Gas sensitised water-in-oil explosive emulsion

Abstract

Production of a gas sensitised water-in-oil explosive emulsion, involving a flowing stream of (i) water-in-oil explosive emulsion, and (ii) an aqueous liquid having a substantially annular profile around the water-in-oil explosive emulsion. A chemical gassing agent is introduced into the aqueous liquid, to react with an ammonium salt to form a gas. The water-in-oil explosive emulsion comprises a solid ammonium salt that at least partially dissolves into the aqueous liquid and mixes with the chemical gassing agent to produce an activated aqueous liquid capable of forming gas through reaction of the gassing agent and the dissolved ammonium salt derived from the solid ammonium salt; and mixing the water-in-oil explosive emulsion with the activated aqueous liquid to produce the gas sensitised water-in-oil explosive emulsion.

Description

[0001] GAS SENSITISED WATER-IN-OIL EXPLOSIVE EMULSION

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a method of producing gas sensitised water-in-oil explosive emulsions commonly used in mining and blasting operations.

[0004] BACKGROUND OF THE INVENTION

[0005] Mining and blasting operations regularly involve the use of hazardous materials and consequently safety is of utmost importance. A key high risk activity undertaken is the loading of explosive material into previously drilled boreholes and its subsequent detonation.

[0006] Explosive material commonly used in such operations include so called water-in-oil (W / O) explosive emulsions. As those skilled in the art will appreciate, such emulsions comprise a discontinuous aqueous oxidiser phase and a continuous oil phase.

[0007] Water-in-oil explosive emulsions are typically pumped into a borehole using a pump attached to a conduit / hose. However, due to their highly viscous nature the emulsions can be difficult to pump, particularly over long distances (for example, when loading deep boreholes) and / or through small diameter conduits used in borehole loading. Pumping such high viscosity material gives rise to high pump pressures, which poses considerable operational and safety concerns in the context of pumping explosive material.

[0008] In most applications, elevated pump pressure associated with conveying high viscosity fluids through conduits can be averted by using large diameters conduits of minimal length. However, several factors prevent the use of large diameter, short length conduits in loading of water-in-oil explosive emulsions into boreholes. Those include, for example: the need for transportation of a borehole-loading-delivery system (such a mobile manufacture unit or MMU) around a mine site from borehole to borehole, borehole characteristics - including depth, diameter and direction; and difficulty in accessing boreholes, especially in underground mining. Instead, long, flexible and often narrow loading conduits are typically required to transfer water-in-oil explosive emulsions from a delivery system into a borehole. The length of a loading conduit is typically 30 to 60 meters but can be longer, depending upon the depth of the borehole. Several methods have been developed to ensure that pumping pressures for water-in-oil explosive emulsions are maintained within an acceptable / safe range. For example, it is known to use an annular stream of aqueous solution around a core stream of water-in-oil explosive emulsion being pumped through the conduit. The aqueous solution serves to lubricate the water-in-oil explosive emulsion delivery through the conduit. That approach is known as “core annular flow” and the aqueous solution often referred to as an “aqueous-ring” or "aqueous-annulus", with the water-in- oil explosive emulsion being referred to as a “core”.

[0009] To improve their effectiveness, water-in-oil explosive emulsions are sometimes provided with a distribution of voids in the form of microspheres, other solid air entraining agents, or gas bubbles that not only reduce their density, but importantly also sensitise it toward detonation. Water-in- oil explosive emulsions comprising such voids are commonly known in the art as sensitised water- in-oil explosive emulsions. Such sensitised water-in-oil explosive emulsions need to be carefully and safely positioned into their desired location for detonation, for example within a borehole.

[0010] Providing a water-in-oil explosive emulsion with gas bubbles is a particularly convenient and efficient means of sensitisation. Such gas sensitisation is generally achieved by mixing the water- in-oil explosive emulsion with a chemical gassing system that reacts within the water-in-oil explosive emulsion to produce the gas / gas bubbles and form the gas sensitised water-in-oil explosive emulsion. A common gassing system used to sensitise water-in-oil explosive emulsions involves the reaction of nitrite with ammonium to produce nitrogen gas. Sodium nitrite is often used as the source of the nitrite and ammonium nitrate is often used as the source of the ammonium.

[0011] For surface applications, the chemical gassing reactive species can be blended into the explosive emulsion before being pumped through the conduit. However, if the pump is stopped, the gassing reaction may occur significantly within the conduit resulting in pressure build up and potential operational problems. For underground applications, gassing occurring within the conduit during pumping is more problematic and the chemical gassing reactive species are generally not blended into the explosive emulsion before being pumped through the conduit.

[0012] To prevent an undesirable effect of substantive gassing occurring within the conduit during pumping of the water-in-oil explosive emulsion, the chemical gassing reactive species are typically isolated from each other and pumped with the water-in-oil explosive emulsion through a conduit to a mixing head positioned toward the end of the conduit. The chemical gassing reactive species and the water-in-oil explosive emulsion are only mixed at that point and then loaded into the borehole. Once in the borehole the gassing reaction proceeds and produces the required gas bubbles for sensitisation of the water-in-oil explosive emulsion.

[0013] For example, as disclosed in US 6,397,719, it is known to include a chemical gassing agent such as sodium nitrite in the flow of an aqueous-annulus around a water-in-oil explosive emulsion core being pumped via a conduit into a borehole, wherein the discontinuous aqueous oxidiser phase of the water-in-oil explosive emulsion comprises ammonium nitrate While being pumped, the sodium nitrite in the aqueous annulus remains isolated from the water-in-oil explosive emulsion core until it reaches the mixing head where it is mixed with the water-in-oil explosive emulsion. That mixing process enables ammonium nitrate from the water-in-oil explosive emulsion to combine and react with the sodium nitrite after mixing such that the mixed composition entering the borehole undergoes gassing to form the gas sensitised water-in-oil explosive emulsion.

[0014] It is also known to include a chemical gassing agent such as sodium nitrite as an isolated aqueous stream within the water-in-oil explosive emulsion core.

[0015] However, such techniques are prone to relatively poor and irregular mixing of at least the chemical gassing reactive species (e.g. nitrite and ammonium) due to (i) the aqueous based gassing agent stream and the water-in-oil explosive emulsion core being substantially immiscible, and (ii) for safety concerns the need to mix those components at relatively low intensity. Consequently, the composition exiting the mixing head and passing into the borehole can exhibit non-reproducible gassing, which in turn can give rise to unreliable / non-reproducible detonation.

