WO2021180868A1 - Vessel for performing subsea drilling operations - Google Patents

Vessel for performing subsea drilling operations Download PDF

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Publication number
WO2021180868A1
WO2021180868A1 PCT/EP2021/056232 EP2021056232W WO2021180868A1 WO 2021180868 A1 WO2021180868 A1 WO 2021180868A1 EP 2021056232 W EP2021056232 W EP 2021056232W WO 2021180868 A1 WO2021180868 A1 WO 2021180868A1
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WO
WIPO (PCT)
Prior art keywords
mooring
deck
box structure
vessel
guide
Prior art date
Application number
PCT/EP2021/056232
Other languages
French (fr)
Inventor
Diederick Bernardus Wijning
Willem Jan VAN DRIEL
Original Assignee
Itrec B.V.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Itrec B.V. filed Critical Itrec B.V.
Publication of WO2021180868A1 publication Critical patent/WO2021180868A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
    • B63B1/00—Hydrodynamic or hydrostatic features of hulls or of hydrofoils
    • B63B1/02—Hydrodynamic or hydrostatic features of hulls or of hydrofoils deriving lift mainly from water displacement
    • B63B1/10—Hydrodynamic or hydrostatic features of hulls or of hydrofoils deriving lift mainly from water displacement with multiple hulls
    • B63B1/107—Semi-submersibles; Small waterline area multiple hull vessels and the like, e.g. SWATH
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
    • B63B21/00—Tying-up; Shifting, towing, or pushing equipment; Anchoring
    • B63B21/50—Anchoring arrangements or methods for special vessels, e.g. for floating drilling platforms or dredgers
    • B63B21/507—Anchoring arrangements or methods for special vessels, e.g. for floating drilling platforms or dredgers with mooring turrets
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
    • B63B35/00—Vessels or similar floating structures specially adapted for specific purposes and not otherwise provided for
    • B63B35/44—Floating buildings, stores, drilling platforms, or workshops, e.g. carrying water-oil separating devices
    • B63B35/4413—Floating drilling platforms, e.g. carrying water-oil separating devices
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B7/00—Special methods or apparatus for drilling
    • E21B7/12—Underwater drilling
    • E21B7/128—Underwater drilling from floating support with independent underwater anchored guide base
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
    • B63B3/00—Hulls characterised by their structure or component parts
    • B63B3/14—Hull parts
    • B63B2003/147—Moon-pools, e.g. for offshore drilling vessels

Definitions

  • the invention relates to a drilling vessel, more in particular to a semi-submersible drilling vessel, for performing subsea drilling operations.
  • performing subsea drilling operations requires the vessel to be substantially stationary above a subsea location, e.g. a subsea bore hole. It is known to position a vessel at a fixed position using mooring lines. As an alternative, the vessel can be provided with thrusters that are configured to keep the vessel at a fixed position. The latter requires continues use of the thrusters, which in turn requires the vessel to hold a considerable volume of fuel. Also, in areas with heave currents, mooring is preferred.
  • the invention provides a semi-submersible drilling vessel according to claim 1.
  • a semi-submersible drilling vessel, for performing subsea drilling operations, according to the invention comprises:
  • a deck box structure having an upper deck, a box bottom, and a moon pool centred in the deck box structure and extending through the deck box structure;
  • one or more pontoons e.g. two parallel pontoons, arranged below the deck box structure and at a distance from the deck box structure, and on opposite sides of the moon pool;
  • mooring installation for anchoring the semi-submersible to the sea floor, the mooring installation comprising:
  • a mooring ring rotatable supported via a support bearing by the deck box structure with the firing line at its centre, wherein preferably the mooring winches are supported by the mooring ring for rotation about the firing line;
  • a mooring guide supported by the mooring ring to revolve with the mooring ring, and extending from the mooring ring in a downward direction and away from the deck box structure, wherein the mooring guide comprises line guides for guiding each of the mooring lines, away from the deck box structure, below the one or more pontoons and towards the anchors.
  • a semi-submersible is provided with a positioning system comprising a mooring installation for anchoring the vessel at a particular area, and multiple thrust producing devices for rotating the semi-submersible about the firing line, to thus optimally position the vessel relative to sea currents and or wave patterns acting on the vessel, more in particular on the pontoons and support columns of the vessel.
  • the mooring installation is provided with a revolving mooring guide that is configured to guide the mooring lines away from the deck box and radially outward below the pontoons of the vessel.
  • the revolving mooring guide extends from the mooring ring in a downward direction and away from the deck box structure, such that the line guides are spaced from the deck box structure.
  • a mooring guide has a centre line that coincides with the firing line, and comprises one or more winch supports supporting the one or more mooring winches and is at its bottom end provided with line guides for guiding the mooring lines in a radial direction outward from the mooring structure.
  • the mooring guide thus allows for revolving the vessel, and thus to orient the vessel in a direction to minimize wind and water forces on the hull, i.e. pontoons and support columns. Marine bottom drilling operations can be carried out from the vessel by operating downwardly through the mooring guide.
  • the mooring system furthermore comprises a lower support bearing for supporting a lower end of the mooring guide, wherein the lower support bearing is located below, and spaced from, the support bearing mounted in the deck box structure, and the mooring winches are mounted on the mooring ring or mooring guide, such that they rotate in lines get with the line guides supported by the mooring guide
  • mooring guide comprises multiple arm like structures, preferably arm like trusses, extending away from the deck box structure.
  • the mooring guide is an annular structure, the annular structure being provided with the line guides, for example guide ramps and/or guide sheaves, for each of the mooring lines.
  • the annular mooring guide comprises an annular wall, extending about the moon pool.
  • the annular mooring guide is a truss structure.
  • the mooring system furthermore comprises a lower support bearing for supporting a lower end of the one or more mooring guides, wherein the lower support bearing is located below, and spaced from, the support bearing mounted in the deck box structure.
  • the mooring guide is embodied as a cylindrical shaped body, comprising one or more concentric annular walls, defining an enclosed interior space comprising the moonpool.
  • the mooring lines extend through the interior space between the mooring winches and the line guides.
  • the mooring guide is embodied as a cylindrical shaped body, comprising an inner and an outer annular wall and an annular interior space between these two walls.
  • the mooring lines extend through the interior space between the mooring winches and the line guides.
  • a deck box structure having an upper deck, a box bottom, and a moon pool centred in the deck box structure and extending through the deck box structure;
  • one or more pontoons e.g. two parallel pontoons, arranged below the deck box structure and at a distance from the deck box structure, and on opposite sides of the moon pool;
  • mooring installation for anchoring the semi-submersible to the sea floor, the mooring installation comprising:
  • mooring winches with associated mooring lines, for each anchoring the vessel to an anchor;
  • a mooring ring rotatable supported via a support bearing by the deck box structure with the firing line at its centre, wherein preferably the mooring winches are supported by the mooring ring for rotation about the firing line;
  • a mooring guide having a centre line that coincides with the firing line, wherein the mooring guide is supported by the mooring ring to revolve with the mooring ring, and extending from the mooring ring in a downward direction towards a bottom end, which bottom end of the mooring guide is away from the deck box structure, wherein the mooring guide is at the bottom end provided with line guides, which line guides are spaced from the deck box structure, for guiding each of the mooring lines, away from the deck box structure, below the one or more pontoons and towards the anchors, and wherein the mooring winches are mounted on the mooring ring or mooring guide, such that the mooring winches rotate in unison with the line guides supported by the mooring guide at the bottom end thereof.
