GB2195740A

GB2195740A - Pig launcher

Info

Publication number: GB2195740A
Application number: GB08721708A
Authority: GB
Inventors: Per Kristian Walentin
Original assignee: SEANOR ENG AS; BP PLC
Current assignee: SEANOR ENG AS; BP PLC
Priority date: 1986-09-18
Filing date: 1987-09-15
Publication date: 1988-04-13
Also published as: GB8622466D0; GB8721708D0

Abstract

A single-shot pig launcher comprises a pig launcher module A and a saver-sub module B. The pig launcher module A comprises an upper connector 11 for lifting or lowering by a running tool, a pig storage chamber 2, an outlet from the pig storage chamber leading to an inlet to the saver-sub module B, means for applying pressure eg. via kick valve 3 to the storage chamber 2 whereby the pig stored therein is released and forced out of the outlet and a lower connector 1 for connection to the saver-sub module B. The saver-sub module B comprises an upper connector for connection to the pig launcher module A, an inlet from the pig launcher module A, an outlet to the production line to be pigged, an isolation valve 7 between the inlet and the outlet and a lower connector 5 for connection to the production line to be pigged. The launcher is suitable for inserting a pig into a subsea pipeline, particularly in deep water in a diverless operation. <IMAGE>

Description

SPECIFICATION Pipeline pig launcher This invention relates to apparatus for inserting a pig into a subsea pipeline, particularly in deep waters.

A considerable proportion of the world's remaining oil reserves is believed to lie offshore under depths in excess of 200 metres, in relatively small oil fields, and in hostile environments. As any one of these conditions intensifies, and more particularly when two or more are present together, the cost of conventional offshore recovery systems wherein drilling and production facilities are mounted on the deck of free standing platforms rises rapidly and soon becomes uneconomic.

For this reason attention has been given to subsea systems where a favoured technique is to drill a number of locational wells close together and to mount the well head control equipment on the sea bed. In order to do this, a structure known as a template is employed.

In essence this is a large frame with guide tubes for drilling which is deposited on the sea bed in a desired location. After drilling, well head completion and production equipment are mounted on the frame and these facilities remain on the sea bed.

Although remotely operated vehicles (ROVs) are also known for inspecting, testing and servicing the production systems, water depths, up until now, have nearly all been such that the systems have been accessible to divers.

As the water depths in which oil is found and produced increase, totally diverless systems will be needed. Even in shallower depths, however, diverless systems could be economically attractive. It may also be necessary or desirable to dispense with guidelines, depending on the depth of the water.

Oil produced from such systems is transported by subsea pipelines either to on- or offshore facilities where it is treated for gas and water removal before being dispatched to refineries for further processing.

Production from single subsea wells or groups of wells associated with a template is delivered to the treatment facilities by pipelines of relatively small diameter known as flowlines. When the treatment facilities are on an offshore platform, total production is combined on the platform and exported after treatment by means of a large diameter pipeline known as the main oil line.

After the construction of a pipeline it is necessary to clean it out before use, for example, to remove rust, scale, sand and other contaminants. During use; deposits may form on the internal surface and, if not removed, these may build up and reduce the capacity of the pipeline.

For these duties, it is established practice to force a tightly fitting object known as a pig through the pipeline by exerting fluid pressure behind it.

Pigs may be of various configurations, depending on their intended functions. They may be cylindrical or spherical in shape.

Cylindrical pigs are frequently fitted with brushes and/or scrapers and are used for removing deposits such as wax which form on the internal surface of the pipeline. Such pigs are also fitted with cup-like washers which form a seal against the pipeline.

Spherical pigs are generally hollow, inflatable globes made from elastomeric material which are inflated with liquid to a diameter slightly exceeding the diameter of the pipeline so that they make a tight fit with the pipeline wall.

They roll and turn in an unpredictable manner as they travel through the line. Spherical pigs are usually used for initial cleaning operations, for maintenance of gas lines (and also for product separation in liquid lines, although this duty is unlikely to be required in subsea flowlines).

Pigs are inserted into and recovered from pipelines by devices known ss pig launchers and pig receivers. They are generally inserted into the lines from single shot pig launchers mounted on surface facilities, and recovered in a similar way. Access for pig insertion and maintenance is readily available. Such pig launchers are not suitable for use in diverless subsea systems.

We have now devised a single-shot pig launcher suitable for use in pigging flowlines in diverless subsea operations.

Thus according to the present invention there is provided a single-shot pig launcher comprising (1) a pig launcher module and (2) a saver-sub module, the pig launcher module comprising (a) an upper connector for lifting or lowering by a running tool, (b) a pig storage chamber, (c) an outlet from the pig storage chamber leading to an inlet to the saver-sub module, (d) means for applying pressure to the storage chamber whereby the pig stored therein is released and forced out of the outlet, and (e) a lower connector for connection to the saver-sub module, the saver-sub module comprising (f) an upper connector for connection to the pig launcher module, (g) an inlet from the pig launcher module, (h) an outlet to the production line to be pigged, (i) an isolation valve between the inlet and the outlet, and (j) a lower connector for connection to the production line to be pigged.

The means for applying pressure to the pig storage chamber may comprise a kick system including a kick valve and a flexible kick line; Kick fluid may be supplied from the surface to a position in the storage chamber behind the pig to push the pig out of the storage cham ber, through the pig launcher module, through the sub-saver module and into the flowline.

The pig storage chamber is preferably fitted with a pig locking mechanism, e.g. a hydraulically operated valve or locking pin.

The connectors between the pig launcher module and the saversub module and between the latter and the production line are prefera bly of the collet type and may be operated by a mechanism comprising push rods activated by hydraulic jacks in a running tool.

