Patent Publication Number: US-6220346-B1

Title: Thermal insulation vessel

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This application relates generally to downhole tools, and more particularly to a thermal insulation vessel that may be used in conjunction with downhole tools for thermally isolating various components. 
     2. Description of the Related Art 
     Oil and gas wells subject downhole tools to extreme environmental conditions. Ambient pressures can be several orders of magnitude greater than atmospheric pressure. Temperatures can exceed 200° C., and loads and vibrations associated with fluid flow, string weight and impacts with formations and casing can be immense. The design of tools to operate in the downhole environment involves careful consideration of these pressure, temperature and load factors. 
     Throughout much of the history of the oil and gas well industry, heat transfer considerations played a subordinate role to other design considerations, such as tool static and fatigue strength, seal integrity, and corrosion resistance, to name just a few. With the advent of tools incorporating various electrical components, such as logging tools, measurement while drilling (“MWD”) and logging while drilling (“LWD”) tools, heat transfer considerations became more important and designers began to turn their attention toward providing thermal insulation for certain types of thermally sensitive electrical and electronic components housed within a tool. There are currently many examples of components used in downhole tools that may benefit from thermal protection. Examples of these include, integrated circuits, sensor packages, battery packs, and electric motors to name just a few. 
     One type of downhole tool employed in oil and gas wells is an initiating device or initiator. An initiator is commonly used to provide a short burst of high pressure gas or a gaseous mixture that is used to actuate some type of mechanical mechanism in another downhole tool, such as a packer, an intervention tool, or other such tool. Many conventional initiators consist of a tubular housing that encases a firing head which includes a propellant charge for delivering the high pressure gaseous mixture, and an onboard power and control system. The initiator is brought into engagement with the packer or intervention tool either at the surface or downhole, and fired with the aid of a timer set to trigger at a preselected time after downhole insertion or by command sent from the surface. After the initiator fires, it is normally withdrawn from the bore hole. As with many types of modern tools, initiators can incorporate components that may benefit from thermal isolation, such as battery packs and integrated circuits. 
     Heat transfer between structures within a downhole tool involves a complex combination of conductive, convective and radiative heat transfer. Although, conduction is often the primary heat transfer mechanism, forced convection may be significant where there is through-tool and external fluid flow. Natural convection can come into play where fluids such as air and hydraulic fluids are housed within the tool. Several methods have been employed in the industry to control heat transfer in downhole tools. 
     Some conventional downhole tools rely upon the forced convective heat transfer associated with mud or other working fluid flow through the tool to carry away heat. Others incorporate heat sinks into the internal structure of the tool. Still others attempt to shield or otherwise isolate a thermally sensitive component from ambient sources of heat. Some of these conventional thermal isolation designs involve the encasement of the thermally sensitive component within a shell or housing that is provided with a thermally insulating blanket or jacket that shrouds the housing. Another common conventional thermal isolation design involves the encasement of the thermally sensitive component within a tubular flask that is, in turn, encased within another housing and supported therein by a plurality of support pegs that are in physical contact with the outer housing and the inner flask. Various materials have been used to fabricate the support pegs, such as carbon and alloy steels, aluminum, and- synthetic materials, such as plastics, and various ceramic materials. 
     There are several disadvantages associated with conventional thermal isolation designs. Reliance on forced convection via a working fluid introduces unpredictability, as actual flow rates, densities and temperatures observed downhole may deviate from anticipated norms. Those designs which incorporate an insulation flask supported by pluralities of support pegs reduce somewhat the potential for conductive heat transfer between the component in the flask and external structures. However, the pegs themselves still present multiple conductive heat transfer pathways. This is particularly so where the support pegs are fabricated from materials with relatively high thermal high conductivities, such as metallic materials. The incorporation of support pegs fabricated from non-metallic materials with lower thermal conductivities reduces the potential for damaging heat transfer for a given flask. However, even with non-metallic support pegs, there remains a plurality of physical conductive heat transfer pathways. Where the temperature difference between the interior and the exterior of the flask, i.e., ΔT is large enough, significant heat transfer may still occur across the support pegs. 
     The present invention is directed to overcoming or reducing the effects of the one more of the foregoing disadvantages. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the present invention, a thermal insulation vessel is provided that includes a first housing that has a first internal cavity and an inner wall. A first magnet is coupled to the first housing. A second housing is positioned in the first internal cavity and has a second internal cavity and an outer wall. A second magnet is coupled to the second housing. The second magnet interacts with the first magnet to maintain a gap between the inner wall and the outer wall. 
