连续循环阀气体钻井技术及其现场试验

目前气体钻井面临大出水地层生产时效低，中断循环后可能引起井壁垮塌、卡钻等井下复杂，充气钻井井底压力波动大、井控风险高等问题。为此，介绍了新研制的一种基于连续循环阀的钻井系统的技术原理以及现场试验情况。该系统主要由连续循环阀和地面控制系统两个部分组成，钻进中将连续循环阀接在钻杆上，接单根、起下钻时，通过连续循环控制系统切换循环通路，实现井下连续循环。在宁211井氮气钻井和月005 H1井充气钻井2口井现场试验的结果表明，接单根作业井底压力恒定，缩短了重新建立正常循环的时间，实现了接单根和起钻作业过程中的连续循环，初步证实了连续循环系统的可靠性与工艺的可行性。连续循环钻井技术在充气钻井过程中的试验成功，标志着该项技术从单一循环介质迈向了两相循环介质的新台阶，可为钻井液条件下的欠平衡井、窄密度窗口井、大位移井、长段水平井安全高效钻井提供新的技术手段。

Field tests of gas drilling technology with continuous circulation valves

The current gas drilling is always challenged by a rather low ROP and low drilling efficiency due to a huge volume of formation water invasion in a well. Besides, once the circulation system is interrupted, the accumulated water in the bottom of the well will tend to cause the lower wall caving, the drill tools’ sticking, a great BHP surge in aerated drilling, or a high risk of well control. In view of this, we introduced a newly developed continuous circulation system as well as its principles and pilot tests. The system is mainly composed of continuous circulation valves connected to a drill pipe and a ground control system to achieve the downhole continuous circulation through changing the circulation channels when the drilling operation is done such as making a connection or tripping. Field tests in Well Ning 211 nitrogen drilling and Well Yue 005 H1 aerated drilling showed that this system achieved the continuous circulation in the drilling operation; the BHP was kept constant when making a connection and the time was reduced of restoring normal circulation. It was also preliminarily confirmed that the system has structural reliability and technological feasibility. The success of pilot test of this system in aerated drilling marks that this technology achieves a new level from single phase to two phase circulation media, providing a new safe and effective method for the UBD wells, wells with a narrow window of density, extended reach drilling (ERD) wells, and horizontal wells with long intervals.