双壁钻杆低压钻井工艺技术

The Low Pressure Drilling Technique with Dual-Wall Drillpipe

双壁钻杆低压钻井工艺技术是利用一种特制的双壁钻杆、旋转充气水龙头和井下气液混流器等特殊装置,以正循环的方式,分别从双壁钻杆的环形间隙和中心水眼内,同时向井内充(泵)入一定量的压缩空气和钻井液,压缩空气从井下某一位置处的气液混流器进入井眼环空中,钻井液从钻头水眼处上返,在井眼的环空中形成了两个不同压力梯度的气液混合段和纯液相段,从而达到降低井底液柱压力的目的。同时由于从井口到井底始终存在着连续的液相流,常规井下动力钻具和随钻仪器的性能不受影响,可以进行正常的井眼轨迹控制。系统介绍了该工艺技术原理、专用配套工具的结构与功能,并结合现场一口井应用实例,对该工艺技术的工艺流程、操作要点、应用效果、范围和发展方向进行了系统阐述和评价。

The dual-wall drilling pipe low pressure drilling technique uses the special dual-wall drilling pipe, spinning aerated swivel and downhole air ＆ fluid mixing device to pump the compressed air and drilling fluid through the annulus of dual wall drilling pipe and the central circulating hole respectively. The compressed air enters the annulus through the air ＆ fluid mixing device at a certain depth, and the drilling fluid flows back from the circulating hole of the bit. Therefore, the gas ＆ fluid mixed section and the pure fluid phase section with two different pressure gradients were formed so that the downhole fluid column pressure is reduced. Meanwhile, the downhole motor and MWD are not affected and wellbore trajectory can be controlled because of the continuous fluid phase flow throughout the bore hole. This paper introduces the principle of this technique, structure and functions of the associated tools. Combined with a field well application, the technical procedure, operation key points, application effect, scope and development are described and evaluated in this paper.