     In accordance with another aspect of the present invention, a downhole tool assembly is provided that includes a downhole tool and a thermal insulation vessel coupled to the downhole tool. The thermal insulation includes a first housing that has a first internal cavity and an inner wall. A first magnet is coupled to the first housing. A second housing is positioned in the first internal cavity and has a second internal cavity and an outer wall. A second magnet is coupled to the second housing and interacts with the first magnet to maintain a gap between the inner wall and the outer wall. 
     In accordance with another aspect of the present invention, a thermal insulation vessel is provided that includes a first housing that has a first internal cavity and an inner wall. A first plurality of magnets is coupled to the first housing and positioned proximate the inner wall in circumferentially spaced-apart relation. A second housing is positioned in the first internal cavity and has a second internal cavity and an outer wall. A second plurality of magnets is coupled to the second housing and positioned proximate the outer wall in circumferentially spaced-apart relation. The second plurality of magnets interacts with the first plurality of magnets to maintain a gap between the inner wall and the outer wall. 
     In accordance with another aspect of the present invention, a method of thermally insulating a first component from a second component that is positioned in the first component is provided. The method includes magnetically levitating the second component within the first component to eliminate physical contact between the first and second components. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings in which: 
     FIG. 1 is a side view of an exemplary embodiment of a thermal insulation vessel in accordance with the present invention; 
     FIGS. 2A-2F are sectional views of the thermal insulation vessel shown in FIG. 1 in accordance with the present invention; 
     FIG. 3 is a sectional view of FIG. 2B taken at section  3 — 3  in accordance with the present invention; 
     FIG. 4 is a sectional view of FIG. 2C taken at section  4 — 4  in accordance with the present invention; 
     FIG. 5 is a partially exploded pictorial view of the thermal insulation vessel in accordance with the present invention; 
     FIG. 6 is a magnified view of a particular portion depicted in FIG. 4 in accordance with the present invention; 
     FIG. 7 is a pictorial view like FIG. 5 showing other types of components enclosed within the thermal insulation vessel in accordance the present invention; 
     FIG. 8 is a sectional view like FIG. 4 depicting an alternate exemplary embodiment of the thermal insulation vessel in accordance with the present invention; 
     FIG. 9 is a sectional view like FIG. 4 depicting an alternate exemplary embodiment of the thermal insulation vessel in accordance with the present invention; 
     FIG. 10 is a magnified sectional view like FIG. 6 depicting another alternate exemplary embodiment in accordance with the present invention; 
     FIG. 11 is a pictorial view like FIG. 5 showing another alternate exemplary embodiment of the thermal insulation vessel in accordance with the present invention; 
     FIG. 12 is a pictorial view like FIG. 5 showing another alternate exemplary embodiment of the thermal insulation vessel in accordance with the present invention; 
     FIG. 13 is a pictorial view like FIG. 5 showing another alternate exemplary embodiment of the thermal insulation vessel in accordance with the present invention; 
     FIG. 14 is a sectional view like FIG. 2C depicting another exemplary embodiment of the thermal insulation vessel in accordance with the present invention; 
     FIG. 15 is a sectional view like FIG. 2C depicting another exemplary embodiment of the thermal insulation vessel in accordance with the present invention; and 
     FIG. 16 is an exploded pictorial view of an alternate exemplary embodiment of the thermal insulation vessel in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS 
     In the drawings described below, reference numerals are generally repeated where identical elements appear in more than one figure. Turning now to the drawings, and in particular to FIG. 1, there is shown a schematic side view of an exemplary embodiment of a thermal insulation vessel  10  that is coupled to a downhole tool  12 . The downhole tool  12  consists of upper and lower segments or subs  14  and  16  connected to the thermal insulation vessel  10  and a firing head  18  connected to the lower segment  16 . The downhole tool  12  is provided with an upper connector  20  that is adapted to couple to a tubular member  22 , which may be a conducting or non-conducting wireline, another downhole tool, a section of drill pipe, coiling tubing or the like. As described more fully below, the thermal insulation vessel  10  is designed to provide thermal isolation between a component or components stored therein and the environment external to the thermal insulation vessel  10 . Although the downhole tool  12  may be virtually any type of downhole tool, in the embodiment illustrated in FIG. I and in various of the figures to be described below, the downhole tool  12  is an initiator designed to provide initiation of a propellant or chemical charge, or a mechanical mechanism to actuate various types of downhole tools, such as, for example, setting tools, intervention tools, packers or the like. 
