钻井开停泵井底波动压力变化特征研究

为了准确了解钻井过程中开停泵对井底压力的影响，指导安全钻井作业，根据不稳定流动理论，建立了开停泵井底压力波动模型，采用特征线的求解方法，并借助计算机编程对其求解，利用现场实测数据对模拟结果进行验证，分析了压力波在井内的传递与转化过程，研究了开停泵持续时间、钻头距井底距离及钻井液性能对井底压力波动的影响。模拟结果显示:开停泵持续时间越长，异常压力窗口比越小；钻井液密度越大，异常压力窗口比越大；钻井液稠度系数与流性指数越大，异常压力窗口比越小。研究表明，钻井开停泵时，开停泵持续时间、钻井液稠度系数及钻井液流性指数对井底压力的影响极为明显。建立的开停泵井底压力波动模型可以为现场开停泵作业提供参考。 

Study on the Fluctuation of Bottomhole Pressure While Starting and Stopping the Drilling Pump

In order to accurately understand the effect of pump on/off on bottomhole pressure and provide guidance for safe drilling,a model of bottomhole pressure fluctuation caused by pump on/off has been built according to unstable flow theory.The authors analyzed the process of transmission and transformation of pressure waves in the well by means of the solution of characteristic line, and computer programming and well simulation results using field experimental data.The effect of duration of pump on/off,the distance of drilling bit to the bottom fo the hole and the drilling fluid properties was also studied.The simulation results showed that the longer the duration of pump on/off,the smaller the abnormal pressure window ratio;the greater the drilling fluid density,the larger the abnormal pressure window ratio;the larger the drilling fluid consistency coefficient and flow index,the smaller the abnormal pressure window ratio.The study indicated that duration of pump on/off,drilling fluid consistency coefficient and flow index of drilling fluids had a conspicuous effect on bottomhole pressure.The model of pressure fluctuation caused by pump on/off during drilling can provide theoretical reference for starting and stopping the pump on site and can predict mud pump damage.