Patent Publication Number: US-2016237777-A1

Title: Metal Chevron Seal

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National Phase Application under 35 U.S.C. §371 and claims the benefit of priority to International Application Serial No. PCT/US2013/067336, filed on Oct. 29, 2013, the contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND 
     Downhole conditions in a well present numerous sealing challenges. For example, components of many well tools must be able to move relative to one another and be sealed against fluid communication. Polymer seals are typically used in such applications, because they do not damage adjacent metallic sealing surfaces when passed over the surfaces. Additionally, polymer seals can provide effective sealing, and can be reinforced or provided with back-up rings to seal against high pressure differentials. For example, typical chevron seals, having a polymer O-ring that energizes multiple, polymer, chevron cross-sectioned seal rings on each side, will have a more ridged back-up ring on each end. 
     A seal chamber in a metal component carrying a polymer chevron seal stack must be longer than the chevron seal stack, long enough to accommodate the differential thermal expansion of the polymer seal stack and metal component assembly. When sealing, the chevron rings on the high pressure side of the seal stack are not compressed with the pressure differential. They can become misaligned and deform in the long chamber as the sealing surfaces move relative to one another. Additionally, the O-ring can roll in various places along its circumference and, due to the high temperature, take a set in its deformed condition. When the pressure is reversed and the sealing surfaces move in the opposite direction, the chevron seal stack shifts to the opposite end of the chamber. The chevron rings deformed in the first pressure cycle will remain partially deformed, and the chevron rings on the new high pressure side will be loose and can become misaligned and deform. As this is repeated over and over, the elastomeric parts become deformed to the point they will no longer seal, and the seal begins to leak. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic side view of an example well with a well tool. 
         FIG. 2  is a side cross-sectional view of a well tool incorporating an example seal assembly. 
     
    
    
     Like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     Referring first to  FIG. 1 , a well  10  includes a substantially cylindrical wellbore  12  that extends from a wellhead  14  at the surface  16  downward into the Earth into one or more subterranean zones of interest  18  (one shown). The subterranean zone  18  can correspond to a single formation, a portion of a formation, or more than one formulation accessed by the well  10 , and a given well  10  can access one, or more than one, subterranean zone  18 . In certain instances, the formations of the subterranean zone are hydrocarbon bearing, such as oil and/or gas deposits, and the well  10  will be used in producing the hydrocarbons and/or used in aiding production of the hydrocarbons from another well (e.g., as an injection or observation well). The concepts herein, however, are applicable to virtually any type of well. A portion of the wellbore  12  extending from the wellhead  14  to the subterranean zone  18  is lined with lengths of tubing, called casing  24 . 
     The depicted well  10  is a vertical well, extending substantially vertically from the surface  16  to the subterranean zone  18 . The concepts herein, however, are applicable to many other different configurations of wells, including horizontal, slanted or otherwise deviated wells, and multilateral wells. 
     A tubing string  20  is shown as having been lowered from the surface  16  into the wellbore  12 . The tubing string  20  is a series of jointed lengths of tubing coupled together end-to-end and/or a continuous (i.e., not jointed) coiled tubing, and includes one or more well tools (e.g., one shown, well tool  22 ). The string  20  has an interior, center bore that enables communication of fluid between the wellhead  14  and locations downhole (e.g., the subterranean zone  18  and/or other locations). In other instances, the string  20  can be arranged such that it does not extend from the surface  16 , but rather descends into the well on a wire, such as a slickline, wireline, e-line and/or other wire. 
     The well tool  22  is of a type having an inner tubing nested in an outer tubing, so that the tubings can move axially relative to one another. The well tool  22  has a sealing arrangement that allows the tubings to move while maintaining a seal between the tubings under high temperature and high pressure differential. In certain instances, the seal formed by the seals can be gas tight. The well tool  22  can be a number of different tools incorporating inner and outer tubings that move relative to one another. In certain instances, the tool  22  is a valve where the inner and outer tubings define walls of pressure chamber that, by pressure in the chamber, drives the tubings to move axially relative to one another in actuating the valve. Other types of valves, as well as other types of tools, are within the concepts herein. 
