Evaluation of an In-Situ Retorting Experiment in Green River Oil Shale
Authors: Carpenter H.C. , Burwell E.L. , Sohns H.W. 
Published: December 2007

Following the retorting phase of this test conducted near Rock Springs, Wyoming, 18 core holes ere drilled to sample the section of oil shale involved. In this first experiment, resource utilization and oil recovery were low, but the information obtained suggests ways of improving the efficiency of future investigations.

Introduction
An in-situ combustion experiment was conducted by the U. S. Bureau of Mines in Green River oil shale at a site near Rock Springs, Wyo. The combustion phase of the experiment that was conducted during phase of the experiment that was conducted during the late spring of 1969 has been described previously. Two methods of evaluation were used. previously. Two methods of evaluation were used. One, based on data obtained from continuous gas analyses and flow measurements that were made during the entire burning phase of the experiment, was previously reported. The other, based on analyses and assays of cores taken before combustion was initiated and after it was terminated. is the primary subject of this paper. In addition some time after the experiment an infrared temperature survey was made to obtain information on direction of travel and areal extent of the combustion zone.
The purpose of our evaluation was to obtain information on the amount of oil shale that was affected by underground combustion, the amount of oil that was produced, the amount of oil that could be recovered, the areal extent, thickness, and depth of the combustion zone, and the preferential direction of travel of the zone.
The combustion experiment was conducted in a section of oil shale 20 ft thick located 68 to 88 ft beneath the surface of the ground. Two core holes were drilled before combustion was started, and 18 additional ones were drilled after the experiment was ended 6 weeks later Areal extent of the zone investigated was approximately 10,000 sq ft. Approximately 30,200 gal of oil was produced, of which 8,000 gal was recovered aboveground. Most of the remainder, although not actually recovered during the test, was later located within the test area. A relatively small amount of the total 1,400 gal, or 4.6 percent either migrated beyond the test area or was burned. The oil that was recovered was of satisfactory pipeline quality, having a gravity of 31.7 degrees API, a pour point of 5 degrees F, and a viscosity of 41.0 SUS at 100 degrees F.

Background
The combustion experiment was performed in the Tipton member of the Green River oil shale formation. 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. For purposes of the experiment, a 20-ft-thick section of the oil shale located from 68 to 88 below be surface was selected for study. The average oil yield of this section (as determined by Fischer assay was 21.7 gal/ton. The porosity and permeability of the oil shale were extremely low. To permeability of the oil shale were extremely low. To create effective permeability through the oil shale for the combustion experiment, the first step consisted of fracturing the oil shale section. Sufficient breakage was achieved to permit satisfactory heat transfer between hot gases and the oil shale, and to allow the air, combustion gases, and produced oil to move through the formation.
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