     The detailed structures of the thermal insulation vessel  10  and the initiator  12  may be understood by referring now to FIGS. 2A-2F,  3  and  4 . The thermal insulation vessel  10  and the initiator  12  are of such length that they are shown in six longitudinally broken cross-sectional views, visa vis, FIGS. 2A-2F. Referring initially to FIG. 2A, the initiator  12  is provided with a tubular housing  24  that consists of a number of tubular sections interconnected together. The upper section  26  of the housing  24  is adapted for connection to the tubular member  22  shown in FIG.  1 . This connection may be by threaded connection as indicated by the threads  28 , or by a variety of other well known joining methods. A fishing neck  30  is provided beneath the threaded connection  28  to enable the initiator  12  to be readily fished from the downhole environment in the event the tubular member  22  depicted in FIG. 1 fails or has insufficient strength to withdraw the initiator  12  from the downhole environment. The lower end  32  of the upper section  26  is provided with a reduced diameter that defines a downwardly facing annular shoulder  34 . This downwardly facing annular shoulder  34  may be substantially horizontal or angled as shown in FIG.  2 A. The downwardly facing annular shoulder  34  abuts against an upwardly facing annular shoulder  36  formed on an intermediate section  38  of the housing  24 . The outer diameter of the lower end  32  of the upper section  26  is threadedly engaged with the inner diameter of the intermediate section  38  at  40  and sealed by O-ring  41 . The outer surfaces of the upper section  26  and the intermediate section  38  are provided with respective wrench slots  42  and  44  to enable the sections  26  and  38  to be readily threaded together at  40 . 
     An internal bore  46  is provided inside the upper section  26 . The bore  46  is vented to the exterior of the initiator  12  by a passage  48 . The upper end  50  of a piston  52  is slidably positioned within the bore  46 , and sealed against fluid passage by O-rings  54 . The lower end  56  of the piston  52  is provided with a flange  57  that defines an upwardly facing annular shoulder  58  that abuts against a downwardly facing annular surface  60  of the lower end  32  of the upper section  26 . The piston  52  is normally biased against the annular surface  60  by a spring  62  that shoulders against the flange  57  at its upper end and against an upwardly facing annular surface  63  of the intermediate section  38 . 
     The lower end  56  of the piston  52  is fitted with a magnet assembly  64 . The detailed structure of the magnet assembly  64  may be understood by referring now to FIG.  2 B and to FIG. 3, which is a sectional view of FIG. 2B taken at section  3 — 3 . The magnet assembly  64  includes a magnet holder  66  that is threadedly engaged in a bore  68  formed in the lower end  56  of the piston  52 . The magnet carrier  66  includes bores  70  in which respective magnets  72  are positioned. The number, size and spacing of the magnets  72  are largely matters of design discretion. In the illustrated embodiment, the magnet carrier  66  is provided with four circumferentially spaced permanent magnets  72 . 
     The magnet assembly  64  is designed to activate a magnetic switch assembly  74  that consists of a plurality of magnetic switches  76  mounted to a mounting board  78 . The magnetic switches  76  are connected in parallel to two or more conductors  80  which transmit electrical power throughout the initiator  12 . The combination of the spring-biased piston  52 , the magnet assembly  64  and the magnetic switch assembly  74  provides a pressure activated on/off switch for electrical power transmission inside the initiator  12 . In operation, the spring  62  biases the piston  52  against the lower annular surface  60  as shown in FIGS. 2A and 2B. This position provides a significant gap between the magnet assembly  64  and the magnetic switch assembly  74  such that the magnetic switches  76  are open and the circuit for the conductor  80  is open as well. With the piston  52  in this position, the initiator  12  is not energized and may be safely handled by operators at the surface. However, when the initiator  12  is placed in a downhole environment, ambient pressure venting through the port  48  will act upon the upper end  50  of the piston  52 . When the force of the pressure acting on the upper end  50  of the piston  52  exceeds the spring force of the spring  62 , the piston  52  will move axially downward and bring the magnet assembly  64  into proximity with the magnetic switch assembly  74 . When the magnet assembly  64  is brought into close proximity with the magnetic switch assembly  74 , one or more of the magnetic switches  76  will close, enabling electrical power to pass through the conductors  80  and  81 . A plurality of magnetic switches  76  may be provided to ensure that at least one of the switches  76  will close when the magnet assembly  64  is moved downward. Redundancy in the number of magnetic switches  76  is desirable to ensure that at least one of the switches  76  will close regardless of the particular angular orientation of the magnet carrier  66 . 
