This paper presents a Lesson Learnt, based on case history, on how the chemical strategy selected for the oil treatment can impact on water unit efficiency, consequently causing or overcoming oil production limitations. A proper "global "chemical strategy has to be carefully designed in order to assure a non-stop oil production in particular in off-shore fields where the water overboard discharge has to satisfy severe limitations. The paper describes the main issues related to the produced water disposal in offshore operations (including FPSO operations) in presence of asphaltic crude oil and sulfuric acid (H2S). The main objective, in particular, was the meeting of the correct specifications for the produced waters overboard discharge. The missed discharge, in this case, would have meant "production stop" to allow the water disposal by auxiliary vessels.
The work has been focused on the overall whole chemical strategy, including the optimization of the water treatment unit in terms of chemical additives, injection points, dosages and operational solutions. More in detail, the impact of the emulsion breaker (suitable for water in oil emulsions) and asphaltene inhibitor dosages on the produced water quality has been analyzed. The final optimization has included not only a proper chemical water treatment design but also a review of the emulsion breaker/asphaltene inhibitor injected ratio. This optimization leads to a significant improvement on the water quality to be handled by the water treatment unit already-in-place. The complete process includes also the optimization of the H2S stripping step by use of a chemical support to increase the efficiency of H2S removal. Laboratory and field activities, conducted in parallel, have been essential for the result achievement.
