地层粘土水化的总体机理和影响因素

THE GENERAL MECHANISMS AND INFLUENCINGFACTORS IN FORMATION CLAY HYDRATION

地层粘土水化的总体机理可分为两步：第一步是水化学势之差引起的宏观水迁移，渗透压和毛细管力可在该步中起显著作用；第二步是粘土颗粒与水结合，导致粘土膨胀、软化、脱落或分散运移。对这两步都有影响的因素为：粘土的矿物成分、交换性阳离子、分散度和颗粒间结合力等；主要影响第一步的因素有井眼水的压力、粘度和活度。目前很难改变前一类因素，通常主要是控制后一类因素以尽量阻缓水向地层中迁移。

he hydration process of formation clay can be divided into two stages. Stage Ⅰ:the entrance of water from the drilling mud into the formation pores under a difference in chemial potentials as driving force, in which osmotic pressure and capillary force may take marked parts. Stage Ⅱ: the hydration of clay particles leading to their swelling, softening and/or dispersion in some extent. The factors influencing the both two stages are: clay mineralogy, kinds of exchangeable cations, joining forces among particles, and dispersion degree. The factors influencing primarily the first stage are: wellbore water activity, pressure and viscosity, which are practically the only controllable parameters in well drilling.