US3586377A

US3586377A - Method of retorting oil shale in situ

Info

Publication number: US3586377A
Application number: US831945A
Authority: US
Inventors: Rex T Ellington
Original assignee: Atlantic Richfield Co
Current assignee: Atlantic Richfield Co
Priority date: 1969-06-10
Filing date: 1969-06-10
Publication date: 1971-06-22
Anticipated expiration: 1988-06-22

Abstract

This invention relates to a process for the recovery of oil from an underground, unmined zone of oil shale. Access is obtained at at least two points in the zone, which can be, for example, in a shallow zone, near the top and bottom of the zone, communication is established between the access means, and at least part of the oil shale zone is fragmented. The heat of retorting is supplied through one of the access means, as by a gas, and the pyrolyzed oil is recovered from the other access means.

Description

United States Patent [56] References Cited UNITED STATES PATENTS [72] Inventor Rex'LEllington Tulsa, Okla.

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mented. The heat of retorting is supplied through one of the access means, as by a gas, and the pyrolyzed oil is recovered from the other access means.

[50] Field AIR METHOD OF RETORTING OIL SHALE IN SITU The recovery of oil from oil shale has heretofore generally been accomplished by one of two methods. The first such method includes mining the oil shale out of the ground, crushing and then retorting or pyrolyzing the crushed oil shale in a fixed retorting plant or structure to retort the oil contained therein. The predominant processes of retorting oil shale are the downflow and upflow gas combustion retorts processes and the hot pebble solid-solid heat transfer process. The second such recovery method is the retorting of the oil shale in situ, or in place, which eliminates the need for a retorting plant and its attendant apparatus. Generally, the in situ method has used conventional injection and producing wells in naturally fractioned zones in the shale body, or the use of communication paths established between the wells by explosive, hydraulic, chemical or electric fractioning means. Recently, nuclear devices have been considered to create a chimney of broken shale with which communication could be established for pyrolysis.

The above ground retorting operations employed generally are cumbersome and expensive, involving large equipment and high operating costs per unit of shale processed. Important factors contributing to these economic burdens have been poor heat heat recovery in the retorting system and the expense, equipment and time consumed in mining and crushing the shale, and in subsequently recovering the products of retorting. These conditions have led to many efforts to process the oil shale in place to eliminate the expense of a crushing and retorting plant.

Retorting oil shale in situ as shown by the prior art has certain disadvantages. Operation through wells in naturally fractioned zones has the disadvantage that fracture patterns may not be known and the effective porosity and penneability of the formation may not represent desirable values. In addition, all the oil that is developed may not be carried to the producing well because of it banking up ahead of the driving gas. In technical terms, the displacement efficiencies and the sweep efficiency may thus be so low as to render the process uneconomic. Also, if the natural fracturing does not expose sufficient surface area, it may not be possible to pass sufficient heat into the shale body to develop sufficient oil in a given period of time to make the process profitable.

U.S. Pat. No. 3,342,257 discloses the utilization of nuclear devices to fragment shale to recovery of the hydrocarbons in situ. The chimney may, however, fill with water and require operating at pressures too high to be profitable. Furthermore, the hazards of such a process are apparent. The broken shale may also be distributed nonuniformly as to size and give rise to channeling of combustion gases and result in technical and economic failure. Massive walls will also have to be left between successive shots to prevent breakthrough and these will remain largely unretorted resulting in a waste of natural resources. Furthermore, this method cannot be used in shallow or thin beds near outcrops, or near mine workings.

It is also known that the first oil and gas produced from nuclear chimney retorting may be contaminated with radioactive products and be unuseable. Ground water may be contaminated. Further, nuclear chimneys may be so tall that the loading of material above retorting zones in the lower part of the chimney may exceed the strength of the oil shale at high temperatures and cause local collapse with resulting shutoff of flows.

The present invention is a process for breaking up and pyrolyzing oil shale in situ in a wide variety of areas, such as near outcrops, above and below mine workings, under close control, thereby eliminating the need for a crushing plant, conventional materials handling, retorting plant, and spent shale disposal. This invention can also be used in the production of raw shale oil underground by the thermal treatment of the solid carbonaceous material in outcrop zones which may be too incompetent or too lean for mining. The present invention also creates relatively small chimneys of broken oil shale for pyrolysis under closely controlled conditions so that fragmentation is optimized. The present invention also provides for control of the rate of pyrolysis not possible with current in situ methods by generating and distributing porosity in the body. The present invention also produces raw shale oil underground by means which do not require transport of a major amount of the shale to the surface and do not require construction of a surface retorting plant, although such may be desirable for optimum utilization. Further, the present invention provides an inexpensive method of processing essentially in situ zones of oil shale too lean for profitable recovery by other means.

