US3393013A - Process of mining ore from beneath an overburden of earth formation - Google Patents

Description

o. HAMMER ETAL 3,393,013 PROCESS OF MINING ORE FROM BENEAI'H AN OVERBURDEN OF EARTH FORMATION 2 Sheets-Sheei 1 9 8 l 6 7 w 1 6 w l J .w. m I m flay/a; (I Harp er IN VENIORS ATTO/P/VEVJ July 16. 1968 l O HAMMER ETAL 3,393,013

PROCESS OF MINING ORE FROM BENEATH AN OVERBURDEN OF EARTH FORMATION Filed Jan. 17, 1966 2 Sheets-Sheet 2 z Ozzo Hammer flouy/a: 6'. Harper INVENTORS BY w? United States Patent 3,393,013 PROCESS OF MINING ORE FROM BENEATH AN OVERBURDEN 0F EARTH FORMATION Otto Hammer, Dallas, and Douglas C. Harper, Houston,

Tex., assignors, by mesne assignments, to Dresser Industries, Inc., Dallas, Tex., a corporation of Delaware Filed Jan. 17, 1966, Ser. No. 521,056 9 Claims. (Cl. 299-17) ABSTRACT OF THE DISCLOSURE Water-insoluble ore, such as phosphate, is mined from a subterranean bed lying beneath an overburden of earth by the introduction of a water jet that forms an ore-water slurry carried up a production casing by an air lift or the like. The jetting water stream and the producing conduit are moved downwardly into the cavity formed in the ore body independently of the production casing which is sealed to the overburden. The jetting water stream as well as the producing conduit are oscillated vertically so as to erode ore from the body and increase turbulence in the ore-water slurry to hold a maximum amount of solids in suspension. Make-up water, in addition to the water required to produce the slurry is added in order to retain adequate pressure within the ore cavity.

This invention relates in general to the mining of ore existing as a deposit in the earth beneath a substantially thick overburden, a portion of which is water impervious, and particularly to a method of mining and removing such ore through an access well provided through the overburden and without the entry of a human being into the ore deposit.

The mining of such ore deposits by means of access wells extending from above the overburden into the ore deposit has been heretofore proposed and, in connection with the mining of certain substances such as sulfur and salt, has been extensively practiced. However, in the mining of an ore which cannot readily be reduced to a molten state and in such state removed from the ore body and caused to flow up through the well to the earths surface, as in the case of sulfur, or an ore not readily and highly soluble in water and thus readily removable by dissolution from the ore body into flowing streams of water and thence caused to flow to the earths surface, great difficulty has been encountered. In fact, attempts to produce mineral substances not so readily rendered fluid by melting or solubility have been unsuccessful either because of being too expensive to economically justify the operation in connection with the recovery realized, or involving too much risk or danger to equipment, such as the possibility of cave-ins of the overburden into the cavity provided by removal of ore from the ore body.

Much of the difficulties experienced have been due to the fact that in the removal of ore from an ore body in the form of a slurry or suspension, attempts have either been made to cause the slurry or suspension of material carrying the ore to flow upwardly from the cavity in the ore body by placing pressure thereon in excess of that at the upper end of the well sufficient to cause the slurry or suspension to flow, or by producing such slurry or suspension through the use of an air or gas lift device, either of which results in rather high pressure differentials between the cavity and the ore body and the space above the more or less impervious formation. With such pressure differentials great difficulty has been encountered in attempting to provide a seal sufficiently strong to withstand the pressure differentials with the result that seal rupture has frequently caused the complete loss of pressure differential and impossibility of production and consequent 3,393,013 Patented July 16, 1968 necessity of abandoning the well, or such necessity has resulted from caving of the formation. Attempts to overcome these difficulties by more expensive sealing arrangements such as complicated packers and cementing operations have not only proven too expensive to be economically justifiable but for the most part have proven ineffective.

