Water jet mining system and method

Abstract

A water jet borehole mining system controlled and operated aboveground includes a high-pressure cutting nozzle that is delivered to an underground resource body through a relatively small diameter borehole. A series of water and air streams at various pressures are delivered to the resource body, and the target resource is disaggregated and/or fluidized and conveyed back to surface via the water jet borehole mining pipe which serves as the conveyor of the system. The mining pipe is used to transport a high-pressure stream of water fluids that have been directed and aligned into laminar flow to a focused water jet cutting head. The central bore of the mining pipe brings the disaggregated and slurrified resource to the surface. The mining pipe transports the slurry via airlift, fluid eduction or a combination of both.

Claims

1. A method for mining either a submerged or a dewatered subterranean resource in situ at a mining site comprising the steps of: a. drilling a borehole from the earth's surface through any subsurface overburden material to a top of the subterranean resource; b. cementing the borehole whereby any groundwater at the mining site is protected and leaching of the subterranean resource is prevented; c. drilling a borehole at least partially through the subterranean resource; d. inserting a mining string into the borehole, the mining string having a top end, a bottom end, an elongate portion extending coaxially along a longitudinal axis intermediate the top and bottom ends, and an eductor bit positioned at and operatively connected to the bottom end; e. injecting a high pressure mining fluid via the mining string into the borehole; f. creating laminar flow in the high pressure mining fluid; g. redirecting the high pressure mining fluid into a nozzle, the nozzle being structured and arranged to create a supersonic, high pressure, high volume stream of laminar mining fluid; h. directing the supersonic, high pressure, high volume stream of laminar mining fluid into the subterranean resource, whereby the subterranean resource is disaggregated and a mining cavity and a slurry of disaggregated subterranean resource solids and mining fluids are created; i. injecting a low pressure, high volume stream of fluid into the slurry to mix therewith, whereby the slurry is transported via eduction into a slurry return line in the mining string; j. injecting a gaseous material into an airlift line positioned in the slurry return line at a selected airlift line placement depth, whereby a suction is created to assist the eduction in lifting the slurry to the surface; k. separating solids, fluids and water at the surface at a dewatering facility; and l. recycling the water for reuse.

2. The method of claim 1 wherein the high pressure mining fluid injected into the borehole at step 1.e has an energy, and wherein the step of creating laminar flow in the high pressure mining fluid increases the energy delivered to the subterranean resource.

3. The method of claim 1 further including the step of adjusting the airlift line placement death in the slurry return line in response to the subterranean resource being mined.

4. The method of claim 1 further including the step of controllably rotating the mining string in the borehole in response to the amount of solids, fluids and water that is sent through the dewatering facility.

5. The method of claim 1 wherein the borehole drilled from the earth's surface is drilled vertically.

6. The method of claim 1 wherein the borehole drilled from the earth's surface is drilled at any angle between the vertical and the horizontal.

7. The method of claim 1 further including the step of capping the borehole.

8. The method of claim 1 further including the step of inserting a casing string into the borehole.

9. The method of claim 8 further including the step of cementing the casing string.

10. The method of claim 1 further including the step of delivering low pressure water to the borehole to keep the borehole full of water.

11. The method of claim 10 further including the step of forcing the low pressure water past a seal whereby additional pressure is introduced to the borehole thereby boosting the recovery of disaggregated subterranean resource.

12. The method of claim 1 further including the step of dropping the mining string to a bottom portion of the mining cavity to remove any disaggregated subterranean resource that fell to the bottom portion of the mining cavity.

13. The method of claim 1 further including the step of adding a cut polymer material to the supersonic high pressure, high volume stream of laminar mining fluid whereby an effective hydraulic horsepower of the stream at a face of the subterranean resource is increased.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a general schematic of a hydraulic borehole mining system situated at a mining site in accordance with an embodiment;

(2) FIG. 2 is a side elevation view of the hydraulic borehole mining string of the system of FIG. 1;

(3) FIG. 3 is a side partial sectional view of a monitor subassembly for the hydraulic borehole mining string of FIG. 2 having shielding portions removed to show the elements thereof in greater detail;

(4) FIG. 4 is a sectional view of a low pressure and high pressure combination swivel in accordance with an embodiment;

(5) FIG. 5 is a side perspective view of the monitor subassembly with shielding and bit attached for hydraulic borehole mining applications in accordance with an embodiment.

