Study On The Influence Of Polymer And Surfactant-polymer Flooding Displacement Agent For Suspended Solids And Emulsified Oil

With the large-scale development of tertiary oil recovery in various oil fields,polymer flooding and dual flooding technology are widely used,and it is considered to be a more effective technology for increasing production.The oil-dispersing agents such as polymers and surfactants makes it difficult to handle the produced fluid.In this paper,the single-agent screening,compounding,and quantity optimization of the different types of flocculants were studied using the on-site production fluids from the joint station.The effects of pH,flocculation temperature,settling time,and other parameters on the flocculation efficiency were studied.Through the analysis of the quality of water produced on site,polymer flooding and binary flooding simulation production fluids were prepared.The viscosity,emulsified oil and suspended solids content,interfacial tension,interface strength,oil droplet size,and flocculation efficiency were studied.The effects of HPAM and DWS on the stability of polymer flooding and binary flooding simulated production fluids were analyzed.The experimental results show that:The flocculation efficiency of PAC and CPAM is optimal.Oily wastewater was treated by compound flocculants composed of PAC and CPAM,the removal rate of emulsified oil and suspended solid reachs 88.06%and 92.13%.PAC is used as inorganic polymer flocculant,its molecular formula is[Al₂?OH?_nCl_6-n]_m.These complexes have a large net structure and can sweep flocs in the flocculation process.Additionally,PAC can form positively charged complex compounds through hydrolysation,which diffuses to the interface and are characteristically absorbed onto the double layer at the oil-water interface.These adsorbed complex compounds can neutralize some of negative charges on the oil-water interface.CPAM is a cationic flocculant that can neutralize negative charge of oil drops and lower zeta potential and electric double-layer thickness,reducing the repulsion between the oil drops and destroying their stability.The effects of polymer molecular weight on flocculation are best described in terms of bridging and electrostatic patch character mechanisms,which help the resulting flocs to become larger,allow their aggregation with each other.With the combined use of PAC and CPAM,more positive charges are integrated into the floc hydroxide,which is capable of electrostatic adhesion.The oil removal efficiency of demulsifier?SP169?is good but not stable;With the increase of the concentration of HPAM and DWS,viscosity is increased.The molecular weight increasing,the extent of viscosity is increased.DWS have a marginal effect on viscosity;With the increase of the concentration of HPAM and DWS,the content of emulsified oil and suspended solids is increased.When the molecular weight of HPAM is 7×10⁶,with the concentration of HPAM increases from 0mg/L to 1000mg/L,the content of emulsified oil and suspended solids increases 54.7mg/L and 38.9mg/L,respectively.The molecular weight of HPAM have a marginal effect on the content of emulsified oil and suspended solids.The content of emulsified oil and suspended solids is increased compared with polymer flooding produced liquid.When the concentration of DWS is 300mg/L,with the concentration of HPAM increases from 0mg/L to 1000mg/L,the content of emulsified oil and suspended solids increases 121.5mg/L and 49.4mg/L,respectively.When the concentration of HPAM is500mg/L,with the concentration of DWS increases from 0mg/L to 300mg/L,the content of emulsified oil increases 129.5mg/L.DWS have a huge effect on the content of emulsified oil;With the concentration of HPAM increases from 0mg/L to 500mg/L,interfacial tension only decreases 2.187mN/m.The molecular weight and concentration of HPAM have a marginal effect on interfacial tension.When the concentration of HPAM is 500mg/L,with the concentration of DWS increases from 0mg/L to 300mg/L,interfacial tension decreases8.310mN/m.DWS have a huge effect on the interfacial tension;With the concentration of HPAM increases from 100mg/L to 1000mg/L,the time of film rupture overall increases from6s to 25s.With the increase of the concentration of HPAM and DWS,interfacial strength is increased.The molecular weight of HPAM and DWS have a marginal effect on interfacial tension;With the concentration of HPAM increases from 0mg/L to 500mg/L,the oil droplet size decreases 34.4?m,with the concentration of HPAM increases from 500mg/L to1000mg/L,the oil droplet size only decreases 9.7?m.With the increase of the concentration of HPAM,the oil droplet size of polymer flooding produced liquid is decreased.The concentration increasing,the effect for oil droplet size is decreased.With the increase of the molecular weight of HPAM,the oil droplet size of polymer flooding produced liquid is slightly decreased.When the concentration of DWS is 30mg/L,with the concentration of HPAM increases from 0mg/L to 500mg/L,oil droplet size decreases 10.0?m.The oil droplet size of surfactant-polymer flooding produced liquid is dramatically decreased compared with polymer flooding produced liquid.The molecular weight and concentration of HPAM have a marginal effect on the oil droplet size of surfactant-polymer flooding produced liquid,but the effect of DWS is huge.When the concentration of HPAM is 500mg/L,with the concentration of DWS increases from 0mg/L to 300mg/L,the oil droplet size decreases 25.2?m;With the concentration of HPAM increases from 0mg/L to 1000mg/L,the removal rate of emulsified oil and suspended solids decreases 25.5%and 50.04%,respectively.With the increase of the concentration of HPAM and DWS,flocculation effect become poor.The molecular weight of HPAM have a marginal effect on flocculation.When the concentration of HPAM is 500mg/L,with the concentration of DWS increases from 0mg/L to 300mg/L,the removal rate of emulsified oil and suspended solids decreases 30.08%and 2.15%,respectively.The difficulty of surfactant-polymer flooding produced liquid treatment is dramatically increased.DWS have a huge effect on the removal rate of emulsified oil;The optimum conditions in coagulation process:pH,flocculation temperature,and settling time is 8,45?and 60min,respectively.According to the flocculation test,the influence factors on the flocculation efficiency are:displacement agent,pH,flocculation temperature,settling time.The influence mechanism of polymer and surfactant mainly includes:firstly,the zeta potential of the system increases by the negative charge carried by the polymer;second,the polymer and surfactant increase the viscosity of the produced fluid and increase the strength of the interfacial film;Third,the polymer and surfactant are adsorbed at the oil-water interface,so that the interfacial strength increases,the interfacial tension decreases,and the system is more stable.The coexistence of the two oil-dispersing agents has a synergistic effect and makes the system more stable.