Offshore drilling rig comprising an anti-recoil system

Abstract

Disclosed herein are embodiments of an offshore drilling rig comprising: a drill floor (107) defining a well center (123); a hoisting system configured to advance a tubular string (128) downwards through the well center (123) and to the seafloor (124) and to apply a lifting force to a tubular string (128) extending through the well center (123) and to the seafloor (124), the lifting force being large enough to support at least a major part of an apparent weight of the tubular string (128); and an anti-recoil system (218) configured to cause, in case of a sudden reduction of a load suspended from the drilling rig, the hoisting system to raise the tubular string (128) while preventing damage to the hoisting system.

Claims

1. An offshore drilling rig comprising: a drill floor defining a well center; a hoisting system configured to advance a tubular string downwards through the well center and to the seafloor and to apply a lifting force to a tubular string extending through the well center and to the seafloor, wherein the hoisting system is a hydraulic hoisting system comprising one or more hydraulic hoisting cylinders; and an anti-recoil system configured to cause, in case of a sudden reduction of a load suspended from the drilling rig, the hoisting system to raise the tubular string in a controlled fashion; wherein the anti-recoil system is operationally connected to the one or more hydraulic hoisting cylinders.

2. The offshore drilling rig according to claim 1 wherein the anti-recoil system comprises a fluid reservoir and an anti-recoil valve, the anti-recoil valve being adapted for connecting the one or more hydraulic hoisting cylinders to the fluid reservoir.

3. The offshore drilling rig according to claim 2 and further comprising a control system being adapted: to detect a sudden reduction of a load suspended from the drilling rig, and to activate the anti-recoil valve when a sudden reduction of a load suspended has been detected.

4. The offshore drilling rig according to claim 3 wherein the anti-recoil valve during normal operation is open and connects the one or more hydraulic hoisting cylinders to the fluid reservoir, and wherein activation of the anti-recoil valve causes the anti-recoil valve to close the flow path except for a residual flow that is still allowed to flow between the fluid reservoir and the one or more hydraulic hoisting cylinders.

5. The offshore drilling rig according to claim 2 wherein the anti-recoil valve during normal operation is open and connects the one or more hydraulic hoisting cylinders to the fluid reservoir, and wherein activation of the anti-recoil valve causes the anti-recoil valve to close the flow path except for a residual flow that is still allowed to flow between the fluid reservoir and the one or more hydraulic hoisting cylinders.

6. The offshore drilling rig according to claim 1 the lifting force being large enough to support at least at least a majority part of an apparent weight of the tubular string.

7. The offshore drilling rig according to claim 1 wherein the tubular string is a Completion Work-Over Riser (CWOR) system connected to a vertical xmas tree or a high-pressure conduit connected to a subsea test tree.

8. The offshore drilling rig according to claim 1, wherein the hoisting system is a draw works hoisting system comprising a crown compensator comprising one or more crown compensating hydraulic cylinders, and wherein the anti-recoil system is operationally connected to the one or more crown compensating hydraulic cylinders.

9. The offshore drilling rig according to claim 8 wherein the anti-recoil system comprises an anti-recoil valve and a fluid reservoir fluidly connected via the anti-recoil valve to the one or more crown compensating hydraulic cylinders.

10. The offshore drilling rig according to claim 1 wherein the anti-recoil system comprises an anti-recoil valve and a fluid reservoir fluidly connected via the anti-recoil valve to the one or more hydraulic hoisting cylinders.

11. The offshore drilling rig according to claim 1 wherein the hydraulic hoisting system comprises a sheave movably supported by the one or more hydraulic hoisting cylinders, and a hoisting line extending over the sheave; the hoisting line having a dead end; wherein the dead end is connected to a support structure of the drilling rig via one or more heave-compensating hydraulic cylinders; and wherein the anti-recoil system is operationally connected to the one or more heave-compensating hydraulic cylinders.

12. The offshore drilling rig according to claim 11 wherein the anti-recoil system comprises an anti-recoil valve and a fluid reservoir fluidly connected via the anti-recoil valve to the one or more heave-compensating hydraulic cylinders.

