TECHNICAL FIELD

The present invention relates to a subsea equipment operations arrangement for an offshore platform or vessel for the oil and gas industry.

BACKGROUND

Extracting hydrocarbons from the earth is a complicated and sometimes dangerous endeavour. A well is drilled in the ground or the seabed from a drilling structure located at or above the surface. The drilling structure must be capable of allowing workers access to work on equipment such as e.g. replacing or serving the drill bit, assembling or disassembling drill pipe, whilst also allow for machinery to be located in the vicinity for driving the drilling process. Additionally, the drilling structure must allow the lowering of heavy equipment to the well, such as a valve assembly ("X-mas tree") for controlling production at the well or a blowout preventer (BOP) for e.g. closing the well during drilling operations. In offshore drilling the drilling structure is located on an offshore platform (e.g. a semi-submersible platform) or vessel (e.g. drillship).

Similar handling and lifting of heavy equipment is carried out also at offshore platforms or vessels other than drilling platforms, such as intervention or workover platforms. There may, for instance, be requirements for re-entering a well for intervention and/or workover of the well, which typically includes replacement of production tubing, X-mas tree, etc.

Such heavy equipment can weigh several hundreds of metric tonnes and are therefore difficult to move about the deck of the offshore platform or vessel. The size and weight of the equipment, compounded with the often harsh climate aboard offshore platforms or vessels, especially if these are located out in the open sea with harsh winds, large waves and rainfall, means that handling and preparing such heavy equipment can be a hazardous activity. This is particularly true if the equipment is lifted/hoisted which requires large lifting forces and may cause crushing injuries during accidents due to swinging of the hanging equipment. SE 531 718 C2 discloses a method for handling a blow-out preventer on a drilling platform equipped with a removable rotary table. The rotary table is lifted from the rotary table opening in the drilling deck. A spider is arranged on top of a blow-out preventer using a derrick arranged above the rotary table opening, The blow-out preventer is then positioned above said opening, and lowered through the rotary table opening using the derrick so that the spider is positioned in the rotary table opening and arranged to support drill riser pipes. The blow-out preventer can subsequently be further lowered towards the well. The blow-out preventer (and spider and rotary table) can be transported into position on a trolley, sledge or other means, along tracks into position. US3498375 discloses a smaller and older type of oil well derrick substructure where, after removal of a rotary table support, the BOP can be transported to and from a position under the derrick by means of a dolly supported by a pair of rails.

While the solutions described above may have provided advantages over previous techniques, there is still room for improvements with regard to work efficiency and safety. SUMMARY OF THE INVENTION

An object of the present invention is to provide an improved subsea equipment operations arrangement for at least partly remedying the issues described above. Another object of the present invention is to provide an offshore (semi-submersible) platform, vessel or drillship equipped with an improved subsea equipment operations arrangement. An object of the present invention is achieved by a subsea equipment operations arrangement for an offshore platform or vessel according to claim 1. The subsea equipment operations arrangement comprises: a working deck provided with an opening configured to allow passage of subsea operation equipment, such as drilling tubulars, including drill pipes, or a X-mas tree or a blowout preventer (BOP), to a position below the working deck, e.g. either to a support deck or to the sea-bed; a lifting structure configured to lift and handle heavy subsea operation equipment, said lifting structure being positioned above said opening such as to be capable of lifting and lowering the heavy equipment through the opening; and a system for transporting the heavy equipment laterally over the working deck to and from the opening, said system comprising a rail structure arranged on the working deck for supporting and guiding a movable carrier configured to carry the heavy equipment.

The subsea equipment operations arrangement is characterised in that the opening extends in a lateral direction from a lifting position below the lifting structure to a point aside of the lifting position of the lifting structure, wherein a first deck section is movably arranged in the opening. The first movable deck section is arranged to cover only a portion of the opening and to be movable along the opening between at least a first position, the lifting position below the lifting structure, and a second position, aside of the lifting position of the lifting structure. The first movable deck section is provided with a rail member configured to, at least when the first movable deck section is in its first position, be operationally aligned with and thereby form part of the rail structure of the working deck.

