Shale Oil Recovery by In-Situ Retorting-A Pilot Study

Abstract

Results of this in-situ combustion experiment, conducted by the U. S. Bureau of Mines near Rock Springs, Wyoming, to produce shale oil from oil shale, indicate that a combustion zone can be established in a fractured oil shale body by using air injection and a propane burner. During the six-week period that combustion was maintained, 8,000 gallons of oil was produced. produced. Introduction This paper describes an in-situ combustion experiment conducted by the U. S. Bureau of Mines in the Green River oil shale formation near Rock Springs, Wyo. The experiment was designed to study the engineering problems associated with the establishment, maintenance, and control of a self-sustaining combustion zone in the oil shale and the use of this process to produce shale oil. A 20-ft-thick section of the oil shale located from 68 to 88 ft below the surface of the ground was ignited by use of a propane burner in the central well of an expanded five-spot development pattern. A combustion zone was established in the formation and maintained with little difficulty for a 6-week period, at the end of which time air injection and the combustion phase of the project weld terminated. Several thousand phase of the project weld terminated. Several thousand gallons of shale oil were recovered and stored for analysis. Permeability loss at the injection well and high viscosity of shale oil were problems experienced by other investigators during oil shale retorting, but were not encountered during this test. Geology The combustion experiment was performed in the Tipton member of the Green River oil shale formation near Rock Springs, Wyo. The Tipton member in the area of the test-site has a 2-percent dip to the west and a general geologic strike to the north, Green River oil shale is a dolomitic marlstone with a finely laminated structure consisting of an intimate mixture of organic and inorganic materials. The mineral portion ranges from 92 weight percent of shales having an oil yield (as determined by Fischer assay) of 10 gal/ton to 60 weight percent of those having a yield of 75 gal/ton. It consists largely of dolomite, calcite, feldspars, quartz, and illite clay. In the leaner shales cementation is primarily inorganic; however in rich strata it appears that the organic material is the principal cementing agent principal cementing agent Both the porosity and the permeability of oil shale are extremely low because the solid, essentially insoluble organic material serving as a cementing agent blocks the major portion of any pores that might be present. present. Site Preparation Since the success of any in-situ combustion oil recovery experiment in oil shale depends directly on the ability of air, combustion gases, and produced oil to move through the shale formation, produced oil to move through the shale formation, the first part of the site preparation consisted of an intensive fracturing program. Fracturing techniques that were investigated included electrolinking, hydraulic fracturing, and explosive fracturing. P. 1520