塔河油田稠油机抽井杆失效原因分析

Analysis on Rod Failure Reason of Heavy Oil Pumping Wells in Tahe Oilfield

塔河油田属于碳酸盐岩岩溶缝洞型重质未饱和底水油藏,近年来,随着地层能量下降,含水上升,为提高采收率,采用加深泵挂深抽、注氮气三次采油等一系列采油新工艺,但随之而来的是抽油杆柱疲劳、腐蚀加剧,杆失效现象逐年增加。5口典型井断杆样本的理化检测分析结果表明,失效杆的化学成分、金相组织、洛氏硬度、拉伸性能等均符合行业标准,但结合失效杆断面宏微观特征和能谱分析结果,推断出导致抽油秆断裂的原因为疲劳断裂和腐蚀疲劳断裂,并对不同原因导致的断口样貌形成过程和机理进行探讨。依托实验数据,从断裂力学角度对其失效扩展过程及主要影响因素进行分析,指出疲劳为随机过程,应力强度因子幅值是疲劳扩展的主要驱动力;杆柱承受交变应力大小与裂纹扩展速率成正相关,通过生产管理和设计优化改善杆柱受力,可以大大延长杆柱使用寿命。

Tahe oilfield is a fracture-vuggy karst carbonate oil reservoir with heavy unsaturated bottom water. In recent years,the formation energy dropped and water cut rose.Deepening pumping and nitrogen injection and other new technologies of oil production were applied to enhancing oil recovery ,which lead to more rod string fatigue,severe corrosion and rod failure year by year.Physical and chemical testing analysis results of the rod failure samples of five typical wells show that chemical component,metallographic structure,Rockwell hardness and tensile properties of the failure rod are in accordance with industry standards.Combined with macro- and micro-characteristics of fracture surface and energy spectrum analysis result of the failure rod, the reason of rod failure was inferred as fatigue fracture and corrosion fatigue fracture.Formation process and mechanism of the fracture appearance for different reasons were discussed.The sensitive factors of rod failure and failure extension process were analyzed from the angle of fracture mechanics based on the experimental data.It points out that fatigue is a random process and the main driving force of the fatigue extension is stress intensity factor amplitude.Alternating stress of the rod has positive correlation to the crack growth rate. The working life of the rod may be prolonged when the stress is improved through production management and design optimization.