The subsea equipment operations arrangement according to the invention allows the moveable carrier to move along the rails between a point of the working deck laterally spaced from the lifting structure and a lifting point (the lifting position) above the opening, i.e. onto the movable deck section and below a lifting unit, such as a hook, of the lifting structure. A blow-out preventer (BOP) or other heavy equipment placed onto a moveable carrier on the working deck at a lateral distance from the lifting structure can thus safely and effectively be lowered through the opening by moving the carrier along the rails towards and onto the moveable deck section (set in its first position in the opening, preferably above the well and under the lifting structure/derrick), lifting slightly the BOP using the lifting structure, moving the carrier away from the deck section back to the working deck (or leave it on the deck section), moving the deck section to its second position so as to uncover the opening at the lifting position underneath the BOP, and lowering the BOP through the opening. The same principle (in reverse order) can be used for lifting the BOP (or other heavy equipment) up through the opening and further to a moveable carrier eventually placed on the working deck at a lateral distance from the lifting structure.

The invention is of particular advantage for subsea equipment operation arrangements where the drilling driving unit (if such a unit is present) is contained in the lifting structure at a vertical distance above the opening, i.e. out of the way of the movable deck section, using a top drive. The invention is of particular advantage also for subsea operation arrangements comprising a further deck located below the working deck as equipment handled on this lower deck is allowed to protrude through the opening. This provides for a more compact subsea operation arrangement as handling of equipment with considerable height on the lower deck otherwise requires a large distance between the two decks.

The shape and length of the opening, as well as the size, shape and structure of the movable deck section, can be adapted to the particular situation. Further, one or several additional movable or removable deck sections can be used to cover (parts of) the opening. These additional sections may or may not be moveable along the opening and may or may not be provided with rail members. For instance, the opening may extend in two opposite lateral directions to allow the deck section to be moved in any of two opposite directions from the lifting position.

For the purposes of the invention, the term lifting structure is not limited to typical derricks, e.g. a trussed tower structure, but may simply be a lifting structure capable of performing the task of lifting/lowering/hoisting a weight. The lifting structure may be equipped with a top- drive drill driving system. A lifting structure has some form of vertically movable lifting unit, such as the top-drive or a hook, which is used for the actual lifting/lowering/hoisting. The lifting position, i.e. the first position of the deck section, relates to the lateral position of such a vertically movable lifting unit. This means that the "second position aside of the lifting position" is laterally aside of the vertical passageway of the lifting unit. This "second position" can still be below some part of the lifting structure but may be aside also of the entire lifting structure. The lifting position may be regarded as a lifting point or a lifting zone. Typically, the movable deck section is positioned centrally below the lifting unit (top-drive/hook) when set in its first position.

In an embodiment of the invention the first movable deck section is substantially flush with the working deck adjacent to the opening. This provides for an easy alignment and connection of the rail structure, and no projecting edge is created that would increase the safety risks for the workers on the working deck. In an embodiment of the invention the first movable deck section is equipped with a cut-out at an edge thereof such that the first movable deck section is capable of, when moved towards the first position with said edge forming a leading edge of the deck section, partly surrounding, by means of the cut-out, a drill pipe or other drilling equipment extending through the opening. This way the opening can be covered by the deck section around e.g. a drill pipe extending through and projecting from the cut-out. Workers can thus stand on the deck section close to the drill pipe for e.g. connecting further drill pipes.

In an embodiment of the invention the rail structure is arranged to extend to the opening so as to provide for operational alignment with the rail members of the first movable deck section when said first movable deck section is set in a first position. A moveable carrier carrying equipment can thus be moved on the rails onto the deck section to the lifting position under the lifting structure. The rail structure can also arranged to extend to the opening so as to provide for operational alignment with the rail members of the first movable deck section when said first movable deck section is set in the second position. A moveable carrier carrying equipment can thus be moved on the rails onto or off from the deck section also when the deck section is in the second position.

