Hot dry rock (HDR) is a kind of clean energy with significant potential. Since the 1970s, the United States, Japan, France, Australia, and other countries have attempted to conduct several EGS (Enhanced Geothermal System) projects to extract thermal energy by breaking through key technologies. However, up to now, the development of HDR is still in the research, development, and demonstration stage. An HDR exploration borehole (with 236°C at a depth of 3705 m) was drilled into Triassic granite in the Gonghe Basin in northwest China in 2017. Subsequently, China Geological Survey (CGS) launched the HDR resources exploration and production demonstration project in 2019. After three years of efforts, a sequence of significant technological breakthroughs have been made, including the genetic model of deep heat sources, directional drilling and well completion in high-temperature hard rocks, large-scale reservoir stimulation, reservoir characterization, and productivity evaluation, reservoir connectivity and flow circulation, efficient thermoelectric conversion, monitoring, and geological risk assessment, etc. Then the whole-process technological system for HDR exploration and production has been preliminarily established accordingly. The first power generation test was completed in November 2021. The results of this project will provide scientific support for HDR development and utilization in the future.

Hot dry rock (HDR) is an important geothermal resource and the primary direction of future geothermal development. Granite is particularly rich in radiogenic heat-generating elements (e.g., U, Th, and K) and is thus the main target for HDR development worldwide. Southeastern China contains the most abundant granite distribution in the country and accounts for more than 40% of the total granite area. This paper analyzes the rock radiogenic heat production, geothermal flux, crustal thermal structure, and reservoir temperature in the key exploration areas based on a systematic investigation of the distribution of granite resources and their heat generation characteristics. A heat generation and accumulation model of HDR resources is proposed for southeastern China. The results show that southeastern China can be characterized by a quadratic heat gathering model that includes a mantle source heat supply, intracrustal heat generation, fracture heat transfer, and cover heat preservation. Among these, the radiogenic heat production of granite is one of the main factors that affects shallow geothermal fields in this region. Fracture structure and cover conditions also exert a strong control on the gathering and dissipation of underground heat. The widely distributed and high-heat-producing tuffs and fused tuffs in the Zhangzhou area offer promising heat-generating and heat-gathering conditions for future exploration and development of hot dry rock resources in the area. The results provide important insight on the genesis and heat control factors of HDR resources in southeastern China and a theoretical reference for future HDR resource exploration and development practices in the region.

At medium-deep and deep parts of the Earth's crust lay vast and so far mostly untapped reserves of geothermal energy. This energy source has the potential to meet humanity's needs for energy for thousands of years. However, the large-scale deployment has been hindered by a lack of effective and dependable exploitation technologies. Gravity heat pipes have recently garnered significant attention due to their exceptional heat transfer capability and their ability to harness geothermal heat without water-mining. Nevertheless, it is a persistent challenge to extend gravity heat pipes to depths that are sufficient to exploit deep geothermal energy. In this study, we introduce an innovative ladder-structure inner pipe design to overcome this shortcoming. This design incorporates a series of stepped ladders and small condensate guiding pipes, allowing for the development of super-long gravity heat pipes (SLGHPs). Combined with an optimal working fluid, this novel structure enables kilometers-long gravity heat pipes. As a direct outcome of this innovation, a 4149-meter-long SLGHP was constructed and installed in a geothermal well using ammonia as the working fluid. The SLGHP geothermal system demonstrated the ability of continuous heat output exceeding 1 MW, with a heat flux across the radial section of the SLGHP reaching 4 × 10⁷ W m⁻². Furthermore, an ammonia vapor-driven power generator was developed and integrated with the SLGHP system. During a 72-hour test, this generator successfully produced electricity at a steady rate of approximately 7 kW. The breakthrough design of the SLGHPs holds the potential to unlock Earth's deep geothermal energy reserves, providing a sustainable and reliable energy source for generations to come.

The goal of carbon peaking and carbon neutrality requires major systemic changes in the energy supply sector. As one of the major non-carbon-based energy sources, geothermal energy is characterized by large reserves, stability, and reliability. This paper summarizes the current situation of geothermal resource endowment and industrial development in China. Based on this, a system dynamics model of geothermal industrialization is established, and the potential of geothermal industrialization and carbon emission reduction in China is predicted. The prediction results show that the growth rate of geothermal heating and cooling areas in the next 40 years will follow a trend of acceleration followed by deceleration. China’s geothermal energy heating and cooling area will reach 11.32–14.68 billion m² by 2060, an increase of about 9–12 times compared to 2020. The proportion of geothermal heating and cooling area to the total building area in China will reach 13.77–17.85%. The installed capacity of geothermal power generation will reach 14,452.80–20,963.20 MW by 2060 under the scenario with electricity subsidies. The proportion of geothermal energy in China’s primary energy consumption structure will reach 3.67–5.64%. The annual carbon emission reduction potential of the geothermal industry will reach 436–632 million tons, equivalent to 4.41–6.39% of China’s carbon emissions in 2020. The results of this study can provide a reference for the healthy and high-quality development of China’s geothermal industry and help to achieve carbon peaking and carbon neutrality goals.