GB2297337A

GB2297337A - A riser assembly

Info

Publication number: GB2297337A
Application number: GB9600085A
Authority: GB
Inventors: Philip Head
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-01-27
Filing date: 1996-01-04
Publication date: 1996-07-31
Anticipated expiration: 2016-01-04
Also published as: GB2297337B; GB9600085D0; GB9501642D0; AU4200896A; NO960248D0; GB9514230D0; NO960248L

Description

A Method of Accessing a Sub Sea Well and Apparatus therefore This invention relates to accessing a sub sea oil production well. Such access is required for a number of reasons for example to take further measurements of the reservoir by introducing logging devices, for servicing or installation of electric submersible pumps to enhance production rates or for many other reasons.

Typically for a sub sea production well the original drilling platform will have been removed and the well head will have to be accessed by means of a suitable surface vessel. In order that the required operations can be carried out to the well it is necessary that the movement of the vessel which is floating on the surface of the sea is compensated for to ensure positional consistency with respect to the well itself which is fixed on the sea bed.

This is conventionally provided by means of a heave compensation system on the vessel itself which is extremely cumbersome and expensive.

Preferably the method and apparatus of the present invention will be used with continuous coiled tubing which is advantageous in the speed of deployment but is typically limited in the diameter of tube which can be accommodated. This limits the extent to which certain operations can be carried out using coiled tubing because of the requirement for the larger tube size which is only available by using jointed drill pipe.

Traditionally the outer tubing for intervention purposes has been typically 7 inches in diameter when it necessary to carry out operations which require tool strings and other equipment which necessarily have a diameter of typically 7 inches. This outer tubing is called a riser and is conventionally made of jointed sections. Coiled tubing on the other hand is only available economically at a maximum diameter of 4.5 inches and it is therefore not possible to use continuous coiled tubing as the riser because it has insufficient diameter to contain the tool string and equipment and therefore carry out well intervention operations which require the use of tool strings and equipment having a diameter greater than 4.5 inches.Typically in the present state of the art continuous coiled tubing will be used as the inner tubing which enters the well itself inside the riser to carry out the various intervention operations that are required.

There are a number of disadvantages to the use of a jointed riser. These are that the surface vessel has to be located and anchored accurately above the well head, this can be a very time consuming operation. It will be appreciated that in well intervention operations a large proportion of the cost arises from the hire charges, or lease charges, or cost of capital whatever the financial arrangement, of the expensive capital equipment, as well as the labour cost off shore. The time spent carrying out the required operations has therefore a critical effect on costs. In addition to the task of accurately anchoring the surface vessel it is also necessary to include heave compensation systems to compensate for the movement of the relatively fixed riser and the surface vessel which will rise and fall with the swell of the sea.

It is the purpose of the invention to enable such well intervention operations to be carried out using smaller diameter coiled tubing as the riser instead of the existing methods of using jointed tubing.

An objective of the invention is to overcome this disadvantage to allow a greater number of operations to be carried out using continuous coiled tubing.

By means of the invention a method and apparatus has been devised which also provides positional consistency between the well head and the vessel without the need for an expensive heave compensation system on the vessel. The apparatus and method according to the invention also ensures that there is no damage caused to the well head by bending moments applied by movement of the piping connecting it to the surface vessel.

According to the invention there is provided a riser assembly which is intended to be fixedly connected to a well head and which comprises a well intervention tube and a first continuous coiled riser tube which connects the well head to a surface vessel and also comprises a length of a second tube which runs along at least a portion of the first riser tube from the well head to the surface vessel and which is attached to said riser tube.

According to the invention the first riser tube and the second riser tube are preferably attached together by means of a separate attaching means.

According to a further aspect of the invention the second riser tube will be installed on a reel as continuous tubing and connected by means of suitable wrapping material to the first riser tubing which will also be in the form of continuous tubing to enable speedy implementation of the riser assembly as a whole.

The attaching means will preferably be in the form of a clamp which may be removable.

The second tube may comprises a chamber which is capable of being evacuated of water and filled with air or another suitable fluid in order to control the buoyancy provided to the riser assembly as a whole.

