OFFSHORE FLOATING VESSEL AND A METHOD OF OPERATING THE SAME

Abstract

An offshore floating vessel includes a hoisting system including a drive for moving connecting device and emergency brakes to inhibit motion of the connecting device; wherein the hoisting system is to be operated at least in a hoisting mode and in an active heave compensation mode; wherein hoisting system is to perform an active heave compensation when operated in the active heave compensation mode and to operate without active heave compensation when operated in the hoisting mode; wherein the emergency brakes are operable in a normally-energized mode including a de-energized state where the emergency brakes engage so as to inhibit motion of the connecting device relative to the floating vessel; wherein each emergency brake of the plurality of hydraulic emergency brakes has associated with it a separate accumulator reservoir.

Claims

1-11. (canceled)

12. An offshore floating vessel comprising: a hoisting system adapted for suspending a load attached to a connecting device of the floating vessel and for lowering or raising a load connected to the connecting device from the floating vessel to or from the sea floor, the hoisting system comprising a drive for moving the connecting device; a plurality of hydraulic emergency brakes configured to inhibit motion of the connecting device relative to the floating vessel when the brakes are in an engaged state; a hydraulic system configured to maintain the emergency brakes in a disengaged state by applying a hydraulic pressure to each of said emergency brakes by means of a pressurized fluid; wherein the hoisting system is configured to be selectively operated at least in a hoisting mode and in an active heave compensation mode, wherein the hoisting system is configured to perform an active heave compensation when operated in the active heave compensation mode and to operate without active heave compensation when operated in the hoisting mode; wherein each emergency brake of the plurality of hydraulic emergency brakes has associated with it a separate accumulator reservoir in the hydraulic system.

13. An offshore floating vessel according to claim 12, where the hoisting system when operated in the active heave compensation mode, is adapted to stop active heave compensation responsive to one or more predetermined error conditions; and the hoisting system is further selectively operable in a fixed-to-bottom mode; wherein the hoisting system is configured to perform an active heave compensation when operated in the fixed-to-bottom mode the hoisting system is adapted to maintain active heave compensation despite said one or more predetermined error conditions.

14. An offshore floating vessel according to claim 12, wherein the hoisting system is dimensioned such that the drive is still operable to continue active heave compensation if one of the emergency brakes is applied.

15. An offshore floating vessel according to claim 12, wherein the hoisting system is such that the drive is still operable to continue active heave compensation if only one of the emergency brakes is applied.

16. An offshore floating vessel according to claim 13, wherein the hoisting system is dimensioned such that the drive is still operable to continue active heave compensation if one of the emergency brakes is applied.

17. An offshore floating vessel according to claim 13, wherein the hoisting system is dimensioned such that the drive is still operable to continue active heave compensation if only one of the emergency brakes is applied.

18. An offshore floating vessel according to claim 12, wherein the drive controlling motion of the connecting device comprises a drawworks comprising a drum connected to the connecting device via a cable said drum operated by one or more motors.

19. An offshore floating vessel according to claim 18, further comprising a drawworks controller arranged to provide said active heave causing said one or more motors to operate said drum.

20. An offshore floating vessel according to claim 18, wherein said one or more predetermined error conditions are error conditions of a motor operating the drawworks.

21. An offshore floating vessel according to claim 20, wherein said one or more predetermined error conditions comprises one or more of the group of a low oil pressure and high temperature of a cooling fluid.

22. An offshore floating vessel according to claim 13, wherein the drive controlling motion of the connecting device comprises a drawworks comprising a drum connected to the connecting device via a cable said drum operated by one or more motors.

23. An offshore floating vessel according to claim 22, further comprising a drawworks controller arranged to provide said active heave causing said one or more motors to operate said drum.

24. An offshore floating vessel according to claim 22, wherein said one or more predetermined error conditions are error conditions of a motor operating the drawworks.

