CN214397139U

CN214397139U - Vessel for performing subsea wellbore related activities such as workover activities, well maintenance, installing objects on a subsea wellbore

Info

Publication number: CN214397139U
Application number: CN201990000637.7U
Authority: CN
Inventors: J·鲁登伯格; D·B·韦宁
Original assignee: Itrec BV
Current assignee: Huisman Equipment BV
Priority date: 2018-02-19
Filing date: 2019-02-14
Publication date: 2021-10-15
Anticipated expiration: 2029-02-14
Also published as: WO2019160414A1; EP3755618A1; EP3755618B1

Abstract

The utility model relates to a ship for carrying out the relevant activity of submarine drilling hole such as workover activity, well maintenance, install object on the submarine drilling hole, wherein, the ship includes floating hull (3), elevating gear (7), mobile working deck (15) and mobile deck compensator (18). According to the utility model discloses, the ship configuration is to make elevating gear reduce and promote the object in the operation line and below removing the working deck.

Description

Vessel for performing subsea wellbore related activities such as workover activities, well maintenance, installing objects on a subsea wellbore

Technical Field

The present invention relates to a vessel for performing subsea wellbore related activities such as workover activities, well maintenance, installing objects on a subsea wellbore while a floating vessel is subjected to heave motions due to waves.

The invention also relates to a method performed by a ship according to the claimed invention.

Background

In the prior art, known offshore drilling vessels, for example marketed by the applicant, comprise:

-a floating hull having a deck surface and a moonpool through which a firing line extends;

-a lifting device, such as a crane or a utility tower, mounted on the floating hull and configured for lowering and lifting an object along a firing line, the lifting device comprising:

-a hoist winch and a hoist cable connected to the winch, wherein the hoisting device is configured to support the hoist cable along the firing line;

-a travelling block supported by a hoisting cable for connecting an object; and

-a heave compensation system adapted to provide heave compensation for the hoisting cable, thereby providing heave compensated motion of the travelling block;

-a mobile working deck having a working deck surface, which in a lowered position preferably covers the moonpool, and which in said lowered position of the mobile working deck is level with the deck surface, preferably flush with the deck surface.

A known embodiment is one in which the travelling block is configured to be connected with the mobile working deck, thereby enabling the lifting device to lift the mobile working deck out of the lowered position, so that the mobile working deck moves between the lowered position and the raised position, and to be able to provide a heave compensation motion of the mobile working deck when the mobile working deck is lifted onto the raised position. Such a vessel is disclosed, for example, in WO 2013/169099.

It is also known that a mobile deck is supported by hydraulic power cylinders for providing heave compensation for the mobile working deck. Such a vessel is disclosed, for example, in WO 2016/062812.

It is proposed here that these prior art vessels are used for performing drilling activities. The heave compensated deck is arranged to position the stationary working deck on top of a riser extending between the sea surface and the subsea well. The vessel aims to build and remove these risers on top of the subsea wellbore.

Typically, the working deck of such a vessel is provided with a riser string suspension device which allows the top end of the riser string portion to be suspended from the working deck along the firing line. The riser is configured to couple with a top end of a riser string and to raise and lower the top end of the riser onto and out of the riser string suspension device.

Once the riser string is completed, the mobile working deck may be dropped on top of the riser string due to heave compensation capabilities to provide access to the riser for the worker for wellbore related activities, such as well completion and well maintenance.

A riser string is used to lower an object (typically a subsea blowout preventer, also known as a BOP) towards and onto the wellbore. Moreover, any tools used to perform subsea wellbore related activities are then lowered through the riser.

However, in the case of good maintenance, a riser is not always required. Building and removing risers is very time consuming. Furthermore, large vessels are required to support the risers. Alternatively, it is known to use flexible risers or no risers at all.

SUMMERY OF THE UTILITY MODEL

It is an object of the present invention to provide a vessel which is capable of providing a wide range of wellbore related activities, in particular, the present invention aims to provide a vessel configured to install objects on a subsea wellbore without the use of risers.

The utility model provides a ship, its be used for carrying out the relevant activity of submarine drilling hole, a serial communication port, the ship includes:

-a floating hull having a main deck with a deck surface and a moonpool through which a firing line extends;

-a lifting device mounted on the floating hull and configured for lowering and lifting objects along the firing line and via the moonpool towards and from the seabed, respectively, the lifting device comprising:

-a hoist winch and a hoist cable connected to the hoist winch, wherein the hoisting device is configured to support the hoist cable along the firing line;

-a travelling block supported by a hoisting cable for connection with an object; and

-a vertical mobile working deck having a working deck surface, which in its lowered position covers the moonpool, and which is at the same level as the deck surface of the main deck of the hull;

-a mobile deck compensator connected between the floating hull of the vessel and the mobile working deck, wherein the mobile deck compensator is configured to lift the mobile working deck out of the lowered position, to move the mobile working deck between the lowered position and the raised position, and to provide a heave compensation motion of the mobile working deck moving the mobile deck between a heave compensation maximum height position and a heave compensation minimum height position when the mobile working deck is lifted onto the raised position.

The mobile deck compensator comprises two or more hydraulic mobile deck compensator cylinders.

The hydraulic mobile deck compensator cylinders of the mobile deck compensator are hydraulically connected via hydraulic lines to the heave compensation system of the lifting device, so that the mobile working deck and the travelling block move synchronously when heave compensated.

The mobile deck compensator comprises a series of:

-a lifting power cylinder configured to lift the mobile working deck out of the lowered position and to move the mobile working deck between the lowered position and the raised position; and

-a heave compensation power cylinder configured to provide a heave compensation motion of the mobile working deck when the mobile working deck is lifted onto the raised position, thereby moving the mobile deck between a heave compensation maximum height position and a heave compensation minimum height position.

The lift cylinders are connected to the floating hull and the heave compensation cylinders, and the heave compensation cylinders are connected to the lift cylinders and the mobile working deck.

The lift cylinders are connected to the mobile working deck and the heave compensation cylinders, and the heave compensation cylinders are connected to the lift cylinders and the floating hull.

A single lift cylinder supports both heave compensation cylinders.

The mobile deck compensator comprises a crane or a multipurpose tower comprising a heave compensated lifting device adapted to support the mobile working deck.

The mobile work deck is configured to support a tubular gripping device in the firing line, and the mobile deck compensator is operable to lower and lift the supported tubular and an object connected to the tubular along the firing line.

The vessel is a semi-submersible drilling vessel and the floating hull is embodied as a deck box structure, the semi-submersible drilling vessel including one or more pontoons, and a plurality of support columns extending upwardly from the one or more pontoons and supporting the deck box structure thereon.

The distance between the underside of the mobile working deck and the deck surface of the vessel is at least 3 metres when the mobile working deck is supported in a heave compensated maximum height position, to enable larger objects to be moved into the firing line and below the mobile working deck.

