复杂海流作用下钻井立管的重入井分析（英文）

Analysis of Drilling Riser in Re-entry Operation Under Complex Currents

为了安全准确地完成重入井操作,我们需要研究立管的动态特性,特别是立管的变形和底端到井口的距离变化。尽管重入井操作一般会在恶劣海况变好之后进行,但复杂的海流也许还会存在,而以往对立管重入井的研究并没有考虑海流的影响。在本文中,考虑了三种可能会实际出现的海流(定常流,剪切流,双侧流),建立了一个考虑海流影响的更加准确的立管模型,并采用有限元方法简化偏微分方程组。根据重入井立管的特点,设置了初始状态和边界条件使计算更加有效,而后采用牛顿迭代计算了立管的形变、底端到井口的水平距离。另外,文中考虑立管底端速度可能带来的摆动,我们还比较了不同海流对立管重入井作业的优劣。所得到的一些结果可以为立管重入井控制的设计提供有用的帮助,也可以为精确和安全作业提供参考。

In order to complete the operation accurately and safely, the dynamic characteristics of risers in re-entry, especially the riser deformation and the distance from lower-end to wellhead, should be studied precisely. Although the re-entry operation generally occurs when the destructive sea condition turns slightly better, there most likely exists a complex current due to the great operating water depth. However, the dynamics calculation for re-entry in previous research ignored the influence of currents. In this paper, a more accurate model is provided to describe the dynamic behavior of risers in re-entry operation considering three different currents(uniform, skewed, bilateral) that may occur in real sea-conditions. We adopted the Finite Difference Approximation(FDA) method to simplify the original partial differential equations into a linear equation set. According to the characteristics of the riser in re-entry, the special initial state and the boundary conditions are set up to make the calculation more efficient. The riser deformation(shape), horizontal distance from lower-end to wellhead and the velocity of lower-end were investigated under different currents with Newton iteration scheme. In addition, we compared the effect of different currents on the re-entry operation considering possible swings based on the velocity of lower-end. From the results, some interesting and meaningful information about the riser’s features and behaviors were obtained, which is quite useful for the riser’s control scheme constitution in its practical re-entry and also can offer reference for precise and safe operations.