GB2097449A

GB2097449A - Method of putting in position an equipment for production of hydrocarbons won from the bottom of the sea, and a production equipment for implementimg the method

Info

Publication number: GB2097449A
Application number: GB8211887A
Authority: GB
Original assignee: Coflexip SA
Current assignee: Technip France SAS
Priority date: 1981-04-23
Filing date: 1982-04-23
Publication date: 1982-11-03
Also published as: IT8220915A0; FR2504591A1; ES512260A0; NO821342L; BR8202358A; IT1151739B; FR2504591B1; ES8306213A1

Abstract

A method of putting in position on an undersea wellhead (1) an equipment which includes production tree (5) capable of being connected to the wellhead and undersea pipes (7) which include in particular production pipework, service pipework and remote control lines, capable of being connected by one end to the production tree and by the other end to a surface vessel (18), is characterized by the fact that from one and the same surface vessel the undersea pipes and at least one portion of the production tree are lowered simultaneously, the pipes having been previously connected at the surface to the said portion of the production tree, that after connection to the wellhead of the production tree or of the portion of it which has been lowered at the bottom end of the pipes, the pipes are tilted at the level of the production tree and are laid along the bottom by movement of the surface vessel, the top end of the pipes being connected to the surface vessel. <IMAGE>

Description

SPECIFICATION Method of putting in position an equipment for production of hydrocarbons won from the bottom of the sea, and a production equipment for implementing the method The present invention relates to a method of putting in position an equipment for production of hydrocarbons won from the bottom of the sea, and more precisely refers to the putting in position of a production equipment on a wellhead which has previously been installed following drilling, in order to ensure the placing of the corresponding well in production and the raising of the hydrocarbons produced up to a floating or nonfloating surface vessel.

At present, when such a decision to bring the well into production is taken, one proceeds in the following manner: After having put guide cables in position by means of a floating drilling rig, either with divers or with a drill-pipe string, the protector plug is removed and then the production tree is lowered and is installed on the drill-pipe string by means of the drilling rig. When the production tree has been connected, this connection is tested by putting under pressure the drill-pipe string connected to the production tree. Undersea pipes are lowered, which include production pipework, service and remote-control lines, and they are locked onto the production tree. These operations are carried out by means of a special ship and may deal with rigid or flexible pipes and may call upon automatic connections or connections made manually, that is to say, by divers.After this connection has been tested by putting the undersea pipes under pressure, one proceeds with the removal of the guide cables and with putting in production by connection of the undersea pipes to a surface support for production.

It has proved in practice that installation of the production tree and the testing of its connection onto the wellhead do not usually pose any particular problems. On the contrary the same does not hold for operations of laying and connection of undersea pipes onto the production tree in deep water.

Furthermore putting into production carried out by these conventional methods necessitates a number of different surface vessels, that is, a floating drilling rig for the installation of the production tree, a special ship for the installation, that is to say, the laying, connection and testing of the undersea pipes, and floating production platform for collecting the hydrocarbons at the time of bringing the well into production.

This succession of the various surface vessels over the site shows as very considerable cost and length of time of the operation.

In addition the successive lowering of the various members, that is to say, the production tree and then the undersea pipes, necessitates connection tests after each manipulation.

The present invention consequently proposes to provide a method of putting a production equipment in position, especially at great depth, which enables the employment of equipment which can be made availabie rapidly, is not very costly and is recoverable, and is easy to put to work and to maintain.

The method in accordance with the invention is characterized essentially by the fact that from a single surface vessel the undersea pipes and at least one portion of the production tree are lowered, the pipes having been previously connected at the surface to the said portion of the production tree, that after connection to the wellhead of the production tree or of the portion of it which has been lowered at the bottom end of the pipes, the pipes are tilted at the level of the production tree and are laid along the bottom by movement of the surface vessel, the top end of the pipes being connected to the surface vessel.

In a first embodiment the production tree is of onepiece type and is lowered down to the wellhead hung from the end of the pipes, and is set down and connected onto the wellhead.

By undersea pipes in the sense of the invention are to be understood the production and service lines as well as the lines for hydraulic and/or electrical remote control of the production tree; the invention likewise extends to the pipes for access to the well for work to be carried out by cable.

In a preferred method of implementation of the invention the undersea pipes are flexible pipes such, for example, as those manufactured in great lengths by the COFLEXIP Company. The invention is not, however, restricted and it may be implemented with rigid undersea pipes or rigid pipes connected to the production tree by a short length of flexible pipe.

The lowering of the production tree hung on the undersea pipes may be carried out by way of guide cables previously put into position between the surface vessel and the well head.

As a variant the lowering of the production tree and the putting of it in position on the wellhead may be ensured without guide cables be a system of guidance known in itself as a "re-entry cone", the base-plate of the wellhead as well as the production tree being then equipped with a system of guidance by a cone and a landing ring such as those employed at present in carrying 1out work at great depth.

In accordance with the invention provision is made, after connection of the production tree or of a portion of it onto the welihead, for making the pipes tilt at the level of the production tree and for laying them along the bottom by movement of the surface vessel. For this purpose the pipes are advantageously integral close to their bottom end with a stirrup capable of pivoting with respect to the production tree.

Thus in the production phase the surface vessel is not lying directly above the wellhead which has been equipped.

After finishing the exploitation of the well, or when it is desired to put in position on the wellhead another production equipment, the stages of the method described above are brought into play in the reverse order and one proceeds thus to the raising of the production tree hung on the undersea pipes, still by means of the same surface vessel.

The method in accordance with the invention has just been described for a onepiece production tree, but the method in accordance with the invention may equally well as a variant to be put into effect with a double tree of the "SPLIT TREE" type including a bottom portion or safety unit (MVA) and a top portion unit (PCA).

In this case the bottom safety unit of the production tree is lowered hung on the undersea pipes as indicated above, and after tilting of the pipes, one proceeds with the lowering and the attachment of the top production unit of the production tree by any suitable lowering processes, in particular by a drill-pipe string.

As one and the same surface support is being employed, it is in this case necessary before lowering the production unit to abandon the end of the undersea pipes by attaching them to an immersed or semi-floating buoy, the pipes being taken up again by the surface vessel after connection of the production unit orito the safety unit to form the whole production tree.

Other advantages and characteristics of the invention will appear from the reading of the appended description of embodiments by referring to the attached drawing in which: Figure 1 represents a wellhead equipped with a production equipment during the course of implementation of the method in accordance with the invention; Figures 2 to 6 illustrate the different phases of a first way of implementation of the method in accordance with the invention; and Figures 7 to 1 2 illustrate the different phases of a second way of implementation of the method in accordance with the invention; Figures 13 and 14 represent a wellhead equipped with a variant embodiment of the production equipment during the course of two phases of implementation of the method in accordance with the invention.

In Figure 1 is seen a wellhead 1 including a baseplate 2 and from which a conductor casing 3 extends into the bottom of the sea 4.

On this wellhead a production tree is put into position, which is designated as a whole by 5, more precisely in the embodiment described in Figure 1, it is the safety unit forming the bottom portion of a double tree, this tree including a top portion which is not shown, cailed the production unit.

The tree represented in Figure 1 is equipped with a connector 6 for the connection to the wellhead and is lowered in accordance with the invention by being hung from flexible pipes designated as a whole by 7 and including in the particular example of Figure 1 a flexible service pipe 8. a flexible production pipe 9 and a hydraulic umbilical cord 10.

The pipes 8 and 9 are connected to the production tree by swivelling connectors 11 and 1 2 respectively. In the example shown the pipe 9 comprises a rigid section 9'.

The assembly of pipes 7 is attached to a stirrup 13 mounted to be able to tilt about the production tree by its ends 14 and 15.

Locking mechanisms 1 6 are provided for immobilizing the stirrup with respect to the production tree during the lowering of it. Stops 1 7 are likewise provided for locking the stirrup 13 in rotation.

Reference will now be made to Figures 2 to 6 in order to describe a first way of implementation of the method in accordance with the invention.

On a wellhead 1 on standby after a drilling carried out in the sea bed 4 guidelines 19 are installed by means of divers from a surface vessel 1 8. As indicated diagrammatically in Figure 3 the production tree 5 is the lowered, hung on the flexible pipes 7 which are paid out from the same surface vessel 18. In the embodiment as Figures 2 to 6 the production tree is of onepiece type. The guidance of the lowering is effected by way of guide cables 19.

As may be seen in Figure 4 the production tree 5 is set down on the welihead and the connector 6 is locked.

After having tested the connection by putting the pipes under pressure, the guide cables 1 9 are removed.

