Produced Water WSOs Reduction by Topside Facilities Rearrangement

This paper presents the results obtained in Water Soluble Organics (WSO) content in Produced Water (PW) after changing the process arrangement in one FPSO operated in Santos Basin, offshore Brazil.

The WSO content in oil and grease analysis has been discussed extensively in Brazil since the implementation of Standard Methods (SM) 5520B as the official standard for PW discharge to comply with environmental legislation. Historically, dispersed phase was the major component on water treatment. Therefore, most of offshore water treatment design focuses on physical separation.

Since SM 5520B replaced SM 5520F by the environmental agency, WSO started to share (with dispersed oil) an important variable on the O&W separation.

Most of Santos Basin units present high CO₂ content on the production streams. Due to the gas and water equilibrium, it is expected produced water has an acid pH. The pH level impacts the WSO content during the separation steps. Based on our company experience, in pH values around 5 the polar compounds tend to stay in the oil dispersed phase.

Based on an offshore unit arrangement, depending on which separation step the water is collected, the pH can be as low as 5 or higher than 7. The pH calculations showed that to achieve the lowest pH, it is necessary to remove the most of water on the first three-phase separator. The first separator has the highest pressure (20 barg) and high CO₂ content which leads to lower pHs due to water – CO₂ equilibrium.

Based on the pH calculations, the new alignment was implemented. The impact on Oil and Grease (O&G) measurements were immediately observed. The analysis made on infrared analyzer reduced results up to 71%. Another positive side effect was the possibility to avoid oil production losses by 15 kbpd.

The conclusion is that for units with some amount of CO₂, it is possible to reduce the WSO only by changing the process arrangement.