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CROSS-REFERENCE TO RELATED APPLICATIONS 
   None. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to systems for pressure isolation of one or more tools adapted for use in a wellbore. 
   2. Description of the Related Art 
   Hydrocarbons such as oil and gas are recovered from a subterranean formation using a wellbore drilled into the formation. A number of tools are used throughout the process of drilling and completing the wellbore and also during the production life of the well. Many of these tools are energized using pressurized fluid that is self-contained in the tool, pumped downhole from the surface, or fluid that is produced from the well itself. These tools, which are sometimes referred to as hydraulically actuated tools, can be put to a number of uses. 
   One use for hydraulically actuated tools is to set a liner hanger. During drilling, the wellbore is lined with a string of casing that is cemented in place to provide hydraulic isolation and wellbore integrity. The liner hanger is used to hang or anchor a liner off of a string of other casing string. Several types of liner hangers are known in the art, which includes hydraulic liner hangers. In conventional hydraulic liner hangers, fluid is supplied under pressure into an annular space between a mandrel and a surrounding cylinder. The hydrostatic pressure of the fluid between the cylinder and the mandrel creates a force on the inner surface area of the cylinder that causes the cylinder to slide longitudinally. Hydraulically actuated liner hangers are illustrative of wellbore tools that utilize an applied fluid pressure for operation. 
   Because conventional hydraulically actuated wellbore tools, such as liner hangers, utilize relatively high fluid pressure for activation, these tools can be vulnerable to high fluid pressures occurring after setting or activation. For instance, during pressure testing of a liner hanger assembly, the relatively high test pressures can rupture seals between a cylinder and mandrel or even deform the relatively thin mandrel. Typically, expensive seals and costly materials are used in these wellbore tools to reduce the risk of failure do to exposure to high post-activation pressures. 
   The present invention addresses these and other drawbacks of the prior art. 
   SUMMARY OF THE INVENTION 
   In aspects, the present invention provides systems, devices, and methods to selectively isolate one or more portions of a wellbore tool from applied wellbore pressure. This applied pressure can be communicated to portions of the wellbore tool via a port or other orifice open to the wellbore or tool flow bore. In one embodiment, an isolation device protection device includes a sealing member positioned proximate to the port that moves into a sealing relationship with the port after the wellbore tool has been set. An actuating member positioned next to the sealing member translates or otherwise displaces the sealing member into sealing engagement with the port. In one arrangement, actuating member includes a biasing element such as a spring and is retained in a pre-activated position by a retaining element. The retaining element can include a shoulder or stop formed within the wellbore tool. 
   In certain embodiments, the present invention can be used to protect portions of hydraulically actuated wellbore tools such as liner hangers. Liner hangers typically include a cylinder disposed around a mandrel. The cylinder slides along the mandrel when an applied pressure of a sufficient magnitude is generated in a pressure chamber in the liner hanger. This pressure chamber communicates with the tool flow bore or wellbore via a port formed in the mandrel. For such devices, the sealing member can seal off the port after the applied wellbore pressure sets the wellbore tool. Thus, components such as seals or thin walled cylinders are isolated from fluid pressure in the wellbore. The sealing member can include sealing elements to ensure that fluid does not leak out of the pressure chamber as the applied pressure is setting the hydraulically actuated tool. If, after setting, the fluid in the pressure chamber prevents the sealing member from seating properly over the port, then the sealing member includes a flow element such as a valve that selectively bleeds fluid from the pressure chamber after the wellbore tool has been set. 
   The isolation device can be configured to operate liner hangers as well as other tools used in the wellbore. Moreover, in addition to drilling fluid, the pressurized fluid can be water, synthetic material, hydraulic oil, or formation fluids. 
   It should be understood that examples of the more important features of the invention have been summarized rather broadly in order that detailed description thereof that follows may be better understood, and in order that the contributions to the art may be appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject of the claims appended hereto. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For detailed understanding of the present invention, references should be made to the following detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, in which like elements have been given like numerals and wherein: 
       FIG. 1  schematically illustrates one embodiment of an isolation tool made in accordance with the present invention; 
       FIG. 2  schematically illustrates a sectional view of an embodiment of a sealing member; 
       FIG. 3  illustrates a sectional view of embodiment of the isolation device during activation; 
       FIG. 4  illustrates a sectional view of embodiment of the isolation device after activation; 
       FIG. 5  schematically illustrates a sectional elevation view of a wellbore system utilizing an isolation device made in accordance with the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The present invention relates to devices and methods for pressure isolation of hydraulically actuated wellbore tools. The present invention is susceptible to embodiments of different forms. There are shown in the drawings, and herein will be described in detail, specific embodiments of the present invention with the understanding that the present disclosure is to be considered an exemplification of the principles of the invention, and is not intended to limit the invention to that illustrated and described herein. Indeed, as will become apparent, the teachings of the present invention can be utilized for a variety of well tools and in all phases of well construction and production. Accordingly, the embodiments discussed below are merely illustrative of the applications of the present invention. 
