Abstract:
This invention relates to an undersca riser bearing designed to operate at higher temperatures over an extended time frame while maintaining performance advantages of high capacity laminate (HCL) elastomeric composite bearings.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority to U.S. Provisional Patent Application No. 61/814,885 filed on Apr. 23, 2013 by Keith R. Ptak, et al., entitled “ELEVATED TEMPERATURE RISER BEARING,” which is incorporated by reference herein as if reproduced in its entirety. 
     
    
     BACKGROUND 
       [0002]    Offshore hydrocarbon drilling systems may comprise a drilling riser that extends between a blow out preventer near a sea floor and a drilling rig. In some cases, the drilling riser may be perturbed relative to the blow out preventer by water currents, vortex induced vibrations, waves, and/or a variety of other perturbing forces acting on the drilling riser and/or the drilling rig to which the drilling riser is attached. Some riser bearings provide flexibility and/or relative movement between upper and lower portions of a fluid conduit under high temperatures and/or pressures. Some riser bearings are prone to premature wear and/or degradation as a function of riser bearing components being exposed to the relatively high heat conditions. Other riser bearing are prone to premature wear and/or degradation as a result of exposue to caustic drilling fluids and/or production fluids, which may be operating at elevated temperatures. Additionally, some riser bearings comprising high capacity laminate (HCL) elastomeric composite bearings may fail prematurely because of exposure to relatively high heat conditions. 
       SUMMARY 
       [0003]    In many aspects, this invention provides for a riser bearing for elevated temperature operations. In one aspect, the invention provides a riser bearing capable of being positioned about a drill riser joint. The riser bearing comprises a pressure housing, a flange, a load carrying bearing, a first end plate, an intermediate plate, a sealing bearing, a second end plate and a sleeve. The pressure housing has a top and a bottom. The flange is secured to the top of the pressure housing, the flange has an inner surface oriented towards the bottom of the pressure housing. The load carrying bearing is a composite laminated bearing having a plurality of elastomeric members and non-extensible shims, wherein the elastomeric members and non-extensible shims are laminated together with an outer elastomeric member oriented towards and incorporated with the inner surface of the flange and an inner elastomeric member oppositely positioned from the outer elastomeric member. The first end plate has an inner surface and an outer surface, the outer surface oriented towards and incorporated with the inner elastomeric member of the load carrying bearing. The intermediate flange is proximate to and engaged with the inner surface of the first end plate. The sealing bearing is a composite laminated bearing having a plurality of elastomeric members and non-extensible shims, wherein the elastomeric members and non-extensible shims are laminated together with an outer elastomeric member oriented towards and incorporated with the inner surface of the intermediate flange and an inner elastomeric member oppositely positioned from the outer elastomeric member. The second end plate has an inner surface and an outer surface, the outer surface oriented towards and incorporated with the inner elastomeric member of the sealing bearing. The sleeve has an inner surface and an outer surface, the inner surface being positioned about the riser joint, wherein the sleeve has an upper ring and a lower ring. The sleeve is bonded to the upper and lower rings, wherein the outer surface of the sleeve is positioned proximate to at least the sealing bearing. 
         [0004]    Numerous objects and advantages of the invention will become apparent as the following detailed description of the preferred embodiments is read in conjunction with the drawings, which illustrate such embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  illustrates a prior art riser bearing. 
           [0006]      FIG. 2  is a schematic view of a hydrocarbon drilling system according to an embodiment of the disclosure. 
           [0007]      FIG. 3  is an orthogonal quarter cutaway side view of a riser bearing of the hydrocarbon drilling system of  FIG. 2 . 
           [0008]      FIG. 4  is an orthogonal cross-sectional side view of the riser bearing of  FIG. 3 . 
           [0009]      FIGS. 5 and 6  identify dimensions of a sleeve of the riser bearing of  FIG. 3 . 
           [0010]      FIG. 7  is an orthogonal quarter cutaway side view of a riser bearing according to an alternative embodiment. 
           [0011]      FIG. 8  is an orthogonal cross-sectional side view of an intermediate riser bearing of the hydrocarbon drilling system of  FIG. 2 . 