The power cylinder has a working line parallel to the working line.

Furthermore, the present invention provides a vessel configured for performing subsea wellbore related activities such as workover activities, well maintenance, installing objects on a subsea wellbore.

According to the claimed utility model, the ship comprises:

-a lifting device, such as a crane or a multipurpose tower, mounted on the floating hull and configured for lowering and lifting objects along a firing line and via a moonpool towards and from the seabed, respectively, the lifting device comprising:

-a mobile working deck having a working deck surface, which in a lowered position preferably covers the moonpool, and which in a lowered position is at the same level (preferably flush) with the deck surface;

-a mobile deck compensator connected between the hull of the vessel and the mobile working deck, wherein the mobile deck compensator is configured to lift the mobile working deck out of a lowered position, to move the mobile working deck between a lowered position and a raised position, and to provide a heave compensation motion of the mobile working deck when the mobile working deck is lifted onto the raised position, so that the mobile deck moves between a heave compensation maximum height position and a heave compensation minimum height position;

-and preferably an object loading device for introducing objects below the mobile working deck and into the firing line, such that objects can be coupled with the travelling block of the lifting device to enable the lifting device to move objects along the firing line below the mobile working deck.

The lifting device may be used for lifting and lowering objects along the firing line below the mobile working deck for lowering and lifting objects towards and from the seabed, respectively, via the moonpool. Possibly, the lifting device may also be used for lifting and lowering objects along the firing line above the mobile working deck.

The hoisting device comprises a heave compensation system. It is proposed here that heave compensation systems for hoisting devices are known in the prior art and usually comprise active and passive heave compensation provided by hydraulic power cylinders supporting sheaves for guiding the hoisting cables. Since these types of heave compensation systems for hoisting devices are well known, they will not be discussed in detail herein.

The mobile deck compensator is configured to raise the mobile working deck out of the lowered position and to move the mobile working deck between the lowered position and the raised position. Furthermore, the mobile deck compensator is configured to provide a heave compensation motion of the mobile working deck when the mobile working deck is in a raised position. In providing heave compensation, the mobile working deck is lowered and raised relative to the raised position to compensate for the motion of the vessel due to the heave of the waves. The mobile deck compensator may lift the mobile working deck to a heave compensated maximum height position relative to the raised position and lower the mobile working deck to a heave compensated minimum height position relative to the raised position.

For example, in an embodiment, in the raised position of the mobile working deck, the distance between the mobile working deck surface of the mobile working deck and the deck surface of the deck is 5 meters, at the maximum heave compensation height of the mobile working deck, the distance between the mobile working deck surface of the mobile working deck and the deck surface of the deck is 7.5 meters, and at the minimum heave compensation height of the mobile working deck, the distance between the mobile working deck surface of the mobile working deck and the deck surface of the deck is 2.5 meters.

In an embodiment, the distance between the underside of the mobile working deck and the deck surface of the vessel is at least 3 meters, preferably at least 4 meters, when the mobile working deck is supported in the raised position (preferably in the heave compensated maximum height position), to enable larger (i.e. more than 2 meters in height) objects to be moved into the firing line and below the mobile working deck.

In an embodiment, the mobile deck compensator comprises two or more (preferably four) hydraulic mobile deck compensator cylinders. Preferably, the power cylinder has a working line parallel to the working line.

In an embodiment of the vessel according to the invention, the mobile deck compensator comprises a crane or a multipurpose tower comprising a lifting device adapted to support heave compensation of the mobile working deck. In such an embodiment, a second lifting device has been provided for lowering and lifting the object.

In an embodiment, the mobile deck compensator (more specifically, the two or more hydraulic mobile deck compensator cylinders of the mobile deck compensator) is hydraulically connected to the heave compensation system of the lifting device via hydraulic lines such that the mobile working deck and the travelling block move synchronously while being heave compensated.

In an embodiment, the mobile working deck compensator comprises a series of:

-a heave compensation power cylinder configured to provide a heave compensation motion of the mobile working deck when the mobile working deck is lifted onto the raised position, thereby moving the mobile working deck between a heave compensation maximum height position and a heave compensation minimum height position.

In an embodiment, the lift cylinders are connected to the floating hull and to the heave compensation cylinders, and the heave compensation cylinders are connected to the lift cylinders and to the mobile working deck. It is also conceivable that the lifting power cylinders are connected to the mobile working deck and to the heave compensation power cylinders, which are connected to the lifting power cylinders and to the floating hull.

In combination with a compact design that can be stored in a floating hull, in particular in the deck box of a semi-submersible vessel, the connected lifting power cylinders and heave compensation power cylinders enable a large operating range for the mobile deck compensator. This arrangement enables a relative reduction in the length of the one or more heave compensation rams since the stroke length of the one or more rams only has to be adjusted to the desired heave motion compensation. Lifting the mobile working deck into a raised position, for example avoids any risk of the working deck reaching its rest position during a heave movement operation, and for example enables pipes, tubes etc. to be passed from below the working deck (e.g. from a diverter and/or a Rotating Control Device (RCD)) to a position outside the moonpool (e.g. on the upper deck).

For example, a single lift cylinder supports two heave compensation cylinders, e.g., a single lift cylinder located between two heave compensation cylinders.

For example, the working deck lifting power cylinders are fixed with their rods pointing downwards, and each heave compensation power cylinder has its cylinder body fixed to the cylinder body of the lifting power cylinder, e.g. via a frame, and the rod of each heave compensation power cylinder points upwards towards the working deck.

In an embodiment, the mobile working deck compensator is configured to support the mobile working deck in a raised position (preferably in a heave compensated maximum height position) while an object can be moved into the firing line below the mobile working deck. Preferably, the mobile deck compensator is configured to provide sufficient clearance between the deck and the underside of the mobile working deck for introducing objects from the deck into the firing line and below the mobile working deck when the mobile working deck is in the raised position. Preferably, the mobile working deck is configured to support the mobile working deck in a maximum heave compensation height position to provide additional clearance and enable objects to be introduced into the firing line below the mobile working deck. Once in this position, the object may be coupled with a travelling block of a lifting device supported by the mobile deck and/or the mobile working deck and/or a coupling device (e.g. a pipe), and/or a guide rope, to enable the object to be moved along the firing line below the mobile working deck.

In an embodiment, the object is moved in a substantially horizontal direction from the deck surface of the vessel into the firing line. It is also conceivable that the objects are stored above or below the deck surface and that the objects are moved along a non-horizontal movement path.

Preferably, the vessel is provided with an object loading device for introducing objects below the mobile working deck and supporting the objects above the moonpool and along the firing line, such that the objects can be coupled with the travelling block of the lifting device supported by the mobile deck and/or the mobile working deck and/or the coupling device (e.g. pipe), and/or the guide line, to enable the objects to be moved along the firing line below the mobile working deck.

