摘要
目的针对油井管材质13Cr马氏体不锈钢在ρ=1.15 g/cm^(3)氯化钠和ρ=1.25 g/cm^(3)甲酸钾环境中的腐蚀行为差异性进行研究,以期为13Cr油井管在含甲酸钾油气田中的应用提供科学依据。方法将13Cr材质挂片分别放置于氯化钠和甲酸钾溶液中进行高温高压失重试验,试验后采用SEM、EDS、激光共聚焦显微镜、XPS等表征方法对试样表面的宏观、微观腐蚀形貌、腐蚀产物成分、点蚀进行观察,结合极化曲线、交流阻抗谱(EIS)等电化学测试技术,研究了13Cr马氏体不锈钢在2种完井液环境下的腐蚀差异,探索其在甲酸钾环境中腐蚀严重的原因。结果相同温度下,13Cr马氏体不锈钢在甲酸钾环境中的平均腐蚀速率为氯化钠环境中的11~15倍,90℃甲酸钾环境中的腐蚀速率达到5.1179 mm/a,并且甲酸钾环境中的点蚀速率为氯化钠环境中的2倍以上,由微观形貌可以看出,13Cr甲酸钾环境中的腐蚀产物膜被完全破坏。从电化学测试结果可以看出,13Cr在2种环境中的腐蚀均由阳极反应控制,甲酸钾环境中的自腐蚀电位比氯化钠环境中低,自腐蚀电流密度增大,交流阻抗值减小,腐蚀热力学趋势增大。结论甲酸钾是一种强碱弱酸盐,其水溶液呈弱碱性,在高温高压环境中,甲酸根离子与CO_(2)共存时,Cr元素溶解与甲酸根反应,阻碍了具有保护作用的腐蚀产物膜Cr(OH)_(3)和Cr_(2)O_(3)产生,同时CO_(2)溶于水形成H_(2)CO_(3),促进了腐蚀过程的阴极反应,因此13Cr在CO_(2)与甲酸钾共存环境中的腐蚀严重。
With the development of deep and ultra-deep wells in oil and gas fields,the high temperature and high pressure environment puts forward higher requirements for the performance of completion fluid.Formate completion fluid is more popular in oilfield application due to its advantages of high density,good thermal stability,strong anti-pollution and low corrosion.13Cr martensitic stainless steel is the main material of high CO_(2) well casing.When the failure of downhole packer leads to the invasion of CO_(2) into the annulus of oil casing,the coexistence of weak alkaline environment of potassium formate completion fluid and CO_(2) may cause complex corrosion problems of 13Cr materials.There is still a lack of systematic understanding of the dissolution characteristics of potassium formate under the synergistic action of CO_(2),the stability of passivation film and its corrosion behavior to metals.It is necessary to further explore its corrosion mechanism to optimize the safety design of deep well completion.13Cr samples(50 mm×10 mm×3 mm)were polished(240#–1200#sandpaper),cleaned,dried,and weighed(0.1 mg accuracy).After N_(2) deaeration(2 h)in a high-temperature/high-pressure autoclave,corrosion tests were conducted at 60℃/90℃under 10 MPa CO_(2)(static,5 days).After the test,samples were reweighed to calculate uniform corrosion rates.Pitting depth and rates were measured via laser confocal microscopy.Surface morphology and corrosion products were analyzed through SEM and XPS.In-situ electrochemical tests,including polarization curves and electrochemical impedance spectroscopy(EIS),were performed to analyze the microscopic corrosion behavior of 13Cr steel in different corrosive environments under high temperature and high pressure conditions.In addition,a Pt counter electrode and an Ag/AgCl reference electrode were adopted in the tests.Samples(φ15 mm×3 mm)were polarized in NaCl solution from-300 mV to+300 mV(vs.ocp)and in potassium formate solution from-300 mV to+1300 mV(vs.ocp),with a scan rate of 0.2 mV/s.For EIS measurements,an AC signal amplitude of 10 mV and a frequency range of 10 mHz to 100 kHz were applied.Data from the EIS spectra were analyzed with ZSimpWin.In the comparison of potassium formate and sodium chloride environment,13Cr showed more negative self-corrosion potential and larger self-corrosion current density in the potassium formate system,and the anodic polarization curve showed a significant passivation zone,which was directly related to the reaction of formate(HCOO-)with dissolved Cr element to form Cr(HCOO)_(3) surface sediment.EIS analysis showed that the AC impedance value in the potassium formate environment was significantly lower than that in the sodium chloride environment,and the protective passivation film of Cr_(2)O_(3)/Cr(OH)_(3) on the surface was completely destroyed.The formation of Cr(HCOO)_(3) not only hinders the formation of Cr(OH)_(3) and Cr_(2)O_(3) passivation film,but also accelerates the dissolution of anode metal.At the same time,the H2CO3 generated by CO_(2 )dissolves in water,enhancing the cathodic hydrogen evolution reaction,and the synergistic effect of the two leads to a significant increase in the corrosion rate of 13Cr in the presence of CO_(2)-potassium formate.
作者
陈浩东
魏安超
肖平
李祝军
娄益伟
于延钊
张鑫鑫
刘佳乐
CHEN Haodong;WEI Anchao;XIAO Ping;LI Zhujun;LOU Yiwei;YU Yanzhao;ZHANG Xinxin;LIU Jiale(CNOOC(China)Co.,LTD.Hainan Branch,Haikou 570311,China;Key Laboratory of Deep Sea Deep Formation Energy Engineering of Hainan Province,Haikou 570311,China;CNOOC EnerTech-Drilling&Production Co.,Hainan Branch,Haikou 570311,China;China University of Petroleum(Beijing),Beijing 102249,China)
出处
《表面技术》
北大核心
2025年第12期124-133,共10页
Surface Technology
基金
中海油集团公司“十四五”重大科技项目(KJGG2021-0800)。
关键词
13Cr马氏体不锈钢
甲酸钾完井液
氯化钠完井液
CO_(2)腐蚀
13Cr martensitic stainless steel
potassium formate completion fluid
sodium chloride completion fluid
CO_(2) corrosion
