基于井液流动特性的抽油杆柱力学模型及应用

Development of Mechanical Model for Rod String Based on Well Liquid Flow Characteristics

基于流体的流动特性,对井液流动以及接箍效应对杆柱受力的影响进行研究,并建立杆管环空中井液流动所产生压差力的数学模型,由此给出杆柱中和点和轴向力的计算方法。结果表明,研究杆管偏磨时,需考虑抽油杆柱的接箍效应,井液流动对接箍产生的压差力可占杆柱重力的11%以上。杆柱与管柱环空中的井液流动对抽油杆接箍产生压差力,且该压差力会随着冲程与冲次的乘积以及井液动力黏度的增大而显著增大,而随杆管间过流面积的增大而逐渐减小。井液流动产生的压差力会加大悬点载荷的变化幅度和不平衡性,同时对杆柱轴向力的影响较大,且杆柱轴向力随井深与曲柄转角的变化显著。考虑井液流动特性的杆柱中和点更加接近实际偏磨杆柱段的位置,计算结果的相对误差可以控制在3%以内,井液流动产生的压差力将造成杆柱的中和点位置上移15%以上,使得杆柱的偏磨范围显著增加。

The influence of well liquid flow and coupling effect on rod string is analyzed and the mathematical model of the differential pressure force in the rod and tubing annulus is developed based on the fluid flow characteristics. And the computation of neutral point and axial force is obtained with the limit of well liquid flow. The results show that the coupling effect should be involved due to the ratio of pressure force to rod weight over 11%. The differential pressure forces on rod coupling are resulted by well liquid flow in annulus. And an enhanced product of pumping stroke and speed, an increased dynamic viscosity of well liquid and a reduced area of flow section lead to the increased pressure force. Furthermore, the great impact of pressure force on axial force increases the variation range and imbalance of polished rod load. And the axial force changes greatly with well depth and crank angle The neutral point obtained with the limit of well liquid flow is increased by 15% and closer to actual length of partial-wear while the errors of results are just less than 3%. Then the range of partial wear for rod string increases significantly.