AU3559502A - A thermal cover for an inflatable borehole plug - Google Patents

Description

A THERMAL COVER FOR AN INFLATABLE BOREHOLE PLUG FIELD OF THE INVENTION This invention is directed to various means to provide thermal protection to an inflatable borehole plug, prior to inflation to prevent the can and/or reagents and bag from radiant heat buildup when left out in the sunlight.

BACKGROUND ART Boreholes are drilled so that explosive charges may be placed in the borehole at a particular position. Sometimes, the borehole is entirely filled with explosive, but other times an explosive charge must be placed somewhere along the bore hole length. For this type of use, a plug is lowered down the borehole to the desired area to form a support platform for the explosive.

Inflatable borehole plug assemblies are well known. The assemblies comprise an inflatable bag that can be inflated to form the bore hole plug. Inside the bag is a pressurised can that contains the inflating substance. The can is provided with a valve that can be opened to expel the inflating substance into the bag to inflate the bag. The pressurised can has a one-way valve that can be locked into the open position to expel the inflating substance (typically hydrocarbons). The plug assembly is attached to a measured length of rope and is lowered down the hole to be supported by the rope until the plug inflates to be jammed against the wall of the borehole.

In the past, the valve was opened and the plug assembly was quickly lowered down or pushed down the borehole and it was hoped that the plug assembly could be positioned before the bag was inflated to the point where it formed the plug.

It is known to use reagents which, when mixed, create a gas which expands in the inflatable bag to create the plug. A major disadvantage with this arrangement is that the reaction rate varies depending on temperature and other climatic condition that makes it difficult to ensure that the plug assembly is correctly positioned in the bore hole before substantial inflation takes place. Often, the inflation occurred too quickly, which meant that the inflatable bag would plug the borehole at an undesired position.

More recently, pressurised cans have been used to inflate the bag. As the bag can be lowered some considerable distance down the borehole, it is necessary to actuate the can valve prior to lowering the bag down the borehole. For this reason, various attempts have been made to provide some form of time delay between activating the can valve and substantial inflation of the bag.

One attempt involves a specially filled pressurised can that contains a quantity of water as well as the inflating substance (typically hydrocarbon). The water and the hydrocarbon do not mix and the water, being heavier than the hydrocarbon, settles at the bottom of the can. The can has an internal small diameter tube extending from the adjacent the bottom of the can and connected to the valve. When the valve is opened, the water will initially be expelled into the inflatable bag and, after the water has been expelled, the inflating substance will pass into the bag to cause inflation. The amount of water, the diameter of the internal tube, and other parameters can be varied to cause a time delay typically from between 10 to 40 seconds that is considered sufficient to lower the bag down the bore hole and to hold it by the rope until inflation is complete.

While this arrangement was more reliable and provided a more reliable time delay, it suffers from a number of disadvantages. The main disadvantage is that the can can only be used in the upright position. Should the can be tilted, the water will not completely pass out of the can before the inflating substance passes out of the can. This causes premature inflation. It should be appreciated that as the bag is lowered down the hole, the bag can catch on the sides of the borehole and can be tilted or twisted. This can reduce the time delay provided by initial expulsion of the water from the can.

The bag also needs to be carefully held in the vertical position after opening the valve and before lower into the hole. A second disadvantage is that the pressurised can cannot be completely filled with the inflating substance that means that larger cans may be required. A third disadvantage is that specially designed and filled cans are required.

Each of the above systems still uses a pressurised can that is within the inflatable bag. If the can is hot, it can begin to leak prematurely, can, in extreme cases, rupture, or when activated, can expel the can contents much more quickly than desired, resulting in a too fast inflation of the bag. It is also possible for the can to explode causing the top sealed section of the can to blow through the bag causing destruction of the bag. This can also be a hazard to operators using the bag.

The borehole plug assembly is often left in the sun, and in many locations, the daytime temperature can easily exceed 400 centigrade. The borehole plug assembly may be placed on the ground for prolonged periods of time, and the ground temperature can easily exceed 600 centigrade. Often, a number of borehole plug assemblies are required, and many are left in the sun. As the pressurised can is within a sealed inflatable bag, the temperature inside the bag and/or can can become quite high.

OBJECT OF THE INVENTION The present invention is directed to various means to provide thermal protection or thermal insulation to the bag and/or can and/or reagents.

It is an object of the invention to provide thermal protection of inflatable borehole bag assemblies.

In one form the invention resides in an inflatable borehole plug assembly which comprises an inflatable bag, inflation means (for example a pressurised can, or reagents which generate a gas when mixed) to inflate the inflatable bag, and thermal protection means to protect the inflatable borehole plug assembly or the inflation means against excessive heating.

