自生酸酸化中液—液可混合流体在井筒中混合流动模拟研究

Miscible liquid and liquid flow simulation of self-generated acid in the wellbore

在自生酸酸化施工时,为降低酸液对井下管柱的腐蚀,将酸母体(中性原液)在隔离液段塞分隔下交替注入,此过程中酸母体有可能在管柱内混合生酸。建立多段塞液体在井筒内液—液混合流动的二维物理模型,对模型壁面关键区域进行网格加密,基于VOF流动模型和标准湍流模型,采用二维非稳态、隐式分离求解算法和双精度求解器对模型进行数值计算,分析了排量、隔离液段塞长度影响下的自生酸中性原液在井筒垂直管道内的流动混合规律。研究表明,排量与酸母体初次混合点井深近似呈线性关系,适当增大施工排量是增加酸母体初次混合点井深,减小酸母体在管柱内混合生酸,降低酸液对井下设备腐蚀程度的一种有效可行方法;小排量施工时,仅靠增加隔离液段塞用量来提高酸母体初次混合点井深,防腐蚀效果并不明显。

In order to reduce the corrosion of acidizing fluid for downhole string, acid matrix（neutral original solution） alternately injects in slug separation of spacer fluid during the acidizing treatment of self-generated acid, however, in this process, acid matrix may produce acid fluid inside tubing string. This paper establishes two dimension physical model of multiple slug liquid in miscible liquid and liquid flow, and conducts mesh refinement in the key area of model wall surface. Based on VOF flow model and standard turbulence model, this paper adopted two dimension unstable state implicit separation algorithm and double precision solver to calculate numeric value, and analyzed flow mixing rule of self-generated acid neutral original solution in vertical string, which was affected by displacement and slug length of spacer fluid. The research shows that, due to the linear relation of mixture point depth of displace- ment and acid matrix, displacement increase is an effective method to increase mixture point depth, reduce miscible acid fluid pro- duction of acid matrix, and decrease corrosion damage of acid fluid to underground equipment. When in small displacement construction, in order to improve initial mixture point depth, anti-corrosion effect is not obvious only by increasing separation liquid slug.