(6) FIG. 6.A is a side perspective view of a quartic straight nozzle in accordance with an embodiment.

(7) FIG. 6.B is a sectional view of the nozzle shown in FIG. 6.A;

(8) FIG. 7.A is a side perspective view of a mining pipe in accordance with an embodiment; and

(9) FIG. 7.B is a side sectional view of the mining pipe shown in FIG. 7.A having portions removed to show the elements thereof in greater detail.

DETAILED DESCRIPTION OF THE INVENTION

(10) Referring now to FIG. 1, a system and a process of hydraulic borehole mining for a subterranean resource in accordance with the present invention is described in detail. A rig shown generally at 1 is brought to the mining site, situated at a preferred location at the site, and operated to drill a well, wellbore or borehole, (as the terms are used in the art) 2 to the top of the resource body. The wellbore may be drilled at any angle from vertical to horizontal depending upon the geotechnical mining conditions down-hole and the structure of the ore body itself. If required, casing string, 3 is then run into the initial wellbore and cemented into position to give it strength. A conventional drilling string is then fed into the casing string, and a pilot hole is drilled at least partially into or through the resource body. The conventional drilling string (not shown) is thereafter removed from the hole.

(11) Referring now to FIG. 2, a mining string 5 is illustrated in greater detail. The mining string is run into the wellbore and includes a bottom end 6, a top end 7, an elongate portion 8 extending co-axially along a longitudinal axis 9 thereof intermediate the top and bottom ends, and, an eductor bit 10 positioned at the bottom end of the string and attached to a high pressure monitor pipe 12. The monitor joint or pipe houses at least one quartic-straight jet nozzle 15 (FIGS. 6.A and 6.B) and a plurality of integrated laminar flow vanes within the high pressure monitor pipe 12 as will be described in greater detail below. The monitor pipe 12, is secured to the bottom end 6 of the mining string 5 that extends from the surface 14 and is operatively connected to a rig floor or platform 16 and associated surface equipment down to a subterranean resource deposit 21 (FIG. 1).

(12) The mining string includes a swivel 22 operatively connected to the top end 7 of the mining string. As shown in greater detail in FIG. 4, swivel 22, connects the mining string 5 via port 120 to the surface equipment providing air and high and low pressure water. As well be described in greater detail below, the swivel 22 consists of a combination of high pressure and low pressure fluid courses; the interconnections of which provide all of the fluid connections needed for the process. The swivel takes the high pressure feeds of water for the quartic-straight jet nozzle, the air to the air lift system, high and low pressure fluids for the eductor turns these fluids and air ninety degrees and sends them down the respective lines or annular concentric pipes in the mining pipe to the attachments down the string. The swivel 22 also provides a passageway or a return line 130 to conduct the slurry up the hole and to direct the slurry to one or more surface processing facilities, generally shown at 26 in FIG. 1. A unique and novel feature of the system of the present invention is the significantly enhanced ease of maintenance and efficiency of its operation as compared to any prior art systems and methods.

(13) Referring again to FIG. 1, the configuration of the surface portion of the mining system is illustrated in greater detail. The surface equipment includes high-pressure, high-volume jet mining pump(s) (not shown), which deliver water down hole via the swivel and high pressure line 32. An air compressor delivers air to the swivel via high pressure line 36 to be delivered down hole to an airlift assist line or pipe 19 (FIG. 5). A lower pressure water pump delivers water to the backside of the well head via low-pressure water line 44 to keep the surface hole full of water. The supply of low pressure water to the backside optionally may be forced in past a seal, introducing an additional amount of pressure and force to the backside of the pipe. This additional force above the weight of the column of water on the backside gives a boost to the recovery system by essentially forcing fluid under pressure up the mining string's lower density return line and thereafter to surface.

(14) The return line 130 runs from the swivel to a dewatering system via a low-pressure slurry return line 50. This portion of the system removes the water from the resource and returns the water to a dirty water storage pond or tank (not shown). A storage facility 56 stores the dewatered resource while awaiting further processing by the mine. The water from the dewatering system then flows to a settling pond where any fines that have collected into the water are permitted to settle before flowing into a clean water storage area (not shown). The clean water storage area holds the clean water, which feeds all of the pumps.

(15) The clean water is boosted into one or more high pressure pumps and then pressurized and pumped into the high pressure mining swivel 22 (FIG. 4) where it is turned 90 degrees and down the mining string 5 through the mining pipe. The pumps) feeds the mining pipe line via high-pressure line inlet 32. The line is connected to the swivel 22 and then runs the length of the pipe via one ring 96 of the concentric annular triple wall mining pipes illustrated in greater detail in FIGS. 7A and 7.B.

(16) Referring now to FIGS. 7.A and 7.B, the elements of the mining string 5 are shown in greater detail. In the embodiment shown, by way of example and not of limitation, the string includes three elongate cylindrical tubes or pipes (also referred to in the art as “subs”), 70, 72 and 74, of selectively decreasing diameter, d, with respect to an outer surface 71 of the mining string (only one of which diameters is shown) concentrically disposed about and extending substantially parallel with one another along a longitudinal axis 9. The inner most pipe 70 forms a center return line or bore 92 for returning the slurry to the surface. Tube 70 cooperates with tube 72 to form an outside annular ring or pipe 94, and tube 72 cooperates with tube 74 to form an annular ring or pipe 96 extending circumferentially around the bore 92; the bore 92 and the annular rings 94 and 96 being concentric with one another. The interconnections between progressive adjoining sections of the mining string 5 utilize full flow concentric connections at each joint to provide a high pressure seal between each inner concentric mining pipe sections 72 and 74 and an adjoining section (not shown) via special high pressure, expandable O-rings 76 (FIG. 7.A) seated in grooves 78 formed in a first end 75, 77 of each of the concentric pipes 72, 74 respectively (FIG. 7.B). The end of each of the subs fits inside a corresponding mating flange (not shown) on a second end of each of the concentric pipes. This novel configuration allows for the full inside diameter (internally flush) of the concentric lines of the mining pipe to be maintained in a concentric relationship with one another to the connection sub. The connection subs are utilized in the connection of the individual segments of the entire mining pipe string 5 (FIG. 2) and the connection of the monitor pipe 12 (FIG. 3). Due to the internally flush—full bore, restriction-free structure of the subs, the pressure drop in the concentric high pressure rings at the connections is substantially reduced over prior art systems, an advantage which manifests itself over a large number of connections in a string, where the pressure drop over the overall distance would be significant. Moreover, the threaded connections found in prior art system, which are subject to galling are eliminated in the internal portions, thereby significantly reducing system downtime and extending the useful life of the mining string. Only the external pipe 70 includes a male threaded end 80, which is adapted to be threadably connected to a corresponding female threaded end of an adjacent section.

(17) As shown in FIGS. 3 and 5, the monitor joint or pipe 12 includes a first section or portion which contains laminar flow vanes positioned perpendicular to one another and which are structured and arranged to create and maintain a laminar flow of the mining fluid. The monitor includes laminar vanes (not shown) which are adapted to preliminarily align the otherwise turbid flow of the water into a laminar flow stream configuration, thereby providing increased hydraulic horsepower to the jet stream. As noted above, the laminar flow is established utilizing the vanes to split and align the flow. The vanes are formed of a suitable material such as steel and are positioned securely in the monitor.

(18) Referring to FIG. 3, and, as shown in greater detail in FIG. 7.A., the annular high pressure water rings 94, 96 of the mining pipe feed the water flow to the monitor pipe 12 where the water becomes laminar, thus ensuring that laminar flow is maintained while the water is joined to and then forced through the monitor 12. In an embodiment, the high pressure water flow may be limited to only the inner annular ring or pipe 96, the outer annular ring 94 serving to deliver low pressure water and also as a safeguard against any high pressure leakages. The monitor maintains the water flow in a laminar stream without introducing turbidity into a second section or portion 17 which is in fluid communication with the first section 13 and then turns the water flow into at least one quartic-straight jet nozzle 15 (FIGS. 6.A and 6.B). As a result, more water at a higher velocity can be provided through the system because of the continuation of the laminar flow. The quartic-straight jet nozzle delivers the laminar flow into a focused jet through a nozzle orifice 90 delivering a high pressure, high volume stream of fluid at supersonic velocity into the rock face.

(19) As the water jet impacts the rock face it begins to disaggregate the material. The disaggregated material mixes with the water creating a slurry stream which is then carried to the eductor bit 10 as shown in FIGS. 2 and 5. The eductor bit pushes the slurry stream up a slurry return pipe 92 in the monitor 12 which is connected to the slurry return pipe 92′ in the mining string, whereupon it is accelerated by a vacuum created in the return pipe 92 by the combination of airlift assist and the pressure applied to the outside of the mining string 5, in part via the low pressure water line 44 as described above. This vacuum is created in two unique ways. First, the airlift assist is charged by air from a compressor and is carried through the mining pipe via an airlift assist line 19 that runs inside the internal slurry return pipe 92 where it terminates at the ideal airlift placement, depending on conditions, typically at a depth of approximately 200 feet. The air then escapes through the open ended pipe within the slurry return 92 via the airlift entry point. The tiny bubbles that are introduced at depth expand as they move up the slurry return line. The bubble expansion lowers the density in the slurry return line which causes a u-tube effect on the outside of the mining string, and fluid moves through an eductor bit opening 108 and into the mining pipe slurry return line. This suction recovers the slurry created by the quartic-straight jet nozzle 15 and the disaggregated ore.

(20) The airlift assist line 19 is typically placed at depth in a vertical well at a level to maximize the lift of slurry. This depth is adjusted according to the type of resource being mined. For instance, when mining Kimberlites, the depth of the airlift sub in the well is controlled closely to keep velocities of the resource lower to limit diamond breakage. For mining uranium, on the other hand, an example of ore where grain size after cutting is not monitored, the airlift assist line is placed lower in the well to increase the tonnage/mining rate per hour. On horizontal wells the airlift release is generally within the vertical section of the well for lift, and the eductor pushes the cut ore through the horizontal section. Critical velocities are matched to each ore type and the direction of the well to ensure the slurry is maintained in suspension without erosion of the system. The airlift assist is a significant improvement over previous systems that only incorporate a fluid eductor for the recovery of the slurry, inasmuch as the airlift assist reduces the total amount of horsepower that is needed on location to drive the system. It is through this reduction of horsepower that a significant reduction of overall capital costs is attained, not only by eliminating an additional pump, but also by reducing the overall cost of the operating expenses as a result of the lower horsepower demands.

(21) The second part of the slurry return system and a key element of the system and method of the present invention is the eductor bit 10 discussed above with reference to FIG. 2. The eductor bit is operated with relatively low pressure and with a high volume stream of water. This water stream is selectively delivered through one of the concentric rings 94, 96 in the mining pipe 5. This water is delivered to the monitor pipe which houses the eductor assembly and turned 180 degrees via a conduit and directed back up the inner bore or slurry return line 92 of the mining string 5. The water flow creates a suction that draws slurry into the eductor and forces it up the hole.

(22) The slurry passes through a narrower gauge 92′ of pipe within the eductor housing while being simultaneously boosted through that section of the eductor with the clean water from the surface via the outside concentric ring 94. The acceleration of the fluids through the narrow section and then up the slightly larger inner bore of slurry return line 92 of the mining pipe causes a vortex and, effectively, a vacuum on the down hole side of the eductor. The two fluid streams converging in the narrow body of the eductor accelerate and then are released into the larger return pipe diameter. The differential pressure does not allow the fluid out the bottom of the bit, so it accelerates the flow up the well bore continuously. The slurry is then carried up the hole, through the swivel 22 and through and out of the swivel 22, via return line 130 where it is sent to the surface dewatering facility 26 via a slurry return pipe 50 (FIG. 1).

(23) Each resource type dictates the specific mining strategy utilized. The formation of the mined cavity can be by drilling a pilot ahead and through the resource body and starting at the bottom of the hole and mining up or back towards the rig in the case of a horizontal well, or starting at the top of resource body and utilizing the eductor bit of the present invention to drill and mine at the same time from the top down. The competency of the formation of the target resource and the geotechnical parameters surrounding it dictates the mining approach and strategy. In either direction, the cavity is developed through the disaggregation action of the hydraulic jet and the rotation of the mining string. The string is rotated at a preselected rotational speed, by a rotation apparatus operatively connected thereto, for example, an electrical motor coupled to the string via a gear mechanism or the like, the speed of rotation being determined by the competency of the formation and the distance or length of the cut at any given point within the resource body. The jet is rotated sufficiently slowly to allow enough effective interaction between the hydraulic jet and the rock face to perform the disaggregation and the slurrification of the resource. The rotational speed is determined by the amount of material that is returned and sent through the dewatering facilities. The time on the ore face coupled with the combination of flow and pressure is adjusted to maximize production. As the mining string is slowly rotated, a larger and larger cavity is created. This cavity in a vertical application can be a full 360 degree circle or pillars can be left in place to support the surrounding resource as the cavity is cut. As the returns diminish, the tool string is moved vertically and another rotational pass is made. This basic technique is continued until the desired cavity is cut from the targeted zone. Several times during the process, the mining string can be dropped to the bottom and the suction system can be used to remove any slurrified material that passed the mining string and fell to the bottom of the hole. Dependent on the resource being cut polymer can be added to the jet stream to increase the effective hydraulic horsepower at the ore face, which increases the cutting distance of the tool. The entire cutting process is repeated to enlarge the cavity. Upon completion of the cavity mining the entire mining string is removed from the borehole.

(24) When the hydraulic borehole mining is performed in a high angle or horizontal application, the technique used to create the cavity can be different than that of the vertical application. In a horizontal application, the system of the instant invention is ideally drilled and directed to the bottom of the targeted resource. A pilot hole will be drilled from the surface to the bottom of the targeted resource body and then horizontally out as far as reasonably possible into the formation on the depth of the horizontal hole depends upon the characteristics of the formation material. The hole will be drilled out as far as possible without collapsing on top of the tool string. The drilling string will be removed and replaced with the mining string of the present invention. The mining system will be run out in the lateral direction to the end of the hole. Thereafter, the jet will be turned on. In the horizontal application, the monitor pipe will be rotated no more than 180 degrees. Since the tool is on the bottom of the resource zone, the targeted areas will be to the side and the top of the monitor pipe. In thicker resource zones, one lateral well can be mined above the other. If the competency of the resource body is low, then the monitor pipe can be manipulated to perform 60-degree sweeps to either side of the tool, thereby making a bowtie pattern in the resource body. The advantage to this pattern in a low competency formation is that it permits recovery of the resource on the sides, which is facilitated by the natural subsidence of the formation over the mining string. As a section of the cavity is excavated, the mining string is slowly extracted, making the cavity larger and longer as the tool is retracted into the surface casing string. Upon completion of the cavity the mining system is removed from the hole.

(25) Although the present invention has been described with reference to a particular embodiment thereof, it will be understood by those skilled in the art that modifications may be made without departing from the scope of the invention. Accordingly, all modifications and equivalents which are properly within the scope of the appended claims are included in the present invention.