Downhole heating apparatus and method

Abstract

A downhole heater (110) comprises a volume of intermetallic including at least two powdered metallic elements and an initiator. The heater is run into a bore (102) and the initiator operated to trigger an exothermic reaction between the metallic elements.

Description

[0001] DOWNHOLE HEATING APPARATUS AND METHOD FIELD This disclosure relates to a downhole heating apparatus and method and particularly downhole heating utilising intermetallic reactions. BACKGROUND In downhole operations, such as in oil and gas exploration and production, heaters may be provided for a variety of purposes, such as fluidising or softening materials. Downhole heaters may take various forms, including electric heaters and exothermic reaction heaters, such as thermite heaters in which a reaction is initiated between a metal and a metal oxide. Electric heaters may be supported on electric wireline and run into a bore and located adjacent an object or apparatus to be heated. Similarly, thermite heaters may be run into a bore on a support and activated adjacent an area to be heated, and the heater removed following activation. Alternatively, a thermite heater may be provided as an element of a downhole tool and may remain in the bore following activation. SUMMARY According to an aspect of the present disclosure there is a downhole heater comprising a volume of intermetallic comprising at least two powdered metallic elements and means for initiating a reaction between the metallic elements. According to another aspect of the disclosure there is provided a downhole heating method comprising: providing a volume of intermetallic comprising at least two powdered metallic elements; running the volume of intermetallic into a bore, and activating the intermetallic.   An intermetallic reaction may progress rapidly and release significant quantities of energy, and the reaction products may be sufficiently strong to form structural members and bond to other metals. In a downhole application an intermetallic reaction may provide heat for a wide variety of different purposes, for example a reaction may provide heat to melt or mobilize bonding and sealing materials in tubing bores and annuli. Such sources can also heat the surrounding rock formation to enable penetration of sealing media (such as polymers or low melt temperature alloys), accelerate creep closure in certain geological media, or stimulate flow and production of oil or geothermal fluids. Activation of the intermetallic reaction may be accomplished by providing sufficient energy to overcome an activation energy threshold and initiate the reaction. Initiation of the reaction may occur by providing energy at single or multiple points of the volume and may be at a discrete point or applied over a broader area. The energy may be in the form of a high energy spark, a thermal pulse, or a mechanical impact sufficient to initiate the reaction. Sources of electrical energy may include batteries, capacitive discharge units, ultra-capacitors, or piezoelectric devices. Thermal energy may be delivered by lasers or non-contact electrical sources, such as induction heating systems. Mechanical impact energy may be generated by fluid pressure- or motion-delivered forces on spring-activated switches, or from the sudden release of tension or compression forces initially restrained by shear pins or other releasable couplings. Energy sources may act on small quantities of intermediate, high sensitivity energetic materials, which then initiate the intermetallic reaction. Such energetic materials may comprise intermetallic or other materials in the form of a multi-layer foil. The materials may have been deposited using vapor deposition techniques, for example vapor deposited intermetallic nanoparticles. Intermetallic reactions are exothermic reactions involving two or more metals and may produce ordered solid-state compounds. The   reactions may not require oxidizers or generate non-condensable gas products. The metallic reaction products may be of high mechanical strength. The volume of intermetallic material may be formed using powder compaction techniques, with the ingredients being blended in powdered form and then pressed into final form under high compressive stresses. The resulting compacts may be sintered under elevated temperature to increase final form strength. The volume of intermetallic material may be hermetically sealed within a housing or coating. The intermetallic ingredients may be readily available, non-toxic, easily formed into compacted forms, and sufficiently insensitive to avoid handling risks. The intermetallic ingredients may have thermophysical properties to release significant thermal energy and self-propagate under the anticipated downhole conditions. The ingredients may be selected or modified to form solid product shapes following activation identical to the unreacted shape, or if desired, allow plastic deformation to alter the shape during the reaction. Intermetallic systems suitable for downhole applications include titanium / boron; titanium / carbon; zinc / carbon; zirconium / carbon; zirconium / boron; vanadium / silicon; nickel / aluminium. The majority of these reacting systems achieve peak adiabatic reaction temperatures of 1500°C, with some much greater (up to 2700°C). Reaction propagation rates of the undiluted reactants are dependent on physical form and compact density, but can range from cm / second to tens of cm / sec. Other reacting systems are described by Fischer, S H, and Grubelich, M C. in “A survey of combustible metals, thermites, and intermetallics for pyrotechnic applications.” United States: N. p., 1996. Web, the disclosure of which is incorporated herein in its entirety.   