AU2007201040A1

AU2007201040A1 - Improvements in explosives decking systems

Info

Publication number: AU2007201040A1
Application number: AU2007201040A
Authority: AU
Inventors: Michael John Martin; Ernesto Mollica
Original assignee: Crinum IP Pty Ltd
Current assignee: Crinum IP Pty Ltd
Priority date: 2006-03-09
Filing date: 2007-03-09
Publication date: 2007-09-27

Description

G

P/00/011 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: "IMPROVEMENTS IN EXPLOSIVES DECKING SYSTEMS" The following statement is a full description of this invention, including the best method of performing it known to us: 1

STITLE

"IMPROVEMENTS IN EXPLOSIVES DECKING SYSTEMS" FIELD OF THE INVENTION This invention is concerned with improvements in explosives decking systems.

The invention is concerned particularly with a method and apparatus for anchoring expandable borehole plugs in a borehole containing N water or other fluids.

BACKGROUND OF THE INVENTION Expandable borehole plugs generally are employed to form a support or "deck" within an explosives borehole to support a column of explosive composition thereabove. Selective placement of one or more borehole plugs in a borehole enables selective concentration of explosive energy in one or more regions along the length of the borehole.

Expandable borehole plugs or modified forms thereof suitable for use with the present invention are described in Australian Patent 763474 and Australian Patent 779463 to the same assignee, the disclosures of which are incorporated herein by reference. These expandable borehole plugs comprise a sealed bladder in which is located a container of inflating medium such as a compressed gas, a gas liquid admixture or a mixture of chemicals capable of reacting to form a gaseous inflation fluid.

It is not uncommon, when drilling explosives boreholes, to intersect an underground aquifer which results in the accumulation of a body of water within the borehole. In open cut mining operations a preferred 2 explosive composition for overburden removal operations is ANFO (ammonium nitrate/fuel oil) because it is relatively inexpensive. ANFO is 0however adversely affected by water and this may necessitate the use of more expensive emulsion explosives which are unaffected by water in the 5 bottom of the borehole.

SIn some cases it is possible to employ an expandable borehole plug to form a closure in the borehole above the level of water therein, the expanded plug forming a support deck for ANFO subsequently introduced into the borehole.

A problem arises however when it is required to form a deck within a column of water in a borehole below the surface of the water.

Where the borehole intersects several coal or mineral seams, it is common practice these days to locate explosive composition in the region of the interburden and overburden layers and this may necessitate precise placement, within a flooded borehole of a base borehole plug to support a column of explosive within an interburden layer. After filling the interburden region with explosive, further borehole plugs are employed on top of the explosive column and at the intersection of the next coal/interburden or overburden layer to isolate the coal seam from the explosive introduced into the borehole.

With inflatable borehole plugs, it is not possible to accurately locate the plug at a required depth because when it starts to inflate, the plug assembly becomes increasingly buoyant as it expands.

One proposal to overcome the problem of establishing a deck at a required level within a column of water within a borehole is a generally cup-shaped frusto-conical plastics plug device having an end wall formed on the smaller diameter end and top wall edge tapering from one side of the larger diameter end to the other side thereof. After inserting a detonation cord and detonator into the borehole, the plastics plug device is partially filled with borehole chippings and is lowered on a string line to a required depth.

The plastics plug device is so configured that when the string line is tensioned, the plug device rotates through about 1500 with the outwardly tapering frusto-conical wall facing downwardly with the free edge thereof frictionally engaging the borehole wall and the upwardly facing base forming a support surface.

While generally effective for their intended purposes, these cup-like plug devices have an unacceptable failure rate when loaded with a column of explosive composition where localized spalling in the borehole wall prevents an adequate frictional engagement by the free edge of the device.

Accordingly, it is an aim of the present invention to overcome or alleviate at least some of the disadvantages of underwater borehole decking systems and otherwise to provide consumers with a more convenient choice.

SUMMARY OF THE INVENTION According to one aspect of the invention there is provided a method for installation of an inflatable borehole plug within a body of water in a borehole, said method comprising the steps of:lowering, in an upright position, to a predetermined depth in said borehole via a string line, a bore anchor member, said string line being slidably secured in at least one guide member located adjacent one end of said anchor member, said string line being releasably engaged to said anchor member at or adjacent an opposite end of said anchor member; tensioning a first free end of said string line passing through said at least one guide member to effect rotation of said anchor member until opposite ends of said anchor member frictionally engage in a wall of said borehole; tensioning a second free end of said string line releasably engaged to said anchor to release said string line from engagement with said anchor; and, drawing said string line through said at least one guide member to locate an actuated expandable borehole plug assembly, secured to said string line, at a predetermined position adjacent said anchor member and allowing said expandable borehole plug to fully expand to frictionally engage with the wall of the borehole.

According to another aspect of the invention there is provided a borehole anchor member for installation of an inflatable borehole plug within a body of water in a borehole, said anchor member comprising:a body member, in use, adapted at opposite ends thereof to frictionally engage with a borehole wall; at least one guide member located adjacent one end of said body member to slidably locate a string line therein; and, an attachment site adjacent an opposite end of said body member to permit, in use, releasable engagement of said string line.

If required, said attachment site may comprise a guide member slidably locating said string line after disengagement therewith.

Suitably, said body member includes one or more tapered engagement members adapted, in use, to at least partially penetrate said borehole wall.

The body member may include one or more resilient engagement members adapted, in use, to frictionally engage against said borehole wall.

If required, the body member may be a rigid member.

Preferably, said body member is comprised of a resiliently flexible material.

According to another aspect of the invention there is provided an inflatable borehole plug assembly for use with the aforementioned method, said borehole plug assembly including an elongate sleeve encapsulating an inflatable bladder assembly, said assembly being adapted for attachment adjacent one end thereof to said string line for selective location of said plug assembly within a body of water in a borehole against buoyancy forces caused by inflation of said plug assembly.

Suitably, said sleeve, in use, forms a substantially tubular bladder expansion restraint of predetermined volume, said sleeve being yieldable at a predetermined bladder pressure to allow complete expansion of said bladder.

If required, said sleeve may be formed from sheet material having one or more regions of reduced tear strength formed therein.

(If required, said sleeve may include a neck region adapted for tattachment to said string line.

Preferably, said sleeve includes an attachment aperture

O

adjacent one end for attachment of said string line.

Alternatively, said sleeve may include an aperture formed Sadjacent a lower end thereof to enable attachment of said string line to an attachment aperture associated with said bladder.

BRIEF DESCRIPTION OF THE DRAWINGS In order that the various aspects of the invention may be readily understood and put into practical effect, reference will now be made to preferred embodiments illustrated in the accompanying drawings in which:- FIG. 1 shows a plan view of one form of borehole anchor; FIG. 2 shows a plan view of an alternative configuration of borehole anchor; FIG. 3 shows an in-situ side elevational view of yet another configuration of borehole anchor; FIGS. 4-7 show sequentially the sequence of operations in installing the borehole anchors of the invention and the subsequent installation of an expandable borehole plug utilizing the anchor; and FIG. 8 shows an expansion restraint sleeve for use with the inflatable borehole plug assembly.

In the accompanying drawings like numerals are employed for like features for simplicity in understanding the description.

DETAILED DESCRIPTION OF THE DRAWINGS As illustrated in FIG. 1, borehole anchor 1 comprises an elongate body 2 having opposite ends adapted to engage against the wall of a borehole.

One or both ends may comprise tapered tooth-like projections 3 capable of partial penetration into the borehole wall. Alternatively, one or both ends may comprise blunt finger-like projections 4 capable of wedging frictional engagement against the borehole wall. One or more of finger-like projections 4 may have a chisel-like taper 5 on one end to enhance engagement with the borehole wall surface depending upon the hardness of the earth formation through which the borehole extends. Spaced hook members 6 enable sliding engagement with a string line, the purpose of which will be described later.

FIG. 2 shows an alternative configuration of borehole anchor wherein one end 7 is formed with an arcuate shape having a radius approximating that of a borehole in which it is intended to be used. Secured over the arcuate end 7 is soft resilient moulded polymeric pad 8 which, under compression in a borehole, enhances the frictional engagement between the anchor and the borehole wall. The opposite end of the anchor is shown formed as a series of splayed fingers 9, again with an arcuate perimeter having a radius generally corresponding to the radius of a borehole. Fingers 9 terminate in soft resilient pads 10 adapted to increase frictional engagement with a borehole wall. Spaced apertures 11 in body 2 serve as guide members through which a string line can slidingly extend.

8 According to this aspect of the invention, the borehole anchors are comprised of a non-metallic material as required by mine operators. The anchors 1 may be comprised of moulded plastics or rubber polymers or they may be formed from sheet materials including polymeric materials and timber.

FIG. 3 shows a borehole anchor 1 engaged in a borehole 12.

As can be seen, the length of the anchor is slightly greater than the diameter of the borehole whereby the anchor may be wedgingly engaged against the borehole wall 13. The anchors may be comprised of a rigid material or, as illustrated, they may be formed from a stiff resiliently flexible material which bends to a degree when installed thereby providing an outwardly directed resilient restorative force between the ends of the anchor and the borehole wall 13. Where the earth formation 14 in which the borehole is formed is relatively soft, the borehole wall 13 may be subject to spalling during drilling or as a result of ingress of water to form cavities 15 in the borehole wall surface. Pointed teeth 16 on one end of anchor 1 can penetrate the borehole wall and provide a fulcrum point about which anchor 1 can rotate to permit a tapered chisel-like end 17 to be wedgingly engaged against borehole wall 13.