Alternatively at least one of the first and second riser tubes can be connected intermittently to support buoys along its length. These buoys may be attached as the riser tubes are being unreeled from the continuous tubing reel.

The support buoys are preferably connected to the first and second riser tubes by air line tubes which enable air to be removed from and added to the support buoys to adjust the amount of buoyancy they provide. The support buoys air lines are preferably connected to a main air line running along side or within the first and second riser tubes and may be connected thereto by clamps which may be the same clamps which hold the two riser tubes together.

The second riser tube may also comprise conduits within it such as a hydraulic line and electrical and power signal lines to operate equipment at the well head such as the blow out preventer. The second riser tube may also include a conduit which carries air or another suitable fluid (the control fluid) for adjusting the amount of buoyancy provided by other buoys in the riser assembly as a whole.

According to a further aspect of the invention the second riser tube is also connected to at least one guide buoy which can be evacuated and refilled to align the riser assembly accurately above the well head. In addition the second tube is connected to at least one well head buoy may be evacuated to apply an upward tensile force to the well head to prevent bending of the well head.

According to a further aspect of the invention the first and second riser tubes may be wrapped around each other. In addition a third riser tube may be used and wrapped together with the first and second riser tubes. This provides additional strength and also reduces the effects of ocean currents by vortex shedding to reduce vibration induced in the system. The third riser tube may alternatively be located concentrically with respect to the first and second riser tubes forming an additional barrier to prevent environmental damage in the event of a disaster.

According to a further aspect of the invention at least one of the riser tubes may be contained inside one or two of the other riser tubes. Conduits may be provided in the annular space or spaces provided between the concentrically arranged riser tubes. Such conduits may preferably be arranged to be wrapped around the outside diameter of the inner riser tube in the form of a helix.

According to a further aspect of the invention there is provided at least two support buoys which are connected by guide lines to the coiled tubing at intermittent points along its length, the guide lines also connect the buoys to each other and also to the riser assembly and the vessel.

According to a further aspect of the invention the riser assembly includes a blow out preventer and a flex or stress joint as a safety precaution to prevent any bending moment in the riser being transmitted to the well head.

According to a further aspect of the invention the support buoys as well as the guide buoys and the well head buoys will be constructed to permit the evacuation and refilling of water to adjust the buoyancy effect. They may preferably comprise a system to admit a controlled amount air or another suitable fluid (the control fluid) which is lighter or heavier than water.

According to a further aspect of the invention the buoys will comprise two chambers separated by a piston. The first chamber will contain the control fluid and the second chamber will contain water. Furthermore the buoy will have an exit valve to allow the control fluid to escape from the buoy. The buoy will also comprise an inlet valve to allow the control fluid to enter the buoy. The buoy will also have a inlet and outlet control valve for the water.

According to a further aspect of the invention the tubing buoy and support buoys are adjusted to ensure the desired profile of the well intervention tube necessary for the ready transmission of equipment and instruments down the well. The bending of well intervention tube thus automatically accounting for the ocean heave avoiding the requirement for a heave compensation system.

According to the invention an apparatus for accessing a sub sea well comprising a surface vessel and a riser assembly which is to be fixedly attached to a well, wherein the riser assembly comprises a continuous length of coiled tubing which extends from the well head to the surface vessel and that support buoys are provided attached to the coiled tubing along its length to provide support for the coiled tubing and maintain it in a smooth continuous curve permitting equipment to be transmitted inside between the surface vessel and the well.

The support buoys have adjustable buoyancy by evacuation or filling of the buoys which is controlled remotely from the surface vessel to maintain the coiling tubing of the continuous riser in a smooth continuous curve. The support buoys also comprise pressure sensors which relay information on the condition and position of the support buoys to the surface vessel. They may also comprise a highly magnetised component which can be detected by sensing means on the vessel, this providing an image of the positions of all the support buoys and therefore of the profile of the riser.

