水饱和煤岩储层甲烷运移动态特征

Dynamic characteristics of methane transport in water saturated coal

为了获取低渗煤层两相流动参数,系统分析了水饱和煤层甲烷运移动态特征。通过水饱和煤样气体运移实验明确了两相流体流动行为,获取了气相渗透率、排驱压力和吸附速率等参数。结果表明:水饱和煤岩中甲烷运移需克服毛细管排驱压力,渗透率越小其值越大;基于压差与排驱压力的大小关系,水饱和煤层中甲烷运移可分为毛细管力控制和扩散控制两个阶段;气体存在损失现象,毛细管力控制阶段甲烷滞留于煤岩孔隙,扩散控制阶段甲烷吸附于煤岩表面;水相降低了气体扩散能力,渗透率越高吸附速率越小。研究成果有助于原地条件下低渗水饱和煤层两相流动参数测试方法的改进,有利于水饱和煤层气藏排采制度优化。

To obtain the two-phase flow parameters of low-permeability coal reservoirs,the dynamic characteristics of methane migration in water-saturated coal were analyzed systematically in this study.The two-phase fluid flow behaviors were identified through the gas migration experiment of water-saturated coal samples.Meanwhile,certain parameters were acquired,such as gas-phase permeability,displacement pressure,adsorption rate and etc.The results show that capillary displacement pressure needs to be overcome during the methane migration in water-saturated coal,and its value is increasing with the decrease of permeability.Based on the size relation between pressure difference and displacement pressure,the methane migration in water-saturated coal can be divided into two stages,i.e.,capillary-force control and diffusion control.Gas loss exists,and methane remains in coal pores during the capillary-force control stage,while methane is adsorbed on coal surface during the diffusion control stage.The capacity of gas diffusion is reduced due to water phase.The higher the permeability is,the smaller the adsorption rate will be.These research results are favorable to improve the test method of two-phase flow parameters in low-permeability water-saturated coal and optimize the production system of water-saturated coalbed methane reservoirs.