不同材质油套管钢的CO2腐蚀行为

目的不同管材的CO_2腐蚀行为存在差异,为优选经济型抗CO_2腐蚀材质油套管,探究不同腐蚀条件下常规管材的CO_2腐蚀特征。方法以实际油田的地层水样为腐蚀介质,在高温高压的条件下,对不同材质的油套管进行模拟实验。利用X射线衍射仪(XRD)分析腐蚀试样表面腐蚀产物的形貌特征,研究CO_2分压、温度、测试时间对油套管腐蚀速率的影响规律。结果随着CO_2分压的增加,普通碳钢和低Cr钢的腐蚀速率显著变化,当CO_2分压为0.3 MPa时,普通碳钢腐蚀速率为2.2021 mm/a,而13Cr的腐蚀速率很低,仅为0.1052 mm/a,未表现出明显的规律;腐蚀速率随着温度的升高呈先增加后降低的变化规律,N80,1Cr钢的腐蚀速率远高于13Cr钢;在较短的测试周期内,N80,1Cr,3Cr油套管钢的腐蚀速率略有增加,随着测试周期持续增加,油套管钢的腐蚀速率明显下降;从腐蚀形貌来看,普通碳钢试样的腐蚀程度严重,以均匀腐蚀为主,1Cr,3Cr钢表面存在少量的局部浅斑,以局部腐蚀为主;13Cr材质钢的表面平整,有光泽且无点蚀,腐蚀程度轻微。结论普通碳钢的腐蚀速率对CO_2分压的影响比含Cr合金材质钢更敏感,温度和测试周期均对金属表面的腐蚀产物产生影响,随着温度和测试周期的持续增加,金属表面形成Fe CO3保护膜,含Cr钢表面因铬的富集形成钝化膜,抑制油套管的腐蚀速率,研究成果对CO_2腐蚀环境中的油套管选材具有理论指导意义。

CO2 Corrosion Behavior of Oil Casing Steel Made from Different Materials

In light of difference in CO2 corrosion behavior of different steel casings, the work aims to explore CO2 corrosion characteristics of conventional steel materials under different corrosion conditions in order to optimize economical CO2 corrosion resistant oil casings. With formation water of actual oilfield as corrosive medium, simulation experiment was performed to oil casings made from different materials. Morphology characteristics of corrosion products on the surface of corrosion samples were analyzed by X-ray diffractometer so as to study the influences of CO2 partial pressure, temperature and test period on corrosion rate of oil casings. With the increase of CO2 partial pressure, the corrosion rate of normal carbon steel and low Cr steel changed significantly; at the CO2 partial pressure of 0.3 MPa, corrosion rate of normal carbon steel was 2.2021 mm/a and 13Cr as low as 0.1052 mm/a, showing no obvious law; as temperature increased, the corrosion rate firstly increased then decreased, corrosion rate of steel N80 and 1Cr steel was far higher than that of 13Cr steel. Corrosion rate of steel N80, 1Cr and 3Cr oil casings increased slightly in shorter test period and decreased significantly as the test period increased continuously; as for corrosion morphology, normal carbon steel sample was subject to serious corrosion and mainly uniform corrosion. There was a small amount of local light spots with local corrosion on the surface of 1Cr and 3Cr steel; the surface of 13Cr steel was smooth, glossy, pitting-free and slightly corroded was. The influence of corrosion rate of normal steel on CO2 partial pressure is more sensitive than that of Cr alloy steel. Temperature and test period have influences on corrosion products on the surface of metal. With the continuous increase of temperature and test cycle, FeCO3 protection film takes shape on the surface of metal. A passivation film takes shape on the surface of steel containing Cr due to enrichment of Chromium, which has inhibited the corrosion rate of oil casings. The research has theo-retical guiding significance on material selection of oil casings in CO2 corrosion environment.