GB2304771A - Subsea oilfield equipment protection - Google Patents

Abstract

A protective structure comprising a framework 46 is secured to subsea oilfield equipment e.g. a pair of riser pipes (not shown) by upper 80 and lower 76,78 clamps between which collars attached to the framework 46 are sandwiched. A tool for aligning the clamps 76,78 at the correct height on the riser pipes is also disclosed.

Description

SUBSEA OILFIwDn EOUIPMENT PROTECTION This invention relates to a subsea oilfield equipment protective structure, and means for its installation.

In many subsea oilfields it is necessary to protect equipment (such as wellheads and Christmas trees) projecting above the mudline against damage from trawl nets. Usually the equipment is enclosed in a cage or framework having sloping sides extending to the sea bed to guide fishing nets over the equipment with reduced risk of snagging. Where snagging occurs, the framework is designed to absorb the snag loads without damage. To be effective, the framework must be securely anchored in place, usually by piling driven into the sea bed or by weighting the framework. Both of these securing methods are slow to carry out, and weighting may not prevent the framework from shifting and damaging the equipment under high snag loads.

The present invention aims to provide trawl protection for subsea oilfield equipment that is quickly installable (preferably diver installable in less than 48 hours) and at least as effective as prior protective structures.

Accordingly, the present invention provides a structure for the protection of subsea oilfield equipment against snagging damage, comprising a protective shield having a coupling for engagement with the equipment to secure the shield in place.

The shield is thereby prevented from shifting relative to the equipment and causing damage under snag loads. Where the equipment is securely anchored to the sea bed (for example a subsea wellhead assembly or conductor pipe) the shield will likewise be securely anchored. Because such equipment is designed to withstand substantial bending loads encountered during well drilling and completion operations, it can easily withstand snag loads imposed on the shield.

The coupling preferably comprises a clamp engageable with the equipment. Advantageously, the clamp is adapted to be secured to a conductor pipe. In a preferred arrangement, lower and upper clamps are attached to the equipment with a collar secured to the shield sandwiched between them. The structure may be secured to more than one conductor pipe using corresponding numbers of lower and upper clamps and collars.

One of the clamps may be a close fit with its co-operating collar and a first conductor pipe, permitting substantially no lateral movement between the collar and the first pipe in any direction.

As the conductor pipes can usually be installed to a spacing accuracy of only +3 inches (75 mm) or so, these large tolerances must be accommodated by the structure. A preferred means for doing so is to make a second clamp a loose fit with its collar along an axis aligned with the first pipe and a close fit with its collar in a direction perpendicular to that axis, whereby the structure is substantially fixed against movement perpendicular to the axis but variation in the spacing of the pipes along the axis can be accommodated.

The clamps and collars for any further riser pipes are made a loose fit in all horizontal directions. Once all the clamps have been installed with the collars sandwiched between them, bolted or other fixed connections can be made up between the clamps and the structure for additional security.

The structure preferably comprises telescopic support legs extendible into contact with the sea bed. It may also comprise outwardly extending deflector legs hingedly connected to the remainder of the structure to accommodate slopes or unevenness in the sea bed and to permit access beneath the structure for maintenance.

The clamps must be installed at the right height relative to the conductor pipe or other piece of subsea equipment to which they are attached. For this purpose the present invention provides an installation tool for running and locating a clamp on a piece of subsea equipment, comprising a seating for location on the equipment and a holder for the clamp disposed at a predetermined spacing from the seating for proper location of the clamp relative to the equipment. Where the equipment comprises a pair of conductor pipes, the seating may comprise a probe for engagement with the end of one of the pipes and an adjustable height saddle for location on the end of the other pipe, whereby the tool may be properly levelled with respect to the pipes.The holder may comprise a pair of horizontal beams for supporting a pair of the clamps in horizontal alignment for installation about respective riser pipes. The tool may be provided with means to maintain the or each clamp in the correct angular alignment with respect to the equipment. Such means may for example comprise longitudinal slots in the beams engaged by projections such as bolts extending from the clamps.

The holder may be mounted on a swing arm for disengagement from the clamp after installation.

These and other preferred features of the invention will be further understood from the following description of an illustrative embodiment, made with reference to the drawings in which: Figs 1 and 2 are plan and side elevational views of a subsea wellhead protection structure forming an embodiment of the present invention; Figs 3 and 4 are plan and end elevational views of the structure of fig 1 installed over two adjacent wellheads; Fig 3a is a cut away plan view showing an equipment platform and collars of the structure; Figs 5 and 6 are plan and side elevational views showing collars of the structure in greater detail; Figs 7 and 8 are plan and elevational views of a first lower clamp for the structure of fig 1; Figs 9 and 10 are plan and elevational views of a second lower clamp for the structure of Fig 1;; Figs 11 and 12 are plan and elevational views of an upper clamp for the structure of Fig 1; Fig 13 is a plan view showing the upper clamps installed on and bolted to the collars; Fig 14 is a side elevational view showing the upper and lower clamps installed and bolted to the collars; Fig 15 is a section on live XV - XV in Fig 14; Fig 16 is a plan view of a running and installation tool for the lower clamps of Figs 7-10, 14 and 15; Fig 17 is a side elevational view of the tool of Fig 16; Fig 18 is an end view on arrow A in Fig 17 and Fig 19 is an end view on arrow B in Fig 17.

