随机波浪及平台运动下控压钻井隔水管端部轴向位置预测方法

VERTICAL POSITION PREDICTION METHOD OF RISER RCD FOR MANAGED PRESSURE DRILLING UNDER RANDOM WAVE AND VESSEL MOTION

控压钻井(managed pressure drilling,MPD)技术是深水钻探时解决泥浆密度窗口较窄问题的重要技术。MPD隔水管端部为旋转控制头(rotating control device,RCD),其轴向位置的变化会直接影响井底压力。目前关于深水MPD隔水管端部轴向位置预测方法的文献较少。本文基于欧拉-伯努利梁理论,考虑管内高压和钻井液流速的影响,采用直接刚度矩阵法建立MPD隔水管系统动力学理论模型,采用Newmark-β积分法对MPD隔水管系统的动力学方程进行求解,并进一步开展随机波浪及平台运动下隔水管端部轴向位置的动态预测研究。以南海某1600 m水深隔水管为例进行分析,算例表明,一年一遇随机海况、管内高压为12 MPa,钻井液流速为2 m/s,钻井液密度为1600 kg/m^(3)时,隔水管端部轴向位置改变量在0.5~0.6 m之间波动;当进一步考虑平台慢漂运动时,隔水管端部轴向位置改变量在0.2~0.7 m之间波动。据此可计算得到井底压力的波动范围,从而可为控压钻井作业时井底压力的精确调控提供参考。

Managed pressure drilling(MPD)is an important technique to solve narrow drilling mud density window problem in deepwater drilling.The top end of the MPD riser is a rotating control device(RCD),and the variation of its vertical position will directly affect the bottom hole pressure.Currently,literatures regarding the prediction method of vertical position of the RCD could be found sporadically.In this work,based on Euler-Bernoulli beam theory,considering the influence of high pressure inside the riser and drilling fluid flow rate,the dynamic theoretical model of MPD riser system was established by using direct stiffness matrix method,and Newmark-βintegral method was employed to solve the dynamic equations of the MPD riser system.Further,dynamic prediction of the vertical position of the RCD under random waves and vessel motion was researched.Taking a 1600 m deepwater riser in the South China Sea for example,the calculation showed that under one year return sea states,when inside pressure of the riser is 12 MPa,the drilling fluid flow rate is 2 m/s,and the drilling fluid density is 1600 kg/m^(3),the vertical position of the RCD fluctuated between 0.5 to 0.6 m.However,when the drift motion of vessel was taken into account,the fluctuation of the vertical position of the RCD will be 0.2~0.7 m.Based on this,the fluctuation range of bottom hole pressure could be calculated according,thus providing a reference for precise control of bottom hole pressure during managed pressure drilling operations.