     Referring again specifically to FIG. 2B, the lower end of the intermediate section  38  is threadedly engaged to an intermediate section  82  at  83 . The joint between the intermediate section  38  and the intermediate section  82  is sealed against fluid passage by a pair of O-rings  84 . The axial spacing between the intermediate section  38  and the intermediate section  82  may be adjusted by the incorporation of an annular spacer  85  positioned between the upper end of the intermediate section  82  and a downwardly facing annular shoulder  86  of the intermediate section  38 . 
     The magnetic switch assembly  74  is housed within a chamber  88  in a chassis  90  positioned inside the intermediate section  82 . The chassis  90  consists of a cup  92  secured to a cylindrical chassis  94  by two or more bolts  96 . The chassis  94  has a centrally disposed bore  98  through which the conductors  80  and  81  pass. 
     The detailed structure of the thermal insulation vessel  10  may be understood by referring now to FIG. 2C, to FIG. 4, which is a sectional view of FIG. 2C taken at section  4 — 4 , and to FIG. 5, which is a partially exploded pictorial view. The thermal insulation vessel  10  includes an external housing  100  that has an internal cavity  102  and an inner wall  104 . The external housing  100  is threadedly engaged at its upper end to the lower end of the chassis  94  at  106  and at its lower end to another chassis  108  at  110 . The external housing  100  is provided with a plurality of magnets  112  that are dispersed in circumferentially spaced-apart relation. The magnets  112  are positioned in respective longitudinal slots  114 . Another housing  116  is positioned inside the internal cavity  102 . The housing  116  has an internal cavity  118  for holding a component for which thermal isolation is desired. In the illustrated embodiment, thermal isolation is desired for a plurality of batteries  120  which are designed to provide electrical power to the initiator  12 . The batteries  120  are positioned in a tubular insulating sleeve  121 , which may be composed of a material that provides magnetic shielding of the batteries  120 . The housing  116  includes an external wall  122  and may be provided with one or more longitudinal slots  123  to accommodate conductors, such as the conductor  81 . A plurality of magnets  124  are positioned in respective longitudinal slots  126  in the housing  116 . The plurality of magnets  124  coupled to the housing  116  interact with the plurality of magnets  112  coupled to the housing  100  to maintain a gap  128  between the inner wall  102  of the housing  100  and the outer wall  122  of the housing  116 . This magnetic levitation of the housing  116  within the housing  100  eliminates the several points of contact normally found in conventional vacuum flasks which represent pathways for conductive heat transfer. 
     The detailed interaction of the plurality of magnets  112  with the plurality of magnets  124  may be understood by referring now also to FIG. 6, which is a magnified view of the portion of FIG. 4 circumscribed generally by the dashed oval  130 . The magnets  112  and  124  are positioned such that their like poles, i.e., north or south, face towards each other. In the illustrated embodiment, the magnets  112  and the magnets  124  are positioned such that their respective south poles face each other, and thereby repel to maintain the gap  128  between the inner wall  104  of the housing  100  and the outer wall  122  of the housing  116 . The magnets  112  and  124  are positioned in close enough proximity so that the interactions of the north poles of the magnets  112  and the south poles of the magnets  124  provides an attractive force that aids in maintaining the gap  128  and stabilizes the rotational position of the housing  116  relative to the housing  100 . When the housing  116  is inserted into the housing  110  during assembly, the housing  116  will rotate relative to the housing  100  until a position of magnetic force equilibrium is reached, as illustrated in FIG.  6 . The housing  116  is then effectively locked into position. 
     Still referring to FIG. 4, radiative heat transfer to the housing  116  may be inhibited by providing the outer wall  122  of the housing  116  with a reflective surface. This may be accomplished by polishing the outer wall  122  where the housing  116  is fabricated from a material that may be polished or electro polished to produce a high sheen. Alternatively, the outer wall  122  may be coated with a highly reflective material, such as chrome, gold, nickel or the like to achieve the desired reflective properties. 
     Referring again to FIG. 2C, the housing  116  may be provided with upper and lower end caps  130  and  132  which are respectively threadedly engaged with the housing  116  at  134  and  136 . The end cap  130  is provided at its upper end with one or more magnets  138  that interact with a corresponding plurality of magnets  140  coupled to the lower end of the chassis  94 . The lower end of the end cap  132  is similarly provided with one or more magnets  142  that interact with a corresponding set of magnets  144  coupled to the upper end of the chassis  108 . The interactions between the sets of magnets  138  and  140  and  142  and  144  maintain gaps  146  and  148  between the end cap  130  and the chassis  94  and the end cap  132  and the chassis  108 . In this way, the housing  116  and its contents may be physically isolated from surrounding structure with the exception of the conductor wires  80  and  81  and a corresponding set of conductor wires  152  and  154  emanating from the lower end of the end cap  132 . In this way, the multiple potential heat transfer pathways associated with conventional thermal protection flasks have been eliminated. 