In an embodiment of the invention said working deck is provided with a drilling tubular storage unit arranged in association with the lifting structure. The drilling tubular storage unit may be placed on one side of the lifting position (the first position), i.e. in association with the lifting position but aside thereof to avoid blocking the opening.

Preferably, the drilling tubular storage unit is arranged above said opening aside of the lifting position of the lifting structure. This means that the opening extends below the drilling tubular storage unit so that the movable deck section can be moved along the opening into a space under the storage unit (which may form the second position of the deck section). This is a way of saving space (or rather area of the working deck) as part of the opening and the drilling tubular storage unit occupy the same area. The storage unit may be somewhat raised from the working deck, i.e. a bottom of the storage unit may be located at a level somewhat above the level of the surrounding working deck to give sufficient room for the deck section to be moved in and out below the storage unit. The opening may extend also in the opposite direction, i.e. from the lifting position away from the drilling tubular storage unit. Preferably, the drilling equipment storage unit extends across the opening in a direction perpendicular to a longitudinal direction of the opening.

Preferably, the drilling tubular storage unit is configured to store vertically arranged drilling tubulars. This simplifies handling since the drilling tubulars are positioned vertically also when lowered or lifted up through the opening.

The function and advantages of the drilling tubular storage unit is not dependent on the exact design of e.g. the movable deck section or the rail structure. For instance, it is not required that the rail member can be operationally aligned with the rail structure as described above.

In an embodiment of the invention the arrangement comprises a guiding structure arranged to guide heavy subsea equipment as it is lowered or hoisted through the opening, said guide structure comprising at least one guide member extending in a substantially vertical direction from a position above said working deck. Preferably, the at least one guide member extends to a position below said working deck, and more preferably, the at least one guide member extends through the opening. In the case where the guide member extends through the opening, the guide member may be provided with a removable section that includes a portion of the guide member where it extends through the working deck opening.

A vertically extending guide member is useful for guiding the heavy equipment and/or the lifting device used for lifting the equipment while lifting or lowering the equipment through the opening in the working deck. Such guiding can prevent the equipment or lifting unit from e.g. swinging to and fro when the platform or vessel is moving due to environmental actions (waves and wind). Typically, the guiding member is fixed to the lifting structure and, if it extends also below the working deck, to a support below the working deck. It is generally an advantage to let the guiding member extend all the way through or aside of the opening since this allows the heavy equipment to be connected to the guide member by a connection (that typically extends in a horizontal direction) that can follow the equipment vertically as the equipment passes through the opening. That is, the connection is movable along the guiding member.

By letting the guide member extend aside of the opening it does not prevent the movement of the moveable deck section. In such a case the guide member is preferably arranged in a cutout at the side of the opening to allow the movable connection between the equipment and the guide member to pass the opening without having to be disconnected and re-connected at the other side of the working deck. Alternatively, the guide member may extend through the opening. In such a case the guide member may comprise a removable section to allow the movable deck section to pass along the opening. In a variant the guide member extends through the opening in a fixed manner. Such a fixed guide member can be made more robust and is less complex. By arranging such a fixed guide member at a side of the lifting position, the deck section can still be moved between its first position and a second position away from the guide member. A further moveable deck section can be arranged at the other side of such a fixed guide member.

A guide member that is arranged only above the opening and the working deck, i.e. a guide member that does not extend through or aside the opening, is also useful as it still can guide equipment and the lifting device, in particular when the part to be guided is positioned above the working deck. Such a guide member has also the advantage that it does not affect the operation of the movable deck section.

In an embodiment of the invention the guiding structure comprises at least a first (upper) guide unit (such as a "dolly") movably arranged onto the guide member so as to be vertically movable along the guide member, wherein the first guide unit is arranged to be securable to a lifting unit (such as a top-drive or hook) configured to carry the equipment to be lowered or hoisted, said first guide unit thereby being capable of guiding said lifting unit along the guide member during lowering or lifting. Such a guide unit can form a secure (typically horizontal) connection between the guide member and the lifting unit during lifting and lowering. This is useful also when the guide member extends only above the working deck. In an embodiment of the invention the guiding structure further comprises a second (lower) guide unit (such as second "dolly") movably arranged onto the guide member so as to be vertically movable along the guide member, wherein the second guide unit is arranged to be securable to the equipment to be lowered or lifted and thereby being capable of guiding said equipment along the guide member during lowering or lifting. This is of particular advantage when the guide member extends through or aside of the opening and further below the working deck because the second guide unit can follow the equipment as it is lowered or hoisted through the opening. The function and advantages of the guiding structure is not dependent on the exact design of e.g. the movable deck section or the rail structure. For instance, it is not required that the rail member can be operationally aligned with the rail structure as described above.