[0016] To achieve more effective mixing between such chemical gassing reactive species (e.g. ammonium nitrate and sodium nitrite), on face value one approach might be to simply introduce a water annulus into the conduit that comprises the required reactive species (e.g. both ammonium nitrate and sodium nitrite). However, as alluded to above and as is mentioned in US 6,397,719, such an approach is problematic since the chemical gassing reactive species (e.g. ammonium nitrate and sodium nitrite) will begin reacting in the annulus as it travels down the full length of the conduit and result in an undesirable degree of gassing taking place within the conduit rather than primarily in the borehole. Within the mining and blasting industries an opportunity therefore remains to develop methodology for more efficiently and effectively producing gas sensitised water-in-oil explosive emulsions

[0017] SUMMARY OF THE INVENTION

[0018] The present invention provides a method of producing a gas sensitised water-in-oil explosive emulsion, the method comprising: providing in a conduit a flowing stream of (i) water-in-oil explosive emulsion, and (ii) an aqueous liquid having a substantially annular profile around the water-in-oil explosive emulsion; introducing into the aqueous liquid a chemical gassing agent that is capable of reacting with an ammonium salt to form a gas, wherein the water-in-oil explosive emulsion comprises a solid ammonium salt that at a point downstream from where it is introduced into the conduit at least partially dissolves into the aqueous liquid and mixes with the chemical gassing agent to produce an activated aqueous liquid that is capable of forming gas through reaction of the gassing agent and the dissolved ammonium salt derived from the solid ammonium salt; and mixing the water-in-oil explosive emulsion with the activated aqueous liquid to produce the gas sensitised water-in-oil explosive emulsion.

[0019] It has now surprisingly been found that in core-annular flow an ammonium salt can be introduced into an aqueous annulus comprising a chemical gassing agent (that is capable of reacting with the ammonium salt to form a gas) such that little or no adverse premature gassing occurs prior to the water-in-oil explosive emulsion core and the aqueous annulus being intentionally mixed toward the end of the conduit

[0020] In contrast with an undesirable core-annular flow approach that introduces into the conduit an aqueous annulus comprising a combination of a chemical gassing agent (that is capable of reacting with the ammonium salt to form a gas) and an ammonium salt, the method of the present invention advantageously provides a conduit with a flowing aqueous annulus stream comprising a chemical gassing agent (that is capable of reacting with the ammonium salt to form a gas) where solid ammonium salt located in the water-in-oil explosive emulsion core dissolves into the aqueous annulus at a point downstream from where it was introduced into the conduit. The method therefore advantageously provides a means of producing in situ an activated aqueous annulus that is capable of forming gas through reaction of the gassing agent and the dissolved ammonium salt derived from the solid ammonium salt The formation of that activated aqueous annulus is delayed in the sense that it takes place in the conduit downstream from where both the water-in- oil explosive emulsion and the chemical gassing agent (that is capable of reacting with the ammonium salt to form a gas) are introduced into the conduit. That delay in formation of the activated annulus minimises the distance it has to travel toward the end of the conduit and be mixed with the water-in-oil explosive emulsion and thereby avoids adverse premature gassing occurring in the flowing aqueous annulus.

[0021] Without wishing to be limited by theory, it is believed that the solid ammonium salt present in the water-in-oil explosive emulsion core is progressively agitated in the core as it flows downstream from the point of being introduced into the conduit. That agitation is believed to facilitate at least momentary penetration of the solid ammonium salt through the core-annulus interface and into the aqueous environment of the annulus. During such momentary penetration at least some of the solid ammonium salt is believed to dissolve in the aqueous annulus. Through a multiple of such momentary penetrations occurring as the water-in-oil explosive emulsion core travels down the conduit, the concentration of the dissolved ammonium salt cumulatively increases in the aqueous annulus and reaches a suitable stoichiometry to react with the gassing agent. At that point the aqueous annulus is considered to be activated in the sense the aqueous liquid of the annulus is capable of forming gas through a stoichiometric reaction of the gassing agent and the dissolved ammonium salt derived from the solid ammonium salt. The flow rate of the core-annular flow can be readily controlled to ensure that shortly after the activated annulus forms it approaches the end of the conduit and is mixed with the water-in-oil explosive emulsion core, with the resulting mixture being directed into the desired location, for example a borehole. Once in the desired location, the gassing reaction proceeds to produce the gas sensitised water-in-oil explosive emulsion. In that way undesirable premature gassing within the conduit can advantageously be avoided.

[0022] Notably, unlike conventional gas sensitising core annular flow techniques, the step of mixing the water-in-oil explosive emulsion with the activated aqueous annulus according to the method of the present invention is not required for combining the chemical gassing reactive species (as that has already taken place in the so formed activated annulus). Rather, the mixing step according to the method of the present invention simply and advantageously serves to disperse / distribute the activated aqueous liquid, which comprises the mixed gassing agent and ammonium salt, throughout the water-in-oil explosive emulsion. That mixing / dispersion step can be readily controlled and will operate efficiently for that purpose at relatively low intensity. The method of the present invention therefore consequently enables gassing to occur in a more efficient and reproducible manner, which in turn improves the reliability and efficiency of detonation.

[0023] Further aspects and / or embodiments of the invention are discussed in more detail below.

[0024] BRIEF DESCRIPTION OF DRAWINGS

[0025] The present invention will herein be described with reference to the following non-limiting drawings in which:

[0026] Figure 1 is a schematic representation of the various stages in performing an embodiment of the method according to the invention;

[0027] DETAILED DESCRIPTION OF THE INVENTION

[0028] The water-in-oil explosive emulsion

[0029] The method of the present invention makes use of a water-in-oil explosive emulsion.

[0030] Those skilled in the art are familiar with water-in-oil explosive emulsions. Such emulsions comprise a discontinuous aqueous oxidiser phase and a continuous oil phase. An emulsifier can be used to assist with stabilising the emulsion.

[0031] 7 he discontinuous aqueous oxidiser phase

[0032] In the context of the water-in-oil explosive emulsions used in accordance with the invention, those skilled in the art will appreciate the discontinuous aqueous oxidiser phase will comprise an aqueous solution of one or more oxygen releasing compounds (i.e. the oxidiser).

[0033] The discontinuous aqueous oxidiser phase will typically be present within the continuous oil phase in the form of droplets, for example micro-droplets

[0034] The one or more oxygen releasing compounds may be selected from one or more oxygen releasing salts. Examples of suitable oxygen releasing salts include alkali and alkaline earth metal nitrates, alkali and alkaline earth metal chlorates, alkali and alkaline earth metal perchlorates, ammonium nitrate, ammonium chlorate, ammonium perchlorate, and a combination thereof.

[0035] In some embodiments, the water-in-oil explosive emulsion comprises a discontinuous aqueous oxidiser phase that comprises one or more dissolved oxidiser compounds selected from alkali and alkaline earth metal nitrates, alkali and alkaline earth metal chlorates, alkali and alkaline earth metal perchlorates, ammonium nitrate, ammonium chlorate, ammonium perchlorate and a combination thereof.

[0036] In other embodiments, the water-in-oil explosive emulsion comprises a discontinuous aqueous oxidiser phase that comprises an aqueous solution of ammonium nitrate.

[0037] The aqueous oxidiser phase may contain any amount of dissolved oxidiser compound that would make it suitable for use in a water-in-oil explosive emulsion.

