Abstract:
A high pressure ring seal for tube assembly joints provides structural foundation ring having inside and outside circumferential channels between end rims. The channels and rims are separated by a web of integral ring material. This web is perforated by a plurality of apertures. As an integral coating within both channels and integrally tied through the web apertures is a coating of polymer sealant material. Inside and outside faces of the sealant are pressure equalized by vent apertures through the web apertures.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to earth boring arts and devices for subterranean well completion. In particular, the invention relates to fluid sealing elements for axially translated tubular members that are dynamically operative in chemically hostile, high pressure environments such as cross-over flow assemblies.  
           [0003]    2. Description of Related Art  
           [0004]    Deep subterranean wells are drilled to recover economically valuable fluids such as natural gas and crude petroleum. In many cases, these wells penetrate geologic zones that confine extreme pressure. When encountered, high pressure must be controlled and maintained. For those reasons, high pressure zones are often isolated by packers and casing liners.  
           [0005]    Completion of a well for extended fluid production includes many complex procedures. Among these procedures are formation fracturing, gravel packing and cementing. To execute some of these procedures, it is necessary to redirect the normal course of well working fluid. Well working fluids are generally characterized as “mud” but the term expansively includes water, solvents and particulate mixtures for gravel and sand packing. The normal working fluid circulation route in a well starts from the fluid pumps at the surface. The fluid pump discharge is piped into the well tubing string (or drill pipe) and down the central flow bore of the tubing string. The working fluid exits the flow bore at the bottom of the tubing string or at a desired intermediate point through selectively opened apertures in the tubing wall.  
           [0006]    In many cases, an annular space exists between the tubing string and the well bore or casing wall. This annular space, characterized as the annulus, provides a channel for the working fluid return flow stream to the well surface and back to fluid reservoir pits or the pump suction.  
           [0007]    There are many circumstances in the life of a well that require fluid and pressure isolation of an axial section of the annulus from an adjacent section. For example, it may be desired to isolate the bottomhole pressure from the upper annulus and at the same time, shield a bottomhole production zone from contamination fluid entering the well bore from a higher strata. This desire is satisfied by means of a “packer” that provides an annular barrier between the tubing string and the well wall. Difficulty arises, however, when other well operations below the packer require fluid circulation. The packer blocks the working fluid return flow channel. This difficulty is overcome by means of a “cross-over assembly” which provides an additional flow annulus between the tubing string inner flow bore and an inner bore of the packer. Depending on the cross-over assembly setting, fluid may be pumped down the tubing flow bore into the annulus below the packer. From the annulus below the packer, the well working fluid (mud) may be channeled into the cross-over inner annulus to by-pass the packer and back into the well annulus above the packer.  
           [0008]    In another typical example, working fluid may be pumped down the tubing flow bore to a cross-over point below the packer but above the tubing string bottom end. At the cross-over point, the working fluid is channeled out into the lower well annulus below the packer. The working fluid flows down the lower annulus to the bottom end of the tubing string to enter the tubing string flow bore. Working fluid flow from the bottom end of the tubing string is up the flow bore to the cross-over point where the flow enters the cross-over inner annulus. Further upward fluid flow proceeds along the inner annulus to a point above the packer where the flow is channeled out into the upper well annulus to complete the return flow circuit.  
           [0009]    Typically, a cross-over assembly comprises an outer tube to which the packer is secured. Below the packer, the outer tube may have apertures through the tube wall. These outer tube apertures are internally isolated by reduced I.D. ring sections having smoothly finished sealing surfaces along the I.D. wall face of a ring section. A cross-over tube secured to the end of a tubing work string, has an O.D. less than the sealing surface of the outer tube ring section I.D. O.D. ring seals along the length of the cross-over tube are dimensioned to cooperate with the sealing surface I.D. Depending on the relative axial alignment between the cross-over pipe and the outer packer tube, controlled circulation flow past the packer is achieved while maintaining a pressure differential across the packer and ring seals.  
           [0010]    Due to the hydrostatic head and bottom hole temperature of certain wells, this pressure differential across the packer and ring seals is considerable and imposes great pressure loads against the seals between the cross-over pipe and the sealing surfaces in the outer packer tube. These hydrostatic pressure and geothermal stresses may be compounded by an extremely hostile chemical environment. For example, a well may be treated with amine corrosion inhibitors to reduce the corrosive deterioration of the casing and production tube. Compounds such as zinc bromide may be used for well pressure containment and control. Additionally, inhibitor and containment compounds may be used in mixed combination. Both such well treatment compounds have aggressive consequences on the elastomers and polymers normally used to seal the tubular interface of completion and production equipment.  
