Separation Scheme For Cleaning Up Oily Waste
Authors: Hoffman E. 
Published: March 2010

It is well known that heavy oil and oil sands thermal recovery operations produce oil-laden solids and sludges which are difficult to treat and to dispose of safely. The oil-laden sediments and sludges, which commonly accumulate in oil field produced fluids separators and treaters and at the bottom of storage tanks, are usually not readily amenable to conventional methods of treatment and disposal. Such materials, commonly called produced so/ids, typically consist of oily sand, precipitates and emulsified oil and water. The nature of produced solids at Shell Canada '5 steam-enhanced heavy oil recovery facility at Peace River is described; and the development of a new process for treating produced solids that allows removal, and recovery, of hydrocarbons associated with the solids and thereby assists in the safe disposal of the residual solids is discussed. The process comprises mainly feed conditioning, hydrocarbon removal and recovery, and water removal steps. The basic concepts of the process may also be applicable to oily waste other than produced solids such as soil contaminated in an oil spill or from oil storage or refinery operations.

Introduction

In the production and treatment of crude oils, especially in heavy oil and oil sands thermal recovery operations, the generation of oily produced solids waste is a well known problem and poses difficulties in the treatment of produced fluids and in disposal of the solids.

Based on industry surveys(l), the annual volume of oily produced solids, excluding untreatable slop oils and spill debris, at Canadian heavy oil operations approaches 50 000 m3. In comparison, the volume of produced sand, tank bottoms, separator sludges and associated solids in the United States is in the order of 200 000 m3 (more than half in California)(2).

Due to their appreciable hydrocarbon and brine contents and their physical nature, produced solids are not readily amenable to conventional methods of treatment and disposal and can represent a significant loss in crude oil production. In many cases, produced solids are combined with slop oils and spill debris and stored in on-site "ecology pits". Such oily mixtures have been utilized for road dust suppression and in the preparation of road surfacing material(3). Studies on land farming methods for disposal of oily waste sludges suggest that this concept may be possible but major changes in soil properties could adversely influence end use of the land(4,5).

Previously, numerous methods have been investigated for recovery of oil from produced solids including thermal retorting by the AOSTRA Taciuk Process(6,7), use of coal(8) solvent extraction and mechanical means(9). An oily sand cleaning system, consisting of a set of hydrocyclones for removal of oil and water and a dewatering screen for removal of additional water is reported(10). Incineration methods may also be an attractive option for decontaminating the solids and energy recovery. Injection of a slurry of the oily produced solids and water into an underground formation has been demonstrated to be a viable option but successful injection is greatly affected by the characteristics of the produced solids and the disposal formation selected(11).