Abstract:
A drilling derrick ( 1 ) for offshore drilling operations arranged to be a protecting enclosure ( 3 ) accommodating a drill pipe device adapted to perform drilling operations and allowing a pipe section to be moved to and from the drilling derrick ( 1 ), the drilling derrick ( 1 ) accommodating a pipe racking structure for stacking and retaining pipe sections for use in drilling operations, the drilling derrick ( 1 ) is adapted to be mounted on a deck ( 2 ). The drilling derrick ( 1 ) comprising a stressed-skin structure having external load carrying panels ( 3 ). The invention also relates to an offshore platform comprising at least one drilling derrick ( 1 ).

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to the field of offshore drilling, and more particularly, to weather protected offshore drilling having a drilling derrick mounted on a deck of an offshore platform, including, but not limited to drill ship or drill platform or drill rig. 
       BACKGROUND 
       [0002]    Today, there exist various examples of weather protected offshore drilling solutions. These solutions refer to conventional truss or framework structured drilling derricks having a limited weather protected work area. 
         [0003]    These types of drilling derricks, restricted to truss or framework drilling derricks also provide heavy and bulky constructions. Further, these present examples are restricted to a time consuming assembly, installation, maintenance, and have limited construction flexibility. 
         [0004]    U.S. Pat. No. 4,613,001 describes a type of derrick which is enclosed in a weather protecting cover, from which tunnels extend out over the drill deck and comprises lifting means for handling of pipes and tubes between the drill deck and an underlying main deck. This type of drilling derrick is restricted to conventional truss or framework structured derricks providing a heavy and bulky construction for the offshore drilling. 
         [0005]    There is thus a need for an improved drilling derrick removing the above mentioned disadvantages. 
       DESCRIPTION OF INVENTION 
       [0006]    The present invention relates to the field of weather protected drilling derricks for offshore drilling providing for weather protected storage, handling and working area within the drilling derrick. More specifically, the present invention relates to a solution with stressed-skin structure where weather protection and load carrying structure is combined in the external enclosure forming the drilling derrick. It is desirable to provide relatively light-weight and relatively non-bulky and compact drilling derrick constructions having weather protected storage, handling and working area. 
         [0007]    The object of the present invention is to suggest an improved and easy to implement drilling derrick for offshore drilling which improves the working and storage environment for drilling operations and reduces the weight of the drilling derrick. 
         [0008]    The present invention is defined by the appended independent claims. Various examples of the invention are set forth by the appended dependent claims as well as by the following description and the accompanying drawings. 
         [0009]    With the above description in mind, then, an aspect of the present invention is to provide an improved solution of a drilling derrick construction which seeks to mitigate, alleviate, or eliminate one or more of the above-identified deficiencies in the art and disadvantages singly or in any combination. 
         [0010]    The object is achieved by the features of claim  1  wherein, a drilling derrick for offshore drilling operations arranged to be a protecting enclosure accommodating a drill pipe device adapted to perform drilling operations and allowing a pipe section to be moved in and out of the drilling derrick, the drilling derrick accommodating a pipe racking structure for stacking and retaining pipe sections for use in drilling operations, the drilling derrick is adapted to be mounted on a deck, characterised in that the drilling derrick comprising a stressed-skin structure having external load carrying panels. Thereby, the drilling derrick is a relatively light-weight construction. Since the drilling derrick is a stressed-skin structure construction it enables a flexible construction which can be adapted to be shaped such that the effect of wind forces acting on the drilling derrick can be reduced. No additional parts, load-bearing frameworks or trusses are required to provide the inventive drilling derrick since the inventive drilling derrick is a stressed-skin structure having external load carrying panels. This enables a relatively non-bulky and compact drilling derrick having reduced weight. 
         [0011]    According to a further advantageous aspect of the invention, the external load carrying panels are external stiffened panels comprising of outer plating skins reinforced by inner vertical stiffeners and inner horizontal rib members in a substantially rectangular pattern, wherein the stressed-skin structure will provide the support load carrying structure for loads acting on the drilling derrick, and the stressed-skin structure will simulataneously provide weather protection. 