Another difficulty encountered in previous attempts has been the relatively small amount of ore removable through a single well because of the fact that the effects of jets of water directed laterally from adjacent the axis of the well within the ore body do not penetrate very far radially if surrounded, as is usually the case, by a body of water which, except for the jet action, is relatively quiescent. Attempts to overcome this difficulty by displacing the water within the cavity in the ore formation with air or gas so as to render the jet action more effective, have necessitated the creation of even greater pressure differentials between the pressure within the ore body and that above the cavity than were necessary in cases in which the ore body cavity was filled with water. The evil results of excessive pressure differential were thus even more pronounced with the excessive air or gas pressure causing the air or gas to break through the surface and necessitating abandonment of the well in many cases.

It has been found also that in most cases the amount of water injected into a well for jetting laterally against the formation to break it up and form the slurry desired, taken with the water produced by the ore bearing formation and flowing therefrom into the well, has been insuffi cient to make up the water necessary for providing the proper consistency of slurry of ore for carrying the ore to the surface. Under these circumstances, the pressures within the well have been unduly lowered and excessive pressure differentials between the cavity in the ore deposits and the pressure above the ore deposits have occurred causing breakdown of the seals therebetween. Increasing the amount of water provided through the jets not only increases the amount of power required for injecting the the same, but may result in excessive pressures within the cavity in the ore deposit, likewise leading to a breakdown of seals thereabove.

It is one object of this invention to provide the proper amount of water within the ore deposit for forming a slurry of the desired consistency with the ore dislodged without either producing excessive pressure differentials between the cavity in the ore body and the locations above the ore body, or introducing extra work requirements involved in injecting such make up water through a jet stream, or introducing too much water thereby involving the necessity for removing extra water with the slurry.

It is an object of the present invention to provide a prac tical and economical method of mining relatively diflicultly fusible and substantially insoluble or poorly soluble ores such as, for example, phosphate ore existing as a deposit beneath a very substantial thickness of overburden.

It is a more specific object to provide a practical and economical method of mining such ore from such a deposit from which mining by conventional mining methods and dredging are not considered feasible because the mining must be conducted beneath a substantial body of water such as tide water or the like.

Another object is to provide a method for mining such deposits in situations in which dredging or other conventional mining methods are not considered feasible because of excessive depth, unstable characteristics of the overburden which is subject to subsidence, and the like.

Another object is to provide a method for mining such deposits with water bearing formations existing above or below the ore bodies and which may be sources for domestic water supplies without any detriment to the water in such water bearing formations.

Another object of this invention is to provide a high volume, low cost mining method that will produce a relatively large volume of solids from a given access well in the shortest possible time and at a cost per ton of crude ore produced in keeping with the economic requirements.

Another object is to provide a method for mining such deposits in which the necessity for or the involvement of excessive pressure differentials between a cavity within the ore deposit and that existing above the impervious portion of the overburden will not be present to a degree to either interfere with the mining operation or require expensive operations or equipment in order to guard against accidents.

Another object of this invention is to provide such a method in which the amount of ore recoverable from a single well may be greatly increased over that normally recoverable in methods employing jetting through a body of liquid completely filling the cavity in the ore formation, but without the necessity for providing excessive pressures within the ore formation tending to cause accidents due to failure of the seal between the ore formation and the impervious formation thereabove.

Another object of this invention is to provide a method facilitating the extensive and practically exhaustive mining of ore from such an ore formation not only by increasing ultimate production from a given well penetrating such formation, but by facilitating the drilling, equipping and production of such wells and the salvaging of equipment therefrom so as to make a multiplicity of such wells into subterranean ore formations economically feasible.

Another object is to provide for adding make up water to a cavity within an ore deposit in connection with the mining of such ore and removing it in the form of a slurry, in which water is added at substantially the exact rate required to make a slurry of the desired consistency without resulting in substantially increased or decreased pressures within such cavity.

Another object of this invention is to provide apparatus components for carrying out the various steps in the proc ess of this invention.

