Swivel

Details Swivel Swivel

1999-02-26

2001-05-01

Bagnell, David (Department: 3673)

Wells

Submerged well

Connection or disconnection of submerged members remotely...

C166S355000, C166S368000

Reexamination Certificate

active

06223825

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a swivel device for installation at a well for subsea production of oil or gas and adapted to be connected to a production vessel at the sea surface, comprising a main or fluid swivel having at least two fluid passages and an electric/hydraulic auxiliary swivel for signal communication and power transfer.
BACKGROUND OF THE INVENTION
When developing marginal offshore production fields it is important to keep the costs low. A substantial cost factor with known forms of development, is due to subsea pipelines and cables between christmas trees at the wells and product receiver sites, for example a platform or a floating production vessel. Typically there may here be the question of distances like 2 km. In this connection it is to be noted that modern drilling technology makes it possible to produce by means of a reduced number of christmas trees, because the boreholes or wells can have several branches. This will make it possible to develop subsea fields in some instances by employing only one subsea christmas tree.
International patent application PC/NO96/00201 dated Jul. 8, 1996 relates to a system for offshore production of hydrocarbons by employing a moored production vessel or ship. The present invention can be regarded as a further development thereof and is based on the idea that the production vessel can by lying directly above or in the immediate vicinity of the christmas tree at the seabed and that the well fluid flows are transferred directly between the christmas tree and the vessel without relying on pipelines or cables on the seabed.
Advantageously the solution to be described in the following specification can employ a particular and preferably simplified form of christmas tree, being more or less integrated into an arrangement according to the invention as will appear from the following description.
Thus, in a device as stated in the introduction above, the novel and specific features according to the invention primarily comprise therein that the fluid swivel is provided with a rotatable swivel housing at the top of a stationary christmas tree, preferably comprising a small number of valves, such as a production master valve and an annulus master valve, and that said passages are through-running vertically in a central core member of the fluid swivel in order to make possible well intervention from the upper side of the fluid swivel.
On the basis of this fundamental solution, which in actual practice can be embodied in various forms, it is possible to obtain a number of advantages, of which in particular the following are mentioned:
The production vessel employed does not need any modifications worth mentioning, in relation to common ship designs, and therefore will be relatively inexpensive,
the same production vessel can be used for installing and possibly retrieving the swivel device, or also for well maintenance, which contributes to reduced operational costs,
very small marginal subsea fields can be profitable by using this novel arrangement, so that the degree of extraction can be increased for the fields,
the equipment employed can be re-used by moving it from field to field.
SUMMARY OF THE INVENTION
The present invention is a swivel device for installation at a well for subsea production of oil or gas and adapted to be connected to a production vessel at the sea surface comprising a main fluid swivel having at least two passages and an auxiliary swivel. The swivel device is provided with a rotatable swivel housing on top of a stationary christmas tree and that the passages are through-running vertically in a central core member of the fluid swivel, in order to make possible well intervention from the upper side of the fluid swivel. Further, at the lower part of the christmas tree, there is provided a force transferring housing being rotatably journalled about a common vertical axis on a base structure. The swivel device further comprises a mooring yoke having two legs, the free ends of which are rotatably connected to either side of the force transferring housing, and the opposite ends of which are adapted to be attached to the end of a mooring line. Between the force transferring housing and the swivel housing, there is provided a mechanical coupling for causing the swivel housing to perform the same rotary movements as the force transferring housing under the influence of the yoke.
Further, the mechanical coupling between the force transferring housing and the swivel housing comprises a rod element extending in parallel to the common vertical axis at the side of the christmas tree and the swivel housing.
The swivel device of the present invention may further comprise a retrievable top member incorporating the auxiliary swivel. The top member at its lower part is provided with a connector adapted to cooperate with the core member of the fluid swivel.
The top member may further contain a control module for the christmas tree and may be provided with a handling head for installation and retrieval.
The swivel device of the present invention may further comprise a bridging arm extended outwards and downwards from the top member and provided with a connector plate at its lower end. The connector plate is adapted to cooperate with a complementary connector part associated with a laterally projecting connecting member on the swivel housing.
A further embodiment of the instant invention provides the swivel housing with laterally directed connecting members for at least two risers being oriented substantially in the same plane as a connecting member for an umbilical. The connecting members are directed substantially outwards centrally between the yoke legs.
The swivel device may be characterized such that the wellhead comprises a conductor tube, characterized in that the force transferring housing is rotatably provided on a base structure being connected to the conductor tube for transferring mooring forces directly from the yoke to the conductor tube.


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