WO2009109008A1

WO2009109008A1 - Borehole plug with a primary bladder inflation device and a pressure booster

Info

Publication number: WO2009109008A1
Application number: PCT/AU2009/000266
Authority: WO
Inventors: Michael John Martin
Original assignee: Trouperdale Pty Ltd
Priority date: 2008-03-04
Filing date: 2009-03-04
Publication date: 2009-09-11
Also published as: PA8817801A1; CL2008001108A1

Abstract

A borehole plug assembly for installation within a body of water in a borehole comprising a borehole anchor member adapted to frictionally engage with a borehole wall and locate an inflatable bladder adjacent thereto. The inflatable bladder encapsulates a primary bladder inflation device comprising a housing having a primary inflation medium and a pressure boosting device adapted to raise the internal pressure within said housing when said internal pressure falls below a predetermined level to thereby dispense substantially all of said primary inflation medium from said primary bladder inflation device and inflate said inflatable bladder.

Description

BOREHOLE PLUG WITH A PRIMARY BLADDER INFLATION DEVICE AND A PRESSURE BOOSTER

FIELD OF THE INVENTION

This invention is concerned with improvements in explosives decking systems. The invention is concerned particularly with an apparatus and method for anchoring and inflating expandable borehole plugs in a borehole containing water or other fluids.

BACKGROUND OF THE INVENTION

Expandable borehole plugs are generally 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 are described in Australian Patent 763474 and Australian Patent 779463, 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 explosive composition for overburden removal operations is ANFO (ammonium nitrate/fuel oil) because it is relatively inexpensive. ANFO is, however, adversely affected by water and this may necessitate the use of more expensive emulsion explosives, which are unaffected by water, in the bottom of the borehole.

In 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 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 150° 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.

Australian Patent Application 2007201040, the disclosure of which is incorporated herein by reference, discloses a borehole anchor which is particularly effective at lodging an inflatable plug assembly in place while the plug is expanding. This allows the borehole plug to be accurately placed within a borehole which contains a body of water.

The borehole plug can be dragged down, during inflation, to the level of the anchor and held in place while the plug fully expands to form a seal with the borehole walls. This arrangement works well at depths of up to 15 metres or so.

A problem is encountered, however, when the borehole plug is to be inflated at depths approaching, and beyond, 20 metres. The hydrostatic pressure from the column of water above the expandable borehole plug at these depths is so great that full inflation cannot be achieved. Adequate placement and inflation at depths of about 50 metres, which is required in many operations, is simply not possible. This is due to the external pressure equalising that within the container of inflating medium before said medium is fully dispensed.

If the borehole plug is not fully inflated then an incomplete seal with the borehole wall may be the result. This clearly has negative implications for the precise placement of explosive compositions upon the deck formed as the compositions may slip down the sides of the borehole plug. Further, if the plug is not firmly engaged with the borehole wall, its buoyancy means it places greater stress on the borehole plug anchor to hold the entire assembly in place. 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

In one form of the invention there is provided a borehole plug assembly for installation within a body of water in a borehole, said assembly comprising:

a borehole anchor member having a body member, in use, adapted at opposite ends thereof to frictionally engage with a borehole wall; at least one guide member associated with said body member to slidably locate a string line therein; and

an inflatable bladder, encapsulating a primary bladder inflation device, said inflatable bladder attached to one end of said string line to thereby, in use, locate said inflatable bladder assembly adjacent said borehole anchor member;

wherein, said primary bladder inflation device comprises a housing including a primary inflation medium and a pressure boosting device adapted to raise the internal pressure within said housing when said internal pressure falls below a predetermined level to thereby dispense substantially all of said primary inflation medium from said primary bladder inflation device and inflate said inflatable bladder.

Preferably, said primary inflation medium is at a first internal pressure and said pressure boosting device comprises a container having a booster inflation medium at a second internal pressure, said second internal pressure being higher than said first internal pressure.

In use, said primary bladder inflation device may be activated to release said primary inflation medium resulting in a drop in said first internal pressure which pressure drop actuates, at a predetermined pressure, release of said booster inflation medium from said pressure boosting device to inflate said bladder and engage said borehole plug assembly against the walls of said borehole Suitably, release of said booster inflation medium from said pressure boosting device is actuated when substantially all of said primary inflation medium has been released from said housing.

