井底恒压控压钻井井口回压分析研究

Analysis on the Back Pressure of Constant Bottomhole Pressure MPD

针对目前钻井中遇到的窄密度安全窗口日趋频繁的问题,基于井底恒压控压钻井技术工艺技术原理,以通用圆管流量方程和稳态波动压力理论为基础,精确计算了赫-巴流变模式下的系统环空循环压耗及波动压力,将钻井过程划分为若干工况,综合流型+过程+工况的组合模式得到井口回压计算模型。结合实例对回压计算模型进行验证,验证结果表明,用该模型计算的井口回压与实际值相差很小,能够满足工程精度要求。用该模型进一步分析了不同工况下井口回压与排量、钻井液密度、起下钻速度以及起下钻时间的关系,分析结果对控压钻井的安全实施具有重要的参考意义。

To address the increasingly frequent encountered issues of narrow mud weight window,for the constant bottomhole pressure MPD technology,the annulus circulating pressure loss and the fluctuation pressure under the Herschel-Buckley model has been calculated based on the common pipe flow equation and steady pressure fluctuation theory. The drilling process is divided into several conditions. The back pressure calculation model is established by integrating flow patterns,process and operation conditions. The back pressure calculation model has been validated with practical examples. Verification results show that the calculated back pressure by the established model has a small difference with the actual value, and could meet the engineering requirements for accuracy. Further analyses have conducted on the effects of displacement,fluid density,tripping speed and tripping time on the back pressure under different operation conditions,which could provide important references for safety MPD application.