基于赫巴流变模式的旋转套管顶替效率计算

旋转套管是提高固井顶替效率的重要措施。为了定量计算注水泥时旋转套管的顶替效率，使用微元分析法，对旋转套管时水泥浆驱替钻井液状态进行了受力分析，建立了顶替界面达到平衡时的顶替效率计算模型，可以计算出不同旋转套管转速时的不同周向角顶替效率。计算表明，当旋转套管转速大于10 r/min时，会有效减小近井壁钻井液滞留层厚度，适当提高稠度系数，流性指数在0.4～0.7之间时，旋转套管能使顶替效率显著提升。 

Calculation of Displacement Efficiency When Casing String is Rotating Based on Herschel-Bulkley Model

Rotating casing string during well cementing is an important measure of increasing displacement efficiency. To quantitatively calculate the displacement efficiency when casing string is being rotated during pumping of cement slurry, infinitesimal method is used to analyze the stresses exerted on the cement slurry which is displacing drilling fluid while the casing string is being rotated, and a model was established for calculating the displacement efficiency of cement slurry when the displacement interface reaches an equilibrium. Using this model, different circumferential displacement efficiencies at different casing string rotational speeds can be worked out. Calculation using the model showed that when the rotational speed was greater than 10, the thickness of the stagnant retention layer of drilling fluid on the surface of the borehole wall can reduced. When the consistency coefficient of the cement slurry was increased, and the flow index was between 0.4 and 0.7, rotating casing string can remarkably increase displacement efficiency.