Abstract:
A retractable stern reaction frame for reinforcing self elevating platform cantilever beams. The preferred embodiment contemplates a support framework mounted on a self elevating platform transom and positioned to engage the cantilever to project the reaction point farther towards the cantilever reach. The frameworks are to be retractable (or portable) to allow the self elevating unit to position itself closer to the jackets than would otherwise be possible. The framework is designed to transmit the reaction forces back to the main deck, cantilever support bulkheads, inner bottom and bottom structure.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to structural supports, and particularly to a system for selectively enhancing the support configuration of cantilever beams on jack-up drilling units or the like. 
   2. Description of the Relevant Art 
   A major limitation with oil well drilling or work over activities involving jack-up units utilizing a platform jacket and cantilever beam is the reduced drilling load available, due to the outreach position of said cantilever beams. 
   In such systems, the drill-floor that carries the drilling derrick is typically supported by 2 independent beams via a substructure that forms the cantilever assembly. The drill-floor skids transversely, to reach the drilling template ports, and as a result of this movement, the drilling load is applied unequally on the two cantilever beams. Thus, maximum outreach and offset of the drill-floor are dictated by the allowable load limits of the beams. 
   To assist the operator, a chart specific to every vessel indicates the position of the floor in relation with the allowable drilling load, and on average, the maximum drilling load is achievable over a limited portion of the drilling envelope. Generally, when drilling over a platform jacket the cantilever works at a far outreach only where the drilling load is reduced. 
   Accordingly, the reduced drilling loads impose limitations on operations, the greater extent maximum drilling load being achievable only within the pre-established drilling envelope. Self elevating platforms (jack-ups) which have good load chart capabilities surely are preferred by operators in a competitive market. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a retractable auxiliary support to the cantilever beams of self elevating units such as jack-up units or the like. 
   Another object of the present invention is to provide additional supports mounted on the transom along the cantilever beam path so as to sustain positive reaction, provide additional support, and thereby improve the cantilever rated load charts. 
   Still another object of the present invention is to provide selectively deployable supports to an approximate reported length of approximately one third of the cantilever beam working envelope, a length to which generally would not be practical for a self elevating unit to have permanently installed, as it would reduce the ability to stand close by a platform jacket installation. 
   To achieve the above-mentioned objects a retractable or portable structure is secured on the transom of the vessel. Sound mechanical interface connections are provided to transmit the efforts of the portable structure onto the bottom and support bulkhead of the jack-up vessel. The horizontal efforts are transposed to the vessel at the upper end of the cantilever beam support bulkhead, and at the lower end to the inner bottom structure. The structure is retractable or portable for two reasons; first the auxiliary structures need to be out of the way for jacking operation where if deployed they would interfere with the jacket envelope, secondly if they are not required for a drilling program the associated added weight can be removed without any negative impact on the payload of the vessel. 
   By the present invention, the new reaction added to the cantilever support arrangement has a primary purpose of increasing the rated capacity of the cantilever beams on the farther outreaches of the drilling envelope. The rating is improved by reducing the overhanging extent of the beams, where the bending effort of the cantilever beam is reduced by the same ratio. 
   The auxiliary structure is equipped with a low friction reaction pad to interact with the cantilever beam and transmit purely the vertical reaction. The structure can be designed to withstand, totally or partially, the reaction load at that point, depending of the requirement. The total load reaction is achieved by engineering the structure, considering no load sharing with the transom reaction point. 
   Partial load reaction is obtained by designing the auxiliary structure to share the cantilever beam loading once a certain level of deflection is reached. Partial reaction can be computed for any given support arrangement, where the relation between deflection and load is proportional. 
   From the load rating gain, the benefits of the invention become useful in many aspects. This gain gives the ability to carry the full drill string load (set back load) throughout the drilling envelope, with adequate hook load in reserve. This gain can also allow the conductor tensioning to be achieved from the cantilever beam itself rather than from the transom of the vessel which is the common traditional method. 
