考虑水分影响的煤岩渗透率模型及演化规律

Coal permeability model and evolution law considering water influence

在开采环境的不断变化过程中,煤岩通常处于气-水共存的状态。为了探究水分与煤岩渗透率之间的反应机制,利用等温吸附装置和含瓦斯煤热-流-固耦合三轴伺服渗流装置,分别进行不同含水条件下的等温吸附试验和孔隙压力升高的渗流试验。基于水膜与孔裂隙表面的相互作用及水膜之间分离压的影响,并且考虑压缩变形及滑脱效应对煤岩渗流的贡献率,构建考虑水分影响的渗透率模型,进而分析不同含水条件下煤岩吸附与渗流变化规律。研究结果表明:①在不同含水条件下,煤岩瓦斯吸附量随孔隙压力增大而增大,而随含水率增大,瓦斯吸附量呈减小趋势。同时,吸附变形随着煤岩的吸附作用而变化。②煤岩中的水分易在孔裂隙表面形成吸附性水膜占据气体渗流的通道,并且气态和液态水分子会制约瓦斯流动,因而瓦斯流量随含水率增大而减小。当煤岩含水率恒定时,渗透率随孔隙压先增大后减小趋于平缓;恒定孔隙压力条件下,渗透率随含水率增大显著减小。③考虑压缩变形、吸附变形、水分和孔裂隙间水膜对裂隙宽度的影响,构建了考虑瓦斯和水分耦合作用的渗透率模型,而且煤岩渗透率计算值与实测数据基本保持一致,可以较好的表征含水煤岩的渗透率变化规律。

Coal is usually in a state of coexistence of gas and water during the changing process of the mining environment.In order to explore the reaction mechanism between water and coal permeability,the coal containing gas heat-fluid-solid coupling device of three axis servo seepage and isothermal adsorption device was used to carry out the experimental studies on the permeability of the coal when the increased pore pressure are under different water contents.Based on the interaction between water film and pore surface,and the effect of disjoining pressure between water films,considering the contribution rate of compression deformation and slippage effect to coal seepage,a permeability model that considers the effects of moisture was constructed.Furthermore,the variation of coal adsorption and seepage under different water conditions is analyzed.The results show that ① under different water-bearing conditions,the adsorption amount of coal increases with the increase of pore pressure.With the increase of water content,the adsorption amount decreases gradually,and the sorption-induced deformation also has the same trend.At the same time,the adsorption deformation changes with the adsorption of coal.② The water in the coal rock is easy to form an adsorption water film on the surface of the pore crack to occupy the channel of gas seepage.And gaseous and liquid water molecules can restrict gas flow.Therefore,gas flow decreases as the water content increases.Under the condition of constant water content,the permeability of coal decreases first and then decreases with the increase of pore pressure.Under constant pore pressure,the permeability decreases significantly with the increase of water content.③ Considering the effects of compression deformation,sorption-induced deformation,water content and water film thickness on the fracture width,a permeability model under gas-water environment was constructed.The permeability value of coal is in good agreement with the measured data,which can better characterize the water-bearing law of coal permeability.Meanwhile,relevant research results also provide a theoretical guidance for the management of coal mine gas disasters.