Fielfl of »he Invention The present invention relates to borehole plugs of the types described in AU595887, US 5,346,005 and AU4,846,278 and the propeltant for inflation of these borehole plugs, more particularly, to low vapour pressure non flammable propellent for aerosol cans used for the inflation of borehole plugs. Background

Typically explosive charges for mining and other excavation activities are placed in boreholes. Frequently such charges are supported at some point below the surface that is at some desired depth in the borehole. Inflatable plugs in the form of gas tight bags are used for this purpose. A plug pressure release valve is activated then the plug is lowered to a desired depth and inflated such that it becomes firmly engaged with the sides of the borehole.

Typically, inflation is by means of an aerosol canister attached to the bag and arranged so as to discharge its pressurised contents during the descent of the bag down the borehole.

A common problem experienced with such an arrangement is that in some situations the high ambient temperatures can raise the internal pressure of the aerosol canister above the rated capacity of the aerosol canister. A second problem is that common aerosol propellents are flammable increasing the hazards associated with the use and storage of the Inflatable borehole plugs.

Typically refrigerant gases are used as non flammable propeiiams HFC-I34a, 1 , 1 , 1. 2-tetrafluoroethane, HFC- 152a, HFC125 and alike. There are also those propellants that have been deemed to affect the ozone layer such as CFC-12, R-11.R-12, R-500, R40, Dichlorodifluoromethane, HCFC-22.HFC-22, HFC-123, HFC-227 and alike. It has been realised lately that HFC-134a has a high global warming potential. It is with this background that the present invention has been developed. Reference to prior art documents is not an admission that they form part of the common general knowledge of a skilled person in any jurisdiction.

Summary of the Present Invention

The invention relates to a more reliable and safer gas or liquid propellant for use in borehole plugs.

According to one aspect of the present invention there a gas or liquid propellant that is non flammable, non toxic, has a low vapour pressure and low global warming potential. According to an aspect of the present invention there is an inflatable borehole plug with a sealed gas tight container containing a pressure canister, said pressure canister containing a non-flammable fluorinated propellant with a global warming potential below 500. In an embodiment the propellant has a global warming potential below 200,100, 50, 20 or 10.

In an embodiment the propellant comprises HFO-1234ze, HFO-1234yf or a mixture of both. In an example embodiment the propellant comprises about equal amounts of HFO- 1234ze and HFO-1234yf.

In an embodiment the propellant comprises a mixture of a low global warming potential fluorinated propellant and R-134a. In an embodiment the propellant comprises about 34%, 13%, 6.5%, 3.2% or 1 % by weight R-134a.

In an embodiment the propellant comprises a mixture of a low global warming potential fluorinated propellant and R-152a. ln an embodiment the propellant comprises about 20%, 15%, 12%, 10%, 8%, 6%, or 4% by weight R-152a.

In an embodiment the propellant comprises HFO-1233zd.

In an embodiment the propellant also contains a hydro carbon or other forms of fluid.

In an embodiment the propellant comprises dimethyl ethane. In an embodiment the canister also contains water.

According to another aspect of the present invention there is a method of plugging a borehole comprising inflating a borehole plug by a non-flammable flow of gas or liquid from a canister sealed within a gas tight bag or bladder; said method including the steps of:

a) providing an inflatable borehole plug as defined above;

b) operating a pressure release mechanism so as to release the propellant from the canister into the inflatable bag;

c) lowering or moving inflatable borehole plug into position; and

d) holding the inflatable borehole plug in position until the inflatable borehole plug has inflated and engaged the walls of the borehole.

According to another aspect of the present invention there is a method of inflating a borehole plug by a non-flammable flow of gas or liquid from a canister sealed within a gas tight bag or bladder; said method including the steps of:

e) providing an inflatable borehole plug according to any of the previous claims;

f) operating a pressure release mechanism so as to release the propellant from the canister into the inflatable bag;

g) lowering or moving inflatable borehole plug into position; and

h) holding the inflatable borehole plug in position until the inflatable borehole plug has inflated and engaged the walls of the borehole.

In this specification the terms "having", "comprising" or "comprises" are used inclusively and not exclusively or exhaustively. Description of Drawings

In order to provide a better understanding of the present invention preferred embodiments will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a plan view of an inflatable borehole plug consists of a gas tight bladder or bag (1 ) with a pressure canister or aerosol can (3) sealed inside the gas tight bladder (1 ) usually by means of heat sealing or welding (2) of the gas tight bladder.

