长北气田某气井油管腐蚀速率增大原因

Cause of Increasing Corrosion Rate on Tubing in a Gas Well of Changbei Gas Field

长北气田油管整体腐蚀速率缓慢,但某气井在多臂井径检测中发现,该油管局部腐蚀速率增大,远远大于整个气田的油管腐蚀速率和该井前期的腐蚀速率。进行了水质、气质组分分析、多臂井径检测和腐蚀挂片等试验,分别对腐蚀挂片的宏观形貌及腐蚀产物进行了分析,并结合油管的腐蚀程度和腐蚀情况,对该井油管腐蚀速率突然加快的原因及腐蚀机理进行了分析。结果表明:该井油管腐蚀主要原因是CO_(2)导致的电化学腐蚀,整体腐蚀速率不高。油管局部腐蚀速率加快的原因是后期地层产水量增加,矿化度升高,促进了局部点蚀成型后的"深挖"效应,使得腐蚀速率呈非线性增加;水中Cl^(-)浓度较高,进一步提高了腐蚀速率。

The overall corrosion rate of the tubing in changbei gas field was slow,but it was found in the multi arm caliper detection of a gas well that the local corrosion rate of the tubing increased,which was far greater than the corrosion rate of the whole gas field and the corrosion rate of this well in the early stage.The causes and mechanism of sudden acceleration of corrosion rate of tubing in this well were analyzed by carrying out the analysis of water quality and gas composition,multi arm caliper test and corrosion coupon test,analysing the macro morphology and corrosion products of corrosion coupon respectively,and combining with the corrosion degree and condition of tubing.The results show that the main cause of tubing corrosion in this well was electrochemical corrosion caused by CO_(2),and the overall corrosion rate was not high.The cause for the acceleration of local corrosion rate of tubing was that the formation water production and salinity increased in the later stage,which promoted the"deep excavation"effect after the formation of local pitting corrosion,and made the corrosion rate increase nonlinearly.The higher concentration of Cl^(-)in water further increased the corrosion rate.