25. An offshore floating vessel according to claim 24, wherein said one or more predetermined error conditions comprises one or more of the group of a low oil pressure and high temperature of a cooling fluid.

26. An offshore floating vessel according to claim 23, wherein said one or more predetermined error conditions are error conditions of a motor operating the drawworks.

27. An offshore floating vessel according to claim 25, wherein said one or more predetermined error conditions comprises one or more of the group of a low oil pressure and high temperature of a cooling fluid.

28. An offshore floating vessel according to claim 12, wherein some or all of said emergency brakes is also operable for other operational purposes.

29. An offshore floating vessel according to claim 21, wherein said other operational purposes are selected from the group of parking brake and for controlling the speed of lowering a load.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In the following one or more embodiments of the invention will be described in more detail and with reference to the drawings, where:

[0036] FIG. 1 schematically illustrates an example of a drill ship.

[0037] FIG. 2 schematically illustrates a drawworks in use with the derrick of the drilling rig of FIG. 1.

[0038] FIG. 3 schematically illustrates operational modes of a drawworks.

[0039] FIG. 4 schematically illustrates a hydraulic system for controlling emergency brakes of a drawworks.

[0040] FIG. 5 schematically illustrates another example of a mechanism for selectively preventing an emergency brake from engaging.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0041] Referring to FIG. 1 an example of a floating drilling rig generally identified by reference numeral 10 comprises a drill ship having a rig floor 12 supported on a hull 14. In this way the drilling rig floats at the surface with the rig floor supported some 15-30 m thereabove. The floating drilling rig 10 may be any type of vessel or floating rig, including a semi-submersible. The drill floor of a semi-submersible is supported on columns that in turn are supported by pontoons. The pontoons are flooded with sea water such that the pontoons are submerged to a predetermined depth below the surface of the sea.

[0042] The rig floor 12 supports a derrick 16 that comprises a crown block 18 (fixed relative to the derrick), and a travelling block 20 (moveable up and down the height of the derrick). A hook 22 is suspended from the travelling block 20 for picking up loads such as a drill string 24 via a top drive 25. The travelling block 20 and hook 22 perform the function of a connecting device for connecting/suspending a load 24 to/from the drill ship 10. It will be appreciated, however, that other forms of connecting devices, such as a yoke, etc. may be used.

[0043] Each of the crown block 18 and travelling block 20 comprise a number of sheaves (not shown) through which is threaded a steel rope 26 (sometimes known in the art as a drill line) of 25-50 mm diameter to provide a block and tackle type function. To one side of the derrick 16 the steel rope 26 is fixed to an anchor 28 on the rig floor 12, whereas to the other side of the derrick 16 the steel rope 26 is stored on a drum 29 (see FIG. 2) in a drawworks 30 located on the rig floor 12. For example, the drawworks 30 may have dimensions of about 9.22 m width by 3.91 m depth by 4.65 m high, weighs about 84,285 kg (84.3 metric tons), and can provide about 6 MW of power.

[0044] In use, electrical motors 31 (see FIG. 2) in the drawworks 30 turn the drum 29 so as to reel the steel rope 26 in or out. Assuming that the drilling rig 10 is not in motion itself, reeling the steel rope 26 out results in lowering of the travelling block (and anything attached thereto) toward the rig floor 12, whereas reeling the steel rope 26 in results in raising of the travelling block 20 away from the rig floor 12. In this way the drawworks 30 can be used to move objects to and from the sea floor and even into and out of the wellbore, and to perform other functions. The electrical motors 31 may be of any type including AC motors, DC motors or permanent magnet motors for example.

