Dual hoist derrick system for deep sea drilling

Details Dual hoist derrick system for deep sea drilling Dual hoist derrick system for deep sea drilling

1997-09-22

2001-04-17

Bagnell, David (Department: 3673)

Hydraulic and earth engineering

Marine structure or fabrication thereof

With horizontally movable work deck

C175S005000

Reexamination Certificate

active

06217258

ABSTRACT:

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 be

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