Study On Effective Cycle Of Corrosion Inhibitor Adsorption Film In Pump Recovery Well

The CO₂ as one of the components of oilfield associated gas or natural gas exists in oil and gas. With the development of oil and gas fields entering into the later period, the CO₂ and the moisture content in well liquid rise sharply. In addition, the use of EOR will lead to more CO₂ diffused into the work environment, and it will make the CO₂ corrosion of oil field equipment more and more serious. At present, the problem of CO₂ corrosion has become the outstanding problem that troubles petroleum and petrochemical industry. The technology of adding corrosion inhibitor has been widely used in CO₂ corrosion protection, because it has the advantages of low-cost, less dosage and without changing the original production technology. The efficiency of corrosion inhibitor is influenced by partial pressure of CO₂, corrosive medium, fluid producing rate and so on. So it is necessary to study the corrosion inhibition of corrosion inhibitor in practical working environment, and to evaluate the effective cycle of corrosion inhibitor adsorption film.Based on the analysis of research status at home and abroad, this article studied the laws of CO₂ corrosion and corrosion inhibitor by using the experiment method. The research content includes: Firstly, simulating the actual working environment by using the high temperature and high pressure reactor, studying the corrosion law of N80 and P110 steel in CO₂ corrosion environment, and using the finite-element analysis software to study the distribution of casing stress field under the condition of eroding pits existing. Secondly, confirming the technological parameters of corrosion inhibitor by studying the pre-volatile time and pre-volatile concentration. Thirdly, dividing the oil-well into annular area and oil-water mixed area, studying the corrosion inhibition of corrosion inhibitor in different regions, and confirming the effective cycle of corrosion inhibitor adsorption film. The purpose is to provide theoretical basis for the use of corrosion inhibitor in oil and gas fields. Research shows that:1. The corrosion rate of metal is speeding up with the increase of partial pressure of CO₂, and the corrosion rate in liquid phase medium is greater than that in gas phase medium. Besides, the increasing of the production rate can promote the corrosion reaction. CO₂ corrosion product film is divided into three layers structure, the inner layer combines well with the metal surface. Simulation analysis found that the increase of corrosion pit depth will increase the Mises stress value around the casing corrosion pit, and increase the possibility of yield deformation and stress corrosion cracking of casing.2. The corrosion inhibitor that is used in experiment has excellent corrosion inhibition, and has a good resistance to high pressure performance, preparing membrane for 4 hours can meet the requirements. When the corrosion inhibitor concentration over 150 ppm, the inhibition efficiency will be steady and keep at a higher level. The inhibition efficiency in liquid phase medium is greater than that in gas phase medium. The increasing of the production rate will lead to the inhibition efficiency significantly reduced. When the production rate reaches up to 40m3/d, the inhibition efficiency will fall to less than 90% on the fifth day. The study of corrosion inhibitor in different regions found that the effective cycle of corrosion inhibitor adsorption film was about 7 days, and the effective period of corrosion inhibitor was about 11 days.