粘弹性聚合物驱普通稠油微观渗流数学模型

The Micro-Flow Mathematical Model Study on Viscoelastic Polymer Displacement Viscous Oil

我国海上稠油资源比较丰富,但由于受到海上条件等因素限制,聚合物驱成为提高海上稠油采收率的主要方法.因此深化聚合物溶液驱稠油微观渗流机理对于进一步提高采收率具有十分重要的意义.目前关于粘弹性聚合物渗流机理的理论研究主要局限于弹性聚合物溶液的单相流体在微观孔道内流动特征研究,而针对粘弹性聚合物、油两相流体渗流机理的研究甚少,特别是针对稠油聚合物驱的相关研究未见报道.为此,借助于计算方法较为成熟的OpenFOAM开源平台开展了聚合物驱稠油两相流体渗流机理的研究;以收缩孔道为微观物理模型,建立了粘弹性聚合物溶液、普通稠油两相渗流连续性方程、运动方程及本构方程,并采用VOF(volume of fluid)界面追踪方法建立两相界面相方程;以OpenFOAM开源平台为基础,开发了粘弹性流体、幂律流体两相流体求解器;绘制了不同弹性聚合物溶液在微观孔道内驱油的饱和度分布、速度分布及应力分布特征.结果表明,相对于水驱,纯粘性聚合物溶液前缘突破时间慢,波及面积大,驱油效率高.相比于同等粘度的纯粘性聚合物溶液,粘弹性聚合物的弹性有助于挖潜凸角内的残余油,聚合物溶液的弹性越大,稠油驱油效率越高.随着聚合物溶液弹性的增强,第一法向应力增大,当聚合物溶液进入到孔道突变处时,其弹性发挥的作用最大,法向应力的值最大.研究结果可为矿场实施聚合物驱设计、筛选聚合物溶液提供重要的理论支持.

With the development of economy and the rising demand for oil resources, the exploitation of viscous oil, bitumen and oil shale is an important challenge for the oil industry while the recoverable reserves of conventional crude is decreasing con- stantly. The viscous oil resources of our country is rich, but the polymer flooding is the main method enhancing viscous oil recovery due to restrictions of non-available steam generation facilities off-shore. So it is significant to study on micro flow mechanism deeply for further enhancing viscous oil recovery. The existing study on the polymer flow mechanism is mainly lim- ited to the single phase flow in micro pore, and little study of viscoelastic polymer and oil two-phase flow characteristic has been done especially with viscous oil. In this study, we develop two phases of viscoelastic polymer and viscous oil solver on the OpenFOAM platform based on computational fluid dynamics, and we study the mechanism of viscoelastic polymer flooding vis cous oil based on the solver. In this paper, the contraction model and mathematical model is established, including the continui- ty equation, momentum equation and constitutive equation of two phases, and interface equation solved by VOF （volume of fluid） method. The solver of viscoelastic and power law fluid is developed based on OpenFOAM. The saturation, velocity and stress distribution is drawn with different elastic polymer solutions. The results show that the front breakthrough time is slower, the sweep efficiency is larger and displacement efficiency is higher than water flooding. The elasticity of polymer can enhance oil recovery. The larger is the elasticity, the smaller the dead oil area in convex corner. The stronger of elasticity is,the lager of normal stress is. The elasticity can make the most of displacement oil when the polymer flows in contraction of the model. The results of this paper can supply the theoretical support basis on polymer design and filter, it is significant for implementation of polymer flooding in oil field.