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FIELD OF THE INVENTION 
       [0001]    This invention relates, in general, to equipment utilized in conjunction with operations performed in subterranean wells and, in particular, to remote actuated downhole pressure barriers for use in subterranean wells and methods for use of same. 
       BACKGROUND OF THE INVENTION 
       [0002]    Without limiting the scope of the present invention, its background is described with reference to using dissolvable members in plugging devices, as an example. 
         [0003]    It is well known in the completion and production arts to install and retrieve plugs in subterranean wells via intervention into the wells. For example, when it is desired to plug a well, a plugging device may be latched in an internal profile of a tubular string using a conveyance such as a slickline, a wireline, a coiled tubing or the like. When it is later desired to produce or otherwise access the well, the plugging device may be retrieved using the appropriate conveyance. 
         [0004]    It has been found, however, that in some well configurations, such as certain deviated or horizontal wells, the use of such conveyances may not be desirable or feasible for installation or retrieval of a plugging device. In such well configurations, the plugging device may be installed at the desired location within the tubular string at the surface then conveyed into the well as part of the tubular string in which it is installed. Once installed, such plugging devices have been remotely actuated using a variety of techniques such as dissolving all or part of the plugging device using a chemical solution, ultraviolet light, a nuclear source or an explosive. For example, certain plugging devices have utilized a dispersible plug member that is dissolvable or otherwise dispersible by contact with fluid, including chemical solutions or water. In such cases, the member may be initially isolated from contact with the fluid and then, when it is desired to permit flow through the plugging device, the fluid is placed in communication with the member, thereby dispersing the member. In one commonly used plugging device, the dispersible plug member has been constructed using a mixture of compacted salt and sand. These and other types of plugging devices have used activation mechanisms including timer-controlled mechanical, hydraulic and electrical devices as well as wireless communication systems. 
         [0005]    It has been found, however, that conventional dispersible plug members are not suitable for service over an extended time period and thus cannot operate as pressure barriers. Accordingly, a need has arisen for a plugging device that is suitable installation and deployment in a tubular string. A need has also arisen for such a plugging device that is operable to be remotely actuated. Further, a need has arisen for such a plugging device that has an extended service life and may therefore operate as a pressure barrier. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention disclosed herein is directed to remote actuated downhole pressure barriers for use in subterranean wells and methods for use of same. The downhole pressure barrier of the present invention is suitable for installation and deployment in a tubular string and is operable to be remotely actuated. In addition, the downhole pressure barrier of the present invention has an extended service life. 
         [0007]    In one aspect, the present invention is directed to a downhole pressure barrier that is operatively positionable in a subterranean well. The downhole pressure barrier includes a housing having a flow passage formed therethrough and a plug member positioned within the flow passage that selectively prevents flow through the flow passage and allows flow through the flow passage responsive to contact with an activating agent. At least one retainer assembly supports the plug member within the housing. The retainer assembly selectively prevents communication between the activating agent and the plug member. An activating assembly includes a combustible agent that is positioned between at least a portion of retainer assembly and the plug member. The activating assembly is operable to create a communication path through the retainer assembly upon combustion of the combustible agent to allow communication between the activating agent and the plug member. 
         [0008]    In one embodiment, the plug member may be a mixture of sand and salt. In another embodiment, the activating agent may be at least one of a wellbore fluid and water. In this embodiment, the housing may include a fluid chamber operable to contain the activating agent. In a further embodiment, the combustible agent may be a mixture of a metal powder and a metal oxide. 
         [0009]    In one embodiment, a seal element is positioned between the retainer assembly and the housing to prevent fluid flow therebetween. In another embodiment, the retainer assembly may include a discoidal portion that has a spaced apart relationship with the plug member. In this embodiment, the combustible agent may be positioned in the space between the plug member and the discoidal portion of the retainer assembly. Also in this embodiment, a separator member may be positioned between the combustible agent and the plug member. The discoidal portion of the retainer assembly and the separator member may be metallic. In a further embodiment, the activating assembly may include an ignition agent operably positioned proximate the combustible agent used to ignite the combustible agent. In addition, the activating assembly may include an electronic package operable to receive a wireless signal and to send a signal to the ignition agent. 