     Respective annular spacers  156  and  158  are positioned between the end cap  130  and the inner sleeve  121  and the end cap  132  and the lower end of the inner sleeve  121 . The spacer  156  is provided with a radial passage  160  that extends radially outwardly to one or more of the conductor passages  123  (see FIG.  4 ). The spacer  158  similarly is provided with a radial passage  162  which leads to one or more of the conductor passages  123  (see FIG.  4 ). The thermal insulation vessel  10  is protected from axial shock loads by the incorporation of an elastomeric ring  164  positioned between the lower end of the end cap  130  and the upper surface of the spacer  156 . A substantially identical elastomeric annular member  166  is positioned between the lower surface of the spacer  158  and the upper end of the end cap  132 . 
     The housing  100 , the housing  116 , the end caps  130  and  132 , the chassis  94  and  108  and the spacers  156  and  158  are advantageously composed of non-magnetic materials. Exemplary materials for the housing  100 , the housing  116 , the end caps  130  and  132 , the chassis  94  and  108  include, for example, Inconel  718 , aluminum, aluminum-bronze, beryllium-copper alloys, titanium alloys or the like. Exemplary materials for the spacers  156  and  158  include, for example, fiberglass epoxy or thermo-plastics or the like. 
     Referring now to FIG. 2D, the lower end of the chassis  108  is threadedly engaged to the upper end of a chassis  168  at  170 . An electric buzzer  172  is coupled to the chassis  168  by two or more bolts  174 . As described more fully below, the buzzer  172  is designed to provide audible signals regarding the operation of the initiator  12  that can be readily sensed at the surface. Circuitry for controlling the flow of electrical power to the firing head  18  (see FIG. 1) is mounted on a circuit board  176  that is coupled to the chassis  168  by mounting pegs  178 . The circuit board  176  is protected from shock loads by a pair of elastomeric annular members  180  respectively mounted on the mounting pegs  178 . The conductors  152  and  154  pass through a centrally disposed bore  182  in the upper end of the chassis  168  and tied to the circuit board  176 . 
     Power to activate the firing head  18  (see FIG. 1) is supplied by a plurality of capacitors  184  mounted on the chassis  168 , and connected to the circuit board  176  and to the firing head  18  (see FIG. 1) by conductors  186  and  188 . The capacitors  184  are continuously charged by the batteries  120 . Note that the number of conductors  80 ,  81 ,  152 ,  154  and any others connecting the batteries  120 , the firing head  18  (see FIG. 1) and the circuit board  176  is a largely a matter of design discretion. 
     The structure of the lower end of the lower segment  16  of the initiator  12  and the firing head  18  may be understood by referring now to FIGS. 2E and 2F. Referring initially to FIG. 2E, the lower end  190  of the chassis  168  is threadedly engaged with the upper end  192  of a chassis  194  at  196 . The upper end  192  of the chassis  194  is also threadedly engaged with the intermediate housing section  82  at  198 . The intermediate housing section  82  is provided with an external wrench slot  200  to facilitate the relative turning required to threadedly engage the chassis  194  to the section  82  at  198 . To ensure that proper spacing is provided between the lower end  190  of the chassis  168  and the upper end  192  of the chassis  194 , a jam nut  202  is threadedly engaged to the upper end  192  of the chassis  194  between the lower end  190  of the chassis  168  and the upper end  192  of the chassis  194 . The chassis  194  is provided with a centrally disposed bore  204  that extends longitudinally to the lower end  206  of the chassis  194 . A conductor  208  is disposed in the bore  204  and is connected at its upper end to a connector  210  and at its lower end to another connector  211 . The upper end of the connector  210  is connected to the conductor  186 . The other conductor  188  passes downward through a longitudinal conduit  212  formed in the upper end  192  of the chassis  194 . The conduit  212  terminates at its lower end in an annular chamber  214 . One or more strain gauges  215  are mounted to the chassis  194  within the annular chamber  214 . The strain gauges  215  are designed to sense the selective application of axial loads applied to the initiator  12  from the surface that are used to selectively activate the initiator  12  as described more fully below. The chassis  194  is also provided with a longitudinal conduit  216  that extends from the upper end  192  and terminates in an external vent  218 . The conduit  216  enables the lower section  16  of the initiator  12  to be evacuated if desired. The vent  218  is closed off by a threaded plug  220 . 
