GB2255992A - Subsea guidebase - Google Patents

Abstract

A retrievable guidebase comprising a body which is arranged to be releasable connected to a subsea template 10. The body is adaptable between the primary configuration in which it is provided with a ring of primary guide post receptacles 21 on a API standard centres, and a secondary configuration in which the primary guide post receptacles 21 are removed and the body is provided with a ring of secondary guide post receptacles 17 on centres lying on a circle of lesser radius than that for a API standard centres. <IMAGE>

Description

SUBSEA WELL GUIDEBASE EOUIPMENT In the installation, completion and operation of subsea multi-well systems in oil and gas fields the necessary tools and strings are guided to, and located at, the individual wellheads by a ring of four equally spaced guide posts. These are, usually, removably mounted in receptacles, which are either welded to a multi-well template or are carried by a guidebase, which is secured, possibly releasably, directly or indirectly to the template. Invariably, the guide posts are centred at 900 intervals on a circle of diameter 6 feet, so that the axes of adjacent guide posts are spaced by substantially 2.58 m.

Such centres are established as the API (American Petroleum Institute) standard. It follows that since all running tools cooperating with such guide posts will have funnels and guide sleeves on the same centres as the guide posts, the running tools will be slightly greater than the plan area delimited by the guide posts. Now when the multi-well system is used with a TLP (tension leg platform) or fixed leg platform, all the running tools and, if retrievable, the guidebase, have to be retrieved through respective apertures in the lower deck of the platform. These apertures must therefore be at least as great in plan area as the size dictated by the API standard.Although it has been recognised that it is desirable to position the production risers as closely together as possible where they pass up through their respective apertures in the lower deck to the platform, in order to maximise the number of risers and/or minimise the wellbay plan area, the minimum size of the apertures to accommodate the API standard sized running tools, and the necessary walk-ways between the apertures, has, in the past, been a factor in limiting the closeness of approach of the risers at the platform.

The object of the invention is to enable the production risers to be grouped more closely together at the platform, thereby reducing the wellbay plan area, whilst still enabling drilling and pre-completion installation to be carried out at the subsea wellhead using conventional API standard sized equipment.

In accordance with a first aspect of the present invention, a method of working a subsea multi-well oil or gas field comprises locating on the seabed a template having a plurality of wellslot nodes; developing at each wellslot a well by securing at the node a guidebase having a ring of guide posts on API standard centres and guiding the necessary tools and strings for the well development down onto the guide posts; and subsequently completing and operating the wells by replacing the guidebase at the template node for a respective well by a guidebase having guide posts on centres lying on a circle of lesser radius than that for API standard centres, and providing a platform over the template; and thereafter guiding the necessary tools and strings for completion and operation of the well down onto the guide posts of the replacement guidebase.

With this arrangement, a guidebase can be lowered and secured to the template in a primary configuration for use in drilling and installation work, including running in and cementing the conventional casings, using standard tools having standard API centres, and a standard BOP (blow out preventer) stack conforming to the same API standard. The guidebase is then released from the template and retrieved.

After the platform has been located in positions e.g. a TLP has been tethered, a guidebase, now in a second configuration, can then be lowered through a respective aperture in the lower deck of the platform and resecured to the template in alignment with a wellhead. Tools with funnels and guide sleeves on correspondingly smaller centres than the API standard can then also be run in and retrieved through the aperture in the platform deck for completing and operating the well. Since these tools are now of a smaller size, the apertures in the platform deck can be correspondingly smaller, and closer together, than previously, thereby reducing the wellbay plan area.The improvement is expected to be significant as adjacent guide posts on API standard centres are just under 2.6 m apart whereas it is now envisaged that they may be positioned as closely as 1.4 to 1.9 m, preferably substantially 1.7 m, apart. A reduction in the mutual spacing of the guide post centres from 2.6 m to 1.7 m, allows the wellbay apertures to be decreased from 3 m square to as little as 2.2 m square or less.

In accordance with a second aspect of the present invention, a retrievable guidebase for a subsea wellhead comprises a body which is arranged to be releasably connected to a subsea template, and which is adaptable between a primary configuration in which the body is provided with a ring of primary guide post receptacles on API standard centres, and a second configuration in which the primary guide post receptacles are removed and the body is provided with a ring of secondary guide post receptacles on centres lying on a circle of lesser radius than that for API standard centres.

