GB2368890A

GB2368890A - Buoyant pig launcher

Info

Publication number: GB2368890A
Application number: GB0110591A
Authority: GB
Inventors: David Bone
Original assignee: Ocean Technologies Ltd
Current assignee: Ocean Technologies Ltd
Priority date: 2000-09-02
Filing date: 2001-05-01
Publication date: 2002-05-15
Anticipated expiration: 2021-05-01
Also published as: GB0110591D0; GB0021563D0; GB2368890B

Abstract

A permanently available surface accessible pig launcher has a pig launcher cassette 8 housed in a taut moored buoyant structure 9, which is connected by a flexible hose 3 to a sub-sea target pipeline 17. The buoyant structure 9 provides surface access to the launcher cassette 8 via a sealed hatch 1. Pigs 7 are conducted through the flexible hose 3 between the launcher cassette 8 and a valve assembly connected to the target pipeline 17. Additional valves and pumps allow an internal fluid pressure system to operate with isolated coupling between the valve assembly and buoyant structure 9. The pressure system provides means for driving a pig 10 from the launcher cassette 8 to the valve assembly, with the valve assembly allowing onward travel of the pig 10 to the target pipeline 17 using pipeline fluid in isolation from the internal fluid pressure system.

Description

BUOY SUPPORTED PIG LAUNCHER This invention relates to fluid flow in subsea pipelines.

Pig launchers are used in offshore oil and gas developments to propel pigs (usually spheres) along subsea pipelines running between an offshore oil/gas production facility and either the shore or to a host processing platform, in order to clean the pipelines to allow efficient further use of fluid flow. Currently for underwater deployments in remote locations the pig launcher cassette is situated subsea, or alternatively two pipelines are required, one to send and one to retrieve the pig onshore or at the host facility. Both of these current options involve expensive additional subsea equipment to use the pig. Another option would be to have a service vessel moored nearby to deploy the pig, but this would also prove very costly.

We have now devised a means of pig launching which obviates the above problem.

According to the present invention there is provided a permanently available surface accessed pig launcher, comprising the use of a taut moored buoyant structure to provide surface access above sea level, a sealed hatch for safe insertion of pigs, a pig launcher cassette housed in said buoyant structure and accessed via said sealed hatch, a flexible hose arranged to conduct a pig between said buoyant structure and a valve assembly connected to a targeted subsea pipeline, said valve assembly providing an isolated coupling path between the flexible hose and the targeted pipeline, and an arrangement of valves and pumps to allow an internal fluid pressure system to operate with isolated coupling between said valve assembly and said buoyant structure, said fluid pressure system being used to drive a pig from said launcher cassette to the valve assembly, with the valve assembly allowing onward travel of the pig to the targeted pipeline using said pipeline fluid in isolation from said internal fluid pressure system.

Preferably the buoyant structure is taut moored to a foundation structure on the seabed.

Preferably the buoyant structure is equipped to allow the pigs to be launched remotely.

Preferably the pig launcher cassette extends through the buoy hull and thus does not represent a potential path for leakage of hydrocarbons into the enclosed hull.

In an alternative embodiment the flexible hose may consist of an articulated rigid pipe or a combination of connected flexible and rigid pipes.

In another embodiment the valve assembly may be connected to the underside or inside of the buoy, or inside or on the foundation structure thus providing additional safety and reduced costs.

In a further embodiment for use in deepwater, the system also utilises an intermediate structure (MWF) which may provide additional buoyancy to support a steel catenary riser (SCR) connected from a subsea pipeline thereto, which then has a flexible hose connected between the MWF and the buoy, the SCR and flexible hose providing the pathway for pig insertion into the subsea pipeline.

Specific embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings in which: Figure 1 shows in vertical cross section the buoyant structure and pig launching system.

Figure 2 shows in vertical cross section an alternative form of the pig launching system.

Figure 3 shows a layout for use of a deepwater system.

Referring to Figure 1, the system comprises a taut moored buoyant structure 9, containing a pig launcher cassette 8 that gives access through a flexible hose 3, to a subsea pig launcher 4. The pig launcher 4 gives direct access to the targeted pipeline 17, said pipeline 17 collects oil or gas from a pipeline end manifold 34, and is supported by a support skid 5. Flowlines from wells 6 are connected to the pipeline end manifold 34. The pipeline 17 delivers the oil or gas so collected either to the shore or to another offshore processing facility called the host platform.

The buoyant structure 9 is moored permanently on site with tethers 18, and therefore is always available for access weather permitting. The buoyant structure 9 contains equipment (not shown) which allows the pigs 7 to be launched by telemetry from a location remote to the buoy.

The buoyant structure 9 is also capable of carrying additional equipment for other functions.

In use the pig launcher cassette 8 is accessed from the surface via a loading hatch 1. Pigs 7 (usually spherical) are loaded into the pig launcher cassette 8 through the loading hatch 1. The pig launcher cassette 8 has a storage capacity for one or more pigs and thereby avoids the need for frequent replenishment.

The pigs 7 are propelled towards the targeted pipeline 17 as follows; A single pig 10 is isolated from the pig launcher cassette 8 by actuation of the isolation valve 11, whilst the other pigs are retained by a suitable mechanism. The pig 10 is then released into the flexible hose 3 by operation of the release valve 2, and hydraulic fluid pressure is applied to the pig 10 to aid its transfer along the flexible hose 3 and into the pig launcher 4. Valves 2,12 and 16 are open at this time to allow the hydraulic fluid to circulate using a pump 19. Valves 13, and 26 are closed at this time so that the pipeline 17 fluid flows through the pipeline 17. Once the pig is in the pig launcher chamber 4, valves 2,12, and 16 are closed. The pipeline fluid is diverted into the pig launcher chamber 4 upstream of the pig 10 by opening valves 26 and 13, and closing valve 28.