In an embodiment of the invention also a second deck section is movably arranged in the opening. In a variant of this embodiment where the arrangement also comprises a guide member that extends through the opening, the first and second movable deck sections are arranged in the opening on opposite sides of the at least one guide member, wherein at least one of the first and second movable deck sections is provided with cut-outs or similar at the side/edge facing the at least one guide member, wherein the cut-outs are adapted to the shape and position of the at least one guide members so that the two deck sections can be moved close together at the at least one guide member. This way the two deck sections can be positioned close to each other also where a fixed guide member extends through the opening between the two deck sections.

In an embodiment of the invention the arrangement comprises a lower deck, e.g. a support deck, arranged below the working deck. A further movable deck section can be arranged as described above also in an opening in the lower deck, and the guiding structure can extend through such an opening with the guiding members extending below such a lower deck.

The invention also relates to an offshore platform, such as a semi-submersible platform, or a vessel provided with a subsea equipment operations arrangement of the type described above. BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows a perspective view of an embodiment of a subsea equipment operations arrangement according to the invention,

Figs. 2A-D show perspective views of a sequence of steps for lowering subsea equipment in the arrangement, and

Figs. 3A-D show the sequence of figs. 2A-D in a side cut view.

DETAILED DESCRIPTION OF EMBODIMENT(S) OF THE INVENTION

Figure 1 shows a subsea equipment operations arrangement 10 forming part of a subsea equipment operations platform. The subsea equipment operations arrangement 10 has a working deck 20 and, in this example, a support deck 30 arranged below the working deck 20. The working deck has an opening 21 configured to allow passage of e.g. subsea equipment operations equipment such as drill tubulars 42, a blowout preventer (BOP) 40 (see figure 2A) or a "X-mas tree" 41. A lifting structure 50 for lifting and handling heavy subsea operations equipment is arranged above the opening 21. The support deck 30 is equipped with a support deck opening 31 positioned below and aligned with the working deck opening 21. The opening 21 in the working deck extends in a lateral direction from a lifting position below the lifting structure 50 to a point aside of the lifting position, in this case also aside of the lifting structure 50. The subsea equipment operations arrangement 10 further comprises a system for transporting the heavy equipment laterally over the working deck 20 to and from the opening 21, said system comprising a rail structure 70 arranged on the working deck 20 for supporting and guiding a movable carrier 71 configured to carry the heavy equipment.

In the example shown here, the lifting structure 50 (the derrick) comprises a trussed network of beams, preferably by metal such as steel, or any similar material which is capable of supporting the weights and/or forces required. Parts of the trusswork of the lifting structure 50 have been omitted from the figures to improve the visibility thereof. The lifting structure 50 has a substantially rectangular cross section seen from above, and the trusswork extends down to, in this case, four support points on the working deck 20.

The lifting structure 50 comprises a hoisting winch 51 arranged to lower and hoist a lifting unit 52 by means of a wire and a pulley 53 arranged onto the lifting unit 52. The hoisting winch 51 is in this example located in the top of the lifting structure 50 but may e.g. be located on the working deck (using a further pulley in the top of the lifting structure 50) or on a further deck above the working deck 20. As an alternative to the hoisting winch 51, the whole hoisting arrangement may be based on e.g. hydraulic cylinders.

