Patent Publication Number: US-9404320-B2

Title: Riser stringer hang-off assembly

Description:
BACKGROUND 
     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. 
     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. 
     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 
       For a detailed description of the preferred embodiments of the invention, reference will now be made to the accompanying drawings in which: 
         FIGS. 1A-1B  show a drilling system; 
         FIG. 2  is a perspective view of a hang-off assembly in an open position in accordance with various embodiments; 
         FIG. 3  shows top view of the hang-off assembly of  FIG. 2 ; 
         FIG. 4  shows a perspective view of the hang-off assembly of  FIG. 2  shown cutaway in a plane A-A of  FIG. 3 ; 
         FIG. 5  shows a perspective view of the hang-off assembly in a closed position; 
         FIG. 6  shows a top view of the hang-off assembly in the closed position; 
         FIGS. 7-9  show a sequence of landing a riser string in the hang-off assembly and locking it in place. 
     
    
    
     DETAILED DESCRIPTION 
     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. 
     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. 
     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. 
       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 . 
     Drilling rig  126  further includes a moon pool  128  having a telescoping joint  130  disposed therein. The telescoping joint  130  includes a inner barrel  132  which 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 . 
     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 hang-off assembly  200  as shown in  FIGS. 2-9  to support the riser string  122  after it is detached from the diverter  144  and other equipment. 
     As shown in  FIGS. 2-6 , the hang-off assembly  200  includes a housing  210  with a passage  220  through the housing  210  and an open section  212  allowing access to the entire length of the passage  220  through the side of the housing  210  from the outside. As shown, the housing  210  is mountable to a support structure  211  that may be mounted anywhere on the rig  126  appropriate for supporting the riser sting  122 . The housing  210  also includes an optional cover  214  shown as transparent in the figures. The cover  214  protects the housing and the other components described below. 
     The assembly  200  also includes a gate member  260  movable relative to the housing  210  from an open position shown in  FIGS. 2-4  to a closed position shown in  FIGS. 5 and 6 . The gate member  260  prevents access to the passage  220  through the open section  212  when in the closed position. Preferably, the housing  210 , the passage  220 , and the gate member  260  are curved and the gate member  260  rotates between the open and the closed positions. However, the housing  210  and the gate member  260  can be any suitable configuration, such as a sliding gate. The assembly  200  further includes an alignment member  230  for accepting the riser string  122  as described below. As shown, the alignment member  230  is connected to the gate member  260  using fasteners such as bolts. Alternatively, the alignment member  230  and the gate member  260  may not be connected to each other. The alignment member  230  may also be integral with the housing  210  or the gate member  260 . 
     The assembly  200  also includes a motor  240  that moves the gate member  260  between the open and closed positions. In some embodiments, the motor  240  is a hydraulic drive motor. In some embodiments, the motor  240  is an electric drive motor. As shown, the motor  240  includes a gear that engages an exterior gear profile  262  on the gate member  260 . The motor  240  turns the motor gear to apply force to the exterior gear profile. This force moves the gate member  260  and the alignment member  230  between the closed and open positions. Alternatively, the motor  240  may engage a gear profile on the alignment member  230 . Also alternatively, the alignment member  230  need not move with the gate member  260 . 
     Shown in  FIGS. 7-9 , the assembly  200  also includes an adapter  250  attachable to the riser string  122 . The adapter includes a profile  252  landable in the housing  210  to support the riser string  122 . The adapter profile  252  enables the adapter  250  to land in the housing  210  and be supported by the gate member  260  to support the riser string  122 . As shown, the adapter profile  252  includes at least one shock absorber  254  to absorb impact forces between the adapter  250  and the housing  210  when landing and while landed in the housing  210 . 
     The housing further includes one or more locking mechanisms  218  that engage the adapter  250  to secure the adapter  250  to the housing once landed. 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. Lock state indicators  219  identify the locking mechanism  218  as locked or not locked. For example, extended indicators  219  indicate a locked state, and retracted indicators indicate an unlocked state. Additional back-up or secondary locking mechanisms may also be included. 
       FIGS. 7-9  show a landing and locking sequence for the hang-off assembly  200 . In this embodiment, the hang-off assembly  200  is attached to a platform  400  on the drilling rig  126  in a location suitable to hang the riser string  122 , such as 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 to support and move the riser string  122 . 
     With the gate member  260  located in the open position, the riser string running tool  300  moves the adapter  250  and the riser string  122  into the passage  220  through the open section  212  in the side of the housing  210 . Once in the passage  220 , the adapter  250  is landed such that the adapter profile  252  is supported on the gate member  260  as shown in  FIG. 8 . During landing, the alignment member  230  helps align the riser string  122  and also protects the gate member  260  by absorbing some of the impact forces from the moving riser string  122 . The bottom shock absorber  254  on the adapter profile  252  absorbs some of the landing forces to help protect the adapter  250 . The motor  240  is then used to move the gate member  260  into the closed position along with the alignment member  230  as shown in  FIG. 9 . Alternatively, the motor  240  can move the gate member  260  and the alignment member  230  into the closed position before the adapter  250  is landed. Once the adapter  250  is landed, the locking mechanisms  218  are actuated to lock the adapter  250  into place in the housing  210 . As shown in  FIG. 9 , the slides of the locking mechanisms fit over the top shock absorber  254  on the adapter profile  252  to engage the adapter  250 . The top shock absorber  254  thus absorbs some of the impact forces from the slides if the riser string  122  moves within the housing  210 . Also as shown in  FIG. 9 , when the locking mechanisms  218  are in the locked position, the lock state indicators  219  are extended. With the riser string  122  locked in the hang-off assembly  200 , the rig may now move to a different location while the riser string  122  remains hung below the platform  400 . 
     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.