           [0011]    To resist these highly reactive well treatment compounds, special purpose sealant compounds such as fluoroelastomers based upon alternating copolymers of tetrafluoroethylene and propylene (AFLAS®) have been developed. However, these AFLAS® types of sealing compounds do not bond (Vulcanize) well with metallic substructures. When the high pressure load on a seal is abruptly released over the seal, such as when the cross-over tube is axially shifted, a resulting rush of fluid across a seal tends to dislodge and damage the seal.  
           [0012]    It is an objective of the present invention, therefore, to provide reliable bore sealing elements for substantially coaxial tube members.  
           [0013]    Another object of the invention is a highly improved cross-over assembly seal.  
         SUMMARY OF THE INVENTION  
         [0014]    The present cross-over tube seal comprises a metallic ring member having inside and outside diameter channels between opposite end shoulders. A plurality of radial apertures distributed about the ring circumference penetrate the ring wall between the inside and outside channels.  
           [0015]    The desired, chemically resistant elastomer such as AFLAS® is coated into both channels with a seal band proximate of the opposite end shoulders. Between the seal bands, elastomer surfaces, both inside and outside, are formed to a shallow concavity.  
           [0016]    Additional to traditional surface bonding such as Vulcanizing, the inner and outer coatings of elastomer are unitized through the ring apertures by an integral plug of elastomer. Preferably, each aperture plug is perforated by a smaller aperture for equalizing the pressure differential between the inside and outside cylindrical surfaces of the ring.  
           [0017]    The present sealing ring is positioned in the cross-over tube assembly in the traditional assembly position between adjacent cross-over tube mandrels. Threaded joint assembly of the adjacent joints axially confines the ring between opposing joint shoulders. Inside diameter sealing bands bear a static seal against a cylindrical seal surface on the mandrel pin joint. Outside sealing bands cooperate with the spaced bore surfaces on the cross-over outer tube to provide pressure isolated cells along the cross-over assembly length. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0018]    For a thorough understanding of the present invention, reference is made to the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings in which like reference characters designate like or similar elements throughout the several figures of the drawing.  
         [0019]    [0019]FIG. 1 is a partially sectioned wellbore and cross-over assembly;  
         [0020]    [0020]FIG. 2 is a partially sectioned pipe joint sealed by the present invention;  
         [0021]    [0021]FIG. 3 is an isometric view of the present invention foundation ring; and  
         [0022]    [0022]FIG. 4 is an isometric view of the present invention showing a partial section removal. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0023]    For environmental orientation, a representative application of the present invention is illustrated by the FIG. 1 sectional schematic of a well casing  10 . Within the well casing is a cross-over assembly  20  having an outer tube  22  and an inner, cross-over tube  24 . The cross-over tube  24  is secured by a threaded pipe joint to the lower end of a tubing string  26 . The outer tube  22  is secured to the inside wall of the casing  10  by means of one of more packers  28 . The outer tube  22  and cross-over tube  24  are joined by an assembly thread  34  for downhole placement as a unit. After the packer  28  is located at the desired position, the packer and associated slip (not shown) is set against the inside wall surface of the casing  10 . This packer and slip setting secures the outer tube  22  to the casing  10 . Subsequently, the work string  26  is rotated to disassemble the cross-over tube  24  from the anchored and sealed outer tube.  
         [0024]    The cross-over tube  24  also includes a central flow bore  30  and an inner annular flow channel  32 . The inner flow channel  32  is open by aperture  36  through the cross-over tube wall.  
         [0025]    The length of the cross-over tube  24  comprises a serial assembly of numerous flow mandrels  40   a,    40   b,  etc. joined by threaded seal joints  42 . With respect to FIG. 2, the “pin” (male) portion of a joint  40   a  comprises a sealing sleeve  44  between the thread  42  and a compression shoulder  46 . The “box” (female) portion of a joint  40   b  comprises a compression shoulder  48  about the distal end of the joint portion. The joint elements and features are dimensioned to confine a seal ring  50  between the shoulders  46  and  48  when the thread joint is closed. The inside seals of the ring  50  provide a fluid pressure sealing interface with the sealing sleeve surface  44  and thereby, a fluid pressure seal of the threaded assembly  42  between pressure differentials respective to the mandrel flow bore  30  and the external mandrel environment.  
         [0026]    Outside seals on the ring  50  interface with bore seal surfaces  38  on the outer cross-over assembly tube  22 . Longitudinal dimensioning between the bore seal surfaces and the separation between ring seals  50  is coordinated to accomplish respective cross-over tool functions by each of several axial alignments between the outer tube  22  and the cross-over tube  24 .  
