机械式静态双层推靠自动垂直钻具设计

A static mechanical automatic vertical drilling tool with double-layer positive pushing pistons for slim well drilling

关键词:  垂直钻井  机械式垂直钻具  偏重块  推靠力  纠斜行为

Key words:  vertical drilling  mechanically vertical drilling tool  eccentric block  pushing force  straightening motion

摘要:

为满足小尺寸垂直钻探的作业要求,设计一种外径127 mm、具有双层推靠活塞的机械式静态自动垂直钻井工具。该垂直钻具不含独立的电子和液压系统,仅依靠偏重块在重力作用下自动偏向井眼低边的物理特性,带动环阀转动进而改变钻井液流道的开闭,使钻井液在钻具内部和环空中形成压差,驱动双层分布的8个活塞以相应的组合方式推向井眼高边,实现自动纠斜,维持井眼垂直。该钻具采用全新的环阀设计,避免常规盘阀较大的摩擦阻力,提高纠偏的灵敏度和精度,其推靠活塞为独特的双层分布,纠斜时有3个不同层的推靠活塞同时推出,可在较小的钻头压降下获得较大的推靠力和纠斜力矩,纠斜能力显著提升,而且不同层推出的3个推靠活塞形成稳定的三角结构,有效提升钻具的稳定性和可靠性。在钻具结构设计的基础上,对钻具偏心机构、推出机构的力学性能进行分析,并研究角接触球轴承的摩擦阻力对钻具纠斜行为的影响。结果表明:该自动垂直钻具的推靠合力是单个推靠活塞的1+2倍,理论上其纠斜精度仅在井斜角降至0.154°后才会受到影响,纠斜极限井斜角可达0.059°,具有很好的纠斜能力、纠斜精度和灵敏度,而且该钻具结构设计简单,造价及维护成本较低,其机械式的控制方式不受井下温度影响,具有很好的现场应用前景。

Abstract:

In this study, a new kind of automatic vertical drilling tool, with outer diameter of 127 mm and double-layer positive pushing pistons, was designed for slim well drilling. The new tool has no independent electronic or hydraulic system, but relies on a deflective eccentric weighting block to control its straightening motion in the well borebore. When the eccentric block rotates under gravity, the flow channel will change and then an internal-external pressure difference is formed, by which the pistons are pushed out onto the upper side of the borehole to reduce the deviation and maintain the well path with high perpendicularity. During the structure design, because of the reduction of the friction in comparison to the regular disk valves, a new ring valve was adopted to improve the sensitivity and precision of the drilling tool. Distinctively, with eight double-layer positive pistons, the pushing unit can gain a higher push force and straightening moment, then a better deviation correction performance can be obtained. Three pistons located on different layers can be pushed out and a stable triangle structure is formed by the three action points, thus the stability and responsibility of the vertical drilling tool can be significantly improved. In this paper, based on the structure design of the vertical drilling tool, the functions of the eccentric unit and push unit, as well as the friction resistance of angular contact ball bearing on the straightening motion are analyzed. The results show that the push force of the newly designed vertical drilling tool is 1+2 times of that with only one piston, and its straightening precision reduces or gets lost only after the deviation angle is lower than 0.154° and 0.059°, respectively, thus the vertical drilling tool has high quality, precision and sensitivity. Moreover, due to a simple mechanical structure, its manufacture and maintenance cost is low, and it also has high temperature tolerance. The vertical drilling tool has a good prospective for field application.