Overview: Heavy Oil (June 2005)
Authors: Kovscek Tony 
Published: February 2015

What is heavy oil, and why do you care about it? These are important questions with answers that are simple, but subtle.
Heavy hydrocarbons exhibit gravity less than 20°API. They are characterized by high viscosity that increases as API gravity decreases, low hydrogen/carbon ratios, low gas/oil ratio, as well as significant sulfur, asphaltenes, and heavy metals. In short, heavy-oil reservoirs generally present low-energy and low-productivity wells.
These characteristics make recovery challenging, yet the volume of heavy hydrocarbons in the world warrants a thorough look. Canada and Venezuela each possess heavy-oil resources of approximately 3 trillion bbl. In comparison, the heavy-oil resource of the U.S. is less than 200 billion bbl. This does, however, represent a more-than-40-year supply at current U.S. oil-consumption rates. Significant heavy-hydrocarbon resources also are found in Indonesia, Russia, and China, as well as elsewhere.
A second reason for interest is the difficulty in attaining economical exploitation. It suggests a need for research and development activities. Thermal recovery, and steam injection in particular, is tremendously successful. The addition of heat reduces oil-phase viscosity significantly. Nevertheless, conventional steam-injection candidates are limited to onshore, relatively shallow, thick, and permeable sands. Given the oil volumes in place, the range of reservoir settings, and the difficulties of extraction, a suite of heavy-oil recovery options is needed.
Consider an incomplete list of research and development opportunities. First, primary recovery that uses horizontal and multilateral wells is possible and profitable. The production mechanisms of the heavy-oil solution-gas drive process are, however, not completely elucidated, and performance cannot be simulated by conventional techniques. Second, waterflooding of heavy oil is summarily dismissed because of adverse mobility ratios, but is similarly not well understood. In cold and/or offshore environments, waterflooding may present the only viable recovery option following primary production. Third, steam injection is relatively mature, but steam is considerably less viscous and dense than oil. Cost-effective mobility and profile control by use of aqueous-phase surfactants, gels, or advanced well completions remains an open question. Fourth, in-situ combustion achieved by air injection is technically and economically feasible, especially for deeper, thinner, higher-pressure reservoirs. Combustion has seen less field application than steam because of the difficulty in its description and control. Finally, combustion presents possibilities for in-situ upgrading and sulfur removal.
In short, the cumulative production totals of heavy oil are on the order of billions of barrels, but this is only a small fraction of the oil in place. Whether the potential and promise of heavy oil are realized depends on the collective action of industry, academia, and governments to deliver a suite of technologies appropriate for the wide range of reservoir and oil-phase conditions.
Additional Heavy Oil Technical Papers
Available at the SPE eLibrary: www.spe.org
SPE 93881 Toward an Adaptive, High-Resolution Simulator for Steam-Injection Processes
SPE 93894 A New Reservoir-Simulation Model for Understanding Reservoir Performance in the McKittrick Steamdrive