           [0012]      FIG. 9  is an orthogonal cross-sectional side view of an alternative embodiment of an intermediate riser bearing. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    A prior art example of a riser bearing is the flexible pipe joint assembly  10  described in U.S. Pat. No. 4,183,556, of which the singular figure, col. 5, line 30—col. 7, line 16, col. 8, lines 32-38, and col. 10, lines 13-17 are hereby incorporated by reference and which is illustrated in Prior Art  FIG. 1 . Referring now to Prior Art  FIG. 1 , riser bearing  10  is shown with a load carrying bearing which incorporates elastomeric members  56  and nonextensible shims or laminations  58 . The load carrying bearing is interposed between an upper flange member  22 , or bearing housing, and an end plate  50 . The load carrying bearing incorporates the flange  22  into the outer elastomeric member  56 . Similarly, the load carrying bearing incorporates the end plate  50  into the inner elastomeric member  56 . End plate  50  engages and is supported on annular flange  40  of tubular member  38 , which is the upper pipe associated with the riser bearing. End plate  50  interfaces end plate  60 . The sealing bearing, having elastomeric members  64  and non-extensible shims or laminations  66  is interposed between and bonded to the opposed spherical surfaces of the end plates  60  and  62 . End plate  62  is adjacent to tubular extension  36 , or lower pipe, and housing  18 . Housing  18  is a pressure housing. Housing  18  incorporates tubular extension  36  geometry and flange. The sealing bearing has the same spherical center as the load carrying bearing. Threaded enclosure  94  provides access to cavity  82 . Threaded enclosure  94  is used as the fill and bleed port for cavity  82 . Cavity  82  is pressurized to a desired level. Annular o-rings  52 ,  68 ,  70 ,  72 ,  74 ,  76 ,  78  provide a secondary seal for riser bearing  10 . The upper flange member  22  is secured to housing  18  with load bearing securing devices such as bolts  26 . 
         [0014]    Referring now to  FIGS. 2 , an orthogonal side view of a hydrocarbon drilling system  100  according to an embodiment of the disclosure is shown. Most generally, the hydrocarbon drilling system  100  comprises a drilling riser  102  connected between a drilling rig  104  located near a surface of the water and a blow out preventer  106  located near a sea floor and/or associated with a well bore  108 . In some embodiments, the drilling rig  104  may comprise a buoyant hydrocarbon drilling rig or platform, a freestanding hydrocarbon drilling rig, a ship, and/or any other structure that may be located and/or moved relative to the blow out preventer  106  in a manner that may cause variations in axial forces and/or variations in an amount of bending of the drilling riser  102 . In some cases, the drilling riser  102  may carry drilling fluids and/or other working fluids at relatively high temperatures and/or pressures. The hydrocarbon drilling system  100  further comprises a riser bearing  200  configured to provide a long lasting and/or replaceable sealed movable joint between the drilling riser  102  and the fluid blow out preventer  106  even though the riser bearing  200  is exposed to high temperatures and/or pressures during repetitive perturbations and/or while accommodating axial loads and cocking offsets between the drilling riser  102  and the blow out preventer  106 . The hydrocarbon drilling system  100  further comprises intermediate bearings  400 . The intermediate bearings  400  are disposed along the length of the drilling riser  102  to join longitudinally adjacent portions of the drilling riser  102  while allowing the longitudinally adjacent portions of the drilling riser  102  to cock relative to each other. 
         [0015]    Referring now to  FIGS. 3 and 4 , an orthogonal quarter cutaway side view and an orthogonal cross-sectional side view of the riser bearing  200  are shown. Riser bearing  200  comprises a load carrying bearing  202  and sealing bearing  204 , both of which are generally encapsulated in a space formed by a pressure housing  206  that is joined to a flange  208 . The riser bearing further comprises a cavity  210 , a sleeve  212 , a fluid fill port  214  and a fluid bleed port  216 . The fluid fill port  214  and fluid bleed port  216  are depicted in their positions in  FIG. 4  for illustration purposes only and in alternative embodiments they may be located at any other suitable location for providing selective fluid connectivity between internal spaces of the riser bearing  200  and spaces external to the riser bearing  200 . The cavity  210  is also contained within a space generally bounded by the pressure housing  206  and the flange  208 , and the fluid fill port  214  and the fluid bleed port  216 , in this embodiment, provide selective fluid communication through a wall  217  between a space outside the pressure housing  206  and the cavity  210 . In addition to or instead of the riser bearing  200  comprising a fluid fill port  214  and/or a fluid bleed port  216 , the riser bearing may comprise a volume compensator. 
