无隔水管钻井U型管效应研究

STUDY ON U-PIPE EFFECTS OF RISERLESS DRILLING

无隔水管钻井在无钻柱阀或钻柱阀失效的情况下进行接单根或起下钻等作业会发生U型管效应。U型管效应期间泥浆池液面不断升高,影响溢流的准确判断。同时准确计算井底压力的变化规律对于判断U型管效应期间是否发生井下复杂也非常重要。文章首先推导了无隔水管钻井使得钻柱充满钻井液所需的最小平台泵排量(零立压排量)的计算公式。然后基于流体力学中的一元不稳定流动理论,结合无隔水管钻井工艺,并考虑实际井身结构,建立分析U型管效应的不稳定流动模型。根据该模型研究了U型管效应持续时间、钻杆内液面下降高度、返出流量以及井底压力随时间的变化规律,同时分析了影响U型管效应持续时间和井底压力变化的因素。结果表明,显著影响U型管效应持续时间的因素是钻井液稠度系数和流性指数,显著影响井底压力的因素是排量和流性指数。

If no drill string valves or drill string valves failed during riserless drilling, there will occur U-pipe effects when making connections or during tripping.It will cause gradual increase in pit level, which will result in an inaccurate overflow decision.An accurate calculation of the changes in BHP is also very important to observe any downhole events during U pipe effects period.In this paper the formula for minimum pump rate to fill the drilling string with drilling fluid during riserless drilling is given.And based on the univariate unstable flow theory of the hydrodynamics, considering the drilling procedures and the actual casing program, the U-pipe unstable flow model is set up.Then the U-pipe effects duration, fluid level decrease in drill pipe, return flow rate and BHP changes with the time, and the factors affecting the U-pipe effects duration and BHP changes are studied by this mode.It indicates the factors obviously affecting the duration are drilling fluid’s consistency coefficient and liquidity index, the factors obviously affecting the BHP are flow rate and liquidity index.