GB2285647A

GB2285647A - Subsea manifold system

Info

Publication number: GB2285647A
Application number: GB9426427A
Authority: GB
Inventors: Michael Graham Morgan
Original assignee: FMC Corp
Current assignee: FMC Corp
Priority date: 1994-01-13
Filing date: 1994-12-30
Publication date: 1995-07-19
Also published as: NO950107L; BR9500081A; NO950107D0; GB9426427D0; GB9400565D0; FR2714933A1

Abstract

A subsea manifold system for use with hydrocarbon producing wells comprises a base frame 11, a central pile 10 and a manifold module 13 including various pipe connections. The central pile is cemented in the sea bed and supports the base frame. The manifold module is lowered onto the base frame under the guidance of wires connected between a vessel and guideposts in the base frame. The system is sized so that it can be deployed through a moonpool which is a square with each side 5m long. <IMAGE>

Description

SUBSEA MANIFOLD SYSTEM The invention relates to subsea manifold systems.

A subsea manifold is a collection and distribution centre for a group of subsea wells (such as gas or oil wells), and may comprise a number of pipes and branches. The collection function includes the convergent flow of hydrocarbon products output from outlying subsea wells. This is transported through a production flowline(s) to processing facilities, which may be located on a floating vessel, or a platform fixed to the seabed some few kilometres away. The manifold also distributes a variety of fluid services, as required, to the surrounding wells.A typical manifold may include a production header (ring main) pipe of approx. 305mm (12") NB (nominal bore) which collects the product output from the wells, and connects to the production flowline(s), a production test header pipe of approx. 203mm (8") NB which allows isolation of any particular well for the purpose of measuring its flowrate, and connects to a production test flowline, a gas lift header pipe of approx. 152mm (6") NB which connects to a gas lift flowline and distributes to the associated wells hydrocarbon gas, compressed at the process facility, for the purpose of reducing the kinematic viscosity of oil in order to improve its flowrate, and one or more chemicals injection header pipes of approx. 76mm (3") NB whose number depends on the specific nature of the well and allows chemicals, transported from the process facility, through a chemicals injection umbilical tube to be introduced into the well for improvement or stability of the well and pipework.

According to an aspect of the invention, there is provided a subsea manifold system comprising a base frame carrying a central pile by which the base frame may be supported above a seabed, a manifold being carried on the base frame.

According to a second aspect of the invention, there is provided a method of deploying a manifold system on a seabed comprising lowering to the seabed a base frame having a central pile depending therefrom, locating the pile in a hole in the seabed to position the base frame above the seabed and then mounting a manifold on the base frame.

In either aspect of the invention, the size of the system may be such as to allow the system to be deployed through a moonpool which is square in plan, each side having a length of 5m.

The manifold is intended to be deployed from a drilling facility. This is a vessel such as a semisubmersible rig, or a dynamically positioned drill ship. A moonpool, a through hull opening, of such a vessel has a minimum area in the shape of a square of 5 metre side. As the manifold is deployed through this moonpool, the foregoing limitation defines the maximum size of the principal components of the manifold system. The manifold may have an octagonal shape in plan dictated by the size, and maximizing the quantity of the pieces of equipment fitted to facilitate the tie-in of the pipes connected to the processing facility, and the pipes connected to each of the satellite wells.

The following is a description of an embodiment of a manifold according to the invention with reference to the accompanying drawings, in which: Figure 1 is a side elevation, partly in section, of a subsea manifold system including a base frame and a manifold, Figure 2 is a perspective view of the base frame of Figure 1, Figure 3 is a plan view from above of the manifold of Figure 1, Figure 4 is a second side elevation of the subsea manifold system of Figures 1 to 3, Figure 5 is an elevation of one end of the subsea manifold system of Figures 1 to 4, and Figure 6 is an elevation of the other end of the subsea manifold system of Figures 1 to 5.

This manifold is of modular construction, and comprises three principal component assemblies: a central pile 10, a structural base frame 11 with four remote releasable guide posts 12, and a manifold module 13 with guide funnels 14. The pile 10 is assembled from sections of pipe in lengths of approximately 12.2m (40 feet) screwed together to make a total of about 90m (300 feet). At the top of the pile is a 760mm (30") conductor housing 15. The structural base frame 11 is a steel fabrication which locates to the conductor housing 15 and forms a platform 16 onto which the manifold module 13 is landed and locked. The manifold module 13 comprises pipe work held in an approximately circular arrangement by fabricated diaphragms tied into a central column and a stiff base framework (see Figure 3).

The header pipe 17 (Figure 3) is designed to be "pigged".

Pigging is the process by which a flexible plug (not shown), fitted with flexible seals, is pumped through header pipes 17 to clean the interior surface of the pipe 17, and may, if an "intelligent pig", take readings of the thickness of the pipe wall and other measurements, for maintenance purposes. The radius of the bends in the header pipes 17 of the manifold is not less than 5 x D, the nominal diameter of the pipe. Any radius tighter than this prevents the acquisition and transfer of data during the passage through the header pipe 17 of an "intelligent pig".

The manifold module 13 is of such a size and shape that it will pass through an opening in a horizontal plane 5m x Sm.

The production pipe 18 is pigged in a round trip, i.e. in at one connection and out at the other. The production test and gas lift header pipes 18 are blind ended, and allow the pig to travel to the end of the pipe 18, and be pumped back by reverse flushing; cross over valves (one of which is shown at 19 in Figure 6) in these lines are provided for this purpose.

Underneath the manifold module 13 is a central locking arrangement 20 which secures the manifold module 13 to the base frame 11.

For this purpose, the manifold module 13 is provided with a central vertical tubular core (see Figure 1) that projects from an undersurface of the manifold module 13. The locking arrangement 20 includes a receiver for receiving the projection portion of the core and locks it to the base frame 11.

Valves operable by a remotely operated vehicle ("ROV") are fitted to smaller pipes which branch out from the header pipes 17,18 in six places (see Figure 3), and isolate the services to each of a number of satellite wells (which may be up to six in number). The pipe branches terminate in a single hub 21 (Figures 4 to 6) which is half of a connection and pull-in system which facilitates the make up of flexible jumper pipes to the satellite wells. At each end of the production header ring main pipe 17, and the open ends of the other pipes 18 is a similar hub 21 to facilitate the connection of pipes to the manifold. 305mm (12") and 203mm (8") pipes each monopolize a single hub 21, whereas 152mm (6") pipe shares its hub with a number of smaller pipes of the chemicals transport system.

The manifold described above with reference to the drawings is installed in the following way.

First a suitable hole is drilled in the sea bed, then the system is installed sequentially, beginning with the base frame 11 (see Figure 2). On the vessel the base frame 11 is supported on a pair of spider beams which straddle the moonpool. The guideposts 12 are fitted to the frame 11 (see Figure 2) and guidelines connected to the guideposts 12. The central pile 10 is handled by a cam actuated running tool (not shown) which is assembled into the 760mm housing. Using the tool and the rig derrick, the pile is lowered on drill pipe through a hole 22 (see Figures 1 and 2) in the base frame 11, until the 760mm (30") conductor housing latches into it.The pile 10 and base frame 11 are raised to enable the spider beams to be drawn back, then the pile 10 is run into the predrilled hole to a position where the base frame 11 is close to the seabed. (it may prove necessary to use a temporary guide base for support to ensure the correct height above the seabed). The pile 10 is then cemented in place.

The manifold module 13 is positioned on the spider beams over the moonpool to enable the same cam actuated running tool (not shown) to be fitted to a similar 760mm (3011) housing profile in the centre of the manifold module 13. Gates in the guide funnels 14 are opened, the guidelines inserted and the gates re-secured. The manifold 13 is handled as above, run down the guidelines through the moonpool to land on the base frame 11, where it is secured by the setting of the central locking arrangement 20. The running tool may be retrieved, and an ROV deployed to detach the guideposts 12, whose locking mechanism may be released with vertical access.

As seen in Figures 1 and 2, the base frame 11 is provided with vertically projecting pins 23 which locate in respective holes 24 in the manifold module 13 to locate the module 13 relative to the base frame 11 angularly about a vertical axis so that the manifold module 13 is correctly orientated.

Claims

1. A subsea manifold system comprising a base frame carrying a central pile by which the base frame may be supported above a seabed, a manifold being carried on the base frame.

2. A system according to claim 1 wherein the base frame includes a locking mechanism for latching engagement with the manifold.

3. A system according to claim 2 wherein the manifold includes an undersurface with a single connector projecting therefrom, the locking mechanism on the base frame including a receiver for receiving the connector and for latching the connector to the base frame.

4. A system according to claim 3 wherein the manifold includes a vertical tubular core, an end of said core projecting from said undersurface and forming said single connector.

5. A system according to any one of claims 1 to 4 wherein the base frame and the manifold include co-operating locating means for positioning the manifold angularly about a vertical axis relatively to the base frame.

6. A system according to claim 5 wherein said locating means comprise at least one pin received in a co-operating hole.

7. A system according to claim 6 wherein the at least one pin is carried on the base frame and the at least one cooperating hole is provided on the manifold.

8. A system according to claim 6 or claim 7 wherein there are provided a plurality of angularly spaced pins and holes.

9. A system according to any one of claims 1 to 8 wherein the manifold includes flow means for accommodating a flow of fluid from six wells, the manifold being sized to pass through an opening in a horizontal plane 5m by 5m.

10. A system according to claim 9 wherein the manifold includes a plurality of pipes, each pipe extending from an inlet on the manifold to an outlet on the manifold and including at least one curved portion between the associated inlet and outlet, the radius of the at least one curved portion being not less than five times the dimater of the associated pipe.

11. A method of deploying a manifold system on a seabed comprising lowering to the seabed a base frame having a central pile depending therefrom, locating the pile in a hole in the seabed to position the base frame above the seabed and then mounting a manifold on the base frame.

12. A method according to claim 11 and comprising latching to the base frame, a single central connector projecting from an undersurface of the manifold.

13. A method according to claim 12 and comprising sizing the manifold to allow the manifold to pass through an opening in a horizontal plane of 5m x 5m, and then lowering the manifold through such an opening to the base frame.

14. A method according to any one of claims 11 to 13 and comprising locating the manifold angularly relatively to the base frame about a vertical axis.

15. A subsea manifold system substantially as hereinbefore described with reference to the accompanying drawings.

16. A method of deploying a subsea manifold on a seabed substantially as hereinbefore described with reference to the accompanying drawings.