Study On Corrosion Inhibitors For CO₂ Flooding Oil-extraction Well

Carbon dioxide (CO₂) is a common gas in the exploitation of oil-gas fields. With the exploitation of high CO₂-containing oilfields and the wide application of CO₂ EOR technology, CO₂ corrosion is becoming a critical factor in domestic oil and natural gas industry.A kind of corrosion inhibitor, imidazoline sulfonate, was synthesized with 1-hydroxyethyl-2-alkyl-2-imidazoline and 2-Bromoethanesulfonic acid sodium salt according to the properties of the produced water of an oilfield. The inhibition behavior of the inhibitor in CO₂-saturated simulating produced water was investigated by weight loss and electrochemical measurements. The results indicate that imidazoline sulfonate has good inhibition performance on N80 in the CO₂-saturated simulating produced water. It is a mixed type inhibitor, which can restrain both of the cathodic and anodic processes, but mainly inhibit the anodic process. The adsorption of imidazoline sulfonate on N80 steel obeys Freundlich adsorption isotherm equation. It shows higher inhibition efficiency than the imidazoline intermediate especially at higher temperature. If the overall concentration is 100ppm, when imidazoline sulfonate is mixed with a quarter of concentration of thiourea, the mixed inhibitor reaches the best inhibition efficiency.The inhibition efficiency and physical/chemical properties of a pilot test corrosion inhibitor (R35) were investigated with relevant experiments. The results indicate that the inhibition efficiency of R35 is 99.6% in CO₂-saturated simulating produced water containing 5% crude oil if the concentration of R35 is 100ppm. The portable corrosion rate rapid monitoring device combined with chamber-type corrosion inhibitor on-line evaluation device is suitable for the rapid evaluation of the perforamnce of corrosion inbhibitor in water phase filtered out from produced fluid; according to the data of rapid evaluation experiment, R35 has good inhibition performance on carbon steel in the CO₂-saturated water phase filtered out from produced fluid when its concentration is above 300ppm. The water-solubility, compatibility and demulsibility of R35 could meet the field application standards. However, it will be changed into solid at -18℃,so antifreeze should be added into R35 if it is used in cold weather.