Offshore Gas Fields Have No Fresh Water to Dose With: Rethinking Highly Emulsified Produced Water
Offshore gas fields treat produced water under constraints that have no onshore equivalent. The wastewater quality is harsher, there is no native fresh water at all, operations and maintenance are thinly staffed, getting materials to the platform is slow and expensive, and the effluent standard keeps tightening. Stack those five conditions together and most conventional flowsheets stop being workable.
The produced water itself is difficult in a specific way: very high oil content and extremely stable emulsification. Conventional demulsification is incomplete, oil removal is poor, and the system has little tolerance for a bad day. On top of that, offshore permits increasingly demand ultra-deep desulphurisation alongside oil, which raises the bar on purification precision and on stability under fluctuating feed.
The constraint that actually decides the process
Water scarcity is the binding bottleneck, and it is easy to underestimate. A platform has no municipal supply and no groundwater. Everything it uses comes from rainwater and from recycling its own produced water. In the dry season, with no effective rainfall and no external replenishment, production depends entirely on produced-water self-circulation.
Now look at what a chemical dosing process needs. Demulsifier, PAC, PAM, acid and alkali regulators and a dedicated deep-desulphurisation agent all have to be dissolved, diluted and made up in clean water. The dosing system is therefore competing with the process for the same scarce water, and in the dry season it simply stops. When it stops, the water treatment system trips, and the field is exposed to shutdown, exceedance and production interruption. A process that cannot run through a dry season is not a process for an offshore field.
What the traditional multi-stage train gets wrong offshore
Chemical demulsification, coagulation and flocculation, agent desulphurisation and multi-stage sedimentation and filtration were designed on the assumption of abundant land-based fresh water. Offshore, that assumption breaks in five separate places.
- Water balance: continuous dosing consumes make-up water the platform does not have, so the train is inoperable for part of the year.
- Logistics: many agent types, high consumption rates and long supply chains mean large stocks must be held in limited, humidity-prone storage, and manual make-up and pH adjustment fall to a small crew.
- Sludge: the composite floc-oil sludge is viscous, heavily emulsified and hard to dewater. Even with heated demulsification and screw drying, machines block, dewatering is unstable and moisture content misses specification — and every tonne has to be shipped ashore.
- Purification depth: chemical desulphurisation cannot reliably reach ultra-deep limits. Small feed swings push oil and sulphide over, while open multi-stage tanks let oil, gas and hydrogen sulphide escape, corroding equipment and creating real safety exposure.
- Cost: agent purchase, scarce rainwater, sea freight and storage, high-frequency maintenance and sludge disposal all stack up.
The alternative: four stages, no make-up water
SINOKLE configures a CDFU cyclonic dissolved-air flotation + SiC cyclonic precision filter + KHC coalescing oil remover + CDOF ozone oxidation flotation train for this duty. All four are proprietary units and the whole concept is built on pure physical separation plus advanced oxidation, with dosing removed from the main process.
The first gain is the one that matters most: no coagulant, flocculant, demulsifier or desulphurisation agent is dosed in the core treatment units, so no rainwater or fresh water is consumed making them up. Only the terminal sludge section uses a trace of agent, and no large volume of make-up water. The system runs on produced-water closed-loop circulation, keeps running through a dry season, and removes shutdown risk at the root.
The second gain is separation performance. The SINOKLE CDFU+SIC+KHC+CDOF arrangement works as a gradient. Cyclonic dissolved-air flotation uses nitrogen-enclosed flotation and combines cyclonic separation with micro-bubbles to remove floating oil, large emulsified droplets and suspended solids, completing most of the demulsification up front while stripping part of the sulphides. The SiC cyclonic precision filter then intercepts fine suspended impurities and residual colloids, protecting the downstream units. The KHC coalescing oil remover coalesces and demulsifies the stubborn fine emulsified fraction for deep oil removal. Finally the CDOF ozone oxidation flotation unit combines ozone advanced catalytic oxidation with cyclonic flotation to reach ultra-deep desulphurisation with no desulphurisation agent at all.
Because no chemical reactions generate excess solids, the only sludge is native oil sludge from the system itself. With proprietary heated demulsification and screw drying, moisture content is controlled to specification and total sludge volume falls by more than 90% against the traditional route — which is the number that changes the logistics picture.
Built for the platform, not the mainland
Every core unit is an enclosed skid with an intensive layout, so the footprint is roughly a third of a conventional train. Nitrogen blanketing on the flotation stage isolates oxygen, which helps against the high salt fog and humidity that eat offshore equipment, and all waste gas is collected and centrally purified, so no oil, gas or hydrogen sulphide leaks into the working environment. Automation covers the full sequence, so the small crew is not making up chemicals, trimming pH or clearing blockages. Construction is expensive once and cheap afterwards: with agent purchase, fresh-water make-up, sea freight, high-frequency maintenance and bulk sludge disposal all removed, the investment difference is recovered in roughly three to five years.
What the field gets
The outcome is a system that needs no external fresh water and no bulk chemical store, runs on produced-water recirculation, and holds both oil and sulphide at ultra-deep limits through four-stage gradient purification, with sludge, waste oil and waste gas each disposed of in a closed loop. For offshore gas fields, that combination — zero make-up water, zero main-process chemicals, low sludge, low O&M, high compliance stability and high intrinsic safety — is what makes long-term production possible rather than merely permitted.