US 3084919 A
Description (OCR text may contain errors)
W. L. SLATER April 9, 1963 RECOVERY OF OIL FROM OIL SHALE BY UNDERGROUND HYDROGENATION Filed Aug. s, 1960 SEH This invention relates to a method for in situ recovery of oil from naturally occurring deposits of oil shale. The process is particularly applicable to recovery of oil from subterranean deposits of oil shale. In accordance with the process of this invention, oil shale is hydrogenated in situ to liberate shale oil yand the hydrogen treated shale oil is then produced like crude petroleum.
A number of proposals have been made for the recovery of oil from underground deposits of oil shale by heating the oil shale in place. The oil shale may be heated by burning a portion of the shale oil or by burning an auxiliary fuel. By means of these in situ opera* tions, part of the potential Ioil content of the oil shale may `be recovered in the form of heavy hydrocarbon oil. Oil so recovered is extremely viscous and of very poor quality as compared with crude petroleum. When in situ combustion is employed for retorting the oil shale,
a portion of the fuel value yof the shale, e.g. l0 to 30 percent, is consumed as fuel in the burning operation.
The process of this invention provides for improved yields of shale oil of improved quality as compared with the retorting of oil shale. In accordance with the present hydrogenated in situ by contact with hydrogen at elevated temperature and pressure. The hydrogenation reaction which takes place in the oil shale form-ation produces a liquid product which is readily recoverable as a liquid hydrocarbon oil. The crude liquid product has a higher u API Gravity than oil produced from the same oil shale by conventional retorting operations. Heat required to raise the temperature of the oil shale formation to hydrogenation temperature may be supplied by combustion of shale oil within the oil shale formation.
The accompanying ligure illustrates diagrammatically the method of oil recovery from oil shale by in situ hydrogenation in accordance with the present invention.
The FIGURE, which illustrates a specific embodiment of this process, represents a vertical cross-section through a subterranean oil shale formation.
With reference to the figure, an oil shale formation 2 is overlain by substantially impervious cap rock 3 and is underlain by substantially impervious seam of bedrock 4. A plurality yof Wells are drilled from the surface of the earth into the oil shale formation. As illustrated, well bores 6 and 7 extend through the overburden to a point Iwithin the oil shale formation, preferably to a point near the lowermost portion of the oil shale formation. These Well bores are cased in the usual manner and provided with tubing extending from the surface to la point within the oil shale formation near the bottom of the Well bore. The tubing strings 8 and 9 are set in the well bores 6 and 7, respectively, in conformity with good practice in the art of petroleum production.
To initiate the oil recovery operation, fuel and air are injected through pipes 11 and 12 into well bore 6, Heavy hydrocarbon liquid is suitable as fuel, although some light liquid hydrocarbons, for example, gasoline, is desirable initially. Fuel may be introduced through pipe 11 and tubing 8, or through pipe 12 and the annular passageway surrounding the tubing in the well bore. Air is introduced to the well bore through tubing 8. Initially, a charge of fuel is fed through tubing 8 to the bottom of the well bore Within the yoil shale formation. Then a ice flow of air is started through line 11 and tubing S. The fuel and air mix at the lower end of tubing 8 forming a combustible mixture. Combustion is initiated in the lower part of the well bore at the end of the tubing string by suitable ignit-ing means, heating that portion of the oil shale formation surrounding the Well bore 6. Resulting products of combustion are discharged through annular space between the -wall of the well bore and the tubing string to the surface of the earth. Outflow of gas and pressure in the burning and producing zone are controlled by valve 13. Additional fuel may be charged to the well through line 12. Gas discharged from the well bore may be combustible and can be used as fuel for preheating the hydrogen.
During the initial period of tiring, using an auxiliary fuel, the temperature of the shale bed is raised to the desired temperature for subsequent hydrogenation. Combustion is continued until the desired temperature has been reached, for example, 500 F. to 1500 F., in the shale surrounding the well bore. In some cases, after initial tiring with auxiliary fuel, suicient oil from the oil shale will collect in the Well bore to permit combustion in the absence of the auxiliary fuel. In this case, the introduction of auxiliary fuel may be discontinued while the combustion-supporting gas, suitably air, is continuously supplied to the well bore, burning a portion of the retorted oil and further heating the shale formation.
