双孔双渗煤岩渗透率演化模型及应用

Permeability evolution model and application of dual-porosity and dual-permeability coalbed

为了探究二氧化碳在煤岩封存过程中的渗流变化趋势,视煤岩为双重介质,综合考虑二氧化碳的Fick扩散、Knudsen扩散、表面扩散以及有效应力变化引起的弹性变形和吸附引起的基质膨胀变形的影响,建立煤岩双孔双渗渗透率演化模型。通过二氧化碳注入煤岩的室内实验,验证该模型的有效性。基于有限元软件COMSOL,将建立的渗透率演化模型应用于煤层二氧化碳封存技术,对原位状态下二氧化碳注入煤岩10000天过程中的渗透率演化规律进行数值模拟。结果表明:煤岩基质和裂隙的净渗透率随注入时间和气体压力的增加而减小;在二氧化碳封存过程中,基质渗透率由吸附作用控制,有效应力发挥作用很小;裂隙渗透率由吸附作用和有效应力共同控制,其中吸附作用占主导。

In order to explore the seepage changing trend of carbon dioxide in the process of coalbed sequestration,a permeability evolution model of dual-porosity and dual-permeability coalbed was established by comprehensive consideration of Fick diffusion,Knudsen diffusion and surface diffusion,as well as the elastic deformation caused by effective stress variation and the matrix expansion deformation caused by adsorption.The effectiveness of the model was verified by laboratory experiments by injecting carbon dioxide into coalbed.Based on the finite element software COMSOL,the permeability evolution model was applied to the carbon dioxide sequestration technology of coalbed to simulate the evolution law of permeability during the 10000 days after carbon dioxide injection into coalbed in situ.The results show that the net permeability of coalbed matrix and fracture decreases with the increase of injection time and gas pressure.In addition,in the process of carbon dioxide sequestration,the permeability of the matrix is controlled by adsorption and the effective stress plays a minimum role,while fracture permeability is controlled by both adsorption and effective stress and adsorption plays a dominant role.