GB2451958A

GB2451958A - Riser connector with heave compensation

Info

Publication number: GB2451958A
Application number: GB0814975A
Authority: GB
Inventors: Bjorn Bro Sorenson
Original assignee: Grenland Group Technology AS
Current assignee: Grenland Group Technology AS
Priority date: 2007-08-17
Filing date: 2008-08-15
Publication date: 2009-02-18
Anticipated expiration: 2028-08-15
Also published as: BRPI0815538B1; DK2176506T3; GB0716130D0; GB2451958B; GB0814975D0; EP2176506A2; WO2009024760A2; EP2176506B1; WO2009024760A3; BRPI0815538A2

Abstract

A connector assembly for use on a vessel to eliminate relative vertical movement (heave) between the vessel and a riser (20, fig 4) attached to a sub-sea well, includes a first connector part 4 to be secured to the riser (20, fig 4) and a second connector part 3 to be secured to the vessel. The second connector part 3 is connectable to the first connector part 4 without relative axial movement and disconnectable from the first connector part 4 to allow relative axial movement between the first 4 and second 3 connector parts. There is also an alignment mechanism 30 which, when the first 4 and second 3 connector parts are disconnected, maintains the connector parts 4, 3 in axial alignment and spaced apart in a non-sealed manner by a gap the size of which varies with relative axial movement of the first 4 and second 3 connector parts.

Description

CONNECTOR ASSEMBLY

This invention relates to a connector assembly for use on a vessel to eliminate relative vertical movement between the vessel arid equipment attached to a nser attached to a sub-sea well.

in oil and gas drilling operations there are various techniques for inserting or removing tubing or pipes or lines into or from wells. Well intervention techniques include the use of coiled tubing, wirelines or a process where individual pipe sections are screwed together to form a continuous pipe in the well, also called snubbing. In a coiled tubing intervention, a continuous tube initially wound on a spooi is unwound, straightened and pushed down a hole. In order to do this various items of equipment are located in the area above the well, all supported on a common frame. A typical set-up involves, from top to bottom, a goose neck for guiding and straightening the coiled tubing as it is fed from the spool, an injector head for pushing the tubing into or pulling it out of the well, a stuffing box to form a seal around the tubing, and a blow out preventer. There may be additional components depending on specifics of the operation performed. The blow out preventer itself may consist of a number of components, such as a pipe ram, a slip ram, a shear ram and a blind ram.

Regarding well intervention being performed from a floating vessel in a sub sea well, it is necessary to prepare or rig up all the equipment on top of a riser, which is attached to the top of the well at the sea floor. The riser extends from the top of the well at the sea floor, up to the work-deck of the vessel. The length of the riser depends on the sea depth and may be considerable, so in order to prevent it from collapsing it is supported by a tensioning mechanism attached to the vessel.

The tensioning mechanism compensates for the vessel's heave motion, so that the riser is supported without buckling and the top of the riser does not move vertically relative to the sea floor. However, the well intervention equipment on the vessel moves vertically due to heave induced by waves and currents, and this can be a problem when it is desired to perform operation, testing and maintenance of the intervention equipment In order to deal with this problem, it has been proposed in WO 03/067023 to provide a telescopic connection between the nser and the well intervention equipment. One half of the telescope is secured to the top of the riser and the other half of the telescope is secured to the intervention equipment which can then move with the heave motion of the vessel, causing the telescopic parts to slide with respect to each other. Therefore the well intervention equipment can be stationary relative to the structure of the vessel, making preparation, testing and maintenance of the equipment a safer and easier operation than would be the case if it were fixed to the riser and moving relative to the vessel. The system is thus designed to eliminate relative vertical heave motions between the equipment and the vessel.

The known system involves the provision of a low pressure seal during the heave elimination mode and thus requires that the telescoping cylinders have a dynamic sliding seal acting therebetween. The inventor has now recognised that in many well intervention situations there is in fact no need to provide a continuous sealed conduit between the riser and the intervention equipment.

According to the invention there is provided a connector assembly for use on a vessel to eliminate relative vertical movement between the vessel and a riser attached to a sub-sea well, the connector assembly compnsing a first connector part to be secured to the riser, a second connector part to be secured to the vessel, the second connector part being connectable to the first connector ptrt without relative axial movement and disconnectable from the first connector part to allow relative axial movement between the first and second connector parts, and an alignment mechanism which, when the first and second connector parts are disconnected, maintains the connector parts in axial alignment and spaced apart in a non-sealed manner by a gap the size of which varies with relative axial movement of the first and second connector parts.