   Referring initially to  FIG. 1 , there is schematically illustrated one embodiment of a pressure isolation device  100  made in accordance with the present invention for pressure isolating one or more sections of a tool  10  conveyed via a work string  12  into a wellbore. Although the isolation device  100  can be used in connection with nearly any tool, for simplicity, the isolation device  100  will be discussed in the context of a hydraulically actuated liner hanger having an outer member or cylinder  14  and an inner member or mandrel  16 . In a conventional manner, a port  18  formed in the mandrel  16  provides fluid communication between a tool bore  20  and a chamber  22 . The chamber  22  is hydraulically sealed by seals or packing  24  and the isolation device  100 . During use, a pressure increase in the bore  20  causes a corresponding pressure increase in the chamber  22 . The applied pressure generates a force that urges the cylinder  14  to slide in the direction  24 . This sliding movement can actuate slips (not shown) in the case of liner hangers or open or close a valve or perform some other desired function. As will be seen, after the tool  10  is set, the isolation device  100  seals the port  18  to thereby substantially prevent fluid communication between the bore  20  and the chamber  22  and other external sections of the tool  10 . As should be appreciated, this isolation can shield external components of the tool  10  from relatively high pressures in the bore  20  that may be generated during activities such as pressure testing. 
   In one embodiment, the isolation device  100  includes a sealing member  102  positioned in a space  104  between the cylinder  14  and the mandrel  16 . Referring now to  FIGS. 1 and 2 , the sealing member  102  includes a ring-like body  106  on which are positioned sealing elements  108 . An actuating element  110  adjacent to the sealing member  102  pushes or slides the sealing member  102  over or around the port  18  once a predetermined pressure condition is reached. In one embodiment, the actuating element  110  is a biasing member such as a spring that is retained within the space  104  by a retaining member  112 . However, in other embodiments, the actuating element  110  can use pressurized fluid such as gas, an electric or hydraulic motor, one or more magnetic elements, piezoelectric elements and other devices suited to push or otherwise displace the sealing member  102 . 
   In one embodiment, the sealing elements  108   a - c  are disposed on both the interior and exterior surfaces of the body  106  to form fluid barriers between the body  106  and the cylinder  14  and between the body  106  and the mandrel  16 . The interior and exterior sealing elements  108   a - c  cooperate to allow the chamber  22  to develop a pressure differential sufficient to displace the cylinder  14 . After the cylinder  14  has been displaced, the interior seals  108   a,b  straddle and seal off the port  18 . These seals, which do not need to be a “zero leakage” seals, enable a substantial pressure differential thereacross. It should be understood that any number of different sealing arrangements can be utilized. For instance, in some applications, a sealing element (not shown) can be positioned in the retaining member  112 , which could eliminate the need for a sealing element on the exterior surface. Furthermore, a biased detent element such as a ball may be used to plug the port  18 , which could eliminate the need for a sealing element on the interior surface. In still other embodiments, the tolerances between the sealing member and the mandrel and the cylinder can be selected to reduce fluid leakage to a level where no seal elements would be needed. 
   In some embodiments, the mostly incompressible fluid occupying the chamber  22  could effectively prevent the sealing member  102  from sliding over the port  18 . Referring now to  FIG. 2 , to vent or bleed fluid from the chamber  22 , the sealing member  102  can include one or more flow control elements  112 . The flow control element  112  permits fluid to flow out of the chamber  22  under one or more preset conditions. In one arrangement, the flow control element  112  includes a valve  114  that selectively blocks fluid communication through a conduit  116  traversing the sealing member  102 . In one embodiment, the valve  114  includes a piston member  118  that is urged to an open position by a biasing member  120 . A suitably high hydraulic pressure in the chamber  22  urges the piston member  118  into a closed position. In some arrangements, it may be desired to maintain the valve  114  in a closed position before activation regardless of the pressure in the chamber  22 . One suitable arrangement for holding the valve  114  in the closed position in such situations is shown in  FIG. 1 . As shown, a shoulder  122  is formed on the cylinder  14  that protrudes into the space  104  to provide a seating surface for piston member  118  of the valve  114 . The biasing force generated by the actuating member  110  overcomes the biasing force of the biasing member  120 , which allows the piston member  118  to move. In another embodiment, the flow control element  112  can include a rupture disk (not shown) that fractures or disintegrates at a predetermined pressure. In still other embodiments, the flow control element  112  can include plugs or other elements that melt or disintegrate upon exposure to heat, pressure, a chemical, etc. 
