Abstract:
A dynamic hang-off assembly for supporting a riser string from an off-shore drilling rig including a dynamic tensioning system. The hang-off assembly includes a housing with a passage through the housing. The housing also includes a locking mechanism. The assembly further includes an adapter positionable within the housing passage. The outer surface of the adapter includes a profile. The riser string is also attachable to the adapter. The locking mechanism actuates to engage the adapter profile and secure the adapter to the housing. When the riser string is connected to the adapter and the adapter is secured by the housing, the riser string is supportable by the housing. The housing is also dynamically supportable by the dynamic tensioning system to dynamically support the riser string.

Description:
BACKGROUND 
       [0001]    Offshore oil and gas operations often utilize a wellhead housing supported on the ocean floor and a blowout preventer stack secured to the wellhead housing&#39;s upper end. A blowout preventer stack is an assemblage of blowout preventers and valves used to control well bore pressure. The upper end of the blowout preventer stack has an end connection or riser adapter (often referred to as a lower marine riser package, or LMRP) that allows the blowout preventer stack to be connected to a series of pipes, known as riser, riser string, or riser pipe. Each segment of the riser string is connected in end-to-end relationship, allowing the riser string to extend upwardly to the drilling rig or drilling platform positioned over the wellhead housing. 
         [0002]    The riser string is supported at the ocean surface by the drilling rig and extends to the subsea equipment through a moon pool in the drilling rig. A rotary table and associated equipment typically support the riser string during installation. Below the rotary table may also be a diverter, a riser gimbal, and other sensitive equipment. 
         [0003]    During installation of the riser string, it may be necessary to temporarily move the entire drilling rig, such as for example when a strong storm is approaching. Before moving the rig, it is necessary to pull up the entire riser. If the riser were left in place, movement of the rig would cause the riser string to damage the rotary table, diverter, gimbal, and other sensitive equipment. Pulling up each section of riser string takes a long time, adding cost to the overall drilling operations. Additionally, there may not be enough time to pull the entire riser string before the rig needs to be moved. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    For a detailed description of the preferred embodiments of the invention, reference will now be made to the accompanying drawings in which: 
           [0005]      FIGS. 1A-1B  show a drilling system; 
           [0006]      FIG. 2  shows a perspective view of a dynamic hang-off assembly in accordance with various embodiments; 
           [0007]      FIG. 3  shows a side elevation view of the dynamic hang-off assembly of  FIG. 2 ; 
           [0008]      FIG. 4  shows a top view of the dynamic hang-off assembly of  FIG. 2 ; 
           [0009]      FIG. 5A  shows a side elevation view of the dynamic hang-off assembly of  FIG. 2  shown cutaway in a plane A-A of  FIG. 4 ; 
           [0010]      FIG. 5B  shows a side elevation view of the detail area B of  FIG. 5A ; and 
           [0011]      FIG. 6  shows a perspective view of the dynamic hang-off assembly of  FIG. 2  shown cutaway in a plane A-A of  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    The following discussion is directed to various embodiments of the invention. The drawing figures are not necessarily to scale. Certain features of the embodiments may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in the interest of clarity and conciseness. Although one or more of these embodiments may be preferred, the embodiments disclosed should not be interpreted, or otherwise used, as limiting the scope of the disclosure, including the claims. It is to be fully recognized that the different teachings of the embodiments discussed below may be employed separately or in any suitable combination to produce desired results. In addition, one skilled in the art will understand that the following description has broad application, and the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to intimate that the scope of the disclosure, including the claims, is limited to that embodiment. 
         [0013]    Certain terms are used throughout the following description and claims to refer to particular features or components. As one skilled in the art will appreciate, different persons may refer to the same feature or component by different names. This document does not intend to distinguish between components or features that differ in name but not function. The drawing figures are not necessarily to scale. Certain features and components herein may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in interest of clarity and conciseness. 
         [0014]    In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . ” Also, the term “couple” or “couples” is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct connection, or through an indirect connection via other devices, components, and connections. In addition, as used herein, the terms “axial” and “axially” generally mean along or parallel to a central axis (e.g., central axis of a body or a port), while the terms “radial” and “radially” generally mean perpendicular to the central axis. For instance, an axial distance refers to a distance measured along or parallel to the central axis, and a radial distance means a distance measured perpendicular to the central axis. 
         [0015]      FIGS. 1A-1B  show a drilling system  100  in accordance with various embodiments. The drilling system  100  includes a platform of a drilling rig  126  with a riser string  122  and a blowout preventer stack  112  used in oil and gas drilling operations connected to a wellhead housing  110 . The wellhead housing  110  is disposed on the ocean floor and connected with the blowout preventer stack  112  with a hydraulic connector  114 . The blowout preventer stack  112  includes multiple blowout preventers  116  and kill and choke valves  118  in a vertical arrangement to control well bore pressure in a manner known to those of skill in the art. Disposed on the upper end of the blowout preventer stack  112  is a riser adapter  120  to allow connection of the riser string  122  to the blowout preventer stack  112 . The riser string  122  is composed of multiple sections of pipe or riser joints  124  connected end to end and extending upwardly to the drilling rig  126 . 