The thermal protection means may have various forms. In one form, the thermal protection means comprises a cover. The cover may be flexible or rigid. A typical flexible cover may comprise as a bag that extends about the inflatable bag and/or the pressurised can. The bag may be formed from various thermal insulating means. This can comprise reflective foil, a reflective paint or coating applied to the bag, and the like. A typical rigid or semi-rigid cover may comprise a thicker material which need not be reflective, but which provides installation by virtue of its thickness. The thicker material may comprise paper, cardboard, plastic, foamed plastics and or blends and composites, wood, etc. Of course, the thicker material may also be provided with a reflective layer, sheet etc. The rigid or so my rigid cover may comprise a tube in which the inflatable bag or the can can pass.

Suitably, the cover is a flexible laminate structure. This can comprise a layer of reflective (such as metallised) polyester and a layer of polyester. Suitably the cover comprises three layers being an inner layer of metallised polyester and outer layers of polyester. The metallised polyester can have a thickness of between 5-50um and preferably about 12um and the polyester layer can have a thickness of between 10-100um and preferably between 25-40um. Suitably, one polyester layer has a thickness of about and the other layer has a thickness of about The cover may be of the type that can be removed prior to inflation of the bag. In this version, the cover may be sufficiently thin to be easily opened by tearing, cutting etc. Alternatively, tear lines, perforations, frangible portions and the like may be provided. The cover may however be of the type that is kept with the bag during inflation. For instance, the cover may comprise a flexible material that is sufficiently large to accommodate a fully inflated bag within the cover. Alternatively, the cover may be manufactured such that it will rupture at a certain point during inflation of the bag. In this version, the cover need not be flexible and may be formed of rigid or so my rigid material such as cardboard or paper which can split, tear, break or rupture upon inflation of the bag. Thus, it is not necessary to remove the cover from the bag prior to inflation. In this form, the cover may also function to hold the bag in a partially inflated condition to allow the bag to be lowered down a borehole, after which the inflating pressure is sufficient to rupture the cover to allow the bag to adopt the fully inflated condition. In this version, straps or ties may not be required, as the cover can provide this function.

If the cover is not removed, the cover may be provided with some form of means such that the can can still be activated. For instance, the cover may be provided with a viewing window, a cutout, a slot or recess through which the can can be activated.

In another embodiment, the thermal protection means can be provided inside the bag. The thermal protection means can be used to protect the can against excessive heating. In this embodiment, the thermal protection means can be as described above and can comprise a flexible reflective foil etc. The thermal protection means may comprise a foamed plastic which may be substantially tubular and in which the pressurised can can be placed to insulate the pressurised can from excessive heating. The tube may have an open top to allow the valve of the can to be activated.

In another embodiment, the thermal protection means may comprise a paint that can be applied to the outside and/or inside of the bag.

The paint is preferably reflective to function as a thermal insulator. The paint may be applied as a thin coating, or as a thick layer.

In another embodiment, the thermal protection means may comprise a foam which can be sprayed, painted or otherwise applied to the outside of the bag to provide thermal installation to the bag.

In another embodiment, the thermal protection means may comprise an insulated or reflective sheet. The deflated bag may be rolled up in the sheet to provide thermal installation to the bag and/or the pressurised can.

BRIEF DESCRIPTION OF THE DRAWINGS An embodiment of the invention will be described with reference to the following drawings in which: Figure 1. Illustrates an inflatable borehole plug assembly in the deflated state.

Figure 2. Illustrates the borehole plug assembly of Figure 1 in the fully inflated state.

Figure 3. Illustrates a section view of a borehole plug assembly in a thermally insulating bag.

Figure 4. Illustrates a section view of a borehole plug assembly protected by a thermally insulating wrap that is wrapped around the assembly.

Figure 5. Illustrates an end of view of the assembly of Figure 4.

Figure 6. Illustrates a rigid tubular cover for a borehole plug assembly.

Figure 7. Illustrates a borehole plug assembly protected by a paint layer coated on the outside of the assembly.

Figure 8. Illustrates an end view of a borehole plug assembly protected by a layer of insulating foam.

Figure 9. Illustrates a can having a marker point.