There is now described a detailed embodiment of the invention, in which the well intervention tubing is shown by way of example only as coiled tubing, with reference to the accompanying drawings in which: Fig. 1 is an elevation of the riser assembly and the coiled tubing reel on the vessel, Fig. 2 is a cross section of the first riser tube connected to the second riser tube, Fig. 3 is a longitudinal cross section through the line WW in fig. 2, Fig. 4 is a front view the coiled tubing reel with the first and second riser tubes joined together, Fig. 5 is a cross section through the one of the buoys.

Fig. 6 is an elevation of a riser tubing arrangement according to a further embodiment of the invention including three riser tubes, Fig. 7 is a cross section through XX of the embodiment of Fig. 6, Fig. 8 is a longitudinal cross section of a riser tubing arrangement according to a further embodiment of the invention, Fig. 9 is a cross section through YY of a further development of the embodiment of Fig. 8, Fig. 10 is a cross section through YY of a further development of the embodiment of Fig. 8, Fig. 11 is a cross section through YY of a further development of the embodiment of Fig. 8.

Referring to figure 1 there is provided a riser assembly 1 which is intended to be fixedly connected to the well head 2 and which comprises a first riser tube 4 and a second riser tube 8 which connects the well head 2 to a surface vessel 6. The first riser tube 4, also being the well intervention tube in this embodiment, is used to access the well and allow for the introduction of instrumentation or electric submersible pumps or other equipment into the well to carry out the numerous required operations to monitor, maintain and enhance the production of oil and gas from the well.

The riser assembly 1 comprising the length of second riser tube 8 is comprised of an additional tube running along at least a portion of the first riser tube 4 from the well head 2 to a surface vessel 6 and which is attached to said first riser tube 4. Referring to figure 2 the second riser tube 8 is attached to the first riser tube 4 by means of a clamp 9.

The first riser tube 4 comprises a hollow chamber 5 which is preferably free from obstruction to allow the passage of equipment down to the well.

The second riser tube 8 comprises a chamber 10 which is capable of being evacuated of water and filled with air or another suitable fluid in order to control the buoyancy provided to the riser assembly 1 as a whole. By this means the necessity to provide additional buoys attached to the riser tubes is avoided. This is advantageous because it is sometimes not practical to include the separate support buoys on the coiled tubing reel and the requirement to attach separate support buoys during the deployment of the tubing would be disadvantageously time consuming during deployment.

Alternatively the riser can be connected intermittently to support buoys along its length. These buoys may be attached as the riser is being unreeled from the continuous tubing reel by means of specially adapted attaching means which allow for the speedy attachment of the support buoys to the riser assembly.

The second riser tube 8 will also comprise conduits 12 within it such as a hydraulic line and electrical and power signal lines to operate equipment at the well head 2. The second riser tube 8 will also include a conduit 14 which carries air or another suitable fluid for adjusting the amount of buoyancy provided by other support, well head and guide buoys 22, 18, 16 in the riser assembly 1 as a whole. Air conduits 13, 15 may also be provided on the outside of the first and second riser tubes 4, 8.

Referring again to figure 1, the second riser tube 8 is also connected to at least one guide buoy 16 which can be evacuated and refilled to align the riser assembly 1 accurately above the well head 2. In addition the second riser tube 8 is connected to at least one well head buoy 18 which may be evacuated to apply an upward tensile force to the well head 2 to prevent bending of the well head 2.

Referring to figure 3 the support buoys 22 are preferably connected to the first and second riser tubes 4, 8 by air line tubes 13 which enable air to be removed from and added to the support buoys 22 to adjust the amount of buoyancy they provide. The support buoys air lines 13 are preferably connected to a main air line 15 running along side or within the first and second riser tubes 4, 8 and may be connected thereto by clamps 17. In this embodiment the clamps 17 are the same as the clamps 9 which hold the two riser tubes 4, 8 together.

Referring to figure 4 the second tube 8 is installed on a reel 26 as continuous tubing and connected by means of suitable wrapping material or a clamp 9 to the well intervention tube 4 which will also be in the form of continuous tubing to enable speedy implementation of the riser assembly 1 as a whole.

