WO2012049509A2

WO2012049509A2 - Wellhead and christmas tree assembly

Info

Publication number: WO2012049509A2
Application number: PCT/GB2011/051980
Authority: WO
Inventors: Philip Head
Original assignee: Artificial Lift Company Limited
Priority date: 2010-10-12
Filing date: 2011-10-12
Publication date: 2012-04-19
Also published as: WO2012049509A3; GB201017178D0

Abstract

An adaptor is mounted on a wellhead and includes an access port positioned vertically above the wellbore, a lateral passage, and a port offset from the wellbore and communicating with the wellbore via the lateral passage, on which a conventional Christmas tree is mounted. The Christmas tree is offset from the axis of the wellbore so that the wellbore can be accessed directly through the access port without disturbing the Christmas tree. The novel assembly allows full bore well intervention without oversized valving.

Description

Wellhead and Christmas tree assembly

This invention relates to a wellhead and Christmas tree assembly, particularly but not exclusively for hydrocarbon wells.

Hydrocarbon wells comprise a borehole, usually lined with a casing which defines the wellbore. The casing tenninates at its upper end at a wellhead assembly (hereinafter referred to as the "wellhead"), typically comprising a number of short, flanged tubing portions which are sealingly connected in axial alignment with the casing. The wellhead contains pressure within the casing and supports production tubing which is typically suspended from hangers within the wellhead so as to extend down the wellbore, defining an annulus between the production tubing and the casing which may be accessed via valve connections extending laterally from the wellhead.

A Christmas tree, comprising a plurality of intercommunicating valves connected by pipework, is sealingly connected to the tubing head adapter at the upper end of the wellhead to control the flow of well fluids flowing up the wellbore via the production tubing. Typically the Christmas tree comprises lower and upper master valves, providing redundant shut-off of the wellbore. Conventionally, a pair of wing valves branch off laterally above the upper master valve, comprising respectively a production wing valve which provides a flowpath for fluid produced from the well, and a kill wing valve which allows fluid to be injected into the well, particularly dense fluid which is used to kill the well, which is to say, to provide sufficient hydrostatic head to balance the formation pressure so that the well may be opened to atmosphere without loss.

The upper end of the Christmas tree typically tenninates in a swab valve which is axially aligned with the wellbore. By killing the well and opening the master and swab valves, tooling may be introduced via the swab valve into the wellbore. Pressure and safety considerations mean that wellhead and Christmas tree valving is heavy and costly, and particularly so in larger sizes. Therefore it is undesirably costly and inconvenient to use valving and pipework of a size greater than necessary to handle the fluid produced from the well. However, where a well is in production with a Christmas tree mounted on the wellhead, the internal diameter of the pipework and valving of the Christmas tree is often insufficient to allow tooling of substantial diameter, such as an electrical submersible pump assembly (ESP) or the like, to be removed from or inserted into the wellbore via the swab valve. At the same time it is undesirable to remove the christmas tree to provide full bore access to the wellhead, since this is time consuming and involves a temporary absence of valve control.

It is the object of the present invention to provide a wellhead and christmas tree assembly which is more convenient in use.

In accordance with the present invention there is provided an apparatus as defined in the claims.

The invention provides a simple answer to the long-standing problem of how to insert tooling into a well that is already in production, with a christmas tree attached to the wellhead, while avoiding the need to remove the christmas tree or to employ oversize valving.

An illustrative embodiment of the invention will now be described, purely by way of example and without limitation to the scope of the claims, and with reference to the accompanying figures, in which: Figs. 1 A, IB and 1C are respectively front, side and top views of a first wellhead and Christmas tree assembly including an offset adaptor in accordance with a first embodiment;

Fig. 2 shows a development of the first assembly wherein the kill fluid port is offset to the same position in relation to the wellhead that it would have occupied if the adaptor were not present;

Fig. 3 shows a lubricator attached to the access port of the first assembly;

Fig. 4 is a longitudinal section through a hanger assembly comprising a cable suspended from a hanger mounted on a support;

Fig. 5 shows an ESP being lowered into the wellbore via the access port; and

Fig. 6 shows the hanger assembly of Fig. 4 mounted on the access port to suspend the ESP in the wellbore.