An object of this invention is to minimize residence times at temperatures above about l,500 F. to minimize solubility of secondary minerals in order to facilitate their recovery. A further object is to follow the retorting operation with leaching of the shale ash with water or specific solutions to leach out and recover mineral values as taught in copending application Ser. No. 571,649, filed Aug. 10, 1966, now U.S. Pat. No. 3,516,787. Frequently, oil shale contains quartz, dolomite and dawsonite (sodium aluminum carbonate hydroxide). The above application discloses a method to recover aluminum values from a mixture of this type without substantial precipitation of SiO,,. 7

The present invention comprises establishing access means at at least two points in a zone of unmined oil shale, establishing communication between these access means through the zone, fragmenting at least part of the oil shale in the zone in the area of the communication to produce a porous means of fragmented oil shale, supplying heating means to said fragmented oil shale through one of said access means to pyrolyze shale oil in the oil shale and collecting the said shale oil through other of said access means.

The invention will be further illustrated with reference to the appended drawings in which:

FIGS. la, lb and 1c are a graphic representation of one embodiment of this invention;

FIG. 2 is a representation of another embodiment of this invention using two contiguous zones;

FIG. 3 is a representation of another embodiment of this invention particularly applicable to zones of great height.

FIG. la shows a side view of a section of an oil shale zone, generally designated as a. Two access means such as tunnels or drifts l and 2 are cut into the zone. If the oil shale zone is relatively shallow, these'points can be substantially near the top and bottom of the zone, respectively. A short communication lateral 3 is formed in the zone at a point above tunnel 2 and a cavity 4 is excavated at a point in the zone intermediate access means 1 and 2 but generally in proximity to one or the other of the access means. Any of a number of conventional methods can be used to form the cavity such as by drilling. A communicating hole or pattern of holes 5 is formed from the other of said access means to the cavity 4. The hole (or holes) 5 is loaded with explosive and detonated in such a manner as to result in a chimney 6 filled with fragmented oil shale indicated generally as b in FIG. 1c. The mass of fragmented oil shale b is a porous mass. Heating means can then be supplied through one 'of the access means to heat the fragmented oil shale to pyrolyze the oil contained therein. The pyrolyzed oil can then be collected by means located in or attached to the other access means. The heating means can be, for example, a heated gas, which can be noncombustion supporting, such as natural gas or a mixture of natural gas and up to about 20 volume percent carbon dioxide, or it can be combustion supporting, such as oxygen or air. The gas can further be a mixture of natural gas and air. A combustion supporting gas is preferred, such as air or a mixture of natural gas and air. In operation, it is preferred that the fragmented mass of oil shale be subjected to retorting at a temperature of from about 500 to 1,200 F. to drive off the oil contained therein, followed by a substantially complete combustion of shale. The spent shale can then be treated with an alkaline solution, at atemperature of up to about 220 F. to dissolve any aluminum values present, as in dawsonite, without substantial precipitation of SiO: and the aluminum values can be recovered from the alkaline solution. The leaching and recovery steps are more fully explained in U.S. Pat. application Ser. No. 571,649, filed Aug. 10, 1966, now US. Pat. No. 3,5 [6,787.

HO. 2 shows another embodiment of this invention in which two contiguous zones or two contiguous chimneys in one zone are treated simultaneously although the operation in each zone or chimney at any given moment may be somewhat different as is explained more fully below. Chimneys 6' and 6 contain porous masses of fragmented oil shale indicated as b' and b, formed as porous mass 6 explained above. Air from compressor 7 flows through headworks 8 which contain an ignition system and is ignited therein. The air then flows through the shale mass to offtake duct 9 to the oil recovery system 10, which can be any known oil separation system. The oil contained in the shale is retorted during the airflow and also flows into oil recovery system 10. Preferably, the gas 11 which has been denuded of oil in recovery system 110 is returned, mixed with air from compressor 13 and is passed to the bottom of the second chimney 6". The gas 11 contains primarily combustion products from the air burning and the other noncombustible air compounds. The gas-air mixture is ignited at the bottom of the chimney and preheats the shale mass in chimney 6" in its passage therethrough to a temperature of about 200 to 400 F. The mixture of combustion products and recycle gas passes out through headworks l4 and recycle compressor 15 and can be combined with the air in the headworks 8. The recycle gas has the effect of recovering heat from the spent shale indicated as 16 above the combustion zone 17, of reducing peak temperature in the combustion zone to minimize fusion and clinkering and of increasing the length of the zone above any given temperature up to the maximum.

This control of temperature and time is especially useful in converting minerals which may be contained in the shale oil such as dawsonite to a soluble for ultimate recovery as is more fully explained in the aforesaid copending application Ser. No. 571,649, now U.S. Pat. No. 3,516,787.

When the oil shale in chimney 6 is completely retorted and the combustion zone reaches the bottom of the chimney, air injection can be ceased and an inert gas injected to quench burning. Suitable connections can be made to start ignition in chimney 6" thus beginning retorting while another contiguous chimney (not shown) can be preheated in the same manner as has been previously described.

