Produced Water Treatment

Free, Dispersed, and Emulsified Oil

Produced water is the water coproduced with oil and gas from a reservoir. It carries free oil, dispersed oil, and emulsified oil together with suspended solids and dissolved salts. The treatment train must address each of those fractions because they cannot be removed by a single technology.

Free oil, droplets above about 150 microns, separates by gravity. Dispersed oil, droplets between 10 and 150 microns, separates by coalescence. Emulsified oil, droplets below 10 microns, holds in the water phase by interfacial chemistry and requires chemical or adsorption treatment to release. SorbiTech sizes and delivers the staged train end to end.

The Staged Treatment Train

Treatment is built in stages matched to the oil fractions in the inlet and to the contractual outlet limit. Gravity separation takes out the bulk free oil and the settleable solids. Coalescing polishing merges and removes the dispersed oil down to single digit ppm. Flotation or adsorption polishes the emulsified residual where the limit requires it.

A typical onshore field with a reinjection limit of 20 ppm uses a CPI followed by a coalescing skid; a sensitive offshore overboard discharge tightens the limit and adds nutshell filtration or a hydrocyclone ahead of the CPI.

Stage by Stage Selection

• CPI oil water separator for bulk free oil and settleable solids, outlet below 10 ppm
• Coalescing filtration skid to polish dispersed oil to single digit ppm
• Induced gas flotation or dissolved gas flotation for emulsified residual
• SorbiTech activated carbon polishing where the discharge limit applies to dissolved hydrocarbons
• Solids handling and sludge dewatering matched to the disposal route

Setting the Discharge or Reinjection Target

The treatment train is sized backwards from the contracted limit. Reinjection commonly requires oil in water below 20 ppm together with tight solids control, typically below 10 ppm of suspended solids and a maximum particle size of 5 to 10 microns, to protect the formation. Overboard discharge limits vary by jurisdiction; the OSPAR limit is 30 ppm monthly average, while several national consents apply 15 to 20 ppm.

Confirming the limit before sizing is essential. A train sized for 30 ppm discharge that later faces a 20 ppm consent requires an additional polishing stage that is far cheaper to install during initial construction than as a retrofit.

Offshore Versus Onshore Constraints

Offshore platforms and FPSO vessels enforce three additional constraints beyond the onshore design. Footprint is tight, so the staged train is built upward in multiple decks rather than spread out across a single elevation. Weight is regulated, so the materials of construction shift toward stainless steel and aluminium. Motion induces a constant low frequency vibration that fatigues the internals over time, so SorbiTech replaces flanged connections with welded connections wherever maintenance access allows.

Onshore fields have looser space and weight envelopes but stricter discharge limits and groundwater protection requirements. The treatment train sequence is unchanged but the materials, the redundancy, and the disposal route differ across the two contexts.

Sludge Management and Solids Disposal

A produced water plant generates two solid waste streams. The CPI sludge hopper holds settleable solids together with absorbed hydrocarbons; the coalescer change out releases spent elements with residual oil. Both streams are classified as oily waste under most regulatory regimes and require either thermal treatment, secure landfill, or licensed off site disposal.

Sludge volume is reduced by 70 to 90 percent through a thickener or a plate and frame press before disposal, and the dewatered cake is moved to the disposal route with reduced transport cost.

Single Accountability Delivery

SorbiTech confirms the inlet quality, the contracted limit, and the disposal route, sizes the staged train, and delivers it as one engineered package. The vessels carry the engineered media, SorbiTech handles the EPC for the full project scope, and one performance guarantee covers the complete duty. Rental polishing skids are available for turnarounds and commissioning campaigns. The staged train uses the SorbiTech CPI separator for free oil, the coalescing skid for dispersed oil, and activated carbon for dissolved residual; see the oil & gas sector.