Figure 10. Illustrates a test configuration of a central bag which does not contain a cover and a covered bag at each side of the central bag, and illustrated the position of thermocouples to sense the temperature at various places in the bags BEST MODE Referring initially to figure 1 there is illustrated an inflatable borehole plug assembly 10. The plug assembly is well known and itself forms no part of the invention. The plug assembly comprises an inner inflatable plastic bag (not illustrated) which is housed inside a relatively strong outer plastic bag 11. A pressurised can 12 is located inside the inner inflatable plastic bag. Can 12 has a nozzle which can be pressed or activated through the bag. Once activated, the can will discharge the can contents (the inflating medium) to inflate the inner bag. Figure 2 shows the bag in the fully inflated position and showing that the bag can function as a borehole plug. Typically, when the assembly is deflated (figure it is rolled or folded into a substantially cylindrical configuration. Ties or straps 13 extend at least partially around the assembly to hold the assembly in the cylindrical configuration when deflated. As the bag is being inflated, the ties or straps stretch and burst to allow the bag to form a fully inflated position as illustrated in figure 2. All of these features are entirely conventional. Can 12 is positioned inside the inner bag and can become quite hot if the assembly is left in the sun for too long (and this can be quite common). As the inflation rate can depend on the can temperature, a can that is too hot can cause a too rapid inflation of the borehole plug that is undesirable. As well, the pressure inside the can can increase to the point where the can valve can no longer cope, causing the can contents to leak prematurely. In an extreme situation, the can can rupture or explode which can create a safety hazard or at least result in the bag becoming unusable.

Figure 3 illustrates a thermal protection means that is in the form of a flexible bag 14 in which the assembly is located. Bag 14 can be made of reflective material such as metallised material to reflect heat and to keep the assembly relatively cool. It is envisaged that bag 14 may be inflated with air to further provide insulating properties. Flexible bag 14 in the embodiment may be made of relatively thin material that can rupture or tear. This allows the bag to be opened just prior to use to allow the assembly to be removed from the bag and to allow the can to be activated to begin the inflation process. Alternatively, the can can be activated through the bag 14. In this variation, bag 14 can either be of sufficient size to accommodate the fully inflated borehole plug without rupture of the bag, or can be of a smaller size which will simply burst or split as the borehole plug inflates. The bag may be designed such that it will burst or split only at a predetermined pressure that will provide an operator with sufficient time to lower the bag down a borehole before the bag inflates to a size where it becomes wedged in the borehole.

Figure 4 illustrates a thermal protection means in the form of a flat wrap 15. The assembly can be rolled or wrapped in the wrap. Wrap can be made of metallised reflective material to provide thermal installation or at least thermal reflection to protect the bag assembly against excessive heating.

Figure 6 illustrates a rigid tube 16 which is hollow and which has an open end 17 in which assembly 10 can be placed. Tube 16 provides protection against excessive heating of assembly 10. Tube 16 can be formed from paper or cardboard and can have a sufficient thickness to provide insulating qualities. A thickness of between 3-10 mm appears to be sufficient.

Of course, tube 16 can be formed of material other than paper or cardboard, and can be formed of a foam material, but this may increase the cost. Tube 16 can be designed such that assembly 10 needs to be removed from tube 16 prior to inflation. This allows tube 16 to be reused many times. Tube 16 can also function to protect assembly 10 against damage or puncture prior to use.

8 If desired, tube 16 can be formed with a front cap or lid to provide further installation and/or protection to the assembly Figure 7 illustrates an assembly 10 where the outer bag 11 has been sprayed or otherwise coated with a reflective paint 18. The reflective paint may be a silver or metallised paint, or may be a bright paint which can reflect heat. In this version, there is no separate bag or cover which needs to be removed, or which will rupture or split during inflation.

Figure 8 is an end view of an assembly 10 which has been protected by a layer of foam 19 which has been applied to the outside of bag 11. The foam may include a curable foam which may be sprayed onto the outside of bag 11.

Figure 9 illustrates a pressurised can 20 that has an activation indication means. In an embodiment, this is in the form of a brightly coloured marker 21 positioned on the can nozzle or activator lock down tab 22. Marker 21 indicates the correct location visually to an operator for efficient an effective and correct activation of the unit. In this manner, product loss is reduced. The inclusion of marker 21 substantially contributes to the working of the invention by enabling the bag to be quickly and efficiently inflated without an operator fumbling for the nozzle, especially because the can is positioned within two bags, which can make the position of the can nozzle difficult to see.

Trails conducted with reflective material have achieved a 300C reduction in temperature. For example, a control can/bag left in the sun for hours had a temperature of 75C. An identical can/bag with thermal protection only attained a temperature of 450C after 5 hours. The drop in temperature is important, as pressurised cans tend to fail at temperatures in excess of 60-650(.

Figure 10 illustrates a test configuration testing the temperature difference between a covered bag and a uncovered bag. In this particular test, a gas bag was provided consisting of an aluminium mono block aerosol canister approximately 50 mm in diameter and 210 mm long. The canister was contained in a polyethylene weave gas bag. The gas canister and the 9 polyethylene weave bag was covered by a composite thermal cover. The thermal cover structure consisted of a 12 micron layer of metallised polyester sandwiched between a 25 micron layer of polyester on one side and a micron layer of polyester on the other side. The thermal cover is constructed into a bag approximately 640 mm long and 90 mm in diameter.