The lifting unit 52 may be a so-called top drive unit capable of transmitting torque to e.g. a drilling tubular attached to the bottom thereof. The lifting unit 52 is at least capable of securing equipment such as drill tubulars or other heavy or light subsea operations equipment for lifting and handling purposes. Thus, such equipment can be lowered or lifted through the opening 21 by securing the equipment to the lifting unit 52, and lowering/lifting the lifting unit 52 together with the equipment using the hoisting winch 51. The lifting position is related to the lateral position of the lifting unit 52.

A first movable deck section 22 and, in this example, a second movable deck section 23 are arranged to be moveable along the opening 21 of the working deck 20. Each of the deck sections 22, 23 has a width corresponding to the width of the working deck opening 21, whereas the combined length of the two deck sections 22, 23 is shorter than the length of the opening 21. The first movable deck section 22 and the second movable deck section 23 cover together only a portion of the opening 21.

A third movable deck section 32 is movably arranged in the support deck opening 31. An inner surface of the openings 21, 31 has a bearing surface projecting from the bottom portion of the opening 21, 31 along each of the longitudinal sides of the openings 21, 31. This bearing surface projects inwardly into the opening and acts as a bearing surface for the movable deck sections 22, 23, 32 when these move along the respective opening 21, 31. Each deck section 22, 23, 32 is in this example substantially flush with the working deck or support deck adjacent to the opening, but may be slightly raised above the respective openings. The first movable deck section 22 is movable between a first position below the lifting structure 50, i.e. at the central lifting position below the lifting unit 52, and a second position aside of the central lifting position. The second movable deck section 23 is also movable between a position below the lifting structure 50 (below the lifting unit 52) and a position aside of the lifting unit 52, where the latter position can be at a side of the lifting structure 50 opposite to that of the second position mentioned above.

The opening 21 extends in this example sufficiently far on both sides of the central lifting position, in relation to the length of the movable deck sections 22, 23, to allow one of the deck sections to be moved away sideways to give room for the other deck section in the lifting position under the lifting unit 52.

The first, second and third movable deck sections 22, 23, 32 are equipped with rail members 72 configured to be operationally aligned with and form part of the rail structure 70 of the working deck 20 when the movable deck sections 22, 23, 32 are properly positioned, e.g. when positioned in the above mentioned first and second positions. Thus, when e.g. the first movable deck section 22 is in the first (or second) position, a movable carrier 71 carrying certain equipment can be moved along the rail structure 70 onto the first movable deck section 22 using the rail members 72 thereof.

The rail members 72 extend across each deck section 22, 23, 32 at an upper surface thereof. First rail members may extend in a direction perpendicular to a direction in which the deck section is movable, and second rail members may extend in a direction different from, typically perpendicular to, that of the first rail members (see e.g. figure 2A). The rail structure 70 is arranged such that rails extend to the working deck opening 21, in particular the rails extend so as to allow operational alignment with the rail members 72 of the first movable deck section 22 when set in its first position. The first movable deck section 22 is equipped with a cut-out in the form of a keyhole-shaped slot 25 (see figure 2A). The slot/cut-out 25 is open at an edge of the first movable deck section 22 that forms a leading or trailing edge of the deck section 22 when the deck section is moved along the opening 21. The cut-out 25 is elongated and extends from said edge of the first movable deck section 22 in a direction parallel to the direction in which the first movable deck section is movable. This way, the first movable deck section 22 is capable of being moved back into its first position also when a drill pipe or other drilling equipment extends through the opening 21 so as to partly surround the drill tubular (see figures 2D and 3D).

The working deck 20 is further provided with a drilling tubular storage unit in the form of a raised setback unit 45 arranged in association with the lifting structure 50. The raised setback unit 45 is configured to store vertically arranged drilling tubulars, including drill pipes 42, during operation of the subsea equipment operations arrangement 10. The drilling tubulars are arranged vertically when stored onto the setback unit 45. The raised setback unit 45 extends across the opening 21 in a direction perpendicular to a longitudinal direction of the opening 21 and at a position beside the lifting unit 52. The raised setback unit 45 is raised on supports on opposite sides of the opening 21. The bottom of the setback unit 45 is raised to a level somewhat above the level of the surrounding working deck 20. The raised setback unit 45 allows the first movable deck section 22 (and in some embodiments, also the second movable deck section 23) to be moved underneath said raised setback 45 when moved aside of the lifting position. An advantage of arranging the raised setback unit 45 at a level somewhat above the working deck 20 is that it provides for an effective use of the working deck 20 in that a part of the opening 21 and the raised setback 45 occupy the same space, i.e. a space that can be used for storage of the deck section 22 when not in use. A further advantage is that the setback 45 can be arranged to provide a fall protection equipment with regard to the part of the opening 21 beneath. In combination with a guiding structure (see below) the raised setback 45 provides further advantages.

