CA1232196A - Method for recovering mineral values from a subterranean formation through wellbores penetrating the formation from tunnels - Google Patents

Abstract

ABSTRACT
A method for recovering mineral values from a mineral bearing subterranean formation penetrated by a plurality of wellbores by (a) positioning a shaft from the surface to a subterranean formation lying generally parallel to the mineral bearing formation; (b) positioning at least two tunnels in the subterranean formation with the tunnels being spaced apart a selected distance and in communication with the shaft; (c) positioning wellbores to penetrate the mineral bearing sub-terranean formation from the tunnels; (d) injecting a fluid through at least a portion of the wellbores penetrating the mineral bearing subterranean formation from a first tunnel to enhance the recovery of mineral values from at least a portion of the wellbores penetrating the mineral bearing formation from a second tunnel; and (e) recovering mineral values from at least a portion of the wellbores penetrating the mineral bearing formation from the second well.

Description

METHOD FUR RECOVERING MINERAL VALUES EROS A
SUBTERRANEAN FORMATION THROUGH WHEELBASE
_ PENETRATING THE FORMATION FROM TUNNELS
This invention relates to processes for the recovery of mineral values from a subterranean formation by the use of mining techniques in combination with drilling techniques.
This invention further relates to the recovery of mineral values from a subterranean formation by the use of wheelbarrows penetrating the subterranean formation from tunnels.
This invention further relates to the recovery of mineral values from a subterranean formation by the use of well-bores penetrating the subterranean formation from tunnels and the use of injected fluids to enhance the recovery of mineral values from the subterranean formation.
Many deposits of minerals are known which are not readily recovered by the use of conventional mining techniques or by conventional drilling techniques. Such deposits may be metal ore deposits, hydrocarbon deposits and the like. The factors inhibiting the recovery of -these mineral values from such subterranean formations may be economic, technical and/or environmental. For instance, it may be impractical from an economic or technical point of view to actually remove material from the subterranean formation for processing either under-ground or at the surface to recover mineral values from the material. Such impracticality may arise for a variety of reasons, such as the relative value of the mineral recovered, the cost of the removal and recovery step, the quantities of mineral contained in the reserve, the grade of the metal ore and the like. In other instances, it may be extremely undesir able that the surface be disturbed above the subterranean deposit. In such instances, drilling from the surface is impractical Further, in many instances, when the injection of to Jo a fluid to enhance recovery of the mineral values is required the well spacings required for the effective use of the fluid may be so close as to he prohibitively expensive. In some environments such as in Alaska and other areas where permafrost is present, the difficulty in positioning, maintaining and operating drilled wells is well known. While such can be accomplished, it tends to be relatively expensive. As a result of these and other factors, many deposits are known which are not readily mined or produced by either conventional mining or by conventional drilling techniques.
Mineral reserves which may be recovered by -the use of an injected fluid to enhance recovery are metals such as gold, silver, uranium, copper and the like which may be recovered from subterranean formations by leaching or other fluid contact with the formation, oils such as crude oil, heavy crude oils carbon Nazis material from tar sands, shale oils and the like, Such deposits are known in a variety of locations and the reasons for the difficulty in the recovery of the mineral values from such deposits are as varied as are the number of deposits. The difficulties may arise from the location of the formation, such as in a difficultly accessible area, the depth of the formation, the neology of the particular region, special surface conditions such as permafrost, water, ice, ice floes and the like.
Efforts have been made in some instances to recover mineral values from such subterranean deposits by processes which are described in various publications referring to oil mining. These articles refer to the recovery of oil by various techniques which seek to combine mining and conventional drilling techniques. considerable effort has been directed to the development of such methods and a variety of such methods are shown in the following references which were considered in the preparation of this application:

~;~3~9~
US Patent No 1,506j920 issued September I 1924 to DeChambrier 1,63~,235 issued June 28, 1~27 to Ryan 1,S34,236 issued June OR 9 1927 to Ryan 1,660,187 issued February I 1928 to Erupt 1,667~269 issued April I 1928 to Ryan 1,722,679 issued July 30, 1929 to Ryan 1,735,481 issued November 127 1929 to Urn 1,811,560 issued June 23, 1931 to Ryan 1,811,561 issued June 23, 1931 to Ryan 17812,305 issued June 30, 1931 to Ryan 1,851,446 issued March 29, 1932 to Ryan 1,935,643 issued November 21, 1933 to Laughlin

