GB2096204A

GB2096204A - Improvements relating to slant drilling apparatus

Info

Publication number: GB2096204A
Application number: GB8110695A
Authority: GB
Original assignee: British Gas Corp
Current assignee: British Gas Corp
Priority date: 1981-04-06
Filing date: 1981-04-06
Publication date: 1982-10-13
Also published as: GB2096204B

Abstract

Apparatus for drilling boreholes at an angle to the vertical comprises a drilling mast 15 pivotally mounted on a support structure 14 and a racking tower 16 arranged to accommodate drill pipes and pipe collars in a substantially vertical disposition. A gantry 19 extends between an upper part of the drilling mast 15 and an upper part of the racking tower 16 and is arranged so that at least part of the gantry can be moved relative to the racking tower 16 to tilt the drilling mast 15 to a desired angular position. A travelling crane 23 provided on the gantry is utilized to tilt the drilling mast and to transport drill pipes and pipe collars between the racking tower and the drilling mast. <IMAGE>

Description

SPECIFICATION Improvements relating to drilling apparatus This invention relates to drilling apparatus of a kind suitable for drilling boreholes at an angle to the vertical. Such apparatus, hereinafter referred to as "slant drilling apparatus", may be used either at offshore locations or at inland locations where a plurality of boreholes disposed at an angle to the vertical are required at a location.

In United States Patent Specification No.

3 451 493 there is disclosed slant drilling apparatus for drilling a plurality of boreholes disposed at an angle to the vertical at a predetermined orientation relative to one another around a platform. A tiltable drilling mast is arranged to be tilted to align a drilling axis of the drilling mast with one of a plurality of guide tubes provided on the platform and corresponding in inclination to the vertical and orientation with one of the boreholes to be drilled. The drilling mast is moved around the platform and tilted so that the drilling axis is aligned with each of the guide tubes in sequence so that all the boreholes are drilled in sequence.

In the slant drilling apparatus disclosed in United States Patent Specification No. 3 451 493 the drill pipes and pipe collars are disposed horizontally on the platform in the central portion of the platform inboard of the drilling mast, the individual drill pipes and pipe collars being moved from the horizontal position on the platform to an inclined position on the drilling mast by a pipe elevator. It is a disadvantage of this slant drilling apparatus that disposing the drill pipes and pipe collars horizontally is wasteful of the available space on the platform, especially when the drill pipes and pipe collars have to be moved around the platform relative to the drilling mast as the drilling mast is moved from one guide tube to another.

An object of the invention is to provide slant drilling apparatus which overcomes the abovementioned disadvantage.

According to one aspect of the present invention slant drilling apparatus comprises a drilling mast pivotally mounted on the support structure, a racking tower mounted on the support structure and arranged to accommodate drill pipes and pipe collars in a substantially vertical disposition, and a gantry extending between an upper part of the drilling mast and an upper part of the racking tower, at least part of the gantry being movable relative to the racking tower to tilt the drilling mast to a desired angular position.

Preferably the gantry comprises two interfitting parts, of which a part connected to the drilling mast is movable towards or away from a part connected to the racking tower to tilt the drilling mast to a desired drilling position.

Conveniently, a travelling crane may be provided on the gantry for transporting drill pipes and pipe collars between the racking tower and the drilling mast. The travelling crane provided on the gantry may also be utilized to tilt the drilling mast to the desired angular position. The support structure may be provided with a drag way to enable to drill pipes to be aligned with a drilling axis of the drilling mast.

According to another aspect of the present invention slant drilling apparatus comprises a platform around which a plurality of boreholes are to be drilled at a predetermined angle to the vertical and at a predetermined orientation to one another, a plurality of conductors extending from the platform each corresponding in inclindation to the vertical and orientation with one of the boreholes to be drilled, a drilling mast arranged to be tilted to align a drilling axis of the drilling mast with one of the conductors, a racking tower provided on the platform and arranged to accommodate drill pipes and pipe collars in a substantially vertical disposition, and means for moving the drilling mast and the racking tower around the platform to enable each of the boreholes to be drilled.

The means for moving the drilling mast and the racking tower around the platform may include a complex of rails along which they can be skidded between positions on the platform from which slant drilling is to take place.

The platform may be substantially rectangular in plan view and have a plurality of conductors arranged in a predetermined orientation to one another at each corner.

The platform may be a fixed platform and may be used in conjunction with a mobile platform which provides all the ancillary services.

Preferably the slant drilling apparatus includes a gantry which extends between the upper part of the drilling mast and the upper part of the racking tower, at least part of the gantry being movable relative to the racking tower to tilt the drilling mast to a desired angular position.

The gantry may comprise two interfitting parts, of which a part connected to the drilling mast is movable towards or away from a part connected to the racking tower to tilt the drilling mast to a desired angular position.

Embodiments of the invention in both its aspects will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a perspective view of slant drilling apparatus in accordance with the invention mounted on a drilling platform located alongside a mobile jack-up platform which provides ancillary services; Figure 2 is a side elevation of the slant drilling apparatus shown in Figure 1; Figure 3 is a front elevation of the drilling mast and support structure shown in Figure 2; and Figure 4 is a schematic plan view of the support structure showing the positions of the drilling mast, rotary table, racking tower and draw works.

