提升偏心环空注水泥顶替效率的浆柱结构优化分析.

Casing eccentricity is the key factor that determines the evolution of flow rate and flow pattern in the cementing annulus, which restricts the improvement of displacement efficiency. It is an important way to improve displacement efficiency by optimization of slurry column structure, and the related theoretical mechanism has not been reported. Using computational fluid dynamics of Fluent software, 3 D model horizontal annulus with different eccentric casing were developed, and the changes of displacement efficiency in different eccentric casing were discussed. Combined with the poor displacement efficiency with casing eccentricity of 0.4, the best slurry column structure was recommended through analysis of annulus fluid retention volume fraction in different column structure. The results showed that: ① Due to the combined effect of eccentricity and buoyancy, the displacement efficiency of casing eccentricity of 0.1 is better than that of casing concentricity; When the eccentricity is greater than 0.1, the displacement efficiency decreases gradually with the increase of eccentricity under the coupling effect of casing eccentricity and mass diffusion. ② injecting spacer first and then flushing fluid is beneficial to give full play to displacement effect of spacer under positive density difference, and the flushing effect of low density flushing fluid is utilized to improve displacement efficiency. ③ the velocity of wide side is higher than that of narrow side in the casing eccentricity, which causes the cementing slurry to return from the wide side in advance, while the narrow side retains a large amount of drilling fluid. The simulation results provide an important theoretical basis for the structure design and optimization of slurry column under eccentric annulus. [ABSTRACT FROM AUTHOR]