气体滑脱及有效应力对煤岩气相渗透率的控制作用

动态的煤储层渗透率影响煤层气的开采，已引起广泛关注。针对6块采自沁水盆地南部煤矿的无烟煤样品，测试了4.3MPa围压条件下煤岩气相(氦气)渗透率变化特征，基于气体滑脱及有效应力效应分析进一步探讨了渗透率变化的控制机理。结果表明,气体压力降低过程中:①渗透率呈现“先降低后升高”的变化趋势，转折点进口气体压力约为1.9MPa(对应于平均气体压力1.0MPa)；②平均气体压力小于1.0MPa时，氦气产生滑脱现象；③渗透率—有效应力之间呈近似负相关关系；④进口气体压力大于1.9MPa时，为有效应力负效应作用阶段，导致渗透率降低；进口气体压力降至1.9MPa以下时，有效应力与气体滑脱效应同时作用，此阶段气体滑脱正效应强于有效应力负效应，引起渗透率升高。 

Controls of Gas Slippage and Effective Stress on the Gas Permeability of Coal

Dynamic coal reservoir permeability impacts the production of coalbed methane (CBM)and has been extensively studied.Gas (Helium)permeability change was measured under a 4.3MPa confining stress condition for 6 anthracite coal cores from the southern Qinshui Basin.Furthermore,controlling factors of the permeability change were investigated by comprehensively analyzing the effects of gas slippage and effective stress on the permeability.Results show that during gas pressure decline：①the permeability initially decreases but subsequently increases,during which the rebound begins at an inlet gas pressure of about 1.9MPa(corresponding to a mean gas pressure of 1.0MPa);②gas slippage phenomenon appears as the mean gas pressure falls bellow 1.0MPa;③the permeability is approximately negatively related to effective stress;④the permeability decreases due to the negative effect from effective stress as the inlet gas pressure is greater than 1.9MPa;while it increases when the pressure falls below 1.9MPa because the positive effect from gas slippage is stronger than the negative effect from effective stress.