Study On Treating ASP Produced Water Of Oilfield By Aeration/Settling Process

Oilfield produced water was the maximum amount wastewater resources that derivedfrom the oilfield produced fluid via dehydration process treatment. With the tertiary oilrecovery of ASP flooding in Daqing oilfield, the qualities of produced water were morecomplex which led to the difficulty for treating produced water, especially the suspendedsolid and particle diameter median. The suspended solid which exceeded the standardcontent of reinjection will block the formation pores and increase the pressure of reinjectionso that the oil recovery was decreased. Thus, under the different aeration time andtemperature, the concentration of suspended solid, oil, HPAM, surfactant, sulfide andsilicate colloid was investigated by the simulation aeration and settling experiment. Thecomponents and morphology of suspended solid were analyzed by SEM and EDS. Themajor factors that influenced the content change of suspended solid were also determined inthis study to improve the aeration and settling process.On the basis of the simulation experiment, the content of suspended solid was about500mg/L and3560mg/L, respectively, in the raw ASP produced water of Nanwu,217andLa291. Oil concentration was187mg/L and341mg/L, respectively, in produced water ofNanwu and217; La291was the maximum oil content of1331mg/L. Besides the ASPproduced water contained high concentration of polymer, surfactant and salinity and so onresulting the high viscosity that was4⁶times of water viscosity. By the analysis of SEMand EDS, the main morphology characteristics of suspended solid were particle shape,massive and acicular crystals. The suspended solid was mainly consisted of oil, HPAM,surfactant, and sulfide, carbonate scales, silicate colloid and iron precipitation.By the simulation experiment, the main influence factors that changed theconcentration of suspended solid in ASP produced water were the precipitation of HPAM;HPAM and surfactant combined with the Ca²⁺, Mg²⁺, Ba²⁺, Pb²⁺and so on through theelectrostatic adsorption and chemical bond effect forming the precipitation or colloid;Sulfide was oxided for S or the sulfide precipitation of high valence state; Under thealkaline condition, silicate was transformed the colloid state and the precipitation of ironand carbonate was formed; Silicate, phosphate and FeCl₂formed the precipitation by thechemical graft function. Meanwhile, the fluid destabilization and T and so on were the secondary factor. The experiment results showed that the suspended solid content was320mg/L,130mg/L and330mg/L, respectively, in effluent of Nanwu,217and La291; the oilcontent was16.11mg/L,47.12mg/L and about9.00mg/L, respectively; S^2-was notdetected by the treatment of aeration8h. The effluent satisfied the standard of the next stagetreatment process, therefore, the aeration settling time of8h was available. However theindependent settlement time and zone must be set in the aeration settling tank at the sametime the depositions of surface and settling zone of reactor must be timely removed.