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煤岩基质-裂隙相互作用下渗透特性研究

Study on permeability characteristics of coal rock under the interaction of coal matrix and fracture

  • 摘要: 为研究煤层气开采过程中温度、气体压力对煤岩吸附和渗流特性的影响,利用等温吸附试验装置与含瓦斯煤三轴渗流试验装置,分别进行等温吸附试验及不同温度条件下变气体压力的三轴渗流试验。考虑应力作用下毛细管分形特征,建立了裂隙体积应力敏感性模型,并在此基础上建立考虑煤基质内部膨胀变形、温度及气体压力变化的煤岩渗透率模型。结果表明:①在相同温度下,随着气体压力升高,煤岩瓦斯吸附量逐渐增大,但吸附速率呈相反趋势。在相同气体压力下,随着温度升高,瓦斯吸附量呈下降趋势。当有效应力恒定时,煤岩吸附变形量随着气体压力增大而增大,并且随着温度增大而减少。②在外部应力作用下,煤岩内部毛细管侧面发生收缩并产生径向延展。新建裂隙体积应力敏感性模型计算得到的裂隙压缩系数与实验室所得值在同一数量级,并随有效应力升高呈下降趋势。③新建渗透率模型能较好反映不同温度、气体压力下渗透率演化规律。在相同温度下,随着气体压力升高,煤岩渗透率先急剧下降后趋于平缓,孔裂隙周围基质膨胀变形对于渗透率的影响逐渐降低。

     

    Abstract: In order to study the influence of temperature and gas pressure on the adsorption and seepage characteristics of coal and rock in the process of the mining of coalbed methane, the isothermal adsorption test device and the triaxial seepage test device for gas-bearing coal were used to carry out the adsorption isotherm test and the triaxial seepage test with variable gas pressure under different temperature conditions respectively. Considering the capillary fractal characteristics under stress, the stress sensitivity model of fracture volume is established. On this basis, a coal permeability model considering the expansion and deformation of the coal matrix, temperature and gas pressure changes is established. The results show that: ① At the same temperature, as the gas pressure increases, the gas adsorption capacity of coal and rock gradually increases, but the adsorption rate shows the opposite trend. Under the same gas pressure, the gas adsorption capacity shows a downward trend as the temperature increases. When the effective stress is constant, the amount of coal adsorption deformation increases with the increase of gas pressure, and decreases with the increase of temperature. ② Under the action of external stress, the capillary side inside the coal shrinks and expands radically. The fracture compression coefficient calculated by the new fracture volume stress sensitivity model is in the same order of magnitude as the laboratory value, and it shows a downward trend with the increase of effective stress. ③ The new permeability model can better reflect the evolution of permeability under different temperatures and gas pressures. At the same temperature as the gas pressure increases, the permeability of coal first drops sharply and then tends to be gentle. The influence of matrix expansion and deformation around pores and cracks on permeability gradually decreases.

     

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