Additives may be mixed with the metallic elements to modify the reaction properties or the final product. For example, inert materials with high melt temperatures, including oxides such as alumina and silica, and metals, may be added to dilute the reaction, slowing the reaction rate, and reducing the peak temperature. Alloying metals may be added to alter the final strength or ductility of the product, such as the ductility improvement resulting from the addition of boron to a nickel / aluminium system. Lower melt temperature alloying metals, such as bronze or copper, will remain fluid after the intermetallic products have solidified and may fill pores in the reaction product to reduce the permeability of the product. If supplemented by chemicals which act as fluxing agents, such as boric acid, bronze additives may perform as filler metals and braze the intermetallic products to well tubing or casing. The intermetallic volume may be provided in any appropriate form, for example a rod, solid cylinder, or thin / thick-walled cylinder. The volume may be relatively small, for example if the heat generated by the reacting intermetallic is used to heat / weaken a small pin. The volume may be configured to facilitate heating an enclosed volume of fluid and create expansion force. Larger volumes may be utilised to melt a low melt-point alloy or to heat a near wellbore region. The intermetallic may be provided as a single part or in multiple parts. The intermetallic may be provided in a flowable form, such as balls, tablets, beads or pellets. The flowable elements may be of any appropriate size, for example 0.5 – 5 cm diameter. The use of intermetallic balls may be useful for use in melting alloy in larger wellbores. Initiation of the intermetallic reaction in a first intermetallic ball may trigger a chain reaction with adjacent balls, such that the reaction propagates through the intermetallic volume.   When provided in combination with a volume of alloy intermetallic balls may form a structural and creep resistant component of the resulting formed alloy barrier. The intermetallic may be deployed mounted on a tool or apparatus or may be delivered or deposited into an area or volume of a bore, for example a volume created by expanding downhole tubing or by milling out a section of tubing. In some examples the heater may be provided in an apparatus in combination with a volume of fusible material, such as a volume of low melt alloy. Activation of the heater may cause the fusible material to soften and flow, and on cooling the fusible material may harden to create a seal or plug. The intermetallic volume may be provided internally of the volume of fusible material. The volume of fusible material may be a single part or may comprise multiple parts or elements. The fusible material may be provided in any appropriate form, for example a solid or cast form, a compacted fusible powder with bonding additives, or as a flowable volume of beads. The fusible material may be a powder compacted low melt-point alloy and may comprise a flux material, The fusible material may be provided in an initial configuration to facilitate the location of the apparatus downhole, for example the fusible material may define an outer diameter smaller than an internal diameter of downhole tubing to facilitate translation of the apparatus through and into the downhole tubing. The compaction density of a powder compacted alloy element may be optimised to facilitate radial expansion of the element to contact the downhole tubing or surrounding bore wall when subject to an axial compression force or other setting force The fusible material may be reconfigurable to a setting configuration in which the fusible material contacts one or both of a surrounding tubing or wellbore (if deployed in an open hole), and an inner surface or mandrel. The reconfiguration of the fusible material may facilitate the displacement of downhole fluids and   material which would otherwise adversely the affect the creation of a secure bond between the fusible material and the tubing. The volume of intermetallic may be configured to be integrated in the seal or plug or may be separable from the fusible material. The intermetallic volume may be coated or otherwise treated to minimise fluid penetration. An aspect of the disclosure also relates to a downhole heater comprising: a volume of intermetallic; a first initiator comprising first exothermic reaction components, and a second initiator comprising second exothermic reaction components, whereby activation of the first initiator initiates a reaction of the first exothermic reaction components to generate a first energy output