GB2139267A - Drilling rig - Google Patents

Abstract

A drilling rig, comprises a tiltable drilling mast (1), a turntable (6) for supporting the mast above a support platform, and for permitting rotation of the mast about a substantially vertical axis, and a pair of skid-rails (15) for enabling movement of the turntable along the support platform. The rig preferably includes an intermediate platform (12) adapted for movement along the support platform, and a further pair of skid- rails (11) for enabling movement of the turntable transversely along the intermediate platform. Gripper jacks (13, 17) are provided, to move the turntable and the intermediate platform along the respective skid-rails. <IMAGE>

Description

SPECIFICATION Drilling rig This invention relates to drilling rigs, and has particular, though not exclusive application to offshore oil and gas drilling rigs.

In drilling rigs of this kind, it is quite common for a number of shafts or bores to be sunk from a single platform, utilising the same drilling mast. Typically, for example, sixteen bores may be sunk from a single platform, by positioning the drilling mast at four angular orientations at each of four respective corners of a generally rectangular drilling platform. In order that the drilling apparatus is generally within the protective envelope defined by the legs of the drilling rig, it is common practice for the four orientations to be in a fan-shape, generally towards the centre of the drilling platform.

Rotating conventional drilling masts at the four corners of the rig is a very difficult and time-consuming process, and can typically involve as many as 50 separate jacking operations.

According to a first aspect of this invention there is provided a drilling rig comprising a tiltable drilling mast, a turntable for supporting the mast above a support platform, and for permitting rotation of the mast about a substantially vertical axis, and means for enabling movement of the turntable along the support platform.

The term "turntable" as used herein is intended to mean any generally circular structure which is capable of supporting the mast, whiist permitting its rotation about a substantially vertical axis, and is not intended to imply the need for any complex bearing arrangement or the like. Indeed in its simplest embodiment, the turntable consists simply of a single circular skid rail, on which the drilling mast and its associated support structure may be slid.

The means for enabling movement of the turntable along the support platform preferably includes a pair of skid-rails, and a pair of gripper jacks, adapted to move the platform along the skid-rails. So as to enable four corners of the support platform to be accessed by the drilling mast, an intermediate platform is preferably provided, adapted for movement along the support platform. The intermediate platform is adapted to move along the support platform, preferably along skid-rails, utilising gripper jacks, and the turntable is able to move along the intermediate platform, transversely of the direction of movement of the intermediate platform along the support platform. Again, slide rails and gripper jacks are preferably used for this movement.

The turntable itself preferably comprises, as mentioned above a generally circular skid-rail on which may be slide a mast support platform. Again, a pair of gripper jacks may be used to effect the rotation. The gripper jacks may be arranged to work in opposed directions, at opposite ends of a diameter of the circular slide rail. Thus, the gripper jacks may be rigidly mounted on the base of the mast support platforms, and caused to grip the circular skid-rail on actuation, and to act in opposed directions to rotate the mast support platform.

A further problem which arises with conventional drilling rigs utilising multiple bores is that c'f the connection of services to the mast platform. A very wide variety of services are required during the drilling operation, from electrical power, to cement, water drilling mud and the like. It is particularly desirable that these services should be conveniently grouped together, and preferably grouped in a way which obviates the need for constant disconnection and reconnection.

A method of dealing with services which has been used in the past is the provision of a so-called "drag chain" to which the various services are secured.

In an alternative preferred embodiment of this invention, a drag chain is provided which is so constructed and arranged as to form a coil so as to avoid fouling of the services on rotation of the drilling mast on the turntable.

A preferred embodiment of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 shows a schematic diagram of a drilling rig according to the invention, and Figure 2 is a schematic plan view of the drilling rig of Fig. 1; Referring first to Fig. 1, a drilling rig comprises a drilling mast 1 of conventional form, so constructed and arranged as to be capable of being tilted about axis 2, (as shown by arrow 3), so that it can take up the position shown by the chain-dotted line 4. The tiltable mast 1 is supported on a mast support platform 5. The base of the mast support platform rests on a circular skid-rail 6, which may be for example of "I" or box section.The mast support 5 can be caused to slide over the circular skid-rail 6 by means of hydraulic gripper jacks 8, which are arranged to operate in opposed directions at the opposite ends of a diameter of the rail 6. The jacks 8 are secured to the base of the platform 5, and are such that, on hydraulic actuation, each jack will hydraulically grip the rail below, and a hydraulic ram will cause rotation of the mast about the vertical axis of the support platform 5. Thus, rotation of the mast support platform, and with it the mast, is caused, in the direction shown by the arrow 9. The circular skid-rail 6 thus constitutes a turntable for supporting the mast support platform and the mast.

The turntable assembly 6, 5, 1 is mounted on a transverse skid-base 10, which rests on two skid-rails 11, which are provided on the upper surface of an intermediate platform 12.

Gripper jacks 1 3 are provided to enable the transverse skid-base 10, complete with a turntable assembly, mast support platform, and mast to be skidded bodily along the intermediate support platform 1 2. The gripper jacks 1 3 are similar to the jacks 8, and can grip the skid-rails 11, to cause the lateral translation of the transverse skid-base 10 and associated superstructure.

The intermediate platform 1 2 can itself skid along longitudinal skid-rails 14 in the direction shown by the arrow 16. Gripper jacks 1 7 similar to the gripper jacks 8 and 1 3 are provided to enable movement of the entire intermediate platforms from one end to another of a main support platform (not shown) on which the longitudinal skid-rails 1 5 are supported.

