Improved Cantilever Skidding System On A Drilling Rig

Field of Invention

[0001] The present invention relates to an improved cantilever skidding system on a platform of a drilling rig. In particular, the invention relates to a system for extending a drill-floor beyond a rectangular area that is conventionally accessible with two orthogonal axes of motion.

Background

[0002] A typical offshore drilling rig has a platform supported on legs and a cantilever mounted on the platform. Mounted on a drill operation end of the cantilever is a drill floor. The cantilever is moveable in a longitudinal direction of the cantilever such that the drill operation end of the cantilever extends beyond the platform, whilst the drill floor is moveable on the cantilever in a direction transverse to the longitudinal direction. As a result, the drill point can only be located within a rectangular area described by the longitudinal and transverse axes of the cantilever and the drill floor.

[0003] The transverse distance covered by the drill floor is limited by the width of the cantilever, which is determined by the distance between cantilever beams extending in the longitudinal direction. To obtain a reasonably wide drilling pattern, the cantilever must also be reasonably wide. Another limitation of the conventional cantilever is that the drill floor creates an asymmetric load on the longitudinal cantilever beams, for example, when the drill floor is moved to a maximal distance in the transverse direction and the longitudinal cantilever beam on the side to which this movement takes place is subjected to a heavier load than the other longitudinal cantilever beam. As a result, each longitudinal cantilever beam must be sturdy and heavily constructed.

[0004] Attempts have been made to overcome some of these limitations. For example, US Patent 6,171,027 assigned to Marine Structure Consultants discloses a drill floor that is fixedly mounted on the cantilever so that the load on the longitudinal cantilever beams is centrally or symmetrically located whilst the beams for transverse motion are

located on the platform. This design has the advantage that the longitudinal cantilever beams can be of a lighter construction and the range of transverse motion is increased. However, the drilling pattern is still limited by the longitudinal and transverse motions of the cantilever.

[0005] US Patent 6,729,804 assigned to Itrec B.V. describes a drilling rig having a platform, a cantilever and a supporting cart disposed between the cantilever and the platform. The supporting cart slides transversely on the platform whilst the cantilever slides longitudinally on the supporting cart on four friction reducing bearings. However, the drilling pattern is still limited by the longitudinal and transverse motions of the cantilever.

[0006] US Patent 7,083,004 also assigned to Itrec B.V. describes a drilling rig having a platform, a cantilever and a supporting cart disposed between the cantilever and the platform. The supporting cart pivots about a pivot point on the platform whilst the cantilever slides longitudinally on the supporting cart. The drilling pattern is now part sectorial over the edge of the platform as constrained between two adjacent legs of the drilling rig. US Patent '004 also describes a cantilever with the pivot point being moveable in a direction transverse to the longitudinal direction to create an ellipsoidal drilling pattern. FIG. 1 shows the cantilever described in US Patent '004.

[0007] WO 2007/043856 filed by Itrec B.V. describes a rig having a platform and a cantilever. The cantilever has longitudinal rails for extending the cantilever beyond the platform. WO 2007/043856 further discloses rail extensions at the inner end of the longitudinal rails. The rail extensions allow the longitudinal rails to be further extended so that the drilling area is increased.

[0008] It can thus be seen that there exists a need for another cantilever skidding system for an offshore platform that allows the drill floor mounted on the cantilever to be moved over a large area and yet overcoming the limitations of the prior art systems, such as, the inconvenience in moving the curved rail 444 of US Patent 7,083,004.

Summary

[0009] The following presents a simplified summary to provide a basic understanding of the present invention. This summary is not an extensive overview of the invention, and is not intended to identify key features of the invention. Rather, it is to present some of the inventive concepts of this invention in a generalised form as a prelude to the detailed description that is to follow.

[0010] In one embodiment, the present invention provides a drilling rig. The rig comprises: a platform having a pair of substantially parallel transverse members near an edge thereof; a cantilever mountable on the platform, said cantilever having a pair of substantially longitudinal members along the length of the cantilever, said longitudinal members are substantially orthogonal to the pair of transverse members; and a sliding and swivel assembly connecting the longitudinal and transverse members at each interposition of said longitudinal and transverse members such that a sliding/swivel assembly is moveable relatively on the relevant longitudinal or transverse member to translate and/or rotate the cantilever with respect to the platform.