   The operation of the isolation device  100  will be described with reference to  FIGS. 1-4 . In  FIG. 1 , the isolation device  100  is shown in a pre-activated position wherein the port  18  is unblocked and fluid flows freely between the bore  20  and the chamber  22 . The pressure in the chamber  22  can vary as the tool  10  is tripped into the well; e.g., it could be at, below or above a hydrostatic pressure. These pressure variations do not affect the isolation device  100 . For example, the shoulder  122  prevents sliding or translation of the sealing element  102  in the direction  24 . Additionally, pressure variations will not affect the valve  114 , which is held in a closed position by the actuating member  110  pressing the valve  114  against the shoulder  122 . Thus, prior to an activation pressure of the tool  10  being generated in the well, the tool  10  and the isolation device  10  remain in a static or dormant condition. Devices and methods for preventing unintended setting or activation of the tool  10  are disclosed in co-pending and commonly owned patent application Ser. No. 11/176,094, which is hereby incorporated by reference for all purposes. 
   Referring now to  FIG. 3 , the tool  10  is shown in a condition where the pressure in the chamber  22  has reached a preset value and has caused the cylinder  14  to slide axially relative to the mandrel  16 . This preset pressure value can be selected to fracture a device such as a shear screw  26  ( FIG. 1 ) that initially fixes the cylinder  14  to the mandrel  16 . In one embodiment, the preset pressure value or applied pressure in the chamber  22  is selected maintain the isolation device  100  in a pre-activated or dormant condition even after the shoulder  122  slides away from the sealing member  102 . For example, the applied pressure can overcome the bias of the actuating member  110  ( FIG. 1 ) and thereby urge the sealing device  102  in the direction  28  and can overcome the bias of the spring  120  ( FIG. 2 ) and thereby hold the valve  114  in a closed position. Thus, the applied pressure in the chamber  22  effectively keeps the chamber  22  hydraulically sealed and in fluid communication with the bore  20 . 
   Referring still to  FIG. 3 , once the cylinder  14  has completed its axial travel and the desired tool has be set or activated (e.g., slips), the pressure in the bore  20  and the chamber  22  is allowed to drop. As the pressure drops, the applied in the chamber  22  falls below the value needed to maintain the isolation device  100  in a pre-activated or dormant condition. Thus, once the applied pressure is unable to overcome the bias of the actuating member  110  ( FIG. 1 ), the sealing device  102  moves in the direction  24  due to the actuating member  110  ( FIG. 1 ). Also, the reduced applied pressure in unable to overcome the biasing element  120 , which then pushes the valve  114  to an open position. Because the valve  114  is open, the chamber  22  is no longer hydraulically sealed; i.e., fluid can escape the chamber  22  via the conduit  116 . Thus, advantageously, even after the sealing device  102  seals off the port  18 , fluid can be bled from the chamber  22  via the conduit  116 . 
   Referring to  FIG. 4 , the sealing device  102  is shown surrounding and Sealing off the port  18 . In the embodiment shown, the body  106  and the seals  108   a,b  form a fluid barrier that prevents fluid communication between the bore  20  and the exterior portions of the tool  10 . Thus, advantageously, the tool  10  is isolated from pressure variations, e.g., pressure increases, in the bore  20 . It should be appreciated that such pressure isolation can simplify the design of the tool  10  and also increase the in-service reliability and robustness of the tool  10 . For instance, the seals or packing  24  do not necessarily have to be configured to withstand pressures substantially beyond the pressure needed to operate the tool  10 . Furthermore, the cylinder  14 , which can have a relatively thin wall, also does not necessarily need specialized materials to withstand such pressures. In some arrangements, the isolation tool  100  can include a stop member  140  positioned on the mandrel  16  to axially position the sealing device  102  over the port  18 . For example, the stop member  140  can be a snap ring or other protruding member located such that when the sealing device  102  abuts the stop member  140 , the port  18  will be axially straddled by the seals  108   a,b . Additionally, the stop member  140  can be configured to engage and close the valve  114  in much the same manner as the shoulder  122 . 