Other objects and advantages of this invention will become apparent from the following description taken in connection with the accompanying drawings wherein is illustrated by way of example a preferred embodiment of the invention.

In summary, the present invention includes a system and method for mining an essentially water insoluble ore from a deposit beneath an overburden of earth wherein a growing cavity is formed in the ore body. A casing is driven into the overburden and through it is introduced a producing conduit and a water conduit, the latter producing water jets to be directed against the ore body. Initially an opening of somewhat enlarged diameter is formed in the deposit to facilitate the erosive action of the jet. Both the producing conduit and the water conduit are moved downwardly as the cavity enlarges and are oscillated vertically to agitate the ore-water slurry. The

slurry is caused to flow upwardly through the producing casing as by an air lift. Make-up water in addition to the jet is introduced through the casing to maintain adequate pressure in the cavity.

In the drawings:

FIG. 1 is a side elevation of one type of apparatus constructed in accordance with this invention for both drilling, equipping and producing a multiplicity of wells into an ore formation beneath a body of water and showing such drilling, equipping and producing being accomplished from a floating vessel on such a body of water, one such well being shown in the course of being drilled and two others being shown in the course of being produced.

FIG. 2 is a top plan view of the apparatus illustrated in FIG. 1.

FIG. 3 is a vertical cross section on an enlarged scale through the wellhead apparatus of one of the producing wells illustrating in FIG. 1 taken along the line 3-3 of FIG. 2.

FIG. 4 is a vertical cross section through the same apparatus but at right angles to the plane of FIG. 3 and taken along the line 4-4 of FIG. 2.

FIG. 5 is a fragmentary vertical cross section through the casing and producing string of one of the producing Wells of FIG. 1 adjacent the lower end thereof and showing in elevation the lower ends of the jetting and air lift strings, the jetting shoe and the intake shoe of the producing string.

FIG. 6 is a horizontal cross section through the structure shown in FIG. 5 taken along the line 6-6 of FIG. 5.

Referring more in detail to the drawings, FIG. 1 depicts a formation 10 which is ore bearing and from which it is desired to produce above the earths surface an ore which is not readily liquefiable as by melting or dissolving the same. Overlying such ore body 10 is shown a relatively impervious section of the overburden 12 which may be of the order of one or several feet in thickness. Other overburdens 14 of many hundreds of feet in thickness may be added to the overburden section 12, but which over-burdens 14 are normally of such a thickness and of such a nature from the standpoint of danger of caving and subsidence as to render impractical the mining of the ore from the body 10 by dredging or other conventional means. Or all of the overburden of the ore bearing formation 10 may be relatively homogeneous.

In the illustration the surface of the uppermost earth formation 14 is covered with a body of water 16 which may be a tidal body or a fresh water body of substantial proportions, it being recognized, of course, that the existence of such body of water serves to greatly aggravate the problems normally arising from water intrusion and pressure differentials involved in operations such as heretofore attempted.

In accordance with this invention, where such a body of water exists, a floating vessel such as a barge 18 is provided on the surface of said body of water and barge 18 in turn has lateral recesses or notches or slots 20 at intervals around its outer periphery for the purpose of accommodating the drilling of wells and the production equipment necessary for producing the same, so that a number of wells may be accommodated around the outer edge of a single barge or floating vessel.

This invention also embraces within its concept providing the access wells and mining the ore body 10 by utilizing two separate barges whereby one barge, suitably equipped, provides the access wells and prepares them for production, and a second barge equipped with the equipment necessary to produce the wells is moved into position within the area of the prepared wells. The first barge is then used again to retrieve the production pipe and casing and abandon the wells.

Approximately centrally located on the floating vessel 1t; is a support 22 for a rotating crane housing 24 having a boom 26 capable of being extended upwardly on an angle therefrom. The housing 24 will, of course, carry in conventional fashion the power supply and hoisting mechanism for mainipulating and operating the crane and the boom 26 may be provided with an auxiliary support strut 28 when it is employed as shown in a position to provide an access well.