[0038] In some embodiments, the water-in-oil explosive emulsion comprises a discontinuous aqueous oxidiser phase in which one or more dissolved oxidiser compounds are present in an amount from about 45 wt. % to about 95 wt. %, or from about 60 wt. % to about 90 wt. % of the total water-in- oil explosive emulsion.

[0039] In other embodiments, the water-in-oil explosive emulsion comprises a discontinuous aqueous oxidiser phase that comprises an aqueous solution of an oxidiser compound selected from alkali and alkaline earth metal nitrates, alkali and alkaline earth metal chlorates, alkali and alkaline earth metal perchlorates, ammonium nitrate, ammonium chlorate, ammonium perchlorate and a combination thereof in an amount from about 45 wt % to about 95 wt. %, or from about 60 wt % to about 90 wt. % of the total water-in-oil explosive emulsion.

[0040] In the aqueous oxidiser phase the oxidiser compound(s) is solubilised in water. The amount of water present will generally range from greater than 0 wt. % to about 30 wt. % of the total water- in-oil explosive emulsion. For example, the amount of water present may be from about 4 wt. % to about 25 wt. %, or from about 6 wt. % to about 20 wt. % of the total water-in-oil explosive emulsion.

[0041] In some embodiments, the water-in-oil explosive emulsion comprises a discontinuous aqueous oxidiser phase in which water is present in an amount from greater than 0 wt. % to about 30 wt. %, or from about 4 wt. % to about 25 wt. %, or from about 6 wt. % to about 20 wt. % of the total water-in-oil explosive emulsion.

[0042] The continuous oil phase

[0043] In the context of the water-in-oil explosive emulsions used in accordance with the invention, those skilled in the art will appreciate the continuous oil phase constitutes a primary fuel source of the explosive material. It provides the continuous matrix that hosts the discontinuous aqueous oxidiser phase, which will typically be present in the form of droplets, for example micro-droplets.

[0044] The continuous oil phase will generally comprise one or more organic compounds as the fuel source. Examples of such organic compounds include, but are not limited to, aliphatic, alicyclic, aromatic compounds, and mixtures thereof. The organic compounds will typically be in a liquid state when formulated into the water-in-oil explosive emulsion.

[0045] The organic compounds may be selected from fuel oil, diesel oil, distillate, furnace oil, kerosene, naphtha, wax (e.g. microcrystalline wax, paraffin wax, or slack wax), paraffin oils, naphthenic oils, benzene, toluene, xylenes, asphaltic materials, polymeric oils such as the low molecular weight polymers of olefines, animal oils, vegetable oils, fish oils and other mineral, hydrocarbon or fatty oils, and mixtures thereof. In some embodiments, the organic compound is a selected from liquid hydrocarbons generally referred to as petroleum distillates, which include gasoline, kerosene, fuel oils and paraffin oils.

[0046] In some embodiments, the water-in-oil explosive emulsion comprises a continuous oil phase that comprises one or more organic compounds selected from aliphatic, alicyclic and aromatic compounds.

[0047] In other embodiments, the water-in-oil explosive emulsion comprises a continuous oil phase that comprises one or more organic compounds selected from fuel oil, diesel oil, distillate, furnace oil, kerosene, naphtha, wax (e.g. microcrystalline wax, paraffin wax, or slack wax), paraffin oils, naphthenic oils, benzene, toluene, xylenes, asphaltic materials, polymeric oils such as the low molecular weight polymers of olefines, animal oils, vegetable oils, fish oils and other mineral, hydrocarbon or fatty oils, and mixtures thereof.

[0048] In some embodiments, the water-in-oil explosive emulsion comprises a continuous oil phase that comprises one or more liquid hydrocarbons. Liquid hydrocarbons are also commonly referred to as petroleum distillates and include gasoline, kerosene, fuel oils and paraffin oils.

[0049] Provided the amount of continuous organic phase present is suitable to provide for a water-in-oil explosive emulsion, the continuous organic phase may constitute any fraction of the water-in-oil explosive emulsion.

[0050] In some embodiments, the water-in-oil explosive emulsion comprises a continuous oil phase that represents from about 2 wt. % to 15 wt. % or form about 3 wt. % to 10 wt. % of the total the water-in-oil explosive emulsion.

[0051] Emulsifier(s)

[0052] The water-in-oil explosive emulsion can be prepared using one or more emulsifying agents. As those skilled in the art will appreciate, an "emulsifying agent" (also known as an emulsifier) is typically a compound that has both hydrophilic and hydrophobic characteristics / moieties that interact with the discontinuous aqueous phase and the continuous oil phase, respectively, of the water-in-oil explosive emulsion to assist with stabilising the emulsion. The emulsifiers serve to promote stabilisation of the emulsion by inhibiting coalescence of the discontinuous aqueous phase and consequently phase separation.

[0053] In the context of the present invention, those skilled in the art will appreciate the water-in-oil explosive emulsion will be suitably stabilised for the intended application. The use of emulsifiers for stabilising water-in-oil explosive emulsions is well known to those skilled amount.

[0054] Water-in-oil explosive emulsions used in accordance with the invention may comprise a discontinuous aqueous oxidiser phase, a continuous oil phase and an emulsifier.

[0055] There is no particular limitation on the type of emulsifier(s) that can be used provided it does not adversely interfere with the explosive properties of the water-in-oil explosive emulsion. Those skilled in the art are familiar with emulsifier(s) that can be used for water-in-oil explosive emulsions. Examples of emulsifiers that may be used in accordance with the invention include, but are not limited to, poly(oxyalkylene) fatty acid esters, amine alkoxylates, fatty acid esters of sorbitol and glycerol, fatty-acid salts, sorbitan esters, poly (oxy alkylene) sorbitan esters, fatty amine alkoxylates, poly(oxyalkylene) glycol esters, fatty acid amines, fatty acid amide alkoxylates, fatty amines, quaternary amines, alkyloxazolines, alkenyloxazolines, imidazolines, alkylsulphonates, alkylarylsulphonates, alkyl sulphosuccinates, alkylarylsulphonates, alkylsulphosuccinates, alkylphosphates, alkenylphosphates, phosphate esters, poly (12-hydroxy stearic) acid and a combination of two or more thereof

[0056] Examples of emulsifiers that may be used in accordance with the invention also include condensation products of poly[alk(en)yl] succinic anhydride (PiBSA) with one or more amines such as ethylene diamine, diethylene triamine and ethanolamine.

[0057] Examples of emulsifiers that may be used in accordance with the invention also include oxazolines such as 4,4-bis(hydroxymethyl)-l-heptadecyl-2-oxazoline and 4-methyl-4- hydroxymethyl l-heptadecyl-2-oxazoline, salts of long chain fatty acids such as calcium oleate, magnesium oleate, aluminum oleate, and calcium stearate, sorbitan esters such as polyoxyethylenesorbitanmonooleate, and sorbitan sesquioleate, ethylene oxide condensates of fatty acids, and a combination thereof.