Preferably, release of said booster inflation medium from said pressure boosting device is actuated when the pressure in said housing is equivalent to the pressure inside said inflatable bladder.

The release of said booster inflation medium from said pressure boosting device may be actuated when the pressure in said housing is equivalent to the external hydrostatic pressure acting on said inflatable bladder.

The body member may be an elongate body member.

If required, the elongate body may further comprise an attachment site adjacent an opposite end of said elongate body to that having said at least one guide member to permit, in use, releasable engagement of said string line.

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

The pressure boosting device can further comprise a valve or resistance seal which is activated to move from a closed position to an open position when said first internal pressure drops to said predetermined pressure.

Preferably, said valve is actuated by a movable platform or a resilient diaphragm. Suitably, said movable platform is moved to actuate said valve by means of one or more biasing members.

The resilient diaphragm may form a wall of a pressurised compartment and said resilient diaphragm is deformed to actuate said valve when the internal pressure of said pressurised compartment is greater than said first internal pressure.

Suitably, said valve is biased to said closed position by a second biasing member.

Actuation of said pressure boosting device may result in continuous or intermittent release of said booster inflation medium.

If required, said booster inflation medium may comprise a nonflammable fluid.

Suitably, said non-flammable fluid is selected from the group consisting of nitrogen, carbon dioxide and the noble gases. The inflatable bladder may be encapsulated by an elongate sleeve.

Preferably, said elongate sleeve, in use, forms a bladder expansion restraint of predetermined volume, said elongate sleeve being yieldable at a predetermined bladder pressure to allow complete expansion of the bladder.

According to one embodiment of the invention there is provided a borehole plug assembly for installation within a body of water in a borehole, the assembly comprising: a borehole anchor member having an elongate body, 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 elongate body to slidably locate a string line therein;

an inflatable bladder, encapsulating a primary bladder inflation device, attached to one end of said string line to thereby, in use, locate said inflatable bladder adjacent said borehole anchor member;

said primary bladder inflation device comprising a housing having a primary inflation medium at a first internal pressure and a pressure boosting device; and

said pressure boosting device comprising a container having a booster inflation medium at a second internal pressure, said second internal pressure being higher than said first internal pressure; wherein said primary bladder inflation device is activated to release said primary inflation medium resulting in a pressure drop in said housing which pressure drop actuates, at a predetermined pressure, release of said booster inflation medium from said pressure boosting device to inflate said bladder and engage said borehole plug assembly against the walls of said borehole.

According to another aspect of the invention there is provided a method for installation of a borehole plug assembly within a body of water in a borehole including the steps of:

lowering a borehole anchor member to a predetermined depth in said borehole via a string line;

tensioning a first free end of said string line to allow opposite ends of said anchor member to frictionally engage the walls of said borehole;

actuating a primary bladder inflation device encapsulated within an inflatable bladder attached to said string line;

tensioning a second free end of said string line to locate said attached inflatable bladder adjacent said anchor member; and wherein, said primary bladder inflation device comprises a housing containing a primary inflation medium and a pressure boosting device adapted to raise the internal pressure within said housing when said internal pressure falls below a predetermined level, following actuation of said primary bladder inflation device, to thereby dispense substantially all of said primary inflation medium from said primary bladder inflation device and inflate said inflatable bladder. Throughout this specification, unless the context requires otherwise, the words "comprise", "comprises" and "comprising" will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

BRIEF DESCRIPTION OF THE FIGURES 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 an anchor member; FIG. 2 shows a plan view of an alternative configuration of an anchor member;

FIG. 3 shows an in-situ side elevation view of yet another configuration of an anchor member;

FIGS. 4-7 show the sequence of operations in installing an anchor member and the subsequent installation of an inflatable plug assembly utilizing the anchor;

FIG. 8 shows an expansion restraint sleeve for use with the inflatable plug assembly;

FIG. 9 shows a bladder inflation device comprising one form of a pressure boosting device for use with the inflatable plug assembly;

FIG. 10 shows a further embodiment of a pressure boosting device; and FIG. 11 shows yet a further embodiment of a pressure boosting device.

