Optimization And Mechanism Research On The Efficient Corrosion Inhibitors Used In CO2 Corrosion System

The PVT analysis of oil field found that the salinity and concentration of Cl- in formation water is extremely high, CO₂ acidic gas were also found in the associated gas, all the result indicate that the poor reservoir layer corrosion environment could lead to serious CO₂ corrosion problem during the future oil field exploitation. Among many corrosion control method, the corrosion inhibitor is widely used in the oil and gas industry due to their remarkable effect and convenient operation which could be a proper way to control the CO₂ corrosion problem in Halfaya oil field.As for the serious CO₂ corrosion problem in oil field, the optimization and mechanism research on the efficient corrosion inhibitors were conducted by laboratory simulation, the corrosion environment of CO₂ containing reservoir layer were simulated. The static weight loss test and electrochemical method were adapted to preliminary screen and evaluate the inhibition performance of 13 of commercial corrosion inhibitor under atmospheric pressure; the autoclave were used to study the inhibition performance of optimum inhibitor in simulated formation water and oil/water mixed media under the condition of high temperature pressure in the static and dynamic state; finally the physical and chemical properties of the optimal corrosion inhibitors were tested. This study functions as theoretical basis for corrosion protection work in oil field. The result of this study list as follows:1. The result of static weight loss test shows that imidazoline inhibitor MHS-2?imidazoline quaternary ammonium salt inhibitor KY-5 and quaternary alkynoxymethyl amine IMC80-1 inhibitor exhibit ideal inhibition performance which could effectively inhibit the corrosion of L80-1 carbon steel in CO₂ saturated simulated formation water under atmospheric pressure. The polarization curve and EIS result indicate that MHS-2?KY-5 and IMC80-1 are anodic type inhibitor and function through negative catalytic effect, the electrochemical parameter and inhibit efficiency of MHS-2 and IMC80-1 exhibit extreme value at certain concentration,150ppm for MHS-2 and 100ppm for IMC80-1, KY-5 show no such phenomena, the inhibit efficiency of KY-5 inhibitor increases with the concentration rising2. Due to the ideal inhibition effect of KY-5 showed in simulated formation water under the condition of high temperature pressure in the static state, KY-5 inhibitor was choose as the optimum inhibitor. The weight loss test result obtained in static and dynamic state revealed that the inhibit efficiency rises with the concentration, decreased with temperature; the weight loss test result obtained under static conditions indicate KY-5 inhibitor can well meet the corrosion control requirements of L80-1 corrosion of carbon steel, the corrosion rate can be reduced to the following ministerial standards; But the weight loss test result obtained under dynamic conditions shows that the inhibition efficiency decline at the same concentration compared to static result, at a concentration of 300ppm, although inhibition efficiency remained above 90%, but the corrosion rate is still greater than standards, it is hard for KY-5 to fulfill anti-corrosion requirements of the L80-1 steel at the high temperature under the dynamic condition.3. The thermodynamic calculations result indicated that the adsorption of KY-5 inhibitor on L80-1 carbon steel surface accords with Langmuir adsorption isothermal equation in the static condition; the adsorption process are spontaneous and exothermic process which primarily belongs to chemical adsorption, rising the temperature may cause the desorption of KY-5 inhibitor,lead to the decreased of inhibit efficiency.4. Under oil/water multiphase flow conditions, The weight loss result shows that the inhibition efficiency of KY-5 increased with the increased of KY-5 dosages, but decreased with the increased of oil content, the dispersions ?emulsions? of oil droplets in water could reduce inhibitor performance. The reason why crude oil has negative effect on inhibition efficiency is that the inhibitor has strong affinity to cumulate on the oil/water interface, The oil/water interface may constitute a very large surface area which deplete a critical amount of inhibitor from the corrosion aqueous phase, furthermore the inhibitor are surface-active compounds, part of inhibitor will dissolve in the oil phase causing the concentration in aqueous phase decreased, both two causes will result in the decreased of inhibition efficiency and inhibit performance.5. The physical and chemical property test results show that KY-5 corrosion inhibitor has good water-soluble ability, no obvious tendency of emulsion, and has good compatibility with formation water, antifreeze agent, scale inhibitors, furthermore have KY-5 corrosion inhibitor show no obvious damage to the rubber tube use in the oil field well packer, but viscosity under low temperature is large, must be used in conjunction with the antifreeze agent.