Patent Publication Number: US-2019178040-A1

Title: High degree of freedom riser tensioner system

Description:
FIELD OF THE INVENTION 
     Embodiments described herein relate to systems and methods of providing flexible connections in riser tensioner systems. 
     BACKGROUND 
     Some riser tensioner systems comprise bearings configured to allow relative cocking motions between riser tensioner system components. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of an offshore hydrocarbon production system that includes a high degree of freedom (HDOF) riser tensioner system. 
         FIG. 2  is a partial cutaway view of the HDOF riser tensioner system of the offshore hydrocarbon production system of  FIG. 1 , the HDOF riser tensioner system including an HDOF bearing assembly. 
         FIG. 3  is an oblique view of the HDOF bearing assembly of  FIG. 2 . 
         FIG. 4  is an orthogonal top view of the HDOF bearing assembly of  FIG. 2 . 
         FIG. 5  is an orthogonal cross-sectional view of the HDOF bearing assembly of  FIG. 2  taken along the cutting line  5 - 5  of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , an offshore hydrocarbon production system  100  is shown. The offshore hydrocarbon production system  100  comprises a platform  102  that is secured to the ocean floor  104  by a plurality of tendons  106 . The system further comprises risers  108  that extend between individual wells of a template  110  and a deck  112  that is supported by the platform  102 . The risers  108  are flexibly connected to the platform  102  to permit relative motion between the risers  108  and platform  102  that can be caused by waves contacting the platform  102  and the risers  108  that extend up from the ocean floor  104 . 
       FIG. 2  illustrates a high degree of freedom (HDOF) riser tensioner system  114  comprising a riser  108  extending through a hole  116  of the deck  112 . An upper portion of the riser  108  is coupled to a riser support device  118  that is configured to provide a convenient load bearing connection to the riser  108  capable of supporting the weight of the riser  108 . Actuators  120 , such as, but not limited to, hydraulic actuators, are coupled between the riser support device  118  and the deck  112 . The actuators  120  are selectively controlled to lengthen and shorten to maintain a desired amount of tension applied to the riser  108 . For example, in cases where the platform  102  and deck  112  are moved upward, such as due to ocean wave activity, the actuators  120  can be selectively shortened to maintain a desired tension applied to the riser  108  and/or to prevent over-tensioning the riser  108 . Similarly, in cases where the platform  102  and deck  112  are moved downward, the actuators  120  can be selectively lengthened to maintain a desired tension applied to the riser  108  and/or to prevent too much riser  108  weight from being transferred to the underwater components of the offshore hydrocarbon production system  100 . While the actuators  120  can account for vertical relative movement between the riser  108  and the deck  112 , actual ocean wave activity and other sources of perturbation may cause relative movement between the riser  108  and the deck  112  in any other spatial direction and/or in a variety of directional combinations. Accordingly, bearings are provided between the actuators  120  and the deck  112  as well as between the actuators  120  and the riser support device  118 . More specifically, lower bearing assemblies  122  are disposed between the actuators  120  and the deck  112  and HDOF bearing assemblies  124  are disposed between the actuators  120  and the riser support device  118 . 
     The lower bearing assemblies  122  comprise a high capacity laminate (HCL) lower spherical bearing stack  126  comprising a series of stacked spherical shell segment shaped elastomeric elements and complementarily shaped nonelastomeric shims. The bearing stack is disposed between a convex mount  128  coupled to the deck  112  and a concave mount  130  coupled to a lower end of the actuator  120 . The lower spherical bearing stacks  126  allow relative cocking motions between the convex mount  128  and the concave mount  130 , and hence, relative cocking motions between the deck  112  and the actuator  120 . 
     The HDOF bearing assemblies  124  comprise HDOF spherical bearing stacks  132  substantially similar to lower spherical bearing stacks  126 . The HDOF bearing assemblies  124  also comprise a convex mount  134  and a concave mount  136 . The HDOF spherical bearing stack  132  is disposed between the convex mount  134  and the concave mount  136 . In this embodiment, the convex mount  134  is disposed between the actuator  120  and the HDOF spherical bearing stack  132 . In this embodiment, the HDOF spherical bearing stack  132  is configured to allow relative cocking motions between the convex mount  134  and the concave mount  136 , and hence, between the actuator  120  and the riser  108  via the riser support device  118 . The HDOF bearing assemblies  124  further comprise a plate mount  138  and a planar bearing stack  140  disposed between the plate mount  138  and the concave mount  136 . Similar to the HDOF spherical bearing stack  132 , the planar bearing stack  140  comprises an HCL bearing stack comprising a series of stacked elastomeric elements and nonelastomeric shims, however, the elastomeric elements and nonelastomeric shims of the planar bearing stack  140  are substantially plate-like and are generally flat. The planar bearing stacks  140  are configured to allow translational movement of the plate mounts  138  relative to the concave mount  136 . 
     Accordingly, through the combined utilization of the HDOF spherical bearing stack  132  and planar bearing stack  140 , the HDOF bearing assembly  124  allow enables a six degree of freedom connection between the actuator  120  and the riser  108 . More specifically, in some embodiments, the HDOF spherical bearing stack  132  allows for three degrees of freedom, such as the pitch, yaw, and roll of the cocking offset movements while the planar bearing stack  140  allows for two additional degrees of freedom in forward-backward and left-right substantially planar translational movements. The sixth degree of freedom of upward-downward movements, in some embodiments, is provided primarily by the lengthening and/or shortening of the actuators  120  and secondarily by the somewhat compressible nature of the HDOF spherical bearing stacks  132  and the planar bearing stacks  140 , alternatively referred to as first bearing stacks and second bearing stacks, respectively. 
     Referring now to  FIGS. 3-5 , an HDOF bearing assembly  124  is shown in greater detail.  FIG. 3  is an oblique view of an HDOF bearing assembly  124 .  FIG. 4  is an orthogonal top view of the HDOF bearing assembly  124  of  FIG. 3 .  FIG. 5  is an orthogonal cross-sectional view of the HDOF bearing assembly  124  of  FIG. 4  taken along the cutting line  5 - 5  of  FIG. 4 . HDOF bearing assembly  124  is shown as comprising a mounting receptacle  142  for receiving a portion of an actuator  120  and fastener holes  144  for receiving fasteners that can be used to connect the HDOF bearing assembly  124  to the actuator  120 . 
     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.