When so employed for the drilling of a well there will be suspended from the outboard end of the boom 26 of the crane a traveling block 30 similar to that customarily employed in the rotary drilling of wells and having a hook thereon from which is suspended a rotary power swivel 32 providing rotatable suspension and power drive for a drill string 36. A rotary drive 38 or the like is preferably mounted on the floating vessel 18 over one of the drilling slots 30 through which the drilling operation is to take place, and this rotary drive is formed with suitable well known equipment for engaging drill pipe or casing slips while making or breaking pipe joint connections. The rotary drive 38 may also be used as an auxiliary power unit to rotate the drill pipe in lieu of the power swivel, and it will be understood that rotary drive 38 may be driven by any suitable mechanism such as an electric motor 52.

Carried on the lower end of the drill string is a more or less conventional rotary drilling bit 40. It is contemplated that the well may be initiated either by drilling a relatively large hole from the surface for a relatively short distance into the upper formation and then driving a surface casing 42 into such formation to a driven seal engagement therewith, or by driving the casing directly into the formation without having previously drilled a hole therein. In either case, the surface casing 42 should be driven so tightly within the formation 14 that it provides a driven seal 44 with such formation at the lower end of the surface casing. Thereafter the well, with a relatively smaller bore 46, may be drilled ahead until it reaches a short distance above the ore producing formation 10, stopping preferably a little thereabove and within an overburden of substantially impervious formation 12.

At such point the drilling should be discontinued and a smaller casing customarily referred to as a water string run into the well and driven into the formation 12 until it refuses to be driven further and provides a seal with such formation.

Of course, if the formation be unsuitable for forming a driven seal, some other seal provision, such as an open hole packer, may be employed.

As a slight alternative in cases in which the nature of the overburden formation will permit, the drilling down to the formation -12 may be accomplished by providing a drilling element on the lower end of a string of water casing such as the casing 48 and drilling by rotation of such casing string rather than by a separate drill string with bit attached. Upon reaching the formation 12 (which may be determined by the nature of the cuttings from the drilling operation) rotary drilling with the casing would be stopped and the casing driven into the formation as before to provide a seal between the casing and the formation 12. The drilling shoe on the lower end of the easing would normally have an opening through its mid portion through which later operations could be carried out, and this shoe could be retrieved upon decommissioning of the well after the ore deposit therebelow shall have become depleted.

Likewise, if the nature of the formation overlying the formation 12 should permit, the entire operation of setting the casing 48- might be accomplished by driving the same the entire distance and eliminating all drilling.

The remainder of the bore hole may then be drilled to some predetermined point within the ore bearing formation, if desired substantially to the lower limits thereof, and the drilling equipment removed.

It will be understood that during the drilling operation drilling fluid may be supplied to the drill bit 40 in the usual fashion by means of a standpipe 54 and a rotary hose 56, suitable pumping equipment being provided for pumping drilling fluid through such standpipe and hose and down through the drill string 36 to the bit 40 during drilling, and for taking returns therefrom through the surface casing 42 or the water string casing 48 in an operation conventional in the rotary drilling of oil wells.

' tween the water string casing 48 and the formation 12.

Additionally, the water body 16 will be sealed from the lower portions of the overburden 14 about the surface casing 42 by means of the driven seal 44 and casing 42. Casing 48 serves several purposes including (1) protecting the hole from sloughing off of the surrounding formation and (2) in combination with the driven seal 50 protecting against contamination and loss of underground water.

The drilling below the casing 48 through the ore body may be of approximately the diameter of the inside of the casing 48 as designated at 17 in FIG. 1. However, a most unexpected and spectacular result has been found to come as a consequence of the under-reaming or enlarging of the hole through the formation to a somewhat larger diameter. Contrary to expectations based on previous attempts to disintegrate the walls of a hole a great deal larger than the casing 48, a moderate amount of underreaming of the order of a few inches was found to greatly increase production as compared with proceeding with an initial hole through the ore body of approximately the inside diameter of the casing 48. Such under-reaming is shown at 17a.