         [0016]    In this embodiment, the pressure housing  206  and the flange  208  are configured to contain and/or withstand internal pressures within up to about 6,000 pounds per square inch (about 41,370 kilopascals) to about 9,000 pounds per square inch (about 62,053 kilopascals). The pressure housing  206  and the flange  208  may be configured to meet or exceed ASME boiler and pressure vessel codes. While the pressure housing  206  comprises a bowl-like structure, in alternative embodiments, a pressure housing may comprise a cylindrical structure and a complementary lower flange, and/or any other suitable geometric configuration comprising any other suitable combination of complementary geometric shapes and/or profiles. 
         [0017]    The cavity  210  comprises an open volume and/or space between the load carrying bearing  202  and the sealing bearing  204 . The cavity  210  is configured to house a volume of pressurized fluid. Together, the cavity  210  and the associated pressurized fluid within the cavity  210  may allow motion clearance for the load carrying bearing  202 , the sealing bearing  204 , and associated metal components that may move as a function of movement at least one of the load carrying bearing  202  and the sealing bearing  204 . The cavity  210  may also function as a fail-safe and secondary catch basin for any high pressure working fluid escaping through the seal bearing  204  in a case where the seal bearing  204  may be compromised. 
         [0018]    In this embodiment, the load carrying bearing  202  comprises a high capacity laminate (HCL) bearing comprising alternatingly stacked and/or distributed elastomeric members  218  and, as compared to the elastomeric members  218 , relatively non-extensible shims  220 . In this embodiment, the elastomeric members  218  comprise nitrile. In alternative embodiments, the elastomeric members  218  may comprise any other suitable elastomeric material. In this embodiment, the non-extensible shims  220  comprise stainless steel. In alternative embodiments, the non-extensible shims  220  may comprise steel and/or any other suitable metal and/or sufficiently rigid material. The manufacture of HCL bearings is known to those having skill in the relevant art and is not discussed herein and it will be appreciated that this disclosure contemplates incorporation of any suitable HCL bearing in whole or in part to form either or both of the load carrying bearing  202  and the sealing bearing  204 . 
         [0019]    In this embodiment, the load carrying bearing  202  is interposed between flange  208  and a first end plate  222 . The load carrying bearing  202  incorporates an inner surface  224  into an outer elastomeric member  226 . To incorporate the inner surface  224 , load carrying bearing  202  is bonded with the outer elastomeric member  226 . The load carrying bearing  202  also incorporates an outer surface  228  of the first end plate  222  into the inner elastomeric member  229 . To incorporate the outer surface  228 , the load carrying bearing  202  is bonded with the inner elastomeric member  229 . In some cases, the above-described bonding may be accomplished within a mold during a molding and/or bonding process that also joins the elastomeric members  218  to adjacent metal components. 
         [0020]    Alternatively, the load carrying bearing  202  may be formed using a structural bonding process by which the load carrying bearing  202  is interposed between the flange  208  and the first end plate  222 . In such cases, the load carrying bearing  202  may incorporate the inner surface  224  into an outer metal member  226   a  which may comprise steel and/or any other suitable metal. To incorporate the inner surface  224 , the load carrying bearing  202  may be structurally bonded with the outer metal member  226   a . Similarly, the load carrying bearing  202  may incorporate the outer surface  228  of first end plate  222  into an inner metal member  229   a  which may comprise steel and/or any other suitable metal. To incorporate the outer surface  228 , the load carrying bearing  202  may be structurally bonded with the inner metal member  229   a . The bonding referred to may comprise structural bonding with the adjacent metal components. 
