CA1063012A - Method of recovery of tar sands material - Google Patents

Abstract

METHOD OF RECOVERY OF TAR SANDS MATERIAL

Abstract of the Disclosure A method of recovery of tar sands material from a subterranean layer of such material underlying an overburden comprises sinking a pair of spaced apart mining strings from respective surface rigs down through the overburden and into the layer, and projecting from each string into the material of the layer a jet of water to soften and erode it whereby to form a cavity and generate a slurry of the material and the water. The water projected from the strings is 80 directed and the spacing of the strings is such that the cavities formed by the respective strings are caused to open into each other. The slurry is forced up the strings to the surface for recovery of the material therefrom. The fact that the cavities open into each other enables the slurry forced up one string to be largely the result of water projected from an adjacent string thus minimising the need for a reversal of flow with consequent loss of kinetic energy. The arrange-ment is also conducive to the use of an entire array of strings.

Description

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This applica~ion is a division of appl~cation Serial No. 216,734 filed December 23, 1974.
Tl~ invcnLIoll rclatcs to minlng and llas special re-ference to the recovery of oil-bearing deposits of the type commonly referred to as "bituminous sands" or "tar sands" and found in abundance in the Athabasca region of Alberta. While the mining of tar sands is the primary purpose of the present inven-tion, the method ~nd apparatus disclosed herein may have utility ' in the mining of other subterranean deposits especially those conducive to recovery by hydraulic mining techniques.
The so-called tar sands material consist of an intimate mixture of approximately 85% sand, 3-5~ water and the re-mainder heavy crude oil. The oil has a naphthenic base, is black in colour and contains a characteristically high percentage of sulphur, nitrogen and trace metals. By comparison with conventional crude oils it is a great deal heavier. The Athabasca Deposit con--tains more than 600 billion barrels of bitumen reserves in place.
The immense size of these hydrocarbon reserves has prompted exten-sive interest in their commercial development. Processes have al-ready been developed for separating this material from the sand and utilizlng it for refinement into petroleum products.
Deposits in Alberta of this material, subsequently referred to for convenience as "tar sands", are found typically in layers about 100 feet thick protected by an overburden of earth and rocky deposits (soil mantle and glacial drift). In some places the overburden is as thin as 50 to 100 feet. In other areas the - overburden increases to 600 feet, 1500 feet and even 2000 feet.
;~ The recovery of tar sands has so far been restricted to those areas in whlch the overburden is relatively thin, e.g. up to 100 feet, the overburden having been removed by 8crapers and large bucket wheel excavators and then hauled ln trucks to a 8uitable location for building dike8 or dumplng. ~his operation exposes the tar sands material whlch _. . ~ , . ! : ' .
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is then broken up and conveyed to a separation plant. ~n thc sepsration plant the tar sands msterial which at normal temperatureS is comparatively rlgid, cake-like material, is softened by treatment with hot water and steam to form a slurry from which the sand and the petroleum components are separated from each other by means of chemicals, water, air and floatation.
Subsequently the very fine particles are removed by centrifugal techniques. Such separation methods have already been devel-oped and need not be described in further detail herein. In this connection, reference may be had to "An Envlronmental Study of the Athabasca Tar Sands" prepared by Intercontinensal Engineering of Alberta Ltd. and published by Alberta Environment March 1973, especially page 71 et. seq.
The growth of the tar sands recovery industry has awaited conditions in which the recovery process might become more economlcal or demand for oil has resulted ln an lncreased price for crude oil and petroleum products generally. The excavation of tar sands has hitherto been limited to those areas in which the overburden is thin, both for reasons of economics and the technical difficulties involved in the removal of a thick overburden. Various methods have been suggested for recoverlng~-the deeper deposits of tar ssnds by methods that avoid the removal of ~he overburden, but none of these proposals has yet produced a commercial process that will overcome the practical tests of economics, englneering and especially a reasonsble percentage yield.
The primary ob~ect of the present lnvention is to provite a method for recovering deeper mineral deposits and especially deposits of tar sands materlal. Nowever, while the proposed method is desi8ned to be suitable for use ln the recovery of "deep" tar sands, namely those lying beneath a substantlally

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thick layer of overburden, e.g. at least 100 feet, lt should nevertheless be stressed that the method is equally suitable for the recovery of shallow deposits beneath an overburden of less than 100 feet.
In its broadest aspect the invention can be viewed as a method of recovery from a subterranean layer of a material conducive to hydraulic mining techniques, said layer underlying an overburden, comprising (a) sinking a pair of spaced apart mining strings from respective surface rigs down through the overburten and into said layer, (b) pro~ecting from each said string into the material of said layer a ~et of liquid to soften and erode said material to form a cavity therein while generating a slurry of said material and the liquid, (c) the liquid pro~ected from the strings belng 80 directed and the spacing of said strings being such that the cavities formed by the respective strings are caused to open into each other, and (d) forcing said slurry to the surface for recovery of said material therefrom.
Preferably, the method in a more specific form, involveg the further steps of continuing to erode the material and enlarge the cavities thereby formed until the material above the cavitie~
collapses thereinto, and cont~nuing to pro~ect the liquid from the strlngs to erode and form further cavities in the collapsed ~aterial. Preferably, the cavities are initially formed in a lower part of the layer of materisl, the eroding of the m8terial being continued and repeated until substantially all the material of the layer above the location of the i~itial cavitie~ has been eroded and removed as slurry.

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In a specific version of the method, a body of water is retained by dikes above the overburden and the rigs are floated on such water. After the bituminous components have been separated from the material, the spent sand and water (known as tailings) are discharged into thig body of water to form additional dikes or a surface layer over the overburden, or into ad~acent areas.
In a still further aspect of an embodiment of the inventiOD~
a plurality of further rigs are employed to sink corresponding mining strings spaced from each other in the form of an array.
The liquld projected from the strings is æo dlrected and the spacing of the strings is such that the cavities formed by the respective strings are caused to open into each other.
While the strings may be arranged in many different arrays, a convenient arrangement consists of parallel rows with the strings arranged in a staggered relationship between ad~acent rows. This arrangement has the effect that, with the exception of the strings forming the perimeter of the array, each string i8 surrounded by six sectors of the material with each sector abutting a complementary sector of an ad~acent string. This-assists the opening into each other of complementary sectors.
At this point, reference is made to the accompanying drawings which illustrate embodiments of a method of mining according to the present invention, together with apparatus suitable for use in carrying out such methods. It is to be emphasized that the invention is not limited to the details set forth in the drawlngs and the description thereof, but, in lts broad scope, is as deflned in the sppended claims.

