The Application, Effect and Mechanism of Polyacrylamide in Oilfield

Polyacrylamide (PAM) is a core polymer chemical agent in oilfield wastewater treatment and production development. It plays a key role in the treatment of polymer-containing produced water in the later stage of offshore oilfields, purification of petrochemical wastewater, wastewater reinjection and scale inhibition and corrosion prevention. It can efficiently solve the problems of high oil content, high emulsification, high viscosity and high salinity in oilfield wastewater treatment, and has dual values of water treatment and resource utilization.
In the treatment of polymer-containing produced water in the later stage of offshore oilfields, PAM, as a core component of demulsification and flocculation, is suitable for the short process, fast residence and compact process requirements of the platform. It is mainly used to treat the stable emulsion system produced by polymer flooding (HPAM). The HPAM content in this type of wastewater is 200-1000mg/L, the oil droplet size is only 2-5μm, and the viscosity is 5-20mPa・s. The separation efficiency of conventional processes decreases by 30% to 50%. After PAM's collaborative treatment, the oil content in the effluent is ≤30mg/L, the suspended solids are ≤10mg/L, the oil removal efficiency is 90% to 95%, the polymer retention rate is ≥90%, and can reach up to 95%, and the viscosity of the reinjected polymer increases by more than 30%, achieving the resource utilization of the polymer for reinjection.
In the pretreatment of petrochemical wastewater, cationic PAM performs best, with an optimal dosage of 15mg/L and pH=7.5. Combined with rapid stirring at 300r/min (2min) and slow stirring at 120r/min (15min), the turbidity removal rate is 95.2%, and the COD removal rate is 78.6%. Compared with the traditional aluminum sulfate method, the operating cost is reduced by 28.6%, and the sludge production is reduced by 35.7%, with the effluent stably meeting the standards.
In wastewater reinjection and scale inhibition and dispersion, the long-chain molecules of PAM can wrap the scale-forming particles, improve the stability of colloids, and inhibit the deposition of crystals such as calcium carbonate and barium sulfate. At the same time, combined with filtration, sterilization and anti-corrosion processes, the quality of reinjected water is guaranteed, and the risks of equipment corrosion and blockage are reduced.
The core mechanism of its action includes charge neutralization, adsorption bridging, interface regulation and reversible coalescence: cationic PAM neutralizes the negative charges of emulsified oil droplets and suspended particles, compresses the double electric layer to destabilize the colloid; long-chain molecules achieve adsorption bridging, promoting the flocculation and coagulation of fine oil droplets and suspended solids; through interface displacement, the stable interface film is disrupted, accelerating the liquid film drainage and oil-water phase separation; based on the "second minimum value" theory, reversible coalescence is achieved, protecting the HPAM molecular chain from breaking, and realizing the retention and reuse of the polymer.
In application, key parameters need to be controlled: the dosage is preferably 15mg/L, the pH is suitable for 6.5-8.5, and direct mixing with anionic scale inhibitors should be avoided to prevent the failure of charge neutralization. Synergy with processes such as cyclone, air flotation and high-frequency coalescence can maximize treatment efficiency, overall improving treatment capacity by 30% and reducing operating costs by 20% to 30%.
The mechanism of demulsifier (PAM):
The demulsification of oilfield polymer-containing wastewater is a complex physical and chemical process. The core mechanisms include interface displacement, phase inversion, liquid film drainage, membrane rupture and flocculation coagulation. PAM-type demulsifiers rapidly adsorb and displace the original stable interface film, forming a low-strength new interface layer, promoting the coalescence of oil droplets; it can induce phase inversion for rapid separation, while compressing the double electric layer and weakening electrostatic repulsion, accelerating the drainage and rupture of the liquid film. For O/W type polymer-containing emulsions, PAM first achieves reversible coalescence of oil droplets through charge neutralization and adsorption bridging, and then completes irreversible coalescence through capture, ultimately achieving efficient oil-water separation, and can reduce the degradation of polymers, achieving the synergy of polymer retention and oil removal.