         [0021]    The riser bearing  200  further comprises a debris shield  230  that is freely and moveably positioned above an upper surface  232  of the flange  208 . The debris shield  230  generally extends to and is proximate to a wall  234  of an upper riser portion such as fluid conduit upper portion  108 . The debris shield  230  is configured to reduce and/or minimize debris collection on riser bearing  200 , and in particular, to reduce exposure of an upward facing portion of the load carrying bearing  202  that may otherwise be at least partially open to the environment external to the riser bearing  200 . 
         [0022]    The first end plate  222  extends along the wall  234  and is proximate to a pipe flange  238 . The first end plate  222  comprises an inner surface  240  proximate to and engaging an intermediate flange  242 . The first end plate  222  is supported by the intermediate flange  242  and the first end plate  222  is adjacent to the sleeve  212 . 
         [0023]    The sealing bearing  204  comprises a high capacity laminate (HCL) bearing comprising alternatingly stacked and/or distributed elastomeric members  218  and, as compared to the elastomeric members  218 , relatively non-extensible shims  220 . In this embodiment, the elastomeric members  218  comprise nitrile. In alternative embodiments, the elastomeric members  218  may comprise any other suitable elastomeric material. In this embodiment, the non-extensible shims  220  comprise stainless steel. In alternative embodiments, the non-extensible shims  220  may comprise steel and/or any other suitable metal and/or sufficiently rigid material. 
         [0024]    In this embodiment, the sealing bearing  204  is positioned below the load carrying bearing  202 . In this embodiment, the sealing bearing  204  isolates and protects the load carrying bearing  202  by blocking the fluid that flows through the fluid conduit  102  from contacting the load carrying bearing  202  as well as by providing an insulative heat transfer obstruction between the load carrying bearing  202  and the fluid that flows through the fluid conduit  102 . In cases where the fluid that flows through the fluid conduit  102  comprises a relatively high temperature, comprises abrasive particulate matter, comprises corrosive and/or chemically reactive materials, and/or is provided at relatively high pressures, the sealing bearing  204  may be considered a relatively sacrificial and/or safeguard barrier supplied for the benefit of prolonging a service life of the load carrying bearing  202  to the extent that the sleeve  212  may fail to provide such. In this embodiment, the sealing bearing  204  comprises a relatively higher shape factor as compared to the load carrying bearing  202  and the sealing bearing comprises a center of rotation, radius of curvature, and/or is otherwise geometrically configured and oriented so that the sealing bearing is suitable for withstanding and/or reacting without failure to the high working fluid pressures of the fluid carried by the fluid conduit  102  and/or through the central bore of the riser bearing  200 . Accordingly, while the sealing bearing  204  is configured to allow the same cocking deflections as the load carrying bearing  202 , the sealing bearing  204  transmits and/or carries a relatively lower axial and/or longitudinal load as compared to the load carrying bearing  202 . 
         [0025]    The sealing bearing  204  is interposed between an intermediate flange  242  and a second end plate  244 . The sealing bearing  204  incorporates an inner surface  246  of the intermediate flange  242  into an outer elastomeric member  248  and the sealing bearing  204  incorporates an outer surface  250  of the second end plate  244  into an inner elastomeric member  252 . To incorporate the inner surface  246 , sealing bearing  204  may be bonded with the outer elastomeric member  248 . Similarly, to incorporate the outer surface  250 , the sealing bearing  204  may be bonded with the inner elastomeric member  252 . In cases where the above-described bonding may be accomplished in a mold during a molding process, the sealing bearing  204  may comprise substantially the same center of rotation, radius of curvature, and/or spherical center as the load carrying bearing  202 . 
         [0026]    An inner surface  254  of the second end plate  244  is proximate to an outer surface  256  of the sleeve  212 . Additionally, an upper end  258  of the intermediate flange  242  and an upper end  260  of the sealing bearing  204  are also proximate to the outer surface  256 . A lower end  262  of the second end plate  244  is proximate to and supported by the pressure housing  206 . 
