常低压裂缝性地层气举穿漏钻井技术

为解决常低压裂缝性地层钻井过程中的易漏难堵问题，提出了一种气举高效降压穿漏的钻井新技术。该技术采用少量双壁钻杆注气将井筒上部钻井液举升，降低环空ECD实现易漏地层快速穿越。通过多相流模拟分析了立管压力、双壁钻杆下深、注气量及钻井液排量等关键工艺参数对环空ECD的影响，建立了以“最优气举效率”为目标的优化设计方法，并利用优化后施工方案，完成了一口常低压岩溶漏失井的先导试验。试验结果表明，利用该技术可在不堵漏的情况下快速建立稳定的循环，同时满足携岩及轨迹控制要求，大幅缩短因井漏引起的非生产时效，具有良好推广应用前景。

A drilling technology of running through thief zone based on gas lift suitable for the fractured formations with permanent low pressure

In the process of drilling the fractured formations with permanent low pressure, circulation loss tends to happen easily and can be hardly plugged. In order to solve this problem, a new drilling technology of efficient depressurization and running through thief zone based on gas lift was developed. By virtue of this technology, a little gas is injected through the double-wall drill pipe to lift the drilling fluid in the upper part of the wellbore, so as to reduce the annulus ECD and run through the thief zone fast. Then, the effects of key technical parameters on the annulus ECD were analyzed by means of multi-phase flow simulation, including standpipe pressure, double-wall drill pipe depth, gas injection rate and drilling fluid displacement. Afterwards, the design optimization method with the optimal gas lift efficiency as the objective was developed. Finally, based on the optimized construction scheme, the pilot test was performed in one karst leaker with permanent low pressure. The experimental results show that this technology can build up stable circulation quickly without plugging, satisfy the requirements of cuttings carrying and trajectory control, and greatly shorten the non-productive time efficiency caused by circulation loss, presenting good popularization and application prospect.