基于经典扩散模型不同粒径粒煤瓦斯扩散特征实验研究

为了获取多尺度粒煤在不同初始吸附平衡压力条件下的甲烷扩散特征，完成了0.25～1.00 mm，＞1.00～3.00 mm，＞3.00～6.00 mm和＞6.00～10.00 mm这4种粒径粒煤在1.0 和3.0 MPa初始吸附平衡压力下的甲烷扩散实验，并考察了经典扩散模型对各实验在0～10 min，0～60 min，0～180 min时间段的扩散拟合效果。研究结果表明:同实验时间，扩散率表现为随着粒径的减小呈增大趋势，0.25～1.00 mm相较＞6.00～10.00 mm粒径粒煤最大增大了73%；经典扩散模型不适用于描述甲烷在粒煤中的全阶段扩散，粒径越小拟合精度越低，仅对于初始扩散阶段（0～10 min）拟合效果较好；同初始吸附平衡压力，初始扩散系数D值随着粒径的增大呈递增趋势，＞6.00～10.00 mm相较0.25～1.00 mm粒煤扩散系数增大至7倍。不同尺度粒煤的瓦斯扩散特征，为煤层气达产、稳产、增产提供了储层改造方向。

Experimental study on gas diffusion characteristics of granular coal with different particle sizes based on classical diffusion model

To obtain the methane diffusion characteristics of multi scale granular coal under different initial adsorption equilibrium pressures, the methane diffusion experiments of granular coal with four particle sizes of 0.25～1.00 mm, ＞1.00～3.00 mm, ＞3.00～6.00 mm and ＞6.00～10.00 mm under the initial adsorption equilibrium pressures of 1.0 MPa and 3.0 MPa were carried out, and the fitting effect of diffusion by the classical diffusion model on the experimental data at the time periods of 0～10 min, 0～60 min and 0～180 min were investigated. The results showed that under the same experimental time, the diffusion rate increased with the decrease of particle size, and the maximum increase was 73% for the granular coal with the particle size of 0.25～1.00 mm compared with that of ＞6.00～10.00 mm. The classical diffusion model was not suitable for describing the whole stage diffusion of methane in the granular coal, the smaller the particle size, the lower the fitting accuracy, and the fitting effect was better only for the initial diffusion stage (0～10 min). Under the same initial adsorption equilibrium pressure, the initial diffusion coefficient D increased with the increase of particle size, and the diffusion coefficient of granular coal with the particle size of ＞6.00～10.00 mm increased by 7 times than that of 0.25～1.00 mm. The gas diffusion characteristics of granular coal with different scales provide the direction of reservoir reformation for reaching production target, stabling production and increasing production of coalbed methane.