[0058] In some embodiments, the water-in-oil explosive emulsion comprises one or more emulsifies.

[0059] In some embodiments, the water-in-oil explosive emulsion comprises one or more emulsifies selected from poly(oxyalkylene) fatty acid esters, amine alkoxylates, fatty acid esters of sorbitol and glycerol, fatty-acid salts, sorbitan esters, poly(oxyalkylene) sorbitan esters, fatty amine alkoxylates, poly(oxyalkylene) glycol esters, fatty acid amines, fatty acid amide alkoxylates, fatty amines, quaternary amines, alkyloxazolines, alkenyloxazolines, imidazolines, alkylsulphonates, alkylarylsulphonates, alkyl sulphosuccinates, alkylarylsulphonates, alkylsulphosuccinates, alkylphosphates, alkenylphosphates, phosphate esters, and poly (12-hydroxystearic) acid.

[0060] In other embodiments, the water-in-oil explosive emulsion comprises one or more emulsifies selected from oxazolines, salts of long chain fatty acids, sorbitan esters and ethylene oxide condensates of fatty acids. In other embodiments, the water-in-oil explosive emulsion comprises one or more emulsifies selected from 4,4-bis(hydroxymethyl)-l-heptadecyl-2-oxazoline, 4-methyl-4-hydroxymethyl 1- heptadecyl-2-oxazoline, calcium oleate, magnesium oleate, aluminum oleate, calcium stearate, polyoxyethylenesorbitanmonooleate, and sorbitan sesquioleate.

[0061] In other embodiments, the water-in-oil explosive emulsion comprises one or more emulsifies selected from condensation products of poly[alk(en)yl] succinic anhydride (PiBSA) with one or more amines. Examples of amines include ethylene diamine, diethylene triamine and ethanolamine.

[0062] There is no particular limitation on the amount of emulsifier(s) that can be used provided it does not adversely interfere with the explosive properties of the water-in-oil explosive emulsion. Those skilled in the art are familiar with the amount of emulsifier(s) that can be used in water-in- oil explosive emulsions.

[0063] In some embodiments, the water-in-oil explosive emulsion comprises one or more emulsifies in an amount of up to about 25 wt % of the total the water-in-oil explosive emulsion.

[0064] In other embodiments, the water-in-oil explosive emulsion comprises one or more emulsifies in an amount of about 0.1 wt. % to about 25 wt. %, or about 0.1 wt. % to about 20 wt. %, or about 0.1 wt. % to about 15 wt. %, or about 0.1 wt. % to about 10 wt. %, or about 0.1 wt. % to about 5 wt. %, or about 0.1 wt. %to about 2 wt. % of the total the water-in-oil explosive emulsion.

[0065] 7 he gas sensitised water-in-oil explosive emulsion

[0066] The method of the present invention produces a gas sensitised water-in-oil explosive emulsion. As will be discussed in more detail below, the gas sensitised water-in-oil explosive emulsion is prepared using water-in-oil explosive emulsions as herein described.

[0067] Those skilled in the art are familiar with gas sensitised water-in-oil explosive emulsions, being water-in-oil explosive emulsions comprising dispersed / distributed gas bubbles.

[0068] There is no particular limitation on the degree of gassing (i.e. the amount of dispersed / distributed gas bubbles) of gas sensitised water-in-oil explosive emulsions produced in accordance with the method of the invention. The degree of gassing to be achieved will typically depend upon the intended application and can be readily assessed by those skilled in the art. The degree of gassing in a gas sensitised water-in-oil explosive emulsion is typically expressed in terms of its void fraction, being the volume of gas in the water-in-oil explosive emulsion expressed as a percentage. Generally, the degree of gassing will be greater than about 5% and up to about 60%.

[0069] The degree of gassing can be readily varied by adjusting the concentration of chemical gassing species used in accordance with the invention and / or its rate of introduction to achieve a desired level of sensitisation of the water-in-oil explosive emulsion

[0070] The method according to the present invention is performed by providing in a conduit a flowing stream of (i) water-in-oil explosive emulsion, and (ii) an aqueous liquid having a substantially annular profile around the water-in-oil explosive emulsion.

[0071] For convenience, the aqueous liquid having a substantially annular profile around the water-in- oil explosive emulsion may herein also be referred to simply as the aqueous annulus or the aqueous liquid / annulus.

[0072] The conduit used is of a type conventionally used in the art and may also be known in the art as a pipe or hose. There is no particular limitation on the dimensions of the conduit, Generally they are circular in cross section, have a length ranging from about 30 to about 60 meters (but can be longer), a diameter ranging from about 10 mm to about 80 mm.

[0073] The flowing stream in the conduit of the water-in-oil explosive emulsion and aqueous annulus, also known in the art as “core annular flow”, may be provided by any suitable means On a mining or blasting site, such core annular flow will generally be pumped from a base unit, for example a MMU. Conventional techniques and equipment can advantageously be used to provide for the core annular flow.

[0074] There is no particular limitation on the cross-sectional thickness of the aqueous annulus or the cross-sectional diameter of the water-in-oil explosive emulsion core.

[0075] Generally, the ratio of the cross-sectional thickness of the aqueous annulus to the cross-sectional diameter of the water-in-oil explosive emulsion core will range from about 0.002 to 0.015 mm.

[0076] In some embodiments, the aqueous liquid having a substantially annular profile around the water in-oil explosive emulsion has a cross-sectional thickness ranging from about 0.03 mm to about 1 mm.

[0077] In other embodiments, the water-in-oil explosive emulsion has a cross-sectional diameter ranging from about 10 mm to about 80 mm.

[0078] Such thickness / diameters will of course vary depending on the diameter of the conduit used.

[0079] The water-in-oil explosive emulsion provided in the conduit include those water-in-oil explosive emulsions herein described.

[0080] The water-in-oil explosive emulsion provided in the conduit may itself be pre-sensitised to at least some extent. For example, it may comprise one or more solid sensitising agents such as microballoons / microspheres (glass or polymer) or be partially pre-gas sensitised through use of one or more chemical sensitising agents as described herein The water-in-oil explosive emulsion may also be pre-gas sensitised through the mechanical entrainment of air bubbles. However, it is the intention for the method of the invention to provide as the main source of sensitisation the gas sensitisation initiated by undertaking the method.

[0081] In some embodiments, the water-in-oil explosive emulsion provided in the conduit is a non-gas sensitised water-in-oil explosive emulsion. It will be appreciated that such non-gas sensitised water-in-oil explosive emulsion becomes gas sensitised in accordance with the method of the invention.

[0082] An important feature of the present invention is that the water-in-oil explosive emulsion comprises solid ammonium salt. Provided the solid ammonium salt is capable of dissolving in the aqueous annulus to provide for solubilised ammonium ions, there is no particular limitation on the type of the solid ammonium salt that can be used.

