GB2212189A

GB2212189A - Sub-sea equipment running arrangement

Info

Publication number: GB2212189A
Application number: GB8726130A
Authority: GB
Inventors: James Leon Mank
Original assignee: Ferranti International Signal PLC
Current assignee: Ferranti International PLC
Priority date: 1987-11-07
Filing date: 1987-11-07
Publication date: 1989-07-19
Anticipated expiration: 2007-11-07
Also published as: GB2212189B; GB8726130D0

Abstract

An arrangement for running equipment 10 into a receptacle 12 on a deep sub-sea structure 11 comprises providing on the structure an aperture 29 aligned with the receptacle and a travelling cage 13 for transporting the equipment. The cage has guidance means 17 for maintaining the equipment on a discharge axis 16 and support means 21 for lowering it through an openable base provided by downwardly inclined and downwardly pivotable fingers 25. The raised fingers 25 define a locating cone by which the discharge axis of the landing cage is aligned with the receptacle and the lowered fingers (25) define a guide funnel for ensuring the equipment enters the receptacle. The fingers have projections 31 and the lowered fingers automatically hook under structure members 30 to prevent reactive forces lifting the cage. The lowering of the equipment, and possibly the fingers, may be controlled by an attendant ROV. <IMAGE>

Description

SUB-SEA EQUIPMENT RUNNING ARRANGEMENT This invention relates to sub-sea equipment running arrangements, by which arrangements equipment to be installed on sub-sea structures is run in guided descent from a surface vessel into the appropriate position in the sub-sea structures.

As exploration for, and production of, oil and gas from sub-sea wells has involved the placing of well-head and other control-intensive structures at ever increasing depths a situation has developed whereby installation and maintenance of relatively small items of equipment is required at depths workable only by submersible vehicles. For practical reasons these are usually remotely operated vehicles (ROV's) controlled from a surface vessel with the aid of television which are, as a result of remote operation and working environment and perceived intended tasks, lacking in dexterity.

One particular task involves the lowering of relatively light (less than a few tonnes) control modules which are seated in a receptacle on a sub-sea structure and coupled to electrical and/or hydraulic line terminals, hereinafter referred to as electro-hydraulic terminals, to control the flow of electrical and/or hydraulic power the, or other, sub-sea structures.

Whereas entry of the module into the working receptacle ensures that the electro-hydraulic terminals thereof assume alignment with the corresponding terminals of the receptacle/structure the difficulty is in ensuring that such a module or the like can be lowered from a surface vessel which is undergoing significant vertical and lateral displacements due to sea state.

Installation of heavy sub-sea equipment is often undertaken by attaching guide wires between a sub-sea structure and surface vessel and running the equipment down the wire to the desired location. However such guide wires require to be maintained in tension which in turn requires sophisticated tensioning and/or wave motion compensation facilities at the surface vessel. This is not always practicable, cost effective or desirable for smaller items of equipment. Free lowering of equipment to be collected and manipulated into position by a ROV is also less than satisfactory because precision-manoeuvring the ROV with respect to the lowered equipment to acquire and position it correctly without inflicting damage is time consuming and beyond the skill of all but the best operations.

Proposals have been made which depend upon the equipment being acquired by some manipulative mechanism, being an ROV or an attachment to the sub-sea structure, and positioned by constantly measuring displacement of the mechanism with respect to the desired position. The control arrangements of such mechanisms, are complex and provide a solution which is both expensive and liable to suffer increased failure problems associated with complex equipment.

It is an object of the present invention to provide a sub-sea equipment running arrangement of simple construction which mitigates the above outlined difficulties in positioning a freely lowered piece of equipment with respect to a sub-sea structure.

According to the present invention a sub-sea equipment running arrangement comprises a travelling cage having an openable base arranged to be lowered from a surface vessel to a sub-sea structure, guide means operable to support the equipment within the cage for motion relative thereto along a discharge axis, support means operable to support tile equipment within the cage during transit of the cage to the structure and to lower it with respect to the cage to discharge it through the base, the openable base comprising an array of fingers pivotally supported at one end thereof about the periphery of the cage and extending inwardly towards the discharge axis, said fingers being arranged in a raised unpivoted state to be downwardly inclined to define a conical base to the cage to protect the equipment therein and locate the discharge axis of lowered cage with respect to an apertured structure upon which the cage is landed and arranged to be downwardly pivotable about their supported ends to describe by their locus an open funnel centred on the discharge axis for discharging the equipment therethrough into the structure, said fingers having lateral projections extending downwardly of the raised fingers adapted to hook under members of structure supporting the cage upon downward pivoting of the fingers to hold the cage against movement with respect to the structure along the discharge axis.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which:- Figure 1 shows a sectional elevation through a sub-sea equipment running arrangement according to the present invention in which a freely lowered travelling cage containing the equipment is about to land upon a sub-sea structure of which the equipment is to be positioned, with a remotely operated vehicle in attendance, and Figure 2 shows a sectional elevation of the arrangement of Figure 1 after the travelling cage has landed on, and docked with the sub-sea structure, with the equipment partly discharged from the cage.

Referring to Figure 1 a piece of equipment 10, such as a control module has to be lowered to a sub-sea structure 11 in which is a dimensionally precise receptacle 12 for the equipment. The equipment is relatively light, say less than a few tonnes in weight, and the positioning accuracy available from suspension by a long cable susceptible to sea currents and surface vessel motion is limited.

It is common practice in sub-sea work to undertake all remotely controlled operations with visual feedback provided by a television camera, which may be of a special type lowered to observe the operation, be specifically fitted to a sub-sea structure or be the camera fitted as standard equipment to remotely operated vehicle (ROV's) which may attend and perform the work.

Whilst such ROV's provide the ability to offer rough positional guidance to a load, suspended or carried by the ROV any attempt at precise positioning or operation of equipment is generally considered best avoided.

In accordance with the present invention the equipment 10 is lowered to the structure within a protective travelling cage 13 which docks with the structure 11 and discharges the equipment into the receptacle 13.

The cage is preferably lowered by cable 14 to the vicinity of the structure and viewed by an attendant ROV 15.

The ROV grasps the cage and manoeuvres it above the structure with a roughly predetermined orientation before depositing it, that is, letting it land, on the structure 11.

The travelling cage 13 comprises a framework having a vertical discharge axis 16 along which the equipment is constrained to travel by guide means 17 comprising at least one, but preferably two or more rails 18 extending parallel to the discharge axis for substantially the length of the cage and each supporting a runner 19 having an arm 20 extending radially inwardly towards the discharge axis to collar the equipment 10 and maintain its axial disposition. The runners 19 are freely movable along the guide rails and maintain the equipment on the axis during any movement of the equipment along the axis.

The cage also includes support means 21 to maintain the position of the equipment at any point along the axis for transit and to move the equipment along the axis to discharge it from the cage. The support means 21 may comprise a hydraulic jacking arrangement as shown comprising an extensible arm 22, conveniently formed of telescopic sections, extended to drive the equipment 10 out of the base of the cage. Such a hydraulic jacking arrangement may be powered by pressurised fluid received from the ROV on lines 23 or by the surrounding sea water compressed by pump 24 (shown ghosted) carried by the cage.

The support means 24 may alternatively comprise a cable and winch arrangement (not shown) by which the equipment is permitted to descend through the cage by its own weight.

The support means, whatever its form; is conveniently controlled, that is, its operation initiated, by the ROV 15.

The base of the cage 13 is openable to permit discharge of the equipment and is formed by an array of fingers 25 pivotally supported at one end 26 thereof about the periphery of the cage and extending inwardly towards the discharge axis 16.

The fingers are arranged to assume a raised, unpivoted, state as shown by means of resilient bias means 27, in which state they are downwardly inclined to define a conical base of the cage which protects the equipment during transit.

The sub-sea structure 11 has an upper face which provides a deck 28 for the cage to land on and this deck is apertured, the aperture 29 being defined by a ring 30 forming the permitter thereof. The ring and cage are dimensioned such that as the cage approaches landing on the deck 28 the conical base formed by fingers 25 locates the cage if necessary such that the discharge axis 16 is aligned with the axis of receptacle 12.

The fingers 25 are further equipped with projections 31 lateral to their length which extend downwardly thereof but within the diameter of the ring 30.

Referring now to Figure 2, when the cage 13 has landed upon the deck 28 with the discharge axis 16 and receptacle axis aligned the fingers are pivotally displaced downwardly and open to describe by their locus a funnel centred on the discharge axis and leading to the receptacle.

Preferably the receptacle 30 is provided with an outwardly inclined or flared entrance 32 which is disposed in relation to the ring 30 such that the downwardly pivoted fingers extend into and abut the receptacle entrance and form an uninterupted guidance funnel by which the equipment can be lowered into the receptacle.

It will be appreciated that the act of lowering the equipment along the axis 16 may create a reaction force tending to lift the cage from the structure deck 28, particularly if hydraulic means is used to 'jack' the equipment down.

The projections 31 of the finger are arranged to hook under the ring 30 as the fingers are pivoted downwards and provide a securing or docking arrangement to hold the cage with respect to the structure until the fingers are raised. Such docking also ensures that any external forces acting directly on the cage or through a suspension rope 14 do not disturb the alignment.

Thus when the cage 13 is docked with the sub-sea structure 11 the equipment is lowered into the receptacle, the support means is disengaged therefrom and retracted, if necessary, into the cage, the fingers 25 are then pivoted upwardly to their raised positions and the cage can then be removed from the structure. Removal of the equipment from the receptacle is achieved by the above described docking with an empty cage, lifting the equipment into it and then raising the cage to the surface.

As indicated above, the orientation of the cage about the discharge axis may be roughly defined by the ROV, for example, by aligning visible marks within + 45" and the equipment and receptacle rim may be provided with cooperating guide pegs and recesses (not shown) to effect any finer degree of alignment about the discharge axis as required.