For example, it was found in one case that when the hole through the ore deposit was increased from an initial inside diameter of 15 inches (comparable to the inside diameter of the casing 48 in that instance) to an inside diameter of 28 inches, the rate of production from such ore bearing formation in that well was increased by approximately 50 percent. Thus the initial enlargement by under-reaming or other means of the hole through the ore deposit, to a diameter exceeding the inside diameter of the casing 48 by something of the order of that above indicated is considered an important though not indispensable phase of this invention.

The well having been drilled and equipped with casing and drilled to a predetermined point within the ore hearing formation in the manner described, a production string 58 is then disposed in the well with its lower end having a screen or perforated shoe 60 thereon for the purpose of taking in ore slurry in the manner presently to be described.

Outside of the production string 58 and substantially parallel thereto is then disposed a jet string 62 terminating at its lower end in a jet string discharge manifold or ring guide 64 having jet nozzles 66 horizontally disposed therein although they may be upwardly or downwardly inclined, although not necessarily so. The discharge manifold 64 carrying such jet nozzles 66 is preferably slidably mounted around the production string 58 so that it may slide up and down thereon, and also preferably rotatable thereon so that the jet nozzles 66 may be rotated or oscillated in a rotary direction about the center of the production string 58. This may be produced by oscillation of the jet string 62 from the surface and the nozzles 66 may be so located that upon such oscillation the jet nozzles together may be arranged to cover the full 360 about the production string 58. Likewise, by raising and lowering the jet string 62 the nozzles may be moved upwardly and downwardly preferably by a distance equal to the entire thickness of the ore bed 10 which it is desired to mine from the well so equipped. The formation 10 is thereby eroded forming an ore cavity As previously indicated, flow may be induced up through the production string so as to cause ore slurry to flow upwardly therethrough in any suitable fashion, but preferably in accordance with this invention an air lift string 68 having air jet openings 70 extending outwardly therethrough adjacent its lower end will be suspended within the production string 58 with the lower end of the air lift string somewhat above the lower end of the production string. The jet openings 70 are preferably arranged in some fashion as along a helical line so as to discharge air in practically every direction at every level throughout the extent of such perforations or openings 70, and are preferably upwardly inclined along the directions of the arrows 72 so as to discharge such air in upwardly directed jets to thereby assist in the upward flow of fluid Within the production string.

Referring now to FIG. 3, it will be seen that the upper end of the production string 58 is preferably provided with an inverted U-shaped curve or gooseneck 74 terminating in a downwardly extending portion 76 projecting into a telescoping wash pipe connection 78 having a packing 80 therein and connected to a slurry discharge pipe 82, leading to a suitable slurry receiver for receiving the ore slurry from the well. With this arrangement it will be seen that the entire production string 58 may move upwardly and downwardly a distance permitted by and limited to the dimensions of the telescoping wash pipe 78 without breaking the connection with the slurry discharge pipe 82.

In order to support the production string and reciprocate it longitudinally in this fashion it may be suspended by a cross head 84 by means of slips 86 or the like with the cross head 84 in turn suspended on plungers 88 reciprocably mounted within cylinders 90 supported by the deck of the vessel 18. Any suitable power such as hydraulic fluid or air power may be applied to raise and lower the cross head 84 through the medium of the cylinders 90 and the pistons or plungers 88, and thereby to cyclically reciprocate the production string 58 with a predetermined amplitude and frequency. The extent or magnitude and frequency of reciprocation of the production string is dependent upon the nature of the specific ore body from which production is being taken and the optimum magnitude and frequency must be determined for the specific ore body encountered. For this reason these values may be varied over a considerable range but it is felt that some reciprocation of the production string will in almost every instance be desirable for the maximum production of ore. Such reciprocation serves to assist in agitating the body of fluid within the cavity in the ore body and keep the ore slurry in suspension form while at the same time assisting in the erosion of the walls of the cavity due to the churning action of the slurry in the cavity. It likewise prevents rock fragments and debris from clogging the perforations in shoe 60 and has a tend ency to impart a pumping action to the slurry and assist in raising it through the production string 58.