A looped string line 18 extends through guide members 6 and the free ends of the string line extend beyond the mouth of borehole 12.

One loop element 18a is releasably secured to guide member 6a by a releasable slip knot 19 or the like. The other loop element 18b is slidably engageable in guide member 6b such that when loop component 18b is tensioned, it rotates the anchor 1 into frictional engagement with the borehole wall.

FIGS. 4-7 show progressively the installation of the borehole anchor and an inflatable borehole plug within a body of water 20 in borehole 12.

In FIG. 4, a looped string line 18 comprising loop elements 18a, 18b is secured to anchor 1 via guide members 6a, 6b. As initially, loop 1 element 18a is releasably secured to guide member 18a by a slip knot or the like 19, the anchor may be lowered to a predetermined depth in a body of water 20 in borehole 12 by suspending the anchor vertically from loop element 18a.

Once at a predetermined position within the borehole as shown in FIG. 5, loop element 18a is tied off on peg 21 and tension is applied to loop element 18b which causes partial clockwise rotation of anchor 1 about end la in contact with borehole wall 13 until end 16 engages the borehole wall 13 opposite anchor end 1 a. Continued tension on loop 18b causes end l a to engage firmly against wall 13 while end lb wedgingly engages against a respectively adjacent region of wall 13.

FIG. 6 shows the next sequence wherein with anchor 1 firmly engaged in borehole 12, loop element 18a is tensioned to undo slip knot or the like 19. An inflatable borehole plug 22 of the type referred to in Australian Patents 779463 and/or 763474 is encapsulated in an elongate tubular envelope 23 having one or more attachment eyelets 24 adjacent one end is then secured to the end of loop element 18b and a slow release inflation mechanism for the inflatable bladder is actuated. The borehole plug assembly 22,23 is then hauled down the borehole by tensioning loop element 18a which slides through guide elements 6a,6b on anchor 1.

As the inflatable plug assembly begins to expand it is hauled into the body of water 20 against an increasing buoyancy effect and when it reaches anchor 1, loop element 18a is again tied off on peg 21. Plug 22 continues to expand and as it does so it increases the wedging engagement of anchor 1 in the borehole 12 until it is fully inflated as shown in FIG. 7 whereby the plug 22 is wedgingly engaged in the borehole 12.

Once borehole plug 22 is fully inflated it is then possible to introduce a quantity of emulsion explosive which displaces the body of water above the inflated borehole plug.

Where it is required to locate an expandable borehole plug into a borehole containing a large quantity of water, the hydrostatic pressure applied to the unexpanded borehole plug can interfere with or substantially prolong the expansion of the expandable plug until it engages the wall of the borehole.

Boyle's law provides that for a fixed mass of gas at constant temperature, Pi V 1 P2 V 2 constant where Pi and V 1 are initial pressure and volume respectively, and P2 V 2 are final pressure and volume respectively when the plug is expanded.

11 By initially restricting the volume of the borehole plug into which the inflation fluid may expand, it is possible to substantially increase the initial pressure of the inflation fluid relative to the pressure of the head of water applied to the expandable bladder.

FIG. 8 shows a borehole plug assembly 30 comprising sleeve member 31 formed into a generally tubular shape to locate therewithin an expandable bladder 32 in a rolled up state as shown. Located within the bladder 32 is a container (not shown) of inflating medium such as a mixture of water, ethyl alcohol and dimethyl ether and the container includes a valve actuator mechanism actuable by applied finger pressure from the exterior of the rolled up assembly within the sleeve as shown in FIG. 8.

Typically, expandable bladder 31 comprises a seam welded bag fabricated from a laminate of films of Nylon or Nylon copolymers with an m LLDPE sealant film and the sleeve member 32 may comprise a similar polymeric film laminate or it may comprise a woven polyethylene or polypropylene seam welded along opposing sides to form lines of weakness or regions of reduced tear strength 33. The sleeve member is also welded across its base 34 with an opening 35 therein for access to a tethering eyelet 36 in the lower end of bladder 31.

When the actuator of the container of inflating medium is actuated and the assembly 30 is towed down the borehole to a desired depth as previously described, expansion of bladder 31 is initially restricted by sleeve member 32 and this volumetric restriction allows the pressure in bladder 31 to increase rapidly at a predetermined rate unhindered by the 12 hydrostatic pressure applied by the column of water in the borehole. At a predetermined pressure of say, 70% of the final inflated pressure of the bladder, the welded seam 33 in sleeve member 30 fails by tearing and this allows the bladder 30 to continue to expand rapidly until it firmly engages against the wall of the borehole to form a load bearing plug. The final inflated pressure may be in the range of from 50-120 psi depending upon borehole diameter and other conditions such as ambient temperature, mass of explosive or borehole chippings to be supported, etc.