The test used two covered gas bags as described above and a third gas bag which did not contain the thermal cover. In figure 10, bag and bag 32 are covered gas bags while bag 31 is an identical but uncovered gas bag. Each bag has a lower canister 33-35 which is placed in the bag, this being entirely conventional. Thermocouples were placed about the canisters.

The thermocouples were placed as follows: T1 on the surface of canister 34 (the uncovered gas bag) 50 mm from the bottom. T2 on the surface of canister 3450 mm from the top. T3 on the outside surface of the gas bag level with the midpoint of canister 34. T4 on the surface of canister 33 (a covered gas bag) 50 mm from the bottom. T5 on the surface of canister 33, mm from the top. T6 on the surface of canister 33 at the midpoint. T7 on the outside surface of the thermal cover level with the midpoint of canister 33.

T8 on the outside surface of canister 35, 50 mm from the bottom. T9 on the surface of canister 35, 50 mm from the top. T10 on the surface of canister at the midpoint. T11 on the outside surface of the thermal cover, level with the midpoint of canister 35. T12 away from the gas bags and providing an indication of the ambient temperature.

With the ambient temperature T12 being 31.50 centigrade, the other thermocouples registered the following temperatures: T1 91.10 T2 84.70 T3 79.40 T4 49.10 52.60 T6 50.70 T7 76.10 T8 57.50 T9 55.90 62.90 T11 86.50 In summary, when the ambient temperature was slightly over 300 the temperature in the gas bag when uncovered and next to the aerosol canister was between 840-910 which presents a real danger of the aerosol canister exploding or prematurely discharging. The temperature on the outside of the uncovered gas bag was slightly under 80' which is also far too hot. However, the protected gas bags in the same ambient temperature showed a temperature in the gas bag of about 500 when the outside temperature of the cover was over 760, and a temperature in the gas bag of between 550-630 when the outside temperature of the cover was over 860.

The shows that use of a cover can remarkably reduce the temperature inside the bag and especially the temperature of the canister which allows the gas bags to be used and stored with reduced tendency of canister explosion, premature discharge of the canister and the like.

It should be appreciated that various other changes and modifications may be made to the embodiment described without departing from the spirit and scope of the invention.

Claims (14)

1. An inflatable borehole plug assembly which comprises an inflatable bag, inflation means in the bag to inflate the inflatable bag, and thermal protection means to protect the inflatable borehole plug assembly or the inflation means against excessive heating.

2. The assembly as claimed in claim 1, wherein the thermal protection means is on the outside of the bag.

3. The assembly as claimed in claim 1, or claim 2, wherein the thermal protection means comprises a flexible cover.

4. The assembly as claimed in claim 3, wherein the cover comprises a reflective foil.

The assembly as claimed in claim 4, wherein the reflective foil comprises a metallised polyester.

6. The assembly as claimed in claim 4 or claim 5 wherein the cover comprises a plurality of layers, one said layer being a metallised polyester.

7. The assembly as claimed in any one of the preceding claims, wherein the thermal protection means comprises a flexible cover consisting of a 12 micron layer of metallised polyester sandwiched between a 25 micron layer of polyester and a 35 micron layer of polyester.

8. The assembly as claimed in claim 1 or claim 2, wherein the thermal protection means comprises a rigid insulating material.

9. The assembly as claimed in claim 8, wherein the rigid insulating material is selected from paper, cardboard, plastic, foamed plastics and/or blends and composites, and wood.

10. The assembly as claimed in claim 1, wherein the thermal protection means is inside the bag and about the inflation means.

11. The assembly as claimed in claim 1 wherein the thermal protection means comprises a reflective or insulating sheet member adapted to extend about the bag.

12. A method for forming a borehole plug comprising, using a the borehole plug assembly comprising an inflatable bag, inflation means in the bag to inflate the inflatable bag, and thermal protection means to protect the inflatable borehole plug assembly against excessive heating, the method comprising removing the thermal protection means from the inflatable bag, initiating inflation of the inflating means, and lowering the inflatable bag into a borehole.

13. A method for forming a borehole plug comprising using a, the borehole plug assembly comprising an inflatable bag, inflation means in the bag to inflate the inflatable bag, and thermal protection means to protect the inflatable borehole plug assembly against excessive heating, the method comprising keeping the thermal protection means on the inflatable bag, initiating inflation of the inflating means, and lowering the inflatable bag into a borehole.

14. An assembly substantially as hereinbefore described with reference to the accompanying drawings. Dated this 23 rd day of April 2002 Morwenna De Luis By her Patent Attorneys CULLEN CO.