Hydrocarbon sludge residues are an undesirable by-product of many oil production and refining operations but are especially common and troublesome in oilfield operations that handle the produced crude oil. This oil is typically stored in tanks immediately after production and prior to shipping via (e.g.) tanker or pipeline to refineries. The produced oil, especially in the case of older wells, may contain entrained water, particulate matter such as dirt, and heavy, semi-solid hydrocarbons that are often referred to as waxes. During storage, the water, particulate matter and some of the crude oil (including the waxy material) settle to the bottom of the tank to produce what is referred to as 'sludge' or 'tank bottoms'. This material is seldom of refinable quality. Instead, after the clean crude oil is pumped out of the tank, most of the water and particulate content of the sludge must be removed and the waxy components liquefied before the oil fraction can be handled as marketable oil and blended into the crude oil stream that is being shipped for refining. There then remains an oily residue that must be disposed of. Disposal choices are extremely limited due to environmental constraints.
Traditional ways of treating sludge all have involved repeated heating and cooling. This eventually results in a small reduction of the viscosity of the normally thick sludge, partial liquefaction of the waxes and some separation of water and solids from the oil. This oil can sometimes be blended into the crude being shipped for refining, although much of it used as fuel in the heating process. Overall, the heating process results in only a small portion of the sludge being converted into marketable oil. Since the latter currently has a value in excess of $45 per barrel in most areas, there is a high inventive incentive to recover more.
Treatment with a dilute solution of OIL-XORB ERC (a proprietary commercial surfactant-based formulation) has been shown to be a technically and economically viable alternative. The sludge is contacted with a solution that contains 10% or less of OIL-XORB ERC dissolved in water. The solution and the sludge are heated, agitated and allowed to settle. The OIL-XORB ERC interacts rapidly with the sludge to separate the water and the solids from the oil. The cleaned oil, including the waxes, is of somewhat lower gravity and viscosity than the original crude. It rises to the surface and later can be skimmed off into a separate tank. Virtually all of the oil is recovered. The water enters the OIL-XORB ERC solution and the solids settle to the bottom of the treatment tank and can later be easily be removed and disposed of once the sludge is gone since they are effectively hydrocarbon-free. The skim oil is of refinable quality and can be blended into the crude stream for immediate shipment. The OIL-XORB ERC solution can be re-used numerous times until it is either depleted, excessively diluted with the water stripped from the sludge or, after some 30-45 days, fully biodegraded. It contains no toxic components, is 100% environmentally benign and can easily be disposed of. The OIL-XORB ERC process recovers almost all of the oil since very little is required for heating compared to the traditional process.