Progress and prospect of hot dry rock exploration and development

The exploitation and utilization of clean energy is a resource and environmental issue of common concern for global sustainable development. As a vital strategic and sustainable future energy, hot dry rock (HDR) has attracted more and more attention. In this paper some thoughts on the future research direction of HDR resources in China are provided based on a worldwide experience summary, hoping to provide a useful reference for the future exploration and engineering development of HDR. Since the concept of HDR was put forward in the 1970s, the number of worldwide HDR construction has been increasingly growing. Although a lot of theoretical and technical breakthroughs have been made, only a small fraction of projects still in operation due to the lack of sustained financial support, induced microearthquakes and other issues. At present, the global development of HDR is gradually entering a new stage of exploration, and the basic theories of HDR to tackle the key problems are strengthening around the world. Since 2012, the China Geological Survey has organized and implemented the nationwide terrestrial HDR resources survey, evaluation, exploration and development, and significant stage progress has been achieved. A series of fundamental maps have been compiled, such as terrestrial heat flow value, curie surface depth, distribution of acidic rock, and heat-controlling structure in China. The resource potential of terrestrial HDR in China has been preliminarily estimated and a sounding basis for the target site selection is provided. HDR exploration and evaluation have been carried out in typical areas of Qinghai, Shandong, Hebei, Shanxi and Jiangsu provinces, and a breakthrough has been achieved in the Gonghe Basin of Qinghai. The first HDR resources exploration and production demonstration project in China was carried out in 2019, which made a series of meaningful outcomes in deep HDR exploration, high-temperature hard rock drilling, large-scale reservoir stimulation, reservoir connectivity and flow circulation, organic Rankine cycle (ORC) power generation, etc. The large-scale reservoir stimulation was carried out in 2020, and the first power generation test was completed in 2021. In general, the global exploration and development of HDR has made great progress. Practice has proved that HDR resources are a promising green energy and are expected to become an inexhaustible energy support for the world in the future. However, there is still a large gap between the existing path of HDR development and utilization and the economics of its supporting technologies compared with commercial development expectations at present. Although the development of HDR resources in China has achieved a breakthrough from “0” to “1”, there is still a long way to go from the international level. In order to solve the problems of large-scale and economic development, it is still needed to promote disruptive technological innovation in high temperature hard rock drilling and completion, fine characterization of deep reservoirs, safe large-scale reservoir construction, efficient heat transfer and heat recovery and other aspects.