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.
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.
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.
Attempts have been made to overcome some of these limitations. For example, U.S. Pat. No. 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.
U.S. Pat. No. 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.
U.S. Pat. No. 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.
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.
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 U.S. Pat. No. 7,083,004.
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.
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.
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.
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.
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.
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.
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.
This invention will be described by way of non-limiting embodiments of the present invention, with reference to the accompanying drawings, in which:
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.
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 in 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.
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,
In another example, as shown in
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.
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.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US2007/077956 | 9/10/2007 | WO | 00 | 6/16/2010 |