An operator required a produced water treatment solution because oil was being discharged into the sea. SLB developed a tailored chemistry that increased the operating envelope of the process equipment and consistently reduced total petroleum hydrocarbons (TPH) and total suspended solids (TSS) by more than 95%, bringing the discharge back within governmental regulations.

A water treatment plant processing condensate and water from offshore fields was designed for 54,000 bbl/d of water, with a maximum 4,000-ppm TPH and 160-ppm TSS. The feed fluctuated significantly between 0 and 25,000 bbl/d of water and contained more than 10,000 ppm of TPH and as much as 1,800 ppm of TSS.

The specification for discharge to the sea was 40-ppm TPH and 150-ppm TSS. After learning that off-specification water discharge with an average TPH of 20,000 ppm and TSS of 1,500 ppm was occurring, SLB comprehensively assessed the design of the produced water treatment equipment. The deficiencies were addressed, which yielded only a small improvement in performance.

After studying the fluid rheology, SLB found that the entrained dispersed solids had an average diameter of <2 um and were oil-wet and neutrally buoyant, which created a stable oil in water (OIW) emulsion. Conventional coagulants and flocculants were tested, but they did not yield the required outcome because the hydrocarbons, solids, and water agglomerated into a tight emulsion. To resolve the issue and bring the discharge back within specification, SLB developed a novel chemical approach.

In the laboratory, SLB formulated a novel weighted polymeric surfactant to alter the wettability of the dispersed solids, which would destabilize the OIW emulsion. The surfactant would also accelerate the settleability of the fine solids during the coagulation phase. A coagulant was added to agglomerate the dispersed solids, while a flocculant was added to strengthen the bonds of the agglomerated solids for subsequent processing in the solids management system.  

When the developed chemistry solution was deployed at the plant, it consistently reduced TPH and TSS by more than 95%. The weighted polymeric surfactant dropped out the majority of the solids and released the associated dispersed oil, which enabled the fluids to be separated into distinct oil, water, and solids phases in the water treatment equipment.

The novel chemistry approach brought the water back under the discharge specification 40-ppm TPH and 150-ppm TSS. It also widened the operating envelope of the process equipment, increasing its ability handle off-specification inlet TPH by 500% and TSS by up to 1,000%. As a result, the operator is installing permanent infrastructure for continuous application of the chemistry solution.

This water treatment management solution demonstrates how tailored chemistries can enhance the efficiency of produced water equipment when faced with neutrally buoyant fine solids (<2 um) and emulsified OIW.