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

DETAILED DESCRIPTION QF THE INVENTION It is the combination of a borehole anchor member and an inflatable plug assembly comprising an inflatable bladder containing the primary bladder inflation device having within it the pressure boosting device which enables the borehole plug assembly described hereinafter to be accurately and fixedly placed within a borehole and subsequently fully inflated, even at increasing depths of up to about 50 metres or greater, to sufficiently engage the borehole walls to allow normal blasting operations to proceed.

In one embodiment the invention resides in a borehole plug assembly comprising the combination of a borehole anchor member and an inflatable bladder having a pressure boosting device. The borehole anchor member is adapted to locate the inflatable bladder, which encapsulates a primary bladder inflation device, at a predetermined location within the borehole. The primary bladder inflation device has a housing within which there is found a primary inflation medium at a first internal pressure and a pressure boosting device. The pressure boosting device includes a container having a booster inflation medium at a second internal pressure, the second internal pressure being greater than the first internal pressure.

The primary inflation device can be actuated to release the primary inflation medium and initiate inflation of the bladder. This brings about a drop in the first internal pressure which, when it drops below a set level, results in the booster inflation medium being released from the pressure boosting device. This enables the hydrostatic pressure of the water in the borehole to be more effectively overcome and for the bladder to inflate sufficiently for the borehole plug assembly to engage with the walls of the borehole.

The details of this process are described hereinafter but it will be appreciated that the invention provides for a means of locating a borehole plug assembly within a borehole containing a body of water and a means of overcoming the difficulty in inflating the borehole plug assembly at increasing depths of water due to the restrictive force of the hydrostatic pressure of the water on the release of the primary inflation medium from typical primary inflation devices. 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 serve as guide members to enable sliding engagement with a string line, the purpose of which will be described later.

FIG. 2 shows an alternative configuration of borehole anchor 1 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 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. 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, allowing the anchor to be wedgingly engaged against borehole wall 13. The anchor may be comprised of a rigid material or, as illustrated, 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 and thereby still allow the anchor and borehole plug to be effectively located in such areas. A looped string line 18 extends through guide members 6a and 6b 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 and

18b is secured to anchor 1 via guide members 6a and 6b. As, initially, loop element 18a is releasably secured to guide member 6a 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 and allowing it to sink.

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 1 a in contact with borehole wall 13 until end 1 b engages the borehole wall 13 opposite end 1a. Continued tension on loop 18b causes end 1a to engage firmly against wall 13 while end 1 b wedgingly engages against a respectively adjacent region of wall 13.

FIG. 6 shows the next step in the 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 plug assembly 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 assembly is actuated. The inflatable plug assembly 22 with envelope 23 is then hauled down the borehole by tensioning loop element 18a which slides looped string line 18 through guide members 6a and 6b on anchor 1. 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 described 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 18a and 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. In an alternative embodiment, guide members 6a and 6b may be present as eyelets which are disposed at one end only of the body of the anchor 1. The anchor 1 can then be lowered down into the borehole substantially vertically until the desired depth is achieved and at this time the string attached to the uppermost of the eyelets is tensioned and this will pivot the anchor about the end having the eyelets until it is wedged within the borehole as described previously. The string line which runs through the second eyelet can then be used to drag down the inflatable plug assembly in a manner similar to that already described. This embodiment does away with the need for a slipknot or the like tied in the loop element 18a.

As the inflatable bladder assembly within inflatable plug assembly 22 begins to expand (due to the release of a primary inflation medium from a primary bladder inflation device as will be described hereinafter) 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. Inflatable plug assembly 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 inflatable plug assembly 22 is wedgingly engaged in the borehole 12.

The borehole anchor members and method of use just described thereby allow a borehole plug assembly to be located at a predetermined depth within a borehole under water. The elongate body and ends of the anchor adapted to wedgingly engage the borehole walls ensure the assembly does not move while the inflatable plug assembly is being located adjacent the anchor. This is enables the plug to be placed at increasing depths where the buoyancy effect is relatively large.

Once inflatable plug assembly 22 is fully inflated it is then possible to introduce a quantity of explosive which displaces the body of water 20a above the inflated plug assembly.

However, 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 to engage the wall of the borehole.