   When the tensioning is provided from the cantilever beams the drilling operation for exploration becomes more flexible because the conductor tensioning is possible along the entire length of the drilling envelope. In addition, when exploration drilling is possible further away from the transom, more valuable deck space is made available because the cantilever leaves more of the main deck exposed. 
   The above and further objects, details and advantages or the present invention will become apparent from the following description of preferred embodiments thereof, when read in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an elevation view of the self elevating drilling unit or jack-up vessel alongside a platform ready to elevate into working position for a drilling program over the jacket. 
       FIG. 2  is an elevation view of the self elevating drilling unit or jack-up vessel elevated next to the platform jacket ready to deploy its cantilever beam and drill floor above the drilling template. 
       FIG. 3  is an elevation view of the self elevating drilling unit deployed over the platform jacket ready to drill. 
       FIG. 4  is a plan view of the self elevating drilling unit at the drilling template elevation with projected outline of cantilever and drill floor shown. 
       FIG. 5A  shows sample load charts anticipated rating in relation with the drilling envelope, before implementation of the present invention. 
       FIG. 5B  shows sample load charts anticipated rating in relation with the drilling envelope, after implementation of the present invention. 
       FIG. 6  is an elevation view that shows the self elevating unit or jack-up vessel on an exploration well scenario at an open location. 
       FIG. 7  shows a section view of the cantilever beam showing more details on the conductor tensioning method for exploration wells. 
       FIG. 8A  illustrates a close, up, side view of the reaction frame of the present invention as pivotally attached to the stern of a vessel via mounting bracket, supporting a deployed cantilever. 
       FIG. 8B  is an end view of the reaction frame of  FIG. 8A . 
       FIG. 8C  is a top view of the reaction frame of  FIG. 8A . 
       FIG. 8D  is a bottom view of the reaction frame of  FIG. 8A . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The preferred embodiment of the present invention, contemplating a selectively deployable (i.e., retractable) reaction frame for self-elevating platforms utilizing cantilever beams, is described below with reference to the Figures. The utilization and deployment process of the present invention, as utilized in conjunction with a drilling unit, is also illustrated and discussed in detail, herein. 
   Referring to  FIGS. 1 and 2 , a self elevating drilling unit comprising, for example, a jack up vessel  1  (also known as a jack up rig) is positioned  21  (for example, 5-10 feet, with the distance varying depending upon operator skills, soil, the vessel deployed, etc) so as to be situated adjacent  22  to a platform jacket  4 , then elevated  20  to working position  23 . First  7  and second  7 ′ reaction frames associated with the stern of the vessel are shown in their retracted  24  position, said frames mounted at the transom  11  of the jack up vessel  1 . 
   As shown, in the retracted position  24 , the reaction length of each of the frames is pivoted so that the length of each frame is situated adjacent to the transom, providing a storage position requiring minimal space. 
   A minimum distance “D” is kept between the jack up vessel  1  and the platform  4 , this proximity is required for the cantilever and drill floor to reach out an adequate distance to the drilling template  6 , once the platform is elevated above the platform deck  5 . As shown, the reaction frames  7 ,  7 ′, being situated in their retracted position, allows the jack up vessel  1  to be positioned within the minimum distance “D” required. 
   Continuing with  FIG. 2 , the jack up vessel  1  is shown in its working position  23  elevated above the platform deck  5 . The retractable stern reaction frames  7 ,  7 ′ remain in their stowed position, and thus do not support the cantilever at this point. 
   The cantilever  15 , formed by first  2  and second  2 ′ longitudinally aligned beams, supporting drill floor  3  are shown stowed, ready to be deployed, and the broken lines show the outline of the cantilever  15  and drill floor  3  at working position where the arrow  25  shown within indicates the deployment movement direction. 
