Hydraulic and earth engineering – Subterranean or submarine pipe or cable laying – retrieving,... – Submerging – raising – or manipulating line of pipe or cable...
Reexamination Certificate
1998-09-16
2001-04-24
Lillis, Eileen D. (Department: 3673)
Hydraulic and earth engineering
Subterranean or submarine pipe or cable laying, retrieving,...
Submerging, raising, or manipulating line of pipe or cable...
C405S152000, C405S192000, C405S202000, C405S224200, C114S230120, C114S230130, C166S355000, C166S359000, C166S360000, C441S005000
Reexamination Certificate
active
06220787
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a weathervaning floating oil or gas production system configured to transport oil or gas from subsea wells to a ship type surface vessel on the sea.
2. Description of the Related Art
A ship type floating oil production system has been used as an off-shore oil/gas development platform. In such a system, in order to cope with pitching and rolling of a surface vessel induced by external forces, conduits called flexible risers are used to connect subsea wellheads and the surface vessel carrying processing facilities, thereby enabling the transporting of a produced fluid from subsea wells to the surface vessel on the sea. In such a system, when access to wells becomes necessary for workover operations or like work, another surface vessel specifically designed for such work must be chartered. Accordingly, in an offshore oil/gas field involving frequent access to wells, the economical efficiency of oil/gas development is worsened by the chartering of such a surface vessel.
SUMMARY OF THE INVENTION
In view of the above mentioned problems involved in the conventional ship type floating oil production system, an object of the present invention is to provide a weathervaning floating oil production system which simplifies access to subsea wells through installation of surface wellheads on a ship type surface vessel on the sea.
To achieve the above object, the present invention provides a weathervaning floating oil or gas production system comprising a ship type surface vessel, a cylindrical turret, a plurality of riser pipes, a plurality of surface wellheads, a manifold, and a swivel mechanism. The cylindrical turret is located within a moon pool formed in the ship type surface vessel and moored to a seabed. The riser pipes have a rigid structure and extend downward to subsea wells through the cylindrical turret. The surface wellheads include valves of the riser pipes and are connected to a production flow line on the ship type surface vessel via the manifold and the swivel mechanism.
Preferably, the riser pipes are arranged along the inner circumference of the turret, and the ship type floating oil production system further comprises a workover rig for workover operations and a riser pipe movement mechanism. The workover rig stands, along the vertical centerline or central ovis of the turret, on the ship type surface vessel via support legs. The riser pipe movement mechanism is adapted to move each riser pipe to a position located just under the workover rig.
Preferably, the riser pipe movement mechanism comprises a ringed support frame, a plurality of stationary guide rails, and a swivel guide rail. The ringed support frame is concentrically arranged within the cylindrical turret. The stationary guide rails extend radially between the ringed support frame and the cylindrical turret for guiding respective riser pipes. The swivel guide rail is rotatably provided within the ringed support frame so as to be selectively connected to one of the stationary guide rails in order to further guide to a position located just under the workover rig a riser pipe which has been guided to the ringed support frame along the corresponding stationary guide rail.
Each of the riser pipes preferably has a connector located under the bottom surface of a bottom portion of the ship type surface vessel.
The ship type floating oil production system preferably further comprises a diver entrance chamber and water introduction-discharge means provided in a bottom portion of the ship type surface vessel in the vicinity of a lower end portion of the turret. The diver entrance chamber is equipped with an inner watertight door and an outer watertight door and used by a diver who engages in disconnecting or connecting the connectors. The water introduction-discharge means introduces water into or discharge water from the diver entrance chamber.
In the weathervaning floating oil or gas production system of the invention, the ship type surface vessel is freely rotatable about the cylindrical turret located within the moon pool formed in the ship type surface vessel. Accordingly, as in the case of a conventional ship type floating oil production system, a bow portion of the ship type surface vessel faces to windward. Therefore, the ship type surface vessel is moored in a state less resistant to wind. Also, oil is safely transported from subsea wells to the system through the riser pipes which extend downward to the subsea wells through the cylindrical turret.
The riser pipes have a rigid structure, and the surface wellheads including valves of the riser pipes are connected to the production flow line on the ship type surface vessel via the manifold and the swivel mechanism. Accordingly, oil or gas is smoothly transported to the processing facilities or a storage tank on the ship type surface vessel, irrespective of a rotational movement of the ship type surface vessel. During workover operations, the rigid structure of a riser pipe facilitates the run of workover tools through the surface wellhead of the corresponding riser pipe to thereby facilitate workover operations, in contrast with the conventional workover operations in which a flexible riser pipe is disconnected from a subsea wellhead and another ship engages in carrying out workover operations through the wellhead. Thus, the cost of workover operations is significantly reduced as compared to the conventional workover operations.
Also, since the workover rig stands on the ship type surface vessel along the vertical centerline of the turret, and the riser pipe movement mechanism is provided just under the rig for moving each of the rigid riser pipes arranged along the inner circumference of the turret, the workover operations for wells, which are carried out through respective riser pipes, can be carried out significantly efficiently and promptly.
Further, the riser pipe movement mechanism is configured to move each riser pipe to a central portion of the cylindrical turret by means of the stationary guide rails and the swivel guide rail. The stationary guide rails extend radially from the ringed support frame arranged concentrically in the turret toward respective riser pipes arranged along the inner circumference of the turret. The swivel guide rail is selectively connected to one of the stationary guide rails. Accordingly, the workover operations for wells, which are carried out through movement of each of the riser pipes to a central portion of the turret, can be carried out far more efficiently.
Also, since each of the riser pipes has a connector located under the bottom surface of the ship type surface vessel, the ship type surface vessel can be evacuated to a safe sea area through disconnection of the connectors, for example, when the approach of a typhoon is forecasted. In this case, the upper ends of the riser pipes are plugged, and marker buoys are attached to respective riser pipes.
Further, since the diver entrance chamber equipped with the inner and outer watertight doors and the water introduction-discharge means for the chamber are provided in a bottom portion of the ship type surface vessel in the vicinity of a lower end portion of the turret, there is facilitated the disconnection or connection of the connectors by a diver who enters the water from the entrance chamber. Accordingly, upon issuance of, for example, a typhoon warning, the ship type surface vessel can be promptly evacuated. When a diver is to enter into water, the diver enters the diver entrance chamber through the inner watertight door, and then water is introduced into the chamber. Then, the outer watertight door is opened, so that the diver can enter into water. When the diver is to return to the ship type surface vessel, the reverse procedure of dispatch is performed.
REFERENCES:
patent: 3299645 (1967-01-01), Link
patent: 3548516 (1970-12-01), Lanphier et al.
patent: 4264234 (1981-04-01), Pras
patent: 4436048 (1984-03-01), Gentry et al.
patent: 4448568 (1984-05-01), Gentry et al.
patent: 4601252
Paulling John Randolph
Tanabe Akio
Adams & Wilks
Hartmann Gary S.
Japan National Oil Corporation
Lillis Eileen D.
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