钨合金镀层在油田井下环境中的腐蚀行为

Corrosion Behavior of Tungsten Alloy Coating in the Underground Environment of Oil Field

目的研究钨合金在塔河油田井下(高温、高酸性及注氮气环境)的腐蚀行为规律。方法在高温高压釜中模拟塔河注气井下工况,结合腐蚀失重、镀层厚度测试、显微硬度测试以及扫描电镜、EDS、SRD等分析手段,对钨合金镀层的腐蚀行为进行研究。结果未腐蚀镀层的维氏硬度为825HV,但经过腐蚀后,镀层的显微硬度值因压痕边角塌陷而无法读取。在H_2S主控环境中,镀层试样明显增重,当温度为130℃时,镀层未观察到分层现象,但镀层表面有腐蚀产物;200℃时镀层出现明显分层和鼓泡,并且鼓泡有破裂现象,微观观察镀层表面有局部腐蚀,局部腐蚀处检测到硫元素,说明硫元素渗入镀层内部,生成硫化物。在160℃的H_2S/CO_2共存和CO_2主控环境中,试样增重不明显,也未发生失重,镀层有轻微的分层现象。在注氮气环境中,试样发生明显失重,镀层厚度减薄,镀层的腐蚀以均匀腐蚀为主,同时镀层出现分层现象。镀层在注气井井下环境中腐蚀后变脆。结论钨合金镀层在高含H_2S环境中及注氮气环境中会发生明显分层,并会出现局部腐蚀,耐蚀性较差,而在其他环境中出现轻微分层现象。

The work aims to study the corrosion behavior of Tungsten alloy coating in the underground environment of Tahe oilfield(high temperature, peracidity and N2 injection). The underground environment of Tahe oilfield was simulated in high temperature and high pressure autoclave and the corrosion behavior of Tungsten alloy coating under simulated conditions was studied by weight loss measurement, coating thickness test, mircohardness test, SEM, EDS and XRD. Hardness of sample before corrosion was 825 HV, while the hardness of all samples after corrosion could not be measured because of the collapse of indentation corners. In H2S dominated environment, the weight of samples increased obviously. When temperature reached130 ℃, there was no stratified phenomenon on the coating, but the surface had corrosion products. Stratified phenomenon and bubbling obviously appeared on the coating at 200 ℃ and the bubbles broke out. Local corrosion was also observed on the surface and element S was detected in the local corrosion position by EDS test, indicating that S reacted with Fe to form iron sulfides. The weight of samples did not change significantly after corrosion at 160 ℃ in the H2S/CO2 and CO2 dominated environment and there was no weight loss, either, but light stratified phenomenon appeared on the surface. The weight and thickness of samples decreased significantly in the environment of N2 injection. The coating corrosion was mostly uniform and stratified phenomenon appeared in the coating as well. The coating became brittle after corrosion in all simulated environments. In the environment with high H2S and N2, Tungsten alloy coating has obvious stratified phenomenon, local corrosion and poor corrosion resistance, but shows slight stratified phenomenon in other environment.