     Desired spacing between the lower annular surface  222  of the intermediate section  82  and an upwardly facing annular shoulder  224  of the chassis  194  is maintained by an annular spacer  226  positioned therebetween. Fluid leakage between the intermediate section  82  and the chassis  194  near the lower annular surface  222  is prevented by a pair of O-rings  228 . The exterior of the lower end  206  of the chassis  194  is provided with a wrench slot  230  to facilitate the threaded makeup of the chassis  194  with the intermediate section  82 . 
     The lower end  206  of the chassis  194  is provided with a reduced diameter section that defines a downwardly facing annular surface  232  against which an upwardly facing annular surface  234  of the firing head housing  236  may abut. The firing head housing  236  is threadedly engaged to the lower end  206  of the chassis  194  at  238 . The housing  236  encloses an igniter  240  which is electrically coupled to the connector  211  by a male connector  242 . The connector  211  is positioned within the lower end  206  by a tubular sleeve  244  that is held in position by a spin collar  246 . The joint between the housing  236  and the lower end  206  is sealed against fluid intrusion by a pair of O-rings  248 . The igniter  240  may be any of a variety of commercially available igniter. In an exemplary embodiment, the igniter is a Titan model 6000-000-150 supplied by Titan Specialties, Inc. 
     The operation of the initiator  12  may be understood by referring now to FIGS.  1  and  2 A- 2 F. After the initiator  12  is inserted into a downhole environment, ambient pressure propels the piston  52  shown in FIGS. 2A and 2B downward, activating the magnetic switch assembly  74 . With the magnetic switch assembly  74  turned on, the initiator  12  is operable and ready to receive commands from the surface in the form of axial load pulses delivered through the support member  22 . When the initiator  12  is positioned at the desired location downhole, a preselected series of axial load pulses are transmitted through the support member  22  and into the initiator  12 . These pulses are sensed by the strain gauges  215  depicted in FIG.  2 E. The outputs of the strain gauges  215  are fed to the sensing circuitry on the circuit board  176  shown in FIG.  2 D. In response, the circuit board  176  initiates the firing sequence, which may consist of an instantaneous discharge of the electrical power stored in the capacitors  184  into the igniter  240  depicted in FIG. 2F or a time-delayed discharge of the capacitors  184 . The circuit board  176  also activates the buzzer  172  to transmit an acoustic signal uphole indicating the initiation of the firing sequence. When the igniter  240  is activated, a propellant charge stored therein is consumed, releasing a hot burst of gas which may be used to activate any of the aforementioned tools that may be used with the initiator  12 . While in the downhole environment, the component housed within the thermal insulation vessel  10 , in this case the plurality of batteries  120 , is thermally insulated from the elevated temperatures associated with the downhole environment by the thermal insulation vessel  10 . 
     In the foregoing illustrated embodiment, the component enclosed within the thermal insulation vessel  10  consists of the plurality of batteries  120  shown in FIG.  2 C. However, the skilled artisan will appreciate that the thermal insulation vessel  10  may be used to enclose and thermally isolate a large variety of different types of components. The concept is illustrated in FIG. 7, which is a partially exploded pictorial view like FIG. 5. A component  250 , schematically represented in phantom, is enclosed within the housing  116  of the thermal insulation vessel  10 . The component  250  may be any of a variety of components used in downhole tools that may benefit from thermal isolation. For example, the component  250  may be a heat generating apparatus, such as, for example, a hydraulic pump and motor assembly. In this circumstance, it may be desirable to restrict heat transfer from the component  250  to external structures that may be thermally sensitive, such as electronic circuitry. Conversely, where the component  250  may be sensitive to elevated temperatures associated with the downhole environment, the thermal insulation vessel  10  will limit the amount of heat that may be transferred to the component  250 . In this regard, the component  250  may be a hydraulic motor, one or more capacitors, a transformer, one or more batteries, an integrated circuit, or various combinations of these, to name just a few. 
