Abstract:
A nose seal for forming a fluid seal with a sealing surface in a bore The nose seal is particularly suitable for use in high pressure and high temperature conditions. The nose seal includes a substantially deformable sealing ring, which can form a resilient fluid seal with the sealing surface, and a substantially rigid ring, which prevents or limits extrusion of the substantially deformable sealing ring in high temperature and/or high pressure environments.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to devices and methods for forming a fluid seal within a bore between radially inner and outer members. In particular aspects, the invention relates to the design of a nose seal which creates a resilient and robust seal against a substantially conical, inwardly-directed surface in a bore. 
         [0003]    2. Description of the Related Art 
         [0004]    A number of tools and devices that are used within a hydrocarbon production wellbore feature radially inner and outer members that are slidable with respect to one another. Examples include piston assemblies and sliding sleeve valves. Annular elastomeric o-ring seals are commonly used to create a fluid seal between the radially inner member and that outer member. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention generally provides a nose seal for forming a fluid seal within a bore between radially inner and outer members and, in particular aspects, forming a seal against a substantially conical, inwardly-directed sealing surface in the bore. The nose seal is particularly suitable for use in high pressure and high temperature conditions. In a preferred embodiment, the nose seal includes a deformable sealing ring, which can form a resilient fluid seal with the sealing surface, and a substantially rigid, non-deformable sealing ring, which prevents or limits extrusion of the flexible sealing ring in high temperature and/or high pressure environments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The structure and operation of the invention will be more readily understood with reference to the following drawings, which are illustrative thereof and among which like components are numbered with like reference numerals: 
           [0007]      FIG. 1  is a side, cross-sectional view of an exemplary piston portion of a stepper valve, containing a nose seal constructed in accordance with the present invention. 
           [0008]      FIG. 2  is an isometric view of an exemplary nose seal constructed in accordance with the present invention. 
           [0009]      FIG. 3  is an enlarged cross-sectional view of the nose portion of the piston member within the piston portion shown in  FIG. 1 . 
           [0010]      FIG. 4  is an enlarged cross-sectional view of the nose portion now in sealing contact with the surrounding bore. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0011]      FIG. 1  depicts an exemplary piston assembly  10 . In one embodiment, the piston assembly  10  is a piston assembly incorporated within a “stepper” type metering valve of the type used to meter discrete increments of fluid, including both liquid and gaseous fluids, into or out of a hydraulically-operated well tool. One such stepper valve is the HCM-S series stepper valve which is available commercially from Baker Oil tools of Houston, Tex. The piston assembly  10  includes a tubular housing  12  which defines a longitudinal axial bore  14 . The bore  14  includes an upper, enlarged-diameter portion  16  and a lower, reduced-diameter portion  18 . A conically-shaped inwardly-directed sealing surface  20  is formed between the upper and lower portions  16 ,  18 . The bore  14  is provided with a fluid inlet  22  and a fluid outlet  24 . 
         [0012]    A piston member  26  is moveably disposed with respect to the housing  12  within the upper portion  16  of the bore  14 . The piston member  26  is moveable between the lower position within the upper bore portion  16 , shown in  FIG. 1 , and an upper position within the upper bore portion  16 , which is depicted in phantom lines at  26 ′ in  FIG. 1 . The piston member  26  includes a piston body  28  having an upstream axial end  30  and a downstream axial end  32 . Annular o-ring fluid seals  34 , of a type well known in the art, radially surround the body  28  and contact the upper bore portion  16  to provide fluid sealing between the body  28  and the bore  14 . In operation, the piston member  26  is moved axially along the upper bore portion  16  by pressure increases and decreases which act upon the upstream end  30  of the piston member  26 . 
         [0013]    The downstream end  32  of the piston member  26  is shown in greater detail in  FIGS. 3 and 4 . The downstream end  32  presents a nose portion  34  in which a reduced diameter post  36  extends axially from the body  28 . The nose portion  34  is the portion of the piston member  26  that will form a seal with the sealing surface  20  of the bore  14 . An annular, axially-facing shoulder  38  surrounds the post  36 . A threaded bore  40  is disposed into the post  36 . 
         [0014]    An exemplary nose seal, generally indicated at  42 , is disposed radially around the post  36  and upon the shoulder  38 . A connector, such as screw  44 , is then threaded into the bore  40  to secure the nose seal  42  to the downstream end  32  of the piston member  26 . The nose seal  42  includes a substantially deformable sealing ring  46  and a substantially rigid, non-deformable ring  48 . The substantially rigid ring  48  is relatively harder than the deformable ring  46 . The deformable ring  46  has a larger outer diameter than the rigid ring  48 . It is currently preferred that the two rings  46 ,  48  abut one another. In preferred embodiments, the deformable sealing ring  46  is formed of a readily deformable material such as PTFE (polytetrafluoroethylene). However, other suitable materials may be used. Also in preferred embodiments, the rigid ring  48  is formed of a harder, substantially non-deformable material, such as PEEK (polyetheretherketone). However, other suitable materials may be used. In a preferred embodiment, the rigid ring  48  presents a generally triangular cross-section, as can be seen best in  FIGS. 3 and 4 , with the radially outer surface  50  of the rigid ring  48  forming an acute angle  52  with the axis  54  of the bore  14 . It is preferred that the angle  52  approximate the angle at which the sealing surface  20  of the bore  14  is disposed. In addition, as can be seen from  FIG. 3 , the outer radial surfaces  50 ,  56  of the rings  46 ,  48  preferably bow convexly outwardly. 
         [0015]    The nose seal  42  functions to form a resilient fluid seal with the surrounding bore  14  of the housing  12 .  FIG. 3  illustrates the piston member  26  in a position wherein the nose seal  42  is not sealed against the sealing surface  20 .  FIG. 4  depicts the piston member  26  now in a position wherein it is at its furthest downward position within the bore  14  and in sealing contact with the sealing surface  20  of the bore  14 . As illustrates, the outer radial surface  56  of the flexible sealing ring  46  is pressed against the surrounding sealing surface  20  and forms a fluid seal therewith. This resilient seal will form at relatively low pressures and/or temperatures. In addition, the outer radial surface  50  of the rigid ring  48  is urged against the sealing surface  20 . As pressure increases at the upstream axial end  30  of the piston member  26 , the nose seal  42  will be urged more tightly against the sealing surface  20 . In addition, pressurized fluid may bypass the annular seals  34  of the piston body  28  to act piston body  28  to act upon the flexible seal ring  46 . The rigid ring  48  will block extrusion of the flexible seal ring  46  past the sealing surface  20  and downwardly toward the lower bore portion  18 . 
         [0016]    Although the nose seal  42  has been described herein used with a piston assembly, it may be applied for use in other moveable piston-type devices which incorporate a bore which presents a sealing surface and a moveable member that is slidably disposed within the bore. One example is a sliding sleeve valve or device. These devices will be referred to generally in the claims as a “moveable piston” device. Those of skill in the art will recognize that numerous modifications and changes may be made to the exemplary designs and embodiments described herein and that the invention is limited only by the claims that follow and any equivalents thereof.