In the quest for sustainable energy, scientists and engineers are delving deeper into the Earth’s crust, seeking to unlock the vast potential of hot dry rock (HDR) geothermal resources. A recent review published in Energies, titled “Research Progress and Technical Challenges of Geothermal Energy Development from Hot Dry Rock,” sheds light on the advancements and hurdles in this burgeoning field. Led by Yilong Yuan from the Key Laboratory of Groundwater Resources and Environment at Jilin University in China, the research offers a comprehensive look at the technologies driving the commercialization of HDR geothermal energy.
Geothermal energy, harnessed from the Earth’s heat, is a renewable and sustainable resource that has garnered significant attention in the global energy transition. HDR, rock heated between 150 and 650°C with minimal water content, holds enormous reserves and development potential. According to the Massachusetts Institute of Technology, the amount of HDR resources available for human development is 30 times greater than the combined reserves of oil, natural gas, and coal on Earth. In China, the estimated resource amount at depths of 3–10 km is equivalent to the heat of 860 trillion tons of standard coal, a staggering figure that underscores the resource’s potential.
The primary method for tapping into HDR geothermal resources is through enhanced geothermal systems (EGS). EGS involves hydraulic fracturing to create complex fracture networks in high-temperature rock masses, enabling the transport and heat exchange of heat-carrying media, such as water. This process transforms low-porosity, high-temperature rock into an artificial geothermal reservoir, allowing for the extraction of heat energy over the medium and long term.
However, despite decades of research and pilot projects, the commercial deployment of HDR geothermal energy remains limited. Significant technical, economic, and environmental challenges persist, including efficient reservoir creation, high drilling costs, and effective microseismic control. “The development of HDR geothermal technology is still in the research and development stage of field testing,” Yuan notes. “More countries are joining the global exploration and development of HDR geothermal resources, but a replicable and commercial development model has yet to be established.”
The review identifies three categories of technologies crucial for the commercialization of HDR geothermal resources: base technologies, key technologies, and game-changing technologies. Base technologies, which already have industrial applications, include evaluation and site selection, efficient and low-cost drilling, and geothermal utilization. Key technologies, still in the demonstration and validation phase, encompass high-resolution exploration and characterization of HDR, efficient fracture network reservoir creation, effective microseismic control, and reservoir characterization. Game-changing technologies, currently in the laboratory research stage, involve downhole liquid explosion fracture creation, in-situ efficient heat transfer and power generation, and the use of CO2 and other working fluids for high-efficiency power generation.
The research also highlights the comparative advantages of China and the United States in key HDR development technologies. While the U.S. has made significant strides with programs like the Frontier Observatory for Research in Geothermal Energy (FORGE), China is rapidly catching up, with several target regions identified for HDR geothermal resource exploration.
The commercial impacts of advancing HDR geothermal technology are profound. Successful development could significantly expand the geographic availability of geothermal energy, providing a stable and sustainable power source. Moreover, geothermal energy’s non-carbon-based nature aligns with global efforts to achieve carbon neutrality, making it a crucial component of the future energy mix.
As the world grapples with climate change and the need for sustainable energy solutions, the research led by Yuan offers a roadmap for overcoming the challenges in HDR geothermal development. By addressing scientific problems and key technologies, the energy sector can unlock the vast potential of HDR geothermal resources, contributing to a more sustainable and secure energy future. The insights from this review, published in Energies, will undoubtedly shape future developments in the field, fostering collaboration and innovation in the global pursuit of clean energy.