     Referring to  FIG. 2 , an example well tool  100  that can be used as well tool  22 , is shown in a half side cross-sectional view. The example well tool  100  is generally elongate and tubular, and centered around the longitudinal center axis A-A. Only the upper half of the side cross-sectional view is shown, and the lower half of the side cross-sectional view is identical. The well tool  100  is of a type having an elongate, metal outer tubing  102  receiving an elongate, metal inner tubing  104 , so that the outer tubing  102  and inner tubing  104  can move axially with respect to each other. In this example, the outer tubing  102  concentrically receives the inner tubing  104 . The outer tubing  102  and the inner tubing  104  are sealed to each other by an annular, metal seal assembly  106  that is shown carried in a seal chamber  108  of the outer tubing  102 . Although shown with the seal chamber  108  and the seal assembly  106  associated with the outer tubing  102 , in certain instances, the inner tubing  104  may additionally or alternatively have a seal chamber and seal assembly of the same or different configuration. In certain instances, end walls  118  of the seal chamber  108  are defined by additional components  124  affixed to the outer tubing  102 , as shown in the figure, but the seal chamber  108  could alternatively be partially cut from the material of the tubing. 
     The seal assembly  106  contacts both the inner diameter of the outer tubing  102  and the outer diameter of the inner tubing  104  in the seal chamber  108 . The seal assembly  106  is configured to prevent axial passage of fluids between the outer tubing  102  and the inner tubing  104  both from the left side of the view towards the right side of the view and from the right side of the view towards the left side of the view. Thus, for example, when the well tool  100  residing in a wellbore and axis A-A is generally aligned with the longitudinal axis of the wellbore, the seal assembly  106  is configured to prevent axial passage of fluids both uphole and downhole between the outer tubing  102  and the inner tubing  104 . 
     The seal assembly  106  is a metal chevron-type seal assembly, having a plurality of metal chevron seal rings  110  that contact and form the primary seal between the outer tubing  102  and the inner tubing  104 . In certain instances, the chevron rings are entirely metal, and can be coated or constructed from metal selected to prevent galling with the metal of the tubing. Each of the chevron seal rings  110  is generally chevron shaped, or V-shaped, in cross-section, having a thickest section at the vertex of the V-shape and tapering towards the ends of the V-shape. The V-shape of the chevron seal rings  110  allows the rings to nest within each other as shown in  FIG. 2 . The tapered ends allow the rings to be more flexible to radial loads at their ends. 
     The innermost chevron seal rings  110  are nested into V-shaped recesses  114  on opposing sidewalls of a center ring  112 . In the example, six chevron seal rings  110  are symmetrically arranged about the center ring  112 , with three chevron seal rings  110  oriented with their vertex towards the left side of the view (e.g., uphole), and three chevron seal rings  110  oriented with their vertex towards the right side of the view (e.g. downhole). Fewer or more chevron seal rings  110  could be provided, and they need not be symmetrically arranged about the center ring  112 . The chevron seal rings  110  are held tightly nested within each other and nested into the center ring  112  by an end ring  116  at each end of the seal assembly  106 , which itself abuts the end walls  118  of the seal chamber  108 . The end rings  116  each have a generally V-shaped nose  120  adapted to nest into the chevron seal rings  110  and a flat outer wall  122  that presses flush and square against the flat end walls  118  of the seal chamber  108 . In certain instances, the center ring  112  and or the end rings  116  are metal (entirely or substantially). 
