Exxonmobil’S Electrofrac Process for in Situ Oil Shale Conversion

William A. Symington, David L. Olgaard, Glenn A. Otten, Tom C. Phillips, Michele M. Thomas, and Jesse D. Yeakel
ExxonMobil Upstream Research, Houston, TX

ExxonMobil’s Electrofrac process is an energy efficient method for converting oil shale to producible oil and gas. The method heats the oil shale in situ by hydraulically fracturing the oil shale and filling the fracture with electrically conductive material, forming a heating element. The shale oil and gas are produced by conventional methods.

Electrofrac research has included small-scale experiments, numerical modeling, and resource description work addressing critical technical issues. This presentation provides an overview of the research, highlights of which are: (1) Laboratory experiments demonstrating the following; (1a) Hydrocarbons will be expelled from heated oil shale even under in situ stress, (1b) Electrical continuity of the fracture heating element is unaffected by kerogen conversion, and (1c) Calcined petroleum coke is a suitable conductive material for use as the fracture heating element, (2) Modeling including the following; (2a) A Piceance Basin geomechanical model that shows most of the Green River oil shale is in a stress state favoring vertical, rather than horizontal, fractures, (2b) Heat conduction models that show several fracture designs can deliver heat effectively, and (2c) A phase behavior model that shows volume expansion is a large potential drive mechanism. In situ oil shale can expand by 70% upon kerogen conversion, and finally (3) Resource description work indicating that Piceance Basin oil shales are sufficiently thick and rich for commercial development by the Electrofrac method.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas