Patent Publication Number: US-6217258-B1

Title: Dual hoist derrick system for deep sea drilling

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an offshore drilling system for drilling wells under the bottom of the sea from the surface of the water in the deep sea, and also for a collection of natural resources such as manganese nodule, nickel, cobalt rich clast and the like on the bottom. The deep sea in the present invention referred to a sea the depth being not less than 1000 m. 
     2. Description of the Related Art 
     Hitherto, according to the conventional floating offshore drilling unit, an object of drilling is about 500 m or less in the depth of the water, a floating drilling marine structure is equipped with a fixed derrick, and lifting up and down of pipes are performed by a drilling unit in which a substructure (including a drill floor and a derrick) does not travel. 
     Under drilling in a great depth, a hoist for lifting up and down various pipes undergoes various different loads in compliance with individual works. The maximum load is the sum total of weight of a very long riser pipe due to a large depth, weight of a BOP (blow-out prevention device) and dynamic load caused by a vertical motion of the hull due to a wave, a wind and a wave motion. For example, in case of laout 2500 m of depth of the water, there will be produced a large load such as about 1000 tons in the total weight. Thus, it is indispensable to set up a hoist having a drawbar pull not less than 1000 tons. 
     On the other hand, it is considered that the suspension weight of drill strings, which will yield when a drilling is carried out, is about 400 tons, assuming that a drilling depth is 10,000 m. Therefore, in consideration of only the case of drilling, it is a difficult requirement to provide a 1000 tons class of hoist. Further, in the time of working of a lifting up-and-down pipe for drill strings frequently carried out, a device having a great drawbar pull involves such a problem that a hoisting speed is down on a physical basis in view of excessive pulley diameter, rope diameter, number of stages of rope , and weight, whereby the working efficiency will be extremely lowered. 
     In offshore oil drilling and scientific drilling, in view of special characteristics of work, in many cases, there is performed a coring (sampling of a geologic stratum) work or the like. This causes working hours for a lifting up-and-down pipe for drill strings to be increased. Thus, there is a need to reduce the whole working hours by effectively practicing those processes at higher speed. 
     Further, it is required to reduce a lead time in view of bad weather in a possibility of a typhoon or the like. Drill strings or the like inside a riser pipe is less in resistance and involves no fear of detention. Thus, the use of the drill strings or the like inside a riser pipe makes it possible to contribute to a higher speed as to a lifting up-and-down pipe at the time of passage through the riser pipe. In view of the foregoing, there is a need to make full use of this merit or advantage through high speed hoisting. 
     Hitherto, according to works of horizontal traveling and storage for a BOP on a drilling dredge or ship, it happens that a lifting-down load is not less than 150 tons. Consequently, there is a problem that this involves various dangers when the BOP is lifted up and horizontally traveled. Works on the drilling dredge involve various dangers such as a collision of the BOP with heavy objects due to pitching and/or rolling of the drilling dredge or due to the sway of the BOP, an accident of a fall to the sea, and works on a high scaffolding. It contributes to providing high efficiency of works, labor saving and improvement in safety that works of horizontal traveling and lifting up and down for the BOP system are mechanically performed. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, it is therefore an object of the present invention to provide a novel dual hoist derrick system for deep sea drilling, which contributes to speeding up in hoist speed of offshore drilling units for a deep sea, reducing working hours and improvement in safety. 
     The present invention has been developed to solve the problems mentioned above. According to the present invention, as technical means, there is disclosed a dual hoist derrick system for deep sea drilling characterized in that a hoisting system for drilling and a hoisting system for heavy loading are arranged on a single derrick in parallel. The present inventors named the novel dual hoist derrick system for deep sea drilling as a “dragon lift”. In the dual hoist derrick system for deep sea drilling, said derrick is mounted on a skid beam capable of travelling in a horizontal direction so that said hoisting system for normal drilling and said hoisting system for heavy loading may travel to a working position. This feature makes it possible to optionally select a desired one of the hoisting systems promptly. Further, in the dual hoist derrick system for deep sea drilling, a setting place for a BOP is provided on a spider deck, and an upper substructure (including a drill floor), which is movable in a horizontal direction on the skid beam equipped with said derrick, is provided with a cut wider than a width of a BOP so that the BOP travels within the cut and said upper substructure can lift the BOP. This feature makes it possible to contribute to the stability of the ship in its entirety by lowering the height of the ship system so as to lower the center of gravity, and also to reduce the cost of the hull. It is acceptable that the BOP is lifted up directly by an oil cylinder, rack and pinion, and said hoisting system for heavy loading. This feature makes it possible to contribute to rationalization of a travelling device for the BOP and also to rationalization of works. Furthermore, in the dual hoist derrick system for deep sea drilling, a moon pool is formed with a round shape or an ellipse shape in its cross section, so that both the hoisting system for normal drilling and the hoisting system for heavy loading can be simultaneously used for works. This feature makes it possible to use both the hoisting systems at the same time, if necessary, thereby contributing to providing higher efficiency of works. 
     As described above, according to the present invention: a hoisting system for drilling and a hoisting system for heavy loading are arranged on a single derrick in parallel; the derrick is mounted on the upper substructure provided on the ship in such a way that the upper substructure is movable in a horizontal direction; the drilling hoisting system serves to perform a high speed lifting up and down; and the heavy load hoisting system deals with exclusively heavy load. These features make it possible to safely perform lifting up and down of heavy objects. Further, after reaching the drilling depth, the drilling hoisting system may insert casings promptly; lift up and down speeds of the drill strings may be increased; and during a drilling, it is easy to control load to be applied to bits mounted on the lower end of the drill strings. These make it possible to efficiently perform oil drilling and scientific drilling in great depth. Further, according to the present invention, for example, when a typhoon or the like comes, the drilling hoisting system may hoist the drilling strings to take measures to meet the situation. 
     Further, according to the present invention, when drilling workers perform working for a shift of the BOP within the ship, there is no need to perform works such as a wire furnishing, thereby reducing works for pulley change, re-suspension. In addition, the work in the drill floor is a main work. Thus, works on a high scaffolding are reduced and safety is improved. Furthermore, according to the present invention, the drill floor is formed lower than the top of the BOP, and the upper substructure skidding on the surface of the lower substructure in a horizontal direction is provided with a cut broader than the BOP. These features make it possible to lower the center of gravity of the drilling dredge. 
     Consequently, a rolling of the hull becomes little, and thus it is possible to expect a stable operation or work, thereby making it easy to perform the works in its entirety. Still further, according to the present invention, a moon pool is formed with a round shape or an ellipse shape in its cross section, so that both the hoisting system for drilling and the hoisting system for heavy loading can be simultaneously used for works. This feature makes it possible to use both the hoisting systems at the same time, thereby contributing to reduction of a large amount of working hours and providing higher efficiency of works in great depth of drilling. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevation of a drilling dredge according to an embodiment of the present invention. 
     FIG. 2 is a side elevation of a drilling dredge according to an embodiment of the present invention. 
     FIG. 3 is a perspective view showing a state in which a BOP is loaded. 
     FIG. 4 is an explanatory view useful for understanding a working state of a hoisting system for drilling. 
     FIG. 5 is an explanatory view useful for understanding a working state of a hoisting system for heavy loading. 
     FIG. 6 is a perspective view showing a relation between a skid beam and an upper substructure. 
     FIG. 7 is a perspective view showing a relation between a skid beam and an upper substructure. 
     FIG. 8 is an explanatory view useful for understanding a state in which an upper substructure travels to lift up a BOP. 
     FIG. 9 is an explanatory view useful for understanding a state in which a BOP is moved to a moon pool. 
     FIG. 10 is an explanatory view useful for understanding a state in which both the hoisting system for drilling and the hoisting system for heavy loading are simultaneously operated. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, there will be described embodiments of the present invention referring to the accompanying drawings. 
     FIG. 1 is a side elevation of a drilling dredge  1  according to an embodiment of the present invention. The drilling dredge  1  or ship floats in surface  2  of water. A derrick  10  set up on the ship  1  is equipped with both a hoisting system  20  for normal drilling and a hoisting system  40  for heavy loading. FIG. 1 shows a state in which a drill strings  34  extends from the drilling hoisting system  20  to a drill aperture on bottom  3  of the sea and further extends into a base  35  with a reentry guide cone. 
