Background The dynamic metamorphism of coals, a significant type of coal metamorphism, represents a fundamental research topic of coal geology. The research achievements have been widely applied in fields such as coal resource evaluation, the prevention and control of coal mine gas, and the exploration and exploitation of coalbed methane (CBM), holding great significance for gaining a deep understanding of the microscopic mechanisms underlying coal deformation and metamorphism, coal and gas outbursts, and CBM occurrence.
Method Based on a literature survey and analysis, this study presents a systematic review of the development history of research on the dynamic metamorphism of coals. Accordingly, this study summarizes the indicators, pathways, and mechanisms of the dynamic metamorphism, analyzes its classic applications and extensions in related fields, and proposes future trends in its research.
Advances and Prospects Research on the dynamic metamorphism of coals has undergone nearly a century of development. With the determination of identification indicators dominated by the microscopic deformations and macromolecular structures of coals, the dynamic metamorphism theory of coals has been gradually established and recognized. The pathways and molecular-level mechanisms of the dynamic metamorphism have been thoroughly revealed, yielding abundant research achievements and systematic research methods. The results indicate that the dynamic metamorphism of coals occurs throughout the coal evolution from peat to graphite, with the different chemical structures of organic matter across various evolutionary stages identified as a major inherent reason for the differentiated evolution characteristics of the dynamic metamorphism. Coal deformation and metamorphism feature internal consistency. Specifically, the mechanisms underlying coal deformation affect the characteristics and degree of the dynamic metamorphism, while the metamorphism represents the essence of the microscopic processes and mechanisms of coal deformation. Tectonic stress plays a key role in controlling the deformation and dynamic metamorphism of coals, with its magnitude and property, along with the deformation environment, determining the deformation and dynamic metamorphism intensities of coals. The dynamic metamorphism of coals changes the occurrence state and content of methane while also enhancing the heterogeneity of gas/CBM occurrence and distribution, thereby increasing both the risk of coal and gas outbursts and the difficulty of CBM exploration and exploitation. The dynamic response characteristics of coal molecular structures at varying levels are determined, enriching and improving the dynamic metamorphism theory of coals and facilitating the understanding of actual coal molecular structures.
Prospects In the future, research on the dynamic metamorphism of coals should consider both the molecular structural differences of coal macerals and the catalytic effects of inorganic minerals in coals by combining the systematic chemical theory on coal molecular structures, especially the quantitative characterization of supramolecular structure evolution. Furthermore, it is necessary to continuously enhance fundamental theory research using advanced methods, such as molecular simulation and machine learning. Research on the dynamic metamorphism of coals should focus on national strategic demands for the goals of peak carbon dioxide emissions and carbon neutrality, as well as the optimization and adjustment of the national energy mix. This involves accelerating the application of the research achievements in emerging fields, such as intelligent and green coal mining, carbon sequestration, hydrogen storage, and the exploration and exploitation of minerals paragenetic and associated with coal measures, and broadening the research scope. These efforts will facilitate the rapid transformation and development of the coal industry.
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