The pressure canister or aerosol can is filled with a suitable propellant, as described below, and in some cases a further liquid that may delay the release of propellant or increase the density of the propellant. The inflatable borehole is operated via a latch (4) on the pressure canister or aerosol can. Thereby releasing the inflating agent and thus inflating the borehole plug.

Such further liquid may be for example, water, or dimethyl ether, or a combination, or other of the liquids described in AU656051 . After operation of the latch (4) the inflatable borehole plug is usually lowered into the borehole on a string or similar device and held in place until the inflatable plug inflates and secures itself against the walls of the borehole.

Description of Embodiments of the Invention

According to an embodiment of the present invention there is a low vapour pressure non flammable propellant used in an inflatable borehole plug which uses a pressurised canister such as an aerosol can to inflate the borehole plug. Suitable Inflatable borehole plugs are described in AU 656051 , the contents of which are incorporated herein by reference.

The high global warming potential and/or ozone depletion potential of prior propellants has been recognised by the inventor as needing redress. Global warming potential (GWP) is an index for estimating relative global warming contribution due to atmospheric emission of a kilogram of a particular greenhouse gas compared to emission of a kilogram of carbon dioxide. GWP can be calculated for different time horizons showing the effect of atmospheric lifetime for a given gas. The GWP for the 100 year time horizon is commonly the value referenced. For mixtures, a weighted average can be calculated based on the individual GWPs for each component.

The inventor has identified low GWP fluorinated propellants as suitable propellants for use in inflatable borehole plugs. In particular the inventor has identified that a nonflammable fluorinated propellant, with a global warming potential below 500, is suitable for use in a pressure canister for inflation of an inflatable borehole plug. Further the inventor has identified that a non-flammable fluorinated propellant with a global warming potential below 200 is suitable. Further the inventor has identified that a non-flammable fluorinated propellant with a global warming potential below 100 is suitable. Further the inventor has identified that a non-flammable fluorinated propellant with a global warming potential below 50 is suitable. Further the inventor has identified that a non-flammable fluorinated propellant with a global warming potential below 20 is suitable. Further the inventor has identified that a non-flammable fluorinated propellant with a global warming potential below 10 is suitable. Further the inventor has identified that a non-flammable fluorinated propellant with a global warming potential of about 5 is suitable.

Trans-1 ,3,3,3-tetrafluoropropene, also known as HFO-1234ze and sold by Honeywell™ and 2,3,3,3-tetrafluoropropene, also known as HFO-1234yf and sold by Honeywell™ are examples of such a propellant. HFO-1234ze has a GWP of 6. HFO-1234yf has a GWP of 4. These fluorinated propellants also have no appreciable ozone depletion potential.

Additionally, HFO-1234ze is non-flammable, meeting the additional requirement of a nonflammable propellant. The mildly flammable HFO-1234yr, in mixtures with HFO-1 234ze and other non-flammable fluids, may also be non-flammable, so blends of these propellants also meet this requirement. Equal weights of HFO-1234ze and HFO-1234yf with have a GWP of about 5.

Mixtures including 1 ,1 ,1 ,2-tetrafluoroethane, also known as HFC-134a and R-134a, can be used to ensure that the vapour pressure is not too low, while ensuring that the mixture remains non-flammable, at the expense of a higher global warming potential. R-134a has a GWP of 1430. Examples of suitable mixtures, by weight

HFO-1234ze 33% HFO-1234yf 33% R-134a 34%. This will have a GWP of about 490.

HFO-1234ze 43% HFO-1234yf 44% R-134a 13%. This will have a GWP of about 190.

HFO-1234ze 45% HFO-1234yf 48.5% R-134a 6.5%. This will have a GWP of about 100. HFO-1234ze 48.3% HFO-1234yf 48.5% R-134a 3.2%. This will have a GWP of about 50.

HFO-1234ze 49.5% HFO-1234yf 49.5% R-134a 1 %. This will have a GWP of about 20.

Mixtures including 1 ,1 -difluoroethane, also known as HFC-152a and R-1 52a, can be used to ensure that the vapour pressure is not too low while lowering the GWP. It may be added in combination with R-134a to lower the GWP in quantities to remain non-flammable, at the expense of a higher global warming potential. R-152a has a GWP of 1 20. Examples of suitable mixtures, by weight

HFO-1234ze 40% HFO-1234yf 40% R-152a 10% R-134a 10%. This will have a GWP of about 170. HFO-1234ze 80% R-152a 20%. This will have a GWP of about 30.