         [0027]    With respect to FIGS. 3 and 4, construction of a ring seal  50  includes a structural foundation ring  52  fabricated from a suitable material. The foundation ring material should be selected with due consideration of the intended operational environment. In most well operations, a mild steel alloy is suitable. Wells treated with highly reactive components such as amines and bromides may require a stainless steel alloy or Inconel. Other applications may allow non-ferrous metals or dense polymers as the material source of the foundation ring.  
         [0028]    Assuming an original material shape in the form of a cylinder, an outside channel  54  is formed into the outer ring perimeter between opposite end rims  56 . Similarly, an inside channel  58  is formed between the opposite end rims  56 . A cylindrical web  59  of foundation material remains between the inside and outside channels. Linking the inside and outside channels are a plurality of apertures  60  through the web  59  distributed substantially uniformly about the ring perimeter.  
         [0029]    Cast, for example, on and into the channels  54  and  58  and the apertures  60 , as an integral coating, is a suitable sealing polymer such as the fluoroelastomer AFLAS®. Whether cast or machined, a smaller aperture  64  perforates the polymer web within each of the foundation web apertures  60 . The polymer seal coating is further formed with outside and inside cavities,  66  and  68 , respectively. The outside cavity  66  is formed between a pair of outside seal bands  70  whereas the inside cavity is formed between a pair of inside seal bands  72 .  
         [0030]    The cavities  66  and  68  are functional voids in the invention design to distribute the pressure differential load on the seal substantially uniformly across the transverse plane of the seal (pressure force vectors parallel with the wellbore axis). Although an accurate void shape  66  and  68  is illustrated as the preferred embodiment, it will be understood that other void shapes such as a box or channel may be used to accommodate seal material movement due to pressure distortion and temperature expansion. Ideally, the pressure differential load imposed on that seal band directly engaged with the highest pressure environment is distributed across the full annulus of the low pressure side of the seal whereby the unsupported ridge of low pressure sealing band carries only a fractional portion of the full pressure differential load.  
         [0031]    Dimensionally, the O.D. of the outside seal bands  70  is greater than the O.D. of the end rims  56 . Similarly, the I.D. of the inside seal bands  72  is less than the I.D. of the end rims  56 . It is the outside seal bands  70  that make interface contact with the seal bore faces  38  on the outer assembly tube  22 . It is the inside seal bands  72  that make interface contact with the seal sleeve surface  44  of the mandrel joint pin.  
         [0032]    Those of skill in the art will appreciate the fact that fluid pressures within the cross-over flow bore  30  may be developed in excess of a high formation pressure that is restrained by the packer  28 . These high pressures are generated by surface pumps for some well treatment purpose such as chemical fracturing or cementing. A portion of this high flow bore pressure will bleed past the inner seal band  72  into the inside cavity  68 . At the same time, a portion of the bottomhole pressure will bleed past the outer seal bands  70  into the outer cavity  66 . When a particular seal  50  is drawn above the uppermost bore seal surface  38 , the fluid confined under high pressure in the outside cavity  66  is released abruptly. Although the fluid volume within the outside cavity  66  is small, the escape velocity of such volume over the seal band face is such as may damage or destroy prior art seals. To further resist such decompression destruction, the elastomer sealant of the present invention is vulcanized to the foundation ring to reinforce the mechanical interlock that is inherent with the invention.  
         [0033]    The apertures  64  between the inside and outside cavities serve to equalize pressure differentials that would otherwise develop between the opposing surfaces. The aperture vents  64  of the present invention release the inside cavity pressure at the same time as the outside cavity pressure is released.  
         [0034]    An alternative embodiment of the invention may take the form of independent rings respective to each of the sealing bands  70 / 72  whereby an unsealed mating interface is provided between the outside cavity  66  and inside cavity  68 . This unsealed interface between separate seal band rings provides the same function as the apertures  64  for venting the inside cavity  68  in the event of sudden pressure changes.  
         [0035]    Although the invention has been described in the application environment of a cross-over assembly, those of skill in the art will appreciate the design relevance of this ring seal to many other high pressure, chemically hostile applications such as long term formation fluid production. The design may also be used in many piston/cylinder and rod/tube applications unrelated to subterranean wells.  
         [0036]    It should be understood that this description of our preferred embodiment is by illustration only and that the invention is not necessarily limited thereto. Alternative embodiments and operating techniques will become apparent to those of ordinary skill in the art in view of the present disclosure. Accordingly, modifications of the invention are contemplated which may be made without departing from the spirit of the claimed invention.