High-Polymer Produced Water: Characteristics, Impacts, and Challenges Faced by Traditional Treatment Processes
High-polymer oilfield produced water refers to production wastewater generated during oilfield development—especially after enhanced oil recovery measures such as polymer flooding—in which the produced fluid contains a high concentration of polymers. As waterflooded oilfields enter the medium- to high-water-cut stage, polymer flooding has been widely applied to effectively control water cut and improve oil recovery. Once oil wells begin producing water, polymers that are not fully consumed are produced together with the produced fluids, forming polymer-containing wastewater with unique properties. This type of wastewater contains not only crude oil and suspended solids, but also high concentrations of polymers (such as partially hydrolyzed polyacrylamide, HPAM).
Characteristics and Hazards of High Polymer Content Produced Water
Characteristics:
- High Polymer Content: The concentration of polymers in the produced water is much higher than that in wastewater generated from conventional water injection for enhanced oil recovery.
- Difficult Oil-Water Separation: The presence of polymers makes the oil-water separation process more challenging, which can lead to the wastage of crude oil and increased wastewater treatment costs.
- Severe Damage to Reservoirs: When high polymer wastewater is reinjected into the reservoir, it can easily clog the pore spaces in the oil layer, reducing its ability to absorb water and affecting oil production.
Hazards:
- Environmental Pollution: The discharge of high polymer wastewater can result in excessive levels of pollutants such as COD (Chemical Oxygen Demand) and BOD (Biochemical Oxygen Demand), causing environmental pollution.
- Economic Losses: The treatment of high polymer wastewater is difficult and costly, and the quality of treated water is generally poor, often failing to meet reinjection or discharge standards, leading to economic losses for oilfield companies.
Treatment Technologies and Challenges
A great deal of research has been conducted by scholars and engineers internationally on the treatment of high polymer content produced water in oilfields. Traditional treatment processes typically use combinations such as "inclined plate settling tank + walnut shell/fiber ball filtration" or "settling tank + centrifugal flotation + fiber ball/multi-media filtration + ceramic membranes." Although these methods are applicable within certain limits, they have obvious shortcomings: poor impact resistance, unstable water quality, complex processes, high operating costs, and reliance on chemicals, which can lead to secondary pollution and oily sludge. For reinjection water requirements in low- and medium-permeability reservoirs, traditional processes often struggle to consistently meet standards and are difficult to maintain, presenting numerous challenges.
Challenges:
- Difficult Polymer Degradation: The polymers in high polymer wastewater are difficult to degrade effectively, making it hard to meet water quality standards after treatment.
- Low Oil-Water Separation Efficiency: The presence of polymers reduces the efficiency of oil-water separation, making it difficult to achieve efficient and stable oil-water separation.
- High Treatment Costs: The treatment of high polymer wastewater requires advanced technologies and equipment, leading to high treatment costs.