[0011] In another embodiment, the present invention provides a method of displacing a cantilever on a platform of a drilling rig. The method comprises: disposing said cantilever on said platform, with said cantilever having two substantially parallel members along the cantilever's longitudinal dimension; disposing two substantially parallel transverse members near an edge of said platform; interconnecting said longitudinal and transverse members by a sliding and swivel assembly at each interposition; and connecting an actuator between a sliding/swivel assembly and said longitudinal/transverse member, wherein said actuator is operable to translate and/or rotate said cantilever with respect to said platform.

[0012] In another embodiment of the present invention, the sliding and swivel assembly comprises an upper sliding block, a lower sliding block and a swivel member interconnecting the upper and lower sliding blocks, said upper sliding block is connected to the longitudinal member whilst the lower sliding block is connected to the transverse member. The sliding/swivel assembly also comprises shoulders, necks and

annular surfaces to withstand torsion, tension and compression loads, with each pair of mating surfaces having a bearing plate therebetween.

[0013] In another embodiment of the present invention, a sliding/swivel assembly is connected by an actuator to the longitudinal member and/or transverse member. In one embodiment, the actuator is a fluid actuator; in another embodiment, the actuator is a screw actuator. In a further embodiment, the actuators are connected in series; in another, the actuators are connected in parallel. In yet another embodiment of the present invention, a sliding/swivel assembly is connected by a rack-pinion assembly to the longitudinal/transverse member.

[0014] In a further embodiment of the present invention, the pair of transverse members are unequal in length, with the transverse member near the edge of the platform being longer.

[0015] In yet a further embodiment of the present invention, rotation of the cantilever is created by counter-motions of the actuators or racks/pinions associated with the longitudinal members or transverse members or both members.

Brief Description of the Drawings

[0016] This invention will be described by way of non-limiting embodiments of the present invention, with reference to the accompanying drawings, in which:

[0017] FIG. 1 illustrates a known skidding system described in US Patent 7,083,004.

[0018] FIG. 2 illustrates a plan view of a cantilever system on a drilling rig in accordance with an embodiment of the present invention;

[0019] FIG. 3 illustrates a longitudinal section of the cantilever shown in FIG. 2 in accordance with another embodiment of the present invention;

[0020] FIG. 4 illustrates a transverse section of the cantilever shown in FIG. 2 in accordance with another embodiment of the present invention;

[0021] FIG. 5 A illustrates a sectional view of a swivel member in accordance with another embodiment of the present invention; FIG. 5B illustrates a sectional view of a swivel member in accordance with yet another embodiment;

[0022] FIG. 6A illustrates rotation of the cantilever about a fixed pivot, whilst FIG. 6B illustrates rotation of the cantilever by counter-motions of the actuators in accordance with another embodiment of the present invention;

[0023] FIG. 7 illustrates a locus of a drilling point created by displacing the cantilever shown in FIG. 2; and

[0024] FIG. 8 illustrates rotation of the cantilever of the present invention in a manner that is different from that of a prior art.

Detailed Description

[0025] One or more specific and alternative embodiments of the present invention will now be described with reference to the attached drawings. It shall be apparent to one skilled in the art, however, that this invention may be practised without such specific details. Some of the details may not be described at length so as not to obscure the invention. For ease of reference, common reference numerals or series of numerals will be used throughout the figures when referring to the same or similar features common to the figures.

[0026] FIG. 2 shows a plan view of a cantilever 10 system on an offshore platform 30 according to one embodiment of the present invention. As shown in FIG. 2, the cantilever 10 is operable to extend over an edge 32 of the platform 30 in a longitudinal direction of the cantilever or direction X. The platform 30 is supported by four jack-up legs 40. On a distal or operational end of the cantilever 10 is a drill floor 50, which has

a drilling axis P extending perpendicular to both the drill floor 50 and the cantilever 10, i.e. in direction Z with reference to the coordinates shown in FIG. 2. Each cantilever 10 has a longitudinal beam or member 12 on each of its two sides. Mounted along the edge 32 of the platform 30 is a transverse beam or member 14, which is substantially orthogonal to the longitudinal members 12, i.e. transverse member 14 is aligned in the Y direction. Substantially parallel to the transverse member 14 is another transverse member 14a, the latter being slightly shorter than the former. At each intersection of the longitudinal member 12 and the transverse member 14,14a, as seen in the plan view in FIG. 2, is a sliding and swivel assembly 20; altogether, there are four such sliding and swivel assemblies 20a, 20b ... 2Od. In addition, to prevent the cantilever 10 from overturning, two hold-down claws 60 are provided on the cantilever, for example, at an end opposed to the operational end.

