Abstract:
An offshore well drilling assembly includes a drilling facility or support platform for location at sea. A drilling platform connects to the support platform so the drilling platform is cantilevered from the support platform. The drilling platform extends from the support platform, for positioning over a subsea well. The well drilling assembly includes a staging platform for use in loading and unloading of wellhead equipment. The staging platform is mounted to the drilling platform. The staging platform moves along a side of the drilling platform in directions toward and away from the support platform to a distance over the sea. A method of conveying wellhead equipment uses the staging platform for conveying wellhead equipment between the support platform and a distance over the sea by moving the staging platform along the drilling platform.

Description:
RELATED APPLICATIONS  
       [0001]     This nonprovisional patent application claims the benefit of co-pending, provisional patent application U.S. Ser. No. 60/515,342, filed on Oct. 29, 2003, which is hereby incorporated by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates generally to offshore drilling operations, and more specifically to an apparatus for removing and installing drilling equipment.  
         [0004]     2. Background of the Invention  
         [0005]     An offshore drilling facility includes a drilling rig for various operations performed while drilling a subsea well. A conductor casing extends from the subsea well to an elevation above the surface of the water, where a working platform is connected to an upper portion of the conductor casing for drilling operators to work. On many facilities, the drilling rig is often supported by a drilling platform or cantilever that extends from a side of the drilling facility, over the water, to a location above the drilling platform and conductor casing.  
         [0006]     A string of drill pipe is lowered from the drilling rig, through an opening in the cantilever, into the conductor casing for conducting drilling operations. A blow out preventer (BOP), typically located within the cantilever, engages the upper end of the conductor casing. The BOP regulates fluid flow out of the conductor casing from the subsea well. There are numerous types of BOPs. For example, some have rams that clamp down on the conductor casing. Others are annular which contract to enclose around a drill sting. The term “BOP” as used in this application is not meant to designate either device, but rather to encompass each type known or foreseeable in the art. BOPs can weigh up to 40,000 lbs., and have large pieces that are cumbersome while being moved between various positions.  
         [0007]     During some operations, the BOP must be removed. During these operations, the BOP is typically hoisted and slid along rails to another location within the cantilever. Should a BOP need replacing or to be removed from the drilling facility, the upper surface of the cantilever prevents a crane from lifting the BOP from the storage or stowed position. Rather, the BOP must be moved to a location below the opening the drill pipe typically extends through for engaging the conductor casing.  
         [0008]     The drilling rig cannot lift the BOP and continue drilling operations through the same opening in the upper surface of the cantilever. Therefore, the drilling rig discontinues drilling operations and disconnects from the conductor casing to lift the BOP out of the cantilever. Accordingly, the cantilever and drilling rig must be lifted, or “jacked up”, relative to the conductor casing in order to disconnect from the conductor casing and allow room for the BOP over the conductor casing. In order to lower the BOP onto a vessel, the drilling rig is then slid on the cantilever so that the BOP is at a position that is not directly above the conductor casing. Because the BOP is being lowered from the drilling rig, the vessel is in close proximity to the conductor casing and the supports of the facility. This creates a dangerous environment for the workers and the facilities. During normal weather conditions, this removal process can take two to three days. Under rough weather conditions, the process can take four to six days.  
       SUMMARY OF THE INVENTION  
       [0009]     An offshore well drilling assembly includes a drilling facility or support platform for location at sea. A drilling platform is connected to the support platform such that the drilling platform is cantilevered from the support platform. The drilling platform extends from the support platform, and is positioned over the sea, for positioning over a subsea well. The well drilling assembly includes a staging platform for use in loading and unloading of wellhead equipment. The staging platform is mounted to the drilling platform. The staging platform moves along a side of the drilling platform in directions toward and away from the support platform to a distance over the sea.  
         [0010]     The drilling assembly can also include a rail for the staging platform to move along. The platform can be driven by a motor located on the support platform or on the staging platform. The staging platform can be move along the outside of the drilling platform or along an inside of the drilling platform and extend onto the support platform. The drilling platform can include an opening for the drilling rig to conduct operations on the subsea well. The platform moves along between the support platform and a distance at least as far away from the support platform as the opening.  