Referring to figure 5 the support buoys 22 as well as the guide buoys 16 and the well head buoys 18 will be constructed to permit the evacuation and refilling of water to adjust the buoyancy effect. The will preferably comprise a system to admit a controlled amount of air or another suitable fluid which is lighter or heavier than water.

The support, guide or well head buoys, 22, 16, 18 will comprise two chambers 31, 32 separated by a piston 30. The first chamber 31 will contain the control fluid and the second chamber 32 will contain water.

Furthermore the buoy(s) will have an exit valve 33 to allow the control fluid to escape from the buoy 16, 18, 22. The buoy 16, 18, 22 will also comprise an inlet valve 34 to allow the control fluid to enter the buoy.

Various pressure sensors 38 are preferably positioned on the buoys 22, 16, 18 and in particular the support buoys 22 to relay information of the position and condition of the buoys to the control room at the surface. The support buoys 22 may also comprise a highly magnetised component which can be detected by sensing means on the vessel, this providing an image of the positions of all the support buoys and therefore of the profile of the riser.

Referring to figs. 6 to 11 the first and second riser tubes may be wrapped around each other in the form of a helix. Referring to fig. 6 a third riser tube 46 may be used and wrapped together with the first and second riser tubes 44, 48. This also provides additional strength and reduces the effects of ocean currents by vortex shedding to reduce vibration induced in the system. Referring to figure 10, the third riser tube may alternatively be located concentrically with respect to the first and second riser tubes forming an additional barrier to prevent environmental damage in the event of a disaster.

Referring to Figs. 8 to 11 at least one of the riser tubes 48, may be contained inside one or two of the other riser tubes 44. Conduits 412 may be provided in the annular space or spaces provided between the concentrically arranged riser tubes 44, 48. Such conduits may preferably be arranged to be wrapped around the outside diameter of the inner riser tube 48 in the form of a helix.

There are also support buoys 22 which are connected by guide lines 24 to the second tube 8 and well intervention tubing 4 at intermittent points along the length, the guide lines 24 also connect the support buoys 22 to each other in the event that there are more than one and also to the riser assembly 1 and the vessel 6.

The riser assembly 1 also may include a blow out preventer 20 and a flex or stress joint 21 as a safety precaution to prevent any bending moment in the riser assembly 1 being transmitted to the well head 2.

The tubing buoy 8 and support buoys 22 are adjusted to ensure the desired profile of the well intervention tube necessary for the ready transmission of equipment and instruments down the well. The bending of well intervention tubing thus automatically accounting for the ocean heave avoiding the requirement for a heave compensation system.

Claims

1. A riser assembly 1 which is intended to be fixedly connected to the well head 2 and which comprises a continuous coiled well intervention tube 3 comprising a first riser tube 4 which connects the well head 2 to a surface vessel 6, characterised in that the first riser tube 4 is comprised of continuous coiled tubing.

2. A riser assembly according to claim 1 characterised in that the riser assembly also comprises a length of a second continuous coiled riser tube 8 which runs along at least a portion of the first riser tube 4 from the well head 2 to a surface vessel 6.

3. A riser assembly according to claim 1 characterised in that the second riser tube 8 is attached to said first riser tube 4.

4. A riser assembly according to claim 3, characterised in that the second riser tube 8 is attached to the first riser tube 4 by means of a separate attaching means 9.

5. A riser assembly according to claim 4, characterised in that the attaching means 9 is a clamp or wrapping material.

6. A riser assembly according to either claim 2 or claim 3, characterised in that the second riser tube 8 comprises a chamber 10 which is capable of being evacuated of water and filled with air or another suitable fluid in order to control the buoyancy provided to the riser assembly 1 as a whole.

7. A riser assembly according to any one of the preceding claims, characterised in that the second riser tube 8 comprises conduits 12 within it such as a hydraulic line and electrical and power signal lines to operate equipment at the well head 2.

8. A riser assembly according to any one of the preceding claims, characterised in that the second riser tube 8 also includes a conduit 14 which carries air or another suitable fluid for adjusting the amount of buoyancy provided by other support, well head and guide buoys in the riser assembly 1 as a whole.