   Referring now to  FIG. 5 , there is shown a well construction facility  200  positioned over subterranean formation  202 . While the facility  200  is shown as land-based, it can also be located offshore. The facility  200  can include known equipment and structures such as a derrick  204  at the earth&#39;s surface  206 , a casing  208 , and mud pumps  210 . A work string  212  suspended within a well bore  214  is used to convey tooling and equipment into the wellbore  214 . The work string  242  can include jointed tubulars, drill pipe, coiled tubing, production tubing, liners, casing and can include telemetry lines or other signal/power transmission mediums that establish one-way or two-way data communication and power transfer from the surface to a tool connected to an end of the work string  212 . A suitable telemetry system (not shown) can be known types as mud pulse, electrical signals, acoustic, or other suitable systems. The tooling and equipment conveyed into the wellbore can include, but are not limited to, fishing tools, expansion tools, bottomhole assemblies, tractors, thrusters, steering units, drilling motors, downhole pumps, completion equipment, perforating guns, tools for fracturing the formation, tools for washing the wellbore, screens and other production equipment. 
   For illustrative purposes, the work string  212  is shown as conveying a liner hanger assembly  216  into the wellbore  214 . The liner hanger assembly  216  includes a liner hanger  218  and an isolation device  100 . Once the liner hanger assembly  216  is positioned that a desired depth, the liner hanger  218  can be actuated in a convention manner. For example, a plug or ball can be “dropped” into a tubing bore to isolate fluid communication in the area of the desired depth. Thereafter, the mud pump  210  is operated to increase the applied pressure of the drilling fluid in the drill string  212 . Referring now to  FIGS. 1 and 5 , once a sufficient pressure increase is created, the cylinder  14  slides longitudinally in a manner previously described to engage the slips or other tool. After the pump  210  is secured, the pressure in the work string  212  drops. Once this pressure drops below a preset pressure, the isolation device  100  is activated in a manner previously described and blocks off fluid communication between the interior and exterior of the work string  212 . At this stage, the work string  212  can be pressured up to pressure test the liner hanger assembly  216 . It should be appreciated that the integrity of the hanger assembly  216 , e.g., hydraulic isolation, can be tested with without exposing the exterior elements of the liner hanger  218  to the elevated test pressures. In fact, advantageously, the positive closure of the port  18  by the isolation device  100  increases the overall reliability for the service life of the liner hanger  218 . 
   It should further appreciated that the teachings of the present invention can be readily applied to numerous tools outside the liner drilling context. For example, in certain applications, fluids such as water, acids, fracturing fluids, may be circulated in the wellbore. Also, formation fluids such as oil and water can be utilized in some circumstances to energize the isolation device. Moreover, some embodiments of the present invention can be adapted for use in situations where fluid pressure is not used to energize a tool or device. For example, some tools may be actuated or energized by vibrations, mud pulse, motion of the tool, frequency, electronic signals, etc. 
   Additionally, it should be understood that the terms such as “first” and “second” and “uphole” and “downhole” do not signify any specific priority, importance, or orientation but are merely used in better describe the relative relationships between the items to which they are applied. Also, the term longitudinal generally refers to a direction along the long axis of a wellbore or tool, but as noted above, the isolation device is not limited to motion in any particular direction. 
   The foregoing description is directed to particular embodiments of the present invention for the purpose of illustration and explanation. It will be apparent, however, to one skilled in the art that many modifications and changes to the embodiment set forth above are possible without departing from the scope and the spirit of the invention. It is intended that the following claims be interpreted to embrace all such modifications and changes.

Summary:
An isolation device operatively coupled to a wellbore tool is activated upon receiving fluid that a predetermined applied pressure. When the fluid string reaches the predetermined applied pressure, the isolation device undertakes a specified action such as longitudinal movement, rotation, expansion, etc. that actuates or operates the wellbore tool. Premature actuation of the wellbore tool is prevented by applying a resistive force to the isolation device that, alone or in cooperation with another mechanism, arrests movement of the isolation device. This resistive force is generated by applied pressure of the fluid in the work string.