   In this traditional scenario, (i.e., without the added support of the reaction frames  7 ,  7 ′ of present invention), the cantilever beams  2 ,  2 ′ transmit the load to the jack up vessel  1 , predominantly at points R 1  and R 2 . R 1  has a hold down H/D effort where the cantilever beam is pushing upward under load. R 2  has a push up effort where the cantilever beams are bearing down under load. Accordingly, R 1  &amp; R 2  generates a force couple that counteracts the overturning moment of the cantilever beam  2 ,  2 ′. 
   Continuing with  FIGS. 3 and 4 , cantilever  15  and the drill floor  3 , elevated above the platform deck  5 , may now be deployed  25  into their extended, working position (for example, cantilever extending 20-25 feet above platform), situated in spaced  28  relation above the drilling template  6 . The reaction frames  7 ,  7 ′ are pivoted  26 ,  26 ′ from their stored position, with their length adjacent to the transom, to their deployed  27 ,  27 ′ position, wherein their length is generally transverse the transom, so as to extend added support surfaces  29 ,  29 ′, to the cantilever beams  2 ,  2 ′ at support points R 3  and R 3 ′, respectively. 
   Those support points R 3 , R 3 ′ project significantly outward of the transom, ideally, for example, approximately one third  35  of the cantilever beam working envelope  34 , so as to increase the distance between the reaction points, as well as to generate a more effective force couple, so as to sustain the overturning moment of the cantilever beam  2 . As earlier indicated, partial load reaction can be obtained by designing the reaction frames (i.e., auxiliary structure) to share the cantilever beam loading, once a certain, level of deflection has being reached. Partial reaction can be computed for any given support arrangement, where the relation between deflection and load is proportional. 
   The present invention thereby provides an innovative support arrangement unlike any prior art on a self elevating drilling unit, and defines the basics of the present invention. 
     FIG. 4  shows a plan view at the main deck level of the jack up vessel  1 , the drilling template  6  of the platform  4  ( FIG. 3 ) is also shown as an indication, and the cantilever beams  2 ,  2 ′ and drill floor  3  outlines are also shown. The drilling envelope  8  sets forth the boundaries wherein the well center  30  can be positioned. The illustration also shows the drill floor  3  skidded to port side and the cantilever  15  to its maximum outreach, overlaid over the drilling template  6 . 
   The drilling template  6  comprises many ports for well to be drilled through, the shaded ports show the boundary where the cantilever  15  can drill with full rated load under conventional support arrangement (without the use of the reaction frame of the present invention), beyond this limit the rating is reduced. 
   Once again, an important feature of the present invention is that the reaction frames  7 ,  7 ′ are stowable into a compact storage position allowing the vessel to be positioned within the minimum distance D (for example, 5-10 feet, depending upon soil conditions and operator skills) and be raised to the appropriate position for extending of the cantilever above the drilling template  6 . (as shown in the above discussed  FIGS. 1 and 2 ). 
   Further, as shown in  FIGS. 3 and 4 , the reaction frames  7 ,  7 ′, once in their deployed, extended position to support the cantilever, said reaction frames extend beyond the minimum distance D for lowering the vessel (as said deployed frames would collide with the underlying platform if the vessel is lowered below the platform level), and therefore said reaction frames must be re-stowed (as shown via pivoting  26 ,  26 ′, at the first end of each frame, so that each frame is adjacent to the transom) prior to lowering of the drilling unit. 
     FIGS. 5A and 5B  shows sample load charts,  FIG. 5A  indicating exemplary loads before modification, and  FIG. 5B  after modification). With a conventional support arrangement (i.e., cantilever without added support, as shown on  5 A, only 45 percent of the envelope is rated at full load (100%), where the extremities are reduced to 26 percent of the load rating. 
   After modification, with the auxiliary stern reaction frames, as shown on  5 B, the full load rating can be maintain nearly the entire drilling envelope, 90 percent, and the extremities are reduced to 76 percent only. 