     In the above described exemplary embodiment, the inner and outer housings  116  and  100  of the thermal insulation vessel  10  have a generally circular cross-section. The interacting pluralities of magnets  112  and  124  are provided with a generally arcuate cross-section that matches the profiles of the respective housings  100  and  116 . Furthermore, the respective pluralities of magnets  112  and  124  are positioned such that their respective-like magnetic poles face each other and thereby repel. However, as the skilled artisan will appreciate, a variety of alternative arrangements fall within the spirit and scope of the present invention. FIG. 8 is a sectional view like FIG. 4 of an alternate exemplary embodiment of the thermal insulation vessel, now designated  10 ′, in accordance with the present invention. In this embodiment, the internal housing, now designated  116 ′, may be provided with a plurality of external flats or facets  252  and the outer housing, now designated  100 ′, may be provided with a complimentary plurality of internally facing facets  254 . The incorporation of the pluralities of facets  250  and  252  into the housings  100 ′ and  116 ′ facilitate the incorporation of rectangularly cross-sectioned magnets, now designated  112 ′ and  124 ′. The enclosed component  250  is otherwise protected from heat transfer in the same general manner by the gap  128 . 
     Another alternate exemplary embodiment in accordance with the present invention may be understood by referring now to FIG. 9, which is a sectional view like FIG.  4 . Whereas, in the foregoing illustrated embodiments, respective pluralities of magnets are positioned such that their like poles face each other, the embodiment depicted in FIG. 9, illustrates that respective pluralities of magnets, now designated  112 ″ and  124 ″ may be positioned such that their respective opposite magnetic poles are facing each other. The attractive force between any two adjacently disposed magnets  112 ″ and  124 ″ is counteracted by the attractive force between a diametrically opposed pair of magnets  112 ″ and  124 ″. To aid in retaining the plurality of magnets  112 ″ coupled on the outer housing, now designated  100 ″, the slots  114 ″ in which the magnets  112 ″ are positioned and provided with a bullnosed cross-section. The magnets  112 ″ are formed with a cross-section that has a widened base that engages the bullnosed cross-sections of the slots  114 ″. The plurality of magnets  124 ″ may be provided with similarly widened-base cross-sections to facilitate their retention in bullnosed cross-section slots  126 ″ fashioned in the internal housing  116 ″. 
     The various magnets may be retained on the housings  100  and  116  by interference, adhesives or other well known fastening techniques. In an alternate exemplary embodiment shown in FIG. 10, which is a partial sectional view like FIG. 6, the magnets  112 ′″ are dropped into shouldered slots  255  formed in the housing  100 . The slots  255  may extend to the inner wall  104  of the housing  100 . The magnets  112 ′″ are shaped to seat in the slots  255  so that a portion of each magnet  112 ′″ is exposed to the housing  116 . A similar arrangement may be used to mount magnets on the housing  116  as well. 
     In another alternate exemplary embodiment in accordance with the present invention, the plurality of circumferentially spaced magnets  124  coupled to the housing  116  (see FIG. 5) may be replaced with a single annular magnet  124 . Referring now to FIG. 11, which is a pictorial view like FIG. 5, the housing  116  is fabricated as an annular permanent magnet  124 ″″ with a given magnetic pole, in this example magnetic north, facing radially outwardly. The housing  100  may be provided with the aforementioned plurality of circumferentially spaced-apart magnets  112 . The arrangement shown in FIG. 11 may be flip flopped, that is, the sleeve  100  may be configured as a single magnet  112  while the sleeve  116  may be fitted with the aforementioned plurality of circumferentially spaced magnets. 
     In another alternate exemplary embodiment in accordance with the present invention shown in FIG. 12, both the sleeve  116  and the sleeve  100  may be configured as single magnets wherein the sleeve  116  has a given magnetic pole, in this example, south, facing radially outwardly and the sleeve  100  has the same magnetic pole facing radially inwardly. 
     In the foregoing illustrated embodiments, the respective magnets or sets of magnets have the same type of magnetic pole, that is north or south, facing in a given direction along the entire length of the thermal insulation vessel  10 . However, the pluralities of magnets may be arranged such that some of the magnets have a north or south pole facing in a given direction along a given length of the thermal insulation vessel  10  while others project the opposite magnetic pole in that same direction at a different point along other sections of the thermal insulation vessel  10 . This concept is illustrated in FIG. 13, which is a partially exploded pictorial view like FIG.  5 . As shown in FIG. 10, some of the magnets  124  positioned on the inner housing  116  may have south magnetic poles facing outward while others may have north magnetic poles facing outward. Similarly, the set of magnets  112  coupled to the external housing  100  and facing inwardly, may have south poles facing inwardly along a certain length of the housing  100  and a north poles facing inwardly along the remainder of the outer housing  100 . This alternating arrangement of magnetic poles for the magnets  112  and  124  may facilitate the insertion of the inner housing  16  into the outer housing  100 . In this way, the inner housing  116  may be inserted into the outer housing  100  with a smaller magnitude of repulsive magnetic force that must be overcome while still maintaining a magnetically levitated inner housing  116  and the thermally isolating gap between the inner housing  116  and the outer housing  100 . 
