CO_(2)注气压力对瓦斯扩散系数影响规律实验研究

Experimental study on the influence of CO_(2)injection pressure on gas diffusion coefficient

煤层CH_(4)解吸效率低、扩散慢的特点严重制约着煤层瓦斯抽采的效率,为解决低透气性煤层瓦斯抽采困难的问题,选取晋城赵庄煤矿煤样,研究不同注气压力对驱替CH_(4)过程的影响以及驱替过程中CH_(4)扩散系数的变化规律,利用自主研发的CO_(2)驱替CH_(4)试验平台,在0.6、0.8、1.0 MPa等不同注气压力条件下分别进行CO_(2)驱替CH_(4)实验。结果表明:驱替压力越大,达到最大CH_(4)排放量的时间越短,CO_(2)突破时间越快,置换效率越大,驱替效果越好;CH_(4)气体驱替过程分为3个阶段,先急剧增加再缓慢增加最后保持平稳;在同一注气压力下,瓦斯扩散系数随时间呈先增大后减小的变化规律,注气压力为0.6、0.8、1.0 MPa时,瓦斯扩散系数的最大值分别为2.27×10^(-5)、3.36×10^(-5)、4.62×10^(-5) cm^(2)/s。从实验结果可知,不同注气压力下,CO_(2)对CH_(4)主要起到驱替作用、置换吸附-解吸作用及稀释驱替作用;每个阶段的CH_(4)气体运移情况不同,根据实验阶段合理调整注气流量、压力等参数,使注驱技术搭配更高效。研究结果对CO_(2)深埋与瓦斯(煤层气)高效抽采具有理论指导意义。

Most of the coal seams in China are characterized by low pressure,low permeability and low saturation.The methane gas in the coal seam is slowly desorbed and diffused slowly,which affects the production rate of coalbed methane.The coal samples from Zhaozhuang Coal Mine of Jinmei Group were selected to study the influence of different gas injection pressure on CH_(4) displacement process and the variation law of CH_(4) diffusion coefficient in the process of displacement.Independently developed CO_(2)displacement CH_(4) test platform was used to carry out the experiments under different gas injection pressures such as 0.6,0.8 and 1.0 MPa.The results show that the greater the displacement pressure,the shorter the time to reach the maximum CH_(4) emission,the faster the breakthrough time of CO_(2),the greater the displacement efficiency and the better the displacement effect.The process of CH_(4) gas displacement can be divided into three stages,first increasing sharply,then slowly increasing,and finally keeping stable.Under the same gas injection pressure,the gas diffusion coefficient first increases and then decreases with time.When the gas injection pressure is 0.6,0.8 and 1.0 MPa,the corresponding maximum values of gas diffusion coefficient are respectively 2.27×10^(-5),3.36×10^(-5),4.62×10^(-5) cm^(2)/s.According to the experimental results,CO_(2)plays an important role in CH_(4) displacement,displacement adsorption-desorption and dilution displacement under different gas injection pressures.The migration of CH_(4) gas in each stage is different,so the injection-gas flow rate,pressure and other parameters can be reasonably adjusted according to the corresponding migration of CH_(4) gas in the experimental stage to make the injection and flooding technology collocation more efficient.The research results present a theoretical guidance for deep CO_(2)burial and efficient gas extraction(CBM).