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It should also be pointed out that certain features of the methods and apparatus disclosed below are claimed in the parent application referred to above and in a further divisional application Serial No. 3~ ~,916 filed concurrently herewith.

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In the drawings:- .
Figure 1 is a plan view of a recovery site on a small scale;
Figure 2 is a vertical section of a typical portion of `:
such site as seen on the line II-II in Figure l;
Figure 3 is an idealized diagram taken on a horizontal ., plane of a subterranean portion of Figure 1, on a larger scale;
Figures 4a to 4h are a series of diagrams illustrating, in a fragmentary and somewhat idealized form, the carrying out of a mining method;
Figure 5 is an elevation view of a minlng unit for use in carrying out this method;
Flgure 5a is a section taken on Va-Va in Figure 5;
Figure 5b is a section taken on Vb-Vb in Figure 5a;
Figure 6 is a side view of the assembly seen in Figure ~ .
5 taken on the line VI-VI in Figure 5;
~l Figure 7 is a central sectional view o~ the assembly of Figures 5 and 6 shown with the assembly in use;

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Flgllre 7a ls a section taken on VlIa-Vlla in Flgure 7;
Figure 8 i.~ a fragment of a lower portion oE Figure 7 showlng the parts in a different position;
Figure 8a is a section taken on VIIIa-VIIIa in Figure 8;
Figure 9 ls a section on the line IX-IX in Figure 7;
Figure 10 is a section on the line X-X in Flgure 7;
Figure 11 is a section on the line XI-XI in Flgure 7;
Figure 12 is a fragment of a central portion of a min-ing unit showing an alternative construction;
Figure 13 is a section on the line XIII-XIII in Figure 12;
Figure 14 is a plan view of an embodiment of a floating rig;
Figure 15 is a front elevation of the rig of ::-Fig. 14, partly in section, being taken on the line XV-XV in Flgure 16;
Figure 16 is a horlzontal section taken on the line XVI-XVI in Figure 15;
Figure 17 is a transverse section taken on the line XVII-XVII in Figure 16;
Figure 18 ls a horizontal section, on an enlarged scale,~ :~
taken on the line XVIII-XVIII in Figure 17;
Figure 19 is a fragmentary elevation view taken on the line XIX-XIX in Figure 18;

Figure 20 is a fragmentary section taken on the line XX-8X in Figure 18; . . .
Figure 21 ls an enlarged view of a terminal of the strlng, being a portion of the apparatus of Figure 17, shown as a vertical, central crosæ-section; ~.
. Figure 22 i9 a vertical section of a tilt sensor, taken on the llne XXIl-XXlI in Fig. 23;

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Fi~ure 23 is a horizontal scction taken on the line XXIII-XXIII in Fig. 22;
Figure 24 is a vertical section taken on the line XXIV-XXIV in Fig. 23;
Figure 25 is a front view generally similar to Fig. 22 demonstrating the operation of the sensor;
Figure 26 shows a hydraulic circuit for control by the sensor of Figs. 22 to 25;
Figure 27 is a fragment of Fig. 2 illustrating a modification;
Figure 28 is a fragment of Fig. 1 showing the modification of Fig. 27;
Fig. 29 is a central, vertical section through lower portions of the slurry conduit showing details thereof, this view representing the core of the mining unit of Fig. 7 on an enlarged scale and broken away;
Figure 30 ls an upward extension of Pig. 29;
Figure 31 is a section on the line XXXI-XXXI in Fig. 29;
Figure 32 is a front, fragmentary view, partly cut away, of a feature that may be included in the mining unit;
Figure 33 is a side, cut away, view of Fig. 32; ;~
Figure 34 is a side view of a clamp used in the mining unit of Figs. 32 and 33, shown alone;
Figure 35 is a plan view of the clamp of Fig. 34 also showing its relationship to a casing;
Figure 36 is an elevation view of an outer sleeve of a still further modified mining unit;
Figure 37 is a section taken on the line XXXVII-XXXVII
in Fig. 36;
Flgure 38 is a vertical central section of a modified inner sleeve to engage in the outer sleeve of Fig. 36;

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Figllrc 39 i9 .~ scction tnken on the l~ne XXXIX-XXXIX
in Fig. 38;
Figure 40 is a section taken on the line XL-XL in Fig. 38; and Figure 41 is a central section showing the lower parts of the sleeves of Figs. 36 and 38 engaged with each other.
THE OVER~LL SITE
With primary reference to Figure 2, it is assumed that the mining method is to be 'employed for the recovery of a layer 10 of tar sands material lying on a bed 11 of limestone.
It ls also assumed that the tar sands layer 10 is approximately 100 feet thick and is surmounted by an overburden 12 of earth J' and rock of a thickness of 1000 feet. These dimensions are given purely by way of example and in'no sense limit the applicability of the invention. They are provided to assist ~
an appreciation of typical relative dlmensions that must be ~-contended with in a mining operation of the present character.
Figure 2 also shows an ar'tificial pond 13 of water that' has been obtained from a nearby source, such as a river or natural lake, and confined above the overburden 12 of the ' recovery stie by dikes 14. The manner in which a series of such dikes 14 can be employed to form the pond 13 is perhaps best appreciated from Figure 1. The depth of water in the pond 13 could be typically 10 to 12 feet.
Floating rigs 15 are arranged on the pond 13, each rig 15 consi6ting baslcally of a floatlng pontoon 16 and a derrlck 17. One form of floatlng rlg i6 descrlbed below ln connection with Figs. 14 to 21.
As seen ln Figure 2, ad~acent pairs of pontoons 16 are interconnected by brldge structures 18 asslsted by further pontoons 19 Eloatlng on the pond 13. In the s~aller ocale vlew .

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-` 1063012 Q of Figurc l reference numeral 20 has been employed to designate in more general terms these connections between adjacent rlgs 15, which, it will be noted, have been arranged in three rows of seven or eight rigs. One purpose for these interconnections between the rigs is to carry pipeline assemblies 21 whereby each rig can be connected to a separation plant 22. More details of these pipeline assemblies 21 is given below.
Transverse or other stays or cables (not shown) may be used, as required, to ensure the desired spacing between the row~
of rigs and between the rigs and the surrounding dikes 14.
The rigs 15 shown in Figure 1 will be arranged as far apart as possible, so that a large area is covered, as will -become clear as the description proceeds.
STRUCTURE OF THF FIRST FORM OF MINING UNIT
A hydraulic mining string 30 (Figure 2) can be driven down by each derrick 17 in the usual manner of well drilling.
Alternatively, the hole can be drilled by a conventional drilling rig, the string 30 later belng inserted after a casing has been placed in the drilled hole.
At its lower end the string 30 is provided with a mining unit 31, such as shown in Figures 5 to 11.
Such mining unit 31 consists of an outer sleeve 32 carrying at its bottom end typical drilling cutters 33. As best seen in Figures 7 and 8, the outer sleeve 32 serves to house an inner sleeve 34, these sleeves being connectable together by means of claw assemblies 35. Figures 8 to 8a show the interconnected condition, this being the conditlon em-ployed during drilling or lowering of the strlng into a pre-drilled hole. Once the string 30 has been passed through the overburden 12 ant the tar sands layer 10 lnto the limestone bed 11 for a distance of about 10 feet (as shown in Figure 7) g_ tl~e claw .~seml)lies 35 will bc dlsengaged by a sllght counter-rotation of the string. High pressure fluid, e.g.
water applied through a line 36, is then forced into the cavity 37 between the respective lowet ends of the inner and outer sleeves 34, 32 to raise the inner sleeve 34 and hence the entire string 30 a short distance, as shown in Figure 7 ~ 7a. The purpose of this preliminary operation will become more apparent later from the description of the overall operation of the mining unit.
10The lower end of the inner sleeve 34 is the location of termination of the lower end of a recovery or "slurry" conduit 38 which extends along the centre of the minlng unit and `
ultimately continues up the full height of the string. This conduit 38 contains a series of impellers 39 driven by an axial drive shaft 40. Specific details are provided below ln relation to Figs. 29 to 31.
The upper portion of the inner sleeve 34 constitutes an .
inlet assembly 41 formed by a circumferentlally spaced series of vertically extending fixed vanes 42 which define a cage-like screenin~ structure servlng to admlt liquid, slurry or vlscous ~aterial, while preventing ingress of rock~ and other lsrger pieces of ~aterial. This inlet assembly 41 extends around the full circumference of the unit 31, providing an area for entry of the recovered slurry. This slurry passes -down an annular collection passage 43 defined between tbe inner sleeve 34 and the slurry condult 38, such collection passage 43 leading to a sump 44 at the closed bottom of the lower sleeve 34 at a location immed~ately below the lower end of the slurry conduit 38. Material received in the sump 44 i8 thus caused to begin a ~ourney up the condult 38 by the flrst of the impellers 39. This lower section of the mining . . : . , ' , ' ,. .' .; , . ;' . - ' " ; ' . ' " ' ' , ~
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unit, including tl~e inlet assembly 41, thus constitutes a collection assembly.
The upper section of the mining unit 31 above the inlet assembly 41 consists of a nozzle assembly 48 having a housing 45. These upper and lower sections of the mining unit 31 are interconnected by a portion of the slurry conduit 38 by flanges 202. Above the nozzle assembly 48, the string 30 conslsts of a supply or "water" condult 46 formlng a water supply space 47 between itself and a continuation 38' of the slurry conduit 38 of the mining unit.
The portion of the water conduit 46 which terminates in the nozzle assembly 48 supports a tapering nozzle 49 mounted to be pivotable about a horizontal axis between a lowered or "housed" position (as shown ln Figures 5, 7, 11 and in full lines in Figure 6) and an elevated or "pro~ecting" posltion (as shown in Figures 9 and 10 and in broken llnes in Figure 6).
Other positions intermediate these two extreme posltions are also posslble, movement of the nozzle 49 being controlled by a hydraulic cylinder and piston assembly 50 secured between the nozzle 49 ant the housing 45. As best seen from Figures 9 and 10, the water space 47 leads via por,tion 47a to the ln~
terior of the nozzle 49 (Figure 10).
Spaces in the housing 45 not occupied by the equipment already described have been designated generally by the reference numeral 51 in Figures 7, 9, 10 and 11. These spaces ' will be employed to house the control and monitoring devices -~
required. For example, a pump assembly has been shown d$agrammatically at 52 in a portion of the spaces Sl, such assembly 52 being connected to the pressure line 36 leadin 30 to the cavity 37. Slmllarly, a control valve 53 can be located ln a portion of spaces 51 for control of the cyllnder -` ~0630~2 and pi~oll n~cml~ly 50. Thcfic alld any othcr control and monitoring apparatus required will be connected to the surface by electric cables 160 and specific embodiments are described in more detail below.
At an appropriate time in the drilling operation, a fixed outer casing 54 (Fig. 2) is passed down the hole. When the string 30 is in place the casing 54 will be around the outer surface of the water conduit 46 to end ~ust above the housing 45, as shown in Pig. 7. This casing 54 serves to prevent excessive leakage from underground water streams and pond water and also restrains loose rock and earth of the over-burden 12 from entering the recovery area where the mining unit 31 is operating. The annulus between the water conduit 46 and the casing 54 provides space for instrument and control leads and steam conduits shown generally at 160.
OPERATION OF_THE MINING UNITS
Assuming that one of the mining units 31 has been brought to the condition shown in Figure 7, the liquid is pumped from the surface down through the conduit 47. This liquld will preferably be water carrying clay in suspenslon and may be near boiling temperature. The water temperature will be as found necessary effectively to form a slurry. Steam can also be forced down through separate conduits 160. A need for air may arlse to occupy the space of condensing steam and this air can flow down the annulus between the casing 54 and the water conduit 46. A water/clay suspension tends to be more effective ln its impact on the tar sands material than clear water would be, and also tends to flow with less turbulence. Its wei8ht also tends to assist the subsequent separation process. The water can also be made alkaline by the addition, for example, of sodium hydroxide. Thls alkalinity asslsts the subsequent sepaAration processes. For convenlence thls liquid wlll sub-' A_A

scquently be refcrred to simply ns "water".
Initially the tar sands material occupies the entire area embracing the mining unit 31 and hence it is impossible to raise the nozzle 49. It is thus necessary first to form a cavity around the area of the nozzle 49 by orcing hot water through such nozzle in the downward position while rotating the string. This hot water will mix with the tar sands material and soften it, while eroding a cavity in such mat-erial. The water will also flush the resultant slurry into the area round the inlet assembly 41, and such slurry will flow between the vanes 42 into the sump 44 to be pumped to the surface along the slurry conduit 38.
As this cavity is gradually enlarged, the nozzle 49 can be raised by the hydraulic assembly 50 to an upper position (broken lines in Figure 6) or to any semi-raised position.
Assuming the nozzle 49 has thus been eievated to its maximum raised positioD, it will now be used to blast out a tunnel, such as that shown in Figure 2 at 60. Such tunnel 60 can be expected initially to be only a few feet wide and a few feet high, and eventually to have a length from two to -three hundred feet. To achieve this the hot water will be forced out of the nozzle 49 at high velocity, e.g. using pumps, if necessary, and/or a static head as high as 500 pounds per square inch (at a depth of about a lO00 feet). The consistency of the tar ~ands material is such that no 8reat difficulty should be encountered in forming such elongated tunnel8. If desired, as a preliminary to the mining operation described herein, the area can be sub~ected to blasting in order to form cracks in the rock and tar sands material.

-13- ~ -~ s will be notcd ~rom Fi~ure 2, each tunnel 60 has been shown as slightly upwardly inclined away from the nozzle 49, upper arrows A representing in generallsed terms the flow of water ~hat is eroding the tar sand material to form the tunnels, while lower arrows B represent return flow of slurry to the respective inlet assemblies 41 of the mining units 31. Ideally, once communication between ad~acent tunnels 60 has been opened up, in order to avoid the need for a reversal of flow with consequent loss of kinetlc 10 - energy~ the flow of slurry to one minin~ unit 31, for example the left hand one in Fi~ure 2, will result primarily from the water ejected by an adjacent mining unit, such as -the one shown on the right in Pigure 2. In any event, the downward slope of the tunnels 60 towards the mining units 31 should be sufficient to ensure adequate return of the recoverable slurry to one or other of the mining units. On the other hand, it should preferably be gradual enough to tend to leave the larger chunks of rock found in the tar sands material in the tunnelt and to prevent these rocks pillng up ~ -around the inlet assemblles 41. It i9 important that the tunnel~ 60 do not fill up with water; otherwise the nozzles would not be able to throw ~ets of water the required distance. This situation can be achieved by correl~ting the rates of supPly of water and the removal of the resultin~
slurry, as well as by the admission to the underground site of appropriate quantities of air. Also, once the tunnels have become interconnected, the slopes of the tunnel floors can be reduced.
This permits the nozzles to be used to erode some of the floor material and recover at least some of the tar sands material ~hown for example below the tunnel~ 60 ln Fi8. 2.

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-- ~063012 ~ n advant.~ge of this process, compared with prior methods, is that it is no longer necessary to screen out oversize debris as part of the subsequent separation process, because such large debris either does not wash down the tunnels to the mining units, or, on reaching such units, is prevented from enterlng them by the screening effect of the inlet assemblies 41.
As Figure 2 demonstrates, each ad~acent pair of mln-ing units 31 will co-operate with each other, working in unison to form tunnels that eventually interconnect and feed from one to the other. While Figure 2 shows the formation of such inter-connected tunnels 60 in a direct line between the two mining units 31, the situation will be somewhat more complicated in practice, as will now be explained with the assistance of Figures 1 and 3.
Figure 3 shows one adjacent pair of mining units 31, the directly interconnecting tunnels 60 of Figure 2 bein-g here designated as 60d. Prior to the formation of tunnels 60d, similar tunnels 60a, 60b and 60c will have been formed. In fact, these will not be formed as individual tunnels but as widenings of each other. In one method of operation, tunnels 60d may be forméd `
first and then widened by slight rotation of the drill strings 30 to pro~ect the streams of water from the nozzles 49 at a slight inclination to the direct line between the pair of mining units 31.
The tunnels 60d would thus be enlarged laterally to form the tunnels 60c, 60b and finally 60a. Alternatively, the operation can start with tunnels 60a and move through to 60d. Essentially a slmilar type of lateral expansion operation will be carried out on the other side of the tunnels 60d, i.e. in the upper part of Figure 3. As a further alternatlve, tunnels can flrst be formed at separate locations, e.g. tunnels 60a ~ 60c, to produce a "Swiss cheese" effect, such separate tunnels latter being caused to - extend into each other by eroslon of the material therebetween, -.- , .
' ' - ~063012 c.g. tunnel 60b.
OVERALL OPERATlON
Figure 1 demonstrates the manner ln whlch the entire assembly of floating rigs will be coordinated to co-operate with each other. The area shown in Figure 3 is ~ypically a shaded sector desIgnate~ "1" between adjacent pairs of rigs ln Flgure 1.
At the same time, all the other rigs will be operating in their sectors designated 1. Subsequently, all the rigs wlll have the nozzles of their mining units turned to operate ln sectors 2;
then in sectors 3; and so on up to and lncluding sectors 6. It will be observed ~rom Figure 1 that, except around the edges of the site, each sector is opposed to a similarly numbered sector of an adjacent rig. By the time sectors 1 to 6 have been fully cut out, the entire area within this assembly of rigs will have been covered. At times some of the nozzles will be inoperatlve, since only those rigs extending down the central row of Figure 1 have 6 operative sectors. Obviously the layout of rigs can be varied and expanded as desired. A larger number of rigs achieves more complete utilization of each rlg, i.e. utilises more of its potential sectors.
When the tunnels 60 of Figure 2 are initially formed','~
the solidity of the tar sands material is such as to arch over, i.e. allow the formation of the tunnels without collapsing of the roof. Obviously, as the tunnels are expanded laterally, flrstly ln one of the manners discus'sed above in connectlon with Flgure 3 ~' and ultimately to lnclude-the entlre area covered by the rigs of Flgure l? the tunnel roofs will collapse. An entire slice of '~ material will have been "hosed" out, 80 that the upper part of the entire layer 10 must mo~e downwardly. As8uming that a complete ~llce of tar sands material about 8 feet deep had thus been removed from a lower part of the layer 10, the remainder of the layer 10 will have ~unk down by a correspondlng distance of about 8 feet . .
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togetl~er w~LII Lhe ovcrburdcn 12.
The operatlon ls contlnued by repeatlng the process.
Tunnels 60 are again formed in the same manner in the tar sands material that has sunk down, so that slice after slice of tar sands materlal is removed from near the lower surface of the layer 10.
If each removed slice is assumed to be 8 feet thick, it would require about twelve such operations to remove an entlre layer 10 about 100 feet thick. Obviously, the removal of each slice will not, in practice, form a discretely separate operation, since the ~0 processes of collapsing of the tar sands material and jetting out the collapsed material will take place to some extent simultaneously i.e. these operations will overlap and merge with each other.
It should be noted that the overburden does not sink down to the mining area until virtually all the tar sands material has been removed. It is only during removal of the last tar sands layer'that overburden will be encountered.
While operating conditions will undoubtedly vary, it has been estimated that the hosing or l'~etting" out of the tar sands material of one pair of sectors, such as the sectors 1 shown in Figure 3, would probably require continuous operation for between a day and a half and two days. Under these conditions material' equivalent to that of an entire slice could be removed in about a week to twelve days, requiring a total period of between 3 and 5 months for removal of the entire layer 10 at this particular site.
The pipeline assemblies 21 connecting the rigs 15 with the separation plant 22 will each include at least three maln conduits. A first conduit (155 in Fig. 14) will transmit the recovered slurry of water, sand and crude oil to the separation plant 22. Nere the slurry will'be separated into lt~ components.
The recovered oll will be transmitted to a refinery, while the sand ant water mixture (tailings) will be returned in a second conduit (not separately shown) of each pipeline asæembly 21 to the pontoons ... ' ' .

' 16, where tllose tailings will be used tor building dikes or dumped into the pond 13. The thlrd main conduit (150 in Fig.
14) of the pipeline assemblies 21 will provide water for feeding to the nozzles 49. A heater, if necessary to heat the water, will be included in the installation.
As an alternative to a single separation plant 22, it may be convenient to set up a number of first stage or preliminary separation plants 22a (Figs. 27 & 28), each servicing 2 or 3 floating rigs 15. These plants 22a would carry out the major separation in removing most of the water and sand tailings, a concentrated slurry then being passed to the final separation plant for removing the fine particles. This is done with centrifuges that require firm foundations. This alternative would save piping cost and heat and power losses.
The various parts of Figure 4 demonstrate the effect of this return of tailing from the separation plant 22 (or plants 22a~ to the site. Figure 4a shows the condition of the various strata after the first slice of tar sands material has been removed. The line 61 represents the plane at which the original tunnel 60 was cut, the upper portion 62 of the lsyer 10 being assumed to have collapsed onto the base portion 63.
The overburden layer 12 is unchanged, except that it has dropped about 8 feet, the resulting space at the top having been taken up with a layer 64 of sand tailing returned from the separation plant or plants and dumped into the pond.
Use of a relatively thin layer for each cut, e.g. about 8 feet, has the advantage of minimising the disruptive effect, i.e. the induced earthquake effect, of the sinking of the -overburden. The water level in the pond 13 ahould remain vlrtually unchanged. In practice lt wlll probably rlse slightly as the process proceeds, because the tslling~ sand ', ~'" ' ' ~'. ' .

is less compacte~ Lllall it was wl~en combined wlth the crude oil in the layer 10. This tendency towards a slight increase in volume can be allowed for by ensuring that the height of the dikes 14 is sufficient to permit some rise in the level of the pond 13. If necessary, some of the tailings sand returned from the separation plant can be used to build up the dikes.
Alternatively, an excess of tailings can be used to build dikes on an adjacent site for subssquent mining. There is another reason why dumping all or most of the tailings on an ad~acent site can be advantageous, especially in winter. The water is still hot or warm and can cause fog that impedes `~
operations. If it is allowed to cool on an adjacent site and then allowed to run back to the site being mined, the fog problem can be reduced.
Figure 4b demonstrates the next step, after a further tunnel 60' has been formed to remove a second slice of the tar sands material. When the tunnel 60' bas been enlarged laterally, as before, to cause the upper portion of the layer 10 to drop again, the situation shown in Flgure 4c will exist, the line 61' signifying the plane along which the further collapsed material ~oins the base material. In a similar manner, Figure 4d shows the formation of a typical next tunnel 60" and Figure 4e shows collapse to the line 61'', the process continuing as often as necessary to remove the entire or substantially the entire layer 10. Figure 4f shows tunnei 60' "; Figure 4g shows the last tunnel 60''" ; snd Figure 4h shows the state of affairs when the over-burden 12 has reached the operating level of the mining units 31.
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8y this time the layer of tailings sand 64 will have reached a depth comparable to that of the removed lsyer 10 plu8 swelling.

10630~2 Figllre 4h .show8 a lowcr portion of tnr s~nds materlal 10a remainlng. Obviously, it will be desirable to minimize the thickness of this remaining layer, and as indicated above this may be achieved to some extent by reduction in the tunnel slopes. In this and other respects the drawings are necessarily diagrammatlc, since practical conditions will seldom be as ideal as those shown.
For example, the planes of separation between the tar sands layer 10 and the limestone bed ll and the overburden 12 cannot be relied upon to be perfectly uniform and horizontal, as has been assumed for purposes of illustration.
It should be noted that, as the process of removing slice after slice proceeds, there may be a tendency for debris to `-~collect around the cavity in the vicinity of the inlet assembly 41 of each of the mining units 31. Blockage of such inlet assembly can be reduced by forcing additional fluid into the cavity 37 to raise the inner caslng 34 relative to the outer casing 32 which remains firmly embedded in the limestone bed 11. This action raises the inlet ports of the assembly 41 above debris collected on the floor of the cavity formed around such assembly. An alternative method of minimising this problem i8 discussed below in connection with a modifled form of mining unit shown in Figs. 36 to 41.
While the process demonstrated in Figure 4 has been golng on and before substantially all the recoverable tar sands :~
material has been mined from the site, a new dike enclosure will have been constructed ad~acent the old one and filled with water.
Once ehe old site i~ mined out, the dike between the old and new sites will be breached and the rigs 15 floated into position at ; the new site overlying a fresh layer of tar sands material.
Appropriate restructuring and lengthening of the pipeline assemblies 21 connecting the rigs to the separating plant or plant8 will be nece8ssry. Once the mlned slte has thus been evacuated and the . . ' ,' . ', ' : -, ' . .
- . : ~ , ' '' .