13. The offshore drilling rig according claim 1 wherein the hoisting system comprises a hoisting line and hook arranged to lift loads suspended by the hoisting system via the hoisting line; and wherein the anti-recoil system is configured to control a lifting force acting above the hook.

14. The offshore drilling rig according to claim 13 wherein the drilling rig is operable to perform well control and/or intervention operations with the hook in direct mechanical connection to a Completion Work-Over Riser (CWOR) system or a high-pressure conduit.

15. The offshore drilling rig according to claim 1 comprising a top drive suspended above the drill floor by the hoisting system and configured to impart torque onto a tubular string extending through the well center and suspended by the hoisting system; and wherein the anti-recoil system is configured to control a lifting force acting above the top drive.

16. The offshore drilling rig according to claim 1 wherein the anti-recoil system is arranged to cause the hoisting system to raise the tubular string a height between 1 m and 15 m.

17. The offshore drilling rig according to claim 1 comprising a riser tensioner system wherein the drilling rig is operable to perform well completion and/or intervention operations with a Completion Work-Over Riser (CWOR) system suspended from the hoisting system and with the riser tensioner system disconnected from the Completion Work-Over Riser (CWOR) system.

18. The offshore drilling rig according to claim 1 comprising a riser tensioner system and a trip saver system operable to move the riser tensioner system between an operational position aligned with the well center and a parking position displaced from well center; wherein the drilling rig is operable to perform well completion and/or intervention operations with a Completion Work-Over Riser (CWOR) system suspended from the hoisting system and with the riser tensioner system positioned in the parking position.

19. The offshore drilling rig according to claim 1, wherein the anti-recoil system is configured to be selectively operable in an anti-recoil mode and an immediate shut-off mode; wherein the anti-recoil system is configured, when operated in the anti-recoil mode, to cause, in case of a sudden reduction of a load suspended from the drilling rig, the hoisting system to raise the tubular string while preventing uncontrolled upwards recoil of the tubular string; and when operated in the immediate shut-off mode, to cause, in case of a sudden reduction of a load suspended from the drilling rig, the hoisting system to substantially prevent any upwards recoil of the tubular string.

20. A method of operating an offshore drilling rig, the drilling rig comprising a drill floor defining a well center, a hoisting system configured to raise and/or lower a tubular string through the well center, and an anti-recoil system configured to cause, in case of a sudden reduction of a load suspended from the drilling rig, the hoisting system to raise the tubular string while preventing damage to the hoisting system; wherein the method comprises: suspending, from the hoisting system, a high-pressure tubular string extending through the well center and downwards to the seafloor; detecting a sudden reduction of a load suspended from the hoisting system; controlling the hoisting system to raise high pressure tubular string while preventing damage to the hoisting system; wherein the high-pressure tubular string, when sudden reduction of the suspended load is detected, is raised by controlling fluid flow between a fluid reservoir of the anti-recoil system and the one or more hydraulic hoisting cylinders of the hoisting system.

21. The method of claim 20, wherein high-pressure tubular string is a Completion Work-Over Riser (CWOR) system, and wherein the method further comprises suspending at least a majority part of the apparent weight of a Completion Work-Over Riser (CWOR) system from the hoisting system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above and/or additional objects, features and advantages of embodiments and aspects of the present invention, will be further elucidated by the following illustrative and non-limiting detailed description with reference to the appended drawings, wherein:

(2) FIG. 1 illustrates an embodiment of an offshore drilling vessel;

(3) FIG. 2a-2d illustrates components of an embodiment of an offshore drilling rig with a hydraulic hoisting system; and

(4) FIG. 3a-3c illustrates components of another embodiment of an offshore drilling rig with a draw works hoisting system.

DETAILED DESCRIPTION

(5) In the following description, reference is made to the accompanying figures, which show by way of illustration how the invention may be practiced.

(6) FIG. 1 illustrates an embodiment of an offshore drilling vessel. The offshore drilling vessel of FIG. 1 is a drillship having a hull 101, a moon pool 102, a main deck 115, a drill floor deck 107, and superstructures 197 and 106 extending above the hull and above the main deck. The superstructure 197 is located in the midship portion of the vessel and it extends above the moon pool. Superstructure 197 serves as a substructure supporting the drill floor and a dual activity mast 104.