Boyle's law provides that for a fixed mass of gas at constant temperature, Pi Vi = p₂ V₂ - constant where

Pi and Vi are initial pressure and volume respectively, and

P₂ V₂ are final pressure and volume respectively when the plug is expanded. By initially restricting the volume of the inflatable bladder assembly into which the inflation medium may expand, it is possible to substantially increase the initial pressure of the inflation medium relative to the pressure of the head of water applied to the expandable bladder.

FIG. 8 shows an inflatable plug assembly 30 comprising sleeve member 31 formed into a generally tubular shape to locate therewithin an inflatable bladder 32 in a rolled up state as shown. Located within the bladder 32 is a primary bladder inflating device (not shown) containing a primary inflating medium, for example, a mixture of water, ethyl alcohol and dimethyl ether or nitrogen, carbon dioxide or like non-flammable gases. The device includes a valve actuator mechanism actuable by applied finger pressure from the exterior of the rolled up assembly within the sleeve shown in FIG. 8. Typically, bladder 32 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 31 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 32.

When the actuator of the primary bladder inflation device containing primary inflating medium is actuated and the inflatable plug assembly 30 is towed down the borehole to a desired depth, as previously described, expansion of bladder 32 is initially restricted by sleeve member 31 and this volumetric restriction allows the pressure in bladder 32 to increase rapidly at a predetermined rate, unhindered by the 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 31 fails by tearing and this allows the inflatable plug assembly 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 member 31 serves not only to control the expansion of bladder 32 but also forms a protective sheath around it as it is lowered into and positioned within the borehole to prevent inadvertent damage to or puncturing of, bladder 32.

This restricted expansion process allows the inflatable plug assembly 30, as described, to be very effective in operation in a borehole under a body of water. The effectiveness, however, is decreased as the depth of water in which plug assembly 30 is to be located increases. For example, the present system may by suitable for depths of up to approximately 15 metres but if placement at depths of 18-20 metres, or greater, are desired then full inflation of the bladder 32 may not be achieved. The hydrostatic pressure of the column of water at these depths is such that it greatly restricts or prolongs the expansion of the bladder assembly 32. This is due to the external pressure equalling that in the primary bladder inflation device before the entire amount of primary inflation medium contained within the inflation device has been dispensed. The present invention further provides for a pressure boosting device located inside the primary bladder inflation device, which will, at a predetermined pressure drop, provide an amount of booster inflation medium to temporarily increase the pressure within the primary bladder inflation device. This enables the primary inflation medium to be substantially fully dispensed from the inflation device by temporarily overcoming the external pressure effect of the column of water. Alternatively, the booster inflation medium released may simply replace the primary inflation medium in inflating the bladder.

FIG. 9 shows one form of a primary bladder inflation device comprising a pressure boosting device for use within the inflatable plug assembly. Primary bladder inflation device 40, in its simplest form, has a housing having a channel 41 which runs from the exterior to the internal chamber 43. Located somewhere along the length of channel 41 is valve 42 which, in operation, prevents the release of primary bladder inflation medium 44 which is held within internal chamber 43 at a predetermined first internal pressure until the valve is actuated and inflation begins.

Pressure boosting device 50 is located within internal chamber 43. In the embodiment shown it takes the form of a simple capsule or widget with a spherical container body 51 and an aperture 52. A booster inflation medium will be contained within body 51 , at a second internal pressure, for release via aperture 52 when the pressure differential between the internal chamber 43 (the first internal pressure) and the interior of boosting device 50 (the second internal pressure) reaches a predetermined level. Initially the second internal pressure will be higher than the first internal pressure.

Boosting device 50 must have a seal, valve assembly or other form of control mechanism preventing the uncontrolled release of pressurised booster inflation medium through aperture 52 and allowing the second internal pressure to remain higher than that of the first internal pressure within internal chamber 43.

In the example shown in FIG. 9 the control mechanism for the release of the booster inflation medium from booster device 50 could be as simple as a resistance seal which is outwardly biased. The internal pressure within internal chamber 43 of inflation device 40 is normally such that the seal is held in place and booster inflation medium cannot escape from aperture 52. When inflation device 40 is activated and the inflation medium 44 is released to initiate inflation of bladder 32, the first internal pressure within chamber 43 will begin to drop. Once the pressure drops below a certain level the outward bias of the seal, due to the second internal pressure created by the booster inflation medium, overcomes the resistance to opening of the seal. The seal will then open and all, or a quantity of, the booster inflation medium is dispensed from booster device 50 into internal chamber 43.