  • the mooring system furthermore comprises a lower support bearing for supporting the bottom end of the mooring guide in a lateral direction, wherein the lower support bearing is located below, and spaced from, the support bearing mounted in the deck box structure, and wherein the lower support bearing is supported by support arms mounted to the one or more pontoons and/or the multiple support columns.
  • the support arms and the lower support bearing provide the mooring guide, that extends from the mooring ring in a downward direction and away from the deck box structure, with lateral support away from the deck box.
  • the mooring guide is a partially open structure, preferably is a truss like structure.
  • Such an embodiment of the mooring guide preferably in combination with support arms and the lower support bearing, provides structural rigidity while allowing waves to pass through the moon poll area more or less unhampered.
  • the impact of those waves on the semi-submersible and on the mooring guide in particular is limited.
  • the mooring guide is supported by the mooring ring to revolve with the mooring ring.
  • the mooring winches and the line guides can be rotated about the firing line in unison, and the distance between the mooring winches and the associated line guides is constant.
  • the distance between the mooring winches and the associated line guides is constant.
  • Providing a semi-submersible with a revolving mooring guide allows for rotating the line guides, preferably in unison with the mooring winches, about the firing line. It is submitted that in use, when the semi-submersible is anchored, the semi-submersible will effectively rotate about the mooring guide, the mooring guide being more or less fixed in position by the anchors.
  • the multiple thrust producing devices of the semi-submersible enable rotating the semi-submersible about the firing line, and thus about the mooring guide, to thus optimally position the vessel relative to sea currents and or wave patterns acting on the anchored vessel, more in particular on the pontoons and support columns of the anchored vessel.
  • the invention furthermore provides a method for optimally positioning a semi-submersible according to one or more of the preceding claims relative to sea currents and or wave patterns, the method comprising: using the thrusters to rotate the semi-submersible about the mooring guide.
  • the deck box structure adjoining the moon pool, comprises one or more wireline riser tensioner equipment rooms accommodating therein wireline riser tensioner equipment, e.g. horizontally oriented wireline riser tensioner cylinders, configured to provide top tension to a riser.
  • wireline riser tensioner equipment e.g. horizontally oriented wireline riser tensioner cylinders
  • the deck box structure comprises, adjoining the moon pool, a subsea BOP (Blow Out Preventer) storage room, e.g. on a lower deck of the deck box structure, e.g. the lowermost deck of the deck box structure, and preferably wherein a set of BOP handling cart rails is provided, e.g. skid rails, extending from the subsea BOP (Blow Out Preventer) storage room towards and along opposed sides of the moon pool, and wherein vessel is provided with a BOP handling cart that is able to travel over said BOP handling cart rails so as to allow for transfer of a subsea BOP (Blow Out Preventer) between the BOP storage room and a position aligned with the firing line.
  • a subsea BOP (Blow Out Preventer) storage room e.g. on a lower deck of the deck box structure, e.g. the lowermost deck of the deck box structure
  • a set of BOP handling cart rails is provided,
  • the vessel is provided with a mobile working deck which is arranged in vertical projection above the moon pool, which working deck is vertically movable, which working deck in a lower stationary resting position thereof is flush with at least an adjoining area of the upper deck of the deckbox structure, preferably wherein said working deck and said adjoining area of the upper deck of the deckbox structure are provided with rail tracks configured to transfer equipment over said rail tracks, e.g.
  • the working deck is configured to be elevated relative to said stationary resting position and to be movable within a motion range including a heave compensation motion range, wherein, 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 said drill string slip device is configured to support a suspended drill string within a riser, wherein the riser spider device is configured to support a suspended riser, e.g. during assembly and disassembly of a riser, and wherein the diverter is configured to divert a hydrocarbon and/or drilling mud stream from a subsea wellbore to the vessel.
  • a drill string slip device is configured to support a suspended drill string within a riser
  • the riser spider device is configured to support a suspended riser, e.g. during assembly and disassembly of a riser
  • the diverter is configured to divert a hydrocarbon and/or drilling mud stream from a sub
  • the drilling tower is embodied as a vertical mast structure erected above the upper deck of the deckbox structure and adjacent a side of the moon pool, the vertical mast structure being located outside of a vertical projection of the moon pool, and wherein the mast structure has an operative face directed towards the firing line through the moon pool, and wherein the drilling installation further comprises a hoisting device comprising at least one winch and at least one winch driven cable, which hoisting device is adapted to suspend a load from said crown block structure via said at least one winch driven cable and to manipulate said suspended load in the firing line that extends along and outside of said operative face of the vertical mast structure.
  • Fig. 1 shows a cross sectional side view of a first exemplary embodiment of a semi- submersible according to the invention
  • Fig. 2 shows an alternative cross sectional side view of the semi-submersible of Fig. 1;
  • Fig. 3 shows a cross sectional top view of the semi-submersible of Fig. 1 ;
  • Fig. 4 shows a cross sectional side view of a second exemplary embodiment of a semi- submersible according to the invention.
  • the figure 1 shows a cross sectional side view of the semi-submersible 1.
  • the semi- submersible 1 comprises a structure 2, two pontoons 3, and multiple support columns 4.
  • the support columns 4 extend upward from the pontoons 3 and support thereon the deck box structure 2.
  • the deck box structure 2 has an upper deck 5 and a box bottom 6.
  • a moon pool 7 is centred in the deck box structure 2 and extends through the deck box structure 2.
  • the semi-submersible 1 is provided with two pontoons 3, which pontoons 3 are arranged below the deck box structure 2 and at a distance therefrom.
  • the pontoons 3 are provided on opposite sides of the moon pool 7, to provide the semi- submersible 1 with optimal stability.
  • semi submersibles are in particular suited for performing drilling activities due to the inherent stability of the hull design.
  • the deck is subjected to relatively little heave compared to a mono hull type vessel.
  • the heave of the deck box structure adjacent the moon pool 7 is kept minimal. This is in particular the case for heave due to waves, or wave fronts, that encounter the semi-submersible 1 at an angle to a longitudinal axis 8 of the respective pontoons 3.
  • the two pontoons may be replaced with a single, annular pontoon.
  • the annular pontoon preferably being concentric with the moon pool.
  • the pontoon extends along the perimeter of the deck box structure, and is spaced, in a lateral direction, from the moon pool located at the centre of the deck box structure. This embodiment also provides a stable deck box structure, in particular at the moon pool.
  • the semi-submersible is provided with three or more pontoons.
  • the semi-submersible can be provided with four separate pontoons, each extending along a side of the deck box structure.
  • the moon pool is spaced from the pontoons, which provides the deck box structure, in particular adjacent the moon pool, with additional stability.
  • the semi-submersible 1 is furthermore provided with a drilling installation 9, for performing subsea drilling operations, e.g. drilling a bore hole in the seafloor.
  • the drilling installation 9 comprises a drilling tower 10, erected above the upper deck 5 of the deck box structure 2, and is adapted to perform drilling operations along a firing line 11, the firing line extending through the moon pool 7.
  • the semi-submersible 1 furthermore comprises a positioning system, the positioning system comprising multiple thrust producing devices 12 and a mooring installation 13.
