Synthesis Of High Temperature CO₂ Corrosion Inhibitor And Its Corrosion Inhibition Mechanism Investigations

With the development of domestic major oil fields into the later stage,the reserves of oil and gas resources have dramatically decreased during the past decades,and the recovery efficiency of major oilfields is still hard to maintain a high level.Faced with this complicated situation,engineers have implemented a series of production-increasing measures,such as water plugging technology,mixed gas huff and puff technology,fire-burning reservoir technology,and CO₂ flooding technology.The implementation of these new technologies will cause high-temperature CO₂ corrosion environments.At present,corrosion inhibitors can effectively inhibit corrosion under low-temperature(<60°C)CO₂ aggressive medium.However,when the temperature rises to 80°C or above,the inhibitive performance will degrade significantly.In the literature research process,it is found that there are few reports of corrosion inhibitors suitable for high-temperature CO₂ environments.Based on this background,research on corrosion inhibitors suitable for N80 steel under high-temperature CO₂ environments has been carried out.Initially,nine corrosion inhibitor molecules were synthesized,including imidazoline,schiff base,imidazoline amide,and thioureidoimidazoline,the molecule structures were determined by infrared spectroscopy and hydrogen nuclear magnetic resonance spectroscopy.Subsequently,preliminary evaluations of the synthesized inhibitors were conducted in 3%Na Cl solution saturated with CO₂ at 80°C.it showed three of them with high inhibition efficiency at 80?environments,the highest inhibitive efficiency can reach up to 94.64%.Afterwards,the above three inhibitors were further evaluated in 1 MPa CO₂ 3%Na Cl aggressive solutions at 120?in the autoclave,it revealed that the inhibitive performances of the three inhibitor molecules present downward trends with the increasing temperature.only(SMLN)inhibitor molecule has a corrosion inhibition efficiency of 86.75%,which is the selected high-performing inhibitor molecule.The synthesized imidazoline furoic acid amide(KMYX)and lauric imidazoline furoic acid amide(YMKX)are two isomers of each other,just the positions of functional groups in molecule are different,while the inhibitive performance changes greatly.Electrochemical measurements are applied to study the inhibitive mechanism differences of the two inhibitor molecules.It is found that KMYX serves as mixed-type corrosion inhibitor which inhibits the electrochemical cathode and anode processes,while YMKX acts as anode-type inhibitor and mainly inhibits the dissolution of metal in anode area.Quantum chemistry calculations were applied to analyze the parameters of these two molecules,it is found that the KMYX molecule has smaller energy gap and larger electron transfer numbers,which indicates that the composite formed by KMYX adsorption on metal surface is more stable and therefore better inhibitive performance.Molecular dynamics are conducted to simulate the equilibrium adsorption configuration of two inhibitor molecules on N80 surface.It revealed that the adsorption energy of KMYX is greater than that of YMKX,so the corrosion inhibition performance is better.The corrosion inhibition mechanism is investigated with the selected high-performing SMLN inhibitor molecule,initially the adsorption free energy of SMLN molecules on N80mild steel surface is calculated through corrosion thermodynamics,the results indicated that SMLN adsorbed on N80 steel by physicochemical adsorption process,and the adsorption confirms to Langmiur adsorption model.Afterwards,the self-designed high-temperature and pressure electrochemical measurement device was applied to study the inhibitive mechanism of SMLN molecules.The potentiodynamic polarization scanning measurements indicate that SMLN serves as mixed-type inhibitors,which can simultaneously inhibit the dissolution of the metal at anode and the reduction of the corrosive medium particles at cathode,the equilibrium adsorption configuration of SMLN molecules on N80 surface is simulated with molecule dynamics,the result reveals that the active adsorption sites in SMLN molecules are N and S atoms.At the same time,the diffusion coefficient of HCO₃^-,H₃O⁺,Cl^-corrosive media particles are calculated,the calculation depicts that the SMLN adsorption film can significantly reduce the diffusion coefficient of HCO₃^-and H₃O⁺,which hinders the mass transfer of the corrosive medium particles to metal surface,thus inhibiting the corrosion of metal.