塔河油田注氮气采油是碳酸盐岩油藏重要的提高采收率措施之一,取得了较好的降递减和增油效果。但目前采用的膜分离制氮和碳分子筛分离制氮技术,制氮纯度分别为97 %和99 %,注入气中含一定量的氧气。随着注气轮次的增加,井筒腐蚀日趋严重。针对注氮气井井筒腐蚀问题,采用高温高压动态腐蚀模拟装置,开展注氮气井井筒腐蚀机理研究,测定注气氧含量、温度、注气压力和注入速度对腐蚀速率的影响。实验表明,温度从70 ℃升至110 ℃,模拟井下环境管材腐蚀速率增大1.3~2.0倍,达到4.23 mm/a;注气氧含量从0.7 %提高至1.5 %,模拟井下环境管材腐蚀速率增大0.7~1.0倍,达到2.91 mm/a。分析井筒腐蚀的主控因素为注气氧含量和温度。进行注氮气采油井筒腐蚀对策讨论,提出了提高制氮纯度减少氧含量,配套内衬管和缓蚀剂的思路,可有效治理注氮气采油井筒腐蚀。

Nitrogen injection in Tahe oilfield is one of the important measures to enhance oil recovery in carbonate reservoirs, and has achieved good effect of reducing the gradual decrease and increasing oil production. However, the purity of nitrogen produced by membrane separation and carbon molecular sieve separation is 97 % and 99 %, respectively. And the injected gas contains a certain amount of oxygen. With the increase of gas injection cycle rounds, borehole corrosion becomes more and more serious. In order to solve the problem of wellbore corrosion in nitrogen injection wells, dynamic corrosion simulator of high temperature and high pressure was used to study the corrosion mechanism of nitrogen injection wellbore, and the effects of oxygen content of gas injection, temperature, injection pressure and injection rate on corrosion rate were measured. Experiments show that the corrosion rate of pipe in simulated downhole environment increases by 1.3~2.0 times from 70 ℃ to 110 ℃, reaching 4.23 mm/a; the oxygen content increases from 0.7 % to 1.5 %, and the corrosion rate of pipe in simulated downhole environment increases by 0.7~1.0 times, reaching 2.91 mm/a. Thus, the main controlling factors of wellbore corrosion are oxygen content and temperature. Meanwhile, corrosion countermeasures of nitrogen injection wellbore are discussed, and the idea of improving purity of nitrogen production, reducing oxygen content, matching liner and corrosion inhibitor is put forward. It can effectively control corrosion of nitrogen injection wellbore.