UCG pilot tests in EU countries: A review of history and progress

Underground coal gasification (UCG) is an important way of transforming China’s coal energy structure. European Union (EU) countries explored UCG for over 80 years, and their rich experience can be used as a reference for promoting UCG industrialization in China. The UK prepared for UCG pilot tests for the first time in the world. From 1944 to 2014, based on the experience of the former Soviet Union and the United States, EU countries successively implemented at least 12 UCG pilot test projects in three stages, making important contributions to the progress in UCG technologies. They invented the blind-hole method and a V-shaped gasifier structure, successfully extending UCG pilot tests from shallow parts to depths of 500‒1000 m first. The systematic monitoring results of the environment provided a practical basis for reducing the concern for the UCG-induced risks to environmental safety. Meanwhile, the cases of successful and unsuccessful UCG pilot tests of EU countries have brought valuable insights into the future development of UCG technologies. It is critical to investigate the geological conditions associated with UCG gasifier gas tightness and develop targeted engineering and technical measures. Furthermore, the key to achieving the commercial competitiveness of UCG projects is to improve gasification efficiency and product gas quality. The risks to the groundwater environment near a UCG gasifier can be eliminated automatically in a short time relying on its self-repair. However, it is necessary to enhance dynamic environment monitoring.