Cleaning, measuring and inspection of pipelines is very topical in connection with oil production. Such operations are carried out by means of different types of"pigs"which are designed for the topical operation, and which are carried through the pipeline in question, usually in that they are entrained by the oil flow proper, or by means of a propulsion mechanism of their own. In connection with underwater production solutions, the systems for pigging of pipelines have had a tendency to be complicated, relatively extensive and very time-consuming to use.

The object of the invention is to provide a compact system for the stated purpose, wherein the system in a simple manner is able to be integrated in existing underwater production solutions, and which consists of a few units which will reduce the installation time and the time for carrying out the pigging operations.

The above-mentioned object is achieved with a system of the introductorily stated type which, according to the invention, is characterized in that the pig launching unit comprises an upwardly open sleeve-shaped barrel at the end of the pipeline, and the pig receiving unit comprises an insert member adapted for introduction into the barrel by means of the running tool, and for releasable securing in the barrel, so that the two units in connected condition form a launching trap for a pig placed in the insert member.

The invention will be further described below in connection with an exemplary embodiment with reference to the drawings, wherein Fig. 1 shows a schematic view of a pig launching system according to the invention, in an operational phase wherein a trap insert with a pig is in the process of being installed in

the associated trap barrel by means of a running tool; Figs. 2 and 3 show corresponding views to that of Fig.

1, but of other operational phases; and Fig. 4 shows a schematic view of a pig launching system with an embodiment of a pipe arrangement for introduction of a pig into the topical pipeline by means of the fluid flow from a reservoir under the sea bed.

As appears from Figs. 1-3, the pig launching system according to the invention comprises a pig launching unit in the form of an upwardly open, sleeve-shaped barrel 1 which is arranged at one end of a pipeline 2 in which a pig is to be launched, and a pig receiving unit 3 comprising an insert member 4 adapted for introduction into the barrel 1 by means of a running tool 5, and for releasable securing in the barrel, so that the two units 1,3 in connected condition form a launching trap for a pig 6 placed in the insert member 4.

The sleeve-shaped barrel 1 is installed in a wellhead 7 which is only schematically suggested in Figs. 1-3, for example in a wellhead base 8 for a production Christmas tree 9, as schematically shown in Fig. 4.

The pig receiving unit 3 may, in a commonly known manner, be lowered and drawn up from the wellhead 7 by means of the running tool 5 which may be of a conventional design. The running tool is lowered and drawn up by means of a lifting wire 10 operated from a non-illustrated vessel at the water surface, the movement of the running tool being controlled by means of a pair of guide lines 11 which are carried through associated guide sleeves 12 at the running tool 5 and at their lower ends are connected to guide posts 13 at the wellhead 7.

The pig receiving unit 3 in the illustrated embodiment comprises an upper head member 14 from which the insert member 4 projects downwards, and which is designed for releasable connection with, the pig launching barrel 1. Thus, the head member 14 has a downwards projecting flange member 15 which, together with an upper portion of the insert member 4, defines an annular slot 16 for receiving the upper edge portion of the barrel 1. In the flange member 15 there are arranged a number of radially movable locking pins 17, and the interconnection between the unit 3 and the barrel 1 takes place in that the locking pins are

brought into engagement in a peripheral groove 18 arranged in th « e outer surface of the barrel 1 at the upper end thereof.

It will be clear that the means for interconnection of the pig receiving unit 3 and the launching barrel may be designed in many different ways. For example, instead of the stated locking pins, there may be used a clamp coupling having typically three segments, a coupling having rotating locking pins, a coupling of the"collet"type, etc. The connecting means may be remotely operated, either via the umbilical (mentioned below) or by means of a remotely operated vehicle (rov).

The unit 3 is provided with a sealing means for sealing engagement with the barrel 1 when the insert member 4 has been introduced into the barrel, so that leakage of process fluid from the launching trap to the surrounding sea is prevented. The sealing means may consist of suitable gaskets which may be arranged in connection with the locking means mentioned above, or it may comprise a gasket which is arranged at the bottom of the annular slot 16.