Referring in the first instance to Figure 1 , the slant drilling apparatus 1 in accordance with the invention is mounted on a fixed drilling platform 2 shown at the left hand side of the Figure alongside a mobile jack-up platform 2 shown at the right hand side of the Figure. The fixed drilling platform 2 is mounted on four tubular legs 4 which extend to the seabed and contain piles which are driven into the seabed to secure and anchor the apparatus. Bracing members 5 extend between the legs 4 and are also connected to intermediate positions on the underside of the platform 2. The platform 2 is provided with a complex of rails along which the various items of equipment can be skidded from one position on a deck 6 of the platform to another as will be described below.

The platform 2 is provided with a plurality of tubular conductors 10, each corresponding in inclination to the vertical and in orientation relative to one another with one of a plurality of boreholes which are to be drilled in the seabed.

Each of the tubular conductors 10 extends from an aperture 11 in the deck 6 and terminates in the seabed and is secured by guides 13 on the bracing members 5 and the underside of the platform 2 to maintain it in this position. Three apertures 11 are provided at each corner of the deck 6 and a tubular conductor 10 extends downwards from each aperture 11 although for simplicity only three such conductors 10 are shown in the Figure. The slant drilling apparatus 1 which is mounted on the deck 6 comprises a support structure 14 on which is carried a drilling mast 15 and a racking tower 1 6. The racking tower 1 6 is rigidly secured to the support structure 14 and extends vertically upwards so that drill pipes 33 and pipe collars can be accommodated therein with their longitudinal axes arranged substantially vertically.

As shown in more detail in Figures 2 and 3 a gantry 19 extends between an upper part of the racking tower 16 and an upper part of the drilling mast 1 5 in a substantially horizontal direction. The gantry 1 9 comprises two interfitting parts 20 and 21 of which the part 20 is secured to the drilling mast 15 and is movable within the part 21 which is secured to the racking tower 1 6. A travelling crane 23 is provided on the gantry and is movable between the racking tower 1 6 and the drilling mast 15 for transporting drill pipes 33 and pipe collars 35 therebetween.A dragway 24 extends from the rear of the support structure 14, that is the end on which the racking tower 1 6 is located, and provides protection for pipes (not shown) extending from the mobile jack-up platform 2 which convey services such as mud and cement.

The travelling crane 23 is arranged to move the part 20 of the gantry 1 9 away from the racking tower 1 6 so that the part 20 slides within the part 21 and moves the drilling mast 15 between the vertical position shown in Figure 2 of the drawings and the tilted position which is also shown in that Figure. The drilling mast 1 5 tilts about a horizontal axis 25 so that its drilling axis 26 is aligned with one of the tubular conductors 10. As shown in Figure 4 a rotary table 27 is provided at the base of the drilling mast 1 5 to enable the drill pipes 33 to be gripped, and a rotary drive 28 is provided to enable the rotary table 27 to be rotated. The support structure 14 is also provided with draw works 29 and with winches 30 and 31.The racking tower 1 6 is provided with pipe racks such as 32 for accommodating the drill pipes 33 and with racks such as 34 for accommodating the pipe collars 35.

The mobile jack-up platform 3 which is located alongside the fixed platform 2 comprises a buoyant structure 41 which is supported on three retractable legs 42. As shown in Figure 1 the three legs 42 are lowered into contact with the seabed so that the structure 41 is raised clear of the water and a deck 43 is at substantially the same level as the deck 6 of the fixed drilling platform 2. The structure 41 also includes buildings 45 which provide living accommodation for the crew and a helicopter landing pad 46. Three cranes 47 are installed on the deck 43 for moving equipment about the deck and for transferring equipment such as drill pipes 33 and pipe collars 35 about the deck 43 and between the deck 43 and the dragway 24 of the support structure 14.

Gangways 48 provided with pairs of rails 49 extend between the deck 43 and the deck 6 to enable the support structure 14 to be moved between the two decks.

In use of the slant drilling apparatus 1 in accordance with the invention the mobile platform 2 is brought alongside the fixed platform 2 and the legs 42 lowered to the seabed to anchor the platform 2 in this position. The support structure 14 is then skidded from the deck 43 along the rails 49 on the gangway 48 and onto the rails 7 of the deck 6 of the drilling platform 2. The support structure 14 is then skidded along the rails 7 to one of the corners of the deck 6 in the vicinity of an aperture 11. While the support structure 14 is skidded along the rails 7 and 49 the drilling mast 1 5 is maintained in a substantially vertical position parallel to the racking tower 14.

The support structure 14 is then adjusted on the rails 7 so that the base of the drilling mast 1 5 is above the aperture 11 in the deck 6 and is secured in this position. Guides 1 3 are secured to the bracing members 5 and the underside of the platform 2 at positions aligned with the angle to the vertical at which a borehole is to be drilled in the seabed. The drilling mast 1 5 is tilted by the travelling crane 23 so that the drilling axis 26 is aligned with the guides 13 and a string of conductors 10 is placed in the guides 13 and lowered through the guides to the seabed. The string of conductors 10 is then driven into the seabed with a pile driving hammer (not shown) until it cannot be driven further.

