静态推靠式导向翼肋陷入井壁风险分析

Analysis on the risk of static push-the-bit steering rib plunging into well wall

静态推靠式旋转导向钻井系统依靠导向翼肋支撑井壁提供导向力,井壁在翼肋推靠力作用下可能发生屈服和塑性变形,会降低钻压传递效率和造斜率,不利于定向钻井施工。采用有限元软件对旋转导向钻井过程中导向翼肋陷入井壁的过程进行了模拟,并对影响井壁变形的因素及规律进行了分析,给出了可降低导向翼肋陷入软地层的若干技术措施。结果表明,现有的单柱塞铰接式导向翼肋与井壁为角接触,接触面积小,导致接触应力分布不均匀,最大应力位于导向翼肋上端;井壁岩石的弹性模量以及塑性参数(内聚力和内摩擦角)对井壁变形影响较大;在钻进软地层时导向翼肋会陷入井壁,陷入深度随运动时间的延长近似呈线性增加。改进导向翼肋结构、适当减小导向翼肋的推靠力、做好地层适应性评价等均有助于降低导向翼肋陷入井壁风险。

The static push-the-bit rotary steering drilling system provides steering force by making use of the steering rib to support the well wall,and the well wall may suffer yield and plastic deformation under the thrust force of the rib,which can lead to the decrease of WOB transfer efficiency and build-up rate,so as to have adverse impact on the construction of directional drilling.In this paper,the plunging process of steering rib into the well wall during the rotatory steering drilling was simulated by using the finite element software.Then,the factors influencing the deformation of well wall and the deformation laws were analyzed.Finally,several technological measures to reduce the plunging of steering rib into soft formations were proposed.The results show that it is angular contact between existing single-plunger articulated steering rib and well wall and the contact area is small,so the distribution of contact stress is nonuniform with the maximum stress lying at the upper end of steering rib.What’s more,the elastic modulus and plastic parameters(internal cohesion and internal friction angle)of wall rocks have greater influence on the deformation of well wall.Furthermore,when drilling soft formations,the steering rib can plunge into the well wall and the plunging depth increases linearly approximately as the movement goes on.It is beneficial to reduce the risk of steering rib plunging into the well wall by improving the structure of steering rib,reducing the thrust force of steering rib appropriately and carrying out formation adaptability evaluation.