The adaptation of the guidebase between its first and second configurations may be accomplished in a variety of ways. Thus the primary receptacles and secondary receptacles may alternatively be releasably secured, i.e.

bolted on, to the body of the guidebase. Alternatively, the secondary receptacles may be permanent fixtures and the primary receptacles releasably secured, i.e. bolted on, to the body of the guidebase preferably immediately adjacent to the corners of the guidebase at which the primary receptacles are positioned. If, as is preferred, the guide posts are releasably securable in the receptacles, common guide posts may be alternately securable in either the primary or secondary receptacles.

If, as is usual, the template comprises one or more layers of horizontal elongate members extending parallel and perpendicular to one another and crossing one another at nodes at which wellslots, providing potential receptacles for wellheads, are provided, the guidebase body preferably has saddles which seat over the four members of the template extending away from the respective node at which the guidebase is fitted, and is provided with latches which are engagable beneath portions of the template members to secure the guidebase to the template. These latches may be pairs of latching dogs which are pivotable between release and lock positions and are set by an hydraulic power tool, for example by means of mandrels which are advanced to force the pawls to rotate from their release to their locking position, and thence to hold the dogs in their locking positions.

In addition to the advantage of decreasing the wellbay plan area requirements for a given number of wellheads, the invention leads to a number of other advantages. For example, the fact that the guidebase can be locked directly to the template structure without any significant template modifications, and can be retrieved and reinstalled on another wellslot, saves fabrication costs and time and simplifies installation. The fact that the guidebase can be retrieved so easily through the platform deck can readily relieve congestion near the template, for example when inspection or remedial work is necessary. Also, the reduced spacing of the centres of the guide posts during platform operation, enables the use of smaller, cheaper and lighter equipment than is conventionally possible. The ready removability of the guidebase from the template also enables the same guidebase to be retrieved and reinstalled on another wellslot, particularly during pre platform operations.

According to a third, independent, aspect of the invention, a running tool for use with a guidebase according to the second aspect of the invention comprises a body to which are releasably secured a ring of guide sleeves on centres corresponding to those of the secondary receptacles in the secondary configuration of the guidebase, and being releasable and resecurable to the body with interposed respective spacers whereupon the guide sleeves are on centres corresponding to those of the primary receptacles when the guidebase is in the primary configuration.

In this way the running tool, which may carry one or more hydraulic actuators for setting the locking dogs, when provided, on the guidebase body, or for any other purpose associated with a wellhead, can readily be adapted for use with the guidebase in one or other of its configurations.

An example of subsea wellhead equipment constructed in accordance with the invention is illustrated diagrammatically in the accompanying drawings, in which: Figure 1 is a perspective view showing a guidebase on a multi-well template; Figure 2 is a plan of the guidebase showing the guidebase in its second configuration; Figure 3 is a view seen in the direction of the arrow "X" in Figure 2; Figure 4 is a partly sectional view as seen in the direction of the arrow "Y" in Figure 2; Figure 5 is a view similar to Figure 4 but to a larger scale and showing a setting tool in cooperation with the guidebase; Figure 6 is a plan of the guidebase, similar to Figure 2 but showing the guidebase in its first configuration; Figure 7 is a plan of the running tool shown in Figure 5; and, Figure 8 is a view similar to Figure 7 showing the running tool in a different configuration.

As shown in Figure 1, the guidebase is used in conjunction with subsea multi-well template comprising horizontal, mutually parallel and perpendicular sets of elongate tubular members 10 which intersect at nodes provided with wellhead receptacles 11. The guidebase is of square frame configuration and consists of two yokes, bolted together at flanged connections 12, providing four upright side walls 13,14,15 and 16. The flanges allow the frame to be assembled around an installed riser. At each corner, the respective pair of walls are permanently fixed to a secondary socket receptacle 17 for a removable guide post 18. At each end of each side wall, are a pair of pads 19 each formed with a pair of screw threaded apertures 19.

These can be used to bolt on end brackets 20 fixed to primary socket receptacles 21 which are similar to the socket receptacle 17, in being able releasably to accommodate the same guide posts 18.

Each of the side walls 13-16 of the guidebase forms a saddle with a downwardly open curved recess 22 and a flared entry for self alignment when the guidebase is lowered onto a node of the template. When it has come to rest on the members 10, the guidebase is locked in position by use of a running tool which is shown in Figures 5 and 7. This has a square frame 23, again formed in two yokes interconnected at flange connections 24 and diagonal braces 25 to each of which a guide sleeve 26 is bolted by a flange connection 27. Two hydraulic actuators 28 are mounted one on each of two opposite sides of the frame 23.

