水的后置侵入对瓦斯解吸影响试验研究

Experimental study of the later water intrusion effects on the gas desorption

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。

The paper takes its aim at introducing the results of our experimental study of the later water intrusion effects on the coal-mine gas desorption. As is known, in order to improve the gas extraction efficiency through gas desorption, it is necessary to increase the coal bed permeability by way of hydraulic fracturing, and, for this purpose, we have proposed and invented our own gas desorption-measuring device under the condition of external solution intrusion and conducted the related contrast experiments. The experiments suggested are totally made up of such gas adsorption balance pressure experiments, as 3.5 MPa, 3.0 MPa, 2.5 MPa, 2.0 MPa, 1.5 MPa, 1.0 MPa, and the environmental pressure experiments, respectively, as 3.0 MPa, 2.5 MPa, 2.0 MPa, 1.5 MPa, 1.0 MPa, 0.5 MPa, whose internal and external pressure difference lies in 0.5 MPa. Through the six group contrast experiments, we have gained the related experimental data and six groups of gas accumulation desorption contrast change curves. The analysis results show that： after the hydraulic fracture of the gas-latent coal, the external water later intrusion can not only help to greatly reduce the gas-desorbed coal quantity, but also can facilitate the end time of gas desorption come earlier. Furthermore, provided that the internal and external pressure difference can reach 0.5 MPa, the gas desorption amount of coal after water intrusion is only 23%-45% as compared to that without water intrusion, merely 67.5% of that was before on average. At the same time, the end time of gas desorption would come ahead about 1h because it helps to get rid of the likely damage coming from the water in pores in forming the capillary resistance. Therefore, in evaluating whether to adopt hydraulic fracture to increase coal bed permeability and improve gas extraction efficiency, it is necessary to take into consideration the three aspects when dealing with the problem of coal bed permeability, that is, water-driving gas, water damaging effects on the gas desorption, and ways for enhancing the gas extraction efficiency. Thus, the present study is certain of its due reference worth for heightening the gas extraction efficiency via hydraulic fracture.