In an embodiment, the object loading device is a dedicated jack or carrier configured to pick up and lift an object located on deck, move the object towards the moonpool, and support the object above the moonpool along the firing line. In an embodiment, the object loading device is a heavy robotic arm configured to pick up objects located on deck and support the objects above the moonpool (in the expanded configuration) along the firing line.

The object loading device for example comprises a carrier rail comprising a rail for moving a carrier and/or object into the firing line and below the mobile working deck when the carrier and/or object is suspended from the carrier rail or when supported by the carrier rail, wherein preferably the carrier rail is located on the deck surface or below the deck surface on the moonpool deck. Preferably, the truck and/or the object is slid or slid into the firing line in a substantially horizontal direction. Preferably, the cart track comprises tracks on opposite sides of the firing line for moving the cart and/or object into the firing line and below the mobile work deck when the cart and/or object is suspended by or supported by the cart track.

Possibly, the object is supported on the truck or directly on a track, i.e. an object integrated with the truck. In another embodiment the mobile working deck is further provided with a carrier rail, the rail of which is aligned with the rail of the carrier rail on the deck surface of the vessel when the mobile working deck is in the lowered position, to enable a carrier or an object to be moved in a substantially horizontal direction from the deck surface of the vessel directly along the rail onto the mobile working deck and vice versa.

In an embodiment the object loading means comprises a sliding deck section, preferably supported on rails, comprising rails on opposite sides of the firing line, wherein the sliding deck section is located near a moonpool opening in the deck surface, and preferably the sliding deck section is slidable on the moonpool opening in the deck surface when the mobile working deck is in a raised position, preferably in a heave compensated maximum height position, for moving the object into the firing line and below the mobile working deck while supported by the sliding deck section, thereby enabling coupling of the object with a travelling block and/or mobile deck and/or coupling means (e.g. pipes), and/or guide lines supported by the mobile deck.

In an embodiment, wherein the mobile deck compensator comprises two or more hydraulic mobile deck compensator cylinders located on opposite sides of the moonpool, the mobile deck section is configured to be located above the moonpool between the hydraulic mobile deck compensator cylinders.

In embodiments, the cart track is located on a deck surface of the vessel, or alternatively, the cart track is below the deck surface of the vessel and located on a lower deck level, e.g. a so-called moonpool deck.

Preferably, the rails (e.g. rails or skids) of the trolley track extend on opposite sides of the firing line, preferably along opposite sides of the moonpool. In an embodiment, the object loading device comprises a removable rail or sliding deck portion that can be placed above the moonpool to support objects along the firing line above the moonpool and below the mobile working deck. Thus, the firing line passes between the rails. A truck supporting an object or an object supported directly on a track has one end supported on one of the tracks (e.g., one of the rails) and the other end supported on the opposite track (e.g., the other rail). Thus, the rail can support the object along the firing line.

In an embodiment, a second drill floor is provided below the mobile working deck to support an object above the moonpool along the firing line. In such embodiments, for example, the skid rails comprise rails on the deck of the vessel and rails on the second drill floor, which rails on the deck of the vessel and rails on the second drill floor are aligned when the mobile working deck is supported in the raised position (preferably, in the maximum heave compensation height position) to enable objects to be skidded from the deck onto the second drill floor.

Preferably, the mobile working deck is configured to support the tubular gripping device along the firing line, thereby enabling the mobile working deck to support a tubular or a column of tubulars in the firing line. Furthermore, in such embodiments, the mobile deck compensator may be used to lower and lift supported tubulars and objects connected to the supported tubulars, such as other tubulars or BOPs, along the firing line.

Preferably, the mobile work deck is configured to removably support the tubular gripping device such that the tubular gripping device can be removed from the firing line, thereby enabling the travelling block and lifting cable to pass through the mobile work deck and to lift and lower objects through and/or below the work deck. In an embodiment, the tubular gripping apparatus may be lifted onto and out of a working position in the mobile working deck and may be removed from the mobile working deck when not in use. In another embodiment, the tubular gripping apparatus is slidable between an active position in which the tubular gripping apparatus is aligned with the firing line, and a parked position in which the tubular gripping apparatus is not in line with the firing line. In such embodiments, for example, the tubular support gripper may be supported in a sliding deck section, and the tubular support gripper may be moved into and out of the firing line by sliding the deck section.

In an embodiment, the mobile working deck is configured to support a tool (e.g., a skid or a gimbal device) along the firing line in a manner similar to that set forth above with reference to the tubular gripping device.

In an embodiment of the claimed invention, the vessel further comprises at least one guide rope winch and a guide rope, which guide rope is to be connected to the subsea well, e.g. to a subsea set of devices (subsea stack) mounted on the well or on a drilling template, such that the guide rope extends parallel to and spaced apart from the firing line, wherein the guide rope winch comprises a heave compensation system adapted to keep the guide rope under a substantially constant tension when the guide rope is fixed to the subsea well for guiding an object to be lowered along the firing line towards or lifted from the seabed.

In an embodiment of the claimed invention, the vessel comprises at least one guide rope winch mounted to the mobile working deck, and a guide rope connected to said guide rope winch, which guide rope is to be connected to the subsea well, e.g. to a set of subsea devices mounted on the well or to a drilling template, such that the guide rope extends parallel to and spaced apart from the firing line, wherein the guide rope winch comprises a heave compensation system adapted to keep the guide rope under a substantially constant tension when the guide rope is fixed to the subsea well, for guiding objects to be lowered along the firing line towards or lifted from the seabed, when the mobile working deck is kept in a fixed position relative to the vessel.

In such embodiments, when the mobile deck compensator provides heave compensation for the mobile working deck, the heave compensation also provides heave compensation for the guide line winch, which can be used to maintain the guide line under substantially constant tension when it is secured to the subsea well. This is advantageous as it will extend the life of the guide rope since there is no need to continuously wind the guide rope on the guide rope winch (or on the heave compensation sheave) or to continuously wind the guide rope on the rotating guide rope winch to provide heave compensation.

In embodiments wherein at least one guide rope winch is mounted to the mobile working deck, it is conceivable that the guide rope winch is provided on the working deck surface. In a preferred embodiment, the at least one guide rope winch is located below a mobile working deck surface of the mobile working deck. The guide rope winch is not mounted on the deck surface of the mobile working deck, which can provide the mobile working deck with an unobstructed deck surface for emptying, which is particularly advantageous when the mobile working deck is in a lowered position and the deck surface of the mobile working deck is level with the deck surface of the deck of the vessel.

In an embodiment, the guide rope winch is movably mounted to enable the position of the guide rope winch to be adapted relative to the guide rope anchoring point at the borehole so that the guide rope extends parallel to the firing line. Additionally or alternatively, a guide rope guide (e.g. a movable sheave) may be provided on the mobile working deck to enable adjustment of the trajectory of the guide rope, in particular such that the guide rope extends parallel to the firing line.

