Abstract

Large volumes of produced water are generated during production of heavy crude oil and large volumes of surface water often are needed to produce, transport, and upgrade heavy crude oils and bitumens. The most important alternatives for managing produced and process waters include volume minimization, underground injection, discharge to surface waters, and beneficial reuse. Produced and process waters often contain high concentrations of inorganic salts, metals, hydrocarbons, and organic acids. They may cause ecological damage if discharged untreated to surface waters or soils. Salts harm terrestrial vegetation and naphthenic acids and polycyclic aromatic hydrocarbons are toxic to aquatic organisms. Most produced water is either reinjected into a non-producing formation or used for enhanced oil recovery (EOR) technologies, such as cyclic steam stimulation (CSS) and steam-assisted gravity drainage (SAGD), or bitumen transport and upgrading by slurry pumping and alkaline extraction. Before use or discharge to surface waters, the produced water must be treated to remove dissolved salts, organic acids, hydrocarbons, and suspended solids. Wastes from cold heavy oil production with sand (CHOPS) usually are pumped to stock tanks where the gas, water, oil, and solids are separated and the produced water is piped to a disposal well. The solids are stored in tailings ponds. Wastes produced during processing oil sands bitumen from surface mining with hot alkaline water also are stored in tailings ponds. Water may be decanted from the tailings ponds and reused or reinjected into a non-producing formation. Tailings ponds containing mature fine tailings may be reclaimed as lake basins. Several new technologies are being developed to remove salts, organic acids, and hydrocarbons, and to break stable heavy oil-water emulsions so that produced and process waters can be reused without damaging production equipment and producing formations or discharged without harming the environment.

Introduction

Vast crude oil reservoirs occur in several parts of the world. Total proven in-place world crude oil reserves are in the range of 9 to 12 trillion barrels (1.4 to 2.1x10¹² m³) (1). Approximately 70% of these reserves are classified as heavy crude oils. Heavy crude oil has a density (measured as API gravity) less than 22.3ºAPI and viscosity greater than about 20 centipoises (cP: a measure of viscosity in dyne seconds/cm²). Heavy crude oils with an API gravity of 10º or less are classified as extraheavy crude oils; they often have viscosities of 10,000 cP or higher. Extraheavy crudes that are viscous tars or solids at room temperature usually are classified as oil sands or bitumens. Bitumens and extraheavy crude oils account for 30% and 25%, respectively, of total world oil reserves. Heavy crudes represent 15% and conventional crudes represent the remaining 30% of world reserves. An estimated 97% of total recoverable reserves of heavy crude oils and bitumen are in Canada, Venezuela, and the former Soviet Union.

High viscosity, density, and, frequently, high concentrations of metals (particularly nickel and vanadium) and sulfur are the physical/chemical properties of heavy crude oils that make them difficult and expensive to produce, transport, and upgrade. Environmental challenges of heavy crude oils also stem from these properties, as well as the large amounts of energy and water required for some production and upgrading technologies and the large amounts of waste and byproduct solids, water, and air emissions requiring treatment or disposal. The major challenge facing the oil industry is to develop cost-effective new technologies for production, upgrading, and transport of heavy and extraheavy crude oils, while preventing or minimizing harm to the environment.

Several liquid, solid, and gaseous wastes and byproducts are generated during production, transport, and upgrading of heavy crude oils and bitumen. Byproducts, in this context, are materials, such as petroleum coke and sulfur, produced in addition to the fossil fuels that may have a commercial use and value. We review the characteristics of and current management practices for waste waters associated with heavy crude oil and bitumen production and upgrading.