         [0010]    In another aspect, the present invention is directed to a downhole pressure barrier that is operatively positionable in a subterranean well. The downhole pressure barrier includes a housing having a flow passage formed therethrough. A plug member, formed from a mixture of sand and salt, is positioned within the flow passage to selectively prevent flow through the flow passage and allow flow through the flow passage responsive to contact with an activating agent. At least one retainer assembly supports the plug member within the housing. The retainer assembly selectively prevents communication between the activating agent and the plug member. An activating assembly includes a combustible agent that is integrally formed in the plug member. The activating assembly is operable to create a communication path through the retainer assembly upon combustion of the combustible agent to allow communication between the activating agent and the plug member. 
         [0011]    In a further aspect, the present invention is directed to a downhole pressure barrier that is operatively positionable in a subterranean well. The downhole pressure barrier includes a housing having a flow passage formed therethrough. A plug member, formed from a thermosetting polymer, is positioned within the flow passage to selectively prevent and allow flow through the flow passage. At least one retainer assembly supports the plug member within the housing. An activating assembly includes a combustible agent that is integrally formed in the plug member. The activating assembly is operable to create a communication path through the downhole pressure barrier upon combustion of the combustible agent. 
         [0012]    In a further aspect, the present invention is directed to a method for remotely actuating a downhole pressure barrier positioned in a subterranean well. The method includes receiving a wireless signal at a receiver positioned within the downhole pressure barrier, generating a activation signal responsive to the received wireless signal, activating an ignition agent responsive to the activation signal, igniting a combustible agent with the ignition agent, creating a communication path between an activating agent and a plug member of the downhole pressure barrier responsive to the combustion and contacting the plug member with the activating agent to disperse the plug member, thereby opening a communication path through the downhole pressure barrier. 
         [0013]    The method may also include one or more of sensing a series of pressure fluctuations via the receiver, activating a magnesium fuse, igniting a mixture of a metal powder and a metal oxide, contacting the plug member with at least one of a wellbore fluid and water, contacting a mixture of sand and salt with the activating agent and containing the activating fluid in a fluid chamber of the downhole pressure barrier. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    For a more complete understanding of the features and advantages of the present invention, reference is now made to the detailed description of the invention along with the accompanying figures in which corresponding numerals in the different figures refer to corresponding parts and in which: 
           [0015]      FIG. 1  is a schematic illustration of an offshore oil and gas platform operating a remote actuated downhole pressure barrier according to an embodiment of the present invention; 
           [0016]      FIGS. 2A-2B  are cross sectional views of consecutive axial sections of a remote actuated downhole pressure barrier according to an embodiment of the present invention; 
           [0017]      FIGS. 3A-3B  are cross sectional views of consecutive axial sections of a remote actuated downhole pressure barrier according to an embodiment of the present invention; 
           [0018]      FIGS. 4A-4B  are cross sectional views of consecutive axial sections of a remote actuated downhole pressure barrier according to an embodiment of the present invention; 
           [0019]      FIGS. 5A-5B  are cross sectional views of consecutive axial sections of a remote actuated downhole pressure barrier according to an embodiment of the present invention; and 
           [0020]      FIGS. 6A-6B  are cross sectional views of consecutive axial sections of a remote actuated downhole pressure barrier according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts, which can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention, and do not delimit the scope of the invention. 
         [0022]    Referring initially to  FIG. 1 , a remote actuated downhole pressure barrier being operated from an offshore oil and gas platform is schematically illustrated and generally designated  10 . A semi-submersible platform  12  is centered over an offshore oil and gas formation  14  located below sea floor  16 . A subsea conduit  18  extends from deck  20  of platform  12  to wellhead installation  22  including subsea blow-out preventers  24 . Platform  12  has a hoisting apparatus  26  and a derrick  28  for raising and lowering pipe strings such as work string  30 . 
         [0023]    A wellbore  32  extends through the various earth strata including formation  14 . A casing  34  is cemented within wellbore  32  by cement  36 . The portion of wellbore  32  extending through horizontal portion  38  includes a plurality of perforations  40  that allow fluid communication between formation  14  and wellbore  32 . Work string  30  includes various tools such as a plurality of sand control screens  42 , a remote actuated downhole pressure barrier  44  and a packer  46 . In operation, remote actuated downhole pressure barrier  44  provides a pressure barrier that allows the operator to set production and isolation packers as well as pressure test the production tubing. 