When the desired temperature, eg. 900 F., in the shale formation is reached, the introduction of air is disprocess, shale in an underground oil shale formation is '3: Continued At this time# 'air is Vented from the tubing and from the well bore through valve 14. Hydrogen from a suitable source is then supplied through line 15 and tubing 8 to the oil shale formation. Hydrogen is introduced into the formation, under pressure from compressor 16, until a pressure is reached within the range of about 1,000 to 5,000 pounds per square inch gauge, depending upon the depth of the formation below the surface of the earth. The hydrogen may be supplied directly to the well at pump discharge temperature or may be preheated to a suitable temperature, e.g. 500 to 1000* F., in heater 17. The -hydrogen is permitted to remain in contact with the formation for a period of from about six hours to about two weeks or longer. Additional hydrogen is furnished as necessary during this period to maintain the desired pressure. During the reaction period oil is released from the oil shale and partially hydrogenated. The resulting hydroretorted oil has improved properties, e.g. lower viscosity and lower sulfur content, than conventionally retorted shale oil. This oil accumulates in the Well bore. The oil may be periodically produced through tubing string 8 by discontinuing the flow of hydrogen and permitting the oil to ow from the pressurized well bore through line 18 to a suitable gas-oil separator 19. Gas separated from the oil may be passed through line 21 to a gas holder 22 where it -is available for further use in the hydrogenation of the oil shale.
While retorting of oil shale and hydrotreating of the liberated shale oil is taking place in Well bore 6, preheating of the oil shale formation about well bore 7 is carried out by introduction of fuel and air to the well bore and initiating combustion therein as described above in connection with well bore 6. When sufficiently preheated, hydrogen separated from oil produced from well bore 6 may be introduced into well bore 7 for -hydrotreating the subsurface oil shale formation surrounding well bore 7.
When the rate of reaction between hydrogen and oil shale drops to an impractical low value, as indicated by the rate of pressure decline or rate at which hydrogen must be introduced into the formation to maintain reaction pressure (either of which may be determined at the surface), the introduction of hydrogen is stopped and the well depressured by permitting gas and oil to flow from the well through tubing 8 (or 9), and through line 13 to separator 19. Following depressuring, the formation surrounding the. well `bore may be reheated by again introducing air and fuel to. the well as described above. When reheated to the desired temperature, for example, 500 to 1500 F., and purged of air, hydrogen may Vbe again introduced through the well bore to the formation to effect further hydrogenation Iand recovery of oil therefrom.
By providing a plurality of well bores, as illustrated in the ligure, the gas holder requirements may -be minimized or eliminated. With a multiplicity of wells, some wells may be in the preheat stage while others are in the pressuring, processing, or depressuring stages. Leakage or migration of oil and gas from one well to another is not detrimental and is generally beneficial. When such leakage progresses to the point where flow of gas is established from one well to the next, oil may be produced through the tubing string of one well at the same time as hydrogen is introduced to the other. Also, when this condition exists, the formation may be heated during the heating period by in situ combustion within the formation with either concurrent or countercurrent movement of the ame front and the combustion air through the formation between communicating well bores. In situ combustion techniques are well known in the art.
Although only one set of well bores is illustrated in the drawing for the purpose of illustration of the process of this invention, it is to be understood that multiples may be employed in a suitable pattern, for example, the iive spot or seven spot patterns well known in the art of secondary recovery from petroleum reservoirs.
Means other than direct combustion may be employed for supplying -heat to the oil shale formation, for example, by means of an electrical heater.
I claim: Y
1. A process for obtaining shale oil from a subterranean oil shale stratum penetrated by a well bore provided Ywith tubing extending from the surface of the earth into the oil shale formation, which comprises supplying liquid hydrocarbon fuel to the bottom of said well bore within the oil shale formation, thereafter supplying air through said tubing into contact with said liquid hydrocarbon fuel in the oil shale formation and initiating combustion therein, withdrawing products of combustion from said oil shale formation through the annular space between the wall of the well bore and the tubing while continuing the supply of air thereto through said tubing effecting heating of said oil shale to a temperature within the range of about 500 to 1500 F., discontinuing the introduction of air to said well bore, venting air from said tubing, introducing hydrogen through said tubing to the oil shale formation until a pressure is reached within the range of about 1,000 to 5,000 pounds lper square inch gauge, permitting the hydrogen to remain in contact with the oil shale formation while maintaining said pressure within said range for a period of at least 6 hours effecting release of shale oil from said oil shale and reaction between said shale oil and hydrogen, and withdrawing liberated oil from said well bore.
2. A process according to claim 1 wherein hydrogen is introduced into the well bore at a temperature within the range yof 500 to 1000" F.
3. A processk according to claim 1 wherein a plurality of spaced well bores extending into said formation are employed and wherein preheating of'oil shale formation surround-ing a first of said well bores is carriedout simultaneously with hydrogen treatment of oil shale formation surrounding a second of said well bores, the steps,y of discontinuing preheating of oil shale formation surrounding said rst well bore, depressuring said second well bore by withdrawing hydrogen therefrom and simultaneously supplying said withdrawn hydrogen to said preheated -rst well bore. 'Y
References Cited in the file of this patent UNITED STATES PATENTS 2,595,979 Pevere et al. May 6, 1952 2,847,306 Stewart et al Aug. 12, 1958 2,970,826 Woodruif l Feb. 7, 1961