         [0027]    An inner surface  264  of the sleeve  212  is positioned about a riser joint  266 , which may comprise a portion of the drilling riser  102 . The sleeve  212  is positioned to separate sealing bearing  204  from riser joint  266  and the temperatures associated therewith. The sleeve  212  protects sealing bearing  204  and generally shields a remainder of the riser bearing  200  from the elevated temperatures, pressures, and/or working/drilling fluids associated with the riser joint  266 , thereby increasing the longevity of the sealing bearing  204  and allowing the riser bearing  200  to operate in higher temperature environments, and in turn, thereby increasing the longevity of the load carrying bearing  202 . In some embodiments, riser bearing  200  may be configured to operate for an extended service life even when exposed to temperatures ranging from about 37° F. (about 2° C.) toabout 350° F. (about 177° C.). In other embodiments, riser bearing  200  may be configured to operate for an extended service life even when exposed to temperatures ranging from about 37° F. (about 2° C.) to about 450° F. (about 233° C.). 
         [0028]    The sleeve  212  comprises an upper ring  270  and a lower ring  272 . The upper ring  270  and the lower ring  272  are thermal insulators comprising annular and/or tube-like shapes comprising of a phenolic, PEEK, and/or elastomer coating configured to provide additional thermal insulative properties and capabilities. Upper ring  270  and lower ring  272  in alternate embodiments be made of other suitable materials such as steel, stainless steel or other metal alloys. As discussed above, the sleeve  212  is illustrated as being positioned about the riser joint  266  and along the central bore  274  of the riser bearing  200 . The central bore  274  generally comprises the space generally bounded by the first end plate  222 , the intermediate flange  242 , the sealing bearing  204 , the second end plate  244 , and the pressure housing  206 . In this embodiment, the sleeve  212  is bonded to both the upper ring  270  and the lower ring  272 . In this embodiment, the upper ring  270  and the lower ring  272  are shown as being anchored into the riser bearing  200 . 
         [0029]    In this embodiment, the sleeve  212  comprises an elastomeric material bonded and capable of resisting temperatures up to about 350° F. (about 177° C.). In alternative embodiments, the sleeve  212  may comprise an elastomeric material that is bonded and capable of resisting temperatures up to about 450° F. (about 233° C.). Furthermore, the sleeve  212  is abrasion and erosion resistant. In some embodiments, the interior diameters of the sleeve  212  are at least large enough to accommodate a drill string therethrough without contacting the sleeve  212 . 
         [0030]    The load carrying bearing  202  may provide support for a critical load path within the riser bearing  200 . Referring back to  FIG. 2 , the HCL portion of the load carrying bearing  202  may allow as much as ±20 degrees of cocking of the riser joint  268  between the drilling riser  102  and the blow out preventer  106  while retaining a required minimum axial load capacity. In some embodiments, about ±10° of cocking may be allowed by the riser bearing  200 . In some embodiments, the required minimum axial load capacity is at least about 3,500,000 pounds force (about 15,569 kilonewtons) while in other embodiments the required minimum axial load capacity is at least about 4,000,000 pounds force (about 17,793 kilonewtons). In alternative embodiments, the riser bearing may be configured for any other selected axial load. 
         [0031]    In some embodiments, the fluid fill port  214  and the fluid bleed port  216  may comprise check valves and be capable of withstanding about 10,000 pounds per square inch (about 68,950 kilopascals) pressure differential between the cavity  210  and the external environment. Additionally, the fluid fill port  214 , fluid bleed port  216  and/or the optional check valves may provide for pressure equalization during a descent of the riser bearing  200  into increasingly deeper fluid environments. 
         [0032]    In this embodiment, the flange  208  is secured to the pressure housing  206  with securing devices  276  in an angular array along a top  278  of the pressure housing  206 . The securing devices  276  are collectively capable of withstanding a pressure differential between the cavity  210  and the environment external to riser bearing  200 , as well as any external tensile load applied to the riser bearing  200  such that there is no gap between pressure housing  206  and the flange  208  when the riser bearing  200  is fully loaded and fully pressurized. 
