Method For The Recovery Of Shale Oil

Abstract

A method for recovering shale oil from a subterranean oil shale formation by forming a rubbled zone therein and emplacing first and second layers of fluid therein. The first fluid layer overlies the second fluid layer which is of a higher specific gravity and is largely immiscible therewith. A shale oil-extractive fluid of a specific gravity intermediate that of the first two fluids is then circulated through the zone between the first and second layers and in contact therewith until shale oil is entrained in the shale-oil extractive circulating fluid layer. Shale oil is then recovered from the shale oil-extractive fluid.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the recovery of hydrocarbons from relatively impermeable subterranean earth formations. More particularly, it relates to oil shale recovery by in-situ retorting and/or kerogen conversion within a rubbled portion of a subterranean oil shale formation.

2. Description of the Prior Art

Large deposits of oil in the form of oil shale are found in various sections of the United States, and, particularly, in Colorado and surrounding states and in Canada. Various methods of recovery of oil from these shale deposits have been proposed and the principal difficulty with these methods is the high cost which renders the recovered oil too expensive to compete with petroleum crudes recovered by more conventional methods. The in-situ retorting or conversion of oil shale to recover the oil contained therein is made difficult because of the non-permeable nature of the oil shale and the difficulty of applying heat thereto without extensive mining or drilling operations. The mining and removal of the oil shale for retorting of the shale in furnaces outside the formation is commercially uneconomical in most cases.

SUMMARY OF THE INVENTION

It is an object of this invention to provide an economical in-situ recovery method for recovering shale oil from a subterranean oil shale formation.

It is a further object of this invention to provide a method of using largely immiscible fluids of divergent specific gravities to remove shale oil from rubbled oil shale formations.

It is a still further object of this invention to provide an in-situ oil shale recovery method wherein the zone of activity within a rubbled zone formed in an oil shale formation may be controlled.

These and other objects are preferably accomplished by forming a rubbled zone within a subterranean oil shale formation and emplacing first and second layers of fluid therein. The first layer overlies the second layer which is of a higher specific gravity and immiscible therewith. A shale oil-extractive fluid of a specific gravity intermediate that of the first two fluids is then circulated through the zone between the first and second layers and in contact therewith until shale oil is entrained in the circulating fluid layer. Shale oil is then recovered from the circulating fluid layer.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a vertical cross-sectional view of an oil shale formation prior to detonating a relatively high energy explosive device within the formation;

FIG. 2 is a vertical cross-sectional view of the oil shale formation of FIG. 1 after the explosive device has been detonated;

FIG. 3 is a vertical cross-sectional view of the final rubbled zone created by detonating the explosive device of FIG. 1;

FIG. 4 is a vertical sectional view of a method of treating the rubbled zone of FIG. 3 in accordance with the teachings of my invention; and

FIG. 5 is a vertical sectional view of an oil recovery process applied to the treated rubbled zone of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a subterranean oil shale formation 11 having a relatively high energy explosive device 12 located within the formation 11. The device 12 may be either nuclear or non-nuclear; if a nuclear device is detonated within the oil shale formation 11, a strong shock wave from the nuclear device begins to move radially outwardly, vaporizing, melting, crushing, cracking and displacing the oil shale formation 11. After the shock wave has passed, the high pressure vaporized material expands, and a generally spherical cavity 14 (FIG. 2) is formed which continues to grow until the internal pressure is balanced by lithostatic pressure. The cavity 14 persists for a variable time depending on the composition of the oil shale formation 11. The cavity roof 20 then collapses to form a "chimney" or rubbled zone 15 (FIG. 3). Collapse progresses upwardly until the volume initially in cavity 14 is distributed between the fragments of the oil shale of formation 11. The size of the substantially cylindrical rubble zone 15, formed by the collapse of the cavity 14, may be estimated from the fact that the initial cavity 14 (FIG. 2) expands until the pressure within the cavity is about equal to the lithostatic pressure.