floatlng r1g~ nnd otl~er eqll~pment moved to ~ fresh site, the water from the pon~ 13 can be drained, leaving the tailings sand 64 as the exposed surface of the terrain. This sand is relatively clean and compatible with receipt of a layer of surfacP soil and vegetation.
In this way the site can be rehabilitated from the viewpoint of environmental conserv~tion.
When an area has thus been mined out and each float-ing rig is to be prepared for moving to a new site, the cavlty 37 in each mining unit 31 is first depressurlzed to lower the string and re-align the claw assemblies 35. These are then re-engaged by rotation of the string, whereupon elevation and separatlon of the string by its derrlck will recover the outer sleeve 32 from the limestone bed 11 and return the entire assembly to the surface. The nozzle 49 is, of course, turned to its lowered position before the minlng unit is thus recovered.
When the string and mining unit have thus been withdrawn, the casing 54 will also be raised to a point where pond leakage is still not excessive. The interior of the casing 54 can then be sealed by an inflatable rubber balloon. The location of such sealing will be chosen to be below the bottom of the pontoon 16 but above the bottom of the pond. The caslng S4 will then be severed iust above the balloon to enable the ~-pontoon to be moved away to lts new site.
The nozzle 49 on this type of mlning unit can serve two further functlons. Pirstly, if the hole is initially trilled or partly drilled by the mining string, the nozzle 49 can be used in its lowered posltlon during thls drilling operation to ~-distribute water or other lubricating llquid to the cutters 33 and generally around the lower end of the string. Such lucrica-tion ls especially useful durlng drilling through the over-burden 12. The second additlonal use to which the nozzle 49 ' can be pl~t, whon in i~s lowcrcd posltion, is to force water down into thc top of the inlet assembly 41, i.e. through openings 41a (Fig. 5b), to assist in dislodging any stones or other debris that may have accumulated in or around this assembly 41.
The central, slurry recovery conduit 38 can also be used during a drilling operation to assist in removal to the sur-face of material cut out by the drilling cutters.
ALTERNATIVE FORMS OF MININC UNIT
Figures 12 and 13 show an alternative form of nozzle assembly which has been modified to provide a pair of nozzles 49a and 49b each movable between essentially the same lowered and raised positions as in the first embodiment.
These nozzles 49a, 49b are independently movable by cyllnder and piston assemblies, as before, the remainder of this mining unit being essentially unchanged, except for the fact that the shape of the conduits must necessarily be some-what modified. For example, as shown in Figure 13, the slurry conduit 38a is now generally elliptical in shape at this elevation, although of course it is cylindrlcal above and below this location. The water space 47'a is formed around -the conduit 38a and is of like shape.
A double nozzle arrangement is particularly suited for use with floating rigs that are located centrally of the overall ~ite, since they enable two opposite sectors of tar sands material to be worked on simultaneously and hence provlde some economy in the time required for conducting the entire mining operation. If preferred, instead of pro~ecting ln opposite directions, the two nozzles can pro~ect in the same direction from opposite sides of the mining unit and hence reinforce each other's action on the tar sands materlal.

: ' ' ' ': ''' ' ' ~lluLller altcrnaLive form Or mining unit 31' is shown in Flgs. 36 to 41. In this case the outer sleeve 32' is formed with an inlet assembly 41' comprising fixed, vertically ex-tending vanes 42'. As before, these vanes form a slurry inlet screen for excluding rocks and other large lumps of material, but in this case the screen ~s fixed once the outer sleeve 32' has become fixed in the limestone layer 11. Also as before, the noz~le assembly (not shown in Figs. 36-41), which may be of the single type shown in Figs. 5-11 or alternatively of the double type shown in Figs. 12 & 13, will be secured to the upper end of the inner sleeve 34' which consists essentially of the slurry conduit 38 with impeller 39 and a series of vertical spacers 238 that serve to centre the conduit 38 within the outer sleeve 32'. At its lower end the inner sleeve 34' is formed with an annular sump area 44' and a polnted snout 234 that is reinforced by inner struts 235 and carries tlle claws 35 for engagement, as before, with comple-mentary claws 35 on the inside fo the outer sleeve 32'. The outer sleeve 32' includes a liner 232 at its lower end for slidingly receiving and guiding the snout 234. This movement is made, as before, by pressurising the space 37 for releasing and en8aging the claws 35. Once released, the inner sleeve 34' will be rotated within the outer sleeve 32' by the floating rig, as necessary to direct the nozzle assembly as explained ln Figs. 1 & 3, but there will be no need to elevate the inner sleeve 34' further in the outer sleeve 32' as was done in the flrst form of mining unit in order to keep the inlet assembly 41 above any deposit of rocks accummulated in the area around the mining unit. This potential problem iY avolded in the mining unit 31' of Figs. 36 to 41 by havlng a much taller inlet assembly 41', the ùpper part of which can be expected to be bove any accummulation of rocks likely to collect ln this area. ~ -.

~06301Z

rhe mlnlng unit 31' has tl-e further advantage that the opportunity for relative rotation between the nozzle (or nozzles) 49 and tlle fixed inlet assembly 41' enables this nozzle when in its lowered position to flush out the spaces between the vanes 42' around the full perimeter of the unit.

STRUCTURE OF T~E PREFERRED FORM OF FLO/\TING RIG
With initial reference to Figures 14 to 16, more details are shown of a floating rig 15 that may be employed with the apparatus already described. As already stated, such rig consists of a floating pontoon 16 supporting a derrick 17 extend-ing upwardly from the centre of the pontoon. As seen in Figure -14, a roadway 70 for use by pedestrians or small vehicles extends along the centre of the pontoon 16 with a deflected central portion 70a passing around the derrick 17.
It is important that there be provision for main-taining the pontoon 16 level and heDce the derrick 17 erect, in the event of the rig 15 being subjected to an asymmetrical load, such as a vehicle passing on the roadway 70 or exposure to lateral high winds. It will be noted that the preferred shape for the pontoon 16 has been shows as rectangular. Convenient dimensions for the pontoon would be about 100 feet long and about 40 feet wide.
It will be important to ensure that the pontoon is level in both the longitudinal and transverse directions. While other shapes and dimensions for the pontoon can be adopted, when employing those illustrated the greater length of the pontoon will render it much less susceptible to tilting in the longitudinal directlon than in the transverse direction due to transient or wind loads.
To provide for effective leveling of the pontoon 16, it is provided with four hallast tanks 71, 72, 73 and 74 (Pig. 16). The tank 72 i8 shown in cross-sectlon in Flgure 15 aA half full of water. balsnce will be achieved by pu~ping . :' ' :, , ,- . , " 1063012 water bnrk .~nd forLIl as requlred betwecn these tanks. Between tanks 71 and 72, wllich are on opposite sides of the pontoon, there are pipes 75 to 78 interconnected by pumps 79 and 80 driven by motors 82, 81. Pump 72 forces water from tank 72 to tank 71 and pump 80 controls flow back from tank 71 to tank 72. A
similar arrangement interconnects the tanks 73, 74.
In the longitudinal direction, water can be pumped between tanks 72 and 74, for example, by means of lines 85, 86 which are designed to provide flow in respective directlons when operated by associated pumps 87 and 89 controlled by motors 88 & 90. A similar arrangement (not shown) will be provided for ,.
pumping in either direction between tanks 71 and 73.
The manner in which the motors 81, 82, 88 ~ 90 are controlled will be described below.
Referring now more particularly to Figs. 17 to 20, it will be noted that the derrick 17 consists basically of four ver-- tical I-beams 91 which will be cross-braced in an appropriate manner -~
to ensure a rigid structure, most of the cross-bracing having been omitted from the drawings for clarity.
The structure provided by the beams 91 serves to 6upport four vertlcally extending rails 92 (Figs. 18 ~ 19), whlch are engaged by flanged rollers 93 that form part of a vertically movable carriage 94. The carriage 94 has beams 95 (see also Flg. 20), the ends of which support cylinders 96 havlng sprlng urged plstons carrying rollers 97 that run on further ralls 98 forming part of the fixed structure. The ends of the beams 95 are '~
lnterconnected by transverse beams 99 that each serve to support a double acting hydraulic cylinder 100. The cylinder 100 has a centrally positioned piston 101 wlth plston rods 102 extendlng -30 therefrom in both dlrectio~ and support1ng the rollers 93.