         [0016]    The drilling rig  126  further includes a moon pool  128  having a telescoping joint  130  disposed therein. The telescoping joint  130  includes an inner barrel  132  that telescopes inside an outer barrel  134  to allow relative motion between the drilling rig  126  and the wellhead housing  110 . A dual packer  135  is disposed at the upper end of the outer barrel  134  and seals against the exterior of inner barrel  132 . A landing tool adapter joint  136  is connected between the upper end of the riser string  122  and the outer barrel  134  of the telescoping joint  130 . A tension ring  138  is secured on the exterior of the outer barrel  134  and connected by tension lines  140  to a hydraulic tensioning system as known to those skilled in the art. This arrangement allows tension to be applied by the hydraulic tensioning system to the tension ring  138  and the telescoping joint  130 . The tension is transmitted through the landing tool adapter joint  136  to the riser string  122  to support the riser string  122 . The upper end of the inner barrel  132  is terminated by a flex joint  142  and a diverter  144  connecting to a gimbal  146  and a rotary table spider  148 . 
         [0017]    Before, and even after installation of the riser string  122  to the subsea equipment, it may become necessary to detach the riser string  122  from the diverter  144 , the gimbal  146 , rotary table  148 , and any other sensitive equipment. For example, the drilling rig  126  may need to be moved from one location to another and movement of the drilling rig  126  relative to the riser would damage the equipment. In such cases, instead of pulling up and dismantling the entire riser string  122 , the drilling rig  126  may include a dynamic hang-off assembly  200  as shown in  FIGS. 2-6  to support the riser string  122  after it is detached from the diverter  144  and other equipment. 
         [0018]    As shown in  FIGS. 2-6 , the dynamic hang-off assembly  200  includes the tension ring  138  that includes a housing  210  with a passage through the housing  210 . Alternatively, the housing  210  may be designed specifically for the hang-off assembly and replace the tension ring  138 . The housing  210  is connected by the tension lines  140  to a dynamic tensioning system such as described above and as known to those skilled in the art. The housing  210  is shown as a ring but it should be appreciated that the housing  210  may be any suitable shape to support the riser string  122 . Although not shown connected in  FIGS. 2-6 , the tension lines  140  attach to the housing  210  at connection points  212  to support the housing  210  in the moon pool  128 . 
         [0019]    The hang-off assembly  200  also includes an adapter  250  attachable to the riser string  122 . The adapter  250  includes a profile  252  on the outside of a radially extended portion of the adapter  250  as shown. It should be appreciated that the configuration of the adapter  250  and the profile  252  shown are examples only and that different dimensions and locations may be used. The profile  252  is shown as annular but need not be formed continuously on the outside surface of the adapter  250 . The adapter profile  252  is shaped to enable the adapter  250  to be supported by the housing  210  to support the riser string  122  as described below. 
         [0020]    Shown in  FIGS. 5A ,  5 B, and  6 , the housing  210  further includes one or more locking mechanisms  218  that engage the adapter profile  252  to secure the adapter  250  to the housing  210 . In some embodiments, the locking mechanisms  218  are hydraulically operated. In other embodiments, the locking mechanisms  218  are mechanically operated. The locking mechanisms  218  may be either hydraulically or mechanically operated in some embodiments. Shown in the figures are examples of hydraulically operated locking mechanisms  218  that include a slide actuated between locked and unlocked positions with a hydraulic piston. Additional back-up or secondary locking mechanisms may also be included. 
         [0021]    The hang-off assembly  200  is designed to be attached to the tensioning system on the drilling rig  126  to hang the riser string  122  through the drilling rig moon pool  128 . As shown, the riser string  122  and the flex joint  142  are detached from the diverter  144 , the gimbal  146 , and the rotary table spider  148 . The riser adapter  250  is attached to the flex joint  142  using a connection flange on the adapter  250 . A riser string running tool  300  is attached to the adapter  250  opposite the riser string  122 . The riser string running tool  300  is used on the drilling rig  126  to support and move the riser string  122  into position so that the riser string  122  can be supported by the hang-off assembly  200 . With the housing  210  and the adapter  250  positioned as shown, the locking mechanisms  218  are actuated to lock the adapter  250  to the housing  210 . Once in position, the housing  210  thus secures the adapter  250  and supports the riser  122  using the dynamic tensioning system on the rig  126 . This allows tension to be applied by the tensioning system to the housing  210 . The tension is transmitted through the housing  210  and the adapter  250  to the riser string  122  to support the riser string  122 . With the riser string  122  locked in the dynamic hang-off assembly  200  and supported by the tensioning system of the rig  126 , the dynamic hang-off assembly  200  is able to dynamically adjust to maintain tension on the riser string  122 . The rig  126  may now be moved to a different location while the riser string  122  remains suspended through the moon pool  128 . 
         [0022]    Although the present invention has been described with respect to specific details, it is not intended that such details should be regarded as limitations on the scope of the invention, except to the extent that they are included in the accompanying claims.