The tool is run down with the guidebase. The sleeves 26 are located on the guide posts 18 and the hydraulic actuators 18 overlie a respective bridge 29 at the upper edges of the walls 14 and 16. As shown in Figure 4, but better in Figure 5, each hydraulic actuator comprises a ram 30, the cylinder of which is fixed to the frame 23 and the rod of which is fixed to a head 31, which is guided for vertical sliding movement by means of a frame 32, and which engages the upper end of a respective one of the bridges 29.Each bridge carries a pair of depending mandrels 33, which are movable by the ram from a raised position shown of the left-hand side in Figures 4 and 5, in which each mandrel is clear of a respective pivotal latching dog 34, so that the dog may swing free of the member 10, and a lowered position shown on the right-hand side of Figures 4 and 5 in which the mandrels 33 force the dogs 34 to pivot to a position in which they underlie the respective member 10 and positively secure the guidebase to the template.

After locking the guidebase to the template, the running tool can be retrieved in the usual way, and subsequently run down again to release the locking dogs and hence the guidebase from the template.

Figures 1 to 5 show the guidebase in its secondary configuration for TLP or other platform operations, that is without the receptacles 21 bolted on, and with the guide posts 18 fitted to the receptacles 17. In this case the guide post centres will be smaller than API standard centres.

For pre platform operations, the receptacles 21 will be bolted on and the guide post 18 will be fitted only in the receptacles 21. In this configuration the guide post centres will correspond to the API standard. This is shown in chain dotted lines on the right-hand side in Figure 1 and in full lines in Figure 6.

The change over between the two configurations is carried out at the surface after releasing the guidebase from the template and retrieving it. Setting and retrieval of the guidebase in the primary configuration is carried out utilising the Figure 7 running tool but adapted as shown in Figure 8 by unbolting the guide sleeves 26 at the flange connection 27, and interposing a respective extension spacer 35 by means of flange connections 36 and 37. The guide sleeves 26 are then on the same centres as the API standard.

Claims (13)

1. A method of working a subsea multi-well oil or gas field comprising locating on the seabed a template having a plurality of wellslot nodes; developing at each wellslot a well by securing at the node a guidebase having a ring of guide posts on API standard centres and guiding the necessary tools and strings for the well development down onto the guide posts; and subsequently completing and operating the wells by replacing the guidebase at the template node for a respective well by a guidebase having guide posts on centres lying on a circle of lesser radius than that for API standard centres, and providing a platform over the template; and thereafter guiding the necessary tools and strings for completion and operation of the well down onto the guide posts of the replacement guidebase.

2. A method of working a subsea multi-well oil or gas field substantially as described with reference to the accompanying drawings.

3. A retrievable guidebase for a subsea wellhead comprising a body which is arranged to be releasably connected to a subsea template, and which is adaptable between a primary configuration in which the body is provided with a ring of primary guide post receptacles on API standard centres, and a second configuration in which the primary guide post receptacles are removed and the body is provided with a ring of secondary guide post receptacles on centres lying on a circle of lesser radius than that for API standard centres.

4. A guidebase according to claim 3, wherein the secondary receptacles are permanent fixtures and the primary receptacles are releasably secured to the body of the guidebase.

5. A guidebase according to claim 4, wherein the primary receptacles are secured immediately adjacent to the corners of the guide posts at which the secondary receptacles are positioned.

6. A guide post according to any one of claims 3 to 5, wherein the primary and secondary receptacles are capable of alternately releasably receiving common guide posts.

7. A guidebase according to any one of claim 3 to 6, for use when the template comprises one or more layers of horizontal elongate members extending parallel and perpendicular to one another and crossing one another at nodes at which wellslots, providing potential receptacles for wellheads, are provided; wherein the guidebase body has saddles which seat over the four members of the template extending away from the respective node at which the guidebase is fitted, and is provided with latches which are engagable beneath portions of the template members to secure the guidebase to the template.

8. A guidebase according to claim 7, wherein the latches are pairs of latching dogs which are pivotable between release and lock positions and are set by an hydraulic power tool, and thence to hold the dogs in their locking positions.

9. A guidebase according to any one of claims 3 to 8, wherein, in the second configuration, adjacent guide posts are positioned between 1.4 and 1.9 metres apart.

10. A guidebase according to claim 9, wherein in the second configuration, adjacent guide posts are substantially 1.7 metres apart.

11. A retrievable guidebase for a subsea well head substantially as described with reference to the accompanying drawings.

12. A running tool for use with a guidebase according to any one of claims 3 to 11, comprising a body to which are releasably secured a ring of guide sleeves on centres corresponding to those of the secondary receptacles in the secondary configuration of the guidebase, and being releasable and resecurable to the body with interposed respective spacers whereupon the guide sleeves are on centres corresponding to those of the primary receptacles when the guidebase is in the primary configuration.

13. A running tool substantially as described with reference to the accompanying drawings.