All of the booster inflation medium may be dispensed in one continuous burst, particularly if the seal is designed to blow out and not be resilient. If, however, the seal is resilient then a portion of the booster inflation medium may be dispensed from the booster device until the pressure in the internal chamber increases to the point where the resilient seal is forced back into the closed position. This controlled or intermittent release process will be repeated until the pressure within the booster device 50 and the internal chamber 43 of the bladder inflation device remain equal. FIG. 10 shows a pressure boosting device according to a further embodiment of the present invention. Pressure boosting device 60 comprises a cap 61 which, along with opposing walls 63 of the body of booster device 60 and movable platform 64, defines first compartment 62. Running between the underside of cap 61 and the upper surface of movable platform 64 are one or more first biasing members which, in the embodiment shown, take the form of springs 65.

Movable platform 64, along with walls 63 and fixed platform 67, defines second compartment 66. This compartment has one or more apertures 68 in the walls 63 which are continuous with the exterior i.e. the internal chamber 43 of bladder inflation device 40. Located within second compartment 66 is a valve which has a head 69, a stem 70 and a base 71. Head 69 is in contact with the underside of movable platform 64 while stem 70 passes through flow channel 72 formed in fixed platform 67. Base 71 sits inside fluid chamber 73 which contains booster inflation medium 74. A second biasing member which in the embodiment shown takes the form of helical spring 75 is located around stem 70 and is in resilient contact with fixed platform 67 and head 69.

In use, the booster device 60 is placed inside the internal chamber 43 of primary bladder inflation device 40. The booster inflation medium 74 will be charged to a higher pressure within fluid chamber 73 than that of the primary inflation medium 44 within primary bladder inflation device 40. In one non-limiting example, the primary inflation medium 44 within primary bladder inflation device 40 is charged to a pressure of approximately 75 to 90 psi and the booster inflation medium 74 may be charged to between 3000 to 5500 psi.

When primary bladder inflation device 40 is activated and the inflation plug assembly is being located to the correct depth within the borehole, primary inflation medium 44 is released from the device and the pressure within internal chamber 43 starts to drop. This means the pressure in second compartment 66 drops in a like manner due to apertures 68 resulting in open communication between the two. Springs 65 are biased to push movable platform 64 downwards towards fixed platform 67. The pressure in second compartment 66 will resist this movement until it drops below a predetermined level due to inflation medium 43 being dispensed. This level is easily determined by the rating of the springs 65. Once below this level movable platform 64 moves down and in doing so forces down the head 69 of the valve. This force is transmitted down stem 70 to base 71 which is pushed further into fluid chamber 73. This breaks the sealing contact of base 71 with fixed platform 67 and so flow channel 72 is opened and booster inflation medium 74 can escape, firstly, into second compartment 66 and then out to the internal chamber 43 of bladder inflation device 40, via apertures 68.

As the pressure in second compartment 66 is elevated it may reach such a level as to push movable platform 64 back up against the downward force of springs 65. Helical spring 75 also contributes by forcing head 69 upwards. Base 71 will then seal off flow channel 72 and prevent the release of any further booster inflation medium 74 until the pressure drops and the process begins again. Alternatively, depending on the rating of the springs 65 and the initial pressure drop, the pressure in second compartment 66 may be insufficient to force movable platform 64 upwardly and close flow channel 72. In this case, all of booster inflation medium 74 will be dispensed in substantially one burst.

FIG. 11 shows a pressure boosting device according to a further embodiment of the present invention. Pressure boosting device 80 comprises a cap 81 which has a channel 82 extending through it into first compartment 83. Channel 82 has a one way valve 84 allowing fluid only to enter first compartment 83 but not leave. First compartment 83 is defined by the opposing walls 85 of the body of booster device 80, cap 81 and resilient diaphragm 86 and is pressurised. Resilient diaphragm 86 also defines second compartment 87, along with walls 85 and fixed platform 88. Second compartment 87 has one or more apertures 89 in the walls 85 which are continuous with the exterior i.e. the internal chamber 43 of primary bladder inflation device 40. Located within second compartment 87 is a valve which has a head 90, a stem 91 and a base 92. Head 90 is in contact with the underside of resilient diaphragm 86 while stem 91 passes through flow channel 93 formed in fixed platform 88. Base 92 sits inside fluid chamber 94 containing the booster inflation medium 95. A biasing member, which in the embodiment shown takes the form of helical spring 96, is located around stem 91 and is in resilient contact with fixed platform 88 and head 90.