- . , . ........................ , ,.. . ~ , . .

: . . -: .. .. . .

~063012 lhe c.~rrlage 94 is complcted by support members 105 that extcnd downw.~rdly from the beams 95, and t~e rods 106 that extend upwardly therefrom to come together at an eye 107 (Fig. 17) that is engaged by a hook 108 adapted to be raised and lowered by a cable 109 extending over pulleys 110 to a winch 111. This arrangement provides for raising and lowering of the carriage 94.
The downwardly extending members 105 support a lower carriage 115 on which a pipe assembly 116 is supported. A8 best seen in Figure 21, the pipe assembly 116 consiæts of a caslng 117 in which there are formed an inner conduit 118 extending to an opening 118a and an outer, annular conduit 119 extending to an opening ll9a. At its lower end, the casing 117 has an enlarged ~
portion 120 in which a ball or roller bearing 121 is supported by -means of a sleeve 122. The bearing 121 serves to support a flange 123 formed near the upper end of a pipe 124 that is adapted to be connected by flanges 125, 126 and boltsl~7 to the upper end of a water conduit 128 that will eventually be connected through inter-mediate sections to the water condult 46 shown in Figs. 5, 6 and 7.
The plpe 124 is provided with a ~orm wheel 129 engaged by a worm 130 for rotation of the entlre string. 0-rings 131 located between the upper end of the member 124 and the lower portion of the casin 117 seal the ~oint while permitting this rotation of the string relative to the fixed casing 117.
The inner conduit 118 oE the casing 117 terminate8 in a straight portion 118b into which there is fitted, with inter-posed 0-rlngs 132, a sleeve 133, the lower end of which ls threaded to recelve an lnner conduit 134 that will eventually be connected through intermedlate sections to the slurry recovery condult 38' shown in Flg. 7.
Axlally down thls assembly there extends an upper A . , . , . , , ... . . , ,, ~ ,, ~ . . . .

--" 106301Z

portlon 40.l of tl)e shaft 40, also shown ln Flg. 7. At its extreme upper end, thls shaft passes through a stufflng box 137 to a coup-ling 138 whereby it is connected to a motor 139. Lubricant supplied through a pipe 140 to an axlal channel 141 extending along the shaft 40, 40a, will be employed to lubricate the bearings of the impellers distributed along the string. Further details of tllis structure are provided separately below.
As best seen in Fig. 17, the lnlet and outlet open-ings ll9a and 118a are connected to respective elbows 145 and 146 that in turn lead to flexible hoses 147 and 148. The hose 147 is used to supply water down the string, while hose 148 serves to convey the tar sand slurry received from the slurry recovery conduit system 38, 38' and 134. As best seen from Fig. 14, the water hose 147 is connected through a valve 149 to the water supply pipe 150 of the pipeline assembly 21. The recovery hose 148 is connected through valves 151, 152 and a discharge pump 153 driven by a motor 154 to the recovery pipe 155 which also forms part of the pipeline assembly 21. The latter may also ~nclude a steam line 156 and a fresh water line 157. The line referred to above for returning tailings to the pond ls not shown ln Pig. 14.
Figures 15 and 17 demonstrate the manner in which the water conduit 128 will enter the fixed outer casing or shield 54. Control cables 160 that extends down between the casing 54 and conduit 128 can convenlently be wound onto a drum 161.
M ECHAN I S M FOR LEVELLING FLOATING RIG
Mounted on the carriage 94 is a levelling assembly 162 that i6 shown in detall ln Flgs. 22 to 25. The locatlon of thls assembly 162 18 shown ln Fig. 18, but it ha8 been omltted from Flgs. 14, 17, 19 and 20 for clarity of understandlng of the other psrts of the derrick equipment. The e~sentlal aspect of the levelling asse~bly is that lt be mounted at a convenient . ,, . , . . ::.. . .. . . : : -locatioll ~or d~L~rminillg thc transverse tilt Or the upper patt of the derrick due to wind or other asymmetrical loads, this tilt being a measure of the lateral shift of the carriage 94 from which the string extends down into the earth. Obviously, such shift should be corrected as much as possible to avoid distortion of the string and especially its upper components.
As Figs. 22 to 25 show, the levelling assembly consists of a frame 163, from an upper member 164 of which a pivot 165 supports a depending rod 166 carrying a heavy pendulum weight 167 on its lower end. The pendulum swings in the plane in which the section of Fig. 22 is taken, i.e. from left to right in Fig. 23 and not up and down in Pig. 23.
The frame 163 supports horizontal threaded bars 168 along which nuts 169 with enlarged heads 170 are ad~ustable.
A pair of contact frameworks 171 each consists of two legs 172 each with a pivot point foot 173 seated in a conical bearlng cavity 174 formed in frame members 175. The pairs of legs 172 are interconnected by horizontal members 176 and 177, the ends of the latter resting on the nut heads 170 so as to be held out of contact with the pendulum rod 166. When the pendulum swings as a result of transverse tilting of the pontoon (Fig. 25), the rod 166 makes contact with one of the members 177 to close an electrical circuit between cables 178 and 179. When the tilt is in the opposite direction, the contact is between cables 178 ant 180.
Ad~ustment of the nuts 169 sets the backlash, i.e. the distance the rod 166 can move before contact is made. Should the pendulum continue to move, the system can accommodate this further ` travel as shown by the broken lines in Fig. 25. The swinging of the weight 167 is dampelled by a liquid 181.

The hydraulic control clrcult is shown in Fig. 26.

A low voltage power supply 182 energises cable 178. When contsct is made wlth cable 179 or 180, double acting relays 183 b 184 are .

