Study On The Application Of Carboxymethyl Chitosan Thio Derivatives In Oilfield Reinjection Water

In the oil and gas industry,corrosion-related failures account for more than 25% of all safety incidents.Proper addition corrosion inhibitors is an effective way to prevent or reduce metal corrosion.However,many inorganic compounds containing phosphates,chromates,tungstates or other heavy metal ions are toxic,environmentally unfriendly and non-biodegradable.Based on the environmental protection and safety,it is considered important and desirable to develop non-toxic and effective inhibitors which can protect metals from corrosion without causing environmental problems.Macrograph and microstructure observation,chemical composition and corrosion product analysis were used to analysis the reason of oil pipeline perforation.Weight loss experiments and FLUENT simulation were conducted to discuss corrosion mechanism.The results showed that the perforation of the pipeline was mainly caused by erosion and corrosion under the scale.When the flow rate is increased from 0 up to 2.5 m/s,the scale deposition rate firstly increases and then tends to be stable.The shear stress of the fluid leads to uneven deposition of the scale layer and severe perforation.The weaknesses of under deposit corrosion were identified by FLUENT simulation.At the elbows and reducers of the pipeline where flow direction or velocity changes,the scale crust was stripped by the high shear stress and carried away by the fluid.The medium can penetrate the loose product layer and reacts with the substrate.Therefore,high corrosion rate occurs at extrados of elbow and inner diameter of reducer.At the outlet of the pipe,a fine turbulent flow occurs on the pipe,a fine turbulent flow occurs on the intrados where scale accumulates unevenly,forming a concentration cell and accelerate corrosion.By introducing a hydrophobic group,the carboxymethyl chitosan(cmch)was further modified and used to synthesize a green corrosion-inhibiting agent,carboxymethyl chitosan thio derivative(thio-cmch).The corrosion inhibition performance of Q235 B steel in oilfield refilled water at 60 °C was studied by weight loss experiment and electrochemical method.The structure was characterized by hot stage microscopy and FTIR.The inhibition performance of oleic acid imidazoline quaternary ammonium salt,stearic acid imidazoline quaternary ammonium salt and thio-cmch with its compounding were also studied under same conditions.Experimental results showed that the cmch increases first and then flattens with the increase of the content,and the corrosion inhibition rate reaches a maximum of 87.81% at 200 mg/L.The thio-cmch tends to be gradual with the increase of the content,and the corrosion inhibition rate is the maximum at 300 mg/L is 93.89%.The adsorption of cmch and thio-cmch on the surface of carbon steel follows the Langmuir law and is a spontaneous mixed inhibitor.The maximum inhibition efficiency of oleic acid imidazoline quaternary ammonium salt is 84.97%.The oleic acid imidazoline quaternary ammonium salt and thio-cmch can improve the inhibition efficiency greatly by competitive adsorption and synergistic effect.The corrosion inhibition efficiency can reach 95.69% when the mass concentration ratio is 100:200(mg/L).The maximum inhibition efficiency of stearic acid imidazoline quaternary ammonium salt is 91.21%.The stearic acid imidazoline quaternary ammonium salt and thio-cmch canimprove the inhibition efficiency greatly by competitive adsorption and synergistic effect.,The corrosion inhibition efficiency can reach 94.69% when the concentration ratio is 100: 150(mg/L).It is proved that thio-cmch can not only reduce the amount of imidazoline corrosion inhibitor,reduce environmental pollution,but also significantly improve corrosion inhibition efficiency.