  • the thrust producing devices 12 are mounted to the pontoons 3 in spaced relation to the firing line 11, and arranged to produce thrust in a horizontal direction, for rotating the semi- submersible 1 about the firing line 11.
  • the mooring installation 13 comprises multiple mooring winches 14 with associated mooring lines 15, a mooring ring 16, and a mooring guide 17.
  • the mooring winches 14 and associated mooring lines 16 are configured for each anchoring the semi-submersible 1 to an anchor.
  • Fig. 3 shows multiple mooring lines extending in outward direction away from the moon pool and away from the semi-submersible 1 to anchors driven in the sea floor at locations away from the vessel.
  • the anchors are located radially outward from the semi-submersible, such that the semi-submersible is anchored in at the centre of a ring of anchors.
  • the mooring ring 16 is rotatable supported via a support bearing 18 by the deck box structure 2 with the firing line at its centre.
  • the mooring winches 15 are supported by the mooring ring 14, and are rotatable for rotation about the firing line.
  • the mooring guide 17 is supported by the mooring ring 16 to revolve with the mooring ring. Thus, the mooring guide and the mooring winches can be rotated about the firing line in unison.
  • the mooring guide 17 extends from the mooring ring 16 in a downward direction and away from the deck box structure 2.
  • the mooring guide comprises line guides 19 for guiding each of the mooring lines, away from the deck box structure, below the one or more pontoons and towards the anchors.
  • the mooring winches are mounted on the mooring ring such that they rotate in unison with the line guides supported by the mooring guide.
  • the deck box structure is provided with a lowered section, the lowered section housing the mooring ring, the bearing supporting the mooring ring, and the mooring winches mounted on the mooring ring.
  • the mooring winches may be mounted on the mooring guide, e.g. be located below the mooring ring.
  • winches are mounted on the (winches may be mounted below the bearing, i.e. below the top end of the mooring structure),
  • the mooring guide 17 is embodied as an annular structure, the annular structure being provided with twelve line guides, one for each of the mooring lines.
  • the line guides 19 are embodied as sheaves, rotatable supported by the mooring guide 17.
  • the mooring guide 17 supports the sheaves 19 below the mooring winches, and spaced form the deck box structure.
  • the mooring lines, extending between the semi-submersible and the anchors, are thus guided below the pontoons, see for example Fig.
  • the annular mooring guide 17 comprises an annular wall 20, extending about the moon pool 7.
  • the annular wall is at a top end thereof fixed to the mooring ring.
  • a lower end of the annular wall supports the sheaves for guiding the mooring lines.
  • the sheaves are pivotable mounted to the lower end of the annular wall, such that they can pivot about a substantially vertical axis. Thus, they can compensate for a change in the angle of the lines, for example due to the mooring guide being revolved about a vertical axis relative to the anchors.
  • the lower end of the mooring guide When the semi-submersible 1 is moored, the lower end of the mooring guide is located below the water surface.
  • the mooring guide forms an extension of the moon pool opening in the deck box structure, and furthermore shelters the moon pool area, and the mooring lines extending on the inside of the mooring guide, from its direct surroundings.
  • the mooring guide may be a partially open structure.
  • the Mooring guide may be a truss like structure. Such a structure provides structural rigidity, and can still be comparatively light.
  • an open structure allows for waves passing through the moon poll area, i.e. the area vertically below the moon pool opening in the deck box structure. This reduces impact of the waves on the semi-submersible and on the mooring guide in particular.
  • the mooring system furthermore comprises a lower support bearing 21.
  • the lower support bearing 21 supports the lower end of the mooring guide.
  • the lower support bearing 21 is located below, and spaced from, the support bearing 18 mounted in the deck box structure 2.
  • the lower support bearing 21 is configured to support the mooring guide 17 mainly in the lateral direction.
  • the lower support bearing 21 is supported by support arms 22 mounted to the multiple support columns.
  • a support structure, for supporting the lower end of the mooring guide, is mounted to the pontoons or to the pontoons and the support columns.
  • the mooring guide is laterally supported by a mooring support structure, wherein the mooring support structure is embodied in the form of the four support arms 22 extending between the support columns 4 and an annular support structure housing the lower mooring bearing.
  • a semi-submersible typically has a ballast system that enables the vessel to switch between a lowered floating condition and a raised floating condition.
  • the pontoons when the vessel is in the raised floating condition, the pontoons are submerged, but the mooring support structure is above water.
  • the mooring support structure When the vessel is in the lowered floating condition, the mooring support structure is submerged.
  • the vessel 1 is configured for supporting a riser in the firing line, which riser can for example be used for guiding a drill string to a subsea well bore. It is submitted that, due to the vessel being rocked by waves, a riser is typically hingeable supported. Such that angular position of the riser relative to the vessel may change due to the movement of the vessel on the waves.
  • Fig. 2 depicts two risers 24 in one figure, wherein the risers are supported at different angular positions.
  • the mooring guide has a width, in particular at a lower end of the mooring guide, that allows for the angular movement of the riser relative to the vessel.
  • the mooring guide has a similar cross section at the top end and at the lower end of the mooring guide.
  • the mooring guide may for example be conically shaped, having a relatively narrow cross section at the upper end and a relatively wide cross section at the lower end thereof.
  • the drilling installation 9 of the vessel 1 depicted in Fig 1 - Fig 3 comprises a multipurpose tower 10 set up adjacent the moon pool 7. It is noted that the drilling installation can be configured in many ways. For example, instead of a multipurpose tower, the drilling installation may comprise a derrick that bridges the moon pool. It is furthermore submitted that a semi-submersible comprising a positioning system according to the invention may also be configured as a production platform, or as a platform for performing well maintenance purposes.
  • the vessel the riser is supported by tensioners, which tensioners are supported by the deck box structure.
  • the tensioners therefore are in a fixed position relative to the deck box structure.
  • the tensioners are coupled with a top section of the riser, which top section is coupled with the riser via a riser bearing section.
  • this top section of the riser can revolve with the deck box structure about the mooring guide and the main riser section, which are both secured to the sea floor, and therefore are in a fixed position relative to the sea floor.
  • the drilling installation, or parts thereof, and/or the tensioners supporting the riser can be mounted on the mooring ring, such that they are all in a fixed position relative to the sea floor, and the such that the semi-submersible can revolve about the mooring guide and the components of the drilling installation and/or the tensioners supported by the mooring ring.
  • Fig. 4 shows a schematically cross sectional side view of the semi-submersible 101.
  • the semi- submersible 101 comprises a structure 102, four pontoons 103, and multiple support columns 104.
  • the construction of the semi-submersible, in particular the deck box structure, the pontoons and the support columns, is similar to the semi-submersible depicted in Fig. 1 - Fig 3. A difference is that in this embodiment the vessel is provided with a pontoon along each side of the rectangular deck box structure. Similar to the other exemplary embodiment, the pontoons are each at opposite ends provided with a thrust producing device 112.
  • the vessel 101 comprises a positioning system, the positioning system comprising a mooring installation 113 for anchoring the semi-submersible 101 to the sea floor, and to thus fix the semi-submersible in a position relative to the sea floor, and the multiple thrust producing devices 112, for rotating the semi-submersible about the firing line to thus optimally position the vessel relative to sea currents and or wave patterns acting on the vessel, more in particular on the pontoons and support columns of the vessel.
