Before an offshore installation on the Norwegian continental shelf started production of crude oil and condensate, the risk of naphthenate deposition was identified. The total acid number (TAN) of the crude was 3.50-mg KOH/g; TAN values > 1-mg KOH/g are considered high. Further analysis confirmed that the oil contained high-molecular-weight naphthenic acids, which cause precipitation of calcium naphthenate. The deposit forms a viscous interfacial layer, or rag layer, between the water and oil phases in the inlet separator, disrupting emulsion destabilization and water removal. The naphthenate also forms deposits in the system.
Water with pH < 3 is needed to dissolve the calcium naphthenate. However, reducing the pH of the produced water can lead to corrosion issues, and a fill and soak operation to remove deposits would temporarily shut down production. To avoid these challenges, the operator decided to test a number of naphthenate inhibitors at its facilities, and in response, SLB supplied four formulations.
Based on the results of the laboratory trial, EB-89084 was selected for injection at the wellheads right from startup of the installation. The product is based on proprietary technology developed in the SLB laboratory in Bergen, Norway, and it has shown good naphthenate inhibiting efficacy on other offshore installations in the North Sea. EB-89084 is being injected continuously and to date, no issues or downtime related to precipitation of naphthenates in the process system have been encountered.