[0045] Referring to FIG. 2 the drawworks 30 comprises an electric drive 32 controlling a number (e.g. four or six) electrical motors 31 for turning the drum 29 via a gear and pinion arrangement 34. All of the electrical motors 31 are permanently engaged with the drum 29, although the number that are in operation at any one time is controlled by the electric drive 32 according to speed and braking requirements. Hydraulic disc brakes 36 are operationally coupled to the drum 29 and are operable as emergency brakes. In addition or alternative to the emergency brakes, disc brakes may be provided that provide a parking function and/or allow load lowering in the event of a power cut. Some or all of the disc brakes may be operable both as emergency brakes and as parking or other operational brakes. The brakes may be operable to press brake pads against a brake disc of the drum 29 by means of a set of calipers. In particular, the disc brakes may be spring loaded, i.e. they may press the brake pads against the drum by spring force unless the brake is energized, e.g. by means of a hydraulic cylinder causing the brake pads to be pushed away from the drum against the force exerted by the spring. Hence, the emergency brakes are operationally coupled to a hydraulic system 50 providing hydraulic pressure to the emergency brakes. It will be appreciated, however, that other types of emergency brakes may be used.

[0046] A drawworks controller 38, e.g. comprising a programmable logic controller (PLC), provides speed commands, e.g. via a speed controller to the electric drive 32 based inter alia on motor speed and torque data fed back to the controller 38 from a pulse encoder or other suitable sensor on each electrical motor 31, and on inputs from a driller control apparatus 40. The driller control apparatus may comprise a joystick in a driller's cabin on the drilling rig 10; the driller's cabin comprises equipment for computer control of operations on the drilling rig 10. Movement of the joystick by the driller provides an output signal that causes the travelling block 22, via the drawworks 30, to raise or lower the load on the hook 22 at a speed (also controllable via the joystick).

[0047] The drawworks controller 38 also receives inputs from three Motion Reference Units (MRU) 45. The output from each MRU is input to the drawworks controller 38 that processes the signals to provide one output representing the heave acceleration, velocity and position of the drilling rig 10 as a result of ocean swell or heave. The drilling rig 10 will oscillate in response to sea swell or waves with a complex motion comprising three translation modes (known as surge, sway and heave) and three angular modes (known as roll, pitch and yaw). The drawworks controller 38 uses the inputs from the MRUs to provide active heave compensation when the rig moves with sea swell, e.g. as described in U.S. Pat. No. 8,265,811 the entire disclosure is incorporated herein by reference.

[0048] Referring to FIG. 3, the drilling rig 10 may be operated in different modes of operation, including a hoisting mode 301, an active heave compensation mode 302, and a fixed-to-bottom mode 303. The hoisting mode may e.g. be employed when building tubulars or when running a drill string or other tubular equipment or even other subsea equipment towards the sea floor or when raising such equipment from the sea floor. Other such operations include operations where no load is suspended from the floating vessel such that (any part of) the load is in the proximity or at the sea floor, in particular no closer to the sea floor than the maximum heave. In particular, this mode may be preferred when a load is suspended above the sea surface or only slightly below the sea surface. During such operations, active heave compensation is normally not necessary (at least as long the equipment is sufficiently high above the sea floor) and in some embodiments even undesired, as it would typically require unnecessary energy and slow down the hoisting operation. Consequently, in the hoisting mode 301, active heave compensation is disabled or at least not activated. In active heave compensation mode 302, active heave compensation is activated, thus causing the motors 31 to operate the drum 29 responsive to signals from the MRUs or similar sensors in a generally oscillating fashion so as to actively compensate for detected motion of the drilling rig. This mode of operation may e.g. be used when lowering or raising equipment to/from the sea floor while the equipment (or at least a part thereof) is relatively close to the sea floor (closer than the maximum heave amplitude) so as to avoid the equipment to bounce onto the sea floor, well head or other subsea equipment. This mode of operation may also be used during drilling operations so as to ensure that the drill bit has substantially uniform contact with the formation into which drilling operations are performed, or other operations where a load suspended from the vessel is in the proximity of the sea floor, i.e. closer than the maximum heave. During both the hoisting mode 301 and the active heave compensation mode 302, the emergency brakes 36 are operational so as to prevent an uncontrolled lowering of loads in cases of e.g. malfunctioning of the motors 31 or other parts of the drawworks. The transition 304 between the hoisting mode 301 and the active heave compensation mode 302 is performed responsive to an operator command via the driller control apparatus 40 which in turn activates or deactivates the active heave compensation function of the drawworks controller 38. It will be appreciated that the active heave compensation mode may have one or more sub-modes e.g. each performing a different active heave compensation processes, such as a BOP and subsea tools landing mode, a constant WOB mode, and/or the like. Alternatively or additionally, the drilling rig may have additional main modes of operation.

