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(11) | EP 2 871 285 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Device and method for performing well interventions offshore |
| (57) The invention relates to a device for performing well interventions offshore. The
device comprises a jack-up platform which comprises a height-adjustable horizontal
work deck which is supported by vertical legs supporting on an underwater bottom;
a frame of frame parts connected rigidly to each other which comprises at least two
horizontal frame floors of mutually connected frame floor parts, which frame is connected
with a work deck part to the work deck for movement in horizontal directions over
the work deck, and which frame protrudes with an operative part beyond a side edge
of the work deck. The invention also relates to a method for performing well interventions
offshore making use of the invented device.
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[0002] Offshore oil and gas platforms are designed for decades of use. Oil and gas wells are becoming depleted, which creates a need on the one hand to extend the lifespan of these wells and on the other to deactivate and dismantle the wells (well plug and abandonment). These operations can be performed by means of well interventions.
[0003] Well interventions are currently performed by relatively large jack-up platforms supported by three lattice legs with diameters of 6-8 m and more. These were originally designed for the purpose of drilling to oil and gas wells but are increasingly also being applied to perform well interventions. The existing platforms are not easily displaceable and often lack a design suitable for well interventions.
[0004] The above stated trend has created a need to be able to perform well interventions in an efficient and flexible manner. Well interventions can for instance comprise of closing a well, wherein a well is cleaned and filled with a suitable material such as cement, after which the borehole casing is sawn off. Other well interventions comprise maintenance to a borehole, such as taking samples from the wall of the borehole, surveying and logging in order to be able to determine the residual capacity of the well, arranging small explosive charges in order to allow new oil to flow to the borehole, and the like.
[0005] The invention provides for this purpose a device comprising a jack-up platform which comprises a height-adjustable horizontal work deck which is supported by vertical legs supporting on an underwater bottom; and further a frame of frame parts connected rigidly to each other which is configured to support well intervention equipment and comprises for this purpose at least two horizontal frame floors of mutually connected frame floor parts; wherein the frame is connected with a work deck part to the work deck for movement in horizontal directions over the work deck, and the frame protrudes with an operative part beyond a side edge of the work deck.
[0006] The device according to the invention allows, among other actions, a safe assembly of well intervention equipment at a position which can be far removed from the well in which intervention is to take place. Making use of a relatively light jack-up platform which can be transported quickly and is preferably provided with four or more legs with a diameter of a maximum of 4 m further makes it possible to perform a well intervention in rapid and efficient manner. A stable support surface for the frame is obtained by providing the platform with at least four legs. Well intervention equipment can moreover be placed precisely above a well in which intervention is to take place by making use of a frame which is connected with a work deck part to the work deck for movement in horizontal directions over the work deck and which protrudes with an operative part beyond a side edge of the work deck.
[0007] Provided in an embodiment for the purpose of further increasing the positioning precision and reducing the risk of damage to for instance the oil well itself is a device wherein the jack-up platform comprises a Dynamic Positioning platform configured to position itself independently by means of rotatable thruster bodies.
[0008] In an embodiment of the invention a device is provided wherein the work deck of the jack-up platform comprises a lifting means configured to lift a load of between 200 and 1000 tons at a distance ranging between 5 and 50 m, preferably to lift a load of between 500 and 900 tons at a distance ranging between 10 and 40 m, and most preferably to lift a load of between 600 and 800 tons at a distance ranging between 20 and 30 m. Not only can components of well intervention means be taken up and placed in the frame using such a lifting means, components of a borehole of great length can also be pulled to a position above the water surface. A suitable lifting means comprises a crane connected to the work deck for pivoting around a vertical axis. This crane can comprise an upward oriented support arm to which a main boom is pivotally connected. The main boom is provided at the free outer end thereof with a hoisting tackle and can be luffed in and luffed out by means of traction cables.
[0009] In an embodiment of the invention a device is provided wherein the work deck has a thickness and the protruding part of the frame extends vertically along the work deck in the thickness direction thereof. In this embodiment a horizontal frame floor of the protruding part is situated at a level below the upper surface of the work deck, this for instance increasing the accessibility of the well to divers.
[0010] This accessibility is further increased by an embodiment of the device wherein the protruding part of the frame has more horizontal frame floors of mutually connected frame floor parts than the work deck part, and by another embodiment wherein the frame has a width and the protruding part of the frame comprises a horizontal frame floor extending beyond the width.
[0011] A practical embodiment of the invention is characterized in that the work deck part of the frame comprises two horizontal floors and the protruding part of the frame comprises three horizontal floors.
