控压钻井回压压力波在井筒中传播的速度和时间规律

Propagation velocity and time laws of backpressure wave in the wellbore during managed pressure drilling

控压钻井过程中当监测到井底发生气侵尤其是溢流时,通常通过调节回压泵和节流管汇阀门给井筒施加回压来重新构建井底压力平衡。但气侵后回压压力波到达井底的时间有一个明显的滞后,如仍认为井口回压瞬间加载到井底,由此计算得到的井筒相关参数与实际井筒流动参数必然存在着较大的误差,有可能造成井控失效甚至引发井喷。为此,基于整体平均气液两相流模型,以回压压力波在井筒中传播速度和时间为研究对象,建立了环空气液两相流动的压力波传播方程,并引入气液相间作用力对方程组进行耦合求解。计算结果表明:(1)压力波波速随钻井液密度的增加而增大,随含气率、虚拟质量力系数的增加而呈现出减小的趋势,先急剧变化,之后变化幅度缓慢;(2)当含气率大于0.10或虚拟质量力系数大于0.20时,气液相间动量已充分交换,压力波波速的减小幅度变缓,趋于稳定。以四川盆地蓬莱9井为例,计算得到压力波单次传播的平均时间约为50 s,4个回合的总传播时间约为200s,占系统控制响应总时间的67%以上。结论认为,采用该方法计算得到的压力波在环空中的传播速度及传播时间更加符合实际井况,可大幅度提升MPD钻井系统控压响应时间的准确性和自适应节流阀控制的精度。

When gas invasion, especially overflow, occurs at the bottom hole in the process of managed pressure drilling （MPD）, it is common to apply backpressure on the wellbore by adjusting the backpressure pump and throttle valve, so as to rebuild bottom hole pres- sure balance. If it is still thought that the wellhead backpressure is loaded to the bottom hole instantaneously, there will be larger errors between the calculated wellbore parameters and the actual wellbore flow parameters, which will result in well control failure and even well blowout. In this paper, a pressure wave propagation equation suitable for the gas-liquid two-phase flow in the annulus was estab- lished based on the global averaged gas-liquid two-phase flow model to investigate the propagation velocity and time of backpressure wave in the wellbore. Then, gas-liquid interaction was introduced to carry out coupling solution on the equation set. It is shown that pres- sure wave velocity increases with the increase of drilling mud density, but decreases with the increase of void fraction and virtual mass force coefficient. It changes drastically at first, and then slow down. What＇s more, when the void fraction is greater than 0. l or the virtual mass force coefficient exceeds 0.2, the momentum between gas phase and liquid phase is fully exchanged, and the pressure wave velocity decreases slowly, approaching a stable value. In Well Penglai 9 in the Sichuan Basin, for example, the average time of single pressure wave propagation is about 50 s, and the total propagation time of 4 rounds is about 200 s, which accounts for more than 67% of the total time of system control response. It is indicated that the propagation velocity and time of the pressure wave in the annulus calculated by this method can greatly improve the accuracy of managed pressure response time of MPD drilling system and the control precision of adaptive throttle valve.