反转激发的以拍形式存在的钻柱横向振动

在钻井过程中,横向振动对钻柱的影响十分显著。为了解决横向振动造成的钻柱失效问题,建立了钻柱横向振动的微分方程,获得了钻柱横向振动的基本规律。结合大庆油田升深7井,对钻柱横向振动进一步分析得到:反转是造成横向振动的主要原因,反转转速与环隙比有关,当环隙比较小时,反转转速与自转转速基本呈线性关系,当环隙比较大时,反转转速会出现偏离理论值的现象; 在研究钻柱横向振动时,钻柱横向振动固有角频率不仅与钻柱本身的性质有关,还与钻柱所受静态轴向载荷有关,钻柱振动部位距中和点的距离不同,重力与浮力对钻柱振动频率的影响也不同; 反转所激发的横向振动一般以拍的形式出现,由弯曲应力波叠加而成; 在钻柱既有反转又有自转的情况下,当弯曲应力角频率与钻柱横向振动固有角频率接近时,钻柱发生横向共振。

Lateral Vibration of the Drill String in the form of A Beat Induced by An Inverted Excitation

In the process of drilling, lateral vibration has a significant effect on the drill string. In order to solve the problem of drill string failure caused by lateral vibration, the differential equation of lateral vibration of drill string was established, the basic law of lateral vibration of drill string was obtained. The lateral vibration of drill string was further analyzed by combining with Shengshen No.7 well in Daqing oilfield:(1)Inversion is the main cause of lateral vibration, when the annulus gap is small, the reverse rotation speed and rotation speed basically show a linear relationship, when the annulus gap is large, the reverse rotation speed will appear deviation from the theoretical value;(2)In the study of drill string transverse vibration, the natural frequency of drill string transverse vibration is related to the properties of drill string itself however the influence of static axial load on the frequency of the drill string cannot be ignored. The influence of gravity and buoyancy on the vibration frequency of the drill string varies with the depth of the well;(3)The transverse vibration excited by reverse rotation usually appears in the form of beat, which is superposed by bending stress wave;(4)When the drill string both reverses and rotates, when the angular frequency of bending stress is close to the natural angular frequency of drill string, lateral resonance occurs in the drill string.