(7) The drill floor deck 107 is located at a level above the main deck and it spans across the moon pool 102 that is formed in the hull of the drillship. The drill floor deck 107 comprises two holes defining respective well centers 123 located next to the dual activity mast 104. The dual activity mast 104 extends upwardly from the drill floor deck 107 and comprises two mast portions arranged side by side such that they are both located on the same side relative to the well centers. Each mast portion accommodates a hoisting system, each for lowering a drill string through a respective one of the well centers 123 and through the moon pool 102 towards the seabed. In the example of FIG. 1, the hoisting system is a hydraulic hoisting system comprising hydraulic hoisting cylinders 112 that extend upwardly relative to the drill floor deck 107 and that are arranged to raise and lower a yoke sheave 110 from which a top drive 111 is suspended. In alternative embodiments, other hoisting systems may be used, e.g. a draw-works system comprising a draw-works motor/drum which may be positioned at a suitable location on the drilling rig. Each well center is located next to one of the mast portions and the corresponding hoisting system. The side-by-side configuration of the dual activity mast and well centers allows for efficient dual operations, easy access to both well centers, and convenient visual control of both well centers from a single driller's cabin. However, other layouts of the well centers and drilling support structures are possible as well as are drilling vessels with only a single hoisting system and corresponding well center.

(8) In the example of FIG. 1, a completion work-over riser system is suspended from one of the hoisting systems. The completion work-over riser system comprises a HP tubular string (in this case a completion riser string 128) that extends from the drilling vessel to the sea floor 124. The completion work-over riser system further comprises a subsea tree connected to the lower end of the completion riser string and to the well head of a well 122 that extends into the formation under the sea floor 124. The subsea xmas tree 121 is positioned on the sea floor and connected to an emergency disconnect package 119, a lower riser package 120. However it will be appreciated that other embodiments of subsea tree may comprise alternative and/or additional components.

(9) The drilling vessel further comprises a number of additional components all known as such in the art. These may include but are not limited to: a pipe storage area 109 for storing pipes, a storage area 116 for storing marine riser joints, one or more catwalk machines 108 or similar horizontal pipe handling equipment arranged to feed tubulars between one or more of the storage areas and the well centers, other storage areas below the drill floor deck configured for storing a variety of equipment, such as replacement parts, e.g. for mud pumps, etc., an accommodation superstructure 106.

(10) A part of the main deck 115 of the vessel is located beneath the drill floor deck and allows heavy subsea equipment, e.g. a BOP 130 and a Christmas tree 103 to be moved to the moon pool under the well centers so as to allow such equipment to be lowered toward the seabed.

(11) FIG. 2a illustrates components of an embodiment of a drilling rig e.g. a drilling rig installed on the drilling vessel of FIG. 1. The drilling rig comprises a hydraulic hoisting system including a number of cylinders 112 that extend upwards relative to the drill floor deck 107. Each cylinder comprises a piston 214 whose free end is operationally coupled to a sheave 110 such that the sheave is raised when the piston is pushed out of the cylinder 112 and lowered when the piston retracts into the cylinder 112. In some embodiments, the hoisting system comprises two sets of hoisting cylinders, each set comprising one or more cylinders. A hoisting line 213 extends over the sheave 110 and carries a top drive 111 attached to a free end of the hoisting line 213. The hoisting line 213 has a dead end 216 that is anchored at the drill floor or at another suitable support structure of the drilling vessel. It will be appreciated that some embodiments may include a plurality of hoisting lines. The sheave and hoisting line transfer the force exerted by the hydraulic cylinders 112 to a lifting force acting on the top drive 111 and on a tubular string 128 suspended by the hoisting system, e.g. a completion riser string.