which is applied to the second initiator to initiate a reaction of the second exothermic reaction components to generate a second energy output for initiating an intermetallic reaction in the volume of intermetallic. A further aspect of the disclosure relates to a method of activating an intermetallic heater comprising a volume of intermetallic, the method comprising: applying a first energy input to a first initiator and activating a first exothermic reaction to generate a first energy output; applying the first energy output to a second initiator and activating a second exothermic reaction to generate a second energy output greater than the first energy output, and applying the second energy output to a volume of intermetallic and initiating an intermetallic reaction. The skilled person will understand that the various aspects, examples and options described above may have individual utility and may be combined as desired and as considered appropriate or advantageous.   BRIEF DESCRIPTION OF THE DRAWINGS These and other examples of the disclosure will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 shows an apparatus for forming a seal in a bore, with the apparatus located in a wellbore in a running configuration; Fig.2 shows the apparatus of Fig.1 in a setting configuration; Figs. 3, 4, 5 & 6 show alternative configurations of apparatus for forming a seal or plug in a bore; Fig.7 is a schematic of heater activation methods; and Figs. 8 - 12 illustrate examples of arrangements for activating a reaction in an intermetallic heater. DETAILED DESCRIPTION OF THE DRAWINGS Reference is first made to Figs.1 & 2 of the drawings, which illustrate an apparatus 100 for use in forming an annular downhole seal between downhole tubing 102 and a smaller diameter mandrel 104. The tubing 102 may be, for example, casing or liner or open hole wellbore. The mandrel 104 may be smaller diameter casing or liner or may be a hanger or other apparatus that the operator wishes to locate and seal within the tubing 102. A cylindrical alloy element 106 is mounted externally of the mandrel 104 with a backup ring 108 supporting a lower end of the element 106. An upper backup, not illustrated, may be employed to retain the alloy in deviated wellbores. In an initial running configuration, the element 106 describes a smaller external diameter than the internal diameter of the tubing 102. A cylindrical intermetallic heater 110 is positioned externally of the mandrel 104 and internally of the alloy element 106, between upper and lower cylindrical metal fillers 112, 114. The apparatus 100 further comprises a setting piston, signified by arrows 116. The apparatus 100 is mounted on a suitable support, such as wireline, coil tubing, tubing, casing or pipe and run into a wellbore, most   typically lined with the tubing 102 to a desired depth. The setting piston 116 is then activated to axially compress and radially expand the alloy element 106 such that the outer surface of the element 106 contacts the inner surface of the tubing 102, as illustrated in Fig. 2. As the element 106 is radially expanded wellbore fluid 118 between the two surfaces is displaced, and any solid material on the inner surface of the tubing 102 will also tend to be displaced. The heater 110 is then activated by triggering an activator provided adjacent to or part of the heater 110. Energy from the activator overcomes an activation energy threshold and initiates a reaction in the powder compacted metallic elements provided in the heater 110. The reaction propagates through the heater 110, providing sufficient energy to heat and fluidise the alloy element 106. The molten alloy element 106 bonds with the inner surface of the tubing 102 and the outer surface of the heater 110. The activated heater 110 may also bond with the external surface of the mandrel 104. After the intermetallic reaction is complete, the heater 110 and the alloy element 106 cool to ambient wellbore temperature, with the alloy solidifying. The resulting seal of the resolidified alloy 106 creates an element, bonded to the heater intermetallic reaction products 110 and also bonded between the tubing 102 and the mandrel 104. In other examples, as illustrated in Fig. 3 of the drawings, an apparatus 200 comprises an intermetallic heater 210 provided between an external expandable alloy element 206 and an internal fixed diameter alloy element 230. On activation, the heater 210 provides a more uniform distribution of heat and fluidises both alloy elements 206, 230. On cooling, the resolidified alloy elements 206 and 230 form a seal and a bond between the tubing 202 and the mandrel 204 and the heater intermetallic reaction products 210.   