[0083] In some embodiments, the solid ammonium salt is selected from one or more of solid ammonium nitrate, ammonium chlorate, ammonium sulfate, ammonium phosphate and ammonium perchlorate.

[0084] In other embodiments, the solid ammonium salt is ammonium nitrate. The solid ammonium salt may be introduced into the water-in-oil explosive emulsion that is then provided to the conduit. Alternatively, the solid ammonium salt may be introduced into the water- in-oil explosive emulsion already located in the conduit. However, the solid ammonium salt will need to be present in the water-in-oil explosive emulsion such that it has sufficient travel time within and down the conduit that enables at least some of it to dissolve across into the aqueous annulus.

[0085] As an example only, the solid ammonium salt may be provided in the water-in-oil explosive emulsion such that it has at least 10 m, or 20 m, or 30 m, or 40 m, or 50 m, or 60 m, or 70 m downstream travel within the conduit to at least partially dissolve into the aqueous liquid / annulus before the water-in-oil explosive emulsion is mixed with the activated aqueous liquid.

[0086] In one embodiment, the solid ammonium salt is provided in the water-in-oil explosive emulsion at least 10 m, or 20 m, or 30 m, or 40 m, or 50 m, or 60 m, or 70 m upstream from the point in the conduit where the water-in-oil explosive emulsion is mixed with the activated aqueous liquid.

[0087] As previously discussed, without wishing to be limited by theory it is believed that the solid ammonium salt present in the water-in-oil explosive emulsion core is progressively agitated in the core as it flows downstream from the point of being introduced into the conduit. That agitation is believed to facilitate at least momentary penetration of the solid ammonium salt through the core-annulus interface and into the aqueous environment of the annulus. During such momentary penetration at least some of the solid ammonium salt is believed to dissolve in the aqueous annulus. Through a multiple of such momentary penetrations occurring as the water-in-oil explosive emulsion core travels down the conduit, the concentration of the dissolved ammonium salt cumulative increases in the aqueous annulus and reaches a suitable stoichiometry to react with the gassing agent.

[0088] While the water-in-oil explosive emulsion may itself have a discontinuous aqueous phase that comprises a solubilised ammonium salt, for example ammonium nitrate, it has been found that solubilised ammonium salt does not readily transfer across into the aqueous annulus. For example, it has been found that an ammonium nitrate based water-in-oil explosive emulsion can be conveyed down a conduit in a core annular flow and only a very limited amount of ammonium ions can be detected in the aqueous annulus at the end of the conduit. The amount of ammonium ions that do transfer across into the aqueous annulus is significantly below the stoichiometric requirement for reaction with an amount of a chemical gassing agent (such as sodium nitrite) required to produce a desired degree of gassing.

[0089] The presence of solid ammonium salt within the water-in-oil explosive emulsion in accordance with the present invention has advantageously been found to significantly enhance the ability for ammonium ions to transfer across into the aqueous annulus. Most notably, the amount of transferred ammonium ions can be more than adequate to provide the stoichiometric requirement for reaction with an amount of a chemical gassing agent (such as sodium nitrite) required to produce a desired degree of gassing.

[0090] Provided the solid ammonium salt can be combined with the water-in-oil explosive emulsion and conveyed in the conduit, there is no particular limitation of the physical form it may take.

[0091] In one embodiment, the solid ammonium salt is provided in the form of particles having a diameter ranging from about 0.5mm to about 5mm.

[0092] Provided the solid ammonium salt at least partially dissolves into the aqueous liquid / annulus and mixes with the chemical gassing agent to produce an activated aqueous liquid / annulus that is capable of forming gas, there is no particular limitation on the amount that can be used.

[0093] In some embodiments, the water-in-oil explosive emulsion comprises a solid ammonium salt in an amount ranging from about 10 wt. % to about 50 wt. %.

[0094] The water-in-oil explosive emulsion may be combined or provided with the solid ammonium salt conventional techniques known in the art. For example, the solid ammonium salt can simply be blended together with the water-in-oil explosive emulsion using an auger mixing units such as a paddle mixer.

[0095] A key feature of the present invention is that the solid ammonium salt at least partially dissolves into the aqueous liquid / annulus at a point downstream from where the salt is introduced into the conduit. Accordingly, from a flow distance perspective ammonium ions derived from the solid ammonium salt are in effect delayed from crossing over into the aqueous liquid / annulus. As will be discussed in more detail below in the context of forming the activated aqueous liquid / annulus, that delay assists with preventing undesirable premature gassing occurring within the conduit.

[0096] The water-in-oil explosive emulsion and / or the aqueous liquid / annulus provided in the conduit may also comprise one or more conventional additives known to those skilled in the art, for example pH modifiers, gas accelerator agents, thickening agents, antifreeze agents and gas stabilising surfactant.

[0097] The aqueous annulus may be provided in the conduit using conventional techniques and equipment known to those skilled in the art, for example via a MMU using pump / inj ection / metering equipment.

[0098] The aqueous liquid (that the forms the substantially annular profile - i.e. the annulus) will generally represent from about 0.5 wt.% to about 5 wt.% of the total composition being conveyed in the conduit (i.e. the water-in-oil explosive emulsion plus the aqueous liquid / annulus). Conversely, water-in-oil explosive emulsion core will generally represent from about 95 wt.% to about 99.5 wt.% of the total composition being conveyed in the conduit

[0099] According to the method of the invention, a chemical gassing agent that is capable of reacting with an ammonium salt to form gas is introduced into the aqueous liquid / annulus.

[0100] Suitable chemical gassing agents that may be used in accordance with the invention include inorganic nitrite compounds. Examples of inorganic nitrite compounds include alkaline earth and alkali metal nitrite compounds.

[0101] In some embodiments, the chemical gassing agent is an inorganic nitrite compound selected from alkaline earth and alkali metal nitrite compounds.

[0102] In one embodiment, the chemical gassing agent is sodium nitrite.

[0103] The chemical gassing agent will be solubilised in the aqueous liquid / annulus

[0104] Provided the desired degree of gassing is achieved, there is no particular limitation on the amount of chemical gassing agent that may be introduced into the aqueous liquid / annulus. Generally, the aqueous liquid / annulus will be provided with a chemical gassing agent that is capable of reacting with an ammonium salt to form a gas in an amount ranging from about 0.0005 wt. % to about 0.3 wt. %, or from about 0.001 wt. % to about 0.3 wt. %.

[0105] Two or more different chemical gassing agents may be introduced. In a one embodiment, the chemical gassing agent is introduced into the aqueous liquid in an amount ranging from about 0.0005 wt. % to about 0.3 wt. %, or from about 0.001 wt. % to about 0.3 wt. %.

[0106] The chemical gassing agent may be introduced into the aqueous liquid using techniques and equipment well-known to those skilled in the art. For example, using metering pumps, injectors and flow meters.

