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Abstract
Crude oil occurs in many different forms throughout the world. An important characteristic of crude oil that affects the ease at which it can be produced is its density and viscosity. Lighter crude oil typically can be produced more easily and at a lower cost than heavier crude oil. Historically, much of the world’s oil supply came from light or medium crude oil sources. Oil and gas companies are actively looking toward heavier crude oil sources to help meet demands and to take advantage of large heavy oil reserves located in many countries. Heavy oil includes very viscous oil resources like those found in some fields in California and Venezuela and oil (or tar) sands. In this paper, oil shale is also considered as heavy oil.

Produced water is the largest by-product associated with conventional oil production. The cost of managing large volumes of produced water is an important component of the overall cost of producing oil. Most mature oil fields rely on injected water to maintain formation pressure during production. The processes involved with heavy oil production often require external water supplies for steam generation, washing, and other steps. While some heavy oil processes generate produced water, others generate different types of industrial wastewater. Management and disposition of the wastewater presents challenges and costs for the operators. This paper describes water requirements relating to heavy oil production and potential sources for that water. It also describes how water is used and the resulting water quality impacts associated with heavy oil production.

Introduction
This paper is based on a November 2008 report prepared by Argonne National Laboratory for the U.S. Department of Energy, National Energy Technology Laboratory (Veil and Quinn 2008). The full report contains numerous figures and maps plus descriptions of many technologies used to produce heavy oil. This paper does not include that information. Readers can readily view that information by downloading Veil and Quinn (2008) from Argonne’s Environmental Science Division Web site (http://www.ead.anl.gov/pub/dsp_detail.cfm?PubID=2299).

Definition of Heavy Oil
Heavy oil is generally defined in terms of API gravity and may also include viscosity in the definition. API gravity was established as a uniform way of characterizing the density or specific gravity of oil by the American Petroleum Institute. API gravity is an arbitrary scale expressing the gravity or density of liquid petroleum products. The measuring scale is calibrated in terms of degrees API. It is calculated as follows:

API Gravity (°) = (141.5 ÷ specific gravity of the oil at 60ºF) − 131.5

Higher API gravity ratings reflect lighter types of crude oil. The boundaries between different classes of oil (e.g., light, intermediate, heavy, extra heavy) all follow the same trend, but different authors choose slightly different boundaries between categories. Generally, heavy oil has an API gravity of 22° or lower, and extra heavy oil has an API gravity of 10° or lower. Dusseault (2001) recommends that viscosity be measured in situ, and that heavy oil has a viscosity greater than 100 centipoise (cP). He further suggests that the definition for heavy oil could also be expressed in terms of producibility. Heavy oil should have some mobility under naturally existing conditions and can flow to wells and be produced economically. In contrast, extra heavy oils, oil sands, and bitumen typically have both a low API gravity and high viscosity, such that they do not flow naturally. They are typically produced through thermal processes or solvent addition.