[0027] FIG. 3 shows a longitudinal sectional view of the cantilever 10. FIG. 4 shows a transverse sectional view of the cantilever 10. As shown in FIGs. 3 and 4, each sliding and swivel assembly 20a, 20b...2Od inter-connects a longitudinal member 12 with a transverse member 14,14a. Each sliding and swivel assembly 20 is made up of an upper sliding block 21, a lower sliding block 22 and an interconnecting swivel member 23. Each sliding/swivel assembly 20 is translated by a fluid actuator 24,24a relative to each of the longitudinal 12 and transverse 14,14a members. One end of each fluid actuator 24,24a is connected by a pin to a connecting end 25 at the sliding/swivel assembly 20 whilst the other (second) end is connected by another pin to another connecting end 26 at a rail block 27 on the relevant longitudinal/transverse member. Each longitudinal/transverse member has a plurality of holes 29 that are equally spaced apart along the member. Each rail block 27 has a bore and a pivot pin 28 for connection with a hole 29 on the respective longitudinal 12 or transverse member 14,14a. By shifting the pivot pin 28 on the holes 29 along the associated member 12,14,14a and extending/retracting each fluid actuator 24,24a, the relevant sliding/swivel assembly 20 is relatively translated intermittently or stepwise on the member.

[0028] FIG. 5A shows a sectional view of a swivel member 23 according to an embodiment of the present invention. As shown in FIG. 5 A, the swivel member 23 has an upper flange 230 and a lower flange 240. An external side of the upper flange 230 is

connected to the upper sliding block 21, for example, by bolts and nuts, welding, and so on. Similarly, the external side of the lower flange 240 may be connected to the lower sliding block 22 by bolts and nuts, welding, and so on. An internal side of the upper flange 230 has a two-steps neck 232 and an annular end or flange 238. The two- steps neck 232 defines an internal shoulder 234 therebetween. An external side of the lower flange 240 is connected to the lower sliding block 22 whilst the internal side has a neck 242 that defines a shoulder 244 and an annular flange 248. The internal side of the upper flange 230 engages with the internal side of the lower flange 240 in a rotatory manner through bearing plates 250, 252, 254; that is, the shoulders 234, 244 of the upper and lower flanges 230,240 are rotatory connected by bearing plates 250; the necks 232, 242 are rotatory connected by bearing plates 252; and the annular flanges 238,248 are rotatory connected by bearing plates 254. The interconnecting rotatory surfaces on the internal sides of the upper and lower flanges thus allow relative rotation of the upper flange 230 and lower flange 240, yet allowing each sliding/swivel assembly 23 to withstand tension and compression loads.

[0029] FIG. 5B shows a sectional view of a swivel member 23 A according to another embodiment of the present invention. As shown in FIG. 5B, the swivel member 23 A is similar to the swivel member 23 except that swivel member 23A does not have the annular flanges 238, 248. Accordingly, the bearing plate 254 is disposed between the shoulder 244 and a lower surface of the upper flange 230.

[0030] In use, the fluid actuators 24,24a are actuated to extend/retract or push/pull the cantilever 10 in the longitudinal or X-direction, to push/pull the cantilever 10 hi the transverse or Y-direction, to rotate the cantilever 10 about the Z-axis, or any combinations of these movements. In one embodiment, the cantilever 10 has a pair of fluid actuators 24 associated with the longitudinal member 12 and a pair of fluid actuators 24a associated with the transverse member 14, 14a. In another embodiment, the cantilever 10 has two pairs of fluid actuators associated with each of the longitudinal and transverse members. In yet another embodiment, the cantilever 10 has different numbers of fluids actuators associated with the longitudinal and transverse members. For example, to translate the cantilever 10 in the X- or Y-direction, the

pair(s) of fluid actuators 24, 24a in the relevant direction is/are synchronously actuated to translate the cantilever 10 in an intermittent or stepwise manner.

[0031] To rotate the cantilever, one or more fluid actuators associated with an adjacent or opposite sliding/swivel assembly or assemblies is/are actuated in cooperation to create a turning moment or torque to rotate the cantilever in the desired direction. For example, FIGs. 6A and 6B show a cantilever 10 with four sliding/swivel assemblies 20a ...2Od and a pair of longitudinal fluid actuators 24 associated with the longitudinal member 12 and a pair of transverse fluid actuators 24a associated with the transverse member 14, 14a. To rotate the cantilever from position M to position N, as shown in FIG. 6A, with the centre of rotation at sliding/swivel assembly 20a, the longitudinal fluid actuator(s) 24 associated with sliding/swivel assembly 20c and/or 2Od is/are operated to push/pull separately or synchronously with the transverse fluid actuators associated with sliding/swivel assemblies 20b, 20c and 2Od being unlock (or free to extend/retract), or the transverse fluid actuator(s) 24a associated with sliding/swivel assembly 20b and/or 20c is/are operated to push/pull separately or synchronously with the longitudinal fluid actuators 24 associated with sliding/swivel assemblies 20b, 20c and 2Od being unlocked (or free to extend/retract), or the longitudinal and transverse fluid actuators are operated cooperatively. Unlocking a hydraulic cylinder includes activating a solenoid to by-pass a motion-lock or brake valve, such as, a piloted check valve connected across the fluid lines of the fluid actuator.

[0032] In another example, as shown in FIG. 6B, the transverse fluid actuator 24a associated with the sliding/swivel assembly 20a is operated in counter-motion with the transverse fluid actuator 24a associated with the sliding/swivel assembly 20b to create a torque for rotating the cantilever 10 about a virtual centre of rotation lying within the four sliding/swivel assemblies 20. Alternatively, the pair of transverse fluid actuators 24a associated with transverse rail 14a and the pair of transverse fluid actuators 24a associated with transverse rail 14 are similarly operated in counter-motion, as shown by the arrows in FIG. 6B, to rotate the cantilever 10 from position M to position L. In a similar manner, the longitudinal fluid actuator(s) 24 associated with one longitudinal member 12 is/are operated in counter-motion with the longitudinal fluid actuator(s) 24 associated with the other longitudinal member 12 to create a torque to rotate the

cantilever 10. Alternatively, a combination of counter-motions or push/pull of both the transverse and longitudinal fluid actuators in synchronous cooperation creates additive torques to rotate the cantilever 10. In the present invention, rotation of the cantilever 10 involves rotation of each of the four sliding/swivel assemblies 20a...2Od.

[0033] FIG. 7 shows a plan view of the cantilever 10 system with the envelop 100 showing the locus of the drilling point P. The envelop 100 is created by a combination of translations of the cantilever 10 on the longitudinal 12 and transverse 14,14a members and rotation of the cantilever about the four sliding/swivel assemblies 20. As can be seen from FIG. 7, the envelop 100 of the drilling point P according to the present invention is larger than that described by an envelop of a conventional cantilever, such as the rectangular envelop QiPiPi ₁ Q ₂ described in US Patent 6,717,027.

[0034] FIG. 8 illustrates rotation of the cantilever 10 system about the four sliding/swivel assemblies 20 without having to move the transverse rails 14,14a. In contrast, translation of the cantilever of US Patent 7,083,004, as seen from FIG. 1, involves shifting the curved rails 444; such shifting of the curved rails 444 of US Patent 7,083,004 is laborious and time-consuming; in other words, translation of the curved rails of US Patent 7,083,004 is inconvenient and entails unproductive operation.

[0035] In the above embodiments, two or four fluid actuators 24, 24a are associated with each of the transverse and longitudinal members. In another embodiment, more than four fluid actuators are possible; one set of cylinders may be used on each of the two sides of the transverse/longitudinal members, that is, the fluid actuators are arranged in parallel. In yet another embodiment, two sets of fluid actuators are arranged in series so that displacement (translation and rotation) of the cantilever 10 can be operated continuously instead of intermittently/stepwise manner.

[0036] While specific embodiments have been described and illustrated, it is understood that many changes, modifications, variations and combinations thereof could be made to the present invention without departing from the scope of the

invention. For example, the pin 28 on each rail block 27 and the cooperating holes 29 on the transverse/longitudinal member may be aligned vertically (in the Z-direction) instead of horizontally. In addition, the holes 29 need not be equally or uniformly spaced apart on the transverse/longitudinal member. In another example, each longitudinal/transverse member may be translated by means of rack and pinion instead of pin and holes on a rail block. In another example, a screw actuator may be used instead of a fluid actuator. In yet another example, other translation means such as sprocket-chain or pulley-belt system may be used instead of a fluid actuator. Further, the cantilever system of the present invention can also be used on any oil drilling platform having 3 or more legs, on a semi-submersible rig, and so on.