A zone of permeability 17 within and around the fragmented oil shale formation is formed surrounding the chimney 15 as can be seen in FIG. 3. If desired, the permeability of the zone 17 may be increased by surrounding the primary explosive device of FIG. 4 which forms the central cavity with a plurality of devices of lesser explosive energy, subsequently detonated in the manner disclosed in U.S. Pat. No. 3,448,801.

A subsequently void space 18 is formed at the top of the chimney of rubble 15. When used throughout this specification, the terms "fragmented zone" and "fragmented zone of rubble" refer to the rubbled zone 15 or any other rubbled or fracture-permeated zone formed by any means well known in the art. For example, although the formation of a specific type rubbled zone has been discussed hereinabove, such a rubbled zone may be formed by any means well known in the art.

Referring now to FIG. 4, a well bore 1 is extended through over-burden 16 into communication with fragmented zone 15. Well borehole 1 is preferably cased at casing 2 which may be cemented therein, if desired (not shown). An annulus outlet 3 is disposed at the top of casing 2. A tubing string 4 is disposed in well borehole 1 packed off at packing means 5. Casing 2 is perforated at perforation 6. In this manner, fluid may be injected down tubing string 4, past packing means 5 and out the bottom of the casing 2 into zone 15. In this fashion the fragmented zone 15 may be filled with either fluid layers 7 or 8 displacing the fluid initially present in the fragmented zone 15 out perforation 6 up the annulus and out the annulus outlet 3. By means well known in the art, varying proportions of fluid layers 7 and 8 may be introduced and maintained in the fragmented zone 15. Because the fluid layers 7 and 8 are not totally miscible and have different specific gravities, they segregate into layers with the lightest fluid at the top. For example, the fluid of layer 7 may be a gas or mixture of gases such as water vapor, hydrocarbon vapor, carbon dioxide, nitrogen, etc., overlying a layer of water. Although the fluid layers 7 and 8 are shown in FIG. 4 as occupying approximately equal portions of zone 15, the relative proportions of such layers is a matter of choice and the boundary between the layers 7 and 8 may be located at any position within zone 15 by varying the relative amounts of fluids in the system. The system described for introducing the two fluid layers 7 and 8 into the fragmented zone 15 is only one of many possible choices involving one or more wells.

Referring now to FIG. 5, a preferred arrangement for producing shale oil from the fragmented zone 15 of FIG. 4 is illustrated. A well borehole 19 is extended through overburden 16 into communication with rubbled zone 15. The lower end of well borehole 19 is disposed substantially adjacent the juncture of layers 7 and 8. Well borehole 19 may be cased at least along the portion traversing the overburden 16 and oil shale formation 11, as at well casing 20, with casing 20 cemented therein, if desired (not shown), as is well known in the art. Well borehole 19 is preferably equipped with a tubing string 27, packed off from casing 20 as at packer 24.

A like well borehole 30 is also extended into zone 15 adjacent the juncture of layers 7 and 8. Well borehole 30 includes a casing 32 which may be cemented (not shown), if desired. A tubing string 33 is disposed in well borehole 30, packed off at packer 34. However, tubing string 33 and packer 34 may be eliminated, if desired. Although well borehole 30 is shown in FIG. 5, the well borehole of FIG. 4 may of course be used.

In operation, a shale oil-extractive fluid, such as a solvent, of a specific gravity intermediate that of the fluid within layers 7 and 8, is injected down well borehole 19, through zone 15 and in contact with layers 7 and 8 thus forming a third fluid layer 9. This injection is continued for a period of time sufficient to entrain shale oil in the circulating third fluid layer 9. Preferably, as illustrated, such fluid may be preheated as indicated by heater 31 so as to impart thermal properties thereto.