  • the vessel 101 depicted in Fig. 4 comprises a drilling installation 109, for performing subsea drilling operations, e.g. drilling a bore hole in the seafloor.
  • the drilling installation 109 comprises a drilling tower 110, erected above the upper deck 105 of the deck box structure 102, and is adapted to perform drilling operations along a firing line 111, the firing line extending through the moon pool 107.
  • the drilling tower 109 is embodied a derrick that bridges the moon pool.
  • the deck box structure 2 supports a support bearing 118 supporting a mooring ring 116.
  • the mooring ring 116 is rotatable supported via the support bearing 118 by the deck box structure 102 with the firing line at its centre.
  • the mooring guide comprises, four arm shaped trusses, each arm supporting two mooring winches 145 and the mooring lines 115 associated with the respective winches 145.
  • the four arm shaped trusses are supported by the mooring ring 116 to revolve with the mooring ring.
  • the mooring guide, and the mooring winches supported by the mooring guide can be rotated about the firing line in unison.
  • the mooring guide 117 extends from the mooring ring 116 in a downward direction and away from the deck box structure 102.
  • the mooring guide comprises line guides 119 for guiding each of the mooring lines, away from the deck box structure, below the one or more pontoons and towards the anchors.
  • the mooring guide 117 is supported by the mooring ring 116 to revolve with the mooring ring.
  • the mooring guide 117 and the mooring winches can revolve about the firing line in unison, and the vessel can evolve about the mooring guide.
  • the vessel more in particular the hull of the vessel can be positioned.
  • the winches are mounted below the bearing, i.e. below the top end of the mooring guide.
  • the mooring installation 113 comprises multiple mooring winches 114 with associated mooring lines 115.
  • the mooring winches 114 and associated mooring lines 116 are configured for each anchoring the semi-submersible 101 to an anchor.
  • the line guides 119 are embodied as sheaves, rotatable supported by the mooring guide 117, more in particular by the arm shaped trusses of the mooring guide.
  • the mooring guide 117 supports the sheaves 119 below the mooring winches, and spaced form the deck box structure. The mooring lines, extending between the semi-submersible and the anchors, are thus guided below the pontoons.
  • the mooring guide comprising for arm shaped trusses, provides an open structure allows for waves passing through the moon poll area, i.e. the area vertically below the moon pool opening in the deck box structure. This reduces impact of the waves on the semi-submersible and on the mooring guide in particular.
  • a mooring guide according to the invention has a centre line that coincides with the firing line, and comprises one or more winch supports supporting the one or more mooring winches and is at its bottom end provided with line guides for guiding the mooring lines in a radial direction outward from the mooring structure.
  • the mooring guide thus allows for revolving the vessel, and thus to orient the vessel in a direction to minimize wind and water forces on the hull, i.e. pontoons and support columns. Marine bottom drilling operations can be carried out from the vessel by operating downwardly through the mooring guide.
  • the well bore is located substantially vertically of below the moon pool.

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Abstract

The invention relates to a semi-submersible drilling vessel, comprising a deck box structure supported via multiple support columns on one or more pontoons, and a drilling installation. The vessel is provided with a positioning system comprising multiple thrust producing devices and a mooring installation. According to the invention, the mooring installation comprises at least three mooring winches with associated mooring lines, for each anchoring the vessel to an anchor, a mooring ring, rotatable supported via a support bearing by the deck box structure, and a mooring guide, supported by the mooring ring to revolve with the mooring ring and extending from the mooring ring in a downward direction away from the deck box structure. The mooring guide comprises line guides for guiding each of the mooring lines, away from the deck box structure, below the one or more pontoons and towards the anchors.

Description

Vessel for performing subsea drilling operations
The invention relates to a drilling vessel, more in particular to a semi-submersible drilling vessel, for performing subsea drilling operations.
It is submitted that performing subsea drilling operations requires the vessel to be substantially stationary above a subsea location, e.g. a subsea bore hole. It is known to position a vessel at a fixed position using mooring lines. As an alternative, the vessel can be provided with thrusters that are configured to keep the vessel at a fixed position. The latter requires continues use of the thrusters, which in turn requires the vessel to hold a considerable volume of fuel. Also, in areas with heave currents, mooring is preferred.
It is an object of the invention to provide an alternative mooring system for a semi-submersible, it is a further object of the invention to provide an improved mooring system for a semi- submersible.
The invention provides a semi-submersible drilling vessel according to claim 1.
A semi-submersible drilling vessel, for performing subsea drilling operations, according to the invention comprises:
- a deck box structure, having an upper deck, a box bottom, and a moon pool centred in the deck box structure and extending through the deck box structure;
- a drilling installation with a drilling tower erected above the upper deck of the deckbox structure and adapted to perform drilling operations along a firing line through said moon pool;
- one or more pontoons, e.g. two parallel pontoons, arranged below the deck box structure and at a distance from the deck box structure, and on opposite sides of the moon pool;
- multiple support columns extending upward from the one or more pontoons and supporting thereon the deck box structure; - a positioning system, the system comprising:
- multiple thrust producing devices, mounted to said one or more pontoons in spaced relation to the firing line and arranged to produce thrust in a horizontal direction, for rotating the semi-submersible about the firing line;
- a mooring installation for anchoring the semi-submersible to the sea floor, the mooring installation comprising:
- at least three mooring winches with associated mooring lines, for each anchoring the vessel to an anchor;
- a mooring ring, rotatable supported via a support bearing by the deck box structure with the firing line at its centre, wherein preferably the mooring winches are supported by the mooring ring for rotation about the firing line;
- a mooring guide, supported by the mooring ring to revolve with the mooring ring, and extending from the mooring ring in a downward direction and away from the deck box structure, wherein the mooring guide comprises line guides for guiding each of the mooring lines, away from the deck box structure, below the one or more pontoons and towards the anchors.
Thus, according to the invention, a semi-submersible is provided with a positioning system comprising a mooring installation for anchoring the vessel at a particular area, and multiple thrust producing devices for rotating the semi-submersible about the firing line, to thus optimally position the vessel relative to sea currents and or wave patterns acting on the vessel, more in particular on the pontoons and support columns of the vessel. The mooring installation is provided with a revolving mooring guide that is configured to guide the mooring lines away from the deck box and radially outward below the pontoons of the vessel.
The revolving mooring guide extends from the mooring ring in a downward direction and away from the deck box structure, such that the line guides are spaced from the deck box structure.
In an embodiment, a mooring guide according to the invention has a centre line that coincides with the firing line, and comprises one or more winch supports supporting the one or more mooring winches and is at its bottom end provided with line guides for guiding the mooring lines in a radial direction outward from the mooring structure. The mooring guide thus allows for revolving the vessel, and thus to orient the vessel in a direction to minimize wind and water forces on the hull, i.e. pontoons and support columns. Marine bottom drilling operations can be carried out from the vessel by operating downwardly through the mooring guide.
In an embodiment, the mooring system furthermore comprises a lower support bearing for supporting a lower end of the mooring guide, wherein the lower support bearing is located below, and spaced from, the support bearing mounted in the deck box structure, and the mooring winches are mounted on the mooring ring or mooring guide, such that they rotate in lines get with the line guides supported by the mooring guide
In an exemplary embodiment of a vessel according to the invention, mooring guide comprises multiple arm like structures, preferably arm like trusses, extending away from the deck box structure.