The drill pipes 33 and pipe collars 35 are then removed from the racking tower 1 6 and formed into a string which is aligned with the drilling axis 26 so that the string of drill pipes extends through the conductors 10 with its lower end in contact with the seabed. The upper end of the string of drill pipes 33 is clamped in the rotary table 27 and is rotated by the rotary drive 28 to drill the borehole through the string of conductors 1 0.

Further drill pipes 33 and pipe collars 35 are added to the string until the borehole reaches the required depth. When the borehole has been completed the support structure 14 is skidded along the racks 7 until the base of the drilling mast 1 5 is located over the next aperture 11 and the drilling operation repeated. In this way boreholes can be drilled at all the four corners of the platform 2 which are provided with apertures 11 in the deck 6.

It is an advantage of the slant drilling apparatus of the invention that the vertically disposed racking tower 1 6 enables a relatively large number of drill pipes 33 and pipe collars 35 to be accommodated in a relatively small surface area on the support structure 1 4. Moreover, the use of the gantry 19 to tilt the drilling mast 1 5 enables the travelling crane 23 on the gantry to be used not only for transporting the drill pipes and pipe collars between the racking tower and the drilling mast but also to be utilised to provide the drive to tilt the drilling mast.

Claims

1. Slant drilling apparatus comprising a drilling mast pivotally mounted on a support structure, a racking tower mounted on the support structure and arranged to accommodate drill pipes and pipe collars in a substantially vertical disposition, and a gantry extending between an upper part of the drilling mast and an upper part of the racking tower, at least part of the gantry being movable relative to the racking tower to tilt the drilling mast to a desired angular position.

2. Slant drilling apparatus as claimed in Claim 1, wherein the gantry comprises two interfitting parts, of which a part connected to the drilling mast is movable towards or away from a part connected to the racking tower to tilt the drilling mast to a desired drilling position.

3. Slant drilling apparatus as claimed in Claim 1 or Claim 2, wherein a travelling crane is provided on the gantry for transporting drill pipes and pipe collars between the racking tower and the drilling mast.

4. Slant drilling apparatus as claimed in Claim 3, wherein the travelling crane provided on the gantry is also utilized to tilt the drilling mast to the desired angular position.

5. Slant drilling apparatus as claimed in any preceding claim, wherein the support structure is provided with a drag way to enable to drill pipes to be aligned with a drilling axis of the drilling mast.

6. Slant drilling apparatus as claimed in any preceding claim wherein the racking tower is disposed substantially vertically and the gantry extends substantially horizontally.

7. Slant drilling apparatus comprising a platform around which a plurality of boreholes are to be drilled at a predetermined angle to the vertical and at a predetermined orientation to one another, a plurality of conductors extending from the platform each corresponding in inclination to the vertical and orientation with one of the boreholes to be drilled, a drilling mast arranged to be tilted to align a drilling axis of the drilling mast with one of the conductors, a racking tower provided on the platform and arranged to accommodate drill pipes and pipe collars in a substantially vertical disposition, and means for moving the drilling mast and the racking tower around the platform to enable each of the boreholes to be drilled.

8. Slant drilling apparatus as claimed in Claim 7, wherein a gantry extends between the upper part of the drilling mast and the upper part of the racking tower, at least part of the gantry being movable relative to the racking tower to tilt the drilling mast to a desired angular position.

9. Slant drilling apparatus as claimed in Claim 8, wherein the gantry comprises two interfitting parts, of which a part connected to the drilling mast is movable towards or away from a part connected to the racking tower to tilt the drilling mast to a desired angular position.

10. Slant drilling apparatus as claimed in Claim 8 or Claim 9, wherein a travelling crane is provided on the gantry for transporting drill pipes and pipes collars between the racking tower and the drilling mast.

11. Slant drilling apparatus as claimed in Claim 10, wherein the crane provided on the gantry is also utilized to tilt the drilling mast to the desired angular position.

12. Slant drilling apparatus as claimed in any one of Claims 7 to 11, wherein the drilling mast and the racking tower are mounted on a common support structure, and the means for moving the drilling mast and the racking tower around the platform includes a complex of rails along which the support structure can be skidded between positions on the platform from which slant drilling is to take place.

13. Slant drilling apparatus as claimed in any one of Claims 7 to 12, wherein the platform is substantially rectangular in plan view and has a plurality of conductors arranged in a predetermined orientation to one another at each corner.

14. Slant drilling apparatus as claimed in any one of Claims 7 to 13, wherein the platform is a fixed platform and is used in conjunction with a mobile platform which provides all the ancillary services.

1 5. Slant drilling apparatus constructed and arranged to operate substantially as hereinbefore described with reference to the accompanying drawings.

1 6. Slant drilling apparatus in conjunction with a mobile platform constructed and arranged to operate substantially as hereinbefore described with reference to the accompanying drawings.