         [0024]    In the illustrated embodiment, even though remote actuated downhole pressure barrier  44  has been disposed in a horizontal portion of wellbore  32 , it should be understood by those skilled in the art that the remote actuated downhole pressure barriers of the present invention are equally well-suited for use in other well configurations including, but not limited to, inclined wells, wells with restrictions, non-deviated wells, multilateral wells and the like. As such, use of directional terms such as “above”, “below”, “upper”, “lower” and the like are used for convenience in referring to the illustrations. In addition, even though an offshore operation has been depicted in  FIG. 1 , the remote actuated downhole pressure barriers of the present invention are equally well-suited for use in onshore operations. 
         [0025]    Referring now to  FIGS. 2A-2B , therein is representatively illustrated a remote actuated downhole pressure barrier that is generally designated  100 . Barrier  100  includes a generally tubular housing assembly  102 . Housing assembly  102  that includes a top sub  104  that is securably and sealingly connected to a middle sub  106  by a plurality of set screws  108  and seal  110 . At its lower end, middle sub  106  is securably and sealingly connected to a bottom sub  112  at threaded connection  114  and by seal  116 . Disposed within middle sub  106  is an inner mandrel  118 . Seals  120 ,  121  provide a sealing relationship between middle sub  106  and inner mandrel  118 . Housing assembly  102  has a flow passage  122  formed axially therethrough. Even though housing assembly  102  is shown as being made up of several interconnected portions  104 ,  106 ,  112 ,  118 , it is to be understood that greater or fewer numbers of housing portions may be utilized in the housing assembly  102  and the portions may be otherwise configured and otherwise attached to each other without departing from the principles of the present invention. 
         [0026]    Fluid flow through passage  122  is initially blocked by a dispersible plug member  124 . Plug member  124  includes a dispersible portion  126  which is initially compacted within a plug sleeve  128 . Plug member  124  is supported within housing assembly  102  by a pair of oppositely disposed retainer assemblies  130 ,  132 . Retainer assembly  130  is sealingly coupled to inner mandrel  118  by a seal  134 . Retainer assembly  132  is sealingly coupled to bottom sub  112  by a seal  136 . Retainer assemblies  130 ,  132  are axially positioned between lower shoulder  138  of inner mandrel  118  and upper shoulder  140  of bottom sub  112 . Retainer assemblies  130 ,  132  respectively include discoidal portions  142 ,  144  that are generally impervious and serve to isolate dispersible portion  126  from contact with any fluid in flow passage  122 . Retainer assemblies  130 ,  132  including discoidal portions  142 ,  144  are preferable formed from a metal such as a stainless steel including, but not limited to, a 625 stainless steel. 
         [0027]    In the illustrated embodiment, dispersible portion  126  is a compacted salt and sand composition which has sufficient compressive strength to resist fluid pressure in flow passage  122 . When an activating agent such a wellbore fluid, water or other fluid, is permitted to contact dispersible portion  126 , however, the salt constituent will dissolve. This dissolving of the salt constituent significantly reduces the compressive strength of dispersible portion  126 , so that it is no longer able to resist fluid pressure in flow passage  122 . 
         [0028]    Plug member  124  may be dispersed by dissolving dispersible portion  126  or a constituent part thereof using wellbore fluid in flow passage  122 . In certain implementations, however, a wellbore fluid capable of dispersing plug member  124  may not available, for example, if the fluid in flow passage  122  is salt-saturated, oil- based or otherwise incapable of dissolving a constituent part of dispersible portion  126 . In the illustrated embodiment, barrier  100  includes a fluid chamber  146  disposed within inner mandrel  118  and an upper portion of middle sub  106  and is protected from contamination with other fluids and debris in the well during conveyance by a debris barrier  148 . Debris barrier  148  extends laterally across flow passage  122 , thus isolating the fluid in fluid chamber  146  from contact with any other fluid or debris in flow passage  122  above debris barrier  148 . As such, the fluid in fluid chamber  146  is available for interaction with dispersible portion  126  when desired. 