(12) The top drive 111 may be directly connected to the hoisting line or connected to the hoisting line via a suitable load carrier such as a hook, a yoke, a dolly, and/or the like. The stroke of the cylinders causes upwards/downwards movement of the top drive which may be guided along a drilling support structure (not shown in FIG. 2a) via a dolly or another suitable guide system. The top drive is thus positioned between the hoisting line 213 and the tubular string 128 that is suspended by the hoisting system, and the top drive 111 is operable to move upwards and downwards above the drill floor 107. The top drive 111 provides lifting to the tubular string via a lifting frame 230 (such as a coil tubing lifting frame) connected to the top drive via bails 229. A surface flow tree 231 is connected to the tubular string 128 and the load of the tree 231 is supported by the frame 230. The frame 230 is not compensated and thus provides a direct mechanical connection between top drive 111 and the tubular string 128 as well as a direct mechanical connection between the hook 227 and the tubular string 128.

(13) The tubular string 128 is a CWOR connected to an EDP 119, an LRP 120 and (a vertical) subsea xmas tree 121 mounted on the well head 239.

(14) The drilling rig further comprises an anti-recoil valve 218 located in a hydraulic line 225 extending between a fluid reservoir 217 and the hoisting cylinder 112. During normal operation, the anti-recoil valve 218 is in an open state. When a sudden reduction of the load suspended from the hoisting system occurs, e.g. due to an emergency disconnected of a HP tubular string from a subsea tree of a completion work-over riser system, the anti-recoil valve 218 is activated. To this end, the drilling rig may comprise a control system operable to detect a sudden reduction of the suspended load to activate the anti-recoil valve. The control system may comprise one or more sensors operable to detect a sudden reduction of the load, e.g. by detecting the velocity of the piston 214, by detecting a change in the weight suspended from the hoisting system, or by another suitable sensor. Activation of the anti-recoil valve causes the anti-recoil valve to close the flow path 225 except for a residual flow that is still allowed to flow between the fluid reservoir 217 and the hoisting cylinder 112. This may cause the piston 214 to push upwards in a controlled fashion and thus lift the disconnected part of the HP tubular string (in this case the completion riser string 218) upwards so as to ensure that the disconnected part of the completion riser and any pipe or tubing extending though it comes free of any residual equipment at the seafloor from which the disconnected part has been disconnected. It will be appreciated that the hydraulic system for controlling the hoisting cylinders may comprise additional components not explicitly shown in FIG. 2a, such as pumps, valves further conduits, controls, etc. The fluid reservoir 217 may comprise one or more pressure vessels. The fluid reservoir may operate as a passive ‘spring’ so as to provide heave compensation by storing and dissipating the energy associated with wave motion. Alternatively or additionally, the fluid reservoir 217 may comprise a pressure charging module which may comprises additional high pressure storage or otherwise allow the pressure in the hoisting cylinder 112 to be actively adjusted when required, e.g. so as to raise or lower a tubular string.

(15) In FIG. 2a the hoisting system supports the apparent weight solely by the hoisting systems. FIG. 2b illustrates components of another embodiment of invention similar to that of FIG. 2a except in this case a set of riser tensioners 226 are applied to support part of the apparent weight of the CWOR. While this system may be more complex than that of FIG. 2a this system may still enjoy the omission of a compensating tension frame.

(16) FIG. 2c illustrates components of another embodiment of invention similar to that of FIG. 2a,b. In this case the drilling rig is applied to perform a workover or completion operation via a horizontal xmas tree 121 b and the tubular string is a high pressure conduit 128b. The rig and the xmas tree 121 b are connected via the BOP 232 and the marine riser 242 up to the diverter 241. Tensioning for the marine riser is provide by the tensioners 226. The hoisting system supports the high pressure conduit 128b which is connected to the surface flow tree 231 similarly to FIG. 2a,b and to the subsea test tree 233 installed inside the BOP 233.

(17) FIG. 2d illustrates components of another embodiment of a drilling rig. The drilling rig of FIG. 2d is similar to the one of FIG. 2a-c and comprises a hydraulic hoisting system including a number of cylinders 112, a top drive 111, a sheave 110, a hoisting line 213, and a drill floor 107 defining a well center 123, all as described in connection with FIG. 2a-c. While not shown, the drilling rig of FIG. 2d may also be applied using riser tensioners as in FIG. 2b or a marine riser as in FIG. 2c.

