减氧对空气泡沫驱井下管柱的缓蚀作用及减氧界限

Corrosion inhibition effect of deoxygenation on down-hole string of air foam flooding process and deoxygenation limit

氧腐蚀是限制空气泡沫驱油技术应用推广的主要因素,减氧能够降低腐蚀速率。笔者利用高压腐蚀反应釜模拟工况条件,采用失重法测试了N80套管钢在不同氧含量(2%～21%)、不同压力(20～50 MPa)、不同温度(70～120℃)条件下的腐蚀速率,根据测试结果拟合建立了腐蚀速率与氧分压关系的数学模型;采用扫描电镜、能谱仪和X射线衍射分析表征了腐蚀产物的微观形貌和成分。结果表明,空气泡沫驱过程中N80钢的腐蚀速率随空气氧含量的降低呈非线性下降,但无法将腐蚀速率控制在0.076 mm/a标准以下。温度120℃、压力50～20 MPa,N80钢标准挂片的减氧界限为0.021%～0.054%,已经达到纯氮气的标准。工况条件下不同氧含量的N80钢材腐蚀产物疏松多孔,其成分为Fe2O3、FeOOH和Fe3O4,腐蚀产物对基体金属无保护作用,工况的改变并不会显著改变腐蚀产物的形貌和成分。

Oxygen corrosion is a main factor hindering the wide application of air foam flooding.Although deoxygenation can result in the decrease of corrosion rate.In this study,the high-pressure corrosion reaction kettle is used to simulate the working conditions,and the corrosion rate of N80 casing steel is measured using weight loss method under different oxygen contents(2%-21%)at various pressures(20-50 MPa)and temperatures(70-120℃).According to the experimental results,a mathematical model of the relationship between corrosion rate and partial pressure of oxygen is established.The morphology and composition of corrosion products are characterized using the scanning electron microscope,energy disperse spectroscopy and X-ray diffraction.The results show that the corrosion rate of N80 steel presents the nonlinear decrease with the decreasing oxygen contents of air in the air foam flooding process.However,the corrosion rate is impossible to be controlled below the standard value of 0.076 mm/a.The deoxygenation limit of N80 steel is 0.021%-0.054% at 120℃ when the pressure is between50 MPa and 20 MPa,and has reached the standard of pure nitrogen.Under the working conditions,the corrosion products of N80 steel are loose and porous with different oxygen contents as well as Fe2 O3,FeOOH and Fe3 O4,indicating no ability to protect base metal.In addition,the morphology and composition of corrosion products vary little with the changes in the working conditions.