In the examples of Figs.1 – 3, the alloy elements and heaters are generally cylindrical in form, however in the apparatus 300 illustrated in Fig. 4, the heater 310 and the alloy elements 306, 330 are generally conical and wedge-shaped in form. The heater 310 has a conical form and is embedded in an inclined outer surface of the inner alloy element 330. The outer alloy element 306 has a corresponding inner surface such that an axial compression force applied by a setting piston 316 pushes the element 306 down the outer surface of the inner element 330 and radially extends the element 306 into contact with the inner surface of the tubing 302 such that the elements 306, 330 and the heater 310 fill the annulus between the mandrel 304 and the tubing 302. On activation, the heater 310 fluidises both elements 306, 330 such that on cooling the resolidified alloy elements 306 and 330 form a seal and a bond between the tubing 302 and the mandrel 304 and the heater intermetallic reaction products 310. Reference is now made to Fig.5 of the drawings, which illustrates an apparatus 400 in which an intermetallic heater element 410 is mounted on a mandrel 404, without a separate alloy element. The element 410 has an initial smaller diameter configuration (not shown) to facilitate running the apparatus 400 into downhole tubing 402, and may then be axially compressed and radially expanded, by compression between a backup ring 408 and a piston 416, or other compression tool, to fill the annulus between the mandrel 404 and the tubing 402. The heating element 410 comprises a mix of two powdered metallic elements and in one example the powders are initially only loosely packed and describe a smaller diameter configuration. Once the apparatus 400 has been located at a desired position relative to the tubing 402, the element 410 is axially compressed by the piston 416 and expands radially and into contact with the tubing 402. On activation, the element 410 reacts to metallurgically braze itself to both the mandrel 404 and the tubing 402.   In another example the element 410 is activated before being compressed, with the composition of the element 410 being selected to facilitate axial compression and radial expansion of the heated element 410. Reference is now made to Fig.6 of the drawings, which illustrates an apparatus 500 for use in creating a plug in a section of tubing 502. In this example the intermetallic heating element 510 is in the form of a centrally located solid cylinder or core mounted within a metal cylinder 504. A volume of alloy 506 is mounted externally of the cylinder 504 above a backup ring 508. On activation of the intermetallic reaction, heat from the element 510 is communicated to the alloy 506 via the wall of the cylinder 504, melting the alloy 506 and bonding the cylinder 504 to the surrounding tubing 502. Reference is now made to Fig.7 of the drawings, showing a general arrangement for activating a reaction in a cylindrical intermetallic heater 610. An energy source 630, which may be an electrical spark, a heat source, a laser, or a mechanical impact, is coupled via multiple and redundant activation points to an intermediate initiator embedded in the heater 610. Reference is now made to Figs. 8 – 12 of the drawings, which illustrate examples of arrangements for activating a reaction in an intermetallic heater. As illustrated in Fig.8, an energy source 730 is arranged to act on an intermetallic material 710 to initiate a reaction. An intermediate high sensitivity material 750 is used as a ‘first fire’ material, requiring less energy to activate than would the intermetallic 710. The intermediate material 750 may be a vapor deposited film of intermetallic nanoparticles designed as an initiation source, a thermite compound, or some other pyrotechnic initiating compound. The energy source 730 may be: electrical batteries supplying current to a metal filament 750 embedded in the material 710, to heat and vaporize the filament thus initiating a reaction; electrical batteries which charge a   capacitor to a large voltage, then discharging significant current to a filament, bridge wire, or some other resistive electrical device; a mechanically actuated piezoelectric crystal which generates current to energize an electrical initiation device; optical means, such as lasers, which apply heat directly to the intermetallic or intermediate material; mechanical impact devices which provide sufficient kinetic energy to activate the energetic material. As illustrated in Fig. 8, one possible configuration is an electrical source 730 and switch 736 activated by well pressure or tool motion to deliver initiating current to the heater material 710, resistive filament, e- match, or reactive foil embedded in the intermetallic material 710. As illustrated in Fig. 9, another configuration comprises a battery- powered capacitive discharge unit (CDU) 830 activated by setting load to generate high voltage or high current. The unit 830 has four primary components: a battery 832; a capacitor 834; a pressure / temperature (P / T) interlock 835, and a load-activated switch 836. The unit 830 may be accommodated in a backing ring 808, which also accommodates an additional unit to provide redundancy. The high voltage / current output from the unit 830 is directed to four elements 850 of an intermediate initiating material to provide multiple initiation points within the cylindrical heater 810, which is itself located within a cylindrical alloy element 806. Fig.10 illustrates an arrangement in which the intermetallic reaction is activated by operation of a well fluid pressure trigger 936. Fig.11 illustrates an arrangement in which the intermetallic reaction is activated by setting