Research On Mechanism Of Viscosity Reduction And Degradation Of Polymers In Oilfield Produced Water

As the polymers for EOR, fractional hydrolyzed polyacrylamide (HPAM) was widely adopted in oil exploitation. The viscosity of aqueous solution was the important indicator of the polymer flooding. This paper investigated the factors which could affect viscosity of polymer.It has great meaning to take appropriate measures for stable or increasing viscosity of polymer effectively, improve the oil displacement efficiency and reduce the integrated cost of the field that research the influencing factors of viscosity of polymer.It is very important to analyze the composition of oilfield produced water before prepare it. Generally, the contents of anion and cation in water were determined by the volumetric method in oilfield, this paper studied several simple, rapid and accurate methods to measure the contents of anion and cation in produced water. The cations were determined in the oilfield produced water by the inductively coupled plasma optical emission spectrometry, and established a method of indirectly determination the S2- in the oilfield produced water by ICP-AES, at the same time, studied a method of determining the anion in the oilfield produced water by ion chromatography.According to the case that the produced water contained the residual polymer, researched a analysis method which determined the residual polymer in oilfield produced water by UV spectrophotometry. Polyacrylamide, as the polymer using in flooding, was the most commonly used in oilfield. It had been found in the experiment that polyacrylamide had the largest ultraviolet absorption peak at 200nm. In the range of 250 mg/L, absorbance and concentration showed a good linear relationship. the correlation coefficient (R2) was 0.9990. The average recovery was 98.0%～101.2%, relative standard deviation was less than 0.25%, so it could measure the polymer concentration in the oilfield produced water.This paper determined the absorbance of the functional groups of polyacrylamide by UV spectrophotometry from the view of the molecular point. From molecular structure point of view, spectral behaviors were studied, and explaining the reasons for the decline of its viscosity, provide a theoretical basis for researching the mechanism of viscosity reduction of polymer in produced water. By comparative analysis, a theoretical basis was provided for selecting polymer flooding, and researching and development the high performance polymer. This paper also analyze the polymer solution after ultrasonic and oxidated by HPLC, further confirmed the mechanism of viscosity reduction and degradation of polymer made by ultrasonic and oxidation. High salinity and sulfide content in oilfield produced water will have greater impact on viscosity of polymer. The paper studied the better method of sulfide reduction, compared the methods with pumping in air, adding H2O2 or ozone.The research results proved that removal level of sulfide mainly depended on the oxidation of the desulfurizing substance, the stronger oxidation of desulfurizing substance was, the better the effect of sulfide reduction was. Nanofiltration membrane is a new technique of molecular film separation technology, and it is one of the research focus in the world's field membrane separation.This paper applied the nanofiltration membrane technology combined with the activated carbon adsorption and ozone's oxidation and bactericidal to deal with the anions and cations in produced water, thus greatly reduced the salinity, it was of great significance to improve viscosity of polymer.