In an alternative exemplary embodiment of a vessel according to the invention, the mooring guide is an annular structure, the annular structure being provided with the line guides, for example guide ramps and/or guide sheaves, for each of the mooring lines.
In a further exemplary embodiment of a vessel according to the invention, the annular mooring guide comprises an annular wall, extending about the moon pool.
In an alternative further exemplary embodiment of a vessel according to the invention, the annular mooring guide is a truss structure.
In an exemplary embodiment of a vessel according to the invention, the mooring system furthermore comprises a lower support bearing for supporting a lower end of the one or more mooring guides, wherein the lower support bearing is located below, and spaced from, the support bearing mounted in the deck box structure.
In a further exemplary embodiment of a vessel according to the invention, wherein the lower support bearing is supported by support arms mounted to the one or more pontoons and/or the multiple support columns. In an embodiment, the mooring guide is embodied as a cylindrical shaped body, comprising one or more concentric annular walls, defining an enclosed interior space comprising the moonpool. In a further embodiment, the mooring lines extend through the interior space between the mooring winches and the line guides.
In an embodiment, the mooring guide is embodied as a cylindrical shaped body, comprising an inner and an outer annular wall and an annular interior space between these two walls. In a further embodiment, the mooring lines extend through the interior space between the mooring winches and the line guides.
In an embodiment, a semi-submersible drilling vessel, for performing subsea drilling operations, according to the invention comprises:
- a deck box structure, having an upper deck, a box bottom, and a moon pool centred in the deck box structure and extending through the deck box structure;
- a drilling installation with a drilling tower erected above the upper deck of the deckbox structure and adapted to perform drilling operations along a firing line through said moon pool;
- one or more pontoons, e.g. two parallel pontoons, arranged below the deck box structure and at a distance from the deck box structure, and on opposite sides of the moon pool;
- multiple support columns extending upward from the one or more pontoons and supporting thereon the deck box structure;
- a positioning system, the system comprising:
- multiple thrust producing devices, mounted to said one or more pontoons in spaced relation to the firing line and arranged to produce thrust in a horizontal direction, for rotating the semi-submersible about the firing line;
- a mooring installation for anchoring the semi-submersible to the sea floor, the mooring installation comprising:
- at least three mooring winches with associated mooring lines, for each anchoring the vessel to an anchor; - a mooring ring, rotatable supported via a support bearing by the deck box structure with the firing line at its centre, wherein preferably the mooring winches are supported by the mooring ring for rotation about the firing line;
- a mooring guide, having a centre line that coincides with the firing line, wherein the mooring guide is supported by the mooring ring to revolve with the mooring ring, and extending from the mooring ring in a downward direction towards a bottom end, which bottom end of the mooring guide is away from the deck box structure, wherein the mooring guide is at the bottom end provided with line guides, which line guides are spaced from the deck box structure, for guiding each of the mooring lines, away from the deck box structure, below the one or more pontoons and towards the anchors, and wherein the mooring winches are mounted on the mooring ring or mooring guide, such that the mooring winches rotate in unison with the line guides supported by the mooring guide at the bottom end thereof.
In a further embodiment, the mooring system furthermore comprises a lower support bearing for supporting the bottom end of the mooring guide in a lateral direction, wherein the lower support bearing is located below, and spaced from, the support bearing mounted in the deck box structure, and wherein the lower support bearing is supported by support arms mounted to the one or more pontoons and/or the multiple support columns.
The support arms and the lower support bearing provide the mooring guide, that extends from the mooring ring in a downward direction and away from the deck box structure, with lateral support away from the deck box.
It is submitted that providing support arms to support the lower support bearing in the lateral direction provides an open support structure and therefore does not cause an unwanted increase of the impact of waves on the semi-submersible.
In a further embodiment, the mooring guide is a partially open structure, preferably is a truss like structure. Such an embodiment of the mooring guide, preferably in combination with support arms and the lower support bearing, provides structural rigidity while allowing waves to pass through the moon poll area more or less unhampered. Thus, the impact of those waves on the semi-submersible and on the mooring guide in particular is limited.
The mooring guide is supported by the mooring ring to revolve with the mooring ring. Thus, by providing the mooring winches on the mooring ring or the mooring guide, the mooring winches and the line guides can be rotated about the firing line in unison, and the distance between the mooring winches and the associated line guides is constant. Thus there is no risk of the mooring lines getting subjected to peak loads due to the distance between the mooring winches and the line guides changing when the mooring guide is rotated.
Providing a semi-submersible with a revolving mooring guide allows for rotating the line guides, preferably in unison with the mooring winches, about the firing line. It is submitted that in use, when the semi-submersible is anchored, the semi-submersible will effectively rotate about the mooring guide, the mooring guide being more or less fixed in position by the anchors. The multiple thrust producing devices of the semi-submersible enable rotating the semi-submersible about the firing line, and thus about the mooring guide, to thus optimally position the vessel relative to sea currents and or wave patterns acting on the anchored vessel, more in particular on the pontoons and support columns of the anchored vessel.
The invention furthermore provides a method for optimally positioning a semi-submersible according to one or more of the preceding claims relative to sea currents and or wave patterns, the method comprising: using the thrusters to rotate the semi-submersible about the mooring guide.
In an embodiment, the deck box structure, adjoining the moon pool, comprises one or more wireline riser tensioner equipment rooms accommodating therein wireline riser tensioner equipment, e.g. horizontally oriented wireline riser tensioner cylinders, configured to provide top tension to a riser.
In an embodiment, the deck box structure comprises, adjoining the moon pool, a subsea BOP (Blow Out Preventer) storage room, e.g. on a lower deck of the deck box structure, e.g. the lowermost deck of the deck box structure, and preferably wherein a set of BOP handling cart rails is provided, e.g. skid rails, extending from the subsea BOP (Blow Out Preventer) storage room towards and along opposed sides of the moon pool, and wherein vessel is provided with a BOP handling cart that is able to travel over said BOP handling cart rails so as to allow for transfer of a subsea BOP (Blow Out Preventer) between the BOP storage room and a position aligned with the firing line.
In an embodiment, the vessel is provided with a mobile working deck which is arranged in vertical projection above the moon pool, which working deck is vertically movable, which working deck in a lower stationary resting position thereof is flush with at least an adjoining area of the upper deck of the deckbox structure, preferably wherein said working deck and said adjoining area of the upper deck of the deckbox structure are provided with rail tracks configured to transfer equipment over said rail tracks, e.g. equipment arranged on a skid pallet skiddable over said rail tracks, onto and off the working deck, and wherein the working deck is configured to be elevated relative to said stationary resting position and to be movable within a motion range including a heave compensation motion range, wherein, 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 said drill string slip device is configured to support a suspended drill string within a riser, wherein the riser spider device is configured to support a suspended riser, e.g. during assembly and disassembly of a riser, and wherein the diverter is configured to divert a hydrocarbon and/or drilling mud stream from a subsea wellbore to the vessel.
In an embodiment, the drilling tower is embodied as a vertical mast structure erected above the upper deck of the deckbox structure and adjacent a side of the moon pool, the vertical mast structure being located outside of a vertical projection of the moon pool, and wherein the mast structure has an operative face directed towards the firing line through the moon pool, and wherein the drilling installation further comprises a hoisting device comprising at least one winch and at least one winch driven cable, which hoisting device is adapted to suspend a load from said crown block structure via said at least one winch driven cable and to manipulate said suspended load in the firing line that extends along and outside of said operative face of the vertical mast structure.
