Abstract:
A downhole tool in accordance to aspects of the disclosure includes a housing forming a bore to convey a wellbore fluid, an actuating piston moveably disposed in a cylinder located in the housing adjacent to the bore and a barrier fluid isolating the actuating piston from the bore. The downhole tool may include a compensator piston in communication with the barrier fluid and the bore that is moveable to balance the pressure between the barrier fluid and the bore.

Description:
BACKGROUND 
       [0001]    This section provides background information to facilitate a better understanding of the various aspects of the disclosure. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art. 
         [0002]    The present disclosure relates generally to wellbore operations and equipment and more specifically to actuation devices for downhole tools (e.g., subsurface tools, wellbore tools) and methods of operation. 
         [0003]    Hydrocarbon fluids such as oil and natural gas are produced from subterranean geologic formations, referred to as reservoirs, by drilling wells that penetrate the hydrocarbon-bearing formations. Once a wellbore is drilled, various forms of well completion components may be installed in order to control and enhance the efficiency of producing fluids from the reservoir and/or injecting fluid into the reservoir and/or other geological formations penetrated by the wellbore. In some wells, for example, valves are actuated between open and closed states to compensate or balance fluid flow across multiple zones in the wellbore. In other wells, an isolation valve may be actuated to a closed position to shut in or suspend a well for a period of time and then opened when desired. Often a well will include a subsurface valve to prevent or limit the flow of fluids in an undesired direction. 
       SUMMARY 
       [0004]    A downhole tool in accordance to aspects of the disclosure includes a housing forming a bore to convey a wellbore fluid, an actuating piston moveably disposed in a cylinder located in the housing adjacent to the bore and a barrier fluid isolating the actuating piston from the bore. The downhole tool may include a compensator piston in communication with the barrier fluid and the bore that is moveable to balance the pressure between the barrier fluid and the bore. The downhole tool may include a check valve device, for example disposed with the compensator piston, which is adapted to selectively allow fluid to flow across the compensator piston between the bore and the barrier fluid. 
         [0005]    A method according to one or more aspects of the disclosure includes utilizing a downhole tool in a wellbore, the downhole tool including a housing forming a bore to convey a wellbore fluid, an actuating piston moveably disposed in a cylinder that is located in the housing, a barrier fluid isolating the piston seal from the bore; and balancing pressure between the barrier fluid and the bore in response to moving a compensator piston in communication between the barrier fluid and the bore. 
         [0006]    A well system includes a downhole tool connected in a tubular string and disposed in a wellbore, the downhole tool including a housing forming a bore to convey a wellbore fluid, an actuating piston moveably disposed in a cylinder located in the housing adjacent to the bore, a barrier fluid isolating the actuating piston from the bore, and a compensator piston in communication with the barrier fluid and the bore that is moveable to balance the pressure between the barrier fluid and the bore. 
         [0007]    This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of claimed subject matter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The disclosure is best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of various features may be arbitrarily increased or reduced for clarity of discussion. 
           [0009]      FIG. 1  a schematic of a well system incorporating an embodiment of a downhole tool incorporating an isolated tool actuator according to one or more aspects of the disclosure. 
           [0010]      FIG. 2  is a schematic illustration of a wellbore tool utilizing an isolated tool actuator according to one or more aspects of the disclosure. 
           [0011]      FIGS. 3 and 4  are schematic views of a compensator piston of an isolated tool actuator located at travel limits according to one or more aspects of the disclosure. 
           [0012]      FIG. 5  is a schematic illustration of a prior art subsurface valve with a balanced piston actuator. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    It is to be understood that the following disclosure provides many different embodiments, or examples, for implementing different features of various embodiments. Specific examples of components and arrangements are described below to simplify the disclosure. These are, of course, merely examples and are not intended to be limiting. In addition, the disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. 
         [0014]    As used herein, the terms connect, connection, connected, in connection with, and connecting may be used to mean in direct connection with or in connection with via one or more elements. Similarly, the terms couple, coupling, coupled, coupled together, and coupled with may be used to mean directly coupled together or coupled together via one or more elements. Terms such as up, down, top and bottom and other like terms indicating relative positions to a given point or element may be utilized to more clearly describe some elements. Commonly, these terms relate to a reference point such as the surface from which drilling operations are initiated. 
