外加水分对煤层瓦斯压力测定的影响分析

Analysis of the influence of additional water on the measurement of coal seam gas pressure

针对钻孔及煤岩层水对瓦斯压力测定的影响问题,从宏观影响和微观效应两方面分析了水对直接法测定煤层瓦斯压力的影响。宏观影响主要是由水的重力产生的,可以通过测试后计量钻孔中水分进行修正;微观效应通过实验室开展水对煤中瓦斯的置换实验进行分析。实验表明:水能够置换煤微孔隙中的瓦斯,使吸附态的瓦斯变为游离态瓦斯;在未饱和状态下,煤中含水率在2%~10%时,瓦斯的置换量随含水率的增大而增大,最终平衡的瓦斯压力也变大;从置换速率来看,初期置换速率迅速增加到最大,达到顶峰后进入衰减阶段,衰减趋势比较符合指数衰减规律;从卸压后的瓦斯解吸规律来看,煤样瓦斯解吸量随煤层含水率的增大而减小。考虑到现场测试时测压气室的体积、水对煤的润湿范围、煤的含水率等不确定影响因素,现场尚不能进行水对瓦斯压力影响的定量研究。

In view of the problem of water existing in the drilling and coal rock in the process of measuring coal seam gas pressure,the influence of water on the direct method of measuring coal seam gas pressure was analyzed from two aspects of macro effect and micro effect.The macro effect was mainly caused by the gravity of water,which can be corrected by measuring amount of water in the drilling after testing;the microcosmic effect was analyzed by laboratory experiments on gas displacement in coal with water.The experiment shows that:water can replace the gas in coal micropores,so that the adsorbed gas becomes free;in the unsaturated state,when the water content in the coal is between 2%and 10%,with the increase of water content,the gas replacement amount also increases,and the final equilibrium gas pressure also increases;from the perspective of displacement rate,the initial replacement rate rapidly increases to the maximum,then enters the attenuation stage after reaching the peak,and the attenuation trend conforms to the exponential attenuation law;according to the law of gas desorption after pressure relief,the amount of gas desorption of coal sample decreases with the increase of coal seam water content.Considering the uncertain factors such as the volume of the pressure chamber,the wetting range of water to coal and the water content of coal,the quantitative study on the influence of water on gas pressure can not be carried out.