Treatment Difficulties and Process Analysis for High-Polymer Oilfield Wastewater
In the mid-to-late stage of oilfield development, the widespread use of polymer flooding generates large volumes of high-polymer wastewater. This water is complex and hard to treat, and direct discharge or reinjection causes environmental pollution and formation damage. Analysing the treatment difficulties and optimising the process is therefore essential for sustainable oilfield development and environmental compliance. This article reviews the core difficulties in treating high-polymer wastewater and analyses the SINOKLE process.
1. Treatment difficulties for high-polymer oilfield wastewater
High-polymer wastewater contains polymers such as polyacrylamide (HPAM) at mass concentrations of several hundred to several thousand mg/L. Compared with conventional oilfield wastewater it is more viscous, forms stable emulsions and contains more complex pollutants, so treatment is a real challenge. The specific difficulties are as follows:
(1) High viscosity, low settling efficiency
The thickening effect of the polymer raises viscosity markedly, increasing the settling resistance of suspended particles and oil droplets and slowing separation. The viscous environment also hinders droplet collision and coalescence; droplets are small and evenly dispersed, so conventional settling performs far worse and cannot meet downstream or reinjection requirements.
(2) Stable emulsion, difficult oil-water separation
Polymer molecules are both hydrophilic and hydrophobic and act as emulsifiers under the mixing and shearing of production, forming stable oil-in-water (O/W) or water-in-oil (W/O) emulsions. Conventional demulsifiers struggle to break the interfacial film, separation is incomplete and large numbers of fine droplets remain, adding load to downstream treatment.
(3) Hard to remove suspended solids, easy to plug equipment
The water contains inorganic solids such as formation sand and clay along with organic solids such as polymer degradation products and resins or asphaltenes, which form stable flocs under polymer adsorption and wrapping that conventional filtration cannot remove. These fine solids deposit and adhere inside equipment, causing plugging and blocked lines, lowering system efficiency and raising maintenance costs; if reinjection exceeds limits they also plug formation pores and impair oil displacement.
(4) Poor chemical compatibility, high treatment cost
Conventional demulsifiers and flocculants are poorly matched to high-polymer water: the polymer competes for adsorption or reacts with the chemicals, lowering their effective concentration and requiring much larger doses, which raises cost. Dedicated high-performance chemicals are few and expensive, adding further cost pressure.
(5) Poor process compatibility, hard to meet standards
Conventional oil separation, flotation and filtration are not well suited, and no single process meets the standard. Combinations are needed, but the stages are poorly compatible and weak upstream performance easily overloads downstream units. Water quality also fluctuates widely, making process control difficult and stable compliance hard to achieve.
2. Process analysis for high-polymer oilfield wastewater
To address these difficulties, the proven SINOKLE dedicated process uses a stepped flow of preliminary oil removal, gel breaking and viscosity reduction, deep impurity removal and precise polishing. The process combines large-tank settling (free oil removal) + CDOF (ozone oxidation for gel breaking and viscosity reduction) + CDFU (cyclonic dissolved gas flotation for emulsified oil and impurities) + KFM filter (super-hydrophilic media for deep de-oiling). Each unit and its performance are described below.
(1) Core units of the SINOKLE process
1. Large-tank settling: primary free-oil removal unit
As the pretreatment front end, large-tank settling uses gravity to separate free oil and coarse suspended solids: free oil is skimmed off and coarse inorganic solids settle to the tank floor for periodic blowdown. The large volume and ample retention time prevent incomplete free-oil separation in viscous water, reducing free oil to below 50 mg/L and creating stable conditions for the downstream CDOF unit.
2. CDOF unit: core ozone oxidation unit for gel breaking and viscosity reduction
CDOF unit is the key to gel breaking and viscosity reduction. Ozone oxidation destroys the long-chain structure of polyacrylamide, degrading it into short-chain small molecules and lowering viscosity; it also breaks the oil-water interfacial film for preliminary demulsification, without secondary pollution. After treatment viscosity falls by more than 80% and polymer removal reaches 50-70%, preparing the water for downstream stages. The unit adapts well to quality swings and is efficient with controllable cost.
3. CDFU unit: cyclonic dissolved gas flotation for emulsified oil and impurities
CDFU cyclonic dissolved gas flotation separates by purely physical means with no chemicals such as demulsifier or flocculant. Under the surface tension of ultra-fine bubbles, free oil, floating oil, emulsified oil and suspended solids are captured, demulsified and separated quickly, with no extra scum and no secondary pollution. Shock resistance is strong and performance stable.
4. KFM filter: super-hydrophilic media unit for deep de-oiling
The KFM filter is the polishing terminal. Its super-hydrophilic media let water molecules pass quickly while repelling the oil phase, preventing oil film adhesion. Through coalescence, demulsification and efficient interception it captures oil droplets and solids below 1 micrometre. Compared with conventional filters it offers higher precision, better backwash regeneration, lower water consumption and longer cycles, fundamentally easing plugging.
(2) Overall advantages and field results of the SINOKLE process
The SINOKLE process has clear overall advantages: the stepped flow is logically arranged and the units complement each other for stable efficiency; it is highly targeted and solves each core difficulty precisely; it runs stably, tolerates quality swings and resists plugging with low maintenance; and performance is excellent with consistently compliant effluent.
3. Conclusion
The core difficulties of high-polymer wastewater treatment lie in high viscosity, stable emulsions and complex pollutants, which place strict demands on process fit and efficiency. The SINOKLE process provides an efficient solution for this water. Going forward, treatment technology must focus on dedicated chemicals, anti-fouling equipment and intelligent process control, cutting cost and raising efficiency through innovation so that wastewater can be reused as a resource, standards are met and oilfields develop sustainably.