However, it is not necessary that the setback 45 is raised; the setback 45 may instead be arranged in a more conventional way directly onto the working deck 20. In such a case the opening 21 may extend sideways in only one direction from the central lifting position. The subsea equipment operations arrangement 10 is further provided with a guiding structure that extends from a position above the working deck 20 downwards in a substantially vertical direction. The guiding structure is arranged to guide the lifting unit 52 (top-drive/hook) and the heavy subsea equipment when lowered or hoisted through the working deck opening 21 (and in this example also through the support deck opening 31). The guiding structure comprises in the embodiment shown: first and second guide members/guide rails 54, 55; first (upper) and second (lower) moveable guide units ("dollies") 57, 58 slidably arranged onto the guide members 54, 55; and a guide unit winch 81 and wire 82 connecting the guide units 57, 58. The guide members/rails 54, 55 extend from a position on an upper part of the lifting structure 50, to which they are secured, through the opening 21 of the working deck 20, and further through the opening 31 on the support deck 30 to a position below the support deck 30.

The guide members/rails 54, 55 are substantially parallel and extend in a substantially vertical direction at some distance from the central lifting position below the lifting unit 52. The first (upper) movable guide unit (first "dolly") 57 is attached (via a horizontally extending connection) to the lifting unit 52 and as it is slidably arranged to the guide members 54, 55 it is capable of horizontally guiding the lifting unit 52 along the guide members 54, 55 when the lifting unit 52 is lowered or hoisted. The second (lower) movable guide unit (second "dolly") 58 is secured to the first guide unit 57 by means of a wire 82 attached to the guide unit winch 81 which is arranged onto the first guide unit 57. The wire 82 could be replaced by e.g. a telescopic rod or similar.

The vertical distance between the upper and lower guide units 57, 58 is adjusted to suit the height and holding points of the subsea operation equipment to be handled by operating the guide unit winch 81 (i.e. the free length of the wire 82 can be adjusted). The second guide unit 58 can thus be lifted or lowered relative the first guide unit 57. As explained further below, the second guide unit 58 is intended to be secured (via a horizontally extending connection) to the equipment to be lowered or hoisted through the opening 21. Since the second guide unit 58 is slidably arranged to the guide members 54, 55 it is capable of horizontally guiding the equipment when it is lowered or lifted along the guide members 54, 55 (which typically is done with a constant vertical distance between the first and second guide units 57, 58 by operating only the hoisting winch 51 and not the guide unit winch 81). Since the lower guide unit 58 hangs from the upper guide unit 57 in a wire, the upper guide unit 57 can continue to move downwards towards the lower guide unit 58 also when the lower guide unit has stopped at the lower end of the guide rails 54, 55. Each of the guide rails 54, 55 has, in the example shown, a removable, in this case hinged, section 56 that includes a portion of the guide member 54, 55 where it extends through the working deck opening 21. The purpose of this is to allow the movable deck sections 22, 23 to pass the guide rails 54, 55 when moved horizontally along the opening 21 without having to remove the entire guide rails 54, 55. A similar removable section 56 is provided in association with the support deck opening 31. The hinged sections 56 can be set in a closed position, in which they connect upper and lower parts of the corresponding guide rail 54, 55 and allow the guide units 57, 58 to pass the opening 21 while attached to the guide rails 54, 55, and in an open position, in which they are removed from the opening 21 and allow the deck sections 22, 23 to pass.

The sections 56 need not necessarily be hinged, they may for instance simply be detachable, but a hinged arrangement makes handling easy.

