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
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. JPT P. 21
American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. This paper was prepared for the Rocky Mountain Regional Meeting of the Society of Petroleum Engineers of AIME, to be held in Denver, Colo., April 7–9, 1975. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made. provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines. Abstract The effects of pressure, oil shale grade, oxygen enrichment, and steam injection on the quantity and heating value of offgas from oil shale retorting was studied in the laboratory. Equations were developed which show that large quantities of medium Btu gas can be produced in conjunction with shale oil production. Results also indicate that up to 84 percent of the original organic content can be produced as combustible gases and crude shale oil. Btu distribution in the gas-liquid product mixture is up to 1 to 1. Introduction Government and industry oil shale research groups have been working both independently and cooperatively to develop economically feasible and ecologically satisfactory energy recovery processes. One problem that has attracted much processes. One problem that has attracted much attention has been that of increasing process efficiency to insure maximum utilization of the resource. Many processes under investigation involve burning a portion of the oil shale to produce sufficient heat to retort the remainder. During all of these processes some of the original organic material is converted to gases. The low Btu level of gases normally produced, collection and handling costs, and other problems have combined to prevent any widespread usage of these offgases. The object of this study by personnel of the Laramie Energy Research Center was to determine levels of operating variables such that the heating value of the offgases could be maximized. A small retort was assembled and instrumented, and two series of experiments were completed to investigate the effects of pressure, oil shale grade, oxygen enrichment, and steam injection on the quantity and heating value of gas produced during forward combustion of oil shale. Data collected were tabulated for computer analysis and regression equations were developed which satisfactorily describe the system. The volume of offgas that would be produced during a commercial-sized application of the in situ recovery process to oil shale is predicted to be in excess of 1 billion cubic feet per day. Because of the tremendous volume of gas involved, there would be obvious economic advantages to operating in a manner to produce a usable offgas. EXPERIMENTAL DESIGN Application of this process sets inherent limitations on the number of variables that can be controlled and also restricts some to narrow limits.
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