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利用自主设计的外液条件下瓦斯解吸试验装置,首次进行了无水侵入和外来水侵入后含瓦斯煤的瓦斯解吸对比试验。共进行6组,瓦斯吸附平衡压力分别为3.5 MPa、3.0 MPa、2.5 MPa、2.0MPa、1.5MPa、1.0MPa,环境压力分别为3.0MPa、2.5 MPa、2.0MPa、1.5 MPa、1.0MPa、0.5 MPa,含瓦斯煤的内外压力差为0.5 MPa,获得了相关试验数据以及6组瓦斯累积解吸量变化对比曲线。结果表明,在对含瓦斯煤实施水力压裂后,外来水的后置侵入不仅会使瓦斯解吸量大大减少,而且还会使瓦斯解吸的终止时间提前;在压差为0.5 MPa条件下,有水侵入后的瓦斯解吸量仅为无水侵入时瓦斯解吸量的23%～45%,平均降低了67.5%,同时瓦斯解吸终止时间提前约1 h。水的后置侵入对瓦斯解吸具有损害作用,该损害作用源于水在孔隙中形成的毛细管阻力。因此,在评价是否采用水力压裂时,应从煤层渗透率、水驱气、水对瓦斯解吸损害影响3个方面综合考虑。
Using gas desorption test device independently designed for external liquid conditions, the comparative experiments of gas desorption of gas-bearing coal after water intrusion and water intrusion were conducted for the first time. A total of 6 sets of gas adsorption equilibrium pressures were 3.5 MPa, 3.0 MPa, 2.5 MPa, 2.0 MPa, 1.5 MPa and 1.0 MPa respectively. The ambient pressures were 3.0 MPa, 2.5 MPa, 2.0 MPa, 1.5 MPa, 1.0 MPa and 0.5 MPa , The pressure difference between inside and outside of methane-bearing coal is 0.5 MPa, and the related experimental data and comparison curves of the cumulative desorption amount of 6 groups of gas are obtained. The results show that after the hydraulic fracturing of coal-bearing coal, the post-invasion of external water will not only greatly reduce the amount of gas desorption, but also lead to the termination of gas desorption ahead of time. When the pressure difference is 0.5 MPa, Desorption amount of gas after intrusion is only 23% -45% of desorption amount of gas during waterless invasion, with an average reduction of 67.5%. At the same time, the desorption time of gas desorption is about 1 h ahead of time. Post-intrusion of water has a detrimental effect on gas desorption, which is due to the capillary resistance that water forms in the pores. Therefore, in the evaluation of whether to use hydraulic fracturing, we should consider the influence of coal permeability, water purging and water destroying gas desorption.