2,331,072 issued October 5, 1943 to Hansen et at.
2,989,294 issued June 20, 1961 to Coyer 4,099,783 issued July 11, 1978 to erupt et at.
4,165,903 issued August 28, 1979 to Combs ~,201,420 issued May I 19~0 to Luckily en at.
4,227~743 issued October 14, 1980 to Ruin en alto 4,265,485 issued May 5, 1981 to Boxer man en alp 4,283~088 issued August 11, 1981 to Tabakov e and toil Mining A Technical and Economic Feasibility Study of Oil Production by Mining Methods r Final Report on Contract Jo. Joy (USE Department of the Interior, Bureau of Mines colder Associates, October 1978.

mining for Petroleum: Feasibility Study Final Report on Contract No J0275002 Us department of the Interior Bureau of Mines) Energy Department Consultant Inc., July 1978.

toil Mining, WIFE. Reed Jar Junk 1~79, FE-2468-42 (available from NITS
kern River Hot Plate Project Launched, I. Williams, Oil and Gas Journey August 23~ 1982.

While these references show a variety of processes utilizing a combination of mining and drilling techniques for the recovery of oil from subterranean formations there has been little commercial use of such techniques and a continuing search has been directed to the development of imp proved techniques of this type which may be efficiently and effectively used to recover mineral values from subterranean formations.
According to the present invention 7 such mineral values may be recovered from such mineral bearing subterranean Lo formations by a method consisting essentially of pa) positioning a shaft from the surface to a subterranean formation, the sub-terranean formation being positioned generally parallel to the mineral bearing subterranean formation; (b) positioning at least two tunnels in the subterranean formation, the tunnels being spaced apart a selected distance and in communication with the shaft; (c) positioning wheelbarrows to penetrate the mineral bearing subterranean formation from the tunnels; (d) injecting a fluid through at least a portion of the wheelbarrows penetrating the mineral bearing subterranean formation from a first tunnel to enhance the recovery of mineral values from the mineral bearing subterranean formation via at least a portion of the wheelbarrows penetrating the mineral bearing sub-terranean formation from a second tunnel; and (e) recovering mineral values from at least a portion of the wheelbarrows penes treating the mineral wearing subterranean formation Eros the second tunnel.
Such methods are particularly effective when the mineral values to be recovered are hydrocarbonaceous materials such as crude oil, heavy oils, carbonaceous materials from tar sands and the like.
Figure 1 is a cross-sectional schematic diagram of an embodiment of the present invention;
Figure 2 is a topographical schematic diagram of the embodiment of the present invention shown in Figure l; and Figure 3 is a topographical schematic diagram of wheelbarrows positioned in selected tunnels from the embodiment shown in Figure 2.
In the discussion of the Figures, the same numbers will be used throughout to refer to the same or similar combo-nonwhites I

The invention will be discussed by reference to the recovery of oil from an oil wearing subterranean formation, although it will be readily understood that the invention is also useful for the recovery of other mineral values from subterranean formations containing such mineral values, as will be discussed hereinafter.
In Figure 1, a shaft 24 is positioned from the surface 12 through a permafrost zone 14, overburden 18, and an oil bearing formation 10 into a non-oil bearing formation 20. A
main tunnel I joins shaft I at its lower end and extends horizontally into formation OWE A plurality of access tunnels I intersect main tunnel 26 at substantially right angles and a plurality of wells 3Q are drilled into oil bearing formation 10 from tunnels 34. As shown in Figure 1, a second oil bearing formation 22 lies beneath formation 20. Oil can be recovered from formation 22 via a plurality of wheelbarrows 32 which are drilled to penetrate second oil bearing formation 22 from tunnels 34. It will be appreciated that the method of the present invention is equally applicable to the recovery of oil from oil bearing formations which lie above or below the format lion in which the tunnels are positioned. Desirably, formation 20, in which the tunnels are positioned, is a consolidated or semi consolidated formation and preferably contains no oil.
While the method of the present invention could be used even if oil was present in formation 20, it is greatly preferred that formation 20 contain substantially no oil. While it is preferable that formation 20 be consolidated, various mine con-struction techniques such as shields, pressure tunnel linings and the like can be used i-F formation 20 is not consolidated.

