Greenish-brown soap sludge is formed in significant quantities during production of oil from the Serang field, offshore East Kalimantan, Indonesia. The sludge forms upon cooling of oil in subsea pipelines and onshore terminal storage tanks. This interfacial sludge is comprised of entrained free oil, water and solids, and is stabilized by an acyclic "metal carboxylate" soap. In the absence of fluid treatment, removal and disposal of the sludge is tedious, expensive, and represents significant un-recovered oil. The soap also adversely affects discharge water quality.

The sludge has been characterized to understand its formation mechanism, so that remedial actions can be taken to mitigate its deposition.1  A variety of analytical methods indicated that the "soap" emulsion consists of about 30% water, 50% oil, and 20% of C28 – C30 carboxylate salts in sodium form. The "soap" is stabilized by fatty acid-Na-HCO3 complexation, and results from the reaction of long chain fatty acids in oil with sodium bicarbonate-rich waters containing significant volatile fatty acids.

Laboratory and field tests have demonstrated that the sludge can be dissolved by low dosages of commercially available sludge dissolving agents containing combinations of acids. An acid demulsifier, consisting of acetic acid in an aromatic solvent mixture, and a non-acid demulsifier, consisting of ethoxylates and alcohol, have been injected into Serang produced fluid arriving at the onshore Santan terminal since August 2002. The demulsifiers have significantly reduced sludge deposition in oil storage tanks and water-handling facilities. In addition to "dissolving" sludge, incremental oil is recovered, which offsets chemical treatment and sludge disposal costs. Existing sludge is treated with chemicals and hot centrifuging to minimize waste and optimize oil recovery.

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