As an alternative to removable guide rail sections, it is possible to provide for cut-out openings at the sides of the working deck opening 21 and let the guide rails/members 54, 55 extend through these cut-out openings. The guide rails/members 54, 55 thus extend through the working deck 20 (or support deck 30) close to the deck opening 21 at a side thereof through the cut-out openings that are open to the larger working deck opening 21. Such an arrangement allows both the guide units 57, 58 to pass through the opening 21 and the movable deck sections 22, 23 to pass along the opening 21 without having to adjust the guide rails/members 54, 55.

A further alternative is to dispense with any removable guide rail sections and any detachable guide members and instead make use of fixed guide members that extend through the opening 21 and accept that they prevent the moveable deck sections 22, 23 to pass along the opening 21. By placing the guide members at some lateral distance from the central lifting position below the lifting unit 52 (as is the case also in the embodiment shown in figures 1-3) it is still possible to operate a moveable deck section in line with what is described above and below, but only on one side of the guiding members, i.e. the side of the guiding members facing the raised setback 45, see e.g. figure 2B.

In such an alternative one may also dispense with the second movable deck section 23 and let the working deck opening 21 end closer to the guiding members on that side of the opening 21. However, the second movable deck section 23, arranged on the side of the guiding members facing away from the raised setback 45, is still useful because the second section 23 can be used to transport equipment along the opening 21 from a side of the lifting structure 50 to the (fixed) guiding members close to the centrally located lifting point. At the guiding members, the equipment can be skidded over from the second section 23 to the first section 22 when placed in its first position (the lifting position) below the lifting structure 50.

When using guide members that extend through the opening 21 and two movable deck sections 22, 23 arranged in the opening 21 on opposite sides of the guiding members, it is an advantage if at least one of the deck sections is provided with cut-outs or similar at the side/edge facing the guide members, wherein the cut-outs are adapted to the shape and position of the guide members so that the two deck sections 22, 23 can be moved close together at the guide members and thereby allow equipment to be slided from one of the deck sections to the other. Without such cut-outs, the guide members will prevent the deck sections 22, 23 from coming in contact with each other. Fixed guide rails can be made more robust and less complex than guide members with hinged or removable sections. The fixed guide rails may extend down to or through the support deck similar to what is shown for the guide rails 54, 55 in the figures.

Figures 2A-2D show in perspective views some steps in the process of lowering a blow-out preventer (BOP) 40 from the working deck 20 to a position below the working deck 20. Figures 3A-3D show the same steps as 2A-2D but in sectional side views. In similarity to figure 1, parts of the trusswork and supports that make up the lifting structure 50 have been omitted.

As shown in figure 2A/3A, the BOP 40 is located on a carrier 71 on the rail structure 70 at some lateral distance from the lifting structure 50. The hinged sections 56 of the first and second guide members 54, 55 are in their open position, which allows the first movable deck section 22 to be moved along the opening 21 under the upper parts of the guide members 54, 55 towards the first position below the lifting unit 52 in which the rail members 72 of the deck section 22 align with the rail structure 70 of the working deck 20 (see figure 2B/3B). A tubular pipe section 43 is secured to and carried by the lifting unit 52. As shown in figure 2B/3B, the carrier 71 and BOP 40 has been moved (e.g. slided) on the rail structure 70 onto the first movable deck section 22 placed in its first position. The lifting unit 52, the pipe section 43 and the first and second guide units 57, 58 are lowered together, by operating the hoisting winch 51, so as to allow the pipe section 43 to be secured to the BOP 40. The hinged sections 56 of the first and second guide members 54, 55 are set in their closed position so as to allow the second guide unit 58 to be further lowered, by operating the guide unit winch 81, to a position sideways of the BOP 40 for securing the second guide unit 58 to the BOP 40. Since the second guide unit 58 follows and guides the BOP 40 during its subsequent vertical movement down through the opening 21, the BOP 40 will be held in place horizontally when moved along the guide members 54, 55. This greatly improves the safety as high seas may cause pendulum movements in objects hanging from the lifting structure, such as the lifting unit 52 and the BOP 40, which are likely to be heavy and difficult to handle.