Such techniques are considered to be well known to those skilled in the art and will not be discussed further.

In Figure 2, a topographical view of an embodiment of the present invention is shown. Shaft 24 is a main shaft for access to the oil mining operation. Main tunnel 26 and a lateral main tunnel 28 extend from shaft 24 with a plurality of access tunnels 34 being positioned at substantially tight angles to main tunnel 26 at desired spacings. Outer access tunnels 36 and additional vent shafts 38 are provided for both safety and ventilation reasons. The arrangement of the main shaft, main tunnels, access tunnels and ventilation shafts can vary widely depending upon the size of the particular oil mining operation and a variety of other considerations as known to those skilled in the art. For instance, more than one main shaft may be used.
The primary considerations are operating access, safety access to an escape shaft from all points in the oil mining area and adequate ventilation in the tunnels. Fire doors for isolating sections of the mine in emergencies etc. are desirably positioned at strategic locations in the mine as known to those skilled in the art While a rectangular layout is shown, it should be appreciated that the method of the present invention can equally well be used with a variety of configurations although it is preferred that tunnels 34 be substantially parallel.
In the practice of the method of the present invention for crude oil recovery from formation 10, an injection fluid may be injected from the wells in a first tunnel, for instance, injection wheelbarrows 48 positioned in a tunnel I as shown in Figure 3. The spacing of injection wells I in tunnel I is shown in Figure 3 as well as the spacing of production wells 50 in a tunnel 42. It will be recognized that the use of fluid injection to recover oil from subterranean formation 10 can be accomplished in a variety of ways once access to formation 10 has been achieved. In general, fluid is injected into injection wells I to enhance the recovery of crude oil from production wells 50. When injection wells 48 are closely spaced, a goner-ally flat front of injection fluid sweeps through the area of formation 10 between tunnels 40 and 42 pushing oil toward pro-diction wells 50 from which it is recovered. When the recovery of oil from production wells 50 declines indicating at least partial depletion of the oil contained in formation 10 between tunnels I and 42, production wells 50 may be closed in and injection continued through injection wells 48 to enhance the recovery of crude oil from production wells 52 in tunnel 44.

Crude oil may also be recovered from production wells 50 and 52 simultaneously. This sequence of operations could be continued by switching the injection to injection wells 54 in tunnel 46 when the oil has been depleted between tunnels 40 and 44. In a further variation, production could be continued from product lion wells 50 as fluid is injected through injection wells I
Optionally, fluid could continue to be injected through inject lion wells 48 thereby continuing production at reduced levels from production wells 50. A variety of such production tech-piques can be used.

In the use of production techniques which initiate oil recovery from the ends of the zone of formation 10 to be produced from the tunnels, drilling and piping work is normally performed beneath zones which have not yet been produced, i.e.
heated.
Some advantages of the present method are that with the tunnels positioned a relatively short distance from the oil bearing formation, a large number of wells can be drilled relatively inexpensively so that the injected fluid can be effectively injected into substantially the entire formation to enhance the recovery of oil. this permits the use of a flat I

front sweeping effect between the tunnels Such techniques are known to be effective in the recovery of oil from subterranean formations, In some instances, it may be found that no such fluid injection is required, at least initially, for the recovery of oil from formation 10. In such instances, the oil may be allowed to flow naturally from formation 10 through both the injection and the production wheelbarrows until such time as enhanced recovery is required. Enhanced recovery may be accomplished as discussed above or by a variety of other techniques known to those skilled in the art.

