Fracturing oil shale for in situ retorting experiments

TLDR: The first technique to be tested in the field was electrolinking, or electrocarbonization, accomplished by passing high voltage electricity through the oil shale, but no open fractures were obtained as discussed by the authors.

Abstract: Because oil shale is a rock with little or no permeability, it must be fractured or broken to allow the passage of fluids needed for retorting by in situ methods. The Laramie Energy Research Center has investigated a number of fracturing techniques. The first technique to be tested in the field was electrolinking, or electrocarbonization, accomplished by passing high voltage electricity through the oil shale. In the field under overburden pressure, the shale was carbonized by the electricity and small increases in permeability were noted, but no open fractures were obtained. Hydraulic fracturing has also been tested and in many cases results in increasing permeability, but retorting through hydraulic fractures would be extremely difficult because of the low surface area that results from the fracturing. To increase the surface area a number of different explosives and explosive fracturing techniques have also been investigated. Desensitized nitroglycerin displaced into a naturally occurring porous zone and into a sand-propped hydraulic fracture was used in one experiment. In another experiment slurried explosives were detonated in sand-propped horizontal hydraulic fractures. In this experiment, which is still in progress, preliminary evaluation shows the presence of both vertical and horizontal cracks intersecting the wellbores.