         [0015]    In a non-limiting embodiment the downhole tool is a subsurface flow control device or valve in which the tool actuator engages and opens a valve closure member (e.g., flapper, ball, sleeve, etc.). In another embodiment, the tool actuator can progressively operate a variable choke member. The tool actuator includes without limitation devices which are known in the art and commonly referred to as flow tubes and sleeves. The closure member may include various devices such as and without limitation to flappers, ball valves and sleeves. The term piston is utilized in the disclosure to refer to a device that is moved in response to a control signal to actuate a downhole tool. The signal may be, for example, an electric, mechanical, and/or fluidic signal urging the piston to move at least in a first direction. The piston and the control signal (e.g., driving force) may include without limitation a fluidic piston, an electric solenoid, a gear device, and combinations thereof. 
         [0016]    Subsurface valves are commonly actuated to a first position (e.g., open) by the application of hydraulic pressure, for example from the surface, and biased to the second position (e.g., closed) by a biasing mechanism (stored energy assembly), such as an enclosed pressurized fluid chamber or a mechanical spring. The fluidic pressure may be applied to a piston and cylinder assembly, for example, that acts against the biasing force of the biasing mechanism to open and hold the valve opened. The biasing force acts on the piston to move it to a position allowing the closure member to move to the closed position when the actuating fluid pressure is reduced below a certain value. Examples of some subsurface valves are disclosed in U.S. Pat. Nos. 4,161,219 and 4,660,646 and U.S. Patent Application Publications 2009/0266555, 2010/0006295 and 2010/0139923, which are all incorporated herein by reference. 
         [0017]      FIG. 1  is a schematic of a well system  10  incorporating an embodiment of a downhole tool  12  comprising an actuator assembly  14  according to one or more aspects of the present disclosure. Depicted well system  10  includes a wellbore  16  extending from a surface  18  and lined with casing  20 . A tubular string  22  is disposed in wellbore  16 . Downhole tool  12  is depicted in  FIG. 1  as non-limiting embodiment of a subsurface valve or flow control device, e.g., a subsurface valve. Valve  12  is connected within tubular string  22  for selectively controlling fluid flow through tubular valve  12  and tubular string  22 . For example, subsurface valve  12  may be used to block the flow of reservoir fluid  2  through tubular string  22  to the surface when fluid  2  flows from formation  4  through tunnels  6  and into wellbore  16  and tubular string  22  under a greater pressure than desired. 
         [0018]    Depicted valve  12  is operated in this example to an open position in response to a signal (e.g., electric signal, fluidic signal, electro-fluidic signal, mechanical signal) provided via control system  24 . Depicted control system  24  includes a power source  26  operationally connected to actuator apparatus  14  to operate a tool member  30  (e.g., valve member) from the one position to another position. In  FIG. 1 , the valve member is in a closed position blocking fluid flow through the bore of the tubular string  22 . In the non-limiting embodiment depicted in  FIG. 1 , control system  24  is a fluidic (e.g., hydraulic) system in which fluidic pressure  26  is provided through control line  28  to actuator apparatus  14  which applies an operational force that moves the actuator apparatus in a first direction engaging and actuating tool member  30  to an open position allowing the reservoir fluid in tubular string  22  to flow across tool member  30 . Hydraulic pressure is maintained above a certain level to hold the tool member  30  in the open position. To actuate subsurface valve  12  to the closed position, as shown in  FIG. 1 , the hydraulic pressure via control line  28  is reduced below a certain level. As is known in the art, the hydraulic pressure is reduced below the level of the force that biases the valve member  30  to the closed position. 
         [0019]      FIG. 2  illustrates an embodiment of a downhole tool  12  in the form of a subsurface valve and isolated actuation assembly  14  according to one or more aspects of the disclosure. Valve  12  includes a housing  32  having a longitudinal bore  34 . Valve member  30  is a flapper in this embodiment. An engaging member  36  (e.g., flow tube, sleeve, tubular member) having a central longitudinal bore co-axially aligned with bore  34  of housing  32  is movably disposed within housing  32 . Engaging member  36  is referred to herein as a flow tube. In this embodiment, the valve actuation assembly or apparatus  14  comprises an actuation piston  38  operational disposed with the flow tube  36 . Piston  38  is moveably positioned within a cylinder  40 . In this example, piston  38  is a balanced piston and a biasing energy source  42  biases piston  38  toward the closed position (upward in the illustrated embodiment). In the depicted embodiments piston  38  is not fixedly, or permanently, connected to the flow tube  36  and a second biasing mechanism  44  biases flow tube  36  toward the closed position. In some embodiments the piston  38  and flow tube may be interconnected to move together in both the first and second directions. Biasing energy source  42  is illustrated as a pressurized fluid and second biasing mechanism  44  is illustrated as a spring. 