         [0011]     The drilling facility can also include a lower rail to help guide the staging platform along the side of the drilling platform. A plurality of columns, extending from a wall located along the drilling platform, can support the rails such that the lower rail is farther away from the drilling platform. The lower rail can guide a roller located on the staging platform.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  is a perspective view of an offshore drilling facility constructed in accordance with this invention, with a vessel located adjacent the drilling facility.  
         [0013]      FIG. 2  is a top plan schematic view of the drilling facility shown in  FIG. 1 .  
         [0014]      FIG. 3  is an enlarged perspective view of a portion of the drilling facility shown in  FIG. 1 , and showing a loading and unloading assembly constructed in accordance with this invention.  
         [0015]      FIG. 4  is a top plan schematic view of an alternative embodiment of the drilling facility shown in  FIG. 2 .  
         [0016]      FIG. 5  is perspective view of an alternative embodiment of the drilling facility shown in  FIG. 3 .  
         [0017]      FIG. 6  is an enlarged perspective view of the platform in the alternative embodiment of  FIG. 5 .  
         [0018]      FIG. 7  is an enlarged side view of the platform in the alternative embodiment of  FIG. 5 .  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0019]     Referring to  FIG. 1 , a support platform or offshore drilling facility  11  is located adjacent a working platform  13  formed toward an upper portion of a conductor casing  14  extending from a subsea well. A plurality of legs  15  support facility  11  above the surface of the water. A drilling platform or cantilever  17  extends from a side of facility  11  over the water and working platform  13 . A drilling rig  19  is located on cantilever  17 , above working platform  13 , for conducting drilling operations. Cantilever  17  includes a vertical opening  20  for drilling rig  19  to engage conductor casing  14 . A string of drill pipe  21  extends from drilling rig  19 , through cantilever  17 , and enters conductor casing  14  above working platform  13 . A motor or drive unit (not shown), typically located in drilling rig  19 , rotates drill pipe  21  during drilling operations. A crane  24  is preferably located on facility  11  for moving equipment and the loading and unloading equipment and supplies. A vessel  25  is located adjacent conductor casing  14  opposite from facility  11  for loading and unloading drilling equipment.  
         [0020]     During typical drilling operations, a blow out preventer (BOP)  23  is located within cantilever  17 , below drilling rig  19 . BOP  23  engages an upper end of conductor casing  14  to regulate or prevent fluid flow through the upper end of conductor casing  14  during specific operations, or during emergencies. In some operations, BOP  23  is removed from conductor casing  14 . For example, this may be while a tree is being installed. BOP  23  is moved within cantilever  17  to a stowed or storage position away from conductor casing  14 , as shown in  FIG. 1 . Typically, with the assistance of pulleys (not shown), movement of BOP  23  is along an overhead rail  26  because of the weight and size of BOP  23  and its associated parts. When BOP  23  is not located within opening  20 , BOP  23  is in a storage or stowed position within cantilever  17 . As shown in  FIG. 2 , the stowed position can be to a side of opening  20  and conductor casing  14 , or aft—closer to the main portion of facility  11  (not shown). With either stowed position, BOP  23  is within cantilever  17 .  
         [0021]     Previously, when installing or removing BOP  23  within cantilever  17 , BOP  23  was lifted through opening  20  because crane  24  cannot reach BOP  23  below the deck of cantilever  17 . Therefore, during replacement and removal operations, BOP  23  was positioned within opening  20 , and drilling rig  19  disengaged from drilling operations for lifting and lowering BOP  23  to vessel  25 . This is a time consuming, dangerous, and expensive operation.  
         [0022]     Referring to  FIGS. 2 and 3 , a staging platform  27 , connected to an side of cantilever  17 , is moveable between aft (adjacent to facility  11 ) and bow (away from facility  11 ) positions. Staging platform  27  is preferably mounted to a wall  28  positioned along a side of cantilever  17 . As desired, staging platform  27  move along an outside portion of cantilever  17  ( FIG. 2 ) or move along an inside portion of cantilever  17  ( FIG. 4 ). Staging platform  27  comprises a side  29  adjacent cantilever  17 , a base  31  defining a floor of staging platform  27 , and preferably a guardrail  33  extending from the base. Staging platform  27  has been made in a manner known in the art for supporting large masses, for example, at least 40,000 lb. weight of BOP  23 . For example, in the preferred embodiment, staging platform  27  includes a plurality of trusses  34  designed to support the loads described above. Preferably, a plurality of rollers  35  are located along side  29  of staging platform  27 , adjacent the side of cantilever  17  that staging platform  27  slides. At least one rail  37  engages rollers  35  for supporting staging platform  27  from the side of cantilever  17 . Rollers  35  engage rails  37  for staging platform  27  to more easily slide along the side of cantilever  17 . Preferably, cantilever  17  is equipped with rails leading to an opening for loading BOP  23  or other equipment onto staging platform  27 .  
