NL2025131B1 - Vessel for performing subsea drilling operations - Google Patents

Abstract

P34453NL00/MHR A B S T R A C T 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 5 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 10 downward direction away from the deck box structure. The mooring guide comprises line guides for guiding each ofthe mooring lines, away from the deck box structure, below the one or more pontoons and towards the anchors.

Description

P34453NL00 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 positon 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.

Itis 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 ot 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; 40 - 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 45 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 thruster 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.

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 guide 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 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.

40 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.

45 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 40 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 45 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 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. 40 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, for each of the guide 45 lines. In the embodiment shown, the line guides 198 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, 5 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 opens 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 guides. 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 four arms extending 40 between the support arms 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 45 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.

Itis 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 40 104.

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 45 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 1186 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 118 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.

40 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 45 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 form 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 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 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 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 24 124 125 26 126 27 127 28 128 29 129 130

Claims (11)

-10 - P34453NLO0/MHR CONCLUSIONS A semi-submersible drilling vessel, for performing drilling operations, said vessel comprising: - a deck-box structure, having an upper deck, a box bottom, and a moon pool centrally in the deck box structure and extending through the deck box construction; a drilling rig having a derrick arranged above the upper deck of the deck box structure and arranged to perform drilling operations along a firing line through said moon pool; - one or more pontoons, for example two parallel pontoons, provided below the deck box structure and at a distance from the deck box structure, and on either side of the moonpool; - a plurality of support columns extending upwards from the one or more pontoons and supporting the deck box construction thereon; - a positioning system, the system comprising: - a plurality of thrust producing devices mounted on said one or more pontoons remote from 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-submerisble to the seabed, the mooring installation comprising: - at least three mooring winches with associated mooring lines, for each anchoring the vessel to an anchor; a mooring ring rotatably supported via a support bearing by the deck box structure with the firing line at its center, preferably the mooring winches being supported by the mooring ring for rotation about the firing line; a mooring guide supported by the mooring ring for rotation with the mooring ring and extending from the mooring ring in a downward direction and away from the deck box structure, the mooring guide comprising line guides for guiding each of the mooring lines away from the deck box construction, under the one or more pontoons and towards the anchors. Vessel according to claim 1, the mooring guide comprising a plurality of arm-like structures, preferably arm-like truss structures, extending away from the deck box structure. 40 “11 - Vessel according to claim 1, wherein the mooring device is an annular construction, the annular construction being provided with the line guides, for instance guide plates and/or guide discs, for each of the guide lines. Vessel according to claim 3, wherein the annular mooring guide comprises an annular wall extending about the moon pool. Vessel according to claim 3, wherein the annular mooring guide is a truss construction. The semi-submerisble of any of claims 3-5, wherein the mooring system further comprises a lower support bearing for supporting a lower end of the one or more mooring guides, the lower support bearing being located below, and spaced from, the support bearing mounted in the deck box construction. A vessel according to claim 8, wherein the lower support bearing is supported by support arms mounted on the one or more pontoons and/or the plurality of support columns. Vessel according to one or more of the preceding claims, wherein the deck box construction, adjacent to the moon pool, comprises one or more wire riser tensioner equipment rooms, in which wire riser tensioner devices, for example horizontally oriented wire riser tensioner cylinders, are adapted to apply top tension to a provide a tensioner. Vessel according to one or more of the preceding claims, the deck box construction comprising, adjacent to the moon pool, an underwater BOP (Blow Out Preventer) storage chamber, e.g. on a lower deck of the deck box structure, e.g. the lower deck of the deck box structure, and preferably a set of BOP manipulation car rails are provided, e.g. skid rails, extending from the underwater BOP (Blow Out Preventer) storage chamber toward and along opposite sides of the moon pool, and wherein the vessel includes a BOP manipulation carriage which moves on said BOP manipulation carriage rails so as to permit movement of an underwater BOP (Blow Out Preventer) between the BOP storage chamber and a position aligned with the firing line. Vessel according to one or more of the preceding claims, wherein the vessel is provided with a mobile working deck which is provided in vertical projection above the moon pool, which working deck is vertically displaceable, which working deck is flush in a lower stationary rest position thereof. having at least one adjacent surface of the upper deck of the deck box structure, preferably wherein said working deck and said adjacent surface of the upper deck of the deck box structure are provided with rails adapted to move tools over said rails, for example tools provided on a sliding pallet slidable over said railway rails up and down the working deck, and wherein the working deck is adapted to be lifted relative to said stationary -12- rest position and to be moved within a range of motion including a swell compensation range, wherein, preferably, at least one of a drill string slip device (slip device), a riser spider device, and/or a diverter (diverter) is supported by the mobile working deck, wherein said drill string slip device is adapted to support a suspended drill string in a riser, the riser spider device is adapted to support a suspended riser, for example during assembly and disassembly of a riser, and wherein the diverter is arranged to divert a hydrocarbon and/or drilling mud flow from an underwater source to the vessel. A vessel according to any one of the preceding claims, wherein the derrick is constructed as a vertical mast structure erected above the top deck of the deck box structure and adjacent to one side of the moon pool, the vertical mast structure being located outside a vertical projection from the moon pool, and wherein the mast structure has a working side facing the line of fire through the moon pool, and wherein the drilling rig further comprises a hoisting device comprising at least one winch and at least one winch-driven wire, the hoisting device being adapted to support a load from said crown block structure via said at least some winch-driven wire and to manipulate said supported load into the line of fire extending along and beyond said working side of the vertical mast structure.