Preferably, the vessel's deck surface comprises a lifting cable opening, which is aligned with the firing line, for passing the lifting cable of the lifting device. In an embodiment, the lift cable opening of the mobile working deck is large enough for the travelling block to pass through.

In an alternative embodiment, the mobile working deck comprises a frame defining a central passage for passing an object supported by the lifting device, and one or more movable (e.g. pivotable or removable) deck sections.

In embodiments, the movable deck section may be provided in a raised position in which the lifting cable opening is provided large enough for the lifting cable to pass through, or in the case of a lifting arrangement in a multi-fall arrangement, for multiple lifting cables to pass through. In the travelling block position of the movable deck section, which has been moved to enable the travelling block to pass through the central opening in the mobile working deck, the travelling block position of the movable deck section creates a sufficiently large opening for the travelling block to pass through.

In an embodiment, the movable deck section is movable to cover a position where the movable deck section covers the central passage, thereby providing a deck surface above the opening.

In an embodiment, the movable deck section is movable to an open position in which the central opening is open. Preferably, the central opening is large enough to allow large objects to pass through that are to be lowered towards the seabed. For example, in such embodiments, the section of the subsea device group to be installed on top of the well bore may be assembled along the firing line and on the mobile working deck, lifted from the mobile working deck with the lifting device, after which the movable deck section is moved to the open position and objects may be lowered towards the seabed through the mobile working deck and through the moonpool. Preferably, the open position of the movable deck section enables objects occupying four meters by four meters of ground to pass through. It is proposed that the size of the opening through which such objects pass is significantly greater than the size of the opening through which the travelling block passes. The movable deck section may be temporarily removed or may be pivoted or slid away, for example.

Thus, the mobile working deck can be used before lowering the object (i.e. assembling the set of subsea devices), as well as when and after lowering the object. Thus, deck space can be efficiently utilized.

In an embodiment of the vessel according to the invention, the second drilling floor is suspended below the mobile deck. The second drill floor enables objects to be supported below the mobile working deck and provides access to the space below the mobile working deck.

Preferably, the second drilling floor is level with the deck surface of the vessel when the mobile deck is in a raised position, preferably in a heave compensated maximum height position. Thus, when the mobile working deck is in a raised position (preferably in a heave compensated maximum height position), objects may be moved in a substantially horizontal direction from the deck surface of the vessel onto the second drill floor. Once the object is located on the second rig floor, the object may be coupled with a lifting device (i.e., a travelling block) or an object (e.g., a tubular) supported by the lifting device or the mobile working deck and/or a guide line extending between the vessel and the subsea wellbore (preferably, between the mobile working deck of the vessel and the subsea wellbore).

In an embodiment of the vessel according to the invention, the second drill floor comprises a drill floor frame defining a central passage and one or more movable drill floor sections, which are movable (e.g. pivotable or removable) between a covering position in which they cover the central passage to provide a deck surface above the passage and an open position in which the central opening is open, e.g. for passing an object supported by the lifting device.

Additionally or alternatively, once the object is supported by the lifting device and ready to be lowered towards the subsea wellbore, the second rig floor may be disconnected and removed as a whole.

In an embodiment of the vessel according to the claimed utility model, the vessel comprises a heave compensation control system controlling the heave compensation system of the hoisting device, the mobile deck compensator and, if present, the heave compensation system of the guide rope winch. Possibly, synchronous heave compensation is provided. Heave compensation control systems for the same applicant have been described in WO 2016/062812.

Preferably, at least one of a drill string slip device, a riser spider device and/or a diverter is supported by the mobile working deck, wherein the drill string slip device is configured to support a suspended drill string within the riser, wherein the riser spider device is configured to support the suspended riser, for example during assembly and disassembly of the riser, wherein the diverter is configured to divert a flow of hydrocarbons and/or drilling mud from the subsea wellbore to the vessel.

In an embodiment of the vessel according to the invention as claimed, a riser tensioning system is provided for supporting a riser located in the moonpool at an upper end of the riser; a riser extends along the firing line between the subsea wellbore and the vessel. Possibly, riser-tensioning power cylinders are provided in the hull of the vessel and in the deckbox structure of the semi-submersible vessel, said riser-tensioning power cylinders are connected to telescopic joints provided at the upper end of the risers.

The riser tensioning system provides a nearly constant upward force on the riser that is independent of the floating vessel's motion. The riser tensioning system manages the motion differential between the riser and the vessel when the riser is connected to a wellhead on the seafloor. If there is no riser tensioning system and the vessel moves down due to heave, the risers will bend; whereas if the vessel is lifted, large forces will be transferred to the riser and the riser will stretch and break.

The weight of the riser is suspended by a riser tensioning system. Possibly, the riser may be provided with a flotation device (e.g. a flotation tank) to support at least a part of the weight of the riser.

In an embodiment, the rotating control device and/or diverter is suspended from the mobile working deck, to which the top end of the riser (in particular the expansion joint) is attached, preferably via a flexible joint.

In embodiments wherein the position of the mobile working deck (in particular the mobile working deck in its lowered position) is fixed relative to the vessel, the difference in motion between the riser and the vessel can be absorbed by the expansion joints.

In an embodiment, wherein the mobile deck compensator provides heave compensation motion of the mobile working deck and the expansion joint is connected to the mobile working deck, the expansion joint is not typically needed to absorb the motion difference. In such an embodiment, the expansion joints may be locked, thereby fixing the position of the mobile working deck relative to the riser, and the mobile deck compensator is used to support the mobile working deck and optionally part of the weight of the riser. Thus, the mobile deck compensator may be used to absorb motion differences between the riser and the vessel, thereby acting as a riser tensioning system.

It is also conceivable that the expansion joint is not locked and that the expansion joint still absorbs some relative movement.

It is envisaged that the mobile working deck may be used to support risers during assembly.

In an embodiment, the vessel is a semi-submersible drilling vessel and the floating hull is embodied as a deckbox structure, the semi-submersible drilling vessel including one or more pontoons (e.g., two parallel pontoons or one annular pontoon) and a plurality of support columns extending upwardly from the one or more pontoons and supporting the deckbox structure thereon. The deck box structure is a structure that supports the surface of a semi-submersible deck.

In an embodiment, the semi-submersible vessel comprises a moonpool deck located below a deck surface in the deckbox structure. Advantageously, the cart track is located below a deck surface of the vessel, preferably on a moonpool deck, wherein the cart track comprises a track (e.g. rails or skid rails) for moving the cart and/or the object into the firing line and below the mobile work deck when the cart and/or the object is suspended from the cart track or supported by the cart track, to enable coupling with a travelling block supported by the mobile deck and/or a coupling device (e.g. a pipe) and/or a guide rope. Preferably, the rails extend on opposite sides of the firing line.