The saver-sub module may be connected to the production line either vertically or horizontally.

Both modules may be surrounded by guide frames.

The pig launcher module is normally purged with sea water as it is lowered subsea by the running tool. When this is to be the case, a vent is provided.

The running tool will be deployed from a surface vessel.

The pig launcher will normally be used in association with a single subsea satellite well located some distance from a multiwell subsea template with production from the satellite flowing to the template. The pig may be recovered at the template by a subsea pig receiver. A suitable receiver is disclosed in our copending application Case 6469.

In order to deploy and use the pig launcher module, the following sequence of operations takes place.

-The pig is inserted into the launcher on the surface. A flexible kick-line is connected to the launcher and the pig launcher module is attached to a running tool and lowered to the subsea production system.

-The launcher module is connected to a saver-sub module which is connected to the manifold/flowline of the subsea production system.

-The saver-sub module contains an isolation valve and is retrieved only in the event of damage of the connector to the launcher module, or in case of isolation valve failure.

-The pig is launched by direct hydraulic control from surface via an umbilical.

-The pig launcher is retrieved for reloading when the pig has been launched.

The invention is illustrated with reference to Figures 1 to 6 of the accompanying drawings wherein Figure 1 is an elevation of a singleshot pig launcher and Figures 2 and 3 are plan and isometric views respectively. Figure 4 is a simplified schematic flowline drawing and Figures 5 and 6 are elevations, partly in section, of a pig storage chamber; With reference to Figures 1 to 3, the pig launcher comprises a pig launcher module A and a saver-sub module B coupled together by means of a collet connector 1.; The pig launcher module A contains a pig storage chamber 2 fitted with pig locks (shown in detail in Figures 5 and 6). The out let from the pig storage chamber 2 opens into the connector 1. Hydraulic fluid is supplied to the chamber 1 behind a pig through a kick line controlled by a kick valve 3. Push-pull rods 4 are provided to actuate the connector 1.

The saver-sub module B comprises a collet connector 5 for connection to the flowline of a subsea satellite well. A pig line 6 controlled by an isolation valve 7 provides communication between connectors 1 and 5. Push-pull rods 8 are provided to actuate the connector 5.

The pig launcher module A is surrounded by a guide frame 9 and the saver-sub module by a guide frame 10. Frame 9 is joined to a hub 11 for connection to a running tool. Both guide frames 9 and 10 are fitted with shock absorbers 12 to provide soft landing on the saver-sub module and the oil well respectively.

With reference to Figure 4, Items 1, 2, 3, 5, 6, 7 and 11 are as hereinbefore described with reference to Figure 1.

In addition, the pig storage chamber 2 is shown fitted with a purge valve 13, a connector drain 14 and a hydraulically operated pig locking mechanism 15.

The saver-sub module B is connected to a subsea flowline 16 taking production from a line 17 from the Christmas Tree of a subsea well head. Lines 16 and 17 are controlled from a surface platform by isolation valves 18 and 19 respectively.

When a pig is launched into the line 16, its passing is detected by a pig-sig 20.

With reference to Figures 5 and 6, the pig storage chamber 2 is fitted with an end cap 21, an inlet 22 for kick fluid and a pig locating rod 23 with an adjustable collar 24.

A purge valve 13, a connector drain 14 and a hydraulically operated locking mechanism 15 and also.provided, as previously described.

The locking mechanism consists essentially of a piston actuating a locking pin 25.

In order to launch a pig, the following procedure is employed.

The launcher assembly (running tool, pig launcher module A, flexible kick line and control umbilical) is run subsea and connected to the saver-sub module B. Connector drain valve 14 and purge vent/valve 13 are then closed.

Isolation valves 18 and 19 are in the open position. All control functions except the isolation valves 18 and 19 are operated from a SSV (Surface Support Vessel) through the control umbilical.

The saver-sub valve 7 is opened to allow the pressure in the launcher to equalise with the flowline pressure.

The kick line is pressurised to the flowline pressure by pumping down kick fluid from the SSV.

The kick valve 3 is opened and the locking mechanism 15 which secures the pig is un locked to release the latter.

The pig is launched by applying launching pressure to the kick line.

When the pig has passed the production tree outlet, as indicated by a signal from the pig-sig 20, the kick valve 3 is closed and then the saver-sub isolation valve 7.

The pig launcher module A is then ready for retrieval.

Claims

1. A single-shot pig launcher comprising (1) a pig launcher module and (2) a saver-sub module, the pig launcher module comprising (a) an upper connector for lifting or lowering by a running tool, (b) a pig storage chamber, (c) an outlet from the pig chamber leading to an inlet to the saver-sub module, (d) means for applying pressure to the storage chamber whereby the pig stored therein is released and forced out of the outlet, and (e) a lower connector for connection to the saver-sub module, the saver-sub module ccmprising (f) an upper connector for connection to the pig launcher module, (g) an inlet from the pig launcher module, (h) an outlet to the production line to be pigged, (i) an isolation valve between the inlet and the outlet, and (j) a lower connector for connection to the production line to be pigged.

2. A pig launcher according to claim 1 wherein the means for applying pressure to the pig storage chamber comprises a kick system including a kick valve and a flexible kick line.

3. A pig launcher according to either of the preceding claims wherein the pig storage chamber is fitted with a pig locking mechanism.

4. A pig launcher according to claim 3 wherein the pig locking mechanism is a hydraulically operated valve or locking pin.

5. A pig launcher according to any of the preceding claims wherein the connectors between the pig launcher module and the saversub module and between the latter and the production line are of the collet type.

6. A pig launcher according to any of the preceding claims wherein the pig launcher module and the saver-sub module are surrounded by guide frames.