With such an arrangement, during e.g. well intervention operations the first and second connector parts can be disconnected to allow relative axial movement.

The size of the unsealed gap between the connector parts varies with heave motion but as the connector parts are maintained in axial alignment if it is desired to insert any equipment, such as tubular piping, into the riser then this can still be done even though there is a varying gap. In some situations, therefore, this will be a relatively inexpensive solution to the problem of relative movement of a vessel and a riser due to the vessels heave motion.

Preferably, the alignment mechanism comprises a first support extending laterally from the first connector part, a second support extending laterally from the second connector part, and a guiding device laterally spaced from the first and second connector parts and extending between the first and second supports to maintain the first and second connector parts in axial alignment during relative axial movement thereof. The guiding device may comprise a guide member fixed to one of the first and second supports and movable relative to the other of the supports.

The guide member may be fixed to the first support, but preferably it is fixed to the second support.

A protective casing may be provided for the guiding device. The protective casing may take the form of a cylinder. The guide member of the guiding device may be slidably received in the cylinder.

In a preferred embodiment, a plurality of guiding devices are provided, each laterally spaced from the first and second connector parts. This can help to deal with any lateral or torsional loading. Such plural guiding devices are advantageously equiangularly spaced around the central axis of the first and second connector parts.

In a preferred embodiment three guiding devices are provided. There may thus be a plurality of guiding devices disposed laterally outwardly of the connector parts. In order to protect the guiding devices from impacting with other equipment, e.g. in the moon-pool area of the vessel, a protective shield member may be disposed laterally outwardly of the plurality of guiding devices. Such a shield member is preferably generally cylindrical.

The first support may be provided with a flange for connecting it to the first connector, which may have a corresponding flange. The second support may be provided with a flange for connection to the second connector, which may have a corresponding flange.

The first and second connector parts may belong to a quick latch connector of a known type. Such connectors involve one tubular portion mating within another tubular portion and a locking mechanism and a sealing system which is automatically engaged and energized as the two mating halves are brought together by an axial force. The locking mechanism may be released and the seal de-energized by applying hydraulic pressure supplied through a hydraulic line, as long as there is no internal pressure nor axial tension force applied. When it is desired to separate the connector parts, the pressure applied and the two connector parts can be separated by moving them axially apart.

Part of the alignment mechanism of the connector assembly will be fixed relative to the riser and the other part will be fixed relative to the vessel, the two parts being moveable with respect to each other. The alignment mechanism may have at least one clamp for attachment to the riser. In order to provide a stable arrangement, a plurality (e.g. two) of vertically spaced clamps may be provided.

Where a protective casing for a guiding device is provided, and where one or more clamps are provided to secure the alignment mechanism to the riser, then the or each clamp may act as a support(s) for the protective casing.

A preferred embodiment of the invention may now be described by way of example and with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a connector assembly according to the invention; Figure 2 is an enlargement of detail "II" in Figure 1; Figure 3 is an enlargement of detail VIII" in Figure 1; and Figure 4 is an enlargement of detail "IV" in Figure 1.

The connector assembly consists of a first or lower connector part 4 and a second or upper connector part 3. The two connector parts are supported by an alignment mechanism 30 which is arranged to maintain the connector parts in axial alignment whilst they move towards and away from each other. As will be described further below, during such relative vertical movement of the lower and upper connector parts, the lower connector part 4 is in a stationary position relative to a riser, whilst the upper connector part 3 is in a stationary position relative to a vessel.

Referring to Figures 1 and 3, an uppermost section 20 of an intervention riser has a lower flange 21 attached to the next lower section of the intervention riser (not shown), with further sections being provided below to make up the distance down to the well head at the sea floor. The lower end of the complete riser assembly is then attached to the top of the well. At the upper end of the upper intervention riser section 20 a flange 14 is provided (see Figure 3).

The alignment mechanism 30 is secured to the upper riser section 20 by means of an upper clamp 16 and a lower clamp 17. Each clamp supports three vertically extending protection casings 15, arranged at equal circumferential spacings around the riser section 20. Outwardly of the three casings a protection cap 18 protects the casings 15 (and an umbilical if required) against contact with other equipment. The protection cap 18 is only partiy shown in Figure 1.

The alignment mechanism 30 further has three vertical guide members 5, each slidably received in a respective casing 15. At the top of the guide members 5 an upper support 2 is provided. The upper support has an upper flange 1 for connection to the lower end of intervention equipment, such as a blow-out preventer or similar, either directly, or via an extension joint. Typically, the intervention equipment is supported by a frame. Neither the intervention equipment nor the frame is shown in the drawings. The upper support 2 is provided with a lower flange 12 which is connected to an upper flange 10 of the upper connector part 3.