Whilst primarily presented for illustrative purposes with reference to one or more of the figures, any of the technical features addressed below may be combined with any of the independent claims of this application either alone or in any other technically possible combination with one or more other technical features. Advantageous embodiments of the semi-submersible according to the invention and the method according to the invention are disclosed in the sub claims and in the description, in which the invention is further illustrated and elucidated on the basis of a number of exemplary embodiments, of which some are shown in the schematic drawing. In the figures, components corresponding in terms or construction and/or function are provided with the same last two digits of the reference numbers.
The invention will now be discussed with reference to the drawings. In the drawings:
Fig. 1 shows a cross sectional side view of a first exemplary embodiment of a semi- submersible according to the invention;
Fig. 2 shows an alternative cross sectional side view of the semi-submersible of Fig. 1;
Fig. 3 shows a cross sectional top view of the semi-submersible of Fig. 1 ; and
Fig. 4 shows a cross sectional side view of a second exemplary embodiment of a semi- submersible according to the invention.
With reference to figures 1 - 3 a preferred embodiment of a semi-submersible 1 for performing subsea drilling operations will be discussed.
The figure 1 shows a cross sectional side view of the semi-submersible 1. The semi- submersible 1 comprises a structure 2, two pontoons 3, and multiple support columns 4.
The support columns 4 extend upward from the pontoons 3 and support thereon the deck box structure 2.
The deck box structure 2 has an upper deck 5 and a box bottom 6. A moon pool 7 is centred in the deck box structure 2 and extends through the deck box structure 2.
In the embodiment shown in Fig. 1, the semi-submersible 1 is provided with two pontoons 3, which pontoons 3 are arranged below the deck box structure 2 and at a distance therefrom. The pontoons 3 are provided on opposite sides of the moon pool 7, to provide the semi- submersible 1 with optimal stability.
It is noted that semi submersibles are in particular suited for performing drilling activities due to the inherent stability of the hull design. Thus, the deck is subjected to relatively little heave compared to a mono hull type vessel. By positioning the moon pool 7, when seen in a top view, between the pontoons 3, the heave of the deck box structure adjacent the moon pool 7 is kept minimal. This is in particular the case for heave due to waves, or wave fronts, that encounter the semi-submersible 1 at an angle to a longitudinal axis 8 of the respective pontoons 3.
In an alternative embodiment, the two pontoons may be replaced with a single, annular pontoon. The annular pontoon preferably being concentric with the moon pool. In such an embodiment, the pontoon extends along the perimeter of the deck box structure, and is spaced, in a lateral direction, from the moon pool located at the centre of the deck box structure. This embodiment also provides a stable deck box structure, in particular at the moon pool.
In yet another embodiment, the semi-submersible is provided with three or more pontoons. For example, the semi-submersible can be provided with four separate pontoons, each extending along a side of the deck box structure. Also in such an embodiment, the moon pool is spaced from the pontoons, which provides the deck box structure, in particular adjacent the moon pool, with additional stability.
The semi-submersible 1 is furthermore provided with a drilling installation 9, for performing subsea drilling operations, e.g. drilling a bore hole in the seafloor. The drilling installation 9 comprises a drilling tower 10, erected above the upper deck 5 of the deck box structure 2, and is adapted to perform drilling operations along a firing line 11, the firing line extending through the moon pool 7.
According to the invention, the semi-submersible 1 furthermore comprises a positioning system, the positioning system comprising multiple thrust producing devices 12 and a mooring installation 13.
The thrust producing devices 12, are mounted to the pontoons 3 in spaced relation to the firing line 11, and arranged to produce thrust in a horizontal direction, for rotating the semi- submersible 1 about the firing line 11.
The mooring installation 13 comprises multiple mooring winches 14 with associated mooring lines 15, a mooring ring 16, and a mooring guide 17. The mooring winches 14 and associated mooring lines 16 are configured for each anchoring the semi-submersible 1 to an anchor. Fig. 3 shows multiple mooring lines extending in outward direction away from the moon pool and away from the semi-submersible 1 to anchors driven in the sea floor at locations away from the vessel. The anchors are located radially outward from the semi-submersible, such that the semi-submersible is anchored in at the centre of a ring of anchors.
The mooring ring 16 is rotatable supported via a support bearing 18 by the deck box structure 2 with the firing line at its centre. The mooring winches 15 are supported by the mooring ring 14, and are rotatable for rotation about the firing line.
The mooring guide 17 is supported by the mooring ring 16 to revolve with the mooring ring. Thus, the mooring guide and the mooring winches can be rotated about the firing line in unison. The mooring guide 17 extends from the mooring ring 16 in a downward direction and away from the deck box structure 2. The mooring guide comprises line guides 19 for guiding each of the mooring lines, away from the deck box structure, below the one or more pontoons and towards the anchors.
The mooring winches are mounted on the mooring ring such that they rotate in unison with the line guides supported by the mooring guide. In the embodiment shown, the deck box structure is provided with a lowered section, the lowered section housing the mooring ring, the bearing supporting the mooring ring, and the mooring winches mounted on the mooring ring. In an alternative embodiment, the mooring winches may be mounted on the mooring guide, e.g. be located below the mooring ring.
It is submitted that the winches are mounted on the (winches may be mounted below the bearing, i.e. below the top end of the mooring structure),
In the embodiment shown in Fig. 1 - Fig. 3, the mooring guide 17 is embodied as an annular structure, the annular structure being provided with twelve line guides, one for each of the mooring lines.
In the embodiment shown, the line guides 19 are embodied as sheaves, rotatable supported by the mooring guide 17. The mooring guide 17 supports the sheaves 19 below the mooring winches, and spaced form the deck box structure. The mooring lines, extending between the semi-submersible and the anchors, are thus guided below the pontoons, see for example Fig.
1.
In the embodiment shown, the annular mooring guide 17 comprises an annular wall 20, extending about the moon pool 7. The annular wall is at a top end thereof fixed to the mooring ring. A lower end of the annular wall supports the sheaves for guiding the mooring lines. In the preferred embodiment shown, the sheaves are pivotable mounted to the lower end of the annular wall, such that they can pivot about a substantially vertical axis. Thus, they can compensate for a change in the angle of the lines, for example due to the mooring guide being revolved about a vertical axis relative to the anchors.
When the semi-submersible 1 is moored, the lower end of the mooring guide is located below the water surface. In this embodiment, the mooring guide forms an extension of the moon pool opening in the deck box structure, and furthermore shelters the moon pool area, and the mooring lines extending on the inside of the mooring guide, from its direct surroundings.
In an alternative embodiment, the mooring guide may be a partially open structure. In an embodiment, the Mooring guide may be a truss like structure. Such a structure provides structural rigidity, and can still be comparatively light. Furthermore, an open structure allows for waves passing through the moon poll area, i.e. the area vertically below the moon pool opening in the deck box structure. This reduces impact of the waves on the semi-submersible and on the mooring guide in particular.
In the exemplary embodiment shown in Fig. 1 - Fig. 3, the mooring system furthermore comprises a lower support bearing 21. The lower support bearing 21 supports the lower end of the mooring guide. The lower support bearing 21 is located below, and spaced from, the support bearing 18 mounted in the deck box structure 2.