         [0033]    While  FIGS. 2-4  show a bottom  280  of the pressure housing  206  integrally associated with additional mounting fixtures, alternative embodiments of a pressure housing may be associated with different and/or additional mounting fixtures without substantially altering the operation of the load carrying bearing, sealing bearing, and/or sleeve of the alternative embodiment as compared to the operation of those components of the riser bearing  200 . 
         [0034]    In operation of the riser bearing  200 , the cavity  210  may be filled with a neutrally pressurized fluid for a specified working depth of the riser bearing  200 . For example, if the riser bearing  200  is installed at an operating depth of 12,000 feet (about 3,658 meters), the cavity  210  may be filled with fluid and pressurized to about 5,200 pounds per square inch (about 35,860 kilopascals). By equalizing the pressure in cavity  110  to the environmental pressure at the installation depth, the AP across the load carrying bearing  202  will be  0  and/or substantially eliminated and the AP across the sealing bearing  204  is resultantly greatly reduced from the 5,200 pounds per square inch (about 35860 kilopascals) operating pressure. By reducing the pressure differential across each of the load carrying bearing  202  and the sealing bearing  204 , the service life expectancy for both bearings may be increased. In this embodiment, the load carrying bearing  202  is sized and/or otherwise configured to withstand any sudden working pressure increase that may occur in the cavity  210 , such as an unexpected pressure increase due to a failed and/or compromised seal bearing  204 . It will further be appreciated that this disclosure contemplates additionally providing the riser bearing  200  with additional secondary seals known to those skilled in the art, such as o-rings and gaskets, that are capable of providing sealing in a compressive state and/or in an axial direction. 
         [0035]    As illustrated in  FIGS. 5 and 6 , the sleeve  212  comprises a representative aspect ratio of between the respective lengths X1:X2 may be about 1:6 to about 1:12. The X1 length generally refers to the overall longitudinal length of the sleeve  212  while the X2 length generally refers to the longitudinal length of a central generally frustoconical middle portion of the sleeve  212  that joins a top cylindrical ring portion of the sleeve  212  to a bottom cylindrical ring portion of the sleeve. This range of aspect ratios for the sleeve  212  may reduce the strains experienced by the elastomeric material of the sleeve  212  as riser bearing  200  flexes and/or allows the above-described cocking motion. A sleeve  212  thickness, Y 1 , of the abrasion-resistant and erosion-resistant elastomer may provide and/or define a strength and/or durability of sleeve  212 . The thickness of the elastomer of the sleeve  212  may also provide and/or define an effectiveness of the thermal insulative barrier characteristics of the sleeve  212 . Accordingly, it will be appreciated that selection of suitable aspect ratios and thicknesses may directly contribute to achieving any desired increased service life for the seal bearing  204 , and resultantly, any desired increased service life for the load carrying bearing  202 . 
         [0036]    Referring now to  FIG. 7 , an alternative embodiment of a riser bearing  300  is shown. Riser bearing  300  is substantially similar to riser bearing  200  but for a primary difference being that the functionality of the sealing bearing  204  and the sleeve  212  are combined. In this embodiment, a sealing bearing  304  is configured with elastomeric members  318   a , which comprise a different elastomeric composition as compared to elastomeric members  318  of the load carrying bearing  302 . Further, non-extensible shims  320   a  of sealing bearing  318  may comprise a different metal as compared to non-extensible shims  320  of the load carrying bearing  302 . The elastomeric members  318   a  comprise synthetic rubber such as nitrile and/or any other suitable elastomeric material or material combination. Non-extensible shims  320   a  comprise metal. Non-extensible shims  320  comprise steel and/or stainless steel. The elastomeric members  318   a  and the non-extensible shims  320   a  may provide a relatively higher resistance to heat transfer and/or heat degradation as compared to providing a separate sealing bearing and sleeve. In this embodiment, a thickened elastomeric portion  312  of the sealing bearing  304  serves the barrier function in a substantially similar manner to the sleeve  212 . Further, in this embodiment, the integral nature of the sealing bearing functionality and the sleeve functionality may allow for a relatively more uniform central bore diameter through the riser bearing  300  as compared to the riser bearing  200 . It will be appreciated that the riser bearing  300  and any other of the above-described riser bearing alternative embodiments may be utilized in place of the riser bearing  200  of the hydrocarbon drilling system  100 . 