[0107] The chemical gassing agent may be introduced into the conduit with aqueous liquid that forms the aqueous annulus. Alternatively, the chemical gassing agent may be introduced into the aqueous liquid of the annulus already located in the conduit. However, the chemical gassing agent will need to be introduced into the aqueous liquid of the annulus at a point that enables formation of the activated aqueous liquid of the annulus prior to the water-in-oil explosive emulsion being mixed with the activated aqueous liquid of the annulus.

[0108] By being an "activated" aqueous liquid / annulus is meant that as a result of the solid ammonium salt within the water-in-oil explosive emulsion travelling down the conduit, at least some of it dissolves into the aqueous environment of the annulus causing the concentration of dissolved ammonium ions derived from the solid ammonium salt in the aqueous liquid of the annulus to increase. Prior to that occurring the aqueous annulus does not comprise a sufficient concentration of ammonium ions to stoichiometrically react with the chemical gassing agent present in the annulus. As the concentration of dissolved ammonium ions derived from the solid ammonium salt progressively increases along the conduit, it reaches a concentration of ammonium ions that can stoichiometrically react with the chemical gassing agent present. At that point within the conduit the aqueous liquid of the annulus becomes activated in the sense it now capable of stoichiometrically reacting with the chemical gassing agent.

[0109] At the point within the conduit when the aqueous liquid of the annulus becomes activated, those skilled in the art will appreciate the activated annulus will not necessarily spontaneously and rapidly produce gas, rather it is merely capable of doing so. In particular, there will generally be a latent reaction time before gas bubbles would be expected to be produced upon the activated aqueous annulus being formed. For example one might expect a lag time of at least about 5 seconds for gas bubbles to begin forming after the activated annulus has formed. The amount of ammonium ions within the aqueous liquid / annulus required to stoichiometrically react with the chemical gassing agent to form gas will of course depend upon the nature and amount of the chemical gassing agent used. Those skilled in the art are familiar with the reaction chemistry associated with chemical gassing reaction systems. For example, where the chemical gassing agent is sodium nitrite, the nitrite and ammonium ions react in a 1 : 1 molar ratio.

[0110] In some embodiments, the amount of solid ammonium salt that at least partially dissolves into the aqueous liquid provides for at an excess on a molar basis of that required to stoichiometrically react with the chemical gassing agent present.

[0111] In other embodiments, the amount of solid ammonium salt that at least partially dissolves into the aqueous liquid provides for at least 1.5, or at least 2, or at least 3 times on a molar basis of that required to stoichiometrically react with the chemical gassing agent present.

[0112] As the water-in-oil explosive emulsion travels down the conduit toward the mixing point, the concentration of dissolved ammonium ions derived from the solid ammonium salt progressively increases in the within the aqueous liquid / annulus. The amount of ammonium salt dissolved within the aqueous liquid / annulus can represent up 50 wt.% of the aqueous liquid / annulus at the point in the conduit where the water-in-oil explosive emulsion is mixed with the activated aqueous.

[0113] If desired, a gas accelerator agent may also be introduced into the aqueous annulus. Such gas accelerators are known in the art to enhance the rate of gassing and / or the completion of the gassing reaction (i.e. it is a gas reaction accelerator agent). Gas accelerators are typically used in an amount ranging from about 0.1 wt. % to about 20 wt. % of the aqueous liquid / annulus and include compounds such as thiourea, metal thiocyanates (e g. sodium or potassium thiocyanate), metal nitrates (e g. calcium, zinc or magnesium nitrate).

[0114] In one embodiment, a gas accelerator agent is introduced into the aqueous liquid / annulus.

[0115] If desired, a gas stabilising surfactant may also be introduced into the water-in-oil emulsion. Such gas stabilising surfactants are known in the art to assist with stabilisation of liquid / gas interface and promote fine gas bubble formation and minimise gas bubble coalescence within the so formed gas sensitised water-in-oil emulsion. Gas stabilising surfactants are typically used in an amount ranging from about 0.01 wt. % to about 0.04 wt. % of the water-in-oil explosive emulsion and include silicone and fluoroalkyl surfactants.

[0116] In one embodiment, a gas stabilising surfactant is introduced into the introduced into the water- in-oil emulsion.

[0117] The flow rate of the aqueous annulus and the water-in-oil explosive emulsion core can be readily adjusted to assist with formation of the activated aqueous annulus at a point within the conduit that assists with avoiding adverse premature gassing within the conduit. The flow rate in the conduit of the water-in-oil explosive emulsion core is typically provided within the range of about 100 kg / min to about 1000 kg / min, with the aqueous liquid / annulus being provided at a flow rate that is about 0.5 % to about 5% of the flow rate of the water-in-oil explosive emulsion core.

[0118] Once the activated aqueous liquid / annulus has been formed within the conduit, it will then travel through the remaining conduit to be mixed with the water-in-oil explosive emulsion. That mixing step may be undertaken using techniques and equipment well-known to those skilled in the art. For example, mixing the water-in-oil explosive emulsion with the activated aqueous liquid may be undertaken with the assistance of static mixers, orifices and / or connective chambers.

[0119] That mixing will generally take place at or toward the end of the conduit. For example, the mixing can take place from 0 to about 5m upstream from the end of the conduit.

[0120] Unlike conventional gas sensitising core annular flow techniques, the step of mixing the water- in-oil explosive emulsion with the activated aqueous annulus according to the method of the present invention is not required for combining the chemical gassing reactive species (as that has already taken place in the so formed activated annulus). Rather, the mixing step according to the method of the present invention simply and advantageously serves to disperse the activated aqueous liquid, which comprises the already mixed gassing agent and ammonium salt, throughout the water-in-oil explosive emulsion. That mixing / dispersion step can be readily controlled and will operate efficiently for that purpose at relatively low intensity. The method of the present invention therefore consequently enables gassing to occur in a more efficient and reproducible manner, which in turn improves the reliability of detonation.

[0121] Once the water-in-oil explosive emulsion is mixed with the activated aqueous liquid, the resulting composition will generally be transferred into a desired location, such as a borehole. The so formed mixed composition will comprise the water-in-oil explosive emulsion having dispersed / distributed therethrough droplets of the activated annulus that by this time will start to form gas bubbles and produce the gas sensitised gas sensitised water-in-oil explosive emulsion.

[0122] The resulting gas sensitised water-in-oil explosive emulsion can then be used in the same manner as conventional gas sensitised water-in-oil explosive emulsion. However, gas sensitised water- in-oil explosive emulsion produced in accordance with the method of the invention advantageously enhances gassing efficiency and consequently affords improved uniformity and stability of the gas sensitised water-in-oil explosive emulsion.

