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This heavy sludge caused cavitation at the tank circulation pumps and blockage of the return line sampling/bleed-valve. Despite regularly dosing the tank with standard emulsion breakers, the water draw-off always produced ‘black-water’. This presented problems at the API separators outfall as the very fine suspended solids were nearly impossible to remove.

One drum of chemical was circulated through the dosage tank and the tank pump to clear it and its lines. The NAOC personnel immediately noticed the improved performance of the pump. The tank was drained down to under 4 meters and contained about 8,938 equivalent barrels of sludge and 12,000 barrels of oil cutter stock. The oil was used to help agitate and circulate the chemical. The chemical dispersant from United Energy was added in 3 batches to the sludge topped with oil. In total 77 drums of 55 gallons each were pumped into the tank in batches over a 5 day period via the existing on-site equipment.

The 77 drums of chemical equates to 1.1% of the heavy sludge on the tank bottom. The amount of chemical with the regular oil was .84 % and only .48 % of chemical was used for the entire mix of sludge and oil. The tanks circulation nozzle system was used to mix the oil, chemical and the sludge into one homogeneous liquid solution. After the second batch some of the combined chemical and oil was pumped to another tank which reduced even more sludge in the additional tank.

An extract from the NAOC customer documentation on March 23rd,

“Visual and physical inspection of the tank 19 bottoms was made when the manhole was opened and observation was made of the absence of sludge in the tank.” No one was required to enter the tank.

ü On March 19th 3 days after the first drums of chemical were pumped into the tank the recovered oil after settling and water draw-off was API 34.5 prior to transfer to production line.

ü Once the chemical treatment was complete it was found that tank floor plates were visible and that no sludge was detectable. All of the 8,938 bbls of sludge were recovered.

ü It was not necessary for NAOC to use vacuum-trucks or to discharge sludge/recovered oil to the API Separators. The water was separated and clear.

ü NAOC originally intended to discharge the “smooth homogeneous and pumpable” recovered crude to the API skimmer. However, this did not prove necessary as the quality of the recovered oil was monitored by NAOC site laboratory and found to be fully acceptable at an API of 34.5 for transfer to the production line.

Delivering effective, environmentally friendly, cost-saving solutions to the oil industry

Crude Oil Recovery From Sludge at Nigerian Agip Oil Company (NAOC) Brass Terminal, Bayelsa State, Nigeria.

Project Duration 7 days

No. 19 is a 33.8m diameter tank, with fixed roof construction and is fitted with an equally spaced 4” circulation nozzle system. The terminal receives crude oil directly from the production fields, stores it, dewaters it and monitors quality before exporting the oil through its production lines

The sludge volume determined by the NAOC control room measurements at the tank datum plate showed approximately 1.6m height. This equates to 8,938 bbls of sludge volume inside the tank. A sludge sample after taking out the water content showed 93.6% paraffin and resins with 5.8% asphaltene.

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