Prevention Techniques Of Oxygen Corrosion Of Downhole String In Air Injection Process

Air injection technology is regarded as a creative enhanced oil recovery(EOR)technology,which recently more and more attention has been attached to.However,due to the high pressure of oxygen in the injected air and the operational conditions of high temperature and wetness,downhole strings suffer severe oxygen corrosion,which will hinder the normal production of oilfields.In this study,methods of weight loss,XRD analysis,EDS analysis and SEM analysis were used to clarify the corrosion mechanism and regulation.The following results are achieved.(1)Oxygen corrosion rate increases with rising pressure,even in very low concentration of dissolved oxygen(<6mg/L),steels also suffer severe corrosion.In this case,N80 and P110 steel corrosion rates are both greater than the industry standard(0.076mm/a).(2)Oxygen corrosion rate increases firstly and then decreases,usually reaching maximal value around 83?;this rule also shows in the factor of salinity in NaCl solution,and corrosion rate reaches maximal value around 10000 mg/L.(3)With the fluid flow rate increasing,the corrosion rate increases.(4)According to XRD and SEM analysis,the main elements of corrosion products are Fe and O,and the main components include ?-Fe O(OH)? ?-FeO(OH)?Fe3O4? ?-Fe O(OH).The structure of corrosion film is loose and not dense,which results in lower protective effect on steel matrix.Laboratory experiments were carried out to verify the validity of the oxygen corrosion prevention measures.The following results are achieved.(1)N80,P110,1Cr and 3Cr steels suffer severe corrosion,however,the corrosion rates of 13 Cr,304 and 316 stainless steels are lower than 0.076mm/a.(2)The protective film can be formed on the surface of steels after being coated with grease or oil,which can greatly reduce the corrosion process.And the measure above is prior to passivation.(3)The increasing of pH can result in the decreasing of corrosion.(4)Inhibitors can effectively prevent corrosion of downhole strings,and the compound of inhibitor 1 # and 2 # can prevent corrosion rate over 90% in the experiment.In air injection process,facing with complex and severe corrosive environment,downhole strings suffer severe corrosion damage.Experimental study demonstrates that a single anticorrosion measure is difficult to control the corrosion rate under the industry standard,and therefore diverse measures,that is,the comprehensive corrosion prevention system is required.