The upper end of the jet string 62 is likewise provided with a U-shaped or goosenecked bend 92 adapted to be suspended from any suitable device such as a suspension ring or sling 94 carried on the lower end of a cable or the like 96. Reciprocation of the jet string is accomplished by suitable power means such as the cylinder 98 pivotally anchored at 100 to the deck of the floating vessel 18 and adapted when hydraulic or air power or the like is applied thereto to move the piston 102 into and out of the cylinder 98 and draw the pulley 104 downwardly and then release it for upward movement periodically or cyclically. The cable 96 being anchored at its upper end adjacent the pulley 106 passing downwardly through the pulley 104 and then upwardly over the pulley 106, thence downwardly to the suspension 94, will serve, for a relatively short movement of the piston rod or plunger 102 to produce a relatively longer reciprocating motion of the jet string 62. By such reciprocation the jet ring 64 and the jet nozzles 66 will be reciprocated upwardly and downwardly by an amount gauged by the vertical extent of the erosion desired to be produced within the ore body.

The pulley 106 may be supported by any suitable stationary support such as the A-frame 108 which is in turn supported on the deck of the floating vessel 18.

The reciprocation of the jet string as just described serves not only to move the jet discharge nozzles 66 up and down and thus sweep the entire thickness of the ore deposit which it is desired to erode by means of the washing action of these jets, but it also accentuates the turbulence generated by the reciprocating motion of the production string 58 heretofore described, and reciprocating of the manifold 64 adds considerably to the turbulence within the cavity in the ore body. This reciprocation of both the production string and the jet string together with the jet manifold or shoe 64 adds greatly to the action of the liquid and slurry within the cavity in the ore deposlt to erode away the walls of such cavity and put ever increasing amounts of ore into a suspended slurry within the ore cavity and keep it in such state of suspension so that it can readily be drawn in through the perforations 60 in the intake shoe on the bottom of the production string 58 and drawn upwardly through this string.

Simultaneously with the reciprocation of the jet string 62 this string may be oscillated in a rotary direction by any suitable means such as the radially extending arm or handle 110 secured thereto shortly beneath the gooseneck 92. Such oscillatory movement of the arm or handle 110 may be imparted either by manual means or by any power means available such as ropes or cables operated in connection with a so-called cathead or the like, or by other apparatus to produce cyclical oscillation. This oscillatory motion will also be transmitted to the manifold or shoe 64 at the lower end of the jet string, this manifold being rotatable with respect to the production string 58, and while the manifold 64 may not be rotated a full 360 it may readily be arranged for rotation to the extent of for example, so that three jets directed radially from this manifold at equally spaced points about its periphery will together cover the entire 360 around the inner wall of the cavity within the ore body. This oscillation also adds to the turbulence within the cavity of the ore body and assists considerably in the erosive action of the fluid within such cavity.

For the purpose of adding water to the well or mine cavity 16a other than by gravity, a pipe 112 may be inserted into the upper end of the water string of casing 48 alongside the production string 58 and jet string 62, and connected to be supplied by a suitable pump 114 whose intake pipe 116 is disposed beneath the surface of the body of water on which the vessel 18 may be floating, or, if such suitable body of water is not available, then to some other suitable source of supply of water.