[0012] The frame floors are configured to be able to support well intervention equipment. An embodiment of the invention proposes a device wherein an upper horizontal floor of the frame comprises a coiled tubing injector which is connected to frame parts. Provided in another embodiment of the invention is a device wherein a middle floor extends in the plane of the work deck of the platform and comprises a riser constructing apparatus which is connected to frame parts. Provided according to a further embodiment of the invention is a device wherein a lowest floor of the protruding part of the frame comprises a riser ring tensioner which is connected to frame parts. With a ring tensioner it becomes possible to hold pipe parts fixedly.
[0013] A frame comprising the above stated upper, middle and lower frame floors in combination provides many practical advantages, wherein specific equipment is arranged for each floor, this requiring specific operations. The operations can hereby be performed in well-organized manner and with little risk of errors and the like.
[0014] Another embodiment of the invention relates to a device wherein a horizontal floor of the frame can be opened. Such a floor allows equipment to be easily arranged in the frame. It is also possible to provide horizontal floors with smaller hatches and passages through which pipes and tubes can for instance be inserted and fixed.
[0015] The loads acting on the frame are preferably transmitted to the work deck via the connection movable over the work deck. In an embodiment of the invention a device is provided wherein the side edge of the work deck comprises a support rail. The support rail provides an edge reinforcement of the work deck and preferably extends over substantially the whole edge length.
[0016] In an alternative embodiment the work deck of the platform can be provided with a (circular) opening or so-called moon pool which provides access to the water present under the work deck 11. In such an embodiment the frame can also be arranged over and in the moon pool, and the peripheral edge of the moon pool is provided with a support rail in the form of a thick-walled plate.
[0017] The mobile connection to the work deck of the platform can be embodied in many ways. In a suitable embodiment the work deck comprises a skidding beam which runs at a distance from and substantially parallel to the support rail and to which the work deck part of the frame is connected movably over the work deck in a direction running substantially parallel to the side edge. The skidding beam is firmly connected to the work deck so as to be able to absorb the relatively great forces. The mutually parallel support rail and skidding beam are configured to absorb a moment of force of at least 800 tons/m, more preferably at least 1000 tons/m and most preferably at least 1200 tons/m.
[0018] In another embodiment of the invention a device is provided wherein the work deck is provided with horizontal skidding beams which run substantially perpendicularly of the support rail and to which the work deck part of the frame is connected movably over the work deck in a direction running substantially perpendicularly of the side edge.
[0019] In both above stated embodiments the frame can for instance be displaced relative to the work deck by means of hydraulic cylinders disposed between the skidding beam(s) and frame parts of the frame.
[0020] Provided for the purpose of enabling still better absorption of the considerable forces is an embodiment wherein the jack-up platform comprises bulkheads under the work deck which preferably run along the underside of the skidding beam(s). In an embodiment the work deck is further provided with storage containers for liquids, for instance liquids which are used during cleaning of a borehole and which are pumped from the well to the work deck. The storage containers are preferably embodied as internal cavities in the work deck.
[0021] In an embodiment of the invention a method is provided for performing well interventions offshore making use of a device according to the invention.
[0022] Another embodiment of the invention relates to a method wherein the device is employed to perform operations above an existing production platform, so-called workover. Existing production platforms preferably comprise a plurality of boreholes which are brought together on the platform. The device is advantageously employed to perform well interventions above such an existing production platform. Owing to the provided option of moving the frame in horizontal directions the different boreholes brought together on the production platform can be readily accessed from one position of the jack-up platform.
[0023] The invention will now be further elucidated with reference to the description of the accompanying figures, without however been limited thereto. In the figures:
Figure 1 is a schematic front view of a device in accordance with an embodiment according to the invention;
Figure 2 is a schematic side view of an embodiment of the device according to the invention;
Figure 3 is a schematic perspective view of the frame of the device in accordance with an embodiment according to the invention shown in figure 1;
Figure 4 is a schematic side view of the embodiment of the frame according to the invention shown in figure 3;
Figure 5 is a schematic front view of the frame according to the invention shown in figures 3 and 4; and
Figure 6 is a schematic side view of another embodiment of the device according to the invention which can be applied for workover operations.
[0024] An embodiment of a device 20 according to the invention is shown with reference to figures 1 and 2. Device 20 comprises a jack-up platform 1 to which a protruding frame 3 is connected. Jack-up platform 1 comprises substantially a horizontal work deck 21 which is supported by four vertical legs 22 (only two of which are visible) supporting on or in an underwater bottom 15. Because it must be possible to displace jack-up platform 1 in simple manner, legs 22 take a relatively light form as hollow tubes with a diameter of a maximum of 4 m. This becomes possible because frame 3 is not provided with a drilling tower, as is usual in more permanent drilling platforms. Such drilling platforms are generally provided with three legs in the form of lattices with a diameter of 8 m and more.
