Impact of water film on methane surface diffusion in gas shale organic nanopores
Impact of water film on methane surface diffusion in gas shale organic nanopores
复制标题
水膜对含气页岩有机纳米孔甲烷表面扩散的影响
DOI：
10.1016/j.petrol.2020.108045
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发表时间：
2021-01-01
影响因子：
--
通讯作者：
Fang, Dazhi
中科院分区：
文献类型：
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作者：
Bai, Jiajia;Kang, Yili;Fang, Dazhi
当页岩孔隙半径小于10 nm时，表面扩散对页岩多尺度孔隙结构中甲烷输运的贡献将显着增加。了解页岩纳米级有机孔隙中的吸附水膜是否有利于多尺度甲烷输运至关重要。由此，建立了考虑水膜对甲烷表面扩散影响的模型。此外，还讨论了水膜对不同扩散机制的影响。结果表明：首先，当水分子进入页岩有机质孔隙时，吸附界面由气-固转变为气-水，即气体在表面的表面覆盖率增加，表面扩散能力增强；其次，当孔隙半径小于6 nm时，尽管水膜可以降低滑流和克努森扩散，但孔隙中甲烷的总体扩散能力增加。然而，当孔隙半径为8-10 nm时，表观渗透率（K-app）随压力增加。由于孔隙表面含有水膜，K-app 并不总是大于没有水膜的孔隙表面。我们的研究表明，如果压裂液用量和关井时间合理，页岩多尺度孔隙结构中压裂液滞留的影响并不总是对甲烷多尺度运移产生负面影响。
When a shale pore radius is less than 10 nm, the contribution of surface diffusion to methane transport in shale multiscale pore structure will significantly increase. It is critical to understand whether the adsorbed water film in shale nanoscale organic pores is beneficial to multiscale methane transport. Thus, a model considering the effect of a water film on methane surface diffusion is established. Furthermore, the influences of a water film on different diffusion mechanisms are discussed. The results show that, first, when water molecule enters shale organic pores, an adsorption interface changes from gas-solid to gas-water, i.e., the fractional surface coverage of gas in the surface increases so the surface diffusion ability increases; second, when a pore radius is less than 6 nm, the overall diffusion capacity of methane in pores increases, even though a water film can decrease the slip flow and Knudsen diffusion. However, when a pore radius is 8-10 nm, the apparent permeability (K-app) increases with pressure. Since a pore surface contains a water film, K-app is not always greater than that for a pore surface without water film. Our investigation shows that the impact of fracturing fluid retention in shale multiscale pore structure is not always negative for methane multiscale transport if the volume of a fracturing fluid and shut-in time are reasonable.