黏土膨胀储层伤害数值模拟研究

Numerical Simulation of Formation Damage by Clay Swelling

在钻、完井或注水过程中,水基工作液的引入可能导致储层中黏土矿物膨胀而造成储层伤害。关于黏土膨胀储层伤害的研究较多,而对其时间空间变化规律的数值研究相对较少。基于渗透水化和水分子的菲克扩散建立了黏土膨胀储层伤害的数学模型,模拟了井筒周围储层无因次渗透率的时空演变特征,并由此计算了其表皮系数随时间的变化情况。结果表明,黏土膨胀伤害具有早期迅速增加、中晚期缓慢增加直至停止的特点,主要的损害量由早期贡献。储层某点的渗透率降低程度有限,但伤害在空间上的延伸范围较远,可以达到几米的量级,造成明显的伤害效果。总结来看,基于简化的数学模型,定量模拟了井筒周围黏土膨胀伤害的空间分布特征与其随时间变化特点,实现了单因素储层伤害的时空动态模拟,对矿场实践有一定的参考价值。

In drilling,well completion or water injection operations,clays in formation rocks may swell when in contact with water base fluids,causing formation damage.Many studies have been conducted on formation damage caused by clay swelling,the numerical studies on the changing pattern of swelling with time and in space are scarcely seen.In our laboratory studies,a mathematical model has been established based on osmotic hydration of clay and the Fick diffusion of water molecules.Using this model,the changing pattern of the non-dimensional permeability of rocks around a wellbore with time and space was simulated,and the change of skin factor with time was calculated.It was demonstrated that the swelling of swelling has the characteristics of fast increase in the early stage,and slow increase to increase ceasing in the middle and late stages,meaning that formation damage is mainly contributed by the early swelling.At a certain point in the reservoir,the permeability impairment may be small,the formation damage is spatially extended,far from its origin,several meters,for instance,causing remarkable damage to the permeability of reservoir formations.To sum up,this study,based on simplified mathematic model,quantitatively simulated the spatial characteristics of the swelling of clays around a wellbore,and the swelling pattern of the clays with time,realizing the space-time dynamic simulation of single-factor controlled formation damage.The studies shed light on field engineering practices.