Corrosion Behavior Of Oil Gathering Pipeline20# Carbon Steel In NaCl ASP Flooding

The NaCl ASP flooding（NaCl、surfactant and polymer）is an improved flooding technology that can effectively improve recovery and reduce pipeline scaling,however,the addition of NaCl and the presence of microorganisms may cause a certain risk of corrosion to the gathering line steel.For the actual corrosion of NaCl ASP flooding gathering pipeline in Daqing oilfield,the effect of single factors such as polymer（polyacrylamide）,surfactant（petroleum sulfonate）,NaCl and sulfate-reducing bacteria（SRB）as well as orthogonal tests on the corrosion of 20#carbon steel was studied by static weight loss method,electrochemical testing,scanning electron microscopy,laser scanning confocal microscope and X-ray photoelectron spectroscopy.Both polymer and surfactant have an inhibitory effect on the corrosion of 20#carbon steel.Polymer concentration in the range of 0～800mg/L,with the increase of polymer concentration,its corrosion inhibition effect on 20#carbon steel shows a trend of first increasing and then decreasing,the critical value is 400mg/L.When the surfactant concentration is in the range of 0～200mg/L,with the increase of surfactant concentration,its corrosion inhibition effect on 20#carbon steel shows a trend of increasing first and then decreasing,the critical value is 150mg/L.NaCl has a promotion effect on the corrosion of 20#carbon steel.When the NaCl concentration is in the range of 0～20000mg/L,with the increase of NaCl concentration,the corrosion rate of 20#carbon steel shows a trend of increasing-decreasing-increasing,and the corrosion rate of carbon steel is the largest when the NaCl concentration is 10000mg/L.In this paper,the corrosion process of 20#carbon steel in a NaCl ASP flooding system in a sterile system is revealed.The study shows that polymer and surfactant adsorption on the surface of carbon steel is a slow process.At the early stage of immersion,the polymer and surfactant adsorption on the surface of carbon steel is low and the charge transfer transfer is fast.In the middle of the immersion,20#carbon steel surface to generate a strong protective Fe OOH,polymer and surfactants in carbon steel adsorption increased,the synergistic effect of the two impede the transfer of charge.In the late immersion period,the dense Fe OOH decomposed into Fe₂O₃,resulting in a small increase in corrosion rate.The influence and mechanism of action of SRB on the corrosion process of 20#carbon steel from NaCl ASP flooding was revealed.It is shown that SRB is able to use polymers as nutrients for growth,causing large viscosity losses.After 15d,the number of SRB was1.1×108 pcs/m L,which was at a large value.At the beginning of the immersion,the formation of a raw material film on the surface of the 20#carbon steel inhibited corrosion of the carbon steel.In the middle of the immersion,the more reactive extracellular polymer（EPS）promoted the corrosion of the carbon steel.In the later stages of immersion,EPS deactivation led to a decrease in corrosion rate,but remained at a large value.After 15 d of immersion,the thicker biofilm inhibited the cathodic oxygen reduction reaction and promoted the anodic reaction under the action of SRB as well as the Fe S corrosion products,which had a greater promoting than inhibiting effect.After removal of the corrosion products,severe localised corrosion occurred on the surface.An orthogonal experimental design was used to investigate the effect of multiple factors on the corrosion of 20#carbon steel.The results showed that the degree of influence of each factor on the corrosion rate of 20#steel was SRB,NaCl,surfactant and polymer in that order.In the best combination,a denser corrosion product is formed on the surface of the carbon steel,which inhibits corrosion of the carbon steel;in the worst combination,a loose corrosion product is formed on the surface and severe localised corrosion occurs on the surface of the carbon steel.