This invention may be applied in many ways. in very thick oil shales sections there may be zones which are rich enough for profitable mining and above ground retorting. Such a zone would provide a natural access to the top or bottom of a section in which chimneys are to be developed. Thus, the process of the instant invention can be combined with a known above ground retorting process. In sections of lean shale which are too thick to be retorted in a single chimney without the shapes of the chimney, three access tunnels can be originally formed and chimneys developed above and below the middle tunnel.

FIG. 3 illustrates an embodiment of the instant invention in which a chimney of great height can be developed in sections with choke points 18 left in the oil shale structure. At this smaller opening on choke point 18 the oil shale will bridge the opening as it is fragmented and limit the static load of the broken shale at any point in the chimney while still allowing a steady flow of gas and oil. The communication tunnels and drifts, although shown essentially round, can have many shapes.

The advantage of the process is that a large proportion of the oil shale in a given section or bed can be pyrolyzed in situ. This can be done at a fraction of the usual costs per ton for mining, hauling, crushing, handling to retort and spent shale disposal, investment in supply, ignition and recovery systems of the usual above ground retorting plant. The invention is further advantageous for processing leaner shales, operating in areas where disposal and other such problems would preclude surface or subsurface mining and utility and/or more efficiency in areas precluded for other in situ methods.

Also, if mineral dawsonite exists in the oil shale, it will be converted to soluble form by the temperatures of retorting and combustion. Thus, after retorting is completed, water or special solutions may be injected into the chimney to leach out the aluminum salt and soluble sodium salts as is more fully explained in the aforesaid Ser. No. 571,649. The liquor from this operation would be sent to recovery systems designed for this purpose.

While the process described herein has been directed particularly to the recovery of shale oil from oil shale, the present invention may be adopted for the recovery of oil from any subterranean oil-containing or oil-producing solid substance. Accordingly, it is to be understood that the above description is merely illustrative of preferred embodiments of the invention, of which many variations may be made within the scope of the following claims without departing from the spirit thereof.

The embodiments of the invention in which I claim an exclusive property or privilege are defined as follows:

1. A method of obtaining shale oil from a zone of unmined oil shale which comprises establishing access means at at least two points in said zone, establishing communication between these access means through the zone, fragmenting at least part of the oil shale in the zone in the area of the communication to produce a porous mass of fragmented oil shale, supplying heating means to said fragmented oil shale through one of said access points to pyrolyze shale oil in the oil shale and collecting said shale oil through the other of said access means.

2. The method of claim 1 wherein the establishing of communication between said access means includes establishing a cavity in the zone intermediate the access means and proximate to one of said access means in which it is in communication and establishing communication between said cavity and the other of said access means.

3. The method of claim 1 wherein said fragmenting is performed using explosives.

4. The method of claim 1 wherein the heating means is a gas.

5. The method of claim 4 wherein a second porous mass of fragmented oil shale is formed in another area of communication contiguous to the first porous mass and the gas from the first mass is transferred through the second porous mass to thereby preheat the second porous mass.

6. The method of claim 5 wherein the first porous mass is heated to a retorting temperature of from about 500 F. to 1,200 F. and the second porous mass is preheated to a temperature of from about 200 to 400 F.

7. The method of claim 1 wherein the oil shale in the zone is fragmented with two porous masses in the area of the communication separated by an unfragmented area of the communication.

8. The method of claim 1 wherein the pyrolyzed oil shale is treated with an aqueous solution to recover soluble mineral values contained in the pyrolyzed shale.

9. The method of claim 8 wherein the mineral values include quartz, dolomite and dawsonite, the aqueous solution is an alkaline solution, and the pyrolyzed shale is treated with the alkaline solution at a temperature of up to about 220 F. to dissolve aluminum values in said dawsonite without substantial precipitation of SiO,.

Claims

2. The method of claim 1 wherein the establishing of communication between said access means includes establishing a cavity in the zone intermediate the access means and proximate to one of said access meaNs in which it is in communication and establishing communication between said cavity and the other of said access means.
3. The method of claim 1 wherein said fragmenting is performed using explosives.
4. The method of claim 1 wherein the heating means is a gas.
5. The method of claim 4 wherein a second porous mass of fragmented oil shale is formed in another area of communication contiguous to the first porous mass and the gas from the first mass is transferred through the second porous mass to thereby preheat the second porous mass.
6. The method of claim 5 wherein the first porous mass is heated to a retorting temperature of from about 500* F. to 1,200* F. and the second porous mass is preheated to a temperature of from about 200* to 400* F.
7. The method of claim 1 wherein the oil shale in the zone is fragmented with two porous masses in the area of the communication separated by an unfragmented area of the communication.
8. The method of claim 1 wherein the pyrolyzed oil shale is treated with an aqueous solution to recover soluble mineral values contained in the pyrolyzed shale.
9. The method of claim 8 wherein the mineral values include quartz, dolomite and dawsonite, the aqueous solution is an alkaline solution, and the pyrolyzed shale is treated with the alkaline solution at a temperature of up to about 220* F. to dissolve aluminum values in said dawsonite without substantial precipitation of SiO2.