Patent Application
20130106166
This invention relates to a method and system for mining an underground material using a substantially horizontal borehole and high pressure fluidic means for drilling and excavating said material for conveyance through said borehole.
The recovery of material located in underground geological strata or seams has been the subject of extensive technological development. Where the desired material is located relatively close to the surface of the earth, it is possible to recover the material by open pit mining, in which large areas of land are cleared of the surface overburden to allow access to the desired material by heavy-duty surface mining equipment. Depending on the location of the site to be excavated, this overburden can include roots, stumps and thicknesses of clays, sands, muds, and other materials. Depending on the depth of the desired material, additional earth may have to be removed to a depth of 100 feet or more. The removal of this overburden and additional earth can be time-consuming and expensive. The displacement of the overburden and additional earth can create water flow and drainage issues. Replacement of the removed earth and restoration of the overburden to its pre-mined state also can be expensive and time-consuming. It thus would be desirable to provide a means for recovering desired materials located underground by a means that does not create extensive disturbance of the surface.
Methods for excavating underground materials without strip mining include techniques in which vertical or oblique boreholes are provided to a desired depth, and regions are excavated hydraulically. Typically, such systems involve a drill rig that operates a vertically directed drilling head having a drill bit on the far end, and a nozzle several feet back from the drill bit that emits a jet of high pressure water at a right angle to the direction of the drilling head. Thus when the drilling head bores vertically downward to a desired depth, the nozzle excavates a substantially horizontal cavity. Vertical borehole mining also has been suggested for solution mining, and for recovery of hydrocarbons.
Such vertical borehole methods may yield only limited quantities of desired material, because the radius of the substantially horizontal excavated cavity is limited by the reach of the high pressure water jet flowing from the nozzle. In addition, the creation of an excavation cavity directly beneath a drill rig can create instability in the overburden at the surface, posing a possible danger to the crew and the drill rig.
Excavation methods involving horizontal borehole drilling also have been disclosed in the art. For example, U.S. Pat. No. 5,879,057 discloses a system for mining a relatively narrow seam of coal, wherein a water jet cutting head at the end of a drill string is used to drill an excavation cavity substantially horizontally through the coal seam. U.S. Pat. No. 6,688,702 discloses a borehole mining method in which a borehole is driven first vertically downward and then into a production zone at a low-degree angle α, and a hydromonitor directs a water-jet at an angle β to the horizontal plane to create a cavity, with the mining continuing as the hydromonitor progresses through the production zone. During the mining operation the hydromonitor is inserted or removed from the borehole without rotation.
It is one object of the present invention to provide a system and method for efficiently mining materials from a remote underground site, without excessive disturbance of the surface, and which system is adaptable for use with a wide variety of underground materials.
It is another object of the invention to provide a system and method for efficiently mining material from a remote underground site and without excessive disturbance of the surface, using a substantially horizontal borehole, and in which the volume of the excavation cavity can be substantially greater than the volume of the borehole.
It is still another object of the invention to provide a system and method for efficiently mining material from a remote underground site, wherein the material is excavated as the cutting apparatus is being retracted.
It is yet another object of the invention to provide a system and method for efficiently mining material from a remote underground site, wherein the shape of the excavation cavity can be modified during the mining process.
In accordance with the invention, a method and system are provided for excavating a quantity of material from a seam of material to be mined, wherein a substantially horizontal borehole is drilled into the seam of material, a retractable casing is disposed along the borehole, and a high pressure fluidic drilling tool extends through and can protrude through the end of the casing, the drilling tool comprising one or more nozzles for emitting a high pressure fluidic jet, the drilling tool being operable to adjust the direction of the high pressure fluidic jet, the high pressure fluidic jet cutting into the material to be excavated, causing the material to be disaggregated from the seam. The volume of the excavation cavity created by the disaggregation is determined in part by the pressure of the high pressure fluidic jet and the adjustments made to the direction of the high pressure fluidic jet. The high pressure fluidic jet can be either pneumatic (air) or hydraulic (water). The disaggregated material combines with water which can be either water from the hydraulic drilling tool, naturally occurring groundwater, water pumped from an external source, or any combination thereof, to form a slurry which is directed back through the casing toward the surface. The return of the slurry to the surface can be actuated by a pumping means such as an eductor, or it can be directed pneumatically. As mining proceeds the drilling tool, pumping or pneumatic return means, and casing are retracted back through the borehole. The system of the invention comprises a drill rig disposed at the wellhead and remote from the material to be excavated, the drill rig operating a borehole drilling tool for boring a substantially horizontal borehole through the seam of material. The system further comprises a retractable casing adapted to be disposed within and extending the length of the borehole, a high pressure fluidic drilling tool comprising one or more high pressure fluid jetting nozzles adapted to be movably disposed within the casing, and a pumping or pneumatic slurry return means, the system being operable to adjust the direction of the high pressure fluidic jet.
In accordance with the method of the invention, a substantially horizontal borehole is bored into the seam of material to be mined, and the retractable casing is disposed along the length of the borehole. The high pressure fluidic drilling tool is extended to the far end of the casing, and is used to direct high pressure fluidic jets against the material of the seam to disaggregate the material, which falls to the bottom of the cavity and forms a slurry. The direction of the high pressure fluidic jets is adjusted from one orientation to another over the course of the mining operation so that the jets contact different regions of the seam of material to be mined. The pumping or pneumatic return means directs the slurry back toward the drill rig where it can be collected so that the desired seam material can be recovered. In one embodiment of the invention, a single retractable casing houses both a conveyance means for conveying the high pressure fluid to the drilling tool and a conveyance means for conveying the slurry back toward the well head. In an alternative embodiment of the invention, the borehole can accommodate two parallel casings, one of which accommodates the high pressure drilling tool and conveyance means for the high pressure fluid and the other of which accommodates the pumping or pneumatic return means and the return flow of slurry.
The drilling tool comprises one or more nozzles which emit high pressure jets that cut into the seam of material to create an excavation cavity. Advantageously, the direction of the high pressure jets are adjustable to impact the walls of the excavation cavity at different orientations, to create an excavation cavity of substantially greater volume than the borehole, the directions and movement of the high pressure jets being selected by the mine operator depending on the shape and characteristics of the seam of material to be mined. The excavation can continue either until walls of the cavity extend beyond the reach of the high pressure jets, or until the excavation cavity extends beyond the desired seam of material, or until the cavity collapses due to subsidence of the cavity walls. The casing, high pressure drilling tool, and pumping or pneumatic return means are then retracted to a portion of the borehole that has not yet been excavated, and the mining operation continues. If desired, the sequence of retracting the system and mining and extraction can continue until the casing, drilling tool, and pumping or pneumatic return means have been retracted to the site of the drill rig. Thus, when excavation of a seam is complete, no part of the drilling system remains underground.
The present invention will be more readily understood with reference to the Figures herein, which are for purposes of illustration of the concepts disclosed herein and are not necessarily drawn to scale, in which:
The present invention relates to a method and system for mining a material disposed in a location that may be difficult to access from the earth's surface. The material to be mined is capable of being disaggregated by high pressure fluid to form a slurry. Materials suitable for mining by this method include, for example, phosphate ores, potash ores, sulfur, trona, heavy mineral sands, soft coal-bearing deposits, and other sub-surface materials subject to disaggregation by the application of hydraulic pressure, as will be recognized by those skilled in the art. The following detailed description of the invention will be discussed in terms of excavation of a mineral ore, such as a phosphate ore. It will be understood, however, that this description is for purposes of illustration only, and that the materials that can be excavated by the method and system of the present invention are not so limited.
In accordance with the invention, the high pressure fluid used to disaggregate the underground material can be either hydraulic (liquid such as water), or pneumatic (air), or a combination of hydraulic and pneumatic. In addition the means for returning the slurry to the surface can be either a pump means, or a pneumatic means, or both.
The invention will be described first with respect to the embodiment in which the drilling means is hydraulic with the high pressure fluid being high pressure water, and the return means comprises a pumping means such as an eductor. Then other embodiments will be described in which pneumatic means are used in the drilling tool, the return means, or both.
As is known in the art, means for boring a substantially horizontal borehole can include a guided borehole drilling tool, not shown. The guided borehole drilling tool can be controlled from the drill rig 15 to drill borehole 20 to a desired level with respect to seam 22. The drilling tool may comprise one or more rotating drill bits remotely operated from the drill rig 15. Those skilled in the art will understand how to select an appropriate drilling tool depending on the characteristics of the material being mined and the surrounding geological deposits. Following drilling of the borehole, the borehole may be provided with a retractable casing 30, not shown to scale.
Casings can range in diameter from about 20 inches to about 72 inches, with wall thickness varying from about ⅓ to 2 inches, the particular casing dimensions depending on the dimensions of the ore seam 22 to be excavated and the nature of the material being collected. In one embodiment, retractable casing 30 will have an inner diameter large enough to accommodate a pumping means, and a return flow of slurry, as described in greater detail below.
Hydraulic drilling tool 40 is provided with one or more water jetting nozzles 42 each of which emits a high pressure water jet 44. In the illustrated embodiment the water jetting nozzles are positioned in the wall of casing 30, near the distal end thereof. High pressure water is delivered from drill rig 15 through outer channel 46 to nozzles 42 to provide the high pressure water jets 44 that impinge on the seam of ore 22 to disaggregate the material. Hydraulic drilling tool 40 is operable such that the direction of the high pressure water jet 44 is adjustable during the mining operation. In the illustrated embodiment, casing 30 or the distal portion thereof comprising nozzles 42 can be rotated to adjust the direction of the high pressure water jets 44. The intake of pump means 35 preferably is located rearward of rotatable water-jetting nozzles 42 of hydraulic drilling tool 40.
In the illustrated embodiment in
It will be appreciated that as casing 30 is retracted the length of the extraction cavity 50 will increase, and the volume of slurry 28 in the cavity will increase correspondingly. In some uses of the present invention, the excavated cavity will be subject to subsidence by the effect of gravity. That is, the ceiling and surrounding walls of the cavity will naturally collapse by virtue of the absence of the material of seam 22. This subsidence is a helpful aspect of the mining process, because it limits the longitudinal dimension of the cavity, which allows the depth of the slurry to be maintained at a level that permits removal by the pump means. In installations in which subsidence dos not occur spontaneously, then in order to limit the volume of slurry 28 that will be pumped through pump means 35, and in order to maintain the slurry at a sufficient concentration of ore to allow for acceptable operating efficiencies, it may become necessary over the course of the mining operation to effectively limit the length of the excavation cavity in which mining occurs and therefore the volume of slurry 28 that will be pumped by controlling the mining operation to induce subsidence of the cavity ceiling and walls as illustrated in
The method wherein subsidence of the cavity walls is used to create barriers finds particular utility in mining environments in which the seam 22 of material to be mined is readily disaggregated, such as materials having a substantial clay component, and in which the geological layer overlaying seam 22 contains a substantial sand component.
In one embodiment of the invention, the water recovered from the slurry at the drill rig 15 can be recycled as a source of water for hydraulic drilling tool 40.
In another embodiment of the invention, naturally occurring groundwater may be present, and may become part of the slurry that is returned to the drill rig for the recovery of the excavated material.
In another embodiment of the invention, additional water may be pumped into cavity 52 to become part of the slurry that is returned to the drill rig.
In another embodiment of the invention, the water that forms the slurry can be any combination of one or more of drilling water, groundwater, and water pumped into the cavity.
Referring once again to
The nozzles can be either recessed within tool 140 or protruding therefrom, depending on the nature of the material to be mined. In some embodiments of the tool 140, the nozzles 142 can be provided with sliding gate valves, not shown. When the tool 140 is retracted in casing 30 the gate valves can be closed, and when the tool 140 is extended from the casing 30 for drilling operations, the gate valves can be opened.
In the illustrated embodiment, casing 30 serves as a protective housing for hydraulic drilling tool 40 and pump means 35. Casing 30 also provides an outer channel 46 for transporting pressurized water to water jetting nozzles 42, and an inner channel 48 for transporting slurry 28 back to drill rig 15. Casing 30 is extended during installation and retracted during the mining process by means known in the drilling art. Thus, in the event that there is subsidence of the walls 52 of excavation cavity 50, there is no danger that borehole 20 will be compromised, or that the equipment disposed within the casing will be damaged.
The method and system of the present invention provide significant advantages over both vertical and horizontal borehole mining methods of the prior art. In the inventive method the mining is accomplished in the reverse direction, i.e., while the tools are withdrawn from the borehole and while the casing is being retracted, rather than while the borehole itself is being drilled. The rotating nozzles 42 permit the excavation cavity 50 to be expanded to a size and shape that can optimize ore extraction on a customized basis for each mining site. The method and system allow mining of ores to be accomplished over great distances without disturbance of the overburden, and with minimal impact to the immediate environment. The method and system of the present invention are particularly well adapted to the excavation and recovery of ores and other materials that are in substantially horizontal seams or strata beneath the earth's surface. Unlike prior art horizontal drilling methods, the borehole can be drilled with a gentle slope between the drill rig and the point of entry into the ore seam of interest instead of with a sharp angle between a vertical borehole and the horizontal borehole into the material of interest. The absence of a sharp angle can simplify the borehole drilling process, as well as the return of slurry to the drill rig. The rotation of the water nozzles during the excavation process allows for a larger volume of material to be extracted for each borehole that is drilled, thereby improving efficiency and reducing overall costs. The method has the advantage of safety in that the excavation operations are remote from the personnel at the drill rig 15.
A particular advantage of the present invention is that it permits continuous mining operations, rather than the intermittent operations that must be performed in open pit mining. This also permits continuous processing of the slurry that is recovered from the mine, thereby saving both time and costs. Moreover, the method and system of the invention can extend the productive life of a mining site by extracting useful ores that were inaccessible, or accessible only with great difficulty and expense, with prior art mining systems.
In another embodiment of the invention, the apparatus of the invention is substantially the same as that illustrated and described above, except that the drilling tool is pneumatic, such that the high pressure fluid used to disaggregate the material from the cavity walls is high pressure air. Referring to
The disaggregated material will fall to the floor of cavity 50. Water will be present at the floor of the cavity, either from naturally occurring groundwater, or added to the cavity as part of the mining process. The disaggregated material and the water will mix to form a slurry. In one embodiment the slurry can be returned to the surface through inner channel 48 by means of a pump such as an eductor. In another embodiment, a high pressure air conduit 49 can direct high pressure air from outer channel 46 to impel some of the slurry 28 back into through inner channel 48. The air space within cavity 52 above slurry 28 will be pressurized due to the use of high pressure pneumatic jet 44; this pressurization of the cavity will facilitate the movement of the slurry back through inner channel 48. In addition, inner channel 48 can be provided with one or more air distributors 148 such as in the form of annular manifolds having air outputs 149, as illustrated schematically in
In one embodiment, the invention can be practiced wherein the cutting tool comprises both hydraulic and pneumatic cutting jets.
In one embodiment of the invention, the means for returning the slurry back through inner channel 48 may comprise both a pump such as an eductor and a high pressure conduit to direct slurry back though inner channel 48.
The foregoing description of the invention is intended by way of illustration and not by way of limitation. Other alternatives and equivalents will be recognized by those skilled in the art, and are intended to be encompassed by the claims herein.
This application claims priority to U.S. Provisional Patent Application Ser. No. 61/552,102 filed Oct. 27, 2011, which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61552102 | Oct 2011 | US |
