Study On Synergistic Mechanism Of Corrosion And Wax Deposition Of J55 Tubing

Tubing is an important component used in the exploitation of oil and natural gas,which can transport crude oil from the well bottom to the ground under high pressure.Unfortunately,corrosion and wax deposition in tubing will reduce its service life and increase the maintenance cost.In this thesis,the static weightloss experiment was empoloyed to investigate the corrosion behavior of J55 tubing in simulated aqueous media,the wax deposition ratewas examined,and the synergistic mechanism of corrosion and wax deposition was studied with molecular dynamics simulation and potentiostatic polarization.Then,based on these research data,the preventive measures were proposed.The research results show that:（1）When the temperature T≤60℃,the CO₂ uniform corrosion rate enhances gradually with temperature’s increasing,and when it exceeds 60℃,the corrosion rate decreases with the increasing of temperature.With the increasing of CO₂ partial pressure,the highest corrosion rate（1.8441 mm/a）was observed at 60℃and 1Mpa CO₂ partial pressure.（2）Due to various influencing factors,the wax deposition tends to increase.The wax deposition rate increases with the increase of temperature difference between oil flow and pipe wall,roughness of deposition surface and complexity of crude oil components,and decreases with the extension of deposition time.（3）There is a synergistic effect between wax deposition and corrosion.When Ca CO₃ scale layer or Fe CO₃ corrosion product film is formed on the tubing surface,wax molecules are more likely to deposite on the surface.The adsorption tendency of wax molecules on different substrate surfaces is Ca CO₃（10.4）>Fe CO₃（10.4）>Fe（110）.Covering the surface of J55 steel with a complete wax layer can slow down its corrosion,and the corrosion rate is reduced to0.0123mm/a,with a reduction rate of 99.3%.After the wax layer falls off locally,it promotes the formation of macro-corrosion cells,which makes the surface of J55 sample have the characteristics of large cathode and small anode,and intensifies the local corrosion of pipes.The local corrosion rate of J55 steel is increased to 7.641mm/a,with percentage of 314.3%.（4）Solid corrosion inhibitor has satisified corrosion inhibition performance,and the corrosion inhibition efficiency is 85.64%（≥70%）,which can be identified as cathodic corrosion inhibitor.However,when the solid corrosion inhibitor is released for a long time,the corrosion inhibition effect of the solid corrosion inhibitor is significantly deteriorated;The wax inhibitor has a good wax removal effect s,and the wax dissolving rate is 0.0755 g·min^-1(>0.016 g·min^-1).However,the wax removal effect on wax samples in crude oil is poor(far less than 0.016g·min^-1),and the wax removal effect is reduced by 89.94%.（5）Compatibility between corrosion inhibitor and wax inhibitor was poor.The corrosion rate increased to 0.3944mm/a after adding wax inhibitor,and the corrosion inhibition efficiency decreased by 8.18%compared with without wax inhibitor.Wax inhibitor reduces the negative catalytic effect of corrosion inhibitor;Corrosion inhibitor reduces the effect of wax inhibitor.After adding the same amount of corrosion inhibitor to wax inhibitor,the dissolution efficiency of wax balls decreases by 32%.Therefore,the compatibility of corrosion inhibitor and wax inhibitor with other chemicals should be considered in field operation,and the dosage of chemicals should be increased,or similar chemicals with better compatibility should be considered.