As the third fluid layer 9 circulates up tubing string 33 and out of well borehole 30, shale oil and gas entrained in the fluid recovered from the third fluid layer 9 pass through a heat exchanger 28 and into a separator 29. At this point, the shale oil and gas components are separated as is well known in the art. The recovered combustion-supporting gas may be recirculated from separator 29 through pump 26 and heater 31 as is also well known in the art.

By increasing or decreasing the total amount of the fluids in layers 7 and 8, such as gas and water, respectively, layer 9 may be moved vertically upwardly or downwardly through zone 15 so as to recover shale oil from various levels of zone 15. The layer 9 of solvent will always be between layers 7 and 8 thus the volume and direction of flow of the fluid in layer 9 may be controlled through zone 15. Improved recovery thus results over conventional full formation flush methods. The upper and lower layers, that is layers 7 and 8, may or may not be circulated as layer 9 is being circulated. This may be accomplished by extending well boreholes 19 and 30 through zone 15 and perforating at the desired fluid levels with subsequent fluid circulation therethrough (not shown), as is well known in the art. If desired, extractive properties may also be imparted to the fluids in layers 7 and 8.

The solvent or extractive fluid in layer 9 may be any liquid or gas which, by means of thermal, chemical and/or solvent action, interacts with the kerogen components of an oil shale to produce and entrain shale oil, as long as its specific gravity is intermediate that of the fluids in layers 7 and 8. Such a fluid may comprise steam, hot hydrocarbons, hot gases, and/or mixtures of such fluids with chemicals such as acids and/or organic solvents. This fluid may be heated by surface or borehole-located heating devices and/or by means of in-situ combustion within the shale formation. This extractive fluid may advantageously comprise or contain a solvent for the soluble mineral, such as a steam condensate or a hot aqueous solution or organic and/or inorganic acid, having a temperature, such as at least several hundred degrees farenheit. Where the kerogen-pyrolyzing fluid contains or forms aqueous components, its circulation through the treated oil shale formation 11 may enlarge the zone 15, by solution-mining the kerogen therein, while shale oil is being produced. Preheating the fluid in layer 9 also provides a significant reduction in the total amount of extractive fluid required.

Claims

I claim as my invention:

1. In a method for recovering shale oil from a subterranean oil shale formation comprising the steps of:

rubblizing a portion of said subterranean oil shale formation thereby forming a rubbled zone therein;

emplacing at least first and second layers of fluids in said zone, said first fluid layer overlying said second fluid layer and said second fluid having a specific gravity higher than said first fluid and being largely immiscible therewith; and

circulating a layer of a shale oil-extractive fluid having a specific gravity intermediate that of each of said first and second fluids through said zone between said first and second layers and in contact therewith until shale oil is entrained in said circulating extractive fluid.

2. The method of claim 1 including the step of imparting heat to said shale oil-extractive fluid prior to circulating it through said zone.

3. The method of claim 1 wherein the step of circulating a shale oil-extractive fluid through said zone includes the step of circulating a solvent through said zone.

4. The method of claim 1 wherein the step of emplacing a first fluid through said zone includes the step of circulating a gas therethrough and the step of emplacing a second fluid through said zone includes the step of circulating water therethrough.

5. The method of claim 4 including the step of moving said shale oil-extractive fluid layer upwardly within said zone by increasing the amount of water being circulated therethrough.

6. The method of claim 4 including the step of moving said shale oil-extractive fluid layer upwardly within said zone by decreasing the amount of gas being circulated therethrough.

7. The method of claim 1 including the step of recovering shale oil from said circulating shale oil-extractive fluid.

8. The method of claim 1 wherein the steps of circulating said shale oil-extractive fluid is carried out by the step of extending at least a pair of well boreholes downwardly through said zone; and circulating said shale oil-extractive fluid down one end of said well boreholes and out the other of said well boreholes.

9. The method of claim 1 including the step of moving said shale oil-extractive fluid layer vertically within said zone until shale oil is recovered from substantially the entire zone.