Greenish-brown sludge is formed in significant quantities during production of oil and water from the Serang field, offshore East Kalimantan, Indonesia. This interfacial sludge is comprised of entrained free oil, water and solids, and is stabilized by material described as a "metallic soap." In the absence of fluid treatment, removal and disposal of the sludge is tedious, expensive, and represents significant un-recovered oil.
The sludge was carefully characterized to understand its formation mechanism, so that remedial actions could be taken to mitigate its deposition. The sludge was characterized by elemental analyses, x-ray diffraction, nuclear magnetic resonance, Fourier transform infra-red spectroscopy, gas chromatography-mass spectrometry, and scanning electron microscopy. The results of the characterization studies suggest that sludge filtered and dried at 100°C (to remove free oil and water) consists of ~70 wt% branched and straight chain hydrocarbons in the range of C14 – C28. About 20 wt% of the sludge consists of C28 – C30 carboxylate salts and <5 wt% is inorganic minerals. Emulsification of oil, water droplets and solids by carboxylate salts and bicarbonate ions from water is the most likely sludge formation mechanism. 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. As a result of dissolving the sludge, incremental oil is recovered, which offsets chemical treatment and sludge disposal costs. Although the sludge may be dissolved at the Santan onshore processing facility (end-of-pipe), sludge formation is best mitigated by treating the point-of-source at the Serang offshore platform.