A Study On Corrosion Mechanism And Preparation Of Corrosion Inhibitor For Air Foam Flooding

Based on the investigation and sampling analysis of the air foam flooding injection system in a test area of an oil field in Northern Shaanxi Province,as well as the corrosion evaluation experiments which affect the corrosion status of the air foam flooding system,the grey correlation degree between the corrosion factors and the corrosion rate is calculated,the corrosion mechanism of the air foam flooding injection system is proposed,and a compound corrosion inhibitor suitable for air foam flooding system is prepared.The analysis results of the field corrosion pipeline and water sample show that the corrosion of the tube column of the injection system is gradually increased with the increase of the depth of the pipe column.The corrosion products of the pipeline are mainly FeO?OH?and Fe₃O₄,with a small amount of CaCO₃ and SiO₂.The concentration of Ca²⁺and Mg²⁺in the produced water is high.The pH value is weak alkaline and the average mineralization is over17000 mg·L^-1.In the foam liquid,the content of SO₄^2-and CO₃^2-is high,and the content of Ca²⁺and Mg²⁺is lower.The pH value is large and the S^2-is not detected.The trend of scaling exist after the injection of produced water into the formationThe corrosion rate of J55 steel in different corrosion conditions was tested by static weight loss method.The corrosion data were processed by the method of grey correlation in Deng's grey theory and the comprehensive correlation degree of corrosion factors on corrosion rate was obtained.The results show that the change of pH and temperature has the greatest influence on the corrosion rate,the influence of O₂ and CO₂ in the gas source and the influence of pressure is second.The ion factor is weaker comparably.Combined with the results of sampling analysis of the injection system,it is possible to speculate that the main cause of the corrosion of the air foam flooding system is the electrochemical corrosion of dissolved gases and the corrosion caused by scaling.Modified imidazoline was synthesized from oleic acid,hydroxyethyl ethylenediamine and epichlorohydrin according to the corrosion mechanism of air foam flooding system.Then the ternary and quaternary corrosion inhibitor with good corrosion inhibition performance were prepared by modified imidazoline,organophosphorus carboxylic acid,multifunction organophosphate and hydrazine hydrate.The optimum formulation of the ternary corrosion inhibitor is 20%of modified imidazoline,20%of organic phosphorus carboxylic acid and 20%of hydrazine hydrate.The optimum formulation of the quaternary corrosion inhibitor is 25%of modified imidazoline,10%of organic phosphorus carboxylic acid,12.5%of corrosion and scale multifunction organophosphate and 25%of hydrazine hydrate.Under the temperature of80?and the pressure of 4 MPa?O₂ 10%,N₂ 90%?,the corrosion rates of J55 steel were 0.0650mm·a^-1 and 0.0452 mm·a^-1 respectively when the concentration of ternary and quaternary inhibitors was 400 mg·L^-1 in the air foam solution.The scanning electron microscope of the corroded steel show that the composite corrosion inhibitor can adsorb the effective protective on the surface of the J55 steel.The electrochemical polarization data shows that the composite corrosion inhibitor mainly inhibits the cathodic polarization.The electrochemical impedance diagram of the system coincides with the impedance diagram of the coated metal with two time constants.