Corresponding features are indicated by the same reference numerals in each of the figures.

Referring to Figs. 1A - 1C, a wellbore 1 is defined by the inner surface of a fixed steel casing 2 which is cemented into the borehole, and a wellhead 3 comprising flanged tubing portions 3', 3" is sealingly fixed in fluid communication with the upper end of the casing. The wellhead defines a first passage 4 in axial alignment with the generally vertical axis XI - XI of the wellbore. Although the illustration is simplified, it will be understood that production and other tubing (not shown) may be suspended from hangers within the wellhead so as to extend down the wellbore, so that the well fluid produced from the well flows up the production tubing and through the first passage 4 to the wellhead. An adaptor 5 comprising a pressure resistant steel casing is sealingly fixed in fluid communication with the tubing head adapter 3" forming the upper end of the wellhead, the adaptor 5 defining a vertical second passage 6 axially aligned with the first passage 4, and a third passage 7 which extends laterally and horizontally from the second passage.

The second passage 6 terminates at an access port 8 which is arranged in the horizontal upper wall of the adaptor 5 and is axially aligned with the second passage 6, the first passage 4 and the wellbore 1 and sealingly closeable and openable by means of a removable plug or cover plate 9 to provide access via the second and first passages to the wellbore.

The third passage 7 communicates with another port 10, also arranged in the horizontal upper wall of the adaptor 5 but offset from the central axis XI - XI of the wellbore. A Christmas tree 11 is sealingly fixed to the port 10 in fluid communication with the third passage, so that the central axis X2 - X2 of the Christmas tree is generally vertical and parallel with but spaced apart from the central axis XI - XI of the wellbore.

The Christmas tree is of conventional design and comprises a plurality of intercommunicating valves connected by pipework for controlling the flow of well fluid from the wellbore. In the example shown, the Christmas tree comprises lower 12 and upper 13 master valves, a production wing valve 14 providing a flowpath for well fluid (e.g. oil or gas) produced from the well, and a kill wing valve 15 through which a kill fluid may be injected into the well. A valve 16 may be arranged at the upper end of the Christmas tree in the position conventionally occupied by a swab valve; of course, since the Christmas tree is offset from the wellbore, valve 16 is not used as a swab valve. Preferably, the diameter Dl (Fig. 2) of the second passage 6 is substantially not less than that D4 of the first passage 4 which is substantially the same as that D3 of the wellbore 1. In contrast, the Christmas tree may comprise pipework of a smaller diameter D2 (Fig. 2) than that (Dl) of the second passage 6. It will be seen that the valve 16, which conventionally would be used as a swab valve, is narrower than the wellbore, and therefore not capable of accepting a large diameter tool such as an ESP.

Referring to Fig. 2, the wing valves may optionally be provided with bent (e.g. sigmoidal) or jointed pipework which communicates with a port 17 positioned in the same position in relation to the wellhead that it would have occupied if the adaptor were not present. This makes it possible for a conventional Christmas tree to be mounted on the novel adaptor 5 and interfaced with existing surface pipework.

In the example of Figs. 1A - 1C, the access port 8 communicates directly with the first passage 4 without intermediate valving. This enables the access port 8 to be the full diameter of the wellbore without incurring the expense of large diameter valving.

Referring to Figs. 4, 5 and 6, the well is therefore first killed by pumping a kill fluid into the wellbore via kill valve 15 before the plate 9 is removed to open the access port 8 so that a tool such as an ESP 18 suspended on an umbilical connection 19 may be inserted into or removed from the wellbore via the port 8. Other interventions such as wireline or coiled tubing procedures conventionally performed via the swab valve may similarly be performed via the access port 8 without disturbing the Christmas tree.

