应力作用下岩石的化学动力学溶解机制研究

Chemical kinetics dissolution mechanism of rock under stress

通过结合化学热力学及动力学、过渡态理论和岩石力学等方面的知识,建立了应力作用下岩石的溶解动力学模型,分析了应力作用对岩石固相物质活度及矿物溶解动力学速率的影响,探讨了应力作用下水岩相互作用机制。研究结果表明:岩石所承受应力与周围流体压力之间存在的应力差所产生的化学势差是应力作用下溶解反应的驱动力;应力的施加显著提高了岩石中固相物质的活度,由此加快了矿物溶解反应的动力学速率;应力作用下的岩石细观溶解机制可根据固液界面应力分配及优先溶解部位上的差别分别用水膜扩散模型或岛渠模型进行描述;应力作用下水岩相互作用存在着应力、化学与渗流的3场耦合问题:应力推动化学反应的发生,化学作用使得岩石表面的细观形貌发生改变,局部的应力分布及大小也随着形貌的变化而改变,进而影响化学反应发生的位置及进程,同时也改变渗流通道的演化规律。

Based on the chemical thermodynamics and chemical kinetics,transition state theory,rock mechanics,a dissolution kinetic model of rock under stress is established;the effect of stress on solid activity and dissolution rate is analysed;the mechanism of water-rock interaction under stress is discussed.It reveals that： chemical potential difference induced by the stress difference between rock and surrounding fluid is the driving force of rock dissolution.Stress greatly enhances the rock solid activity,hence speeds up the mineral dissolution rate.There are two meso models of rock dissolution which are water film diffusion model and island-channel model,respectively.The differences between the two models are stress distribution in solid-fluid interface and preferential dissolution site.Water-rock interaction under stress raises a mechanical-chemical-hydraulic coupled problem.Stress motivates chemical reaction.Chemical reaction alters the rock surface configuration.Local stress distribution and magnitude change with the surface variation,which return to cause the change of chemical reaction region and process.Meanwhile,it also influences seepage path evolution.