常用完井液中油套管材料应力腐蚀开裂机理研究
发布时间：2018-10-08 19:53
【摘要】：在完井过程中油套管长期处于具有腐蚀性的完井液中,服役条件恶劣同时连续油管还受到弯曲应力、正应力、扭矩等交变应力作用,在腐蚀和交变应力联合作用下,使油管容易发生应力腐蚀开裂,造成油管突然断裂,对油田生产造成巨大损失,甚至造成人员伤亡。因此,深入系统的研究油套管在完井液中腐蚀及应力腐蚀的腐蚀情况,探明腐蚀机理以及存在腐蚀凹坑的油套管断裂机理、断裂临界应力及裂纹萌生和扩展规律就尤为重要。本文选用P110、13Cr两种常用油套管材质在完井液中进行静态电化学分析,考虑温度对其的影响。电化学极化曲线均表现出钝化特性,表现出良好的耐腐蚀性。随着温度的升高材料抗腐蚀性下降,在70℃以上,耐腐蚀性降低速率变慢,腐蚀速率趋于稳定。腐蚀以局部腐蚀为主,但未出现全面腐蚀,对比两种材质表明13Cr具有良好的耐腐蚀性能。在应力存在条件下,13Cr钢在甲酸盐和氯酸盐完井液中腐蚀规律类似,随应力的增加,13Cr钢钝化电流密度逐渐增加,高应力时增幅更为明显,耐蚀性下降。在甲酸盐完井液中,随应力增大,P110钢耐蚀性下降。与甲酸盐完井液不同的是,在氯酸盐完井液中,由于其中含有C1-,随应力增加,P110钢腐蚀电位下降,说明腐蚀倾向降低。与无应力条件相比,一旦施加应力,P110钢钝化电流密度急剧增加。通过使用失重法测得压力、温度、完井液对两种油套管材质腐蚀速率的影响,在.各温度、压力条件下,13Cr的耐蚀性均高于P110。随温度与压力升高,13Cr和P110钢在氯酸盐完井液中钝化稳定性下降,6MPa时腐蚀最为严重,在甲酸盐完井液中则存在临界值,3MPa、90℃时腐蚀最严重。13Cr和P110钢在氯酸盐完井液中发生点蚀,在甲酸盐完井液中则以均匀腐蚀形式发生。使用扫描电镜观察断口形貌,13Cr和P110钢的应力腐蚀破裂为典型的脆性断裂特征。对油套管应用扩展有限元法建模,分析表明在油套管出现三角形缺陷比圆锥形缺陷更具危险性。分析表明断裂临界应力随着缺口深度逐渐降低,在为壁厚一半时最小。随着裂纹弧长的增大而减小,裂纹尖角为30。时临界应力值最小。P110与13Cr材质横向裂纹比纵向裂纹对拉力敏感。而在内压或外压作用下,纵向裂纹比横向裂纹对内压载荷敏感。同时在内外压与拉应力同时作用下,使得裂纹扩展临界拉应力有所降低。结合扫描电镜观察表明,试件在最终断裂时端口无颈缩现象,端口表现为瞬间断裂,端口平整而且裂纹扩展方向与拉伸正应力方向垂直,微观断口形貌表现为解理断裂特征。
[Abstract]:During completion, the casing is in the corrosive completion fluid for a long time, and the service conditions are bad and the continuous tubing is also subjected to alternating stresses such as bending stress, normal stress, torque, etc. Under the combined action of corrosion and alternating stress, The tubing is prone to stress corrosion cracking, which leads to the sudden fracture of the tubing, which results in great loss of oil production and even casualties. Therefore, it is very important to study the corrosion and stress corrosion of oil casing in completion fluid, to find out the corrosion mechanism and the fracture mechanism of oil casing with corrosion pit, the critical stress of fracture and the law of crack initiation and propagation. In this paper, two kinds of commonly used oil casing materials, P110 and 13Cr, are used for static electrochemical analysis in completion fluid, and the effect of temperature on them is considered. The electrochemical polarization curves showed passivation characteristics and good corrosion resistance. With the increase of temperature, the corrosion resistance of the material decreases, and above 70 鈩，
本文编号：2258060
[Abstract]:During completion, the casing is in the corrosive completion fluid for a long time, and the service conditions are bad and the continuous tubing is also subjected to alternating stresses such as bending stress, normal stress, torque, etc. Under the combined action of corrosion and alternating stress, The tubing is prone to stress corrosion cracking, which leads to the sudden fracture of the tubing, which results in great loss of oil production and even casualties. Therefore, it is very important to study the corrosion and stress corrosion of oil casing in completion fluid, to find out the corrosion mechanism and the fracture mechanism of oil casing with corrosion pit, the critical stress of fracture and the law of crack initiation and propagation. In this paper, two kinds of commonly used oil casing materials, P110 and 13Cr, are used for static electrochemical analysis in completion fluid, and the effect of temperature on them is considered. The electrochemical polarization curves showed passivation characteristics and good corrosion resistance. With the increase of temperature, the corrosion resistance of the material decreases, and above 70 鈩，
本文编号：2258060
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