吸附–解吸状态下煤层气运移机制

Coalbed methane migration mechanism under adsorption-desorption condition in coal

带吸附作用的煤层气运移规律一直是煤层气地质学界关注的焦点问题之一。为研究吸附解吸状态下的煤层气运移机制,推导了气体吸附解吸方程并分析了多孔介质扩散渗流理论,开展了煤层气运移实验并对实验结果进行了分析。研究结果发现:煤体孔隙结构对煤层气运移具有“容阻效应”,“容储”“阻降”二重特性并存构成了煤基质的基本功能;气体运移过程中煤体对CO2和CH4吸附能力的差异体现在吸附响应时间、吸附速率增长率、吸附平衡时间和最大吸附体积等4项指标;煤层气运移过程中扩散和渗流两种方式并存,当裂隙及大孔内气体压力较中微孔隙系统气体压力高时,气体运移速率以渗流为主,否则以扩散为主。

The migration law of coalbed methane(CBM) with adsorption has always been the focus of attention in the field of coalbed methane geology.In order to study the mechanism of CBM migration under adsorption-desorption state,the deduction of gas adsorption-desorption equation and theoretical analysis of gas diffusion-seepage in porous media were carried out,and new viewpoints were put forward by means of experimental analysis of CBM migration.The results identified that:(1) for the CBM migration,pore structure of coal body has the storage-resistance effect,the dual functions of gas storage and gas pressure drop form the basic feature of coal matrix,(2) adsorption reaction time,adsorption rate,growth rate,adsorption equilibrium time and the maximum adsorption capacity are 4 key indexes of the different gases,(3) diffusion and seepage coexist in the process of CBM migration.When the gas pressure in fracture and macropore is higher than that in medium-micropore system,the gas migration velocity is dominated by seepage,otherwise diffusion is dominant.