[0049] The drilling rig may further be operated in a fixed-to-bottom mode 303. This mode may e.g. be employed during well testing when a pipe attached to the drilling rig is connected to a well bore and oil is transported to the drill rig. During this and similar operations a string, e.g. a string of tubulars, such as pipes, risers and/or the like, is fixedly connected to the well bore or to heavy subsea equipment such as a BOP on the sea floor. Hence, in order to avoid damaging the string, active heave compensation is active in this mode of operation. Hence, the fixed-to-bottom mode 303 may be regarded as a submode of the active heave compensation mode 302. However, while the emergency brakes are desired during normal active heave compensation modes, activation of emergency brakes during a fixed-to-bottom operation may have serious consequences including breaking of a string of tubulars resulting in oil spill. Consequently, when operated in fixed-to-bottom mode, the emergency brakes are disabled such that they are prevented from engaging even in a situation of power failure, failure of the hydraulic system or the like.

[0050] The transition 305 between the fixed-to-bottom mode and other modes (e.g. another active heave compensation mode) is performed responsive to an operator command via the driller control apparatus 40. In some embodiments the rig can switch directly from the FTB mode 303 and another mode different from AHC 302, e.g. HM 301. In any event, when entering the fixed-to-bottom mode, the drawworks controller disables the emergency brakes and when leaving the fixed-to-bottom mode, the drawworks controller re-enables the emergency brakes. Enabling and disabling of the emergency brakes both require a positive activation signal, i.e. the emergency brakes remain in their current state (regardless whether that is the enabled or disabled state) unless they receive a positive signal causing a change of state. Each emergency brake further comprises one or more sensors determining whether the brake is in its enabled or disabled state. The sensor signals from each emergency brake are fed to the drawworks controller and the driller control apparatus. The drawworks controller is configured to perform operation in the selected mode of operation only when the sensor signals indicate that the emergency brakes are in the corresponding state required by the corresponding mode of operation.

[0051] Examples of mechanisms for selectively operating the emergency brakes in an enabled and a disabled state will now be described with reference to FIGS. 4 and 5 and with continued reference to FIGS. 1-3.

[0052] FIG. 4 schematically shows a part of the hydraulic control of an emergency brake 36, e.g. of one of the emergency brakes of the drilling rig of FIG. 1. In particular, the emergency brake 36 is a hydraulic disc brake comprising a cylinder 442 in which a spring 438 actuates a caliper 437 so as to cause the caliper 437 to push brake pads against the drum 29 of the drawworks so as to inhibit the drum from rotating and, consequently, to inhibit any load attached to the connecting device of the drilling rig from moving up or down. The cylinder 442 is in fluid communication via conduit 441 to a hydraulic system 50 which is configured to provide hydraulic pressure to the brake 36 so as to compress spring 438 such that the caliper 437 is in a disengaged position where the brake pads are not in contact with the drum.

[0053] The emergency brake is further in fluid communication via conduit 443 and block and bleed block 452 with an accumulator reservoir 451. A first valve 440 is positioned in conduit 443 between emergency brake 36 and reservoir 451. A second valve 439 is positioned in conduit 441 between the emergency brake 36 and the hydraulic system 50. The reservoir 451 is further in fluid communication with the hydraulic system 50 via conduit 444, thus allowing the hydraulic system to pressurize the reservoir 451. A third valve 445 is positioned in the conduit 444 allowing isolating the reservoir 451 and the emergency brake 36 from the hydraulic system 50. A shut-off valves 453 may be provided for maintenance purposes.

