海洋弃井套管切割作业偏心工况分析

摘要

Casing-cutting is the key link in the original wellhead equipment retrieval operations for permanent abandonment of offshore wells.The eccentric scenario in cutting operations will easily lead to irregular incision or the casing not being cut off.This kind of situation will cause severe blade wear and even lead to downhole accidents.According to the mechanical model of eccentric cutting scenario,a calculation model of cut face position,the length of the cutter worn out,and eccentric cutting torque was established.Then based on this models some calculations and analyses were carried out taking the cutting operation of the φ339.725 mm casing in Well LH 29-2-1 as an example.The result shows that the length of the cutter worn out increases with the increase in eccentricity.And moreover,the penetration depths in various directions are different under the eccentric scenario,which will cause the failure of cutting operation.Under eccentric scenarios,the total cutting torque of the three cutters fluctuates dramatically.With the cutting operation going on,the individual cutter's torque gradually approaches to the sine curve,and the wave amplitude of the total cutting torque gradually decreases,eventually tending to be a straight line.The above understandings will provide a guidance for judging casing cutting scenario and hence the operation consequence.%套管切割是海洋平台实施永久弃井时原井口装置切割回收的最关键环节,偏心工况切割套管时易形成不规则切口或导致套管未切断,造成刀片磨损严重、切割效率降低甚至导致井下事故.根据套管偏心切割受力模型,建立了切割面位置、割刀磨损长度及偏心切割扭矩的计算模型,并结合LH29-2-1井φ339.725mm套管切割实例进行了计算分析,结果表明:割刀磨损长度随偏心距增大而增大;偏心工况时割刀切入套管各个方向的深度不一致,将导致套管切割作业失败;偏心切割工况时3个割刀切割总扭矩波动较大,随着切割的进行,单个割刀切割扭矩变化逐渐趋近正弦曲线波形,切割总扭矩波动幅度逐渐减小并最终趋于直线.上述认识可为判断套管切割工况及切割结果提供指导.