The present method involves a minimal number of shafts passing from the surface to the production zone, i.e. shafts I and I Such is extremely advantageous when operations in permafrost regions are considered For instance, the injection of hot fluids or the recovery ox hot fluids from a subterranean formation tends to cause the permafrost to melt and collapse in the vicinity of the Wilbur While techniques are known for minimizing or preventing such melting and collapse in per ma-frost zones, they involve added expense and may be prohibitively expensive when close well spacings are necessary In the present method, any pipes which carry warm fluid in communication with the surface can be insulated and positioned inside one of the shafts so that no direct contact with the permafrost is necessary. Even if such lines are positioned through the per ma-frost, the insulation of a few such lines is a much simpler matter than is the insulation of a large number of wheelbarrows.
The use of a minimal number of shafts is also advantageous when the surface above the mineral bearing formation is underwater, subject to ice, ice floes and the like The fluid injected may be water, steam, COY, heated gas, hydrocarbon gases, flue gases, aqueous surfactant solutions muzzler solutions or the like alone or in conjunction with saline solutions, thickened water and other materials known to those skilled in the art for use in secondary and tertiary recovery of oil from subterranean formations By the method of the present invention, access to the subterranean oil bearing formation is accomplished so that such methods may be practiced using close well spacings.
As discussed, it is desirable that tunnels 34 be substantially parallel, although such is not required. Goner-ally, when parallel access tunnels are used, it is anticipated that substantially uniform conditions prevail in formation 10 between the parallel access tunnels so that relatively uniform sweeping action is accomplished. If such is not the case, the tunnels can be spaced in other configurations and the like as required to effectively recover oil from the particular format lions from which oil is to be produced.
The wheelbarrows are desirably positioned at a plurality of spaced-apart locations in the tunnels. The positioning of the wheelbarrows can vary widely so long as the penetration of the oil bearing formation is at the desired locations.
By the use of tunnels as discussed above, close well spacings can be used. Close well spacings are necessary in many instances to insure adequate injected fluid contact with the oil bearing formation. Well spacings will vary widely dependent upon the particular formation. Typically, the well spacing along the tunnels will be at least about 100 feet, although closer spacings can be used if necessary or desirable. The tunnel spacings may also vary widely dependent upon the particular formation.
Typically, the tunnels will be at least about 1000 feet apart, although closer spacings can be used if necessary or desirable The determination of proper well and tunnel spacings for the specific fluid injected and method used for a part-cuter formation is considered to be within the skill of those in the art when access to the formation has been accomplished.
The wheelbarrows may be drilled, cased and completed using standard drilling and casing techniques, including the use of blowout preventers and the like as necessary. The casings are cemented, grouted or the like to prevent the leakage of oil or fluids into tunnels I Suitable valving and piping is provided to inject or recover fluids or oil from the well-bores in the sequences desired. Such operations are considered to be known to the art and will not be discussed further except to note that a closed system is desirably used for drilling wells upwardly into formation 10 from the tunnels.
When heavy oil is to be recovered, a variation in the above process may be desirable. heavy oil as used in this discussion generally refers to petroliferous materials which are so viscous that they do not drain from or move readily within the formation in which they are contained at the temper azure at which they naturally exist. Clearly, if such heavy oils are to be recovered, some sort of enhanced recovery is necessary. In a preferred embodiment of the present method, fluid injection is initiated in injection wells pa and oil is recovered from injection wells 48 until a portion of the oil in zones 56 above tunnel I is recovered Such processes are known to the art and may be accomplished by the use of separate fluid injection and production lines through each Wilbur; by the use of huff-and-puff techniques or the like. Such oil recovery from zones 56 may be accomplished by injecting fluid through alternate injection wheelbarrows 48 and recovering heavy oil from the other injection wheelbarrows. A variety of such techniques can be used to recover at least a portion of the oil from the I
area above tunnel 40. The objective of such recovery is to increase the apparent permeability of oil bearing formation 10 above tunnel 40. Similar techniques may be used to recover at least a portion of the oil from the area above tunnel I if de-sired. After a portion of the heavy oil sufficient to increase the apparent permeability above tunnel 40 has been removed from formation 10 above tunnel 40, fluid injection can be initiated and a flat front can be used to sweep the area between tunnels I and I as discussed previously. The increased apparent per-mobility in the area above tunnel 40 tends to facilitate Eluidmovement from the area above tunnel 40 toward tunnel I as a flat front. If the heavy oil is not removed at least in part from the area of formation 10 above tunnel 40, an irregular sweep front may result with resulting reduced efficiency in the recovery of heavy oil from subterranean formation 10. As noted previously, it may also be despicable to remove a portion ox the heavy oil from the area above tunnel 42 prior to the use of the fluid sweep. The recovery of heavy oil from remaining sections of the formation may be accomplished as discussed previously by a variety of techniques known to those skilled in the art. For instance in the recovery of heavy oils, the use of healed fluids is common with steam being a particularly preferred fluid. Other fluids such as flue gases carbon dioxide, light hydrocarbons and the like can also be used. In some instances, in situ come bastion may be used. Such techniques are considered well known to those skilled in the art and suitable for use in the practice of the method of the present invention.
As will be appreciated by those skilled in the art, the use of such methods as discussed above is extremely Defoe-cult unless the subterranean formation can be reached by well-bores on a relatively close spacing.