         [0020]    Actuating piston  38  includes piston seals  46  sealing the piston in the cylinder  40 . In a traditional balanced piston valve design, as illustrated for example in  FIG. 5 , the piston seals  46  are exposed to the wellbore fluid  2 . The isolated actuating assembly or apparatus  14  as depicted for example in  FIGS. 2-4  isolates the piston seals  46  from the wellbore fluid. 
         [0021]    The isolated from wellbore fluid actuator assembly  14  includes a barrier fluid  48  that is contained with seals  50  on the flow tube  36  and an additional piston  52  disposed in a second cylinder  54  to balance the pressure of the barrier fluid  48  to the wellbore fluid  2 , thus reducing the minimum pressure across the flow tube. This additional piston  52 , referred to as a compensator piston, is designed so that if it reaches a maximum or minimum position (so that it can no longer balance pressure) it activates a flow control device, e.g., check valves or other process, to allow for fluid (barrier or wellbore) to bypass the compensator piston. 
         [0022]    The barrier fluid  48  may be a fluid that is clean relative to the wellbore fluid and may be a selective to be less corrosive than the wellbore fluid. The barrier fluid  48  may provide protection to the piston  38  and/or piston seals  46  from wellbore pressure, chemical properties, state (fluid/gas) and debris in the wellbore fluid. The free floating compensator piston  52  balances, or substantially balances, the pressure across the flow tube  36 . The thickness of the flow tube  36  may be minimized as it will not have to withstand high pressure differentials. 
         [0023]    As there may be minimal fluid losses (or gains) in the barrier fluid  48  volume, due for example to leakage across the seals  50 , the compensator piston  52  must allow fluid bypass if it is no longer able to equalize the pressure. As such, once the compensator piston reaches its maximum operational travel limit positions (uphole or downhole), it will active a check system  58  to allow fluid bypass from the wellbore fluid to the barrier fluid zones. 
         [0024]      FIG. 3  illustrates downhole tool  12  with the compensator piston  52  located at a first travel limit  56 , for example a maximum travel limit in response to wellbore fluid pressure. This limit may be reached for example in response to the loss of barrier fluid  48  across seals  50 . At this first travel limit the wellbore fluid  2  may flow through a check valve system  58  of the compensator piston  52  as illustrated by the arrows and thereby equalize the pressure across the flow tube  36  (between the barrier fluid and the wellbore fluid). 
         [0025]      FIG. 4  illustrates downhole tool  12  with the compensator piston  52  located at a second travel limit  60 , for example maximum travel limit in response to barrier fluid pressure. At this second travel limit  60  the barrier fluid  48  may flow through the check valve system  58  of the compensator piston  52  as illustrated by the arrows and thereby equalize the pressure across the flow tube. 
         [0026]    To open subsurface valve  12 , fluid pressure  26  is applied through control line  28  to piston  38  positioned in the cylinder  40  providing a downward force on flow tube  36 . The terminal end of the flow tube  36  physically contacts member  30  (valve member), or a lever or other closure member device, moving tool member  30  about a pivot connection to an open position permitting fluid flow through bore  34  opened through valve  12  and flow tube  36  toward the surface. Subsurface valve  12  is maintained in the open position by the maintenance of hydraulic pressure against piston  38 . 
         [0027]    To close subsurface valve  12 , for example due to a pressure kick in the well, the hydraulic pressure can be relieved from control line  28  to a level such that biasing mechanisms  42  moves piston  38  upward and biasing mechanism  44  moves flow tube  36  upward permitting valve member  30  to close. As noted above, the piston and flow tube may be connected in a manner to move in unison in the upward and in the downward directions. 
         [0028]    The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the disclosure. Those skilled in the art should appreciate that they may readily use the disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the disclosure, and that they may make various changes, substitutions and alterations herein without departing from the spirit and scope of the disclosure. The scope of the invention should be determined only by the language of the claims that follow. The term “comprising” within the claims is intended to mean “including at least” such that the recited listing of elements in a claim are an open group. The terms “a,” “an” and other singular terms are intended to include the plural forms thereof unless specifically excluded.