表面反应和扩散迁移联合控制的粗糙单裂隙渗流–溶解耦合模型

COUPLED FLUID FLOW AND CHEMICAL DISSOLUTION MODEL BASED ON SURFACE REACTION AND MASS TRANSFER CONTROL IN A ROUGH FRACTURE

裂隙渗流–溶解耦合模型可用于刻画流场、化学场以及裂隙开度等的变化,而溶解速率的表达以及裂隙开度的初始分布对模拟结果皆有影响。在探讨表面反应和扩散迁移联合控制溶蚀机制的基础上,采用分形方法模拟粗糙裂隙,建立此类条件下的渗流–溶解耦合模型,并进行数值求解。结果表明:(1)裂隙开度、流速、Ca2+浓度等在空间上呈"虫洞"状非均匀分布,尤其是中后期形成相对集中的渗流通道;(2)通过裂隙的流量在某一"临界点"后出现激增,即流量在此时刻之前增长相对较缓,而之后明显增大;(3)裂隙各部位反应受控主因素具有时变性,初始时以表面反应控制为主,而后在上游处转为扩散迁移控制,并逐渐向下游延伸扩大。

The variations of flow,chemical fields and aperture in a fracture could be described by the model of coupled fluid flow and chemical dissolution,which were affected by the dissolution rate and the initial distribution of aperture. Two factors,the surface reaction and the mass transfer,were considered to control the dissolution process. A rough fracture was generated numerically with the fractal theory and a model of coupled fluid flow and chemical dissolution was thus established and numerically solved. The results showed that the distribution of aperture,flow velocity and concentration of Ca2+ appeared as inhomogeneous wormholes. The flow through the fracture increased during the whole period of simulation,while the growth rate of flow increased sharply at a certain moment,called the breakthrough time. The factor controlling the chemical reaction varied during the dissolution,was the surface reaction initially and then was turned to the mass transfer on the upstream and extended to downstream gradually.