In such embodiments, the moonpool deck and the cart rails for moving objects into the firing line are located below the deck surface and thus below the mobile work deck when the mobile work deck is in the lowered position. Possibly, there is no need to lift the mobile working deck in order to be able to move objects into or out of the firing line under the mobile working deck.

In an embodiment, the vessel further comprises a cart rail provided on a deck surface of the vessel, the cart rail comprising a rail for moving the cart and/or the object in a substantially horizontal direction from the deck surface into the firing line and below the mobile working deck in a raised position (preferably in a heave compensated maximum height position) when the cart and/or the object is supported by the cart rail, to enable coupling of the object with a travelling cart and/or a coupling device (e.g. a pipe) and/or a guide line supported by the mobile deck.

In such embodiments, the mobile deck compensator is configured to provide sufficient clearance between the deck surface and the mobile working deck (more specifically, the bottom side of the mobile working deck, i.e. the side facing the sea surface) for objects to be moved into the firing line to pass under the mobile working deck.

The utility model discloses further provide utilize according to the utility model claimed the method that the ship carries out.

An exemplary method for installing an object onto the seabed with a vessel according to the present invention comprises the steps of:

-positioning an object below the mobile working deck and in the firing line;

-connecting the object to a travelling block of a lifting device supported by the mobile deck and/or to the mobile working deck and/or to a coupling device (e.g. a pipe), and/or to a guide line; and is

-lowering the object towards the seabed using the lifting device.

Possibly, the method further comprises the step of lifting the mobile working deck from the lowered position to the raised position, preferably to a position of maximum heave compensation height.

A further method according to the claimed invention comprises the steps of:

-connecting at least one guide line from a guide line winch located on the mobile working deck to a subsea well, e.g. a well template;

-maintaining the guide line under a substantially constant tension while the mobile deck is supported in the raised position (preferably, in a heave compensation maximum height position) by means of the heave compensation system of the guide line winch;

-slidably connecting the object with at least one guide rope.

Preferably, the method further comprises the steps of: a mobile deck compensator is utilized to provide heave compensation motion of the mobile working deck and to maintain the guide line under substantially constant tension in place of the heave compensation system of the guide line winch.

In an embodiment, a method for installing an object onto a sea floor with a vessel according to the claimed invention, the method comprises the steps of:

-positioning the object in the firing line preferably while the mobile working deck is supported in the raised position, preferably while the mobile working deck is supported in the heave compensated maximum height position;

-connecting the object to a travelling block of the lifting device;

-using a mobile deck compensator to lift the mobile working deck to a raised position and to provide a heave compensation motion of the mobile working deck;

-using a heave compensation system of the hoisting device to provide a compensating movement of the travelling block and thereby of the object supported by the travelling block;

-preferably, connecting the object with the guide rope; and is

-lowering the object towards the seabed using the lifting device.

The present invention furthermore provides a method for using a wellbore related activity tool comprising a tool winch, a tool cable and a tool in subsea drilling with a vessel comprising at least one guide rope winch, the method comprising the steps of:

-connecting at least one guide line to the subsea well and using a heave compensation system of the guide line winch to maintain the guide line under a substantially constant tension;

-positioning a wellbore related movable tool on a deck surface of a mobile working deck;

-positioning the tool below the mobile working deck, the tool cable passing through an opening in the working deck;

-connecting the tool with at least one guide line;

-using the mobile deck compensator to lift the mobile working deck to a raised position and to provide a heave compensation motion for the mobile working deck;

-replacing the heave compensation system of the guide line winch with a mobile deck compensator to keep the guide line under a substantially constant tension; and is

-using the tool winch to lower the tool towards the sub sea borehole.

Drawings

The invention will be further elucidated with reference to the drawings, in which:

fig. 1 shows a schematic side view in cross section of an exemplary embodiment of a vessel according to the invention in a first operating position;

fig. 2 shows a schematic side view in cross section of an exemplary embodiment of a vessel according to the invention in a second operating position;

figure 3 shows a schematic side view in cross-section of the vessel of figure 1 in a third operating position;

FIG. 4 shows a schematic side view in cross-section of the vessel of FIG. 1 in a fourth operating position;

FIG. 5 shows a schematic side view in cross-section of the vessel of FIG. 1 in an alternative operating position;

fig. 6 shows a further alternative configuration of a vessel according to the invention;

figure 7 shows a further alternative configuration of a vessel according to the invention;

figure 8 shows a further alternative configuration of a vessel according to the invention;

FIG. 9 shows a detail of the configuration of FIG. 8;

FIG. 10 shows the vessel of FIG. 8 in another configuration;

FIG. 11 shows the vessel of FIG. 8 in another configuration;

fig. 12a-12c show the vessel of fig. 10 in different positions.

Detailed Description

First, the invention will be further elucidated on the basis of an exemplary embodiment of an apparatus according to the invention as shown in fig. 1-5. In the drawings, like reference numerals have been used for corresponding elements in the various drawings. Reference numerals are also associated with various aspects in the list of reference numerals. Once such an element has been described with respect to one figure, the description of that element is incorporated by reference into the description of the corresponding element in the other figure, unless otherwise indicated herein or context.

Fig. 1 shows a schematic side view in cross section of an exemplary embodiment of a vessel 1 according to the invention in a first working position in which objects are lowered towards the seabed. Figures 2, 3 and 4 show the same vessel in a second and a third subsequent operating position.

The vessel 1 is configured for performing subsea wellbore related activities such as workover activities, well maintenance, installation of objects 8 on the subsea wellbore 2. According to the claimed invention, the vessel 1 comprises a floating hull 3, a lifting device 7, a mobile working deck 15 and a mobile deck compensator 18.

The floating hull 3 has a deck surface 6, here a main deck. The floating hull 3 also has a moonpool 4 providing a sea access for lowering objects into the sea or lifting them out of the sea. Above the moonpool, the deck 6 has a moonpool opening 27. The firing line 9 extends through the moonpool.

The vessel 1 further comprises a mobile working deck 15. The mobile working deck 15 has a working deck surface 16. Figure 1 shows the mobile working deck in a lowered position. In the lowered position shown, the mobile working deck 15 covers the moonpool 4. In the lowered position the mobile work deck surface 16 is level with the deck surface 6 of the vessel 1, i.e. the mobile work deck surface 16 and the deck surface 6 form one large deck surface that can be used as a whole. In the shown preferred embodiment the working deck surface 16 of the mobile working deck 15 is even flush with the deck surface 6. Thus, persons or objects can be transferred in a horizontal direction from the deck to the mobile working deck. Without having to pay attention to the presence of steps or dips.

A mobile deck compensator 18 is connected to the floating hull 3 and the mobile working deck 15 of the vessel 1.

