A New Breakthrough in Oilfield Wastewater Treatment: Swirl Dissolved-Air Flotation Drives Green Development

I. Industry Background

China is the world's largest oil consumer and one of its largest producers, and oilfield development generates enormous volumes of wastewater. According to statistics, domestic oilfields produce more than 1 billion cubic metres of produced water each year, containing large amounts of petroleum pollutants, suspended solids and harmful substances. Discharged without effective treatment, it would not only cause serious environmental pollution but also waste a precious water resource.

As national environmental policy tightens, in 2024 China's coastal oilfields fully implemented marine discharge standards, requiring petroleum pollutants to be controlled below 5 mg/L. This places higher demands on oilfield wastewater treatment technology and has created an urgent industry need for efficient, low-cost and green treatment solutions.

II. Treatment Difficulties

Oilfield wastewater has the following notable characteristics:

• First, complex composition: besides petroleum substances it contains large amounts of suspended solids, dissolved salts and heavy metal ions.

• Second, a high degree of emulsification: after high-pressure water injection and pipeline transport, oil and water are fully emulsified into a stable water-in-oil or oil-in-water system that conventional separation methods struggle to remove completely.

• Third, large volume fluctuations: from a few hundred cubic metres per day to tens of thousands, placing high demands on equipment adaptability.

In addition, unconventional oilfield wastewater such as fracturing flowback fluid and drilling waste fluid is even harder to treat, often containing high concentrations of organics, bacteria and chemical additives that conventional processes simply cannot handle.

III. Shortcomings of Conventional Technology

For a long time domestic oilfield wastewater treatment has relied mainly on physical methods such as gravity separation, filtration and centrifugation, and on chemical methods such as demulsification and flocculation. These conventional technologies have clear weaknesses:

• Unstable treatment performance - conventional flotation equipment produces bubbles mostly above 50 microns in diameter, with limited ability to capture fine oil droplets, so effluent quality struggles to meet standards consistently;

• High chemical consumption - chemical methods need large amounts of flocculants, coagulant aids and demulsifiers, raising operating costs and bringing a risk of secondary pollution;

• Bulky equipment - conventional treatment systems occupy large areas and consume a lot of energy, limiting their use on space-constrained offshore platforms or remote oilfields;

• High maintenance costs - equipment clogs and scales easily and requires frequent shutdowns for repair, disrupting normal production.

IV. SINOKLE's New Process

Independently developed by SINOKLE, the CDFU (swirl dissolved-air flotation unit) adopts an innovative process combining swirl centrifugal separation with dissolved-air flotation, offering a brand-new solution for oilfield wastewater treatment.

The technology uses CFD-optimised flow-field design to combine perfectly the centrifugal force of swirl separation with the micro-bubble adsorption of dissolved-air flotation, achieving efficient oil-water separation. The bubbles it generates are only 5-30 microns in diameter - one tenth of conventional flotation - greatly improving the capture of fine oil droplets.

V. Technical Features and Advantages

• Purely physical deoiling with no chemicals - CDFU it relies entirely on physical principles for oil-water separation with no chemical dosing, eliminating secondary pollution at the source and aligning with green environmental principles;

• Micro-bubble technology for high separation efficiency - 5-30 micron ultra-fine bubbles penetrate the emulsified layer and capture fine oil droplets that conventional equipment cannot handle, greatly improving deoiling efficiency;

• Skid-mounted structure with a small footprint - the integrated skid design is compact and can save more than 60% of the land area compared with conventional systems, especially suited to space-constrained offshore platforms and remote oilfields;

• High automation and stable operation - the equipment uses PLC intelligent control and can automatically adjust parameters to influent quality, achieving continuous stable operation and reducing manual workload;

• Wide applicability - it not only handles conventional produced water but also performs well on difficult wastewater such as fracturing flowback fluid and drilling waste fluid.

VI. Application Case

In 2024, a large oilfield wastewater treatment project in an African country adopted SINOKLE's CDFU, CDOF and KFM filter combined process with a capacity of 200 cubic metres per hour. The influent was complex mixed wastewater comprising 4,000 m³/day of production wastewater from a gathering and transportation station, 1,750 m³/day of fracturing flowback fluid and 250 m³/day of drilling waste fluid.

Project results show that petroleum content in the treated water fell below 5 mg/L, fully meeting marine discharge standards and earning high recognition from the owner.

VII. Summary

Guided by the 'dual carbon' goals, green oilfield development has become an industry consensus. SINOKLE's CDFU swirl dissolved-air flotation unit, with its purely physical deoiling plus high efficiency, stability, energy saving and environmental protection, offers a reliable choice for oilfield wastewater treatment. In future SINOKLE will continue to deepen its work in oilfield environmental protection, using technological innovation to support the industry's sustainable development.