Unraveling the mechanism of selective dissolution in anthracite coal for enhanced permeability through sodium hypochlorite oxidation treatment
Document Type
Journal Article
Publication Title
Fuel
Volume
374
Publisher
Elsevier
School
Centre for Sustainable Energy and Resources / School of Engineering
Funders
Ministry of Education / National Nature Science Foundation of China
Grant Number
2022-002, 42272176
Abstract
Sodium Hypochlorite (NaClO) oxidation treatment has emerged as a promising method for stimulating coalbed methane reservoirs. However, the variability in reactivity among different coal macerals and mineral compositions, particularly vitrinite and inertinite, and its impact on coal permeability remain incompletely understood. This study aims to reveal the mechanism of selective dissolution in anthracite coal by comparing the change in coal composition and the associated dissolution structures. A Permian coal sample from Zhijing Block, China, was collected and separated into vitrinite-rich and inertinite-rich concentrates using a combination of hand-collecting and sieving methods. Following oxidation treatment for 240 h, the coal permeability exhibited distinct stage characteristics. Results from low-temperature nitrogen adsorption analysis showed that the changes in coal pore structure caused by oxidative dissolution involved two effects: the exposure of more micropores and widening of pore sizes. The variation in coal pore structure at each stage was a combined result of these effects. Measurements of mass loss, total organic carbon content, and mineralogical composition demonstrated strong dissolution of carbonate, pyrite, maceral compositions, and carbonate minerals (calcite, dolomite) in the samples over the experimental time scale. Further examination of the leaching liquid revealed that the reaction stages, characterized by pH changes and oxidation ability, align with the permeability enhancement stages, dividing the process into four stages. During the oxidation process, the reaction of pyrite and minerals with alkaline oxidative solution generated a large amount of H+, causing a shift from alkaline to acidic conditions. In the alkaline phase, maceral compositions and pyrite underwent oxidation and dissolution, yielding numerous water-soluble acids. Upon transitioning to an acidic environment, oxidation of maceral compositions ceased, pyrite oxidation was inhibited, and carbonate minerals (calcite, dolomite) dissolved due to their reaction with H+. This comprehensive analysis underscores the importance of monitoring stage changes in different coal components and pore structure over reaction time to achieve the optimal permeability enhancement through oxidation treatment. These findings serve as a theoretical foundation for the practical implementation of coalbed methane reservoir oxidation treatment and permeability enhancement in field applications.
DOI
10.1016/j.fuel.2024.132494
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Lu, Y., Kang, Y., Li, Z., Yue, M., Zhang, T., He, F., ... & You, Z. (2024). Unraveling the mechanism of selective dissolution in anthracite coal for enhanced permeability through sodium hypochlorite oxidation treatment. Fuel, 374, 132494. https://doi.org/10.1016/j.fuel.2024.132494