In the exemplary embodiment shown, the mobile deck compensator 18 comprises four hydraulic mobile deck compensator cylinders 31. These hydraulic mobile deck compensation power cylinders 31 are located at the corners of the mobile working deck, respectively, and are connected at one end to the floating hull 3 of the vessel 1 and at the other end to the mobile working deck 15. A pair of hydraulic mobile working deck power cylinders 31 are located on one side of the moonpool 4. These power cylinders are visible in the drawings. A pair of hydraulic mobile working deck power cylinders are located on opposite sides of the moonpool 4. These power cylinders are not visible in the drawings, since they are located behind the two visible hydraulic mobile working deck power cylinders 31.

The mobile deck compensator 18 is configured to lift the mobile working deck 15 out of a lowered position (which is shown in fig. 1) and onto a raised position (which is shown in fig. 2-4). Thus, the mobile deck compensator 18 according to the claimed invention may move the mobile working deck 15 between a lowered position and a raised position. Furthermore, according to the claimed invention, the mobile deck compensator 18 is configured to provide a heave compensation motion of the mobile working deck when the mobile working deck is lifted to the raised position, moving the mobile working deck relative to the raised position between a heave compensation maximum height position and a heave compensation minimum height position. Thus, the mobile deck compensator may keep the mobile working deck substantially stationary relative to the seabed when the mobile working deck is lifted to an elevated position.

Possibly, the distance between the bottom side 44 of the mobile working deck 15 and the deck surface 6 of the vessel 1 when supported in the heave compensated maximum height position is at least 3 meters, preferably at least 4 meters, enabling larger (i.e. more than 2 meters in height) objects to be moved into the firing line 9 and below the mobile working deck 15.

A lifting device 7 is provided, which lifting device 7 is configured to lower and lift an object 8 towards and from the seabed 10, respectively, along a firing line 9 and via a moonpool. In the shown embodiment, the lifting device 7 is a multipurpose tower. The multipurpose tower comprises a mast tower mounted on the floating hull 3, which mast tower supports a lifting winch 11 and a lifting cable 12 connected to the lifting winch 11. A travelling block 13 is supported by the hoisting cable 12, said travelling block 13 being intended for connection with an object to be lowered into or lifted from the seabed.

The lifting device is configured to support a lifting cable 12 along a firing line 9 (i.e. a virtual line indicating a vertical trajectory along which an object may be lowered through the moonpool). In the figures, the firing line coincides with the part of the lifting cable that extends between the utility tower (more specifically, the crown block of the utility tower) and the travelling block.

The hoisting device 7 further comprises a heave motion compensation system 14, which heave motion compensation system 14 is adapted to provide heave compensation for the hoisting cable to provide heave compensation motion of the travelling block. It is proposed here that heave compensation systems for hoisting devices are known in the prior art and usually comprise active and passive heave compensation provided by hydraulic power cylinders supporting sheaves for guiding the hoisting cables. Since these types of heave compensation systems for hoisting devices are well known, they will not be discussed in detail herein.

The mobile working deck 15 is provided with a hoist cable opening 17, which hoist cable opening 17 is aligned with the firing line 9 for the passage of the travelling block 13 and the hoist cable 12 of the hoist 7.

In the shown embodiment, an object loading device is provided for introducing objects under the mobile working deck 15 and into the firing line 9, here embodied as a sliding deck section 24. The sliding deck section 25 is supported on rails 24, which rails 24 comprise rails 26 on opposite sides of the firing line 9, here between two pairs of hydraulically movable working deck power cylinders 31. The sliding deck section is located adjacent a moonpool opening 27 (shown in fig. 2) in the deck surface 6, which position is shown in fig. 1 and 2.

When the mobile working deck is in the raised position, which is shown in fig. 2-5, the sliding deck section 25 can slide along the moonpool opening 27 in the deck surface 6 for moving the object 8 into the firing line 9 and below the mobile working deck 15 while supported by the sliding deck section. It is proposed herein that the mobile deck compensator is configured to support the mobile working deck in a heave compensated maximum height position, providing an additional gap between the deck surface and the underside of the mobile working deck for introducing large sized objects into the firing line and below the mobile working deck.

Once the object is located below the mobile working deck, the object is coupled with a travelling block to enable the lifting device to move the object along the firing line below the mobile working deck, more particularly to lower the object 8 towards the seabed, more particularly to lower the object 8 towards the subsea wellbore 2.

In the shown embodiment the vessel 1 further comprises two guide rope winches 28 and 29, said guide rope winches 28 being mounted to the mobile working deck 15 and said guide ropes 29 being connected to said guide rope winches.

The guide line 29 is connected to the subsea wellbore 2, in the embodiment shown to the drilling template 46, such that the guide line extends parallel to the firing line 9 and is spaced from the firing line 9. Each guide line winch 28 comprises a heave compensation system 30, which heave compensation system 30 is adapted to keep the guide line 29 under a substantially constant tension when the guide line 29 is fixed to the subsea borehole for guiding objects to be lowered along the firing line towards or lifted from the seabed.

The heave compensation also provides heave compensation for the guide line winch when the mobile deck compensator provides heave compensation for the mobile working deck, and thus can be used to keep the guide line under a substantially constant tension when the guide line is fixed to the subsea drilling, when the mobile working deck is kept in a fixed position relative to the vessel. This is advantageous since there is no need to continuously wind the guide rope on the guide rope winch and continuously wind the guide rope of the guide rope winch (or on the heave compensated sheave), which will prolong the life of the guide rope.

In the shown preferred embodiment the guide rope winch 28 is located below the deck surface 16 of the mobile working deck 15, which provides an unobstructed deck surface for emptying of the mobile working deck, which is particularly advantageous when the mobile working deck is in a lowered position and the deck surface of the mobile working deck is level with the deck surface of the deck of the vessel, see fig. 1.

It is proposed here that in the situation shown in fig. 1, i.e. with the guide line 29 connected to the subsea well and the mobile working deck in a lowered position (and thus in a fixed position), the heave compensation system of the guide line winch is used to keep the guide line under a substantially constant tension. Furthermore, when the mobile working deck is in the raised position and the object is moved into the firing line, the mobile working deck will be in a fixed position and the heave compensation system of the guide rope winch is used to keep the guide rope under a substantially constant tension. Once heave compensation has been made to the moving working deck, the guide rope winch will no longer need to provide heave compensation.

The vessel 1 allows for the installation of objects 8 onto the seabed, more specifically, a subsea wellbore.

Once the travelling block 13 has been located under the mobile working deck 15, the travelling block 13 can be connected to an object located under the mobile working deck, see fig. 2, with the lifting cables passing through the lifting cable openings 17 in the mobile working deck.