~fd32~9~i As discussed above the fluids used may be water, steam, COY, heated gas hydrocarbon gases flue gases, aqueous surfactant slurries, muzzler solutions and the like, either alone or in conjunction with saline solutions, hackneyed water and other materials known to those skilled in the art for use in secondary and tertiary recovery of oil f rum subterranean formations.
The shafts may be formed by freeze drilling by blind hole boring and the like and cased and/or otherwise completed as known to those skilled in the mining arts. The tunnels may also be formed by conventional mining techniques including mine construction techniques such as shields "linings of various types for the tunnels and the like especially in the event that formation 20 is not consolidated, Other minerals may also be recovered by the method of the present invention using suitable injection fluids. Fur instance, in the recovery of uranium the injection fluid typic gaily comprises an aqueous solution containing ammonium, sodium or potassium carbonates and/or bicarbonates in conjunction with an oxidant such as air, oxygen hydrogen peroxide and the like.
Some such surface leaching processes for uranium leaching are disclosed in US. Patents 4,066,297; r4,082,359; 4,083,6~3; and 4,105,~53, When copper it recovered, the fluid may comprise aqueous solutions containing mineral acids such as sulfuric acid, ammonium carbonate,~ferric sulfate eureka chloride bacterial leaching with oxygen and the like. When gold or silver it recovered Thor 9 cyanides and the like may be used. The practice of the method is substantially the same as that described above for the recovery of oil from subterranean formations. It will be appreciated that a variety of methods ~32~

and tunnel configurations can be used to optimize the effective-news of the fluid contact with the subterranean formation once access to the mineral bearing formation is achieved by the present method.
As shown in Figure 1, tunnels I may be above or below or between subterranean mineral bearing formations. The practice of the present method is substantially the same in either event. In other words, the method is practiced equally well when the mineral bearing formation is above access tunnels 34 or below access tunnels 34, or in some instances, above and below.
As discussed previously, the wells may be drilled and cased as necessary by conventional well drilling techniques and may include the use of blowout preventers and the like Such techniques are considered to be well known to those skilled in the art and need not be discussed in detail While Figure 1 has shown a permafrost zone, it should be appreciated that the use of the present method is not so limited.
The injected fluid used may be produced, recovered and/or recycled by treating facilities in the subterranean zone or by facilities at the surface. For instance, if steam is used, it may be desirable to produce the steam in a subterranean chamber and in some instances, it may be desirable to inject the flue gas into formation 10 as well as the steam. Such variations are subject to a number of considerations known to those skilled in the art and need not be discussed in detail.
rho method of the present invention is not dependent upon the source of the injected fluid. Similarly, the produced oil may be piped to a storage or treating facility in a subterranean zone or directly to the surface and storage facilities or transportation. The method of the present invention is not dependent upon the method chosen for the handling of the oil so produced.
Having thus described the present invention by refer-once to its preferred embodiments, it is pointed out that the embodiments described are illustrative rather than limiting in nature and that many variations and modifications are possible within the scope of the present invention. Many such variations and modifications may be considered obvious and desirable by those skilled in the art upon a review of the foregoing description of preferred embodiments.

Claims (21)

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

1. A method for recovering heavy oil from a heavy oil bearing subterranean formation penetrated by a plurality of wellbores, said method consisting essentially of:
(a) positioning a shaft from the surface to a subterranean formation, said subterranean formation being positioned generally parallel to and above said heavy oil bearing subter-annean formation;
(b) positioning at least two tunnels in said sub-terranean formation, said tunnels being spaced apart a selected distance and in com-munication with said shaft;
(c) positioning said wellbores to penetrate said heavy oil bearing formation from said tunnels;
(d) creating a zone of increased apparent permea-bility in said heavy oil bearing formation beneath a first tunnel;
(e) injecting a fluid through at least a portion of the wellbores penetrating said heavy oil bearing subterranean formation from said first tunnel to sweep said heavy oil from said heavy oil bearing formation toward a second tunnel; and (f) recovering said heavy oil and at least a portion of said injected fluid from at least a portion of said wellbores penetrating said heavy oil bearing formation from said second tunnel.