In the case of a producing well, water will, of course, be supplied to the space within the ore body at the bottom of the Well by the jet string supplying the jets 66, but it is not to be anticipated that water thus supplied to the jets will be sufficient to make up the required slurry of displaced ore and sufliciently suspend the same for production through the production string to the surface. It has been found that if the cavity in the ore formation were first completely filled with water, if no water were added other than the water through the jets, the water supply within the ore cavity would in many cases quickly become depleted, leaving insuflicient water for forming the ore slurry to convey it to the earths surface and very likely reducing the pressure within the ore cavity to a point seriously involving the danger of breaking the seal around the water casing at 50 and permitting flowable non-ore bearing formations or water sands in the overburden 14 to be produced around the lower end of water casing 48 rather than the ore body 10, with the very likely result that the well would have to be abandoned. In some instances it is possible that sufficient water will be produced from the ore bearing formation into the cavity to make up the necessary water for the required slurry to conduct the ore to the surface, but this cannot be depended upon and in accordance with this invention it is contemplated that such make up water will be added by gravity or by means of the pump 114 to the extent that the excess of water required to be removed from the well as a slurry over that injected through the jets 66 and that flowing into the well from the ore body 10 will be supplied in this manner. The exact amount of water to be supplied could, of course, be determined by any suitable form of level indicator disposed at an appropriate point at which it might be desired to maintain the level of the water in the water string 48 or in the cavity in the ore body, but it has been found to be an acceptable practice in most wells to merely maintain the level of the water in the Water string substantially at or just below the upper end thereof, which can, of course, be done either by visually observing such level or by use of suitable means for controlling the flow of water to maintain such a level. By leaving the upper end of the well open the maximum level of water is readily controlled so as to prevent excessive hydraulic head from existing within the ore cavity so as to possibly break through the seal at 50 in an upward direction, and maintaining the water adjacent the upper end of the water string as indicated will prevent a low pressure from developing that might cause breaking of this seal in the opposite direction. In the case of wells being drilled beneath a body of water from a floating vessel as indicated, such an arrangement will normally prevent the differential of pressure across the seal 50 being more than to pounds per square inch. Normally a seal provided by driving engagement of the easing against the formation should not be called upon to Withstand a pressure differential in excess of 25 pounds per square inch as a greater differential could result in breaking of the seal.

With the apparatus illustrated, it is contemplated that in the case of a location beneath a body of water the vessel 18 will be located in a predetermined position and the crane 24 manipulated so as to provide a well through a selected one of the drilling slots as illustrated at the left-hand end of FIG. 1. If required, casing can be set as indicated at 42 and casing for a protective Water string will be set as indicated at 48, the casing in each instance being driven so as to provide a drive seal with the formation and avoid the necessity for cementing the casing in place and then drilling through a cement plug as is customary in completion of wells such as oil and gas wells.

After the casings 42 and 48 have been set an extension of the hole will be provided without casing from below the lower end of the water string to the lower extent of the ore bearing formation from which production is to be obtained through the well. It has been found that the rate of production and total tonnage per well can be substantially increased by under-reaming this open hole section of the well to a diameter larger than the inside diameter of the water string of casing 48. The production equipment will then be lowered into such well until its lower end projects into the open hole and possibly reamed extension of the drilled hole into the ore bearing formation 10. Preferably at this point with the well first substantially filled with liquid employing the pump 114 if necessary, the jetting water will be forced down through the jet string 62 and out through the jets 66, during which time the jet string will be raised and lowered by the mechanism illustrated in FIG. 4 and oscillated by the handle illustrated at 110 so as to play the jets 66 throughout the entire surface of the inner wall of the well within the ore bearing formation. This will result in the washing of ore from the walls of the well and causing it to form with the water in the well a slurry capable of being caused to flow up through the production string 58 to the surface. This slurry will be continuously agitated by the described movement of the jet string and its manifold 64 and by a similar up and down movement of the production string 58 through actuation of the piston and cylinder mechanisms 88 and 90. Flow of such slurry up through the production string may be assisted if necessary in any suitable fashion, one such means being by means of an air lift effected by passing compressed air down through the air lift pipe 68 and out through the holes 70 within the production string. This slurry will then flow to the surface under the impetus of such air lift or pumping action and through the pipe 82 at the earths surface to a suitable slurry storage. During this operation the well will be kept filled substantially to the top of the water string 48 by gravity or operation of the pump 114 as necessary.