In the embodiment showing the sliding deck section, the object loading means may be used to position objects in the firing line 9 below the mobile working deck when the mobile working deck is raised to the raised position, see fig. 2 and 3. In the embodiment of the vessel shown, objects can be moved from the deck surface 6 into the firing line 9 in a substantially horizontal direction and under the mobile working deck 15.

After the object 8 has been connected to the travelling block 13, the object is lifted from the sliding deck section 24 (which is subsequently withdrawn) by means of the guide line 29, so that the object can be lowered towards the subsea wellbore 2 using the lifting device 7. The object is guided by the guide line when lowered so as to be correctly positioned relative to the subsea wellbore, see fig. 4.

Fig. 5 shows a schematic side view of a section of the vessel of fig. 1 in an alternative operating position.

The vessel 1 is here arranged to perform wellbore related activities with a wellbore related activities tool 47. In the illustrated embodiment, the wellbore related activity tools include a tool winch 48, a tool cable 49 and a tool 50 in the subsea wellbore 2.

For example, the wellbore related activity tool may be a coiled tubing tool or a wireline tool, which are well known tools. With such a tool, the tool winch may be used to lower and lift the tool cable and the tool winch. In addition, a separate tool transport 51 can be used, such as opposing rails configured to engage and move the tool cable between the opposing rails to raise and lower the tool.

The guide line 29 has been connected to the subsea wellbore 2, more specifically to the drilling template 46 of the subsea wellbore, and may thus be used for guiding the tool 50.

It is proposed that no wellbore related movable tools with dedicated heave compensation means need to be provided, since the heave compensated mobile working deck can be used to support the wellbore related movable tools.

Once the wellbore related movable tool 47 has positioned the tool 50 below the mobile working deck 15, the tool cable is passed through an opening in the working deck (e.g., a lift cable opening), and the tool 50 may be connected to the guide line 29.

The mobile deck compensator may then be used to lift the mobile working deck to a raised position and provide heave compensation motion to the mobile working deck. When the mobile working deck is heave compensated, both the guide line and the wellbore activity tool are in a substantially fixed position relative to the wellbore. Thus, no additional heave compensation is required, e.g. by means of a heave compensation device of a guide rope winch.

In the embodiment shown in fig. 5, a tool winch 48 is used in conjunction with a tool conveyance device 51 comprising opposing tracks to lower the tool toward the subsea wellbore. The guide line guides the tool and ensures that the tool lands in the correct position on the wellbore, in the embodiment shown on the wellbore-mounted object 7.

It is proposed herein that even with the use of a guide line, a Remotely Operated Vehicle (ROV) can be configured to accurately position and/or install objects and/or tools on a subsea wellbore.

Fig. 6 also shows another alternative arrangement according to the invention, in which the vessel is a semi-submersible drilling vessel, and in which the floating hull 3 is embodied as a deckbox structure, the semi-submersible drilling vessel comprising one or more pontoons (e.g. two parallel pontoons or one annular pontoon) and a plurality of support columns extending upwardly from the one or more pontoons and supporting the deckbox structure thereon. The deckbox structure has a deckboard surface 6 and another lower deckboard surface classified as a moonpool deck 19.

The object loading device is provided for introducing the objects 8 into the firing line below the mobile working deck 15, so that the objects 8 can be coupled with the travelling block 13 of the lifting device 7 supported by the mobile deck and/or the mobile working deck 15 and/or coupling devices (e.g. pipes) and/or guide lines to enable the objects to be moved along the firing line 9 below the mobile working deck 15. The object loading device here comprises a cart rail 20, which cart rail 20 comprises a rail 21 for moving a cart 22 and/or an object carrying the object 8 into the firing line and below the moving work deck 15, when the cart 22 and/or the object carrying the object 8 is suspended from the cart rail or when the cart 22 and/or the object carrying the object 8 is supported by the cart rail. The truck rail 20 is here located below the deck surface 6 on the moonpool deck 19.

Fig. 7 also shows another alternative configuration of the vessel according to the invention. A second drill floor 36 is suspended below the mobile working deck 15, where said second drill floor 36 is at the same level as the deck surface 6 of the vessel 1 when the mobile working deck 15 is in a raised position, preferably in a heave compensated maximum height position. The object 8 can be moved on the deck surface 6 onto a second drill floor 36, on which second drill floor 36 the object 8 can be coupled with the travelling block 13 of the lifting device 7 supported by the mobile deck and/or the mobile working deck 15 and/or coupling devices (e.g. pipes) and/or guide lines to enable the object to be moved along the firing line 9 below the mobile working deck 15.

In fig. 8-12 c, a further alternative vessel according to the invention is also shown in cross-section. In fig. 8, a detail of a semi-submersible vessel 1 is shown, which comprises a deckbox structure 3. Not shown is a semi-submersible vessel comprising one or more pontoons (e.g., two parallel pontoons or one annular pontoon) and a plurality of support columns extending upwardly from the one or more pontoons and supporting the deck box structure thereon.

The deckbox structure 3 has a moonpool 4 through which a firing line 9 extends 4. The deckbox structure 3 has a deckboard surface 6. The lifting device is not shown.

The mobile working deck 15 is provided with a working deck surface 16, which working deck surface 16 is, as shown in fig. 8, at the same level as the deck surface 6 in the lowered position of the mobile working deck 15, here flush with the deck surface 6.

Here, according to a preferred embodiment, a mobile deck compensator 18 is provided, which deck compensator 18 is shown in further detail in fig. 9. The mobile deck compensator comprises a lifting power cylinder 101, which lifting power cylinder 101 is configured to lift the mobile working deck 15 out of the lowered position and to move the mobile working deck between the lowered position and the raised position. The mobile deck compensator further comprises a heave compensation power cylinder 102, which heave compensation cylinder 102 is configured to provide a heave compensation motion of the mobile working deck 15 when the mobile working deck 15 is lifted to a raised position, thereby moving the mobile deck between a heave compensation maximum height position (visible in fig. 12 c) and a heave compensation minimum height position (visible in fig. 12 b). The mobile working deck 15 is supported by two sets of lifting power cylinders and two heave compensation power cylinders.

In the illustrated arrangement, the lift cylinders 101 are connected to the floating hull 3 and two heave compensation cylinders 102, and the heave compensation cylinders 102 are connected to the lift cylinders 101 and the mobile working deck 15.

It is also conceivable that the lifting power cylinders 101 are connected to the mobile working deck 15 and the heave compensation power cylinders 102, while the heave compensation power cylinders 102 are connected to the lifting power cylinders 101 and the floating hull 3.

In combination with a compact design that can be stored in a floating hull, in particular in the deck box of a semi-submersible vessel, the connected lifting power cylinders and heave compensation power cylinders enable a large operating range for the mobile deck compensator. In fig. 9, the operating range is visible: on the right side of fig. 9, the piston 101 'of the lift cylinder 101 and the piston 102' of the heave compensation cylinder 102 are shown in an extended position. On the left side of fig. 9, both pistons are retracted and thus not visible.

