Solving Produced Water Purification in High Water-Cut Oilfields: SINOKLE's Efficient Solution
Keywords: oily wastewater purification solution | oilfield produced water treatment technology | oilfield wastewater treatment process | oilfield wastewater treatment system | oilfield reinjection water treatment technology
Many domestic oilfields have entered the middle and late stages of production, the high water-cut stage. To maintain stable crude output and accelerate new reservoir development, tertiary recovery technologies such as polymer flooding and alkali-surfactant-polymer (ASP) flooding have been vigorously promoted and are now widely used in major oilfields including Daqing, Shengli, Yumen and Dagang. The spread of these technologies markedly raises polymer concentration in produced fluids, increasing liquid viscosity and making emulsified oil more stable. Conventional processes can no longer ensure that purified water meets reinjection standards, so produced water treatment has become a key constraint on the development of oilfield surface engineering.
For a produced water purification project at an oilfield in Daqing, SINOKLE analysed the characteristics of the produced water in depth and innovatively applied the latest CDFU (cyclonic dissolved gas flotation) technology and equipment, successfully achieving efficient separation of the oil phase, water phase and suspended solids in this oily wastewater.
(Produced water treatment unit at an oilfield in North China)
The technology offers the following outstanding advantages:
1) CDFU Treatment uses purely physical methods to remove free oil and scum from wastewater, with a demulsification effect; oil-water separation efficiency is high and performance stable, and is not destabilized by changes in wastewater or slop oil quality.
2) The entire treatment unit is mainly static equipment, with a high degree of automation, low maintenance, long inspection intervals and good reliability.
3) No chemical agents are added, so no additional scum or oily sludge is generated, there is no secondary pollution, and operating and secondary treatment costs are low.
4) Small equipment footprint, skid-mounted design, short manufacturing cycle and fast commissioning.
5) Strong shock resistance and stable treatment performance. Judging from the operation of units we have already commissioned, produced water treatment equipment performs well with thorough oil-water separation; the effluent is clear and bright with no impurities.
6) Fully enclosed pressurized operation with no escape of waste gas or odour — environmentally friendly.
7) High degree of automation and intelligence, enabling IoT remote control and saving labour.
Schematic of the oilfield produced water treatment process
Produced water is lifted by the feed pump into the CDFU unit. Under strong cyclonic action, free oil, dispersed oil, emulsified oil and suspended solids in the water rapidly contact and adhere to the micro/nano bubbles generated by the dissolved gas system. Physical effects such as the surface tension of the micro/nano bubbles rupture the emulsified oil film, achieving purely physical demulsification, while oil on the surface of suspended solids is also adsorbed by the bubbles. The demulsified and adsorbed oil, suspended solids and microbubbles form a multiphase mixture that gathers in the CDFU core zone and floats to the top of the vessel, entering the built-in oil collection chamber and being drawn off through the oil outlet under its own pressure. The purified effluent that meets standards is delivered by the effluent pump to downstream process units. The separated slop oil is discharged by static pressure into the slop tank. In addition, the CDFU off-gas generated is routed to a dedicated waste gas treatment system. Effluent, oil discharge, sludge discharge, gas discharge and gas supply across the whole system are fully automatically controlled, and the dissolved gas intake and surge tank venting are also automatically regulated.
Comparison of influent and effluent treatment performance
The project has a design capacity of 180 m³/h. Influent specifications are oil content ≤150 mg/L and suspended solids ≤300 mg/L. After treatment by a single-stage CDFU (cyclonic dissolved gas flotation) unit, both oil and suspended solids are reduced to below 20 mg/L, fully meeting the customer's design targets. The system has a compact layout occupying less than 30 m², and requires no chemical agents during operation — only a small amount of electricity and nitrogen. By calculation, the treatment cost per tonne of water can be as low as 0.2 yuan, making operating expenses highly competitive and demonstrating excellent environmental and economic benefits.