Sleeve 30 serves not only to control the expansion of bladder 30 but it also forms a protective sheath about the bladder 31 as it is lowered into and positioned within the borehole to prevent inadvertent damage to or puncturing of the bladder 31.

Where multiple spaced explosive charges are located in a borehole adjacent inter-burden strata, it is likely that multiple detonating cords extend down the borehole to detonators located at the base of each explosive charge. A particularly advantageous feature of the anchors according to the present invention is that being in the form of an elongate bar, there is sufficient space on either side of the central body portion 2 for detonating cords to pass without being snagged by the anchor during installation. Because the anchors are suspended in the borehole by a pair of loop elements 18, 18b as shown in FIG. 4, the orientation of the anchor 1 relative to detonating cords in the borehole is easily arranged to avoid contact with the detonating cords.

It readily will be apparent to a person skilled in the art that 13 many modifications and variations may be made to the aspects of the invention described herein without departing from the spirit and scope thereof.

Claims

1. A borehole anchor member for installation of an inflatable borehole plug within a body of water in a borehole, said anchor member comprising:- a body member, in use, adapted at opposite ends thereof to frictionally engage with a borehole wall; at least one guide member located adjacent one end of said body member to slidably locate a string line therein; and, an attachment site adjacent an opposite end of said body member to permit, in use, releasable engagement of said string line.

2. An anchor as claimed in claim 1 wherein said attachment site comprises a guide member slidably locating said string line after disengagement therewith.

3. An anchor as claimed in claim 1 or claim 2 wherein said body member includes one or more tapered engagement members adapted, in use, to at least partially penetrate said borehole wall.

4. An anchor as claimed in claim 1 or claim 2 wherein said body member includes one or more resilient engagement members adapted, in use, to frictionally engage against said borehole wall.

5. An anchor as claimed in any preceding claim wherein the body member is a rigid member.

6. An anchor member as claimed in any one of claims 1 to 4 wherein said body member is comprised of a resiliently flexible material.

7. A method for installation of an inflatable borehole plug within a body of water in a borehole, said method comprising the steps of:- lowering, in an upright position, to a predetermined depth in said borehole via a string line, a bore anchor member according to any one of claims 1 to 6, said string line being slidably secured in at least one guide member located adjacent one end of said anchor member, said string line being releasably engaged to said anchor member at or adjacent an opposite end of said anchor member; tensioning a first free end of said string line passing through said at least one guide member to effect rotation of said anchor member until opposite ends of said anchor member frictionally engage in a wall of said borehole; tensioning a second free end of said string line releasably engaged to said anchor to release said string line from engagement with said anchor; and, drawing said string line through said at least one guide member to locate an actuated expandable borehole plug assembly, secured to said string line, at a predetermined position adjacent said anchor member and allowing said expandable borehole plug to fully expand to frictionally engage with the wall of the borehole.

8. An inflatable borehole plug assembly for use with the method of claim 7, said borehole plug assembly including an elongate sleeve encapsulating an inflatable bladder assembly, said assembly being adapted for attachment adjacent one end thereof to said string line for selective location of said plug assembly within a body of water in a borehole against buoyancy forces caused by inflation of said plug assembly.

9. An inflatable borehole plug assembly as claimed in claim 8 wherein said sleeve, in use, forms a substantially tubular bladder expansion restraint of predetermined volume, said sleeve being yieldable at a predetermined bladder pressure to allow complete expansion of said bladder.

An inflatable borehole plug assembly according to claim 8 or claim 9 wherein said sleeve is formed from sheet material having one or more regions of reduced tear strength formed therein.

11. An inflatable borehole plug assembly as claimed in anyone of claims 8 to 10, wherein said sleeve includes a neck region adapted for attachment to said string line.

12. An inflatable borehole plug assembly as claimed in any one of claims 8 to 10 wherein said sleeve includes an attachment aperture adjacent one end for attachment of said string line.

13. An inflatable borehole plug assembly as claimed in any one of claims 8 to 10 wherein said sleeve includes an aperture formed adjacent a lower end thereof to enable attachment of said string line to an attachment aperture associated with said bladder.

14. A borehole anchor member substantially as hereinbefore described with reference to FIGS. 1 to 7 of the accompanying drawings.

A method for the installation of an inflatable borehole plug within a body of water in a borehole substantially as hereinbefore described with reference to the accompanying drawings. 17

16. An inflatable borehole plug assembly substantially as hereinbefore described with reference to the accompanying drawings. DATED this Ninth day of March 2007. TROUPERDALE PTY LTD By its Patent Attorneys FISHER ADAMS KELLY