.. ' both activaLcd in one scnsc or the other. Assuming cable 179 is energised, the relays 183 & 184 will energise three phase power lines 185 & 186. The lines 185 energlse a motor 187 driving a pump 188 to pressurlse line 189 and move the pistons 101 to shift the carriage 94 laterally in the direction to compensate for the lateral shift of such carriage resulting from tilting of the pontoon. Reverse shifting takes place through energisatlon of lines 190, motor 191, pump 192 and hydraullc llne 193. Various conventional return, check and relief valves and a hydraulic reservolr will be associated with the system, these being shown generally at 194 and not described in detail.
The power lines 186 and companion lines 195 res- ; -pectively control motors 81 and 82 and hence pumps 80 and 79.
Thus, when a significant lateral tilt of the pontoon occurs, an immediate correction is set up by the lateral shlfting of the carriage 94 by the cylinters 100. At the same time water ls pumped between the tanks 71, 72 to provide a more permanent eventual relevelling of the pontoon.
In the longitudinal direction of the pontoon the degree of its tilt can be expected to be so slight, by reason of the greater dimension in thls direction, that it i8 proposed .;
that the only levelling ad~ustment needed will be manual control of the motors 88, 90 (Fig. 16) to set up the pontoon initially in a horizontal orientation. However, if found necessary, and especially i$ the length dimension of the pontoon should be reduced, a system similar to that already described for .
transverse tilt can be employed to provide automatic correction of ~; longitudinal tilt. Such system could provide elther solely for long term correction, i.e. automatic control of the motors 88, 90, or also for quick actlng correction by longitudinal shifting of the carriage 94.
Horeover, similar levelllng systems can be in~talled ,, .

' ' . : ~.'; . ' , '. . ' ; ~' " :~
. . , . : ~ . , ., :

for the separating equipment on tlle floatlng preliminary separation plants 22a, if these are employed.
STRUCTUR~ OF THE RECOVERY SYSTEM
The recovery system is shown in Figs. 21 and 29 to 31.
Fig. 29 shows the lower end of the recovery or slurry conduit 38 on a larger scale than in Flg. 7, together with the shaft 40, the lowermost impeller 39 and bearing supports 200 which are supplied with lubricant through the axial channel 141 and transverse channels 141'. These supports include flow straightening vanes 201. The conduit 38 is constructed in sections to enable assembly and disassembly, the first section 38a being connected to the next section 38b by flanges 202. The section 38b, is asymmetrical, to pass through the nozzle assembly 48. This section is shown in Pigs. 7, 9, 10 and 11, and has been omitted from Fig. 29 except for its upper end 38c which connects to the next section 38d by a screw threaded ~oint 203.
The corresponding sections of the shaft 40 are drivingly connected together by hexagonal or other non-circular nut portions 204 that slide into correspondingly shaped sockets 205 (see Fig. 31). Pro~ecting from each nut portion 204 is a clrcular end portion 206 fitted with O-rings 207 that serve to retain the lubricant in the axial channel 141 which also flows into a space 208 between the end of the end portion 206 and the base of a correspondingly shaped socket 209.
As the upper part of Fig. 29 and Fig. 30 show the conduit 38 and shaft 40 continue as separable sections (e.g. about 2S feet long) ioined respectively by ~oints 203 and nut and socket assemblies 204, 205 until the upper end of the strlng is reached at the conduit 134 and shaft 40a ~compare Flgs. 21 and 30).
Impellers 39 could conveniently be spaced about 100 feet apart.

, - , . ::

" 1063012 ~DDlrIoNAL FE~TURE.S
Fig~. 32 to ~5 show certain Ddditional features.
To facilitate control of the mining unit 31 it may be convenient to record the performance of such unit photographi-cally. To this end Figs. 32 and 33 show a stereoscopic camera 210 that can be lowered from the surface by cable 211 into a channel 212 in the casing 45 of the nozzle assembly. A remotely controlled sliding panel 213 can open and close an aperture 214 giving access to the camera 210 which will include lenses 215, flash lamps 216, batteries and a welght 217.
Pigs. 34 and 35 show a clamp 218 for securing to the water conduit 46. The clamp 218 is hinged at 219 and tightened by a bolt 220. It contains a guide 221 for the camera 210 as well as subsidiary clamps 222 for holding steam and/or air ~ -conduits 223 and 224 for holding electric cables 225 for power and instrumentation.
ALTERNATIVE AP~RANGEMENTS OF P~IGS
While the method of operation described in which the derricks 17are mounted on pontoons floating on a body o water is preferred, it is possible to operate the underground aspects of the present method and apparatus from rigs that are mounted on firm ground. However, the frequent and often irregular subsidence that the overburden can be expected to experience will probably require the mounting of each such rig on a number of ad~u~table legs, preferably sub~ect to automatic control, to insure that the derrick remains vertical.
As a further alternative, instead of each rig 15 bein8 mounted on an individual pontoon 16, one or more much larger pontoons could be constructed each bearing two or more ri8s and perhaps also a prelim~nary separatlon plant. For example, e-ch pontoon mlght take the form of a series of arm~ or spokes .. ... , : , . ,, ,;; - ~ : .

,.: ~ . .. . .

radiating from the location of a preliminary separatlon plant wlth a rig mounted near the end of each spoke. This arrange-ment has the advantage that the large size of the pontoons should eliminate any need for tilting corrections.

Claims (4)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of recovery from a subterranean layer of a material conducive to hydraulic mining techniques, said layer underlying an overburden, comprising (a) sinking a pair of spaced apart mining strings from respective surface rigs down through the overburden and into said layer, (b) projecting from each said string into the material of said layer a jet of liquid to soften and erode said material to form a cavity therein while generating a slurry of said material and the liquid, (c) the liquid projected from the strings being so directed and the spacing of said strings being such that the cavities formed by the respective strings are caused to open into each other, and (d) forcing said slurry to the surface for recovery of said material therefrom.

2. A method according to claim 1, comprising (e) repeating said sinking and projecting steps with a plurality of further mining strings spaced from each other and from the strings of claim 1 to form an array of said strings, (f) the liquid projected from the strings being so directed and the spacing of said strings being such that the cavities formed by the respective strings are caused to open into each other.

3. A method according to claim 2, wherein said array comprises parallel rows of said strings arranged in a staggered relationship between adjacent rows, whereby those strings not forming the perimeter of the array are each surrounded by six sectors of said material, each such sector abutting a complementary sector of an adjacent string whereby cavities formed in such a pair of complementary sectors are opened into each other.

4. A method according to claim 1, 2 or 3, wherein the cavities formed by said mining strings are initially formed in a lower part of said layer of material, and including the steps of (g) continuing to erode said material and enlarge the cavities thereby formed until the material above such cavities collapses thereinto, (h) continuing to project liquid from the strings to erode and form further cavities in such collapsed material until the material above such further cavities collapses thereinto, and (i) repeating step (h) until substantially all the material of said layer above the location of the initial cavities has been eroded.