[0123] With reference to Figure 1, part A is a cross-sectional representation of a conduit (not shown) used in accordance with the invention having an aqueous annulus (10) surrounding a water-in-oil explosive emulsion core (20) that comprises solid ammonium salt (30). Part B is the same cross- sectional representation as part A where a chemical gassing agent capable of reacting with and ammonium salt to form gas has been introduced into the aqueous annulus (40). That chemical gassing agent may be introduced into the aqueous annulus (10) that is already present in the conduit, or it may be introduced into the aqueous liquid that is then introduced into the conduit to form the annulus. In the latter case, part A would not occur. Part C is the same cross-sectional representation as part A and B where the solid ammonium salt (30) has at a point downstream from where it is introduced into the conduit at least partially dissolved into the aqueous liquid of the annulus to form the activated aqueous liquid annulus (50) that is capable of forming gas through reaction of the gassing agent and the dissolved ammonium salt derived from the solid ammonium salt (30). The composition in part C then passes through a mixing head (60) that mixes the water-in-oil explosive emulsion (20) with the activated aqueous liquid (50). The resulting mixed composition is then transferred into a borehole (70) where the chemical gassing reaction proceeds to produce the gas sensitised water-in-oil explosive emulsion (80) comprising gas bubbles (90).

[0124] EXAMPLES

[0125] Example 1

[0126] A water-in oil explosive emulsion was prepared in a mobile manufacturing unit by mixing 30 parts solid ammonium nitrate porous prill (Nitropril from Orica) and 70 parts ammonium nitrate emulsion comprising 70 parts of ammonium nitrate, 7.4 parts of diesel, vegetable oil and emulsifier, and 22.6 parts of water. That water-in oil explosive emulsion was pumped using a progressive cavity product pump through a loading hose of 50.8 mm diameter and 60 m long The velocity in the hose was 2.34 m / s. The hose lubricating water was injected after the product pump as 1.5 % of the product as a lubricating annulus.

[0127] The product was collected at the end of the hose into a vessel and the separated fluid from the lubricated annulus was collected for analysis.

[0128] The analysis confirmed the AN content in the water of 40% and a pH of 4.1 . That confirmed a creation of an ammonium nitrate containing fluid in the lubrication layer sufficient for a prill containing system to react with a sodium nitrite based gassing agent.

[0129] Example 2

[0130] A water-in oil explosive emulsion was prepared in a mobile manufacturing unit by mixing 30 parts ammonium nitrate porous prill (Nitropril from Orica Australia) and 70 parts ammonium nitrate emulsion comprising 70 parts of ammonium nitrate, 7.4 parts of fuel composed of diesel, vegetable oil and emulsifier, and 22.6 parts of water.

[0131] That water-in oil explosive emulsion was pumped using a progressive cavity product pump through a loading hose of 38.1 mm diameter and 40 m long. The velocity in the hose was 4.15 m / s. Water was injected after the product pump as 1.5 % of the product as a lubricated annulus.

[0132] The product was collected at the end of the hose into a vessel and the separated fluid from the lubricated annulus was separated for analysis.

[0133] The collected lubricated fluid was then divided in 2 parts by a centrifuge.

[0134] The water contained 31%, ammonium nitrate, whilst the lubricating fluid with both water and weak emulsion contained 41% ammonium nitrate.

[0135] Those results confirmed the creation of an aqueous liquid comprising sufficient ammonium nitrate to react with the sodium nitrite based gassing agent. Example 3

[0136] A water-in oil explosive emulsion was prepared in a laboratory by mixing 28 parts ammonium nitrate porous prill (Nitropril from Orica Australia), 2 parts of diesel, and 70 parts of ammonium nitrate emulsion. The ammonium nitrate emulsion contained 77% of ammonium nitrate, 6.1 % of fuel composed of diesel, vegetable oil and emulsifier, and 16.9 % of water.

[0137] That water-in oil explosive emulsion was then divided in 2 parts and gassed using just gassing agent with 15 % of sodium nitrite in part 1 (being reflective of prior art approaches) and the same gassing agent premixed with equal volume of ammonium nitrate solution containing 30% of ammonium nitrate (being reflective of a gassing system produced in accordance with the invention).

[0138] The quality of the two products was compared by photo microscopy.

[0139] The product gassed with gassing agent only (part 1) resulted in a crystal rating of 4, the product gassed with the blend of gassing agent and the ammonium nitrate solution (part 2) resulted in a crystal rating of 1.5.

[0140] The crystal rating scale has ratings between 1 and 5, with a rating of 5 being the most crystallised and of lowest quality and a rating of 1 being the least crystallised and of high quality.

[0141] Example 4

[0142] A water-in oil explosive emulsion was prepared in a mobile manufacturing unit by mixing 28 parts ammonium nitrate porous prill (Anopril from Orica Canada), 2 parts of diesel, and 70 parts of ammonium nitrate emulsion. The ammonium nitrate emulsion contained 75% of ammonium nitrate, 6.0 % of fuel composed of diesel, vegetable oil and emulsifier, and 19 parts of water.

[0143] That water-in oil explosive emulsion was pumped using a progressive cavity product pump through a loading hose of 38 1 mm diameter and 30 m long. The velocity in the hose was 4.1 m / s Water was injected after the product pump as 1.5 % of the product as a lubricated annulus and a mixing element was installed at the end of the loading hose.

[0144] A stream of gassing agent with 15% of sodium nitrite was injected into the (a) water-in oil explosive emulsion (comparative), or (b) water lubricating annulus (the present invention).

[0145] Samples of the products produced were collected at the end of the loading hose.

[0146] Product with gassing agent injected directly in the water-in oil explosive emulsion (a) and with gassing agent injected in the water lubricating annulus (b) were collected and compared by photo microscopy.

[0147] Gassing agent injected directly in the water-in oil explosive emulsion (a) resulted in a crystal rating of 4, gassing agent injected in the water lubricating annulus (b) resulted in a crystal rating of 2. The crystal rating scale has ratings between 1 and 5, with a rating of 5 being the most crystallised and of lowest quality and a rating of 1 being the least crystallised and of high quality.

[0148] Comparative Example 1

[0149] A water-in oil explosive emulsion was prepared. The emulsion contained 100% ammonium nitrate emulsion comprising 77 parts of ammonium nitrate, 7 parts of fuel composed of parafinic oil, vegetable oil and emulsifier, and 16 parts of water. The emulsion was pumped in a mobile manufacturing unit. The emulsion was pumped through a 18.5 mm diameter and 60 m loading hose with a piston pump. The product velocity in the hose was 3.3 m / s. Water was injected to the hose at 2.35 wt% of the product as lubricating annulus.

[0150] The water lubricant was collected at the end of the hose immediately after the pump has stopped. The run was performed in duplicate.