Other variations on the above described construction may be employed. For example, in the guide means 17 the runners 18 may be provided by structural members of the cage or non-structural members such as tensioned wires or, if the support arrangement has lateral rigidity as the extensible arm 22 may have, it may provide the guide means and separate means 17 as shown may be omitted.

The base fingers may extend in the peripheral direction, being planar or curved to form a more protective base and continuous funnel.

The base fingers 25 may be arranged such that they pivot downwardly automatically upon landing of the cage, for instance, by engaging the ring 30 or some other part of the structure above the pivot point so that-the Weight of the cage displaces the contact points upwardly and the main portions of the finger downwardly.

Alternatively, the fingers may be just spring biased to the raised portion and displaced downwardly by the weight and motion of the equipment 10 as it is lowered against and through the opening formed by them.

In yet another variation the fingers may be lowered, and indeed raised, by a separate source of power, conveniently hydraulic and conveniently from the attendant ROV which gives the operator full control over the opening of the cage base.

It will be appreciated that operation is not dependent upon the presence of an ROV provided that water depth condition and surface state permits the cage to be lowered the docking can be observed by a camera and the surface operator has means in the suspending line to initiate discharging if the equipment at least.

Similarly the line may be omitted altogether and the cage carried to and from the equipment by an ROV.

The arrangement is flexible enough to permit a wide variety of working practices and in particular control operations performed on the cage by an ROV are of a basic level and may be effected without demanding great dexterity on the part of the ROV.

Claims

Claims:

1. A sub-sea equipment running arrangement comprising a travelling cage having an openable base arranged to be lowered from a surface vessel to a sub-sea structure, guide means operable to support the equipment within the cage for motion relative thereto along a discharge axis, support means operable to support the equipment within the cage during transit of the cage to the structure and to lower it with respect to the cage to discharge it through the base, the openable base comprising an array of fingers pivotally supported at one end thereof about the periphery of the cage and extending inwardly towards the discharge axis, said fingers being arranged in a raised unpivoted state to be downwardly inclined to define a conical base to the cage to protect the equipment therein and locate the discharge axis of lowered cage with respect to an apertured structure upon which the cage is landed and arranged to be downwardly pivotable about their supported ends to describe by their locus an open funnel centred on the discharge axis for discharging the equipment therethrough into the structure, said fingers having lateral projections extending downwardly of the raised fingers adapted to hook under members of structure supporting the cage upon downward pivoting of the fingers to hold the cage against movement with respect to the structure along the discharge axis.

2. A running arrangement as claimed in claim 1 in which the fingers are arranged to be downwardly pivoted to open the cage base by the weight of the cage acting through a sub-sea structure.

3. A running arrangement as claimed in claim 1 in which the fingers are arranged to be downwardly pivoted to open the cage base by downward motion of the equipment lowered through the cage.

4. A running arrangement as claimed in claim 1 in which the fingers are arranged to be downwardly pivoted to open the cage base by powered actuators adapted to be controlled remotely.

5. A running arrangement as claimed in claim 4 in which the actuators are arranged to be provided with operating power from a remotely operated vehicle.

6. A running arrangement as claimed in any one of claims 1 to 5 in which the support means is arranged to be controlled by a remotely operated vehicle.

7. A running arrangement as claimed in claim 6 in which the support means is arranged to receive operating power from the remotely operated vehicle.

8. A running arrangement as claimed in any one of the preceding claims in which the guide means comprise at least one rail extending parallel to the discharge axis of the cage each supporting a runner having an arm extending radially towards the discharge axis to maintain the axial disposition of the equipment during discharge through the base.

9. A running arrangement as claimed in claim 8 in which the support means comprises a winch and cable arrangement operable to lower the equipment with respect to the cage by means of its weight.

10. A running arrangement as claimed in any one of claims 1 to 8 in which the support means comprises an hydraulically extensible arm having lateral stiffness.

11. A running arrangement as claimed in claim 10 when dependent upon any one of claims 1 to 7 in which the extensible arm is disposed to extend along the discharge axis and comprises the guide means.

12. A running arrangement as claimed in any one of the preceding claims in which the pivot points of the fingers are disposed radially and equidistantly of the discharge axis.

13. A running arrangement as claimed in claim 12 including a circularly rimmed part in the sub-sea structure into which the raised fingers of the cage extend upon mating of the cage and structure to define the landing position of the cage relative to the structure and against the underside of which rim the fingers projections of the downwardly pivoted fingers are arranged to hook.

14. A running arrangement as claimed in any one of the preceding claims in which the sub-sea structure is provided with a receptacle for equipment discharged from the cage having an outwardly inclined entrance and the finger lengths and operating angles are arranged such that the downwardly pivoted fingers of a-seated cage extend into and abut the receptacle entrance.

15. A sub-sea equipment running arrangement substantially as herein described with reference to and as shown in, the accompanying drawings.