The protective structure 10 shown in Figs 1 and 2 comprises a framework fabricated from welded box-section steel tubing provided with corrosion protection anodes 12. The framework comprises an equipment platform or frame 14 linked to a top frame 16 by angled struts 18. The top frame houses an access door 20 covered with protective mesh and having R O V handles for opening (not shown).

The side wall areas defined between the struts 18 and frames 14 and 16 may likewise be covered in mesh (not shown).

Extending between the corners of top frame 16 and equipment platform 14 are upper sections 22 of four telescopic legs, lower sections 24 of which (only one shown) are slideably received within the upper sections 22 so as to be extendible and lockable in position in contact with the sea bed after the structure has been landed on a pair of well conductor pipes or casings as will be described below.

Also extending outwardly from the equipment platform 14 at a shallower angle than the support legs 24 are ten deflector legs 26 having flattened ends 28 (only one shown, Fig 1) designed to be easily driven into the sea bed. Trawl nets will ride up over the deflector legs 26 and mesh covered struts 18, with very little risk of snagging, which therefore form a shield protecting the contents of structure 10.

Figures 3 and 4 show the structure in place over a pair of wellhead and Christmas tree assemblies 30, 32 together with their ancillary equipment, mounted on respective conductor pipes 34 (only one visible, Fig 4). The Christmas trees are linked to an umbilical termination assembly (not shown) and a manifold header 36 having two tie in spools 38 isolated with twin manual gate values 40, a manual ball valve 41 to a flowline 42, a temperature sensor, pressure sensor and bleed block (not shown) and a flanged outlet 44 to a pig launcher or future tie-in well.

The equipment platform 14 is shown in greater detail in Fig 3a. It comprises inner framework members 46 carrying an hydraulic and control cable tray 48, an umbilical ramp 50 and a pair of collars 52, 54 having respective upper horizontal flanges 56,58. Upwardly projecting permanent guide base alignment paddles are also provided for angular alignment of PGB's on the conductor pipes.

The collars 52, 54 are shown in still greater detail in Figs 5 and 6. They are arranged at a suitable spacing and are of a suitable diameter to pass over the tops of conductor pipes 34 with a small clearance. Flange 56 has a series of radially spaced holes 60 therein for upper clamp securing studs, as explained below. Similarly flange 58 has a series of elongate slots 62 arranged with their axes parallel to a line joining the collar centres. The collars 52, 54 are provided with respective lower horizontal flanges 64, 66 for added strength, and lead-in funnels 68, 70 for locating the collars over the conductor pipe ends. The funnels carry bottom flanges 72, 74 provided with radially spaced holes (not shown) similar to holes 60.

Figures 7-12 show clamps for application to the conductor pipes. These comprise a pair of lower clamps 76, 78 of slightly different designs, and an identical pair of upper clamps 80. The clamps are each split along a vertical midplane into two halves and comprise a bottom flange 82, semicylindrical jaw members 84 lined with rubber, mating flanges 86 provided with through holes for clamping studs 88 and stiffening gussets 90.

Lower clamp 76 includes six vertical fins 92 dimensioned to be a close sliding fit within collar 52, restraining the structure 10 against translational movement in all horizontal directions when clamp 76 is secured about one of the conductor pipes 34 by studs 88 and funnel bottom flange 72 is landed on the bottom flange 82 of lower clamp 76. Bolts can be inserted through the holes in flange 72 and through similar holes in flange 82 to secure lower clamp 76 to the collar 52.

Lower clamp 78 has four identical vertical fins 94 and a further pair of vertical fins 96 of lesser radial extent than fins 94. The fins 96 are a loose sliding fit in collar 54 to accommodate variations in the spacing between the conductor pipes 34. However the fins 94 are a closer sliding fit to constrain movement of the collar 54 perpendicular to the plane passing through the pipe axes. Flange 82 of clamp 78 is provided with elongate slots 98 arranged to lie with their axes parallel to that plane when the clamps are properly positioned, for securing the clamp 78 to the funnel bottom flange 74 by bolts passing through the slots 98 and the holes in the bottom flange 74.

When the collars 52, 54 are landed on the clamps 76, 78 the upper clamps 80 can be applied to the conductor pipes 34 with their bottom flanges 82 bolted to collar upper flanges 56, 58 via holes 60, slots 62 and further holes 100 provided in the upper clamp bottom flanges 82. The collars are thus sandwiched between the upper and lower clamps. The assembled collars and clamps are shown in figs. 13 and 14. Figure 15 is a sectional view on line XV - XV in figure 14, in which the differing clearances between the fins 92, 94, 96 and the collars 52, 54 can be seen.