     The chevron seal rings  110  are shown in a radially uncompressed state, to illustrate that the seal rings  110  are designed to provide an interference fit with the outer tubing  102  and the inner tubing  104 . In practice, the ends of the chevron seal rings  110  would not overlap with the outer tubing  102  and inner tubing  104 , as shown, but would flex radially inward. In other words, the free outer diameter of the seal rings  110  is greater than the inner diameter of the outer tubing  102  where the chevron rings  110  contact and seal (i.e., the sealing surface, typically of a controlled, fine surface finish). The free inner diameter of the seal rings  110  is smaller than the diameter at the bottom of the seal chamber  108  (i.e., the sealing surface of the inner tubing  104 , also typically of a controlled, fine surface finish). As a result, when the seal assembly  106  is installed into the seal chamber  108  between the outer tubing  102  and inner tubing  104 , the outer ends of the chevron seal rings  110  elastically deform radially inward and apply a contact pressure on the sealing surfaces of the outer tubing  102  and the inner tubing  104 . This contact pressure provides an initial seal between the chevron rings  110  and the outer tubing  102  and inner tubing  104 . As a pressure differential develops in the fluid on each side of the seal assembly  106 , the pressure acts on the interior of the chevron seal rings  110  to pressure energize the rings to increase the contact pressure and form a tighter seal. 
     The seal assembly  106  is shown in an assembled, axially uncompressed, state, where the center ring  112 , chevron seal rings  110 , and end rings  116  are tightly nested, abutting, with no gaps and the rings not substantially axially elastically or plastically deformed. The seal assembly  106 , in this state, is at its assembled, axially uncompressed stack length. The axial distance (length) between end walls  118  of the seal chamber  108  is sized relative to this stack length, so as to be tight to the seal assembly  106 . When tight, there is no substantial gap between the end walls  118  and the seal assembly  106 . For example, because both the seal assembly  106  and seal chamber  108  are metal, there will be no or insubstantial differential thermal expansion. Thus, the seal chamber  108  need not include a gap to account for the differential thermal expansion between an entirely or substantially polymer seal assembly and the surrounding metal. Nominal gaps may be provided, though, to account for tolerances and to facilitate assembly of the seal assembly  106  into the seal chamber  108 . In certain instances, the axial length between the end walls  118  is no longer than the assembled, uncompressed stack length of the seal assembly  106  (of course, accounting for tolerances and ease of assembly). Having the seal chamber  108  tight to the seal assembly  106  holds the seal assembly  106  together, keeping the rings tightly nested within and abutting each other and supporting the rings against misalignment. When the tubings move back and forth relative to one another, there is no relative movement or separation of the seal rings. In certain instances, the axial length between end walls  118  is a fixed length because the components  124  affix to specified locations on the tubing. In certain instances, one or both end walls  118  of the seal chamber  108  can be axially adjustable on the tubing, so that the seal assembly  106  can be clamped and the components  124  fixed, with the end walls  118  pressing on the seal assembly  106 . For example, one or both of the components  124  can be threaded into or onto the tubing, so that it can be axially tightened against the seal assembly  106 . In this configuration, no nominal gaps are needed to account for tolerances and ease of assembly. 
     As the tubings  102  and  104  move axially relative to each other, the rings of the seal  100  do not separate and remain tightly nested. The vertex of the innermost chevron seal rings  110  being tightly nested in the V-shaped recesses of the center ring  112 , holds the innermost chevron seal rings  110  in alignment and supports the rings against rolling or canting. Similarly, the adjacent chevron seal rings  110 , tightly nested in the V-shaped recesses of the innermost chevron seal rings  110 , are held in alignment and supported against rolling or canting, as are the remaining chevron seal rings  110  with each other. The seal assembly  106  is further held in alignment, and held against rolling or canting, by the end rings  116  tightly nested in the V-shaped recesses of the outermost chevron seal rings  110 , and the flat end  122  of the end rings  116  being pressing flush and square against the flat end walls  118  of the seal chamber  108 . 
     A number of embodiments have been described. Nevertheless, it will be understood that various modifications may be made. Accordingly, other embodiments are within the scope of the following claims.