THE ROLE OF LAKE BASINS AND OIL SHALE IN THE GLOBAL QUEST FOR UNCONVENTIONAL HYDROCARBON RESOURCES

Global oil shale resources comprise at least 2.8 trillion barrels (nearly twice as much oil as has been produced from conventional fields since the oil industry began). Potential large increases in the resources have recently been projected. High oil prices and increased emphasis on domestic energy development have brought unconventional hydrocarbon resources to the forefront in industrial exploration and public debates. Unconventional resources are technologically (and economically) more challenging to produce than light oil from conventional petroleum reservoirs, but they are distributed differently than conventional oil. Very large potential reserves exist outside the Middle East. North America has abundant oil shale (mostly Colorado, USA) and heavy oil (mostly Alberta, Canada) resources.

The largest known oil shale resources in the world occur in Eocene lake sediments in western Colorado and adjacent Utah and Wyoming. Colorado oil shale resources are thick (~300 m) and very rich, with areal energy density up to 1.3 million barrels per acre, compared to Wyoming coal (500,000 bbls/acre) and Canadian oil sands (100,000 bbls/acre). Conventional oil field reservoirs are commonly also thinner, and show lower values. Other lake basins that preserved organic material well and were subsequently buried only to shallow depths, have great potential for rich oil shale.

New technology for producing shale oil and increased attention to environmental challenges suggest that the time may have arrived for large-scale production. Shell Oil Company is testing a new approach for in-situ (subsurface) conversion of kerogen into light oil using down hole electrical heaters. ExxonMobil Corporation proposes in-situ heating through conductively propped rock fracture networks, and Chevron proposes to inject CO2 into fractured oil shale to mobilize hydrocarbons.

On the environmental side, it is clear that oil shale production associated with great surface disturbance – such as surface mining and excessive use of water – has a limited future. Moreover, new approaches to limiting CO2 emissions drive nearly all planning for unconventional resource production, and the future for commercial oil shale will depend on rapid development of CO2 capture and sequestration technology to ensure zero emissions from the production sites.