     FIG. 14 illustrates a sectional view like FIG. 2C of an alternate exemplary embodiment in accordance with the present invention in which the inner housing  116  and the outer housing  100  may be evacuated to substantially reduce the potential for gaseous convective or conductive heat transfer. At the time the thermal insulation vessel  10  is fabricated, the internal cavity  102  of the housing  116  may be evacuated and the bore  256  of the end cap  132  may be sealed by inserting a plug therein or by potting with epoxy  258  or the like as shown. In addition, the housing  100  may be evacuated. In this regard, a sleeve  260  may be threadedly engaged to the chassis  108  at  262 . The sleeve  260  is provided with one or more electrical connectors  264 , which are depicted as pin-socket type connectors, but which may be a myriad of different types of electrical connectors. The conductor wires  152  and  154  emanating from the inner housing  116  may be coupled to the connectors  264 . The exterior of the sleeve  260  is provided with an O-ring seal  266  to seal against fluid passage between the inner wall  104  of the housing  100  and the exterior of the sleeve  260 . The sleeve  260  is provided with a vacuum fitting  268 , which may be a check valve or other type of fitting enabling a vacuum to be drawn. The sleeve  260  is threadedly engaged to the housing  100  at  270 . The lower end of the housing  100  is threadedly engaged to an annular member  271  which has the same general structural configuration as the lower end of the chassis  108  depicted in FIG.  2 D. Thus, the internal cavity  102  of the housing  116 , the housing  100  may be evacuated. In addition, the interior of the intermediate section  82  proximate the chassis  168  may be evacuated as described above using the port  218  as shown in FIGS. 2D and 2F. 
     Complete physical isolation between the inner housing  116 , the batteries  120  enclosed therein, and structures external thereto may be provided by inductively coupling the inner housing  116  to conductors external to the housing  116 . This alternate exemplary embodiment may be understood by referring now to FIG. 15, which is a sectional view like FIG.  14 . An inductive coupling  272  is positioned in the housing  100  and includes inductors  273  and  274  axially separated by a narrow gap  276 . The inductor  273  includes an inductor coil  280  wrapped around a core  282 . The core  282  is mounted to a mounting board  284  by pegs  286 . Adhesives or other fastening techniques may alternatively be used. The mounting board  284  is coupled to the end cap  132  of the housing  116  and includes DC to AC conversion circuitry. The inductor  274  similarly includes an inductor coil  288  wrapped around a core  290  that is mounted to a mounting board  292  by pegs  294 . The mounting board  292  is coupled to chassis  108  and includes AC to DC conversion circuitry. The conductors  152  and  154  are connected to the inductor  273 . Current is, in turn, transmitted to and from the inductor  274  by two or more conductors  296  and  298 . Cooperating sets of magnets  298  and  300  positioned, respectively, on the end cap  132  and the chassis  108  aid in maintaining the axial positioning of the housing  116 . A substantially identical inductive coupling  272  may be coupled positioned at the opposite end of the housing  116 . 
     Another alternate exemplary embodiment of the thermal insulation vessel  10  may be understood by referring now to FIG. 16, which is an exploded pictorial view of the housing  116 , the housing  100  and the chassis  94  and  108 . In this illustrative embodiment, a thermally conductive heat transfer member or shell  302  is positioned inside the housing  100  and the housing  116  is, in turn, positioned inside the member  302 . The member  302  is advantageously composed of a material that is both non-magnetic and exhibits a directionally dependent thermal conductivity. Thus, a gap of the type described above is maintained between the housing  116  and the member  302  by the aforementioned magnetic interactions. The member  302  is designed to have a much higher thermal conductivity along its longitudinal axis  304  than along a radial axis between its inner and outer walls. In this way, heat transferred to the member  302  from either the housing  100  or the housing  116  is quickly conducted away by the member  302  along the longitudinal axis  304 . A variety of materials may be used for the member  302 . In an exemplary embodiment, thermal pyrolytic graphite with a metallic shell or ceramic matrix may be used, such as, for example, TC 1050.ALY or TC 1050.MMC supplied by Advanced Ceramics Corporation. 
     The magnets depicted in any of the embodiments described herein may be composed of a wide variety of materials. Exemplary materials include samarium-cobalt, niodidium-iron-boron, or the like. Optionally, although not shown in the drawings, electromagnets may be used in lieu of or in conjunction with permanent magnets. 
     While the invention may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention as defined by the following appended claims.