         [0012]    According to a further advantageous aspect of the invention, the external load carrying panels are external corrugated panels comprising of corrugated plates having vertical corrugations and horizontal rib members, wherein the stressed-skin structure will provide the support load carrying structure for loads acting on the drilling derrick. 
         [0013]    According to a further advantageous aspect of the invention, the drilling derrick comprises closable openings for transferring items, such as for example drill pipes and other drilling equipment, in and out of the drilling derrick. 
         [0014]    According to a further advantageous aspect of the invention, the drilling derrick is positioned upon the deck of an offshore platform, such as a drillship or drilling rig or drilling platform. 
         [0015]    According to a further advantageous aspect of the invention, the drilling derrick has a substantially rectangular horizontal cross section. The horizontal cross section has a surface which may vary in size over the height of the drilling derrick. A flexible construction is provided with the stressed-skin drilling derrick which may be of any type of suitable geometrical form. Whereby, the drilling derrick can provide a relatively large area within the drilling derrick while at the same time providing a relatively compact and non-bulky drilling derrick. According to a further advantageous aspect of the invention, the substantially rectangular horizontal cross section of the drilling derrick may vary in size over the height of the drilling derrick, from a bottom part of the drilling derrick supported on the deck to a top part of the drilling derrick. According to a further advantageous aspect of the invention, the cross section of the top part of the drilling derrick is smaller than the cross section of the bottom part of the drilling derrick. The cross section surface may vary in size from the top part to the bottom part of the drilling derrick. According to a further advantageous aspect of the invention, corners of the drilling derrick may be rounded. 
         [0016]    According to a further advantageous aspect of the invention, the drilling derrick has a substantially round or elliptical horizontal cross section. According to a further advantageous aspect of the invention, the substantially round or elliptical horizontal cross section of the drilling derrick may vary in size over the height of the drilling derrick, from a bottom part of the drilling derrick supported on the deck to a top part of the drilling derrick. According to a further advantageous aspect of the invention, the cross section of the top part of the drilling derrick having a substantially round or elliptical horizontal cross section is smaller than the cross section of the bottom part of the drilling derrick. 
         [0017]    According to a further advantageous aspect of the invention, the drilling derrick comprises outward extending stiffened panels at a lower part of the drilling derrick where a cross section surface of the lower part is at least 50 percent larger than the largest cross section surface of the upper part of the drilling derrick, such that a larger enclosed area above the deck is provided. The stiffened panels can be arranged to provide the enlarged lower part. According to a further advantageous aspect of the invention, the lower part of the drilling derrick is arranged to correspond with structures below the deck, i.e. the main load-bearing structures of the offshore platform. 
         [0018]    According to a further advantageous aspect of the invention, a raised drill floor is arranged and integrated in the drilling derrick above the deck. Thereby, the drilling derrick may provide for structural continuity where the loads acting on the drilling derrick, such as for example loads caused by drilling operations and/or wind forces, may be distributed in a suitable manner. Further, the integrated raised drill floor may provide for more space above the deck. 
         [0019]    According to a further advantageous aspect of the invention, an offshore platform comprises at least one drilling derrick. According to a further advantageous aspect of the invention, an offshore platform comprises two drilling derricks. 
         [0020]    Any of the advantageous features of the present invention above may be combined in any suitable way. 
         [0021]    A number of advantages are provided by means of the present invention, for example:
       providing a solution with a light-weight construction is obtained;   an improved drilling derrick is obtained allowing for non-bulky, compact and flexible construction;   an improved drilling derrick is obtained allowing for a weather protected working and storage environment;   improved drilling derrick is obtained for windloads to be reduced;   an improved integration with the main load-bearing structures of the offshore platform is obtained allowing for an improved load distribution for the drilling derrick;   simplified installation and maintenance is allowed.       
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]    The present invention will now be described in detail with reference to the figures, wherein: 
           [0029]      FIG. 1  schematically shows a pictorial representation of a stressed-skin drilling derrick according to the invention. 
           [0030]      FIG. 2  schematically shows a pictorial representation of a stiffened panel according to the invention. 
           [0031]      FIG. 3  schematically shows a pictorial representation of a stressed-skin drilling derrick having an enlarged lower part according to the invention. 