At the top of the unit 3 there is further shown to be arranged a coupling pin 19 for releasable engagement in a corresponding holder or socket member 20 on the running tool 5.

The interconnection and the release suitably may take place electrically or hydraulically, and be controlled by means of an umbilical 21 extending between the running tool 5 and the surface vessel.

In the illustrated embodiment the insert member 4 is adapted for receiving a single pig 6. However, if desired, the insert member may be arranged to receive several pigs, in order to be able to launch successive pigs consecutively without recovering the unit 3 to the surface for each pig launching. The pig 6 may, e. g., be a cleaning pig, a measuring pig or an inspection pig. Where the insert member is arranged to receive several pigs simultaneously, these may be of different types, according to the topical need. Such an embodiment will be advantageous on fields where there is a need for frequent pigging.

As appears from Figs. 1-3, the pig launching barrel 1 constitutes an extension of the pipeline 2 in which the pig 6 is to be introduced. Below the barrel there is arranged an isolating

valve 22 which is opened when the pig is to be driven out from the launching trap and into the pipeline. To drive the pig into the pipeline, a driving line 23 for the supply of driving fluid is connected to the barrel 1. The driving line is coupled to an opening 24 arranged in the wall of the barrel and communicates with a peripheral groove 25 in the insert member 4 when this has been introduced into the barrel. The annular groove 25 com- municates with the interior of the insert member 4 via a number of openings 26 therein, so that driving fluid is supplied to the interior of the insert member when opening an isolation valve 27 in the driving line 23, and the pig 6 then is driven into the pipeline 2 as shown in Fig. 3.

Fig. 4 shows an embodiment of a pipe arrangement for introducing a pig into the pipeline 2 by means of the flow of production fluid (oil) from an oil reservoir 30 below the sea bed 31. The figure shows a tubing 32 extending between the reservoir 30 and the production Christmas tree in the wellhead 7. In the production Christmas tree there is shown to be connected an isolation valve 33 for shutting-off the oil flow when required.

The driving line 23 with the isolation valve 27 is connected between the barrel 1 and an upstream isolation valve 34 com- municating with the tubing in the production Christmas tree 9.

Further, a wellhead isolation valve 35 is connected in a line connection 36 between the driving line 23 and the pipeline 2 with the pig isolation valve 22. The pipeline 2 and the line connec- tion 36 are both coupled to a flowline 37 extending between the wellhead 7 and a platform 38 on which there is arranged a receiver station 39 for a pig.

The manner of operation of the pig launching system of the embodiment shown in Fig. 4 will be further described below.

When a pigging operation is to be effected, the guide lines 11 are coupled to the underwater system by connecting them to the guide posts 13, and the running tool 5 is lowered and interconnected with the now empty pig-receiving unit 3. The coupling 17,18 between the unit 3 and the barrel 1 is opened, and the unit 3 is raised to the surface. The topical pig is introduced into the unit 3, and this is lowered by means of the running tool 5 as shown in Fig. 1, and the insert member 4 is introduced into the barrel 1 and the units are interconnected as

shown in Fig. 2. The running tool is disconnected and drawn up to the surface (Fig. 3). Thereafter the wellhead isolation valve 35 is closed at the same time as the pig isolation valve 22 is opened, and also the valves 33 and 34 are open. Thereafter the isolation valve 27 in the driving line 23 is opened, and the pig 6 then is pushed out into the pipeline 4 and further into the flowline 37, the pig being driven by the production fluid flow.

When the pig 6 has been pushed out into the flowline 37, the pig isolation valve 22 and the driving line valve 27 are closed. Thereafter the wellhead isolation valve 35 is opened, so that the natural production flow pushes the pig forwards to the receiver station 39 on the platform 38.

As an alternative to the embodiment according to Fig.

4, the driving function for the pig may be provided by means of liquid from the surface vessel via the umbilical 21 and the driving tool 5 forwards to the launching trap.