Patent Publication Number: US-2015060137-A1

Title: Tender Barge for Drillship Operating in Environmentally Sensitive Areas

Description:
BACKGROUND 
     The disclosure relates to tender barges used in association with drill ship floating drilling platforms. More specifically, the disclosure relates to a tender barge that can store materials used during drilling operations on a drill ship and that can store waste products resulting from such drilling operations until the drilling operations are completed and the drill ship is moved from the drilling location. The tender barge may also act as the mooring facility for the drilling vessel. 
     Drill ships are one type of floating drilling platform that may be used to drill wellbores through formations below the bottom of a body of water such as a lake or the ocean. Drill ships may be used in environmentally sensitive areas such as the Arctic. Regulations governing drilling activities in such environmentally sensitive areas may require that no formation cuttings or other waste products, e.g, produced water and/or oil from a formation, resulting from drilling a wellbore be discharged into the water. Further, air pollution regulations may require that only a limited number of additional fossil fuel powered vessels be permitted to operated within a predetermined distance from the drill ship. 
     There is a need for a tender vessel that can store sufficient quantities of consumables for drilling operations at one or more selected well locations and that can store waste products generated as a result of the drilling operations. 
     SUMMARY 
     A tender barge for a drill ship includes a hull internally segmented into compartments. The compartments are for storing wellbore drilling consumables and wellbore drilling waste. The hull has an opening therein for positioning under a moon pool of a drill ship. The barge hull further includes a support structure for contacting a bottom of a hull of a drill ship when the drill ship is positioned over the barge hull. The barge has a mooring system having capacity to either hold the barge in position or hold both the barge and the drill ship when the drill ship is fully supported by the barge out of the water over a wellbore location. 
     A method for drilling a wellbore using a drill ship and a tender barge includes moving the tender barge to a well drilling location. The tender barge is moored on location. The drill ship is moved so that a moon pool therein is positioned over a corresponding opening in a hull of the tender barge. The tender barge is deballasted until a support structure on the hull thereof contacts a corresponding structure on a bottom of the drill ship. Thereafter the tender barge is ballasted to maintain the drill ship in a trim condition for drilling operations. 
     Other aspects and advantages will be apparent from the description and claims which follow. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1 ,  2  and  3  show end views of an example tender barge. 
         FIG. 4  shows a plan view of the tender barge anchored to the water bottom. 
         FIG. 5  shows an oblique view of the example barge of  FIG. 4 . 
         FIG. 6  shows a view of an example barge rotated  90  degrees from the views in  FIGS. 1 ,  2  and  3 . 
         FIG. 7  shows a plan view of an example drill ship. 
         FIG. 8  Shows a portion of the drill ship hull that may be supported by an example barge. 
         FIG. 9  shows a side view of a drill ship indicating an approximate water line. 
         FIGS. 10 ,  11  and  12  show the drill ship positioned in a receiving area of the example barge. 
         FIG. 13  shows a plan view of the drill ship positioned above the barge. 
         FIG. 14  shows a side view of the drill ship positioned above the barge, wherein the barge supports with weight of the drill ship. 
         FIGS. 15 and 16  show more detailed views of the receiving area of the barge. 
         FIG. 17  shows a plan view of an example of the barge which is moored but does not support the weight of the drill ship. 
         FIG. 18  shows a side view of the barge of  FIG. 17 . 
         FIG. 19  shows an end view of the drill ship positioned over the barge, wherein the drill ship weight is not supported by the barge. 
         FIG. 20  shows and end view as in  FIG. 19 , wherein the drill ship is in contact with the barge but the weight thereof is not supported by the barge. 
         FIG. 21  shows a plan view of the drill ship and barge of  FIG. 20 . 
         FIG. 22  shows a side view of the drill ship and barge of  FIG. 21 . 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1 ,  2  and  3  show end views of an example tender barge  10  for use in connection with a drill ship. The barge  10  may include a plurality of anchor lines  12  to moor the tender barge  10  to the water bottom. The barge  10  may include a support platform  10 A with a center opening  10 B to correspond to the position of the moon pool on the drill ship when the drill ship is moved over the tender barge  10 , as will be further explained below. The interior of the hull of the tender barge  10  may include segregated compartments (not shown separately) for storage of fuel, fresh water cement and other consumables used during drilling operations. Other compartments (not shown separately) in the barge hull may be used, for example, to store drill cuttings, waste water from drilling/production testing and any unburned liquids from such testing. During drilling operations, prior to arrival of the drill ship, the barge  10  is moved to a well location, for example, by a towing vessel. Other examples of the barge  10  may be self propelled. Once the barge  10  is moved to the well location, mooring lines  12  may be deployed and tensioned. 
       FIG. 4  shows the barge  10  in plan view with the mooring lines  12  deployed in a selected pattern.  FIG. 5  shows the example barge  10  in oblique view so that more of the barge features may be observed.  FIG. 6  shows a side view of the barge  10 , wherein may be observed the opening  10 B in the hull to be positioned beneath the moon pool of the drill ship. 