[0151] The analysis of both run samples indicated the ammonium nitrate content in water lubrication annulus was very low at 0. 1-0.2 wt %. That in turn confirmed that very little ammonium nitrate is transferred from the water-in oil explosive emulsion core into the water annulus during travel through the hose

[0152] That in turn confirmed that when using a water-in oil explosive emulsion absent solid ammonium nitrate very little ammonium nitrate is transferred from the water-in oil explosive emulsion core into the water annulus during travel through the hose. The minimal level that is transferred is well below the amount required to suitably react with a gassing agent such as sodium nitrite that could be present within the aqueous annulus. Example 5

[0153] A leachability test was conducted on a mixture of 30 parts ammonium nitrate porous prill (Nitropril from Orica) and 70 parts of ammonium nitrate emulsion comprising 70 parts of ammonium nitrate , 7.4 parts of diesel, vegetable oil and emulsifier, and 22.6 parts of water sensitised by a nitrite gassing system to a density of 1. 1 g / cc. A reservoir of water was circulated through a stationary 20 g sample for one hour at a rate of 61 ml / min. The test was conducted in duplicate. Chemical analysis confirmed 5.06 and 5.46% ammonium nitrate loss from the sample.

[0154] Those results confirmed that aqueous liquid / annulus flow assists with promoting transfer of ammonium ions derived from the solid ammonium nitrate in the water-in oil explosive emulsion into the aqueous liquid / annulus.

[0155] Example 6

[0156] A leachability test was conducted on a mixture of 20 parts ammonium nitrate porous prill (Nitropril from Orica) and 80 parts of ammonium nitrate emulsion, sensitised by a nitrite gassing system in presence of ammonium nitrate solution to a density of 0.9-1.0 g / cc. The water-in oil explosive emulsion was placed in a petri dish with known exposed surface area inside a beaker containing 400 g water. An overhead impeller was installed. Tests were conducted at 0 rpm and 350 rpm for one hour.

[0157] Analysis of the water after one hour showed ammonium nitrate loss of 0.04% and 0.13% in the absence and presence of agitation, respectively.

[0158] Those results confirmed that aqueous liquid / annulus flow assists with promoting transfer of ammonium ions derived from the solid ammonium nitrate in the water-in oil explosive emulsion into the aqueous liquid / annulus

[0159] Example 7

[0160] A leachability test was conducted on a mixture of 20 parts ammonium nitrate porous prill (Nitropril from Orica) and 80 parts of ammonium nitrate emulsion sensitised by a nitrite gassing system in presence of a ammonium nitrate solution to a density of 0.9-1.0 g / cc. The water-in oil explosive emulsion was placed in a petri dish with known exposed surface area inside a beaker containing 400 g water. An overhead impeller was installed. The test was conducted at 350 rpm for one hour. Analysis of water after one hour showed ammonium nitrate loss of 0.13%.

[0161] A leachability test was conducted on a mixture of 40 parts ammonium nitrate porous prill (Nitropril from Orica) and 60 parts of ammonium nitrate emulsion, sensitised by a nitrite gassing system in presence of ammonium nitrate solution to a density of 0.9-1.0 g / cc. The water-in oil explosive emulsion was placed in a petri dish with known exposed surface area inside a beaker containing 400 g water. An overhead impeller was installed. The test was conducted at 350 rpm for one hour. Analysis of water after one hour showed ammonium nitrate loss of 0.68%.

[0162] Those results confirmed that increasing the amount of solid ammonium nitrate in the water-in oil explosive assist with promoting transfer of ammonium ions derived from the solid ammonium nitrate in the water-in oil explosive emulsion into the aqueous liquid / annulus.

[0163] The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

[0164] Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS1. A method of producing a gas sensitised water-in-oil explosive emulsion, the method comprising: providing in a conduit a flowing stream of (i) water-in-oil explosive emulsion, and (ii) an aqueous liquid having a substantially annular profile around the water-in-oil explosive emulsion; introducing into the aqueous liquid a chemical gassing agent that is capable of reacting with an ammonium salt to form a gas; wherein the water-in-oil explosive emulsion comprises a solid ammonium salt that at a point downstream from where it is introduced into the conduit at least partially dissolves into the aqueous liquid and mixes with the chemical gassing agent to produce an activated aqueous liquid that is capable of forming gas through reaction of the gassing agent and the dissolved ammonium salt derived from the solid ammonium salt; and mixing the water-in-oil explosive emulsion with the activated aqueous liquid to produce the gas sensitised water-in-oil explosive emulsion.

2. The method according to claim 1, wherein the water-in-oil explosive emulsion comprises a discontinuous aqueous oxidiser phase that comprises one or more dissolved oxidiser compounds selected from alkali and alkaline earth metal nitrates, alkali and alkaline earth metal chlorates, alkali and alkaline earth metal perchlorates, ammonium nitrate, ammonium chlorate, ammonium perchlorate and a combination thereof.

3. The method according to claim 1 or 2, wherein the water-in-oil explosive emulsion comprises a continuous oil phase that comprises one or more organic compounds selected from fuel oil, diesel oil, distillate, furnace oil, kerosene, naphtha, wax, paraffin oils, naphthenic oils, benzene, toluene, xylenes, asphaltic materials, polymeric oils, animal oils, vegetable oils, fish oils and a combination thereof.

4. The method according to any one of claims 1 to 3, wherein solid ammonium salt is selected from ammonium chloride, ammonium nitrate, ammonium chlorate, ammonium sulfate, ammonium phosphate, ammonium perchlorate, ammonium sulfate, ammonium phosphate and a combination thereof.

5. The method according to any one of claims 1 to 4, wherein the solid ammonium salt is provided in the form of particles having a diameter ranging from about 0.5mm to about 5mm.-in -6. The method according to any one of claims 1 to 5, wherein the water-in-oil explosive emulsion comprises the solid ammonium salt in an amount ranging from about 10 wt. % to about 50 wt. %.

7. The method according to any one of claims 1 to 6, wherein the chemical gassing agent is selected from alkaline earth and alkali metal nitrite compounds.

8. The method according to any one of claims 1 to 7, wherein a gas accelerator agent is introduced into the aqueous liquid9. The method according to any one of claims 1 to 8, wherein a gas stabilising surfactant is introduced into the aqueous liquid.

10. The method according to any one of claims 1 to 9, wherein the solid ammonium salt is provided in the water-in-oil explosive emulsion at least 20 m upstream from the point in the conduit where the water-in-oil explosive emulsion is mixed with the activated aqueous liquid.

11. The method according to any one of claims 1 to 10, wherein the chemical gassing agent is introduced into the aqueous liquid an amount ranging from about 0.0005 wt. % to about 0.3 wt. %.

12. The method according to any one of claims 1 to 11, wherein the amount of solid ammonium salt that at least partially dissolves into the aqueous liquid provides for at least 1 5 times on a molar basis of that required to stoichiometrically react with the chemical gassing agent present.

13. The method according to any one of claims 1 to 12, wherein flow rate in the conduit of the water-in-oil explosive emulsion is within the range of about 100 kg / min to about 1000 kg / min, with the aqueous liquid being at a flow rate that is about 0.5 % to about 5% of the flow rate of the water-in-oil explosive emulsion.

14. The method according to any one of claims 1 to 13, wherein so formed gas sensitised water-in-oil explosive emulsion exhibits a degree of gassing expressed in terms of its void fraction of greater than about 5% up to about 60%.

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