   As shown in  FIGS. 6 and 7 , an exemplary system for tensioning the conductor pipe utilizes first  16  and second  16 ′ tension members, each having first  17  and second  17 ′ ends, the first ends  17  engaging the tensioning unit, the second ends  17 ′ engaging cantilever beams  2 ,  2 ′, respectively. This concept shows a portable support structure  12  for the tensioning unit  13  which stabilizes the conductor  14  in an open water location under load from sea current and waves. 
     FIGS. 8A-8C  illustrate an exemplary reaction frame configuration suitable for reaction frames  7 ,  7 ′ discussed earlier in the application. As shown, the reaction frame RF comprises a body  40  having an upper edge  43  having first  44  and second  44 ′ ends, a top  31  and a bottom  31 ′, the first end having formed therein upper  41  and lower  41 ′ mounts, said mounts formed to selectively engage upper and lower base supports  50 ,  50 ′, respectively. Said base supports emanate from, or are otherwise securely anchored to, the vessel (in this example, the transom of the vessel). Preferably, the upper and lower base supports  50 ,  50 ′ are securely integrated through the transom to the bulkhead(s)  39  (which may be further reinforced for increased load bearing and distribution) of the vessel, so as to distribute the load to the structure of the vessel. In drilling units, in general there is a bulkhead inline with the cantilever beams connecting to the transom, which said base supports may integrate with through the transom, so that the load supported by the reaction frames would be transferred to the transom and longitudinal bulkhead simultaneously. 
   The upper  41  mount and lower  41 ′ mounts pivotally engage the upper and lower base supports  50 ,  50 ′ via pivot pins  45 ,  45 ′, respectively, so as to allow the reaction frame to be pivotally  49 ,  49 ′ supported by the vessel. It is noted that the pivot pins  45 ,  45 ′ are not designed to support the reaction frame when in use (i.e., the pivot pins in the present configuration are not configured to support added load); rather, the pivot pins are intended for use during storage and deployment, i.e., for pivoted each reaction frame to and from the storage position, as well as retaining each reaction frame in a storage position, adjacent to the transom or other location on the vessel or structure 
   Formed through the upper mount  41  of the reaction frame and the primary base support  50  on the vessel are bores  51 ,  51 ′, respectively, said bores formed in a fashion such that, when the reaction frame RF is pivotally  49 ′ positioned at its deployed position relative to the transom (as shown in  FIG. 8A ), the bores are in axial alignment  53  (specifically, bore  51  is positioned so as to align with bore  51 ′), so as to receive a load pin  52  therethrough, further, the upper mount  41  is positioned above the upper base support, for support therefrom, while the lower mount  41 ′ is positioned above and supported by the lower base support  50 ′, thereby placing the reaction frame in an engaged, load bearing configuration with regard to the upper and lower base supports  41 ,  41 ′, and the load pin, such that load on the support surface  29  is transferred through upper  41  and lower  41 ′ mounts to upper  50  and lower  50 ′ base supports, respectively, which load passes on to the vessel. 
   Because of the incidence of the reaction frame with the bearing surfaces, the load pins are not particularly envisioned for use as a pivot, but rather to place the configuration into a load bearing configuration. Furthermore, to suit specific needs, the load pins may be engineered to have a profile other than cylindrical so as to resist pivoting. 
   When mounted in the deployed configuration, above, the lower base support  50 ′ receives loads from the reaction frame transmitted via two forces; the horizontal load  56  and the vertical  57  load, which are met with horizontal  58  and vertical  59  reaction efforts from the hull via bearing surfaces  60 ,  54 . Likewise, the upper base support  50  receives loads from the reaction frame transmitted via two forces, the horizontal  56 ′ load and the vertical  57 ′ load, which are met with horizontal  58 ′ and vertical  59 ′ reaction efforts from the hull via the installed  48  pivot pin  52  and upper base support  50 . The framework is thereby designed to transmit the reaction forces back to the main deck, cantilever support bulkheads, inner bottom and bottom structure. 