A lower clamp running and installation tool 101 is shown in figs. 16 - 19. It comprises a square top frame 102 provided with four pad eyes 104 for lowering and raising the tool to and from the sea bed. A pair of side frames 106 are secured to the top frame 102 by hinges 108 and are held in a vertical orientation by transportation braces 110, 112 tack welded to the top frame 102. Braces 110, 112 are removed when the tool is run. The frames carry short inwardly extending beams 114 at their lower corners for supporting a pair of parallel horizontal beams 116. The beams have upper flanges with longitudinal slots 118 to which the bottom flanges 82 of the lower clamps 76, 78 are bolted.At least two bolts pass through each slot 118 so that, when the bolts are slackened and the clamp halves disconnected from each other, each clamp half is free to slide independently upon the beams 116 but is maintained in a substantially fixed angular orientation, with its bottom flange in the plane of the beams 116.

A depending probe 120 is provided for supporting one end of the top frame 102 on the upper end of one of the conductor pipes 34. The other end of the top frame 102 is supported on the other conductor pipe by an I - shaped saddle 122, vertically adjustable relative to the top frame 102 by a screw jack 124 for levelling the beams 116 to the horizontal. The lower clamp halves can thus be guided into position for installation about the conductor pipes at the correct height, in the correct angular orientation, and horizontally aligned with one another. As the tool is lowered, the clamp halves preferably remain firmly bolted to the beams 116 at the correct spacing for engagement over the ends of the conductor pipes 34. To remove the installation tool 101 once the lower clamp halves have been secured together about the conductor pipes 34 by the studs 88, the bolted connections between the beam 116 upper flanges and the clamp bottom flanges 82 are completely removed. The side frames 106 are then swung outwardly, allowing the beams 116 to clear the clamp bottom flanges 82.

Claims (20)

CLAIMS.

1. A structure for the protection of subsea oilfield equipment against snagging damage, comprising a protective shield having a coupling for engagement with the equipment to secure the shield in place.

2. A structure as claimed in claim 1 wherein the coupling comprises a clamp engageable with the equipment.

3. A structure as claimed in claim 2 wherein the clamp is adapted to be secured to a conductor pipe.

4. A structure as claimed in any preceding claim comprising lower and upper clamps attached to the equipment with a collar secured to the shield sandwiched between them.

5. A structure as claimed in claim 4 securable to a plurality of conductor pipes by corresponding numbers of lower and upper clamps and collars.

6. A structure as claimed in claim 5 wherein one of the clamps is a close fit with its co-operating collar and a first conductor pipe, permitting substantially no lateral movement between the collar and the first pipe in any direction.

7. A structure as claimed in claim 6 wherein a second clamp is a loose fit with its collar along an axis aligned with the first pipe and a close fit with its collar in a direction perpendicular to that axis, whereby the structure is substantially fixed against movement perpendicular to the axis but variation in the spacing of the pipes along that axis can be accommodated.

8. A structure as claimed in claim 7 wherein clamps and collars for further conductor pipes are made a loose fit in all horizontal directions.

9. A structure as claimed in any of claims 2 - 8 wherein the or each clamp is secured to the structure by a fixed connection.

10. A structure as claimed in any preceding claim comprising outwardly extending deflector legs hingedly connected to the remainder of the structure.

11. A structure as claimed in any preceding claim comprising telescopic support legs.

12. An installation tool for running and locating a clamp on a piece of subsea equipment, comprising a seating for location on the equipment and a holder for the clamp disposed at a predetermined spacing from the seating for proper location of the clamp relative to the equipment.

13. A tool as claimed in claim 12 comprising a probe for engagement with the end of a first conductor pipe and an adjustable height saddle for location on the end of a second conductor pipe,whereby the tool may be properly levelled with respect to the pipes.

14. A tool as claimed in claim 12 or 13 provided with means to maintain the or each clamp in a fixed angular alignment with respect to the equipment.

15. A tool as claimed in any of claims 12 - 14 wherein the holder comprises a pair of horizontal beams for supporting a pair of clamps in horizontal alignment for installation about respective conductor pipes.

16. A tool as claimed in claim 15 wherein the beams comprise longitudinal slots engaged by projections extending from the clamps.

17. tool as claimed in any of claims 12 - 16 wherein the holder is mounted on a swing arm for disengagement from the clamp after installation.

18. A structure for the protection of subsea oilfield equipment against snagging damage substantially as described herein with reference to or as shown in figures 1 - 15 of the drawings.

19. An installation tool for running and locating a clamp on a piece of subsea equipment substantially as described herein with reference to or as shown in figures 16 -19 of the drawings.

20. A structure as claimed in any of claims 1 - 11 comprising a box section framework.