In the embodiment shown, the lower support bearing 21 is configured to support the mooring guide 17 mainly in the lateral direction.
The lower support bearing 21 is supported by support arms 22 mounted to the multiple support columns. In an alternative embodiment, a support structure, for supporting the lower end of the mooring guide, is mounted to the pontoons or to the pontoons and the support columns.
In the embodiment shown the mooring guide is laterally supported by a mooring support structure, wherein the mooring support structure is embodied in the form of the four support arms 22 extending between the support columns 4 and an annular support structure housing the lower mooring bearing.
It is submitted that a semi-submersible typically has a ballast system that enables the vessel to switch between a lowered floating condition and a raised floating condition. In the embodiment shown, when the vessel is in the raised floating condition, the pontoons are submerged, but the mooring support structure is above water. When the vessel is in the lowered floating condition, the mooring support structure is submerged. By designing the mooring support structure such that its fully above water when the vessel is in the raised floating condition allows for easy access to the mooring guide support structure, for example for visual inspection, for maintenance, etc.
The vessel 1 is configured for supporting a riser in the firing line, which riser can for example be used for guiding a drill string to a subsea well bore. It is submitted that, due to the vessel being rocked by waves, a riser is typically hingeable supported. Such that angular position of the riser relative to the vessel may change due to the movement of the vessel on the waves.
Fig. 2 depicts two risers 24 in one figure, wherein the risers are supported at different angular positions. It is noted that the mooring guide has a width, in particular at a lower end of the mooring guide, that allows for the angular movement of the riser relative to the vessel. In the particular embodiment shown, the mooring guide has a similar cross section at the top end and at the lower end of the mooring guide. In an alternative embodiment, the mooring guide may for example be conically shaped, having a relatively narrow cross section at the upper end and a relatively wide cross section at the lower end thereof.
The drilling installation 9 of the vessel 1 depicted in Fig 1 - Fig 3 comprises a multipurpose tower 10 set up adjacent the moon pool 7. It is noted that the drilling installation can be configured in many ways. For example, instead of a multipurpose tower, the drilling installation may comprise a derrick that bridges the moon pool. It is furthermore submitted that a semi-submersible comprising a positioning system according to the invention may also be configured as a production platform, or as a platform for performing well maintenance purposes.
In the exemplary embodiment shown in Fig. 1 - Fig. 3, the vessel the riser is supported by tensioners, which tensioners are supported by the deck box structure. The tensioners therefore are in a fixed position relative to the deck box structure. The tensioners are coupled with a top section of the riser, which top section is coupled with the riser via a riser bearing section. Thus, this top section of the riser can revolve with the deck box structure about the mooring guide and the main riser section, which are both secured to the sea floor, and therefore are in a fixed position relative to the sea floor.
It is submitted that in an alternative embodiment, the drilling installation, or parts thereof, and/or the tensioners supporting the riser can be mounted on the mooring ring, such that they are all in a fixed position relative to the sea floor, and the such that the semi-submersible can revolve about the mooring guide and the components of the drilling installation and/or the tensioners supported by the mooring ring.
Fig. 4 shows a schematically cross sectional side view of the semi-submersible 101. The semi- submersible 101 comprises a structure 102, four pontoons 103, and multiple support columns 104.
The construction of the semi-submersible, in particular the deck box structure, the pontoons and the support columns, is similar to the semi-submersible depicted in Fig. 1 - Fig 3. A difference is that in this embodiment the vessel is provided with a pontoon along each side of the rectangular deck box structure. Similar to the other exemplary embodiment, the pontoons are each at opposite ends provided with a thrust producing device 112.
According to the invention, the vessel 101 comprises a positioning system, the positioning system comprising a mooring installation 113 for anchoring the semi-submersible 101 to the sea floor, and to thus fix the semi-submersible in a position relative to the sea floor, and the multiple thrust producing devices 112, for rotating the semi-submersible about the firing line to thus optimally position the vessel relative to sea currents and or wave patterns acting on the vessel, more in particular on the pontoons and support columns of the vessel. The vessel 101 depicted in Fig. 4 comprises a drilling installation 109, for performing subsea drilling operations, e.g. drilling a bore hole in the seafloor. The drilling installation 109 comprises a drilling tower 110, erected above the upper deck 105 of the deck box structure 102, and is adapted to perform drilling operations along a firing line 111, the firing line extending through the moon pool 107. In the embodiment shown, the drilling tower 109 is embodied a derrick that bridges the moon pool.
Furthermore, in the embodiment shown, the deck box structure 2 supports a support bearing 118 supporting a mooring ring 116. Thus, the mooring ring 116 is rotatable supported via the support bearing 118 by the deck box structure 102 with the firing line at its centre.
The mooring guide comprises, four arm shaped trusses, each arm supporting two mooring winches 145 and the mooring lines 115 associated with the respective winches 145.
The four arm shaped trusses are supported by the mooring ring 116 to revolve with the mooring ring. Thus, the mooring guide, and the mooring winches supported by the mooring guide, can be rotated about the firing line in unison.
The mooring guide 117, more in particular the four arms of the mooring guide, extends from the mooring ring 116 in a downward direction and away from the deck box structure 102. The mooring guide comprises line guides 119 for guiding each of the mooring lines, away from the deck box structure, below the one or more pontoons and towards the anchors.
The mooring guide 117 is supported by the mooring ring 116 to revolve with the mooring ring. Thus, the mooring guide 117 and the mooring winches can revolve about the firing line in unison, and the vessel can evolve about the mooring guide. Thus, the vessel, more in particular the hull of the vessel can be positioned.
In the embodiment shown in Fig. 4, the winches are mounted below the bearing, i.e. below the top end of the mooring guide.
The mooring installation 113 comprises multiple mooring winches 114 with associated mooring lines 115. The mooring winches 114 and associated mooring lines 116 are configured for each anchoring the semi-submersible 101 to an anchor. In the embodiment shown, the line guides 119 are embodied as sheaves, rotatable supported by the mooring guide 117, more in particular by the arm shaped trusses of the mooring guide. The mooring guide 117 supports the sheaves 119 below the mooring winches, and spaced form the deck box structure. The mooring lines, extending between the semi-submersible and the anchors, are thus guided below the pontoons.
When the semi-submersible 101 is moored, and the vessel is in a lower floating position, the lower end of the mooring guide are located below the water surface. The mooring guide, comprising for arm shaped trusses, provides an open structure allows for waves passing through the moon poll area, i.e. the area vertically below the moon pool opening in the deck box structure. This reduces impact of the waves on the semi-submersible and on the mooring guide in particular.
A mooring guide according to the invention has a centre line that coincides with the firing line, and comprises one or more winch supports supporting the one or more mooring winches and is at its bottom end provided with line guides for guiding the mooring lines in a radial direction outward from the mooring structure.
The mooring guide thus allows for revolving the vessel, and thus to orient the vessel in a direction to minimize wind and water forces on the hull, i.e. pontoons and support columns. Marine bottom drilling operations can be carried out from the vessel by operating downwardly through the mooring guide.
When performing drilling operations, the well bore is located substantially vertically of below the moon pool.
