Research on underground coal gasification from 2023 to 2024: A systematic review

BackgroundThe industrialization of underground coal gasification (UCG) technology presents a potential solution for securing the supply of clean energy. The latest wave of exploration into UCG is currently gaining momentum. MethodsThis review systematically organizes domestic and international literature, expatiates the advances in research on UCG from 2023 to 2024, analyzes the primary challenges in its development, and proposes key areas for future exploration. Advances Transformative technological advancements in the development and utilization of coal energy based on UCG have been proposed. The development of an integrated, synergistic UCG – coalbed methane – carbon capture, utilization, and storage (UCG–CBM–CCUS) process has been identified as a critical pathway for promoting UCG industrialization. Research on the production dynamics and process control of UCG has expanded, refining heat and mass transfer models, as well as relevant simulation methodologies, and establishing mathematical models for key parameters governing UCG cavity growth. Researchers have explored the characteristics of the responses of UCG production behavior to the temperature and pressure within gasifiers, gasification agent formulation, and gas injection processes, as well as the laws of changes in these characteristics. Furthermore, they have demonstrated the inherent advantages and cost benefits of UCG in producing hydrogen-rich gas and have revealed the potential multiple functions of acoustic emission positioning technology for real-time UCG production monitoring. Studies on UCG safety focus on four aspects: operational safety, groundwater protection, land subsidence prevention, and carbon emission reduction. Researchers have investigated the syngas explosion characteristics of UCG, cooling strategies via wellbore spray systems, and the hydrogen corrosion resistance of pipeline materials. Furthermore, high-temperature-resistant new materials for backfill have been preliminarily developed, multiple groundwater pollution prevention techniques have been devised, and various predictive methods for land and residual subsidence have been formed. Additionally, basic strategies for carbon emission reduction via UCG and carbon regulation and reduction (CRR)—an active strategy for carbon active emission reduction—have been proposed. Significant progress has been made in research on the geological constraints and siting assessments, critical underground equipment and tools, and techno-economic assessments of UCG. For geological assessments, highly focused attention is directed to the responses of UCG engineering activities to stratigraphic conditions. Novel concepts have been proposed and validated, involving the catalyst injection process, innovative ignition methods, heating under stimulation of external electromagnetic fields, and improvements in the injection modes and processes of gasification agents. Key equipment and tools, such as combustible casings and coiled tubing, have been successfully created. Many novel concepts of processes and technologies prove innovative and exhibit promising potential for practical application. Studies have demonstrated the economic competitiveness of UCG syngas production and utilization. Moreover, the first on-site technical verification of UCG-enhanced coalbed methane (UCG-ECBM), an efficient integrated extraction process, has been successfully conducted. Prospects In response to critical issues identified in recent UCG field practices, this study proposes three key areas for future exploration, namely geological-engineering integration, the enhancement of construction techniques, and the research and development of critical equipment and tools.