         [0029]    As representatively illustrated, debris barrier  148  includes a body portion  150  extending across flow passage  122  and a somewhat enlarged annular-shaped peripheral portion  152  sealingly received between top sub  104  and middle sub  106  of housing assembly  102 . Such sealing engagement of debris barrier  148  acts to completely isolate the fluid in fluid chamber  146  from other fluids in the well. Debris barrier  148  may be formed from an elastomeric material, however, in certain implementations, debris barrier  148  may alternatively be made of a nonelastomeric material. An elastomeric material is preferred, however, since applications of fluid pressure are made to flow passage  122  to initiate activation of plug member  124  as described below. 
         [0030]    In the illustrated embodiment, barrier  100  includes an activating assembly that is operable to create a communication path through retainer assembly  130  to allow communication between the fluid in fluid chamber  146  and dispersible portion  126 . The activating assembly includes an electronic package and a combustion assembly. The electronic package includes a pressure sensor  154 , a logic module  156 , batteries  158  and various signal and current conductors (not pictured). The combustion assembly includes ignition agents  160 ,  162  and combustible agents  164 ,  166 . As illustrated, separator members  168 ,  170  are positioned respectively between combustible agents  164 ,  166  and dispersible portion  126 . Separator members  168 ,  170  are preferable formed from a metal such as a stainless steel including, but not limited to, a 625 stainless steel. An optional heat shielding sleeve  172  is positioned between plug member  124  and middle sub  106 . Heat shielding sleeve  172  is preferably formed from a ceramic materials or other material capable of shielding middle sub  106  from the heat and temperature generated in the combustion reaction discussed below. 
         [0031]    Pressure sensor  154  is operable to receive and interpret pressure signals sent from the surface. For example, by applying a predetermined number and sequence of fluid pressure fluctuations to flow passage  122  via the tubular string at the surface, pressure sensor  154  receives the signal via the fluid in fluid chamber  146 . The pressure signals are transferred to the fluid in fluid chamber  146  from the fluid in the tubular string through debris barrier  148 . When pressure sensor  154  receives the proper pressure signature, pressure sensor  154  sends a signal to logic module  156  to begin the activation process. Even though the signal for initiating the activation of plug member  124  has been described as a pressure signal received by a pressure sensor, those skilled in the art will understand the other types of signals both wireless and wired could alternatively be used including, but not limited to, acoustic signals, electromagnetic signals, hydraulic signals, electrical signals, optical signals and the like, such signals being received and interpreted by the corresponding type of receiver. 
         [0032]    Logic module  156  receives the activation signal from pressure sensor  154  and causes a current to be sent to ignition agents  160 ,  162 . Logic module  156  may include various controllers, processors, memory components, operating systems, instructions, communication protocols and the like. As should be understood by those skilled in the art, any of the functions described with reference to logic module  156  herein can be implemented using software, firmware, hardware, including fixed logic circuitry or a combination of these implementations. As such, the term logic module as used herein generally represents software, hardware or a combination of software and hardware. For example, in the case of a software implementation, the term logic module represents program code and/or declarative content, e.g., markup language content that performs specified tasks when executed on a processing device or devices such as one or more processors or CPUs. The program code can be stored in one or more computer readable memory devices. More generally, the functionality of the illustrated logic module may be implemented as distinct units in separate physical grouping or can correspond to a conceptual allocation of different tasks performed by a single software program and/or hardware unit. 
         [0033]    Batteries  158  are used to power the electronic devices within barrier  100  such as pressure sensor  154  and logic module  156 . In addition, batteries  158  are used to provide suitable current to initiate the combustion of combustible elements  164 ,  166 . Batteries  158  may be of any suitable type such as alkaline batteries that provide sufficient power and current and are capable of withstanding the temperature in the well environment. 
         [0034]    In the illustrated embodiment, ignition agents  160 ,  162  are metal burning fuses such as magnesium fuses which are activated by the electrical current supplied from batteries  158  in response to the activation signal. Metal fuses are preferred as metals burn without releasing cooling gases and can burn at extremely high temperatures. Magnesium fuses are most preferred as due to the reactive nature of magnesium and temperature at which magnesium burn which is sufficiently high to ignite combustible agents  164 ,  166 . Alternatively, a nichrome wire such as a NiCr60 wire, may be used to directly ignite combustible agents  164 ,  166 . As another alternative, a nichrome wire may be used in an ignition train to ignite a metal burning fuse which in turn ignites one of the combustible agents  164 ,  166 . In this case, both the nichrome wire and the metal burning fuse may be considered to be one of the ignition agents  160 ,  162 . 
