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ABSTRACTS：The ultra-low permeability of coal matrix is a bottleneck that restricts efficient gas extraction. For the traditional permeability enhancement measures, it is difficult to influence the coal matrix, which makes it challenging to sustainably extract gas during the later stage. By injecting high-temperature steam into coal, the gas production from coal matrix could be greatly improved. The steam permeability is a key parameter characterizing the steam injection capacity, however, there is still a lack of understanding of the change and mechanism of steam permeability in coal. In this study, the experiments of high-temperature steam seepage were conducted using a cylindrical coal sample with the diameter of 50 mm and the length of 100 mm under the stress loading, and the seepage of high-temperature steam under different temperatures and pressures in coal was investigated with the analysis on the thermal deformation of coal. The research results show that a new phenomenon of the unsteady flow is periodically presented in the high-temperature steam flowing in coal. As the injected steam temperature increases, the frequency of the steam pulsation permeability increases and the amplitude decreases. The maximum value of the average steam permeability decreases and the minimum value of that increases with the temperature increase. The axial and radial strains as well as the volumetric strains of coal show the expansion phenomenon in different stages with increasing steam temperature. The mechanism of the pulsating seepage of steam and the inward and outward expansion of coal was revealed. The unsteady pressure change of the steam two-phase flow is the main reason for the pulsation of the steam permeability. Under the high-temperature steam, the large and small pores in coal show the inward and outward expansion, respectively. The research results provide a factual basis and theoretical reference for thermal gas extraction by injecting steam.
| Country | china |
|---|---|
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