抽油机悬点与抽油杆柱运动协调及临界冲次研究

Studies on coordination between suspension center's and rod string's movements and critical stroke frequency

稠油粘度高,抽油杆柱在井筒流体中运动摩阻大,特别是下冲程,可能会造成抽油杆柱下不去或抽油杆柱滞后于抽油机悬点的运动而产生冲击载荷等,影响油井的正常生产。为此,基于常规游梁式抽油机与宽带式抽油机悬点运动特性及抽油杆柱受力分析,建立了宽带式抽油机悬点运动规律和抽油杆柱在井筒液体中自由下行运动规律的计算模型,分析了悬点运动与抽油杆柱下行运动的协调性,计算了临界冲次。研究结果表明,抽油杆柱在井筒流体中自由下行时,先做变加速运动,当速度增加、下行粘滞力增大到使抽油杆柱受力平衡时,速度达到最大值,开始做匀速运动;等值粘度越小,抽油杆柱达到匀速运动的时间越长,最大下行速度越大;抽油机悬点与抽油杆柱下行运动之间存在临界冲次,当油井生产冲次小于等于临界冲次时,抽油机悬点与抽油杆柱下行运动才能协调;临界冲次随井筒流体粘度的增加而降低,在相同等值粘度的条件下,长冲程、慢冲次有利于抽油机悬点与抽油杆柱下行运动的协调,从而保证稠油的高效开采。

The rod string stands huge friction forces while moving in tubing fluids especially in the down stroke process due to high viscosity of heavy oil. This may cause the difficulty of rod string's downward moving or produce shock load because of rod string' s hysteresis to suspension center's motion which will affect oil wells' production. In view of this problem, the calculation models of wide-belt pumping unit's suspension center movement law as well as rod string's free movement law in tubing fluids are built, the coordination between suspension center's movement and rod string's downward movement are analyzed, and the critical stroke frequency is calculated based on the analysis of suspension center kinetic characteristic for walking beam pumping unit as well as wide-belt pumping unit and the analysis of rod string's load beating condition. Results show that the rod string firstly moves at an increasing rate and it begins to move at a constant speed after downward viscous force increasing high enough to be able to balance the rod string's beating force and it reaches the maximum rate in the downward moving process; the smaller the equivalent viscosity, the longer the time that rod string uses to reach constant velocity, as well as the greater the maximum downward velocity. There exists a critical stroke frequency in the suspension center's and rod string's downward moving process, and the suspension center's motion will not coordinate with that of rod string until the real stroke frequency is not higher than the critical stroke frequency; the critical stroke frequency decreases with the rise of tubing fluids' equivalent viscosity. Longer stroke and smaller stroke frequency under the same equivalent viscosity are beneficial to the coordination between suspension center's and rod string's movements, and therefore guaranteeing the heavy oil's high productivity.