         [0035]    Combustible agents  164 ,  166  are preferable formed from a composition of a metal powder and a metal oxide that produces an exothermic chemical reaction at high temperature such as a thermite reaction. The metal powder used in the composition may include aluminum, magnesium, calcium, titanium, zinc, silicon, boron and the like. The metal oxide used in the composition may include boron (III) oxide, silicon (IV) oxide, chromium (III) oxide, manganese (IV) oxide, iron (III) oxide, iron (II, III) oxide, copper (II) oxide, lead (II, III, IV) oxide and the like. For example, a composition of aluminum and iron (III) oxide may be used which has a reaction according to the following equation: 
         [0000]      Fe 2 O 3 +2Al-&gt;2Fe+Al 2 O 3 +Heat 
         [0036]    Use of combustible agents  164 ,  166  that produce a thermite reaction is advantageous in the present invention as the reactants are stable at wellbore temperatures but produce an extremely intense exothermic reaction following ignition. The combination of the high temperature and the heat generated by the reaction are sufficient to melt both the metallic separator members  168 ,  170  and discoidal portions  142 ,  144  of retainer assemblies  130 ,  132 . In the illustrated embodiment, this process creates a communication path through retainer assembly  130  to allow communication between the fluid in fluid chamber  146  and dispersible portion  126 . The fluid in fluid chamber  146  dissolves the salt in dispersible portion  126  such that the remaining sand component of dispersible portion  126  lacks sufficient compressive strength to plug flow passage  122 . Accordingly, the sand disintegrates leaving an open bore within plug sleeve  128 . 
         [0037]    Referring next to  FIGS. 3A-3B , therein is representatively illustrated a remote actuated downhole pressure barrier that is generally designated  200 . Barrier  200  includes a generally tubular housing assembly  202  that includes a top sub  204  that is securably and sealingly connected to a middle sub  206  by a plurality of set screws  208  and seal  210 . At its lower end, middle sub  206  is securably and sealingly connected to a bottom sub  212  at threaded connection  214  and by seal  216 . Disposed within middle sub  206  is an inner mandrel  218 . Seals  220 ,  221  provide a sealing relationship between middle sub  206  and inner mandrel  218 . Housing assembly  202  has a flow passage  222  formed axially therethrough. 
         [0038]    Fluid flow through passage  222  is initially blocked by a dispersible plug member  224 . Plug member  224  includes a dispersible portion  226  which is initially compacted within a plug sleeve  228 . Plug member  224  is supported within housing assembly  202  by a pair of oppositely disposed retainer assemblies  230 ,  232 . Retainer assembly  230  is sealingly coupled to inner mandrel  218  by a seal  234 . Retainer assembly  232  is sealingly coupled to bottom sub  212  by a seal  236 . Retainer assemblies  230 ,  232  are axially positioned between lower shoulder  238  of inner mandrel  218  and upper shoulder  240  of bottom sub  212 . Retainer assemblies  230 ,  232  respectively include discoidal portions  242 ,  244  that are generally impervious and serve to isolate dispersible portion  226  from contact with any fluid in flow passage  222 . 
         [0039]    In the illustrated embodiment, dispersible portion  226  is preferably a compacted salt and sand composition, as described above. Barrier  200  includes a fluid chamber  246  disposed within inner mandrel  218  and an upper portion of middle sub  206  and is protected from contamination with other fluids and debris by a debris barrier  248 . Debris barrier  248  includes a body portion  250  extending across flow passage  222  and a somewhat enlarged annular-shaped peripheral portion  252  sealingly received between top sub  204  and middle sub  206  of housing assembly  202 . 
         [0040]    In the illustrated embodiment, barrier  200  includes an activating assembly that is operable to create a communication path, through retainer assembly  230  to allow communication between the fluid in fluid chamber  246  and dispersible portion  226 . The activating assembly includes an electronic package and a combustion assembly. The electronic package includes a pressure sensor  254 , a logic module  256 , batteries  258  and various signal and current conductors (not pictured). The combustion assembly includes ignition agents  260 ,  262  and combustible agents  264 ,  266 . In the illustrated embodiment, combustible agents  264 ,  266  are integrally disposed within dispersible portion  226  such that the greatest concentration of the combustible agents  264 ,  266  is located in the two ends of dispersible portion  226  proximate discoidal portions  242 ,  244  of retainer assemblies  230 ,  232 . Ignition agents  260 ,  262  are preferably metal fuses, as described above. Combustible agents  264 ,  266  are preferably formed from a composition of a metal powder and a metal oxide, as described above. An optional heat shielding sleeve  272  is positioned between plug member  224  and middle sub  206 . 