Fig. 4 shows a hanger assembly 20 comprising a hanger 21 mounted on a support assembly 22 which is sealingly attachable to the access port 8. The umbilical connection 19 comprises three self supporting insulated electrical conductors 23, which may comprise copper clad steel, enclosed in a flexible stainless steel tubing which forms a casing 29. The conductors are supported by wedge assemblies 24 in the insulating ceramic body 25 of the hanger 21, which is fixed by inwardly directed securement screws 26 in the support assembly 22. The conductors are electrically connected to cables 27 which sealingly penetrate a bonnet 28 which provides a pressure tight cap to seal the wellbore.

Referring to Fig. 6, the hanger assembly 20 is sealingly mounted on the access port 8, and once the ESP has been lowered to its deployed position in the wellbore, the bonnet 28 is closed so that the ESP is suspended on the adaptor 5 from the hanger 21 and support assembly 22 and supplied with electrical power via the cables 27. The umbilical connection 19 extends down the wellbore via the first and second passages 4, 6. In alternative embodiments, the hanger assembly 20 can be adapted to support other flexible elements such as coiled tubing or wireline rather than electrical cables, so that the flexible element is gripped by a hanger supported by a support which is mounted on the adaptor 5.

Referring to Fig. 3, in a development, a lubricator 30 comprising a pressure resistant chamber 31 which is openable and closeable by means of a removable top plate 32. The lubricator includes a conventional pressure seal assembly 33 through which an electrical cable, wireline or coiled tubing may be slidingly and sealingly passed into and out of the chamber without losing pressure from the wellbore. The chamber 31 is sealingly fixed in fluid communication with the access port 8, which is sealingly openable and closeable by means of an access port valve 34 arranged between the second passage 6 and the chamber 31. The internal diameter of the access port valve 34 is equal to that of the access port 8 and substantially greater than that of the christmas tree pipework and valving. The lubricator allows an ESP or other tooling to be inserted into or removed from the wellbore without killing the well. By shutting the valve 34, enclosing the tool in the lubricator and then opening the valve 34, the tool may be lowered into a live well on an umbilical connection passing through the seal assembly 33 without loss of pressure. To remove the tool from the live well, it is raised on the umbilical until it enters the chamber 31, then the valve 34 is closed and the pressure within the chamber is bled off via a bleed valve (not shown) until the chamber is depressurised, following which the top plate 32 is opened and the tool removed.

In summary, a preferred embodiment provides an adaptor mounted on a wellhead and including an access port positioned vertically above the wellbore, a lateral passage, and a port offset from the wellbore and communicating with the wellbore via the lateral passage, on which a conventional Christmas tree is mounted. The Christmas tree is offset from the axis of the wellbore so that the wellbore can be accessed directly through the access port without disturbing the Christmas tree. The novel assembly allows full bore well intervention without oversized valving.

Further adaptations will be evident to those skilled in the art on perusing the foregoing description, and it will be understood that the invention is limited only by the claims.

Claims

1. An apparatus for producing well fluid from a wellbore, comprising: a wellhead sealingly fixed in fluid communication with an upper end of the wellbore, the wellhead defining a first passage axially aligned with the wellbore; an adaptor sealingly fixed in fluid communication with the wellhead, the adaptor defining a second passage axially aligned with the first passage and a third passage extending laterally from the second passage; the second passage terminating at an access port, the access port being axially aligned with the second passage and sealingly closeable and openable to provide access via the second and first passages to the wellbore; and a Christmas tree sealingly fixed in fluid communication with the third passage, the Christmas tree comprising a plurality of intercommunicating valves for controlling the flow of well fluid from the wellbore.

2. An apparatus according to claim 1, wherein the second passage is of a diameter substantially not less than that of the first passage.

3. An apparatus according to claim 1, wherein the Christmas tree comprises pipework of smaller diameter than the second passage.

4. An apparatus according to claim 1, wherein the access port communicates directly with the first passage without intermediate valving.

5. An apparatus according to claim 1, wherein a support is provided, and a cable or flexible tubing is suspended in the wellbore via the second passage from a hanger supported by the support.

6. An apparatus according to claim 1, wherein a lubricator comprising an openable and closeable chamber is sealingly fixed in fluid communication with the access port, and the access port is sealingly openable and closeable by means of an access port valve arranged between the second passage and the chamber.

7. An apparatus substantially as described herein with reference to the accompanying drawings.