When the upper and lower connector parts 3, 4 are to move relative to each other, then the upper support 2 is fixed relative to the vessel by virtue of its connection to the intervention equipment via upper flange 1.

A lower support 6 is formed with three vertical openings 23 through which the three guide members 5 extend in a relatively slidable manner. The lower support 6 has a lower flange 7 secured to the upper flange 14 of the riser section 20, and an upper flange 13 secured to a lower flange 11 of the lower connector part 4. Thus, the lower support 6 is fixed relative to the riser, whilst the upper support 2 is moveable relative to the lower support by virtue of the guide members 5 sliding within openings 23.

When in operation in the well, the connector parts 3 and 4 (which in this embodiment make up a quick latch connector) are fixed together and the complete riser including the connector is pressunzed, hence the complete stack moves vertically relative to the vessel as it heaves. In this situation the two parts of the quick latch connector 3 and 4 are engaged into each other, making a pressure tight connection. When no operation is ongoing in the well, valves further down in the riser and well are closed, and the pressure in the upper part of the riser stack can be flushed clean and purged by an inert gas before being bled off. Once bled off, the quick latch locking mechanism is remotely operated by means of hydraulics, and the quick latch connector parts 3 and 4 can be separated by hoisting the tensionilifiing frame upwards by means of a hoist or jack attached to the vessel structure.

When separated, the upper connector part 3 will still be laterally centred above the lower connector part 4, by means of the sliding lower support 6, attached to the lower part 4, sliding along the three vertical guide members 5 which are all fixed to the upper support 2, which is attached to the upper connector part 3. The upper and lower connector parts are separated by an axial gap in non-sealed manner.

All three guides are protected by the three separate protection casings 15, attached to the upper intervention riser section by means of the upper guide clamp 16 and the lower guide clamp 17.

As the riser moves vertically relative to the vessel's structure, the upper connector part 3 and the attached lifting/tensioning frame together with the intervention equipment, is no longer attached to, and is not moving together with, the riser. It can now be parked in a fixed position with no relative movements to the vessel's structure. This fixed parked position without any relative movements allows preparation and maintenance work to be performed in a safe manner. This in turn will increase the operational window of the intervention vessel as the requirements for calm wave and wind conditions are reduced. As the vessel heaves, the size of the axial gap between the upper and lower connector parts varies.

Claims

1 A connector assembly for use on a vessel to eliminate relative vertical movement between the vessel and a riser attached to a sub-sea well, the connector assembly comprising a first connector part to be secured to the riser, a second connector part to be secured to the vessel, the second connector part being connectable to the first connector part without relative axial movement and disconnectable from the first connector part to allow relative axial movement between the first and second connector parts, and an alignment mechanism which, when the first and second connector parts are disconnected, maintains the connector parts in axial alignment and spaced apart in a non-sealed manner by a gap the size of which varies with relative axial movement of the first and second connector parts.

2. A connector assembly as claimed in claim 1, wherein the alignment mechanism comprises a first support extending laterally from the first connector part, a second support extending laterally from the second connector part, and a guiding device laterally spaced from the first and second connector parts and extending between the first and second supports to maintain the first and second connector parts in axial alignment during relative axial movement thereof

3. A connector assembly as claimed in claim 2, wherein the guiding device comprises a guide member fixed to one of the first and second supports and movable relative to the other of the supports.

4. A connector assembly as claimed in claim 3, wherein the guide member is fixed to the second support.

5. A connector assembly as claimed in claim 2, 3 or 4, comprising a protective casing for the guiding device.

6. A connector assembly as claimed in any of claim 2 to 5, comprising a plurality of guiding devices each laterally spaced from the first and second connector parts.

7. A connector assembly as claimed in claim 6, comprising a protective shield member disposed laterally outwardly of the plurality of guiding devices.

8. A connector assembly as claimed in any of claims 2 to 7, wherein the first support is provided with a flange for connection to the first connector.

9. A connector assembly as claimed in any of claims 2 to 8, wherein the second support is provided with a flange for connection to the second connector.

10. A connector assembly as claimed in any preceding claim, wherein the alignment mechanism has at least one clamp for attachment to the riser.

11. A connector assembly as claimed in claim 10, wherein the alignment mechanism has at least two clamps which are axially spaced apart for attachment to the riser at respective vertical positions.

12. A connector assembly substantially as hereinbefore described with reference to the accompanying drawings.