This embodiment works in much the same manner as already described with a few notable exceptions. As inflation progresses and the pressure within second compartment 87 drops, diaphragm 86 is forced down by the internal pressure within first compartment 83 which was previously charged to the desired pressure via channel 82 and one way valve 84. This results in booster inflation medium 95 being released as described before.

The pressure in second compartment 87 will rise and may be sufficient to push diaphragm 86 back up and thereby close flow channel 93. In this manner pressure booster device 80 will dispense booster inflation medium 95 to maintain a relatively constant pressure within primary bladder inflation device 40 until substantially all of the inflation medium 44 has been dispensed and the inflatable plug assembly is fully inflated, even at depths of 15 metres and greater.

The booster inflation medium within the pressure booster device may be selected from a range of suitable fluids which may be the same as or different to the primary inflation fluid. Preferably, the booster fluid will be a non-flammable and/or inert gas such as nitrogen, carbon dioxide or a noble gas. These gases are suitable for supplying the necessary boost in pressure to inflate the bladder to the desired extent and have the added benefit of reducing the overall flammability of the device. This is particularly important in the field of explosive decking systems where an explosion may get out of control if too much flammable material is present. The use of non-flammable gases also aids in obtaining regulatory approval for the decking device.

The pressure boosting devices described herein contain booster inflation medium at a higher pressure than the primary inflation medium in the primary bladder inflation device. To enable this to be achieved the booster inflation medium must be capable of being charged to a higher pressure without initiating the release mechanisms described previously.

Typically, the primary bladder inflation device will be charged first to the desired pressure, for example, 70 to 100psi. This charging process may also add inflation medium to the pressure boosting device if the same fluid is used for both. Access to the fluid chamber of the pressure boosting device can be achieved by provision of a simple one way valve or the like as described previously. To achieve the higher second internal pressure the fluid chamber of the pressure boosting device must then be further charged with a separate fluid source, for example, via a tube inlet attached directly to the valve of the fluid chamber and ending in a fluid source which can be delivered at high pressure. In one non-limiting example, the booster inflation medium may be charged to pressures between 2000 to 6000 psi, preferably 3000 to 5500 psi. There are a number of means known in the art for achieving the higher internal pressure in the fluid chamber of the pressure boosting device. If the booster inflation medium is different to the primary inflation medium then this separate charging means would be used alone to charge the pressure boosting device.

The pressure boosting devices described herein, in combination with the anchor member, allow the decking systems to be, firstly, located and subsequently inflated at depths of water in a borehole which were not previously possible. The boost of pressure they provide enables substantially all the inflation medium to be dispensed from the primary bladder inflation device even against the considerable hydrostatic pressure found at depths of up to and around 50 meters. If all of the primary inflation medium should not be dispensed it may well be that the booster inflation medium released serves to take the place of the primary inflation medium and contributes directly to the inflation of the bladder.

It will be appreciated that the positive effect of the pressure boosting device may well be such that sleeve member 31 , as described previously, is simply unnecessary. Sleeve member 31 acts to restrict expansion of the bladder assembly 32 to allow pressure build up and enable full inflation to be achieved more rapidly. Since the pressure boosting devices described herein promote the dispensing of the inflation fluid from the bladder inflation device in spite of the hydrostatic pressure of the column of water in the borehole, or simply replace the need for all of it to be dispensed, then the use of a sleeve member 31 or the like in the bladder 32 may be inessential depending on the particular booster device used and the depth of water at which the decking is located.

The amount of booster inflation medium within the booster device and the pressure it is kept at will depend on many factors such as the inflation medium used, the depth of water in the borehole in which the assembly is to be located and the nature of the booster device itself. The amount of booster fluid will be calculated so that it will not be entirely dispensed until the primary inflation fluid has been substantially dispensed and/or the bladder is fully inflated.

