大庆油田深层气井CO_2腐蚀规律及防腐对策

CO_2 corrosion rules and anti-corrosion method for deep reservoir gas wells in Daqing Oilfield

气井防腐是天然气开采过程中的一个重要方面。CO2对管柱钢材的腐蚀主要是由于天然气中的CO2溶解于水中生成碳酸后引起的电化学腐蚀。通过对N80和P110试样的失重法实验分析表明：在60℃～110℃温度区间内，局部腐蚀突出；CO2分压增加，腐蚀速率呈增大趋势，腐蚀形态以均匀腐蚀为主；流速增加，使腐蚀速率增大；pH值增大可降低腐蚀速度；凝析水的总矿化度与腐蚀速率呈负相相关关系，即矿化度越高，腐蚀速率越低，而部分负离子的存在会增大腐蚀速率；抗腐蚀合金钢（含Cr钢体）依靠自身的耐腐蚀性能抵抗CO2腐蚀，可以降低CO2的腐蚀速率；腐蚀产物膜对钢体有保护作用，也能降低腐蚀速率。在研究庆深气田井下管柱CO2腐蚀规律的基础上，提出了使用耐蚀合金或涂镀层钢管材优化井身结构、加注缓蚀剂、增加pH值以及使用普通碳钢加强腐蚀检测等综合防腐对策。

Anti-corrosion is an important aspect in gas reservoir development. CO2 corrosion in deep reservoir gas wells is an increasingly serious damage in Daqing Oilfield. CO2 corrosion on steel material of pipe string mainly results from electrochemical corrosion of carbonic acid, which is the product of CO2 dissolved in water. There are many affecting factors to CO2 corrosion rate. Based on the study on weightlessness of steel samples N80 and P110 in CO2 corrosion environments, the following rules are obtained ： localized corrosion predominates in temperature of 60℃ - 110℃ ; corrosion rate increases as CO2 branch- pressure rises, and uniform corrosion is the main corrosion form; corrosion rate increases as flow rate increases; corrosion rate can be decreased by a lower pH value; there is a negative correlation between overall mineralization of condensate water and corrosion rate, i. e. , corrosion rate decreases as overall mineralization of condensate water increases with the exclusion of some anions; anti-alloy （ Cr contained in steel） can resist and reduce CO2 corrosion; corrosion file on steel surface can protect steel from corrosion and consequently decrease corrosion rate. This paper presents the rules of CO2 corrosion on steel materials of downhole pipe strings, and gives anti-corrosion methods including using anti-corrosion alloy or coated pipes to optimize string structure, injecting corrosion inhibitor, increasing pH value and intensifying corrosion inspection using normal carbon steel.