Study On Development And Mechanism Of Barium And Strontium Sulfate Scale Inhibitor

China’s waterflood development oilfields are gradually entering the stage of high water cut,scaling phenomenon is becoming more and more serious,scaling has become one of the main factors restricting the efficient development of water flooding oilfields.Scaling will reduce the inner diameter of pipeline,reduce the utilization ratio of pipeline and increase the resistance of oil transportation.Scaling will also formation concentration batteries on the surface of metal pipelines,accelerating the corrosion of pipeline.Among many kinds of scales produced in oilfields,barium and strontium sulfate scale has the stability of physical structure and chemical properties,so it’s extremely difficult to get rid of it thoroughly by chemical means.Therefore,scale prevention is the main means to deal with barium sulfate/strontium scale.The commonly used scale prevention methods for barium sulfate/strontium scale at present is to use chelating agent with carboxyl or hydroxyl groups just like ethylene diamine tetra acetic acid（EDTA）and diethylene triamine penta acetic acid（DTPA）.Chelating agent chelate the scaling cations in solution and adsorption of physical and chemical properties of scale microcrystals by organic matter,obstructing the growth and attachment of scale nuclei to prevent the formation of scaling.This paper is based on the evaluation of barium sulfate scale prevention performance and three chelating agents with good scale inhibition performance were optimized:low molecular weight sodium polyacrylate,hydrolyzed polymaleic anhydride and aspartic acid.Compound them and evaluate the properties of the complex chelating agent.Aiming at the problem of poor temperature resistance of complex chelating agent,synthesize a thermostable chelating agent and the optimum proportion of synthetic monomers and initiator was determined by evaluating the anti-scaling performance.Structural characterization and performance evaluation of the products were carried out and get a new scale inhibitor by compound.On the basis of evaluation of scale prevention and scale dissolution performance of new scale prevention system,the surface microstructures of barium and strontium sulfate scale with different densities were observed by scanning electron microscopy and then analyze the cleaning and preventing mechanism of barium and strontium sulfate scale.Findings from the study,when the mass ratio of low molecular weight sodium polyacrylate,hydrolyzed polymaleic anhydride and aspartic acid is 2:2:3 can get the best Scale prevention performance.But when the temperature is higher than 70℃,the anti-scaling rate decreased significantly.It was found by experiment that the reason was the poor temperature resistance of low molecular weight sodium polyacrylate.For this preparation of new chelating agent by optimal ratio of reaction monomer is AA:MA:MAA:AMPS=30%:52.5%:5%:12.5%,the amount of initiator（NH₄）₂S₂O₈ is 1.5%of total mass reaction monomer.Replacing low molecular weight sodium polyacrylate with synthetic chelating agent and a new compound system with remarkable improvement in temperature resistance was obtained.At a high temperature of 90℃,the anti-scaling performance did not decrease significantly.When the temperature is 50℃,the concentration of chelating agent is 6%,the concentration of sodium chloride is 6%and the p H is 9,the cleaning efficiency of loose barium and strontium sulfate scale can reach nearly 40%.Although it has no obvious scale-dissolving effect on compact barium and strontium sulfate scale,but when combined with surfactant,the surface structure and properties of scale can be changed,which is beneficial to the subsequent treatment of dense scale.