2. The method of Claim 1 wherein said fluid comprises steam.

3. The method of Claim 1 wherein said fluid com-prises an aqueous surfactant solution.

4. The method of Claim 1 wherein said tunnels are generally parallel.

5. The method of Claim 1 wherein a plurality of tunnels are used.

6. The method of Claim 5 wherein alternate tunnels are used for fluid injection and heavy oil recovery.

7. The method of Claim 1 wherein said zone of increased apparent permeability is created beneath said first tunnel by injecting said fluid into at least a portion of said wellbores penetrating said heavy oil bearing formation from said first tunnel and recovering at least a portion of the heavy oil in said heavy oil bearing subterranean forma-tion beneath said first tunnel through at least a portion of said wellbores penetrating said heavy oil bearing formation from said first tunnel.

8. The method of Claim 7 wherein said zone of increased apparent permeability is created beneath said second tunnel by injecting said fluid into said wellbores penetrating said heavy oil bearing formation from said second tunnel and recovering at least a portion of the heavy oil in said heavy oil bearing formation above said second tunnel through at least a portion of said wellbores penetrat-ing said heavy oil bearing formation from said second tunnel.

9. The method of Claim 7 wherein said fluid is steam.

10. The method of Claim 8 wherein additional quantities of said fluid are injected into said wellbores penetrating said heavy oil bearing formation after said por-tions of said heavy oil beneath said first tunnel and said second tunnel have been recovered to enhance the recovery of heavy oil from said wellbores penetrating said heavy oil bearing formation from said second tunnel.

11. The method of Claim 8 wherein said fluid is steam.

12. A method for recovering heavy oil from a heavy oil bearing subterranean formation penetrated by a plurality of wellbores, said method consisting essentially of:
(a) positioning a shaft from the surface to a subterranean formation, said subterranean formation being positioned generally parallel to and beneath said heavy oil bearing sub-terranean formation;
(b) positioning at least two tunnels in said sub-terranean formation, said tunnels being spaced apart a selected distance and in communication with said shaft;
(c) positioning said wellbores to penetrate said heavy oil bearing formation from said tunnels;
(d) creating a zone of increased apparent permea-bility in said heavy oil bearing formation above a first tunnel;
(e) injecting a fluid through at least a portion of the wellbores penetrating said heavy oil bearing subterranean formation from said first tunnel to sweep said heavy oil from said heavy oil bearing formation toward a second tunnel;
and (f) recovering said heavy oil and at least a portion of said injected fluid from at least a portion of said wellbores penetrating said heavy oil bearing formation from said second tunnel.

13. The method of Claim 12 wherein said fluid comprises steam.

14. The method of Claim 12 wherein said fluid comprises an aqueous surfactant solution.

15. The method of Claim 12 wherein said tunnels are generally parallel.

16. The method of Claim 12 wherein a plurality of tunnels are used.

17. The method of Claim 16 wherein alternate tunnels are used for fluid injection and petroleum recovery.

18. The method of Claim 12 wherein said zone of increased apparent permeability is created by injecting said fluid into at least a portion of said wellbores penetrating said heavy oil bearing formation from said first tunnel and recovering at least a portion of said heavy oil in said heavy oil bearing subterranean formation above said first tunnel through at least a portion of said wellbores penetrat-ing said heavy oil bearing formation from said first tunnel.

19. The method of Claim 18 wherein a zone of in-creased apparent permeability is created above said second tunnel by injecting said fluid into said wellbores penetrating said heavy oil bearing formation from said second tunnel and recovering at least a portion of the heavy oil in said heavy oil bearing formation above said second tunnel through at least a portion of said wellbores penetrating said heavy oil bearing formation from said second tunnel.

20. The method of Claim 19 wherein additional quantities of said fluid are injected into said wheelbores penetrating said heavy oil bearing formation after said por-tions of said heavy oil above said first tunnel and said second tunnel have been recovered to enhance the recovery of heavy oil from said wheelbarrows penetrating said heavy oil bearing formation from said second tunnel.

21. The method of any of claims 18, 19 or 20 wherein said fluid is steam.