In the illustrated embodiment of the vessel 1, visible in fig. 8, a riser tensioning system is provided for supporting a riser (shown in fig. 10, 12a-12 c) located in the moonpool 4 at an upper end thereof, the riser extending along a firing line between the subsea wellbore and the vessel. The riser tensioning power cylinder 110 is arranged in the deckbox structure 3 of the semi-submersible vessel. As can be seen in fig. 10, the riser tensioning cylinder 110 is connected to an expansion joint 115, which expansion joint 115 is provided at the upper end of the riser. Here, the outer part of the expansion joint is designated 115a and the inner part is designated 115 c. Between the outside and inside of the expansion joint is a ring 115b supported by the riser tensioning cylinder 110. In this way, the weight of the riser is suspended by the riser tensioning system. Possibly, the riser may be provided with a flotation device (e.g. a flotation tank) to support at least a part of the weight of the riser.

In fig. 8 it can be seen that the rotating control device 112 and the diverter 113 are suspended from the mobile working deck 15, preferably the top end of the riser, in particular the expansion joint 115c, is attached to said rotating control device 112 and the diverter 113 via a flexible joint 116 (visible in fig. 10). Also visible is a work table 114, where the work table 114 is suspended from the mobile work deck 15.

In embodiments in which the position of the mobile working deck is fixed relative to the vessel (in particular, in a lowered position of the mobile working deck), the difference in motion between the riser and the vessel can be absorbed by the expansion joints, as shown in fig. 10.

In fig. 12a-12c is shown a mobile deck compensator 18 with a lifting power cylinder 101 and a heave compensation power cylinder 102, which mobile deck compensator 18 provides a heave compensation motion of the mobile working deck 15 and to which an expansion joint is connected. In this case, an expansion joint is not generally required to absorb the difference in motion. In such an embodiment, the expansion joints may be locked, thereby fixing the position of the mobile working deck relative to the riser. Thus, the mobile deck compensator may be used to absorb motion differences between the riser and the vessel, thereby acting as a riser tensioning system.

In fig. 12a the mobile working deck has been moved out of the lowered position to the raised position by means of the lifting power cylinder 101, the piston 101' of which lifting power cylinder 101 is now visible. Heave compensation motion of the mobile working deck 15 is provided by heave compensation power cylinders 102. In fig. 12c the mobile deck 15 has been moved to a heave compensation maximum height position, where the piston 102' of the heave compensation power cylinder is fully extended, similar to the situation in the right part of fig. 9. In fig. 12b the mobile deck is in the heave compensation minimum height position and the piston 102' of the heave compensation power cylinder 102 is fully retracted.

In fig. 11 it is shown that the BOP 140 has been slid into the firing line 9 and below the mobile working deck 15 via the truck 122 on the rail 121 from a parking position (in which the BOP 140 protrudes above the deck surface 6), where in a heave compensated maximum height position the piston 102 'of the heave compensated power cylinder 102 is fully extended and the piston 101' of the lifting power cylinder 101 is fully extended.

In an embodiment, a plurality of vertically mounted mobile working deck compensator cylinders is arranged between the deck box structure and the mobile working deck, e.g. two sets of a plurality of compensator cylinders, e.g. two pairs of compensator cylinders, supporting the mobile working deck. Preferably, the mobile deck compensator cylinder is configured to provide heave compensation motion of the working deck relative to the deck box structure. In an embodiment, the first set of work deck compensator power cylinders is arranged outside of a first BOP process truck rail relative to the moonpool, and the second set of work deck compensator power cylinders is arranged outside of a second BOP process truck rail relative to the moonpool, such that a subsea BOP on the BOP process truck passes between the first set of work deck compensator power cylinders and the second set of work deck compensator power cylinders. For example, the working deck compensator rams are extendable to raise the working deck from its lowered, resting position to an elevated position to enable the subsea BOP to enter the firing line from the BOP storage below the elevated working deck. Preferably, the mobile working deck compensator cylinder is not only capable of raising and lowering the working deck, but also for heave compensation movements of the working deck (e.g. in case the riser is connected to the working deck via a locked telescopic joint).

Claims

1. A vessel for performing subsea wellbore related activities, the vessel comprising:

a hoist winch and a hoist cable connected to the hoist winch, wherein the hoist is configured to support the hoist cable along the firing line;

a travelling block supported by a hoist cable for connection to an object; and

a heave compensation system adapted to provide heave compensation for the hoisting cable, thereby providing heave compensated motion of the travelling block;

-a mobile deck compensator connected between the floating hull of the vessel and the mobile working deck, wherein the mobile deck compensator is configured to lift the mobile working deck out of the lowered position, to move the mobile working deck between a lowered position and a raised position, and to provide a heave compensation motion of the mobile working deck moving the mobile deck between a heave compensation maximum height position and a heave compensation minimum height position when the mobile working deck is lifted onto the raised position, wherein the mobile deck compensator comprises a series of:

2. A vessel according to claim 1, wherein the mobile deck compensator comprises two or more hydraulic mobile deck compensator cylinders.

3. Vessel according to claim 2, wherein the hydraulic mobile deck compensator cylinders of the mobile deck compensator are hydraulically connected to the heave compensation system of the lifting device via hydraulic lines such that the mobile working deck and the travelling block move synchronously when heave compensated.

4. A vessel according to claim 1, in which the lift cylinders are connected to the floating hull and the heave compensation cylinders, and heave compensation cylinders are connected to the lift cylinders and the mobile working deck.

5. A vessel according to claim 1, in which the lift cylinders are connected to the mobile working deck and to the heave compensation cylinders, which are connected to the lift cylinders and to the floating hull.

6. A vessel according to claim 1, wherein a single lifting power cylinder supports both heave compensation power cylinders.

7. Vessel according to claim 1, wherein the mobile deck compensator comprises a crane or a multipurpose tower comprising a heave compensated lifting device adapted to support the mobile working deck.

8. A vessel according to claim 1, wherein the mobile working deck is configured to support a tubular gripping device in the firing line, and the mobile deck compensator is operable to lower and lift the supported tubular and an object connected to the tubular along the firing line.

9. A vessel according to claim 1, wherein the vessel is a semi-submersible drilling vessel and the floating hull is embodied as a deckbox structure, the semi-submersible drilling vessel including one or more pontoons and a plurality of support columns extending upwardly from the one or more pontoons and supporting the deckbox structure thereon.

10. Vessel according to claim 1, wherein the distance between the underside of the mobile working deck and the deck surface of the vessel is at least 3 metres when the mobile working deck is supported in a heave compensated maximum height position, to enable larger objects to be moved into the firing line and below the mobile working deck.

11. A boat according to claim 2, characterized in that the power cylinder has a working line parallel to the firing line.