As shown in Figure 5 the stirrup 1 3 is made to tilt and the surface vessel 1 8 is moved away from the wellhead which has been equipped, over to the position for bringing into production, represented in Figure 6.

Reference will now be made to Figures 7 to 12 which illustrate a second way of implementation of the method in accordance with the invention.

This embodiment employs a double production tree comprising a bottom portion or safety unit 5a and a top portion or production unit 5b.

As may be seen in Figures 7 to 9 one proceeds first of all with the lowering of the bottom portion 5a of the production tree in the same manner as in the first embodiment described with reference to Figures 2 to 6 with the exception of the fact that guide cables are not employed, but a conventional guide system by re-entry cone, the base-plate of the wellhead and the production tree being equipped with a system of guidance by cone and landing ring.

This embodiment might, however, be put into effect with guide cables, in the same way that the first way of implementation described may employ not guide cables but guidance by re-entry cone.

As may be seen in Figure 10, once the pipes 7 have been brought into the position corresponding with bringing into production, the end of them is abandoned on a buoy known as a sub-surface buoy 19 or else on the bottom of the sea with a marker buoy.

As illustrated in Figure 11, the top portion 5b of the production tree is then lowered by any suitable means from the same surface vessel 18, and connected to the portion 5a, the end of the pipes 7 being then taken up again by the surface vessel 18 for production as shown in Figure 12.

Reference will now be made to Figures 13 and 14 which illustrates a variant implementation of the invention.

Figure 1 3 is a view similar to Figure 1 and the similar parts in it bear the same reference numbers as those appearing in Figure 1.

The stirrup 13 is hinged at the upper portion of it onto a ball joint 20 integral with the pipes 7.

At the bottom portion of them the pipes are connected by connector pieces 21 to rigid sections of pipe 22 which ensure a connection with the production tree.

In Figure 14 in side elevation there is illustrated the device as Figure 1 3 after pivoting of the stirrup 13.

From examination of Figure 14 it will be understood that the pivoting stirrup 1 3 limits the curvature of the section of pipe between the ball joint 20 at the top end of the stirrup and the connector piece 21 at the end of the flexible pipe.

Supplementary devices which are not shown, may be provided in this section of pipe for limitation of curvature, such, for example, as vertebrate rings.

Although the invention has been described in connection with particular embodiments it is quite obvious that it is in no way restricted to them and that numerous variants and modifications may be applied to it without thereby departing from its scope or its spirit.

Claims

1. A method of putting in position on an undersea wellhead an equipment which includes a production tree capable of being connected to the welihead, and undersea pipes, in particular production pipework, service pipework and remote-control lines, capable of being connected by one end of the production tree and by the other end to a surface vessel, in which form a single surface vessel the undersea pipes and at least one portion of the production tree are lowered, the pipes having been previously connected at the surface to the said portion of the production tree, that after connection to the wellhead of the production tree or of the portion of it which has been lowered at the bottom end of the pipes, the pipes are tilted at the level of the production tree and are laid along the bottom by movement of the surface vessel, the top end of the pipes being connected to the surface vessel.

2. A method as claimed in claim 1 in which the production tree is of onepiece type and is lowered as a whole, hung from the end of the said pipes.

3. A method as claimed in claim 1 in which the production tree is of double type including a bottom portion or safety unit and a top portion or production unit, the bottom portion being lowered hung from the end of the pipes, and the top portion being lowered later and connected to the bottom portion.

4. A method as claimed in any one of the preceding claims, in which after having laid the pipes along the bottom, the top end of them is abandoned, attached to a buoy.

5. An equipment for the production of hydrocarbons, for implementing the method as claimed in any one of the preceding claims, in which it comprises a production tree equipped with means of connection to a well head and a plurality of undersea pipes connected to the said production tree, the said undersea pipes being integral in the vicinity of their bottom end with a stirrup capable of pivoting with respect to the production tree.

6. An equipment as claimed in claim 5, in which the production tree includes a bottom portion or safety unit and a top portion or production unit, in which the said stirrup and the said pipes are attached to the said bottom portion of the production tree.

7. An equipment as claimed in claims 5 and 6, in which it includes a iocking means for immobilizing the said pivoting stirrup on the production tree.

8. A method of putting in position on an undersea well head an equipment which includes a production tree capable of being connected to the well head, substantially as described herein with reference to and as shown in the accompanying drawings.

9. An equipment for the production of hydrocarbons, substantially as described herein with reference to and as shown in the accompanying drawings.