Reference signs
01 semi-submersible 101 semi-submersible 02 deck box structure 102 deck box structure 03 pontoon 103 pontoon 04 support column 104 support column 05 upper deck 105 upper deck 06 box bottom 106 box bottom 07 moon pool 107 moon pool
08 longitudinal axis pontoons 108 longitudinal axis pontoons 09 drilling installation 109 drilling installation
10 drilling tower 110 drilling tower
11 firing line 111 firing line
12 thrust producing devices 112 thrust producing devices
13 mooring installation 113 mooring installation
14 mooring winches 114 mooring winches
15 mooring line 115 mooring line
16 mooring ring 116 mooring ring
17 mooring guide 117 mooring guide
18 support bearings mooring ring 118 support bearings mooring ring
19 line guides 119 line guides
20 annular wall mooring guide 120 annular wall mooring guide
21 lower mooring bearing 121 lower mooring bearing
22 support arms 122 support arms
23 riser 123 riser

Claims

C L A I M S
1. Semi-submersible drilling vessel, for performing subsea drilling operations, said vessel comprising:
- a deck box structure, having an upper deck, a box bottom, and a moon pool centred in the deck box structure and extending through the deck box structure;
- a drilling installation with a drilling tower erected above the upper deck of the deckbox structure and adapted to perform drilling operations along a firing line through said moon pool;
- one or more pontoons, e.g. two parallel pontoons, arranged below the deck box structure and at a distance from the deck box structure, and on opposite sides of the moon pool;
- multiple support columns extending upward from the one or more pontoons and supporting thereon the deck box structure;
- a positioning system, the system comprising:
- multiple thrust producing devices, mounted to said one or more pontoons in spaced relation to the firing line and arranged to produce thrust in a horizontal direction, for rotating the semi-submersible about the firing line;
- a mooring installation for anchoring the semi-submersible to the sea floor, the mooring installation comprising:
- at least three mooring winches with associated mooring lines, for each anchoring the vessel to an anchor;
- a mooring ring, rotatable supported via a support bearing by the deck box structure with the firing line at its centre, wherein preferably the mooring winches are supported by the mooring ring for rotation about the firing line;
- a mooring guide, supported by the mooring ring to revolve with the mooring ring, and extending from the mooring ring in a downward direction and away from the deck box structure, wherein the mooring guide comprises line guides for guiding each of the mooring lines, away from the deck box structure, below the one or more pontoons and towards the anchors.
2. Vessel according to claim 1, wherein the mooring guide comprises multiple arm like structures, preferably arm like trusses, extending away from the deck box structure.
3. Vessel according to claim 1, wherein the mooring guide is an annular structure, the annular structure being provided with the line guides, for example guide ramps and/or guide sheaves, for each of the mooring lines.
4. Vessel according to claim 3, wherein the annular mooring guide comprises an annular wall, extending about the moon pool.
5. Vessel according to claim 3, wherein the annular mooring guide is a truss structure.
6. Vessel according to one or more of the claims 3-5, wherein the mooring system furthermore comprises a lower support bearing for supporting a lower end of the one or more mooring guides, wherein the lower support bearing is located below, and spaced from, the support bearing mounted in the deck box structure.
7. Vessel according to claim 6, herein the lower support bearing is supported by support arms mounted to the one or more pontoons and/or the multiple support columns.
8. Vessel according to one or more of the preceding claims, wherein the deck box structure, adjoining the moon pool, comprises one or more wireline riser tensioner equipment rooms accommodating therein wireline riser tensioner equipment, e.g. horizontally oriented wireline riser tensioner cylinders, configured to provide top tension to a riser.
9. Vessel according to one or more of the preceding claims, wherein the deck box structure comprises, adjoining the moon pool, a subsea BOP (Blow Out Preventer) storage room, e.g. on a lower deck of the deck box structure, e.g. the lowermost deck of the deck box structure, and preferably wherein a set of BOP handling cart rails is provided, e.g. skid rails, extending from the subsea BOP (Blow Out Preventer) storage room towards and along opposed sides of the moon pool, and wherein vessel is provided with a BOP handling cart that is able to travel over said BOP handling cart rails so as to allow for transfer of a subsea BOP (Blow Out Preventer) between the BOP storage room and a position aligned with the firing line.
10. Vessel according to one or more of the preceding claims, wherein the vessel is provided with a mobile working deck which is arranged in vertical projection above the moon pool, which working deck is vertically movable, which working deck in a lower stationary resting position thereof is flush with at least an adjoining area of the upper deck of the deckbox structure, preferably wherein said working deck and said adjoining area of the upper deck of the deckbox structure are provided with rail tracks configured to transfer equipment over said rail tracks, e.g. equipment arranged on a skid pallet skiddable over said rail tracks, onto and off the working deck, and wherein the working deck is configured to be elevated relative to said stationary resting position and to be movable within a motion range including a heave compensation motion range, wherein, 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 said drill string slip device is configured to support a suspended drill string within a riser, wherein the riser spider device is configured to support a suspended riser, e.g. during assembly and disassembly of a riser, and wherein the diverter is configured to divert a hydrocarbon and/or drilling mud stream from a subsea wellbore to the vessel.
11. Vessel according to one or more of the preceding claims, wherein the drilling tower is embodied as a vertical mast structure erected above the upper deck of the deckbox structure and adjacent a side of the moon pool, the vertical mast structure being located outside of a vertical projection of the moon pool, and wherein the mast structure has an operative face directed towards the firing line through the moon pool, and wherein the drilling installation further comprises a hoisting device comprising at least one winch and at least one winch driven cable, which hoisting device is adapted to suspend a load from said crown block structure via said at least one winch driven cable and to manipulate said suspended load in the firing line that extends along and outside of said operative face of the vertical mast structure.
PCT/EP2021/056232 2020-03-13 2021-03-11 Vessel for performing subsea drilling operations WO2021180868A1 (en)

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WO1988008806A1 (en) * 1987-05-04 1988-11-17 Eb Subsea Arrangements for production, storing and transferring of hydrocarbon at sea
WO2002087962A1 (en) * 2001-04-27 2002-11-07 National Oilwell Norway As Disconnectable riser tensioning buoy
KR20130131545A (en) * 2012-05-24 2013-12-04 삼성중공업 주식회사 Floating marine structure
WO2019160420A1 (en) * 2018-02-19 2019-08-22 Itrec B.V. Semi-submersible drilling vessel, e.g. for use in a harsh environment

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NL7410311A (en) * 1974-07-31 1976-02-03 Ir Jacob Johannes Stenger Twin-hull drilling vessel has central opening for anchor cables - depending from winches on turntable and rotatable cable guide ring in lower bottom
WO1988008806A1 (en) * 1987-05-04 1988-11-17 Eb Subsea Arrangements for production, storing and transferring of hydrocarbon at sea
WO2002087962A1 (en) * 2001-04-27 2002-11-07 National Oilwell Norway As Disconnectable riser tensioning buoy
KR20130131545A (en) * 2012-05-24 2013-12-04 삼성중공업 주식회사 Floating marine structure
WO2019160420A1 (en) * 2018-02-19 2019-08-22 Itrec B.V. Semi-submersible drilling vessel, e.g. for use in a harsh environment

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114030562A (en) * 2021-11-30 2022-02-11 中国船舶科学研究中心 Large fishery platform mooring device capable of realizing floating and submerging switching and using method thereof

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