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.