HFO-1234ze 44% HFO-1234yf 44% R-152a 12%. This will have a GWP of about 20. HFO-1234ze 48% HFO-1234yf 48% R-152a 4%. This will have a GWP of about 10.

Mixtures including dimethyl ether, also known as DME and R-E170, can be used to ensure that the vapour pressure is not too low. DME has a GWP of about 2. DME can be used with about 7% ethanol to dissolve water, thereby reducing the flammability of the mixture. In an embodiment the water is about 1 0-40% by weight. In an embodiment the water is about 15-35% by weight. In an embodiment the water is about 20-30% by weight. Use of DME and water is described in Australian Patent 763474, the contents of which are incorporated herein by reference.

Propane and/or butane may be used so that the vapour pressure is not too low. In these embodiments the HFO as a base, R134a to offset flammability if DME, propane, butane (or other hydrocarbons) or R152 is used.

1 -Choro-3,3,3-trifluropropane also known as HFO-1233zd may be used as the low GWP fluorinated propellant, with a GWP of 7. Other hydroflouroolefins (HFOs) or combinations may also be used as the low GWP fluorinated propellant.

In an embodiment the ratio of HFO-1234yf to HFO-1234ze is in the range of from about 0.01 to about 100. The HFO-1234yf to HFO-1234ze ratio or the HFO-1234ze to HFO- 1234yf ratio may be about 1 , 1 .1 , 1 .2, 1.3, 1 .4, 1 .5, 1 .6, 1 .7, 1 .8, 1.9, 2, 2.2, 2.4, 2.6, 2.7, 2.8, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9, 10, 1 1 , 12, 13, 14, 15, 16, 17, 18, 19, 20, 22, 24, 26, 28, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100.

In an embodiment the ratio of HFO-1234yf and/or HFO-1234ze with a mixture thereof to R-134a is in the range of from about 3 to about 100 and more particularly in the range of from about 3 to about 20. The ratio can be about 2.9, 3.0, 3.1 , 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1 , 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.1 , 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, 6.0, 6.1 , 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, 7.0, 7.1 , 7.2, 7.3, 7.4, 7.5, 7.6, 7.7, 7.8, 7.9, 8.0, 8.1 , 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9, 9.0, 9.1 , 9.2, 9.3, 9.4, 9.5, 9.6, 9.7, 9.8, 9.9, 10.0, 10.1 , 10.2, 10.3, 10.4, 10.5, 10.6, 10.7, 10.8, 10.9, 1 1 .0, 1 1 .1 , 1 1 .2, 1 1 .3, 1 1 .4, 1 1 .5, 1 1 .6, 1 1 .7, 1 1 .8, 1 1 .9, 12.0, 12.1 , 12.2, 12.3, 12.4, 12.5, 12.6, 12.7, 12.8, 12.9, 13.0, 13.1 , 13.2, 13.3, 13.4, 13.5, 13.6, 13.7, 13.8, 13.9, 14.0, 14.1 , 14.2, 14.3, 14.4, 14.5, 14.6, 14.7, 14.8, 14.9, 15.0, 15.1 , 15.2, 15.3, 15.4, 15.5, 15.6, 15.7, 15.8, 15.9, 16.0, 16.1 , 16.2, 16.3, 16.4, 16.5, 16.6, 16.7, 16.8, 16.9, 17.0, 17.1 , 17.2, 17.3, 17.4, 17.5, 17.6, 17.7, 17.8, 17.9, 18.0, 18.1 , 18.2, 18.3, 18.4, 18.5, 18.6, 18.7, 18.9, 19.0, 19.1 , 19.2, 19.3, 19.4, 19.5, 19.6, 19.7, 19.8, 19.9, or 20.0.

One aspect of the present invention is to provide a propellant with a global warming potential of less than 500, less than 400, less than 300, or less than 150, less than 100, less than 90, less than 80, less than 70, or less than 60, less than 50, less than 40, less than 30, or less than 20, less than 10, less than 7, 6, about 5, or 4. Advantages of the present invention are that inflatable borehole plugs can be suitably inflated with a propellant that is non flammable or has low flammability and contributes significantly less to global warming when the inflation medium is released to the atmosphere.

The above describes only some embodiments of the present invention and modifications, obvious to those skilled in the art, can be made thereto without departing from the scope and spirit of the present invention. Modifications may be made to the present invention with the context of that described and shown in the drawings. Such modifications are intended to form part of the invention described in this specification.