         [0041]    In operation, pressure sensor  254  receives and interprets pressure signals sent from the surface. When pressure sensor  254  receives the proper pressure signature, pressure sensor  254  sends a signal to logic module  256  to begin the activation process. Logic module  256  then causes a current to be sent to ignition agents  260 ,  262  from batteries  258 . The current is used to ignite ignition agents  260 ,  262  which in turn ignite combustible agents  264 ,  266 . The combination of the high temperature and the heat generated by the reaction of combustible agents  264 ,  266  are sufficient to melt discoidal portions  242 ,  244  of retainer assemblies  230 ,  232 , which creates a communication path through retainer assembly  230  to allow communication between the fluid in fluid chamber  246  and dispersible portion  226 . The fluid in fluid chamber  246  dissolves the salt in dispersible portion  226  such that the remaining sand component of dispersible portion  226  lacks sufficient compressive strength to plug flow passage  222 . Accordingly, the sand disintegrates leaving an open bore within plug sleeve  228 . 
         [0042]    Referring next to  FIGS. 4A-4B , therein is representatively illustrated a remote actuated downhole pressure barrier that is generally designated  300 . Barrier  300  includes a generally tubular housing assembly  302  that includes a top sub  304  that is securably and sealingly connected to a middle sub  306  by a plurality of set screws  308  and seal  310 . At its lower end, middle sub  306  is securably and sealingly connected to a bottom sub  312  at threaded connection  314  and by seal  316 . Disposed within middle sub  306  is an inner mandrel  318 . Seals  320 ,  321  provide a sealing relationship between middle sub  306  and inner mandrel  318 . Housing assembly  302  has a flow passage  322  formed axially therethrough. 
         [0043]    Fluid flow through passage  322  is initially blocked by a plug member  324 . Plug member  324  includes a removable portion  326  which is initially compacted within a plug sleeve  328 . Plug member  324  is supported within housing assembly  302  by a pair of oppositely disposed retainer assemblies  330 ,  332 . Retainer assembly  330  is sealingly coupled to inner mandrel  318  by a seal  334 . Retainer assembly  332  is sealingly coupled to bottom sub  312  by a seal  336 . Retainer assemblies  330 ,  332  are axially positioned between lower shoulder  338  of inner mandrel  318  and upper shoulder  340  of bottom sub  312 . Retainer assemblies  330 ,  332  respectively include discoidal portions  342 ,  344  that are generally impervious and serve to isolate removable portion  326  from contact with any fluid in flow passage  322 . 
         [0044]    In the illustrated embodiment, removable portion  326  may be a compacted salt and sand composition, as described above, that is generally uniformly mixed with a combustible agent  364 . In this embodiment, barrier  300  includes a fluid chamber  346  disposed within inner mandrel  318  and an upper portion of middle sub  306  and is protected from contamination with other fluids and debris by a debris barrier  348 . Debris barrier  348  includes a body portion  350  extending across flow passage  322  and a somewhat enlarged annular-shaped peripheral portion  352  sealingly received between top sub  304  and middle sub  306  of housing assembly  302 . Alternatively, removable portion  326  may be substantially completely formed from a compaction of the combustible agent  364 . In this embodiment, fluid chamber  346  and debris barrier  348  are optional. 
         [0045]    In the illustrated embodiment, barrier  300  includes an activating assembly that is operable to create a communication path through retainer assembly  330  to allow communication between the fluid in fluid chamber  346  and removable portion  326 . The activating assembly includes an electronic package and a combustion assembly. The electronic package includes a pressure sensor  354 , a logic module  356 , batteries  358  and various signal and current conductors (not pictured). The combustion assembly includes a plurality of ignition agents, only two of which, ignition agents  360 ,  362  are shown and combustible agent  364 . The ignition agents are preferably metal fuses, as described above. Combustible agent  364  is preferably formed from a composition of a metal powder and a metal oxide, as described above. An optional heat shielding sleeve  372  is positioned between plug member  324  and middle sub  306 . 
         [0046]    In operation, pressure sensor  354  receives and interprets pressure signals sent from the surface. When pressure sensor  354  receives the proper pressure signature, pressure sensor  354  sends a signal to logic module  356  to begin the activation process. Logic module  356  then causes a current to be sent to the ignition agents from batteries  358 . The current is used to ignite the ignition agents, which in turn ignites combustible agent  364 . The combination of the high temperature and the heat generated by the reaction of combustible agent  364  is sufficient to melt discoidal portions  342 ,  344  of retainer assemblies  330 ,  332 . In those embodiments including fluid chamber  346  and wherein removable portion  326  includes a salt constituent, a communication path is created through retainer assembly  330  to allow communication between the fluid in fluid chamber  346  and removable portion  326 . The fluid in fluid chamber  346  dissolves the salt in removable portion  326  such that the remaining sand component of removable portion  326  lacks sufficient compressive strength to plug flow passage  322 . Accordingly, the sand disintegrates leaving an open bore within plug sleeve  328 . In those embodiments wherein removable portion  326  is substantially completely formed from a compaction of the combustible agent  364 , combustion of combustible agent  364  not only melts the discoidal portions  342 ,  344  of retainer assemblies  330 ,  332  but also creates the open bore within plug sleeve  328 . 
         [0047]    Referring next to  FIGS. 5A-5B , therein is representatively illustrated a remote actuated downhole pressure barrier that is generally designated  400 . Barrier  400  includes a generally tubular housing assembly  402  that includes a top sub  404  that is securably and sealingly connected to a middle sub  406  by a plurality of set screws  408  and seal  410 . At its lower end, middle sub  406  is securably and sealingly connected to a bottom sub  412  at threaded connection  414  and by seal  416 . Disposed within middle sub  406  is an inner mandrel  418 . Seals  420 ,  421  provide a sealing relationship between middle sub  406  and inner mandrel  418 . Housing assembly  402  has a flow passage  422  formed axially therethrough. 
         [0048]    Fluid flow through passage  422  is initially blocked by a plug member  424 . Plug member  424  includes a removable portion  426  which is initially positioned within a plug sleeve  428 . Plug member  424  is supported within housing assembly  402  by a pair of oppositely disposed retainer assemblies  430 ,  432 . Retainer assembly  430  is sealingly coupled to inner mandrel  418  by a seal  434 . Retainer assembly  432  is sealingly coupled to bottom sub  412  by a seal  436 . Retainer assemblies  430 ,  432  are axially positioned between lower shoulder  438  of inner mandrel  418  and upper shoulder  440  of bottom sub  412 . Retainer assemblies  430 ,  432  respectively include discoidal portions  442 ,  444  that are generally impervious and serve to isolate removable portion  426  from contact with any fluid in flow passage  422 . In the illustrated embodiment, removable portion  426  is preferably a polymer material such as a thermosetting polymer including, but not limited to, an epoxy. 
         [0049]    Barrier  400  includes an activating assembly that is operable to create a communication path through passage  422 . The activating assembly includes an electronic package and a combustion assembly. The electronic package includes a pressure sensor  454 , a logic module  456 , batteries  458  and various signal and current conductors (not pictured). The combustion assembly includes a plurality of ignition agents, only two of which, ignition agents  460 ,  462  are shown and combustible agent  464 . In the illustrated embodiment, combustible agent  464  is integrally disposed within removable portion  426  in a substantially even distribution throughout removable portion  426 . The ignition agents are preferably metal fuses, as described above. Combustible agent  464  is preferably formed from a composition of a metal powder and a metal oxide, as described above. An optional heat shielding sleeve  472  is positioned between plug member  424  and middle sub  406 . 
         [0050]    In operation, pressure sensor  454  receives and interprets pressure signals sent from the surface. When pressure sensor  454  receives the proper pressure signature, pressure sensor  454  sends a signal to logic module  456  to begin the activation process. Logic module  456  then causes a current to be sent to the ignition agents from batteries  458 . The current is used to ignite the ignition agents, which in turn ignites combustible agent  464 . The combination of the high temperature and the heat generated by the reaction of combustible agent  464  is sufficient to melt discoidal portions  442 ,  444  of retainer assemblies  430 ,  432  as well as the matrix material of removable portion  426  leaving an open bore within plug sleeve  428 . 