force closing a displacement switch 1036. Fig.12 illustrates an arrangement in which a piezoelectric electrical source 1130 provides the activation energy for the system. Pressure or an impact on a piezoelectric crystal 1130 generates an initiating current to a filament or “first fire” component 1150. In an alternative arrangement, a pin,   which may have a tungsten tip, may impact on a reactive multi-layer foil mounted on an anvil to activate a reaction in the first fire component. The various intermetallic heaters as described above may be produced by blending specific powder formulations and compacting into desired shapes. As noted from the illustrated examples, the heater geometry may take any appropriate form and may be rectangular, cylindrical (hollow or solid), conical, or of any other desired shape to achieve its function. The configuration of the heater in the downhole tool is dependent on various parameters: the application requirements such as the energy needed to heat the surroundings or melt fusible materials, the thermal conditions of the well, the mechanical design of the tool (masses and shapes of metal upon which the heater is mounted), and considerations to effectively integrate the heater into the tool function. The heater consists of metals known to react together and release substantial amounts of thermal energy. Intermetallic systems such as Ni+Al release up to 1380 Joules per gram of reactant, reaching adiabatic reaction temperatures of 1700C. This system produces a specific intermetallic product knows as nickel aluminide, a high strength material used in superalloys. The intermetallic reaction does not require an oxidizer, such as oxygen or fluorine, so can react to completion submerged in fluid or enclosed in a hermetic housing. Other intermetallic combinations include nickel and aluminium in molar ratios of 1:1 (Ni+Al) or 1:3 (Ni+3Al), titanium and boron (Ti+B or Ti+2B), titanium and carbon (Ti+C), zirconium and boron (Zr+2B), zirconium and carbon (Zr+C), or other metal combinations known to produce intermetallic exothermic reactions. The specific intermetallic system selected for a given application depends on exothermic energy and propagation rate requirements as well as practical considerations such as strength, cost, energetic sensitivity, and ease of manufacture. The ingredient formula may be amended to enhance heats of reaction, alter the thermal conductivity or the melting point of an   intermediate reaction phase, modify the reaction kinetic parameters, and enhance the final product mechanical properties. Examples of this are to add carbon or boron to the Ni-Al reactants to improve ignition or propagation characteristics or adding aluminum to Ti+B reactions to modify the heat of reaction. Other fusible metals may be added to modify the product ductility, melt and fill the reactant pores (to reduce permeability to fluid flow), or enable bonding of the element to adjacent metal surfaces. In the latter case, appropriate flux material may be added to the powder ingredients to enhance bonding to adjacent metal surfaces. The ingredient metals and additives are generally initially provided in fine powder form. Particle sizes may be in a range of 0.5 to 100 micrometer diameter, typically 3 to 30 micrometer, but for special applications and to achieve higher reaction rates may be much smaller, for example in the 10- 500 nanometer size range. The particles may be spherical, ellipsoidal, or flake, in purity of at least 99.5%. Binders such as gum arabic may be added in small percentages (0.1 to 5% by mass) to adhere the particles together during compaction. Powder lubricants, such as zinc stearate, graphite, or synthetic wax (0.5 to 5.0% by mass), may be blended with the reactants to assist the die filling and powder compaction process. The ingredients may be blended in powder form and then compacted into final shape using powder metallurgy compaction processes. To achieve maximum density and strength, the pressing may be accomplished using hydraulically or mechanically driven presses using precision dies and punches to yield parts in final net shape. Typical compaction stresses are in the range of 80,000 to 120,000 psi, although lower stresses may be used where less strength or greater final porosity is desired. Compacted forms may be subjected to a sintering process, to strengthen the compact by thermally bonding the particles together. The compact may also be coated, using polymers or thermally deposited metals, to improve handling   characteristics and prevent ingress of fluids into the material matrix. An example of a produced heater is a hollow cylinder with outside diameter of 5.75” and an inside diameter of 5.5”, with a total length of 8”. This cylinder may be formed in one compaction process, or be of multiple stacked short cylinders, such as a quantity of four cylinders 2” tall to achieve the same overall length. The cylinders are produced and mated together to allow propagation from one section to the adjacent section with no loss of energy or propagation rate. When reacted, they are geometrically stable, yielding a very strong product form nearly identical in mass and dimension to the unreacted heater.