9. A riser assembly according to any one of the preceding claims, characterised in that the second riser tube 8 is connected to at least one guide buoy 16 which can be evacuated and refilled to align the riser assembly accurately above the well head 2.

10. A riser assembly according to any one of the preceding claims, characterised in that the second riser tube 8 is connected to at least one well head buoy 18 which may be evacuated to apply an upward tensile force to the well head 2 to prevent bending of the well head 2.

11. A riser assembly according to any one of the preceding claims, characterised in that there is provided at least one support buoy 22 which is connected by guide lines 24 to the second or first riser tubes 4, 8 at intermittent points along its length.

12. A riser assembly according to any one of the preceding claims, characterised in that the guide lines 24 also connect the support buoys 22 to each other, in the event that there are more than one, and also to the riser assembly 1 and the vessel 6.

13. A riser assembly according to any one of the preceding claims, characterised in that the support buoys 22 are connected to the first and second riser tubes 4, 8 by air line tubes 13 which enable air to be removed from and added to the support buoys 22 to adjust the amount of buoyancy they provide.

14. A riser assembly according to claim 13, characterised in that the air lines 13 of the support buoys 22 are connected to a main air line 15 which runs along side or within the first and second riser tubes 4, 8.

15 A riser assembly according to claim 13, characterised in that the air lines 13 are connected to the riser tubes 4, 8 by clamps 17.

16. A riser assembly according to any one of the preceding claims, characterised in that the riser assembly 1 includes a blow out preventer 20 and a flex or stress joint 21 as a safety precaution to prevent any bending moment in the riser assembly 1 being transmitted to the well head 2.

17. A riser assembly according to any one of the preceding claims, characterised in that the second tube 8 is installed on a reel 26 as continuous tubing and connected by means of suitable wrapping material to the well intervention tube 4 which is also in the form of continuous tubing to enable speedy implementation of the riser assembly 1 as a whole.

18. A riser assembly according to any one of the preceding claims, characterised in that the first and second riser tubes 4, 8 are wrapped around each other in the form of a helix.

19. A riser assembly according to any one of the preceding claims, characterised in that a third riser tube 46 is used together with the first and second riser tubes 44, 48.

20. A riser assembly according to any one of claims 2 to 19, characterised in that at least one of the riser tubes 48 is contained inside one or two of the other riser tubes 44.

21. A riser assembly according to claim 20, characterised in that conduits 412 are provided in the annular space or spaces provided between the concentrically arranged riser tubes.

22. A riser assembly according to claim 21, characterised in that conduits 412 are arranged to be wrapped around the outside diameter of the inner riser tube in the form of a helix.

23. A riser assembly according to any one of the preceding claims, characterised in that the second tube 8 and support buoys 22 are adjusted to ensure the desired profile of the well intervention tube necessary for the ready transmission of equipment and instruments down the well such that the bending of well intervention tubing automatically accounts for the ocean heave avoiding the requirement for a heave compensation system.

24. An apparatus for accessing a sub sea well comprising a surface vessel 6 and a riser assembly 1 which is to be fixedly attached to a well head 2, characterised in that the riser assembly 1 comprises a continuous length of coiled tubing 4 which extends from the well head to the surface vessel 6 and that support buoys 22 are provided attached to the coiled tubing 4 along its length to provide support for the coiled tubing 4 and maintain it in a smooth continuous curve permitting equipment to be transmitted inside between the surface vessel 6 and the well.

25. An apparatus according to claim 21, characterised in that the support buoys 22 have adjustable buoyancy by evacuation or filling of the buoys which is controlled remotely from the surface vessel 6 to maintain the coiling tubing 4 of the continuous riser 1 in a smooth continuous curve.

26. An apparatus according to claim 22, characterised in that the support buoys also comprise pressure sensors 38 which relay information on the condition and position of the support buoys 22 to the surface vessel 6.

27. An apparatus according to claim 21, characterised in that the support buoys are attached to the coiled tubing riser as the coiled tubing is unwound from its reel by means of a quick attaching mechanism.