Over time, crude oil in ship tankers will destabilize where heavier component of crude oil such as emulsified crude oil with sands, are partitioned at the bottom of storage tank. The presence of these components at the bottom of the storage tank such as water-in-oil emulsion, sands and insoluble heavy metals, will result in increase in density, viscosity and reduce in flowability. This thick and viscous mixture is called crude oil sludge. This part of the sludge normally tend to have high pour point (higher than ambient), up to 10 wt% of sands, water and heavy metals. The sludge is conventionally removed from the storage tank by using mechanical way in combination with high pressure hot water stream. The treated sludge from this process is normally highly viscous, >10,000 cP, and contain around 5-40 wt% of water. This sludge is a water-in-oil emulsion stabilized by the natural emulsifiers in original crude oil. Fine solid in the sludge is another factor to stabilize the water-in-oil emulsion by adsorbing at the oil/water interface. The high emulsion stabilization and high viscosity leads to difficulties in post-treatment to recover the oil, especially when the sludge has very high wax content.
This paper presents a case study of applying a biodegrable, low IFT (interfacial tension) micellar emulsion and solvent extraction for recovering oil from highly viscous crude oil sludge, which could not be recovered by the current processes. This process yields total hydrocarbon (liquid oil and wax) recovery higher than 80%. It could yield approximately 23% recovery of light oil from this sludge (equivalent to >80% extraction efficiency of light oil recovery calculated based on total light crude oil in the original sludge) while the current process does not recovery any light oil. The water stream can be recycled or easily treated. Sand that disposed was found to have less than 2% of hydrocarbons. Additinally, this process can be run at ambient temperature at around 25°C to30°C.