深水海底举升钻井系统U型管效应研究

Study on the U-tube effect in subsea mud-lift drilling systems in deep water

对于深水海底举升钻井系统,由于钻杆内和环空内的液柱压力不平衡会产生U型管效应,因此精确地预测U型管效应发生时的井筒流动特性和U型管效应持续时间对于钻井操作和井控安全具有重要意义。基于流体力学理论,建立了U型管效应数学模型,并将计算值与实验测量值进行对比,验证了所建模型的准确性。分析了发生U型管效应时钻杆内液面深度、环空排量、泥浆池增量和井底压力随时间的变化规律,在此基础上提出了U型管效应过程中的溢流监测方法,同时分析了钻井液黏度和喷嘴直径对U型管效应的影响规律。本文研究结果可为深水海底举升钻井系统发生U型管效应时的安全作业提供指导。

For the subsea mud-lift drilling system, a U-tube effect will occur due to the imbalance between the liquid column pressure within the drillstring and that in the annulus. For smooth drilling operations and safe well control, it is very important to accurately predict the flow behavior and the duration of the U- tube effect. In this paper, based on the fluid mechanics theory, a mathematical model of U-tube effect was developed and validated with experimental, data. With this mathematical model, the fluid level in drill string, flow rate in the annulus, pit gain, and bottomhole pressure under U-tube effect can all be obtained. Based on the transient flow characteristics, a method of kick detection during the U-tube effect was proposed. Furthermore, the influences of mud viscosity and nozzle size on the duration of U-tube effect were analyzed. The results will provide a theoretical guidance for the operation security during the U-tube effect for subsea mud-lift drilling systems.