     The drilling hoisting system  20  comprises a travelling block  21  movable in a vertical direction, a top drive system  22  for providing a rotation for the drill strings, a hook block  23 , a hoisting accessary system  24  composed of an elevator, link and the like, a hoisting drum, i.e. a drum  25  of the drilling hoisting system, and a rotary table  26 . Those elements are coupled with each other in series in the named order to suspend the drill strings  34 . The drill strings  34  are stored in a drill string storage space  37  called as a pipe rack, and are handled with a drill floor outside drill strings handling system  36 . Further, the drill strings  34  are lifted up by a drill floor inside drill strings handling system  31 , coupled with the top of the drill strings  34  stored in such a fashion that the strings are suspended perpendicularly with respect to a setback  91 , and then descends through a pipe centering system  33 . The drilling hoisting system  20  serves as a high speed pipe lift up-and-down system. 
     The derrick  10  is equipped with the drilling hoisting system  20  and the heavy load hoisting system  40  as well in such a relation that both the systems are arranged in parallel to one another. The heavy loading hoisting system  40  comprises an upper crown block  41 , a vertical motion travelling block  42 , a hook block  43 , a hoist drum  44  of a riser winch and a rotary table  45  on which the hoist drum  44  is put. The heavy load hoisting system  40  serves to suspend heavy load. In such a heavy load hoisting system  40 , many pulleys are used to put a wire rope round the pulleys on a multiple stage basis. The heavy load hoisting system  40  serves as a low speed and great load of hoisting system. On the ship, there are provided a riser storage space  52  referred to as a riser rack, a drill floor outside handling system  51  and a riser tensioner  53 . 
     FIG. 2 is, similar to FIG. 1, a side elevation of a drilling dredge  1 . A different point from FIG. 1 is that the derrick  10  horizontally travels, and the heavy load hoisting system  40  suspends a BOP  70  and a riser pipe  80  up to the place of the bottom  3  of the sea. The derrick  10  is put on a drill floor of an upper substructure  61 . A movement of the upper substructure  61  on a skidding floor of a lower substructure  62  makes it possible to change a position of the derrick  10 . 
     FIG. 3 is a perspective view showing a state in which a BOP  70  is loaded on a spider deck  71 , and top  72  of the BOP  70  projects over the upper substructure  61  and a drill floor  93 . In other words, the drill floor  93  is set up at the position lower than the top of the BOP  70 . And each of the upper substructure  61  movable on a surface of the lower substructure  62  in a horizontal direction and the drill floor  93  is provided with a cut  63  wider than the BOP  70 . 
     FIG. 4 is an explanatory view useful for understanding a working state of the drilling hoisting system  20  in which a riser pipe  80  is suspended into water, and the drill strings  34  are suspended passing through the riser pipe  80 . 
     FIG. 5 is an explanatory view useful for understanding a working state of the heavy load hoisting system  40  in which the BOP  70  and the riser pipe  80  are suspended. Each of FIGS. 6 and 7 is a perspective view showing a relation between the upper substructure  61  and the lower substructure  62 . The upper substructure  61  is provided with a drill floor  93 . The upper substructure  61  skids on the surface of the lower substructure  62 . The upper substructure  61  is provided with the cut  63  wider than the BOP  70 , in the front of a forward direction, and is so arranged that when the upper substructure  61  skids backward, the BOP  70  is accommodated in the cut  63 . 
     FIG. 8 is an explanatory view useful for understanding a state in which the upper substructure  61  travels to lift up the BOP  70 , and the heavy load hoisting system  40  lifts up the BOP  70  accommodated in the cut  63 . In this manner, according to the present invention, it is possible to perform works promptly, safely and efficiently, since the heavy load hoisting system  40  is used to lift up and down the BOP  70 , without the use of the revolving crane in the drilling dredge for the purpose of a movement of the BOP. 
     FIG. 9 is an explanatory view useful for understanding a state in which the upper substructure  61  terminates in skid and the heavy load hoisting system  40  lifts up the riser pipe on which the BOP is mounted, and the lifted up BOP  70  is moved to a moon pool  90 . 
     FIG. 10 is a n explanatory view useful for understanding a state in which both the drilling hoisting system  20  and the heavy load hoisting system  40  are simultaneously operated. The drilling hoisting system  20  suspends the drill strings  34 , and the heavy load hoisting system  40  suspends the riser pipe  80 . For the reason, the moon pool  90  is formed with a round shape or an ellipse shape in its cross section, so that both the hoisting system for drilling and the hoisting system for heavy loading can simultaneously pass through.