         [0051]    Referring next to  FIGS. 6A-6B , therein is representatively illustrated a remote actuated downhole pressure barrier that is generally designated  500 . Barrier  500  includes a generally tubular housing assembly  502  that includes a top sub  504  that is securably and sealingly connected to a middle sub  506  by a plurality of set screws  508  and seal  510 . At its lower end, middle sub  506  is securably and sealingly connected to a bottom sub  512  at threaded connection  514  and by seal  516 . Disposed within middle sub  506  is an inner mandrel  518 . Seals  520 ,  521  provide a sealing relationship between middle sub  506  and inner mandrel  518 . Housing assembly  502  has a flow passage  522  formed axially therethrough. 
         [0052]    Fluid flow through passage  522  is initially blocked by a plug member  524 . Plug member  524  includes a removable portion  526  which is initially positioned within a plug sleeve  528 . Plug member  524  is supported within housing assembly  502  by a pair of oppositely disposed retainer assemblies  530 ,  532 . Retainer assembly  530  is sealingly coupled to inner mandrel  518  by a seal  534 . Retainer assembly  532  is sealingly coupled to bottom sub  512  by a seal  536 . Retainer assemblies  530 ,  532  are axially positioned between lower shoulder  538  of inner mandrel  518  and upper shoulder  540  of bottom sub  512 . Retainer assemblies  530 ,  532  respectively include discoidal portions  542 ,  544  that are generally impervious and serve to isolate removable portion  526  from contact with any fluid in flow passage  522 . In the illustrated embodiment, removable portion  526  is preferably a polymer material such as a thermosetting polymer including, but not limited to, an epoxy. 
         [0053]    Barrier  500  includes an activating assembly that is operable to create a communication path through passage  522 . The activating assembly includes an electronic package and a combustion assembly. The electronic package includes a pressure sensor  554 , a logic module  556 , batteries  558  and various signal and current conductors (not pictured). As illustrated, portions of the electronic package are positioned within removable portion  526 . In other implementations, all of the components of the electronic package could be positioned within removable portion  526 . The combustion assembly includes a plurality of ignition agents, only two of which, ignition agents  560 ,  562  are shown and combustible agent  564 . In the illustrated embodiment, combustible agent  564  is integrally disposed within removable portion  526  in a substantially even distribution throughout removable portion  526 . The ignition agents are preferably metal fuses, as described above. Combustible agent  564  is preferably formed from a composition of a metal powder and a metal oxide, as described above. An optional heat shielding sleeve  572  is positioned between plug member  524  and middle sub  506 . 
         [0054]    In operation, pressure sensor  554  receives and interprets pressure signals sent from the surface. When pressure sensor  554  receives the proper pressure signature, pressure sensor  554  sends a signal to logic module  556  to begin the activation process. Logic module  556  then causes a current to be sent to the ignition agents from batteries  558 . The current is used to ignite the ignition agents, which in turn ignites combustible agent  564 . The combination of the high temperature and the heat generated by the reaction of combustible agent  564  is sufficient to melt discoidal portions  542 ,  544  of retainer assemblies  530 ,  532  as well as the matrix material of removable portion  526  leaving an open bore within plug sleeve  528 . 
         [0055]    While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments as well as other embodiments of the invention will be apparent to persons skilled in the art upon reference to the description. It is, therefore, intended that the appended claims encompass any such modifications or embodiments.

Summary:
A downhole pressure barrier ( 100 ) operatively positionable in a subterranean well. The downhole pressure barrier ( 100 ) includes a housing ( 102 ) having a flow passage ( 122 ) formed therethrough. A plug member ( 124 ) that is positioned within the flow passage ( 122 ) selectively prevents flow through the flow passage ( 122 ) and allows flow through the flow passage ( 122 ) responsive to contact with an activating agent. At least one retainer assembly ( 130 ) supports the plug member ( 124 ) within the housing ( 102 ). The retainer assembly ( 130 ) selectively prevents communication between the activating agent and the plug member ( 124 ). An activating assembly including a combustible agent ( 164 ) that is positioned between the retainer assembly ( 130 ) and the plug member ( 124 ) is operable to create a communication path through the retainer assembly ( 130 ) upon combustion of the combustible agent ( 164 ) to allow communication between the activating agent and the plug member ( 124 ).