Evaluation of structural damage and gas transportability change in coal subjected to ultrasound stimulation using image-based modeling and permeability tests

• Published in: Fuel (Guildford) 2023-10, Vol.349, p.128684, Article 128684
• Main Authors: Li, Quangui, Zhao, Zhengduo, Liu, Peng, Nie, Baisheng, Zhao, Yulong, Liu, Xianfeng, Deng, Bozhi, Wang, Mingjie
• Format: Article
• Language: English
• Subjects: Coal fracture; Coalbed methane recovery; Gas permeability of coal; Ultrasound stimulation
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/j.fuel.2023.128684

•Characterization of structural changes in coal fractures by CT image-based modeling.•Ultrasound treatment improves the fracture aperture and interconnectivity of the coal.•Gas transportability in stressed coal with ultrasound stimulation was studied.•Ultrasound stimulation plays a time-effective role in enhancing coal permeability. Ultrasound stimulation will cause structural damage and modify gas transportability in coal, which is beneficial to enhance coalbed methane production. The image-based modeling and permeability tests were conducted to examine the structural damage and gas transportability change in coal subjected to ultrasound stimulation. The results show that the fracture space volume and structural complexity in coal significantly increased after 2 h’ ultrasound stimulation. The fracture porosity increased by 8.1%∼11.9%, and the interconnected fracture proportion increased by 17.2%∼21.2%. The anisotropy permeability was estimated using gas transport simulation in 3D coal structure, and the average permeability in three-dimensional directions increased by 95.2%∼113.5% after ultrasound stimulation, which implies that ultrasound stimulation can induce multi-dimensional structural damage and expand interconnected fracture networks. The permeability tests show that gas permeability in stressed coal was significantly improved by 34.3%∼43.8% with half an hour of ultrasound stimulation. With continuous ultrasound stimulation, the gas permeability increased rapidly with increasing stimulating duration at the initial stage. Subsequently, the permeability continued to increase, but the trend of permeability increase gradually slowed down. Finally, after several cycles of stimulation, the permeability tended to be constant. It implies that the performance of ultrasound stimulation on enhancing coal permeability is time-effective, and there is an optimal stimulating duration parameter for the target CBM reservoir, which is critical for pursuing the high efficiency application of ultrasound in CBM engineering operations.