(18) The drilling rig of FIG. 2d differs from the drilling rig of FIG. 2a-c in that the dead end of the hoisting line 213 is connected to the drill floor or another suitable support structure of the drilling rig via one or more heave-compensating hydraulic cylinders 327. Heave compensation via cylinder 327 may be performed as active or passive heave compensation or as a combination thereof. To this end the heave-compensating cylinder 327 is in fluid communication with a fluid reservoir 217 via flow path 225.

(19) The drilling rig further comprises an anti-recoil valve 218 located in hydraulic line 225 extending between fluid reservoir 217 and the heave-compensating cylinder 327. During normal operation, the anti-recoil valve 218 is in an open state. When a sudden reduction of the load suspended from the hoisting system occurs, e.g. due to an emergency disconnected of a HP tubular string from a subsea tree of a completion work-over riser system, the anti-recoil valve 218 is activated as described in connection with FIG. 2a-c. As in the example of FIG. 2a-c, it will be appreciated that the hydraulic system for controlling the hoisting cylinders may comprise additional components, such as pumps, valves further conduits, controls, etc.

(20) Hence, in the examples of FIGS. 2 and 3, the anti-recoil valve is integrated in the main hydraulic hoisting system or in the heave-compensation system associated with the main hoisting system. In both examples, the anti-recoil system controls the lifting force acting above the top drive or even above the hook and applied to the top drive and the tubular string. In both systems, the main hoisting system and, optionally the integrated heave compensation system, carries the entire apparent weight of the top drive and of the HP tubular string and any subsea equipment attached thereto.

(21) FIG. 3a,b,c illustrates components of another embodiment of a drilling rig with a draw works hoisting system but otherwise similar to the embodiments and applications shown in FIGS. 2a, 2b, and 2c, respectively. The differences are explained in the following. As on most conventional offshore drilling rig, a draw work 234 supply the active power for controlling the hoisting line 213. The line runs to the crown block 235 and is reeved between it and the travelling block 228. The line proceeds to the dead line anchor 216. The travelling block supports the hook 227 and the top drive 111. A crown compensator with a crown compensator assembly 240 is installed to allow heave compensation of the hook. The crown compensating cylinder 236 is arranged so that the height of the crown block may be varied. Here is shown an exemplary crown compensator which further comprises guide sheaves 237 guiding the hoisting line to the crown block as well as two guide arms 238 guiding the motion of the crown block. The crown block and crown compensator assembly are supported by a four legged derrick (not shown) and the top drive is supported by a dolly (not shown) as discussed in relation to FIG. 2. An anti-recoil system similar to that of FIG. 2 is installed but now connected to the crown compensating cylinder. In the event of a sudden loss in tension the anti-recoil may stroke out the cylinder 236 sufficiently and controlled to provide sufficient lifting of the tubular string without damaging the drilling rig.

(22) Accordingly, in embodiments where the drilling rig further comprises a riser tensioner system 226 operable to support and provide tension to a marine riser during drilling operations, such a riser tensioner system may be brought into a passive state during well completion and/or intervention operations where a completion riser string is employed instead. To this end the riser tensioner system may be moved into a parking position laterally displaced from the well center, e.g. by means of a trip saver. The riser tensioner system 226 of a drilling rig is typically dimensioned so as to be used in conjunction with a marine riser string. Marine risers are typically heavier and have a larger diameter than the completion riser joints used as part of a completion work-over riser system. For example, while typical marine riser joints have a diameter of 50-60 inches, riser joints of a completion work-over riser typically have a diameter smaller than 50 inches, such as smaller than 30 inches, such as between 8 inches and 14 inches.

(23) Even though the above embodiments have been described in the context of a drillship, it will be appreciated that the described features may also be implemented in the context of a semi-submersible or other type of drilling vessel.

(24) Although some embodiments have been described and shown in detail, the invention is not restricted to them, but may also be embodied in other ways within the scope of the subject matter defined in the following claims. In particular, it is to be understood that other embodiments may be utilized and structural and functional modifications may be made without departing from the scope of the present invention. For example, some of the described embodiments comprise two well centers, but it will be appreciated that alternative embodiments may comprise a single well center or a well center and additional work centers.

(25) In the device claims enumerating several features, several of these features can be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims or described in different embodiments does not indicate that a combination of these measures cannot be used to advantage.

(26) It should be emphasized that the term “comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof