无隔水管钻井U形管效应计算模型研究

Study on the Calculation Model of U-tubing Effect in Riserless Mud Recovery Drilling

无隔水管钻井(RMR)在无钻柱阀的情况下停泵、接单根或起下钻会发生U形管效应。U形管效应增加了钻井非作业时间,且发生U形管效应期间井底压力变化复杂,钻井液池液面不断升高,影响溢流的准确判断。鉴于此,基于流体力学中的一元不稳定流动理论,结合RMR钻井工艺,详细推导了U形管效应的不稳定流动模型。根据该模型研究了U形管效应持续时间、钻杆内液面下降高度、液面流速和加速度、返出流量以及井底压力随时间的变化规律,也分析了影响U形管效应持续时间和井底压力变化的因素,同时还提出了RMR钻井存在零立压排量概念,该排量是钻柱内充满钻井液所必需的最小海面泵排量。研究结果表明:不同停泵排量都会快速下降到零立压排量,随后逐渐减小;零立压排量对于实现RMR安全钻井和水力参数优选都具有重大意义。研究结果可为认识RMR钻井U形管效应和缩短U形管效应持续时间提供理论依据。

The U-tubing effect would occur for the riserless mud recovery(RMR)drilling when stopping pump,making a connection or tripping without drillstring valve.The U-tubing effect increases the non-operating time,leading to complex bottomhole pressure variation.The resulted continuous pit gain would affect the timely prediction of kick occurrence.To address the problem,based on the one dimensional unsteady flow theory of fluid mechanics,combined with the drilling technology of RMR,the unsteady flow model of analyzing the U-tubing effect has been derived.Using the model,the duration of the U-tubing effect,descent height of drilling fluid level in the drillpipe,the fluid surface velocity and acceleration,return flow rate,and bottomhole pressure during U-tubing effect were studied.Moreover,the factors influencing the U-tubing effect duration and bottomhole pressure have been analyzed.In addition,a new concept of displacement of zero standpipe pressure(SPP)has been proposed,which is the minimum displacement to fill the drillstring.The results show that different pump stop displacements will quickly drop to displacement of zero SPP and then decrease gradually.The displacement of zero SPP is very important for safe RMR drilling and hydraulic parameters optimization.The results can provide theoretical basis for analysis of U-tubing effect of RMR drilling and shortening the duration of U-tubing effect.