Three-Low Reservoirs and Polymer Flooding Are Reshaping Produced Water: Where CDFU Fits

The World Energy Outlook 2023 puts numbers on the energy transition: overall oil demand from the road transport sector is expected to fall by more than 50% by 2050, and the share of renewable energy is expected to rise from 55% in 2021 to about 70% in 2050. Yet over the next decade or so, global oil consumption will remain broadly stable, and oil will continue to play a key role in the global energy system. The wastewater that comes out of the ground with that oil is not going away either — it is getting harder to treat.

China's weight in the equation

China is the world's largest energy consumer and a major driving force of demand growth, currently in a phase of economic structural transition. The country accounts for about 26% of global total energy consumption and 35% of net global energy consumption growth. Safeguarding energy supply security and improving the national energy layout therefore still require China to keep advancing oil exploration and development over the next decade — and every barrel produced brings produced water with it, at rising water cuts.

The water is getting harder to treat

As domestic oil extraction continues to deepen, more and more "three-low" reservoirs — low output, low permeability, low abundance — are gradually brought into development, and tertiary oil recovery processes such as polymer flooding are widely used. The result is a marked change in the water quality characteristics of oilfield produced water: higher viscosity, intensified emulsification and finer suspended solids, with the overall water quality becoming more complex.

If treated produced water is reinjected into the formation without meeting standards, it may cause pore plugging in the reservoir. That not only increases the difficulty of subsequent water injection operations but also reduces crude oil recovery efficiency. Effective purification of produced water has therefore become a key challenge constraining the sustainable development of the industry throughout the oil production process.

Why one process is no longer enough

Conventional treatment methods cover gravity settling, air flotation, centrifugal separation, filtration and coalescence, while more advanced technologies include ultrafiltration, activated carbon adsorption and biological treatment. Faced with increasingly complex water quality conditions, a single treatment process can hardly meet actual needs any more, and an integrated treatment model in which multiple technologies work together has become an inevitable direction of development. The practical question is no longer which unit process to pick, but which combination can be packed into a footprint and an operating budget that a production site can actually live with.

Compact flotation steps forward

Over the past decades, many research institutions and enterprises around the world have carried out continuous R&D on compact produced water treatment technologies under the concept of "high-efficiency unit technologies and integrated process combinations". Among the outcomes, compact flotation unit (CFU) technology has attracted wide attention — and for good reason: it packs the separation work of large open vessels into pressurised, compact hardware that suits offshore platforms and crowded onshore sites alike.

Inside the CDFU

SINOKLE has successfully combined ultra-fine bubble generation technology, dissolved gas flotation technology, coalescence technology and integrated flotation-cyclone treatment technology to develop a new generation of oil production wastewater treatment equipment: the CDFU (Cyclonic Dissolved Gas Flotation Unit). Targeting the characteristics of fluid mass transfer and heat transfer processes, it uses CFD numerical simulation of fluid mechanics, thermodynamics, heat transfer and mass transfer, and applies physical-chemical equilibrium or conservation equations that describe the limiting performance of the process. That simulation-driven approach achieves a precise description of process design, structural optimisation, engineering scale-up and flow control — the difference between sizing a unit by rule of thumb and sizing it by physics.

What it delivers

The CDFU integrates multiple technologies into one unit, achieves an oil removal rate above 90% and SS removal above 85%, operates under pressure in a closed system, and is safe, environmentally friendly, skid-mounted, automated and digitalised. No open tanks, no fugitive vapours, no sprawling footprint — the treated water leaves a single pressurised vessel ready for the next stage of the train.

Application has already spread beyond oilfield produced water treatment into pressure flowback water, landfill leachate, oily firefighting wastewater, medical wastewater and many other fields. For operators staring down harder water and tighter reinjection standards, a compact pressurised unit that removes most of the oil and solids in one pass is less a novelty than a necessity.

The pattern to take away is the order of operations. The energy outlook may push oil demand down over decades, but the near-term reality is stable output from harder reservoirs, which means water handling capacity becomes as strategic as production capacity itself. Equipment that concentrates several functions into one pressurised vessel — bubbles, flotation, coalescence and cyclonic separation in the CDFU's case — shortens the train, shrinks the plot plan and removes the open-tank failure modes that older produced water systems spent decades fighting.