Study On Barium Sulfate Scale And Scale Inhibitor In Oilfield Water

The balance among phases in the reservoir stratum has been seriously destroyed by water flooding in oil field. The reason is scale formation resulting from chemical incompatibility and thermodynamic instability of water. Barium sulfate has the feature including small solubility, compact structure and large hardness. Once it deposits, it is difficult to be removed. It is significant to investigate the effects on barium sulfate scale and synthesize a kind of environment-friendly copolymer for water flooding in oil field.The effects of temperature, salt content and scaling ion concentrations on barium sulfate scale were obtained by using the titration method and conductivity method in this work. The kinetic parameters of barium sulfate scale, rate constant and activation energy, were calculated by the conductivity method. Polyepoxysuccinic acid was designed as scale inhibitor for barium sulfate scale. In the polymerization experiment, maleic anhydride, sodium tungstate and calcium hydroxide were used as raw material, catalyst and initiator respectively. Three factors, reaction time, pH of cyclization and polymerization initiator amount, were considered to investigate the synthetic process of polyepoxysuccinic acid.The titration method and conductivity method were also used to obtain the effects of temperature, salt content and scaling ion concentrations on scale inhibition performance of scale inhibitor. The rate constant after adding scale inhibitor was calculated by the conductivity method. SEM and XRD were used to analyze barium sulfate wheather adding scale inhibitor or not. The methods of weight loss, SEM, EDS and potentiodynamic polarization curve were used to evaluate the corrosion resistance performance of scale inhibitor and its complexation.The results of scaling obtained by titration method and conductivity method are as follows. The amount of barium sulfate scale decreases with the increasing temperature and increasing salt content, but it increases with the increasing scaling ionic concentration. It is known from the kinetic parameters that the rate constants of crystal nucleation and grain growth increase with the increasing degree of supersaturation of the solution. The rate constant of crystal nucleation is much larger than that of the grain growth. Crystal nucleation is greatly influenced by temperature, but the grain growth is less affected by temperature. Further more, crystal nucleation needs less activation energy than grain growth at the same supersaturation. The activation energy of crystal nucleation decreases with the increasing degree of supersaturation of the solution. But the activation energy of grain growth has little difference.The best synthetic conditions of PESA are polymerization time of180min, cyclization pH of9and polymerization initiator amount of0.7mg. The results of scale inhibition effect obtained by titration method and conductivity method are introduced here. The inhibition efficiency reaches to100%when the adding scale inhibitor is10mg/L. When the temperature of the solution is70°C, the inhibition efficiency is the highest one. And salt content can contribute to scale inhibition. The inhibition efficiency decreases with the increasing scaling ion concentration. It is known from the kinetic parameters that the induction period time has been prolonged by adding scale inhibitor. And the rate constants of crystal nucleation and grain growth decrease multiply when adding scale inhibitor. That indicates PESA can prevent the formation of barium sulfate scale effectively. Scale inhibitor can prolong the time of scaling. It has great inhibitory effect to crystal nucleation, but has little influence on grain growth. The microstructure and crystalline state of scale after adding scale inhibitor are different from the not adding case. Scale inhibition mechanism of polyepoxysuccinic acid is a complex role of small dose effect, electric charge dispersion, chelation solubilization mechanism and electrostatic repulsive force effect.The scale inhibition efficiency is more than90%in the oilfield water with high concentration of barium ions (much higher than the solution in standard). The results of corrosion experiment were obtained in formation water of Qigequan oilfield. Corrosion inhibition performance of PESA is poor, but the complexation of scale inhibitor and imidazoline corrosion inhibitor has good corrosion inhibition effect. And it has less impact on the scale inhibition performance. So the complexation has good inhibition performance to scale and corrosion at the same time.