欠平衡钻气井井口回压控制理论及实践

Theory and Practice of Controlling Wellhead Back Pressure in UBD

欠平衡钻气井的井控问题长期以来一直是该技术领域的一道难题。通过分析井筒流动规律并耦合地层产气得出欠平衡钻气井井控的有效方法——施加井口回压。建立了井筒流动方程和地层产能方程以及求解方法,阐述了施加井口回压可以提高欠平衡钻气井井控效果的理论机理,并通过案例分析得出施加井口回压对欠平衡钻气井的井控效果。研究发现,施加井口回压既可以使进入井筒的地层气体减少,又可以使气体体积变小,有利于欠平衡钻井的携砂和井控。

Well control is very thorny during underbalanced drilling (UBD) of gas wells. In this study, based on an analysis on wellbore flow principle coupled with gas production from formation, an effective method of UBD well control,imposing wellhead back pressure, is gained. Moreover, the wellbore flow equation, formation deliverability equation and solution method are established; the imposing wellhead back pressure may increase a theoretical mechanism of well control; and a wellcontrol effect on UBD is obtained based on case study. The results show that the imposing wellhead back pressure can not only reduce the formation gas entering into wellbore but also lessen the gas volume entering into wellbore. which are favorable for sandcarrying and wellcontrol during UBD.