       FIG. 7  shows a plan view of an example drill ship  14  to illustrate the position of the drilling unit  14 A thereon and the position of the moon pool  14 B.  FIG. 8  shows a cut away end view or cross sectional view of the drill ship  14  to illustrate the portions of the drill ship hull, particularly the moon pool  14 B, that are to be disposed over the barge ( 10  in  FIG. 1 ). A side view of the drill ship  14  showing the approximate position of the water line  16  may be observed in  FIG. 9 . 
     In the present example, the drill ship hull may be fully supported by buoyancy provided by the barge ( 10  in  FIG. 1 ). During operation, the drill ship ( 14  in  FIG. 7 ) is moved into position above the barge ( 10  in  FIG. 1 ), and the barge may be deballasted (e.g., by pumping water out of ballast chambers therein) so that its buoyancy supports the weight of the drill ship ( 14  in  FIG. 7 ).  FIG. 10  shows an end view/cross sectional view of the drill ship  14  moved into position above the barge  10 , after the barge  10  has been moored as shown in  FIG. 4 . Note that there is a gap between the base of the hull of the drill ship  14  and the support structure on the barge  10 . Thereafter the tender barge  10  is ballasted to maintain the drill ship  14  in a trim condition for drilling operations. 
       FIG. 11  shows the barge  10  being deballasted. The support structure on the barge  10  is now in contact with the base of the drill ship  14  hull. In  FIG. 12 , the barge  10  is fully deballasted and the drill ship  14  may be moved upwardly so that no part of the drill ship  14  hull is beneath the water surface. 
       FIG. 13  shows the drill ship  14  disposed on the barge  10 , wherein the barge  10  is fully moored.  FIG. 14  shows a side view of the drill ship  14  and barge  10  combination wherein the drill ship  14  is fully supported out of the water. It will be appreciated by those skilled in the art that the mooring system for the barge  10 , and the amount of buoyancy provided by the barge  10  may be selected to maintain position of both the barge  10  and the drill ship  14 , and to fully support the weight in air of the drill ship  14 , including any downward force exerted by the drill ship  14  during drilling operations. Such downward force may be as much as is capable of being supported by the drilling unit, as a non-limiting example, two million pounds. 
     Another example of the barge  10  is shown in end view/cross section in  FIG. 15 . The example shown in  FIG. 15  may have buoyancy sufficient to hold the barge  10  in position when suitably moored, however, such example of the barge  10  may not be required to support the weight of the drill ship  14 . Another end view/cross section of the present example barge  10  is shown in  FIG. 16 . 
       FIG. 17  shows the example barge  10  of  FIGS. 15 and 16  in plan view, including a mooring system having been deployed. The number of mooring lines  12  may be fewer than the example shown in  FIG. 13  because the barge mooring is not required to support the weight of the drill ship  14 . A side view of the present example barge  10  is shown in  FIG. 18 . In operation, the barge  10  may be moved to a well drilling location and moored in place. The drill ship  14  may then be moved into position over the barge. This is shown in end view/cross section in  FIG. 19 . The barge  10  may then be deballasted, as explained with reference to the previous example and shown in  FIGS. 10 ,  11  and  12 , however, as shown in  FIG. 20 , the base of the drill ship  14  hull may just contact the support structure  10 A without transfer of any substantial amount of the weight of the drill ship  14  to the support structure  10 A. 
       FIG. 21  shows a plan view of the barge and drill ship of the present example. 
       FIG. 22  shows the barge  10  and drill ship  14  in side view. Notably, the drill ship  14  is immersed in the water, wherein the approximate position of the water line  16  on the drill ship  14  hull is shown. The drill ship  14  may be dynamically positioned, for example, using thrusters as known in the art. 
     It is contemplated that when the drill ship  14  is positioned over the barge  10 , in either the present example or the previous example, various lines (not shown separately —which may be rigid conduits having suitable swivel and other connections, or may be or may include flexible hose) may be connected between the drill ship  14  and the appropriate compartment (not shown) in the barge  10 . Pumps (not shown) to transfer the various materials stored in the barge to and from the drill ship may be located on the drill ship  14 , on the barge  10  or both. In the present two examples, deballasting pump(s) may be disposed on the barge  10 . Such pumps (not shown) may be powered by equipment on the barge  10 , or may be powered, for example by electric power communicated from the drill ship  14 . 
     After drilling operations are completed, the barge  10  may be reballasted to come out of contact with the drill ship  14  (i.e., the drill ship  14  is in free flotation). The drill ship  14  may then move away from the wellbore location, e.g., to a next wellbore location. The barge  10  may then be unmoored, deballasted and moved to another location for emptying the compartments holding waste materials, and refilling the compartments storing the consumables to be used on a subsequent well drilling operation. 
     A tender barge according to the various examples explained herein may provide wellbore drilling operators with means to eliminate discharge of drilling waste into the water, and may provide enough consumables to avoid the necessity of having any other self powered vessels approach the vicinity of the drill ship during drilling operations. 
     While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.