           [0032]      FIG. 4  schematically shows a pictorial representation of stressed-skin drilling derrick having an integrated drill floor structure according to the invention. 
       
    
    
       [0033]    It should be added that the following description of the examples is for illustration purposes only and should not be interpreted as limiting the invention exclusively to these examples/aspects. 
       DETAILED DESCRIPTION 
       [0034]    All the  FIGS. 1 to 4  are schematically illustrated. 
         [0035]    The following examples of the present invention relate, in general, to the field of offshore drilling in particularly, to offshore drilling using drilling derricks for weather protected drilling operations. 
         [0036]    Examples of the present invention will be described more fully hereinafter with reference to the accompanying drawings, in which examples of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the examples set forth herein. Rather, these examples are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like reference signs refer to like elements throughout. 
         [0037]      FIG. 1  show an example of an inventive stressed-skin drilling derrick  1  mounted on a deck  2 , wherein the drilling derrick  1  is a welded load-bearing unitary construction. The drilling derrick  1  comprises a plurality of stiffened panels  3  which are respectively attached to the opposing edges  4  of adjacent external stiffened panels or adjacent structural sections which may constitute part of the drilling derrick  1 . The drilling derrick  1  may either fully or partly comprise of stiffened panels  3 . 
         [0038]    Further, the drilling derrick  1  may vary in size over the height of the drilling derrick  1 , from a bottom part  9  of the drilling derrick  1  supported on the deck  2  to a top part  10  of the drilling derrick  1 . The drilling derrick  1  is arranged to accommodate any suitable equipments for drilling operations, such as for example a drill pipe device (not shown), pipe sections (not shown) and a pipe racking structure (not shown). The drilling derrick  1  comprises closable openings (not shown). The drilling derrick  1  may be adapted to provide a relatively large working, handling and storage area inside the drilling derrick  1 . 
         [0039]    The stressed-skin construction technique which is used in the inventive drilling derrick  1  supports structural loads by using the exterior or shell of the drilling derrick  1 , as opposed to using a conventional drilling derrick having a load-bearing frame or truss which is then covered with a non-load-bearing skin or coachwork. The stiffened panels  3  constitute the exterior or shell of the drilling derrick  1 . 
         [0040]      FIG. 2  schematically shows a pictorial representation of a stiffened panel  3  according to the invention. The external stiffened panel  3  comprises an outer plating skin  7  reinforced by inner vertical stiffeners  5  and inner horizontal rib members  6  in a substantially rectangular pattern  8 . The inner vertical stiffeners  5  and inner horizontal rib members  6  may be mounted and connected to the outer plating skin  7  by any conventional method such as welding, screwing, riveting or bolting. Preferably, the inner vertical stiffeners  5  and inner horizontal rib members  6  are mounted and connected to the outer plating skin  7  and to each other by welding. Normally, when the inventive drilling derrick  1  is mounted as a unitary construction on the deck  2  of an offshore platform, the inner horizontal rib members  6  are horizontal and the inner vertical stiffners  5  are substantially vertical. 
         [0041]    The inner vertical stiffeners  5  and the inner horizontal rib members  6  may be any type of structural member such as for example HP-bulb profile, L-profile, Flat bar profile, Trapetzoid-profile, Box-profile, U-profile or T-profile. The inner vertical stiffeners  5  and the inner horizontal rib members  6  in a stiffened panel  3  may be of different types structural members. The inner vertical stiffeners  5  and the inner horizontal rib members  6  in a stiffened panel  3  may be the same type of structural member. 
         [0042]    The stiffened panels  3  which are used in the stressed-skin structure of the drilling derrick provide a type of construction in which the outer plating skins  7  and the inner vertical stiffeners  5  and inner horizontal rib members  6  interact, thus contributing to the overall strength of the drilling derrick. 
         [0043]    The stiffened panels  3  can be mounted and connected to each other by any conventional method such as for example welding, screwing, riveting or bolting. Preferably, the stiffened panels  3  are mounted and connected to each other by welding. 
         [0044]    The stiffened panel  3  may comprise of any suitable number of inner vertical stiffeners  5 . The stiffened panel  3  may comprise of any suitable number of inner horizontal rib members  6 . Normally, the stiffened panel comprise of more inner vertical stiffeners  5  than inner horizontal rib members  6 . 