[0002] REFERENCE NUMERALS apparatus 100 downhole tubing 102 mandrel 104 alloy element 106 backup ring 108 intermetallic heater 110 metal fillers 112, 114 setting piston 116 wellbore fluid 118 apparatus 200 tubing 202 mandrel 204 alloy element 206 intermetallic heater 210 alloy element 230 apparatus 300 tubing 302 mandrel 304 alloy element 306 heater 310 setting piston 316 alloy element 330 apparatus 400 downhole tubing 402 mandrel 404 backup ring 408 heater element 410 piston 416 apparatus 500 tubing 502 metal cylinder 504 alloy 506 backup ring 508 heating element 510 intermetallic heater 610 energy source 630 intermetallic material 710 energy source 730 switch 736 intermediate material 750 alloy element 806 backing ring 808 heater 810 capacitive discharge unit (CDU) 830 battery 832 capacitor 834 P / T interlock 835 load-activated switch 836 elements 850 well fluid pressure trigger 936 displacement switch 1036 piezoelectric electrical source 1130 component 1150

Claims

CLAIMS:

1. A downhole heater comprising a volume of intermetallic comprising at least two powdered metallic elements and means for initiating a reaction between the metallic elements.

2. The heater of claim 1, wherein the means for initiating the reaction comprises an initiator for providing sufficient energy to overcome an activation energy threshold and initiate the reaction between the metallic elements.

3. The heater of claim 2, wherein the initiator comprises a first initiator and a second initiator, the first initiator comprising first exothermic reaction components and the second initiator comprising second exothermic reaction components, whereby activation of the first initiator initiates a reaction of the first exothermic reaction components to generate a first energy output which is applied to the second initiator to initiate a reaction of the second exothermic reaction components to generate a second energy output for initiating an intermetallic reaction in the volume of intermetallic.

4. The heater of claim 2 or 3, wherein the initiator comprises one or more of means for generating an energy output selected from: a high energy spark; a thermal pulse, and a mechanical impact.

5. The heater of claim 2, 3 or 4, wherein the initiator comprises a reactive foil.

6. The heater of any preceding claim, wherein ingredients of the intermetallic are selected or treated to form a solid product shape following  activation: identical to the unreacted shape, or to allow plastic deformation to alter the product shape during the reaction.

7. The heater of any preceding claim, wherein the intermetallic comprises one or more of: titanium / boron; titanium / carbon; zinc / carbon; zirconium / carbon; zirconium / boron; vanadium / silicon; and nickel / aluminium.