To remove the carrier 71 carrying the BOP 40 and return it to the rail structure 70, the hoisting winch 51 of the lifting structure 50 is used to lift the blow-out preventer 40 slightly upwards. It is only needed to lift the BOP 40 high enough to gain clearance from the carrier 71 so that the carrier 71 can be removed. The blow-out preventer 40 may be lowered and allowed to rest on the first movable deck section 22 for further manipulation before it is ready to be lowered to a position below the working deck 20, or the lowering may proceed immediately.

The BOP 40 is lifted slightly, by using the hoisting winch 51, to allow the first movable deck section 22 to be moved aside of the BOP 40. As shown in figure 2C/3C, the deck section 22 is moved along the opening 21 to a position below the raised setback 45. At that stage the BOP 40 may be lowered below the working deck 20 through the opening 21 using the hoisting winch 51. The guide unit winch 81 is not operated while lowering the BOP 40 so the distance between the guide units 57, 58 is kept constant (as shown in figures 3C and 3D). The BOP 40 can now be further lowered through the opening 31 in the support deck 30 towards the oil or gas well (as shown in figure 3D).

Figures 2D and 3D show the situation where the blow-out preventer 40 has been somewhat further lowered and the first movable deck section 22 has been moved back to a position directly below the lifting unit 52. The drill pipe section 43 is now arranged in the keyhole slot 25 of the first movable deck section 22. The drill pipe section is supported in the circular part of the keyhole slot 25 by means of a removable bushing 75.

Guiding of equipment during lifting is improved also in the case where the guiding members extend only above the working deck 20, i.e. where the guiding members do not extend through the opening 21. In such a case the upper guide unit 57 guides the lifting unit 52 during the lifting or lowering operation. As the guide members do not extend through the opening 21 in this case, guiding of the equipment while passing through the opening 21 must, however, be carried out in another way than described above and in the figures.

The support deck 30 is not necessary for the function of the working deck 20 and its opening 21, movable deck sections 22, 23 etc. or for the function of the guiding structure, but the support deck 30, i.e. a further deck located below the working deck, is useful for handling of certain equipment. The working deck opening 21 can be used to allow equipment placed on the support deck 30 to protrude upwards through the working deck 20 and thereby decrease the distance needed between the two decks. The second deck section 23 is also movably arranged in the working deck opening 21 and it has a size that covers only a part of the portion of the opening 21 that is not covered by the first movable deck section 22.

Each of the movable deck sections 22, 23, 32 shown in this example is capable of supporting heavy subsea operations equipment. More simple covering sections may be used to cover openings for safety reasons.

In the example shown, the working deck opening 21 has an elongated shape and extends in two opposite lateral directions from a central position below the lifting structure 50, each of which extending to a point aside of the lifting position and further aside of the lifting structure 50. It is possible to let the opening 21 extend mainly in one of these directions. The first movable deck section 22 is movable along a longitudinal direction of the opening 21. The relative dimension between the opening 21 and the first deck section 22 is such that the space occupied by the first movable deck section 22 when positioned in the first position (the lifting position) does not overlap with the space occupied by the first movable deck section 22 when positioned in the second position, aside of the lifting position. The subsea equipment operations arrangement 10 may typically be used on a subsea operations platform or a drillship.

FIGURE REFERENCES

10 Subsea equipment operations arrangement

20 Working deck

21 Opening in working deck

22 First movable deck section

23 Second movable deck section

30 Support deck

31 Opening in support deck

32 Third movable deck section

40 Blow-out preventer (BOP)

41 Valve assembly (Christmas tree)

42 Drill pipes

45 Raised setback

50 Lifting structure

51 Hoisting winch

52 Lifting unit (which may include a drive unit, e.g. a top drive)

53 Pulley

54 First guide member

55 Second guide member

56 Hinged section

57 First dolly

58 Second dolly

60 Bearing surface projections

70 Rail structure

71 Carrier

72 Rail members