         [0037]    Referring now to  FIG. 8 , an orthogonal cross-sectional side view of the intermediate riser bearing  400  is shown. The intermediate riser bearing  400  generally comprises components substantially similar to components of riser bearing  200 , however, there are multiple load carrying bearings  402  and multiple sealing bearings  404 . More specifically, the intermediate riser bearing  400  comprises an upper load carrying bearing  402   a , a lower load carrying bearing  402   b , an upper sealing bearing  404   a , and a lower sealing bearing  404   b . The intermediate riser bearing  400  further comprises multiple sleeves  412 , namely, an upper sleeve  412   a  associated with the upper load carrying bearing  402   a  and the upper sealing bearing  404   a . Similarly, the intermediate riser bearing  400  comprises a lower sleeve  412   b  associated with the lower load carrying bearing  402   b  and the lower sealing bearing  404   b . As a group, the structure and operation of the upper load carrying bearing  402   a , upper sealing bearing  404   a , and upper sleeve  412   a  is substantially similar to the structure and operation of the group of the load carrying bearing  202 , sealing bearing  204 , and sleeve  212 . Further, as a group, the structure and operation of the upper load carrying bearing  402   b , upper sealing bearing  404   b , and upper sleeve  412   b  is substantially similar to the structure and operation of the group of the load carrying bearing  202 , sealing bearing  204 , and sleeve  212 . In this embodiment, the above-described upper components are substantially similar to the lower components but are oriented as a mirror image to each across a horizontal plane  401  represented in  FIG. 8  as a dashed line that generally bisects the intermediate riser bearing. 
         [0038]    Intermediate riser bearing  400  also differs from riser bearing  200  because it comprises a generally cylindrically shaped tubular connection ring  403  to which a flange  408   a  associated with the upper load carrying bearing  402   a  and a flange  408   b  associated with the lower load carrying bearing  402   b  each attached to capture the upper load carrying bearing  402   a , the lower load carrying bearing  402   b , the upper sealing bearing  404   a , and the lower sealing bearing  404   b  within a space at least partially bounded by the connection ring  403 . It will be appreciated that the intermediate riser bearing  400  may allow twice the amount of cocking offset as compared to a riser bearing  200  comprising substantially similar, but fewer, components. Accordingly, in some embodiments, the intermediate riser bearing  400  may provide up to about +/−40 degrees of cocking offset. In alternative embodiments, any other desired amount of allowed cocking offset may be provided by configuring the bearings differently. 
         [0039]    Referring now to  FIG. 9 , an alternative embodiment of an intermediate riser bearing  500  is shown. Intermediate riser bearing  500  is substantially similar to intermediate riser bearing  400  but for a primary difference being that the functionality of the sealing bearings  504   a , 504   b  and their respective sleeves  512   a , 512   b  are combined in a manner substantially similar to that described above with regard to the riser bearing  300 . In this embodiment, thickened elastomeric portions  512   a , 512   b  of the sealing bearings  504   a , 504   b , respectively, serve the barrier function in a substantially similar manner to the sleeves  412   a , 412   b . It will be appreciated that the intermediate riser bearing  500  and any other of the above-described intermediate riser bearing alternative embodiments may be utilized in place of the intermediate riser bearing  400  of the hydrocarbon drilling system  100 . 
         [0040]    It will further be appreciated that in alternative embodiments and/or when the hydrocarbon drilling system  100  is configured for production rather than drilling of hydrocarbons, the drilling string  102  may be replaced by a production riser that may comprise a relatively more dramatic curvature. Still further, it will be appreciated that any of the elastomeric bearing elements disclosed herein may be provided with a high performance coating, such as, but not limited to a protective flexible elastomeric coating configured to adhere to the elastomeric elements of the bearing to provide an additional manner to protect and lengthen a service life of the riser bearings. 
         [0041]    Other embodiments of the current invention will be apparent to those skilled in the art from a consideration of this specification or practice of the invention disclosed herein. Thus, the foregoing specification is considered merely exemplary of the current invention with the true scope thereof being defined by the following claims.