注水泥环空动态顶替界面长距离数值模拟

Numerical Simulation on Dynamic Displacement Interface in the Process of Cementing in Annulus

借助流体力学软件FLUENT对环空注水泥层流顶替进行了长距离的数值模拟。利用流体体积法(VOF)对两相顶替界面进行了界面重构。对顶替界面达到动态稳定形态的过程进行了描述,对不同偏心度、密度差、顶替速度和流体黏度条件下的顶替界面进行了模拟。模拟结果显示,顶替开始后界面长度不断拉长,在正密度差下界面会达到动态稳定(在一个范围内波动)或者绝对稳定,并以此稳定界面向前推进,而动态稳定界面会使得窄间隙留下无法驱替的滞留层。在同心环空中,只要存在正密度差即可达到绝对稳定的界面;在偏心环空中高密度差下界面会达到绝对稳定,其他情况会获得动态稳定界面,此密度差节点与偏心度呈正相关;负密度差下界面均无法达到稳定;从对顶替界面达到稳定状态的影响效果来看,从大到小依次为偏心度、密度差、顶替速度和流体流变性能。该模拟结果对水泥浆密度设计、隔离液用量和环空注水泥施工有很好的指导性作用。

In this paper,the displacement process of cement in annulus was simulated by FLUENT software.Displacement interface of two-phase in 300 m annulus is to be re-constructed by Volume of Fluid(VOF)method.Under conditions of different density contrast,rheological property,displacement rate and eccentricity of casing,the dynamically interfaces were simulated and the changing processes were recorded.Simulation results showed that,the interface is absolute stable as long as the density difference is positive in concentric annulus.This positive value needs higher in eccentric annulus and its node is positively related to the eccentricity;otherwise a dynamic stable interface which fluctuates in small scope would be achieved.Under the negative density contrast,the interface cannot reach a steady state.The influence factors from high to low are:degree of eccentricity,density difference,displacement velocity and fluid rheological properties.Smaller casing eccentricity,larger density difference and displacement rate,can reduce the dynamic interface length and enhance the displacement efficiency.The length of the interface is shorter.The simulation results could guide the design of spacer and cementing.