Ammonium and/or sodium bisulfite are commonly used as oxygen scavengers in the wash water used for crude oil de-salting purpose. Its purpose is to deoxygenate the wash water and export crude systems to minimize chances of oxygen corrosion. Often biocides are added in the wash water continuously or as shock treatment to control bacteria growth in process facilities as well as downstream. However, there are instances of compatibility issues arising between these two types of chemicals making both of them ineffective in meeting their performance requirements. It is not unusual to see that the dissolved oxygen content is not reduced to the expected levels even after using recommended quantity of an oxygen scavenger chemical. Similarly, the biocides remain ineffective in controlling bacteria growth.
This paper gives details of a field trial conducted in one of the Kuwait Oil Company* facilities to find reasons for the observed non-performance of oxygen scavenger. The trial was carried out for a duration of three months by keeping the oxygen scavenger injection constant throughout the trial period and varying the biocide dosages. The dissolved oxygen content was measured regularly during the trial to find out the impact of biocide injection on the oxygen scavenger performance. The findings from the trial indicate a definite possibility of certain biocides being non-compatible with the oxygen scavengers used in the oil field. Additionally, the paper provides theoretical reasoning for oxygen corrosion in wash water system and highlights the practical concerns existing in the field.