[0054] The first valve 440 may be switched between an open position and a closed position. The second valve 439 may be switched between an open position and a non-return position. In the non-return position, the second valve allows fluid flow from the hydraulic system towards the emergency brake but is closed for return flow, i.e. it prevents hydraulic fluid to return from the cylinder 440 of the emergency brake. The third valve 445 may be switched between a closed position and a non-return position. In the non-return position, the third valve allows fluid flow from the hydraulic system towards the reservoir 451 but it is closed for return flow, i.e. it prevents hydraulic fluid to return from the reservoir towards the hydraulic system.

[0055] When the drilling rig is operated in hoist mode or in active heave compensation mode, the first valve is in its closed position, the second valve is in its open position and the third valve is in its non-return position. Hence, in this state, the emergency brake 36 is isolated from the reservoir. In fact, the reservoir 451 is isolated from the remainder of the system. Consequently, when the hydraulic system reduces the pressure at the emergency brake, the brake is activated by the spring 438. Even if the hydraulic system fails resulting in an unintentional pressure loss, the emergency brake is activated.

[0056] When the drilling rig is operated in the fixed-to-bottom mode, the first valve is in its open position, the second valve is in its non-return position and the third valve is in its non-return position. Hence, in this state, even if the hydraulic system reduces hydraulic pressure, the emergency brake remains pressurized by the pressure that is still present in the reservoir 451. Consequently, even in situations of malfunctioning of the hydraulic system 50, the emergency brake is prevented from engaging, at least for a certain period of time as long as the reservoir 451 is capable of maintaining a sufficiently high pressure.

[0057] The first, second and third valves are configured such that they always remain, regardless of their current position, in their current position unless positively actuated, i.e. they do not automatically return to another position unless actuated. Moreover, at least the first and second valves and optionally all three valves are interlocked, i.e. configured to only be switchable together. For example the interlocked valves may be provided in a single valve housing and actuated by the same actuator. The actual position of the valves is further detected by a position sensor (not shown) and communicated to the drawworks controller.

[0058] It will be appreciated that, even though FIG. 4 only shows a single emergency brake 36, hydraulic system 50 may provide hydraulic pressure to multiple emergency brakes, e.g. to all emergency brakes of the drum 29. Nevertheless, each emergency brake 36 has associated with it a separate reservoir 451 and first and second valves 440 and 439, so as to avoid a failure of a single reservoir or valve to inadvertently activate all brakes at the same time.

[0059] FIG. 5 schematically illustrates an alternative mechanism for selectively enabling/disabling an emergency brake. In this example, an emergency brake 36 is shown which is similar to the emergency brake described in connection with FIG. 4. The emergency brake is controlled by a conventional brake control system 50, e.g. a hydraulic system.

[0060] Each emergency brake is associated with a movable blocking member, e.g. a wedge 561, that may be moved between a disengaged position (as shown in FIG. 5) and an engaged position (as illustrated by arrow 564) where it blocks the caliper 437 from engaging the brake pads. Actuation of the wedge 561 is performed by a hydraulic cylinder 562 which is connected to a hydraulic system via valve 563. Valve 563 may be switched between two positions. In one position the pressure from the hydraulic system moves the wedge into its engaged position. In the other position the pressure from the hydraulic system moves the wedge into its disengaged position. As in the example of FIG. 4, the valve is configured such that it always remains in its current position unless positively actuated, i.e. it does not automatically return to another position unless actuated. The actual position of the wedge and/or the valve is further detected by a position sensor (not shown) and communicated to the drawworks controller.

[0061] 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.

[0062] 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.

[0063] 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.