Mining or in situ disintegration of hard material – Processes – Breaking down by direct contact with fluid
Reexamination Certificate
2002-12-16
2004-02-10
Bagnell, David (Department: 3677)
Mining or in situ disintegration of hard material
Processes
Breaking down by direct contact with fluid
C405S055000, C405S058000, C299S016000, C175S067000, C175S062000
Reexamination Certificate
active
06688702
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
This invention generally relates to systems for carrying out remote hydraulic extraction (mining) of rocks, minerals and industrial materials, and more specifically, but not by way of limitation, to hydraulic borehole mining (BHM) systems, applied through non-vertical (near-horizontal) boreholes which allow simplification of the technology and reduction of drilling procedures by increasing the volume of material to be mined per borehole.
This BHM method is intended for extraction of mineral resources and industrial materials and creation of underground caverns through inclined boreholes, including deviated boreholes. This technology can be applied from the earth surface, as well as from underground mines, open pit floors, valleys and from water surfaces. The technology can be used in geological exploration for bulk sampling; in building of underground storage; in stimulation of in-situ leaching, oil, gas and water production; in construction of custom foundation, underground collectors, walls, and barriers; etc. The technology can be used to solve environmental problems, underground firefighting and fire prevention and other applications requiring remote operating and control of the mining processes.
(b) Discussion of Known Art
Borehole mining as a remote underground mining method is based on water jet cutting of rock material. It is accomplished by pumping high-pressure water down to the working area from the surface (pit floor, underground mine or floating platform) by a BHM tool, lowered into a pre-drilled borehole. At its bottom, the tool has a hydromonitor with a nozzle, which creates a water jet to cut rock and create slurry. The created slurry is simultaneously pumped back to the surface by the eductor, located mainly at the tool's very bottom. The slurry is then separated in a settling pit or tank, and clarified water is pumped down again to the borehole. While extracting rock material, underground caverns (stopes) can be created. The shape and proportions of these stopes are the matter of tool manipulation in a hole, which is simply a combination of rotating the tool and sliding it along the borehole axis. Being sufficiently extended along the borehole, these caverns may be used as underground storage for oil, gas and other gaseous or liquefied products.
BHM boreholes are drilled mostly vertically. There are several factors requiring this orientation. First, the BHM tool is rotated in a borehole while mining. During this rotation, the water jet is “flying” just over the slurry level, which naturally is strictly horizontal. Thus, if the tool has even a slight deviation from the vertical axis, the water jet may hit the water (slurry), which will break the jet and decrease its rock cutting ability.
Another problem is transportation of the slurry from the rock face to the tool's eductor zone or borehole sump. If the tool is deviated from the vertical axis, then one side of the cavern created will be above the other. The transporting slope from one side will therefore be steeper than from the other, creating uneven conditions for slurry transportation and making a created cavern asymmetrical. It finally may affect the stability of the cavern and cause an unwanted collapse.
The vertical (chimney-like) ore body shape would be the most appropriate for conventional vertical borehole mining. This requires drilling a borehole along a vertical axis followed by extraction of the ore. Meanwhile, most of the known sedimentary deposits and ore bodies have horizontal or near-horizontal shape and orientation. Except Kimberlite “pipes” and a few known unique-shape deposits, all other ore bodies could be qualified as horizontal or being developed by horizontal layers. In order to develop them by vertical BHM, numerous equally spaced boreholes have to be drilled. The distance (D) between boreholes usually equals the BHM tool reach diameter (usually up to a max. of 9-11 m) plus some offset, if required for between-stope pillars (2-4 m), so then D=10+3=13 m.
It is easy to calculate, for example that the number of boreholes required for the development of an ore body whose plane square area equals to 10,000 m
2
will be:
10,000/(13×13)=59 boreholes, which is a significant number for a 100 m×100 m area. This means that for the development of those types of ore bodies, using conventional BHM, a massive drilling stage will increase the project budget. Additionally, since every drill hole requires surface area, most if not all of the surface over the deposit will be disturbed.
Also, most geo-technological and environmental tasks require near-horizontal development and/or construction (ground walls, drainage collectors and so on), requiring massive drilling along those features. It could be more easily created through a single deviated borehole or one drilled from underground works.
Conventional (vertical) borehole mining suffers from another disadvantage. The vertical BHM is accomplished by moving the tool up (bottom-up schematic) or down (top-down schematic) the borehole. Both of these schematics have problems. While moving the tool “bottom-up”, the eductor is moving together with the tool away from the stope bottom (sump) area, where slurry will collect. In this configuration the material cut from the rock face is free-falling and accumulating on the bottom instead of being removed from the stope.
While moving the tool “top-down” the tool becomes suspended in the stope. Any collapse or fall-off from the stope wall may easily damage the tool, even to a point where it may become impossible to remove the tool from the hole.
Additionally, while increasing the diameter of a cavity, the roof or portion(s) of it may collapse while mining. These collapsed rock masses may interfere with the water jet and be an obstacle on its trajectory between the nozzle and the cutting rock face. In other words, these collapses may prevent BHM process from achieving the maximum possible diameter of the cavern and thus decrease the entire BHM effectiveness. To overcome these disadvantages, a mining technology using inclined, deviated, or near-horizontal boreholes is required, and is the topic of this invention.
The U.S. Pat. No. 4,536,035 to Huffinan et al covers a double-drill hydraulic mining method which includes drilling a slant borehole along the production vein footwall and a vertical borehole to intersect the bottom of the first one. Then, the mining tool is inserted into the slant borehole, while a pumping unit is inserted into the vertical borehole. The mining tool includes a water jet nozzle which cuts the rock while the tool is slowly rotated back-and-forth through 180° and pulled slowly out from the borehole. The created slurry rolls down to the bottom part of the vertical borehole to the pumping unit and is delivered to the surface. This method allows the creation of extended caverns along the slant borehole.
The Huffman method of mining suffers from the following disadvantages:
First, a large diameter (24″) borehole has to be drilled to remove the mined material. This increases drilling procedures and overall mining cost.
Second, the drilling of two boreholes requires a certain footprint on the earth's surface to be developed for drill rig sites, sediment ponds and the other equipment. This is not always possible due to the natural landscape, agricultural and environmental requirements and/or other land surface usage (city or industrial zone, private lands and so on).
Third, the Huffman method has a limited application area. It can be applied “at an angle-pitched mineral vein extending downwardly”, as it is stated in their claim 1. In other words, application in an irregular-shaped ore body will not be as effective as in that of a sloping vein. Additionally, this method is developed to mine seams “having dip angle ranging from 25° to 75°” as it explained in their Detailed Description. Thus, this method cannot be applied in seams lying in a “flat” range between 0° and 25°.
Fourth, this method
Abramov Grigori A.
Wiley Marcus A.
Bagnell David
Mitchell Katherine
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