Technical Challenges and Process Innovation in Oilfield Produced Water Treatment

Oilfield produced water is a highly complex wastewater generated during crude oil extraction, characterized by high oil content (up to 5,000 mg/L), severe emulsification and a wide particle size distribution of suspended solids, and it often contains polymers, heavy metals and other refractory substances. Conventional treatment faces three core bottlenecks:
Low efficiency: relying on gravity settling and walnut shell filtration, oil removal is only 60%-80%, effluent oil is hard to keep below 10 ppm, and emulsified oil (0.1~10 μm) is almost untouched;
Secondary pollution: demulsifiers and flocculants are required, producing hazardous oily sludge and higher disposal costs;
Poor adaptability: weak tolerance to water quality fluctuations — at one oilfield in Xinjiang, high polymer content caused frequent clogging of the conventional flotation system and soaring maintenance costs.
SINOKLE's CDFU +KFM combined process overcomes these limits through purely physical separation plus precision filtration:
Stage 1 CDFU: a cyclonic dissolved gas flotation unit that uses 5~30 μm micro-bubbles to rapidly separate free and emulsified oil (single-stage removal >90%, minimum removable particle size ≤2 μm), with retention time <5 minutes and a footprint only 10% of conventional flotation.
Stage 2 KFM filter: silicate-based active filter media adsorbs residual oil and suspended solids, giving effluent oil ≤6 ppm, suspended solids ≤2 ppm, a median particle size ≤1.5 μm and a backwash cycle of 8~12 hours.

 Figure: CDFU +KFM three-stage treatment flow, with effluent schemes tailored to different permeability formations

2. Comparison of Technical Advantages

3. Application Cases
PetroChina Changqing Oilfield: capacity 350 m³/d; the CDFU +KFM combination delivered effluent oil ≤10 ppm and suspended solids ≤5 ppm, with annual benefits from recovered crude oil exceeding CNY 3 million.
Xinjiang Oilfield fracturing flowback: two-stage CDFU +KFM treats high-oil wastewater (≤2,000 ppm), meeting reinjection standards (oil ≤5 ppm) at an operating cost of CNY 0.3 per ton.

4. Economic Analysis
Payback period: <2 years (based on a CNOOC project with an annual operating cost of CNY 580,000 and crude oil recovery revenue of CNY 3.02 million).
O&M cost: CNY 0.2~0.3 per ton of water, 80% lower than conventional processes (≥CNY 1.5 per ton).
Through physical separation plus precision filtration, this process achieves efficient purification and resource recovery of oilfield produced water, and is especially suitable for offshore platforms and reinjection in high-permeability formations.