Services such as mud, cement, electricity, and the like are conducted to the transverse skid-base 10 by means of a drag chain 20, which is caused to unwind along the direction of the arrow 14, as the skid-base 10 moves along the rails 11. A junction 21 may be provided to enable the services to be supplied to the movable intermediate platform 1 2.

These services may be fed to the junction 21 by means of a conventional trailing catenary.

Connection of services from the transverse skid-base 10 to the mast support platform 5 may be by means of a special form of drag chain, having a construction such that it will assume a coiled shape, and thus follow rotary movement of the mast support platform about its vertical axis.

In an alternative and preferred embodiment, as illustrated in Fig. 1, a catenary 30 of generally conventional form is utilised, one end being secured to a support on the intermediate platform 12, and the other end secured to the mast support platform 5. The catenary is simply positioned manually on rotation of the mast support platform.

As an alternative to the skid-rails described above, rollers or rails of an alternative sort may be utilised, provided that sufficient locking of the structure is carried out before operation.

In typical use, the intermediate platform 1 2 is first slid along the rails 1 5 to the desired position, normally an end position of the rails 15, and the intermediate platform is then locked in position by clamps. The transverse skid-base 10 is then slid along the skid-rails 11 to the desired position, normally one or other corner of the main drilling platform. The transverse skid-base 10 is then clamped in position over the desired location.

The mast support platform 5 is then rotated on the turntable constituted by the skid-rails 6 and 7, and utilising the hydraulic jacks 8, until the desired angular orientation is achieved. During this rotation operation, the catenary 30 maintains connection of services with the mast support platform 5.

When the appropriate rotational orientation has been selected, the mast support platform 5 is clamped in position to the intermediate platform 12, and the drilling mast 1 tilted about axis 2 until the required angle to the vertical is achieved.

To produce a second bore at the same position, all that is required is that the mast 1 is first aligned to its vertical position, the clamps between the mast support platform 5 and intermediate platform 12 are released, new orientation is achieved using the gripper jacks 8, the platform 5 reclamped, and the mast 1 re-tilted. A slight movement in either direction 14 or 16 will in general also be necessary, to ensure that the new bore does not interfere with pipework associated with the previous bore.

Claims (1)

1. A drilling rig comprising a tiltable drilling mast, a turntable for supporting the mast above a support platform, and for permitting rotation of the mast about a substantially vertical axis, and means for enabling movement of the turntable along the support platform.

2. A rig as claimed in Claim 1, wherein the means for enabling movement of the turntable along the support platform includes an intermediate platform, adapted for movement along the support platform, and means are provided for enabling movement of the turntable along the intermediate platform, transversely of the direction of permitted movement of the intermediate platform along the support platform.

3. A rig as claimed in Claim 2, wherein the intermediate platform includes a pair of skid rails, to enable the turntable to be slid along the intermediate platform.

4. A rig as claimed in Claim 3, and including a pair of gripper jacks, adapted to grip the skid-rails, and to move the turntable along the skid-rails.

5. A rig as claimed in any one of Claims 2 to 4, including a drag chain assembly on the intermediate platform to enable services to be conducted to the turntable at different positions of the turntable along the intermediate platform.

6. A rig as claimed in any one of the preceding claims, wherein the turntable includes a generally circular skid-rail.

7. A rig as claimed in Claim 6, including at least a pair of gripper jacks, adapted to rotate the mast on the skid-rail about the said substantially vertical axis.

8. A rig as claimed in Claim 7, wherein the said pair of gripper jacks are positioned substantially at opposite ends of a diameter of the said circular skid-rail, and are arranged so as to operate in opposed directions.

9. A rig as claimed in any one of the preceding claims, wherein the support platform includes a pair of skid-raiis, and a turntable and/or the intermediate platform is adapted for sliding movement along the said skid-rails.

10. A rig as claimed in Claim 9, including a pair of gripper jacks adapted to grip the skid-rail on the supported platform, to cause movement of the turntable and/or the intermediate platform along said skid-mils

11. A rig as claimed in any one of the preceding claims, and including a drag chain for supplying services from the base of the turntable to the rotatable part of the rig.

1 2. A rig as claimed in Claim 11, wherein the said drag chain is adapted to form a coil on rotation of the mast.

1 3. A rig as claimed in Claim 11 or Claim 12, and including a catenary for supplying services to the mast.

14. A drilling rig substantially as hereinbefore described with reference to, and as illustrated by, Fig. 1 of the accompanying drawings.

1 5. A method of operating a drilling rig which method comprises providing on an upper surface of a support platform a pair of skid-rails, skidding a turntable supporting a drilling mast along the skid-rails from a first position to at least one further position, rotating the drilling mast on the turntable to a plurality of orientations at each of the said drilling positions, and drilling a respective shaft at each of the said orientations.

16. A method as claimed in Claim 15, wherein four shafts are drilled from each of at least four positions.

17. A method as claimed in Claim 16, wherein the four positions are at four respective corners of a generally rectangular support platform.

1 8. A drilling method substantially as hereinbefore described with reference to, and as illustrated by the accompanying drawings.

1. A drilling rig comprising a tiltable drilling apparatus including a tiltable drilling mast to allow drilling at an angle to the vertical, a turntable for supporting the mast above a support platform, and for permitting rotation of the mast about a substantially vertical axis, and means for enabling movement of the turntable along the support platform.