         [0023]     A drive assembly, comprising a motor  39  and gear assembly  41 , engage a tensionable draw line  43  for moving staging platform  27  between aft and bow positions. Gear assembly  41  can comprise a toothed end of a shaft extending from motor  39  that directly engages draw line  43 , or a plurality of toothed gears that are rotated by a shaft from motor  39  and engage draw line  43 . In the preferred embodiment, motor  39  is a bi-directional motor in order to engage draw line  43  to move staging platform both toward and away from facility  11 . In either embodiment, the toothed surface is rotated by motor  39 , and acts as a pinion for engaging draw line  43 .  
         [0024]     Draw line  43  can be any known apparatus for engaging a toothed gear or pinion. For example, draw line  43  can be a loop of chain links that loop around gear assembly  41  to pull either the upper or lower portions of the chain loop, depending on the direction of rotation of the pinion, to slide platform between aft and bow positions. Alternatively, draw line  43  could also be a metal rod with a toothed profile for tangentially engaging the pinion, so that the rod and staging platform  27  slide between aft and bow positions depending upon the direction of rotation of the pinion. As is readily apparent by those skilled in the art, there are numerous alternatives for moving an object closer or farther away from motor  39  located on facility  11 .  
         [0025]     In the embodiment shown in  FIGS. 5-7 , staging platform  27  slides along rail  37 , with motor  39 ′ and gear  41 ′ being located on staging platform  27 . A plurality of teeth  51  are formed on rail  37  for gear  41 ′ to engage in order to move staging platform  27  along rail  37 . As best shown in  FIG. 6 , a plurality of support columns  53  are connected to the wall  28 . In the preferred embodiment, support columns  53  connect rail  37  to wall  28  via a support member  59  ( FIG. 7 ). A base rail  55  is preferably positioned below rail  37  for guiding rollers  35 ′ extending from base  31  of staging platform  27 . Columns  53  also support base rail  55 . Preferably, columns  53  have inclined faces  57  so that base rail  55  extends farther away from wall  28  than rail  37 . In the preferred embodiment, a rear support  61  extends from staging platform  27  over rail  37  to the side of rail  37  closest to wall  28 .  
         [0026]     In operation, BOP  23  is removed from conductor casing  14  in a manner readily known in the art, and drilling rig  19  can continue with operations. BOP  23  is loaded onto staging platform  27  from within cantilever  17 . Preferably this is performed with the assistance of rails and a side opening in cantilever  17  near a stowed position for BOP  23 . After securing BOP  23  to staging platform  27 , motor  39  engages draw line  43  through gear assembly  41 , to move staging platform  27  away from facility  11  to the bow of cantilever  17 . Rollers  35  turn along rails  37  to allow for easier movement of staging platform  27  relative to the side of cantilever  17 . Staging platform  27  slides along rails  37  and wall  28  to a position farther away from facility  11  than opening  20 , rig  19 , and conductor casing  14 .  
         [0027]     Crane  24  offloads BOP  23  from staging platform  27  to vessel  25 . Vessel  25  remains a greater distance away from facility  11  than conductor casing  14 , which reduces collision dangers previously associated with loading an unloading a BOP from an offshore facility. Using crane  24  from vessel  25  allows the operator to continue using rig  19  for drilling operations rather than lifting and lowering BOP  23 . Using crane  24  also allows vessel  25  to load and unload BOP  23  from a position that is not as close to conductor casing  14  as leg  15  was previously required when using rig  19  to load and unload BOP  23 .  
         [0028]     The description and figures are merely illustrative of various embodiments. While the invention has been shown in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention. For example, while the equipment being transferred by platform has be described as BOP  23 , it will be readily apparent to those skilled in the art that staging platform  27  can be used for transferring a variety of wellhead equipment, like rams and swivels.