is that this roadmap concludes that deployed capital, rather than technology, is the primary limiting factor. This is a dangerous (and expensive) departure for almost every other industry of comparison (telecom, computing, drug development, etc.) where advances in technology are the sole reason for dramatic cost reduction. Second, energy is a fierce commodity where only cost matters and advanced geothermal is competing with dramatic advances already being made in next-generation nuclear fission and solar plus battery storage. As such, the competitive cost of energy is a moving target and technologies need to compete not with today’s cost of energy, but the costs of energy once those advancements are online.
In our previous prediction on next-generation geothermal power, we anticipated that EGS and AGS would achieve notable milestones by 2030. These technologies have indeed made significant strides, but the potential of SHR geothermal energy represents an even more transformative opportunity. With higher power densities and the promise of cost-effective power generation, SHR geothermal energy could play a pivotal role in meeting global energy demands sustainably. Looking ahead, with continued investment, technological breakthroughs, and collaborative efforts, it is plausible that SHR geothermal energy could achieve commercial viability within the next decade.
Prime Movers Lab invests in breakthrough scientific startups founded by Prime Movers, the inventors who transform billions of lives. We invest in companies reinventing energy, transportation, infrastructure, manufacturing, human augmentation, and agriculture.
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