Pressure is applied (by the diverted fluid from the pipeline 17) to force the pig 10 out of the pig launcher 4, in the direction of the arrow 14, and into the targeted pipeline 17. Once in the pipeline 17, the pig 10 can be propelled using the pipeline 17 fluid. Valves 26 and 13 are now closed and valve 28 is opened.

The pump 19 is located in the buoyant structure 9. The hydraulic fluid is returned to the system with an arrangement of pipes 15 and valves 16 and 26. The hydraulic fluid is replenished when necessary using a fluid reservoir (Figure 2,20) located in the buoyant structure 9.

Referring to Figure 2 an alternative form of the pig launcher system is shown that incorporates the basic principles used in Figure 1 and additional refinements. Pigs 7 are loaded through a watertight hatch 1. A quick closure cap 22 is provided at the top of the launcher cassette 8. Pig retaining latches 21 are used to stack the pigs 7 inside the cassette 8. To facilitate operation the lower pig retaining latch 21 is released and the pig 10 is then located above a concentric reducer 23 in the lower launching cassette 24. To drive the pig 10 down to the pig launcher/launch chamber 4, the launcher inlet valve 12 is opened and the launch pump 19 is operated with the return line isolation valve 16 open. Thus the insertion drive fluid is circulated through the hose 3 and returned from the launch chamber 4 via the insertion drive return line 15. Once the fluid drive has caused the pig 10 to pass the launch inlet valve 12, a pig detector 25 detects its position. Notification from the pig detector 25 causes the pump 19 to be stopped, and the return line isolation valve 16 and launcher inlet valve 12 to be closed. To drive the pig 10 from the launch chamber 4 to the targeted pipeline 17, the produced fluid diverter valve 26 and the launcher release valve/isolation valve 13 are opened, and the pipeline isolation valve 28 is closed. The pig is driven by production fluid pressure into the pipeline 17 where its presence is detected by a second pig detector 27. Notification from the pig detector 27 causes the launcher isolation valve 13 and the fluid diverter valve 26 to close, and the pipeline isolation valve 28 is then opened. A barred tee 29 is used to prevent the pig 10 from travelling in the wrong direction.

The launcher inlet valve 12 is interlocked to the fluid diverter valve 26 and to the return line isolation valve 16 to prevent ingress of pipeline fluid to the hose 3 or the return line 15. A relief valve 30 and relief vent 31 are provided as an extra precautionary measure.

Referring to Figure 3, modifications necessary for the deepwater system are shown. An intermediate structure (MWF) 32 provides a connecting point between a flexible hose 3 and a steel catenary riser (SCR) 33, and flotation support for the SCR 33. The SCR 33 extends to the launch chamber 4 and hence provides access to the subsea pipeline 17. Pigs 7 are loaded and dispensed as in the previous examples. The launch chamber 4 is preferably located inside or on the MWF 32 or buoy 9. The MWF 32 is within diving range so that locating the launch chamber 4 thereto allows ease of maintenance.

Claims

CLAIMS 1. A permanently available surface accessed pig launcher, comprising the use of a taut moored buoyant structure to provide surface access above sea level, a sealed hatch for safe insertion of pigs, a pig launcher cassette housed in said buoyant structure and accessed via said sealed hatch, a flexible hose arranged to conduct a pig between said buoyant structure and a valve assembly connected to a targeted sub-sea pipeline, said valve assembly providing an isolated coupling path between the flexible hose and the targeted pipeline, and an arrangement of valves and pumps to allow an internal fluid pressure system to operate with isolated coupling between said valve assembly and said buoyant structure, said fluid pressure system being used to drive a pig from said launcher cassette to the valve assembly, with the valve assembly allowing onward travel of the pig to the targeted pipeline using said pipeline fluid in isolation from said internal fluid pressure system.
2. A permanently available surface accessed pig launcher as claimed in Claim 1, wherein the buoyant structure is taut moored to a foundation structure on the seabed.
3. A permanently available surface accessed pig launcher as claimed in Claim 1 or Claim 2, wherein the buoyant structure is equipped to allow the pigs to be launched from a remote location.
4. A permanently available surface accessed pig launcher as claimed in any preceding claim, wherein the pig launcher cassette extends through the buoy hull.
5. A permanently available surface accessed pig launcher as claimed in any preceding claim, wherein the flexible hose consists of an articulated rigid pipe or a combination of connected flexible and rigid pipes.
6. A permanently available surface accessed pig launcher as claimed in any preceding claim, wherein the valve assembly is connected to the underside or inside of the buoyant structure.
7. A permanently available surface accessed pig launcher as claimed in any of claims 1 to 5, wherein the valve assembly is connected inside or on the foundation structure.
8. A permanently available surface accessed pig launcher as claimed in any of claims 1 to 5, wherein the valve assembly is connected inside or on a sub-sea area manifold.
9. A permanently available surface accessed pig launcher as claimed in any preceding claim, wherein the system also utilises an intermediate structure (MWF) which may provide additional buoyancy to support a steel catenary riser (SCR) or flexible hose connected from a sub-sea pipeline thereto, which then has a flexible hose or SCR connected between the MWF and the buoyant structure, the SCR and flexible hose providing the pathway for pig insertion into the sub-sea pipeline.
10. A permanently available surface accessed pig launcher as claimed in Claim 8, wherein the valve assembly is located inside or on the MWF.
11. A permanently available surface accessed pig launcher substantially as herein described and illustrated in the accompanying drawings.