Dynamic evolution mechanism of water-bearing coal permeability and water film under stress
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摘要:
为探究应力−吸附−水与滑脱效应多因素综合作用下煤岩渗透率演化机制，考虑应力−吸附诱导煤岩变形的影响，修正水膜厚度表达式，并分析煤岩孔隙的动态变化。基于此，进一步量化含水煤岩气体滑脱效应的强度，建立考虑应力−吸附−水与滑脱效应多因素综合作用的煤岩渗透率模型。此外，结合煤岩渗透率试验研究，通过试验数据验证渗透率模型的可靠性，以揭示应力−吸附−水多因素综合作用下煤岩渗透率、动态水膜及滑脱因子的演化机制。研究结果表明：同一含水饱和度条件下，煤岩渗透率随有效应力增大先急剧减小后趋于平缓；同一有效应力条件下，煤岩渗透率随含水饱和度增大逐渐减小。水膜厚度在应力−吸附−水作用下动态变化，水膜厚度与应力、吸附呈负相关趋势，而与含水饱和度呈正相关趋势；随含水饱和度增大，滑脱因子逐渐增大，但在低应力条件下，增大趋势平缓，高应力条件下增大趋势急剧。此外，基于气−液−固表面分离压，推导应力−吸附作用下正方形、正三角形内动态水膜表达式，并分析不同几何形态孔隙的煤岩渗透率、动态水膜及滑脱因子演化机制的差异。其中，因角孔存在，不同几何形态孔隙内水膜厚度从大至小排序为圆形、正方形、正三角形，煤岩渗透率排序与其相反；圆形孔隙内滑脱因子较含角孔隙更大，而正方形与正三角形孔隙内滑脱因子差异较小。
Abstract:To explore coal permeability evolution mechanism under the comprehensive action of multiple factors including stress - adsorption - water and slippage effect, considering the coal deformation induced by stress - adsorption, the expression of water film thickness was corrected to quantitatively characterize the effective pore size, and based on this, the intensity of gas slippage effect of water-bearing coal was further quantified and the permeability model was established under the comprehensive action of multiple factors. Combined with experimental research to verify the reliability of permeability model, and then the evolution mechanism of coal permeability, water film and slippage factors under the comprehensive action of multiple factors was further revealed. The results show that under different water saturation conditions, the permeability decreases sharply first and then tends to flat with the increase of effective stress; under the same effective stress condition, the permeability decreases with the increase of water saturation. The water film thickness changes dynamically under the action of stress - adsorption – water, the water film thickness has a negative correlation with stress and adsorption, but a positive correlation with water saturation; the slippage factor increases gradually with the increase of water saturation, but the increase trend is gentle under low stress condition, and more sharply under high stress condition. In addition, based on the disjoining pressure of gas-liquid-solid surface, the expressions of dynamic water film in square and equilateral triangle under the effect of stress-adsorption were deduced, and the evolution mechanisms of gas permeability, water film and slip coefficient of pores with different geometric shapes are compared and analyzed. Due to the presence of corner holes, the order of water film thickness in pores of different geometric forms is circle > square > equilateral triangle from large to small, the order of permeability is opposite; the slippage factor in circular is larger than that in angular pore, while the slippage factor in square and equilateral triangle pore has little difference.
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Keywords:
- coal /
- dynamic water film /
- permeability model /
- slippage effect /
- pore geometry
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图 2 不同含水饱和度条件下煤岩渗透率随有效应力演化规律
Figure 2. Evolution of coal permeability with effective stress under different water saturation conditions
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图 4 不同应力条件下滑脱因子随含水饱和度演化规律
Figure 4. Evolution of slippage factor with water saturation under different stress conditions
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图 5 不同孔隙压力条件下滑脱因子随应力演化规律
Figure 5. Evolution of slippage factor with stress under different pore pressure conditions
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图 6 正方形及正三角形孔隙有效孔径示意
Figure 6. Schematic diagram of effective pore radius of square and equilateral triangle
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图 7 不同几何形态孔隙的煤岩渗透率随应力−水演化规律
Figure 7. Evolution of coal permeability with stress- water in pore of different geometry
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图 8 不同几何形态孔隙内水膜厚度随应力−水演化规律
Figure 8. Evolution of water film thickness with stress- water in pore of different geometry
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图 9 不同几何形态孔隙内滑脱因子随应力演化规律
Figure 9. Evolution of slippage factor with stress in pore of different geometry
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