From the description provided it will be appreciated that there must be some degree of release of primary inflation medium and, hence, drop in the first internal pressure for the pressure boosting device to be actuated. It should be understood that the degree of this pressure drop required to actuate the pressure boosting device can be set and so may be minimal or considerable. In one non-limiting example, the pressure boosting device is actuated to release the booster inflation medium when the internal pressure in the primary bladder inflation device drops below about 70 to 75 psi. In one embodiment the pressure boosting device will be actuated when the primary inflation medium has been released to such an extent that the first internal pressure has dropped to become equal with the pressure of primary inflation fluid now in the bladder (this will generally occur when the matching pressure in the bladder of the external hydrostatic pressure is reached). It will be at this point that the effect of the pressure boosting device will be essential to achieve any further inflation.

A number of different embodiments of the booster device have been shown but essentially any device which can deliver a sufficient quantity of a booster inflation medium to aid in dispensing substantially all the inflation medium from the bladder inflation device is considered useful.

A very simple example of the kind of device which achieves a pressure release effect is described in U.S. Patent No. 5,110,012 which discloses a dispenser for a beverage, such as beer, in which the contents of the container are pressurized by gas from a cartridge in the container. A pressure responsive member in the container is movable in response to differences in pressure between that of the atmosphere and of the inside of the container. It should now be clear from the advantages of the borehole plug assembly described herein that the invention lies in the combination of a borehole anchor member suitable to reliably locate and maintain an inflatable plug assembly at a predetermined depth in a borehole and a pressure booster device contained within a primary bladder inflation device which in turn is encapsulated within an inflatable bladder. This combination enables the location and subsequent inflation of the bladder in a depth of water to an extent such that the borehole plug assembly will engage against the walls of the borehole even at increasing depths of upwards of 15 metres and even at depths as great as about 50 metres, under a column of water. Without an anchor member which can form a strong wedging engagement, as described above, the inflatable plug assembly could not be drawn down to the desired depths while simultaneously inflating. This is because the buoyancy effect at such depths would overcome any weak engagement with the borehole wall and the placement would be lost. The anchor member also needs a suitable mechanism, such as one or more guide members and associated string line, to locate the inflatable plug assembly containing the inflatable bladder etc, adjacent to the anchor member.

Likewise, without the use of a pressure booster device, such as those discussed above, the placement of the borehole plug assembly at increasing depths would be pointless as the inflatable bladder could not be fully inflated due to the hydrostatic pressure of the column of water. This results in the plug not engaging the borehole walls with sufficient force to support explosives compositions and prevent them escaping around the plug assembly.

Throughout the specification the aim has been to describe the preferred embodiments of the invention without limiting the invention to any one embodiment or specific collection of features. It will therefore be appreciated by those of skill in the art that, in light of the instant disclosure, various modifications and changes can be made in the particular embodiments exemplified without departing from the scope of the present invention.

Claims

1. A borehole plug assembly for installation within a body of water in a borehole, said assembly comprising:

a borehole anchor member having a body member, in use, adapted at opposite ends thereof to frictionally engage with a borehole wall;

at least one guide member associated with said body member to slidably locate a string line therein; and

2. The borehole plug assembly of claim 1 wherein said primary inflation medium is at a first internal pressure and said pressure boosting device comprises a container having a booster inflation medium at a second internal pressure, said second internal pressure being higher than said first internal pressure.

3. The borehole plug assembly of claim 2 wherein, in use, said primary bladder inflation device is activated to release said primary inflation medium resulting in a drop in said first internal pressure which pressure drop actuates, at a predetermined pressure, release of said booster inflation medium from said pressure boosting device to inflate said bladder and engage said borehole plug assembly against the walls of said borehole.

4. The borehole plug assembly of claim 3 wherein release of said booster inflation medium from said pressure boosting device is actuated when substantially all of said primary inflation medium has been released from said housing.

5. The borehole plug assembly of claim 3 wherein release of said booster inflation medium from said pressure boosting device is actuated when the pressure in said housing is equivalent to the pressure inside said inflatable bladder.

6. The borehole plug assembly of claim 3 wherein release of said booster inflation medium from said pressure boosting device is actuated when the pressure in said housing is equivalent to an external hydrostatic pressure acting on said inflatable bladder.

7. The borehole plug assembly of claim 1 wherein the body member is an elongate body member.

8. The borehole plug assembly of claim 7 wherein said elongate body member is comprised of a resiliently flexible material.

