Influence Mechanism Of Oilfield Special Working Conditions On CO₂ Corrosion And Effectiveness Of Corrosion Inhibitor

With the development of energy demand and technology,the proportion of offshore oil/gas exploration is increasing year by year.The transportation medium of submarine pipeline is multiphase medium of oil,gas and water.The flow pattern is complex and the corrosion problem is increasingly prominent.Although there have been a lot of relevant researches on CO2-H2S corrosion of carbon steel at home and abroad,the corrosion mechanism under multiphase flow and the effectiveness of corrosion inhibitor under special conditions are still lack of systematic theoretical understanding and sufficient data support.This paper focuses on the influence of oil and gas field special working conditions on the electrochemical behavior of carbon steel,micro corrosion mechanism of carbon steel and inhibition mechanism of corrosion inhibitor.The corrosion law of carbon steel and the inhibition mechanism of corrosion inhibitor under special working conditions of oilfield were investigated by using corrosion simulation experiment,electrochemical test,characterization of corrosion products,quantum chemistry calculation,density functional theory calculation and molecular dynamics simulation,etc.Firstly,the effect of different H2S partial pressure on the corrosion behavior of Q125SS and S13Cr and the formation mechanism of corrosion product film were clarified for the supercritical CO2 condition in the development of offshore oil fields with high CO2 content.The main components of the corrosion product film are Fei-xS(pyrrhotite type pyrite),FeCO3 and Cr(OH)3/Cr2O3.The change of the film structure affects the corrosion process and ion diffusion resistance,induces the increase of local potential,and forms a micro galvanic cell with the substrate,which promotes the development of local corrosion.Secondly,the aggregation behavior of organic molecules at the oil/water medium was investigated by corrosion simulation experiments and multi-scale simulation calculation.The distribution behavior of diethyl sulphate and disodium lauroamphodiacetate in the oil/water two-phase was analyzed from the micro level,and the corrosion inhibition mechanism in the oil-water two-phase interface was revealed.It is clear that the phase distribution of disodium lauroamphodiacetate is better than that of diethyl sulphate.Thirdly,for the more complex multiphase flow submarine pipeline with solid phase,the impact mechanism of sand scale on the effectiveness of corrosion inhibitor under solid particle deposition was revealed,and the inhibition mechanism of the inhibitor in the corrosion medium is clarified.The synergistic effect of the scale inhibitor HPAA on the corrosion inhibition effect of disodium lauroamphodiacetate is also found.An experimental device was established to simulate pigging operation of submarine pipeline,and the corrosion law of pigging process on oil and gas pipeline was obtained.Meanwhile,the laboratory evaluation and theoretical evaluation of the effect of corrosion inhibitor under the condition of solid particle deposition were realized.When both LAD and HPAA are added in the system,the adsorption of scale inhibitor effectively covers the active sites on the surface of CaCO3 grains,hinders the growth of crystal,and plays a good role in the inhibition of the corrosion inhibitor LAD.By simulating the pigging process and batch treatment of corrosion inhibitor,it is found that when the surface of the sample is pigged first and then filming treatment,it not only reduces the sediment and liquid on the surface of the sample,but also forms an adsorption film on the surface due to the action of corrosion inhibitor molecules,which hinders the direct contact between the sample and the corrosive medium and further reduces the corrosion of carbon steel.Finally,for the acidizing process in oil/gas well development,a new type of green and efficient organic corrosion inhibitor was synthesized by hydrothermal method based on the mechanism of corrosion inhibitor obtained in the previous study.The inhibition efficiency of ?-HA is up to 94.1%.The adsorption of inhibitor molecule obeys Langmuir adsorption isotherm,which can be divided into two stages:rapid adsorption and rearrangement of inhibitor molecules.Based on the results of quantum chemical calculation and molecular dynamics simulation,the corrosion inhibitor ?-HA has good adsorption capacity on Fe(110)surface,and the Fe-O bond length of ?-HA is smaller than that of MHB and PE.As both MHB and PE are environmentally friendly chemicals,this result is expected to have a wider application in corrosion protection of oil and gas field.