   An attribute or appendage  55  associated with the lower base support  50 ′ is shown as well, and depending on the loading, this appendage also can be used to transmit some of the vertical load by providing vertical support to the lower mount  41 ′ at bearing surface  54 . 
   In the preferred embodiment of the present invention, the pivot points are auxiliary and are positioned off center and separate from the load pin, for space conservation, as well as to provide a better incidence between the 2 bearing surfaces at the bottom, where the pivot point is offset from the 2 bearing surfaces (similar to a hinge mechanism). 
   As earlier indicated, the second end  44 ′ of the reaction frame is provided with support surface  29 . The support surface may include a raised engagement portion  46  which may be formed into the body, or may comprise a separate component, which may be adjustable as to height (i.e., vertically  38  adjustable via threaded engagement  37 , for example) or location on the upper edge  43 , the support surface formed to engage the underside of the cantilever beam(s), or otherwise engage and support the cantilever structure. 
   The engagement portion  46  may comprise a bearing surface of, for example, bronze, to provide low friction and corrosion resistance. The engagement portion (also may be referenced as a load pad) ideally will be adjustable to account for cantilever beam deflection under its own weight. A tapered bearing housing mounted on a slope may be provided for this purpose, which bearing housing may be selectively lockable at different positions to adjust the cantilever beam underside. 
   While the preferred embodiment of the auxiliary support structure of the present invention is shown as pivotal from a stowed to a deployed position, this pivotal operation is shown only as an example, and is not intended to be limiting. For example, other auxiliary support structures may also work in suitable fashion to accomplish the goals of the present invention which could comprise, for example, quick mount units engaging mounting brackets on the transom or other portion of the vessel which may be mounted prior to deploying the cantilever beam, and removed after retracting the cantilever beam, as required. 
   Further, mechanical devices may be utilized to position the reaction frames, adjust the raised engagement portion  46 , or to install or remove the load pins into the system, as required. 
   LIST OF ELEMENTS 
   # Description 
   
       
       R 1  point 
       R 2  point 
       R 3  support points 
         1  vessel 
         1  jack up vessel 
         2  cantilever beam 
         3  drill floor 
         4  platform jacket 
         4  platform 
         5  platform deck 
         6  drilling template 
         7 ,′ first and second stern reaction frames 
         8  drilling envelope 
         9  load charts before modification 
         10  “after modification 
         11  transom 
         12  portable support structure 
         13  tensioning unit 
         14  conductor 
         15  cantilever structure 
         16 ,  16 ′ first, second conductor tensioning members 
         17  first second ends 
       
         18 
       
       
         19 
       
         20  elevated 
         21  positioned 
         22  adjacent to 
         23  working position 
         24  retracted/stowed 
         25  deployed cantilever 
         26  pivoted 
         27 ,′ deployed support/reaction frame 
         28  above 
         29 ,′ support surface 
         30  well center 
         31 ,  31 ′ top, bottom 
         32 ,′ 
         33 ,′ 
         34  cantilever beam working envelope 
         35  distance support point  29  is projected by reaction frame (Example about ⅓  34 ) 
       
         36 
       
         37  threaded engagement 
         38  vertically adjustable 
         39  bulkhead 
       RF Reaction frame 
         40  body 
         41 ,′ upper, lower mounts 
         42  support surface 
         43  upper edge 
         44 ,′ first, second ends 
         45  pivot pin 
         46  raised engagement portion 
         47  upper, lower support members 
         48  installed 
         49  pivot 
         50 ,′ upper, lower base supports 
         51 ,′ longitudinally aligned bores 
         52  load pin 
         53  axial alignment 
         54  bearing surface 
         55  appendage 
         56  horizontal load 
         57  vertical load 
         58  horizontal reaction effort 
         59  vertical reaction effort 
         60  bearing surface 
     
  
   The invention embodiments herein described are done so in detail for exemplary purposes only, and may be subject to many different variations in design, structure, application and operation methodology. Thus, the detailed disclosures therein should be interpreted in an illustrative, exemplary manner, and not in a limited sense.