         [0045]    The inner vertical stiffeners  5  and the horizontal rib members  6  are arranged to be mounted and connected to each other at inner crossing sections  11 . The inner vertical stiffeners  5  and inner horizontal rib members  6  are arranged in the rectangular pattern  8  having inner crossing sections  11 , where either the inner vertical stiffeners  5  or the horizontal rib members  6  may be mounted and connected to each other and arranged through each other at the inner crossing sections  11 . The connection of the inner vertical stiffeners  5  and inner horizontal rib members  6  at the inner crossing sections  11  may be done by using any conventional method such as for example welding, screwing, riveting or bolting. Preferably, the inner vertical stiffeners  5  and the horizontal rib members  6  are mounted and connected to each other by welding. 
         [0046]    The stiffened panel  3  comprising the outer plating skin  7 , the inner vertical stiffeners  5  and the inner horizontal rib members  6  can be made of any suitable material. The stiffened panels  3  can be arranged to be connected to each other forming any suitable geometrical form, for example such that wind force influence on the drilling derrick can be reduced. Thus, the inventive solution can simultaneously provide both a weather protected working, handling and storage area and a non-bulky and light-weight drilling derrick which also can reduce the wind force influence on the drilling derrick. 
         [0047]      FIG. 3  shows an example of a drilling derrick  31  having an enlarged lower part  32 , such that a larger enclosed working, handling and storage area above the deck  2  can be provided. The drilling derrick  31  comprises extending stiffened panels  33  at a lower part  32  of the drilling derrick  31 , such that a larger enclosed area above the deck  2  is provided. The lower part  32  of the drilling derrick  31  has a cross section surface which is substantially larger than the largest cross section surface of the upper part  34  of the drilling derrick  31 . The lower part  32  of the drilling derrick  31  has a cross section surface which is at least  50  percent larger than the largest cross section surface of the upper part  34  of the drilling derrick  31 . This drilling derrick  31  having an enlarged lower part  32  may provide a larger enclosed area above the deck  2  than if it had a continuous variation in size from the top part to the bottom part of the drilling derrick. 
         [0048]      FIG. 4  shows an example of a drilling derrick  41  having a raised integrated drill floor structure  42 , such that additional working, handling and storage area can be provided at the deck  2 . The raised drill floor  42  is arranged above the deck  2  on which the drilling derrick  41  is mounted. 
         [0049]    The drilling derrick according to the invention may be used in any type appropriate drilling operation. Several drilling derricks according to the invention may be provided on the deck of an offshore platform. 
         [0050]    The drilling derrick may be a multiple activity drilling derrick providing accommodation for multiple drilling pipe devices, pipe section and pipe racks. 
         [0051]    The invention is not limited to the example described above, but may be modified without departing from the scope of the claims below. 
         [0052]    The terminology used herein is for the purpose of describing particular examples only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” “comprising,” “includes” and/or “including” when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
         [0053]    Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
         [0054]    The foregoing has described the principles, preferred examples and modes of operation of the present invention. However, the invention should be regarded as illustrative rather than restrictive, and not as being limited to the particular examples discussed above. The different features of the various examples of the invention can be combined in other combinations than those explicitly described. It should therefore be appreciated that variations may be made in those examples by those skilled in the art without departing from the scope of the present invention as defined by the following claims. 
       Reference Signs 
       [0055]      1 : Drilling derrick 
         [0056]      2 : Deck 
         [0057]      3 : Stiffened panel 
         [0058]      4 : Opposing edges 
         [0059]      5 : Inner vertical stiffener 
         [0060]      6 : Inner horizontal rib member 
         [0061]      7 : Outer plating skin 
         [0062]      8 : Rectangular pattern 
         [0063]      9 : Bottom part of drilling derrick 
         [0064]      10 : Top part of drilling derrick 
         [0065]      11 : Inner crossing section 
         [0066]      31 : Drilling derrick 
         [0067]      32 : Enlarged lower part of drilling derrick 
         [0068]      33 : Outward extending stiffened panels 
         [0069]      34 : Upper part of drilling derrick 
         [0070]      41 : Drilling derrick 
         [0071]      42 : Integrated drill floor structure