After the operation of the production equipment in a well for a time it will be understood that the effectiveness of the jetting action and the agitation of fluid within the 10 ore body will decrease as the cavity within such body increases in size, until it will be found that the production of ore in the form of slurry will fall to a rate making it uneconomical to continue.

Either at this point or during the actual production additional wells may be drilled through the other slots 20 of the vessel 18 and suitably equipped for production. Eventually a number of such wells around the vessel 18 will serve to substantially exhaust the supply of ore in the area immediately in the vicinity of the vessel whereupon the vessel must be moved to another location.

When desired to abandon a well because of too low a rate of production to be feasible, it will be readily possible to salvage the equipment in the well by first removing the production equipment and pulling the casing and all this may be accomplished from the floating vessel illustrated.

From the foregoing it will be seen that this invention is one well adapted to attain all of the ends and objects hereinabove set forth, together with other advantages which are obvious and which are inherent to the method.

It will be understood that certain features and subcombinations are of utility and may be employed without ref-' erence to other features and subcombinations. This is contemplated by and is within the scope of the claims.

As many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

The invention having been described, what is claimed 1s:

1. The process of mining an essentially water insoluble ore from an ore deposit beneath an overburden of earth wherein a cavity of increasing volume is formed as said ore is mixed comprising the steps of:

(a) disposing a casing from the earths surface into the overburden to a point above the ore deposit and sealing it to the overburden;

(b) mechanically forming an open hole larger in diameter than that of said casing at least partly through said ore deposit;

(c) introducing a producing conduit within said casand beyond the lower end thereof into said open o e;

(d) introducing a water conduit within said casing and adjacent the lower end of said producing conduit;

(e) directing a jetting water stream through said Water conduit into said ore deposit to erode said deposit and create an ore slurry;

(f) causing flow of said ore slurry through said producing conduit tothe earths surface;

(g) moving said producing conduit and said water stream independently of said casing and of one another downwardly into said ore body as said ore deposit is eroded; and

(h) continuously introducing water through said casing independent of said water conduit introduction.

2. The process in accordance with claim 1 including the step of maintaining an adequate head of water within said casing to prevent internal collapse of the cavity formed within said ore deposit.

3. The process of claim 1 including the step of introducing compressed air within said producing conduit to cause said slurry to flow to the earths surface by means of an air lift.

4. The process of claim 1 wherein said jetting water stream is oscillated vertically within said ore deposit to maintain ore in suspension in said slurry.

5. The process of claim 1 wherein said producing conduit is oscillated vertically within said ore deposit independently of said casing and said water conduit.

6. The process of claim 1 including the step of introducing a head of water within said casing prior to the introduction of said jetting water stream through said conduit.

1 1 1 2 7. A system for mining ore from an ore deposit beup said producing conduit to the surface of the neath an overburden of earth, said system comprising: earth.

(a) a casing extending into said overburden and ter- 8. The system of claim 7 wherein the means for causminating at a point above said ore deposit; ing flow of said ore-Water slurry up said producing con- (b) means sealing said casing to said ore body; 5 duit is an air lift system. (c) a producing conduit positioned within said casing 9. The system of claim 7 including means for oscillatand vertically moveable independent of said casing; ing said nozzle means angularly with respect to the ore (d) a water conduit positioned within said casing and body.

vertically moveable independent of said casing;

References Cited (e) nozzle means at the lower end of said water conduit for producing a jet stream; 10 UNITED STATES PATENTS (f) means for introducing Water through said nozzle 823,749 6/1906 Wanner 175-67 X means to direot it against said ore body to form an 2,518,591 8/ 1950 Aston et a1. 175-67 X ore-water slurry; 2,745,647 5/1956 Gilmore 2995 (g) means for introducing additional water through 15 3,311,414 3/1967 Cannon et al 299-8 X said easing into said ore body, and (h) means for causing flow of said ore-water slurry ERNEST R. PURSER, Primary Examiner.

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