9. The borehole plug assembly of claim 7 or claim 8 wherein said elongate body member includes one or more tapered engagement members adapted, in use, to at least partially penetrate said borehole wall.

10. The borehole plug assembly of claim 7 or claim 8 wherein said elongate body member includes one or more resilient engagement members adapted, in use, to frictionally engage against said borehole wall.

11. The borehole plug assembly of any one of claim 7 to claim 10 wherein said elongate body member comprises an attachment site adjacent an opposite end of said elongate body to that having said at least one guide member to permit, in use, releasable engagement of said string line.

12. The borehole plug assembly of claim 11 wherein said attachment site comprises a guide member slidably locating said string line after disengagement therewith.

13. The borehole plug assembly of claim 3 wherein said pressure boosting device further comprises a valve or resistance seal which is activated to move from a closed position to an open position when said first internal pressure drops to said predetermined pressure.

14. The borehole plug assembly of claim 13 wherein said valve is actuated by a movable platform or a resilient diaphragm.

15. The borehole plug assembly of claim 14 wherein said movable platform is moved to actuate said valve by means of one or more biasing members.

16. The borehole plug assembly of claim 14 wherein said resilient diaphragm forms a wall of a pressurised compartment and said resilient diaphragm is deformed to actuate said valve when the internal pressure of said pressurised compartment is greater than said first internal pressure.

17. The borehole plug assembly of claim 13 wherein said valve is biased to said closed position by a second biasing member.

18. The borehole plug assembly of any one of claim 2 to claim 17 wherein said booster inflation medium comprises a non-flammable fluid.

19. The borehole plug assembly of claim 18 wherein said non-flammable fluid is selected from the group consisting of nitrogen, carbon dioxide and the noble gases.

20. The borehole plug assembly of claim 19 wherein said non-flammable fluid is nitrogen.

21. The borehole plug assembly of claim 1 wherein said inflatable bladder is encapsulated by an elongate sleeve.

22. The borehole plug assembly of claim 21 wherein said elongate sleeve, in use, forms a bladder expansion restraint of predetermined volume, said elongate sleeve being yieldable at a predetermined inflatable bladder pressure.

23. A method for installation of a borehole plug assembly within a body of water in a borehole including the steps of:

tensioning a second free end of said string line to locate said attached inflatable bladder adjacent said anchor member; and

wherein, said primary bladder inflation device comprises a housing containing a primary inflation medium and a pressure boosting device adapted to raise the internal pressure within said housing when said internal pressure falls below a predetermined level, following actuation of said primary bladder inflation device, to thereby dispense substantially all of said primary inflation medium from said primary bladder inflation device and inflate said inflatable bladder.

24. The method of claim 23 wherein said primary inflation medium is at a first internal pressure and said pressure boosting device comprises a container having a booster inflation medium at a second internal pressure, said second internal pressure being higher than said first internal pressure.

25. The method of claim 24 wherein, in use, said primary bladder inflation device is activated to release said primary inflation medium resulting in a drop in said first internal pressure which pressure drop actuates, at a predetermined pressure, release of said booster inflation medium from said pressure boosting device to inflate said bladder and engage said borehole plug assembly against the walls of said borehole.

26. The method of claim 23 wherein said string line is slidably secured in at least one guide member located adjacent one end of said anchor member.

27. The method of any one of claim 23 to claim 25 wherein said pressure boosting device further comprises a valve or resistance seal which is activated to move from a closed position to an open position when said predetermined pressure is reached.

28. The method of claim 27 wherein said valve is actuated by a movable platform or resilient diaphragm.

29. The method of claim 28 wherein said movable platform is moved to actuate said valve by means of one or more biasing members.

30. The method of claim 28 wherein said resilient diaphragm forms a wall of a pressurised compartment and said resilient diaphragm is deformed to actuate said valve when the internal pressure of said pressurised compartment is greater than an internal pressure of said housing of said primary bladder inflation device.

31. The method of claim 24 wherein said booster inflation medium comprises a non-flammable fluid.

32. The method of claim 31 wherein said non-flammable fluid is selected from the group consisting of nitrogen, carbon dioxide and the noble gases.

33. The method of claim 23 when performed using the apparatus of any one of claim 1 to claim 22.