8. The heater of any preceding claim, wherein additives are mixed with the metallic elements to modify reaction properties or a reaction product.

9. The heater of claim 8, wherein the additives comprise at least one of: inert materials with high melt temperatures dilute the reaction, slow the reaction rate, and reduce the peak temperature; alloying metals to alter the final strength or ductility of the product; lower melt temperature alloying metals which remain fluid after the intermetallic products have solidified and fill pores in the reaction product to reduce the permeability of the product; and chemicals which act as fluxing agents.

10. The heater of any preceding claim, wherein the intermetallic volume is provided in a form comprising at least one of: a rod; a solid cylinder, and a cylinder.

11. The heater of any preceding claim, comprising a sealed enclosure for the volume of intermetallic.

12. The heater of any preceding claim, wherein the heater is provided in combination with a volume of fusible material, whereby activation of the  heater causes the fusible material to soften and flow, and on cooling the fusible material hardens to create a seal or plug.

13. The heater of claim 12, wherein the intermetallic volume is provided internally of the volume of fusible material.

14. The heater of claim 12 or 13, wherein the fusible material is provided as at least one of: a solid or cast form; a compacted fusible powder with bonding additives, and a flowable volume of beads.

15. The heater of claim 12, 13 or 14, wherein the fusible material comprises a powder compacted low melt-point alloy and a flux material.

16. A downhole heating method comprising: providing a volume of intermetallic comprising at least two powdered metallic elements; running the volume of intermetallic into a bore, and activating the intermetallic to generate heat.

17. The method of claim 16, further comprising utilising the heat generated to melt and mobilize materials in a tubing bore or annulus.

18. The method of claim 16 or 17, further comprising utilising the heat generated to heat a rock formation surrounding the volume of intermetallic.

19. The method of claim 16, 17 or 18, further comprising activating the intermetallic by providing energy from at least one of: a high energy spark, a thermal pulse, and a mechanical impact.

20. The method of any of claims 16 – 19, further comprising blending and then pressing ingredients of the intermetallic into a final form to form a compact.

21. The method of claim 20, further comprising sintering the compact under elevated temperature.

22. The method of any of claims 16 – 21, comprising initially providing the two powdered metallic elements as a loosely packed mix describing a smaller diameter configuration and then, once the mix has been located in the bore, axially compressing the mix and radially expanding the mix into contact with a surrounding tubing.

23. The method of any of claims 16 – 22, further comprising sealing the volume of intermetallic within an enclosure.

24. The method of any of claims 16 – 23, further comprising providing the volume of intermetallic in combination with a volume of fusible material, activating the intermetallic to cause the fusible material to soften and flow, and allowing the fusible material to harden to create a seal or plug.

25. The method of claim 24, further comprising providing the fusible material in an initial configuration to facilitate the location of the apparatus downhole and then reconfiguring the fusible material to a setting configuration in which the fusible material contacts one or both of a surrounding bore wall and an inner surface.

26. A downhole heater comprising: a volume of intermetallic; a first initiator comprising first exothermic reaction components, and  a second initiator comprising second exothermic reaction components, whereby activation of the first initiator initiates a reaction of the first exothermic reaction components to generate a first energy output which is applied to the second initiator to initiate a reaction of the second exothermic reaction components to generate a second energy output for initiating an intermetallic reaction in the volume of intermetallic.

27. The heater of claim 26, wherein the first initiator comprises a vapor deposited film of intermetallic nanoparticles.

28. The heater of claim 26 or claim 27, wherein the second initiator is embedded in the volume of intermetallic.

29. A method of activating an intermetallic heater comprising a volume of intermetallic, the method comprising: applying a first energy input to a first initiator and activating a first exothermic reaction to generate a first energy output; applying the first energy output to a second initiator and activating a second exothermic reaction to generate a second energy output greater than the first energy output, and applying the second energy output to a volume of intermetallic and initiating an intermetallic reaction.

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