[0025] Work deck 21 is height-adjustable in a height direction 16 by means of four rack and pinion jacks 23 located at the corner points of work deck 11 and each operating a corresponding leg 22. In an embodiment (not shown) work deck 21 of platform 1 can likewise be provided with a (circular) opening or so-called moon pool which provides access to the water 17 present under work deck 11. In such an embodiment frame 3 can also be arranged over and in the moon pool.
[0026] Work deck 21 has a thickness 24 in order to give it the required bending stiffness, for which purpose an internal (not visible) support structure of support beams and partitions extends over the thickness. As shown in figure 1, a side edge of work deck 21 is reinforced with a support rail 2. In an embodiment in which frame 3 is arranged over and in the moon pool the peripheral edge of the moon pool comprises a support rail.
[0027] Jack-up platform 1 is further provided with a Dynamic Positioning (DP) system. Such a DP system is configured to enable independent positioning of platform 1 and comprises a number of thruster bodies (or thrusters) 25, provided under work deck 21, of propeller blades rotating around a horizontal axle. In the shown embodiment four thruster bodies 25 are arranged along a lower edge of work deck 21. Using thruster bodies 25 a work deck 21 floating in the water 17 can be precisely positioned relative to for instance an oil well, particularly in that they are likewise rotatable around a vertical axis 26. The use of thruster bodies 25 has the advantage that it is not necessary to apply anchor cables during positioning of platform 1. The risk of for instance oil wells being damaged is hereby reduced.
[0028] Work deck 21 is further provided with a lifting means in the form of a crane 27. The crane is connected for pivoting around a vertical axis 270 to work deck 21 by means of base 271. It further comprises an upward oriented support arm 272 to which a main boom 273 is pivotally connected. Main boom 273 is provided at the free outer end thereof with a hosting tackle 274 with which the components used to perform well interventions can be taken up and displaced. Main boom 273 can be luffed in and luffed out by means of traction cables 275. Smaller auxiliary cranes are also present on work deck 21 if desired.
[0029] According to the invention, frame 3 is connected with a work deck part 31 to work deck 21 for movement in horizontal directions (18, 19) over work deck 21. Referring to figures 3 and 4, the work deck part 31 of the frame comprises the part which extends over work deck 21 and does not therefore protrude. Frame 3 protrudes with an operative part 32 beyond a side edge 28 of work deck 21. Frame 3 is constructed from frame parts (33, 34) connected rigidly to each other. Frame parts 33 extend in a longitudinal direction 35 of frame 3, while frame parts 34 extend in a transverse direction 36 of frame 3. The longitudinal direction 35 of frame 3 extends parallel to the horizontal direction 18 of work deck 21, whereas the transverse direction 36 of frame 3 extends parallel to the horizontal direction 19 of work deck 21. As shown in figures 1 and 2, the protruding part 32 of frame 3 extends in vertical direction 16 along work deck 21 in the thickness direction thereof over a length which can vary.
[0030] In order to enable displacement of frame 3 relative to work deck 21 a skidding beam 11 is arranged on work deck 21. Skidding beam 11 runs at a distance 111 from and substantially parallel to support rail 2. The distance 111 can be freely chosen subject to the moment and forces to be transmitted to support rail 2 and skidding beam 11. Running between skidding beam 11 and an attachment to a frame part 34 are hydraulic cylinders 110 with which frame 3 can be displaced in the longitudinal direction 35 thereof relative to skidding beam 11. The distance between protruding part 32 of frame 3 and side edge 28 can hereby be increased or decreased so that protruding part 32 can be placed precisely above an oil well. Frame 3 can in the same way be displaced in the transverse direction 36 thereof relative to skidding beam 11. The relative position of protruding part 32 of frame 3 and platform 1 can hereby be adjusted in horizontal direction 19 so that protruding part 32 can be placed precisely above an oil well.
[0031] In order to be able to absorb the great forces on skidding beam 11 it is advantageous to provide work deck 21 with partition walls or bulkheads running in thickness direction 16 and preferably running along the underside of skidding beam(s) 11.
[0032] In the shown embodiment the frame parts 34 extending in transverse direction 36 form the frame floor parts of three horizontal frame floors (12, 13, 14) of protruding part 32 of frame 3. The work deck part 31 of frame 3 has two frame floors (12, 13). Specific equipment required to perform well intervention operations is present on each frame floor (12, 13, 14), as will be further elucidated hereinbelow.
[0033] In order to be able to understand the equipment it will be useful to briefly illustrate the construction of a borehole. Reference is made here to figures 1 and 2. A borehole is obtained by driving drill strings vertically into the ground and placing casings which close off the borehole from the surrounding rock using a drilling tower. Once the target to be drilled, usually a formation or "reservoir" containing hydrocarbon, has been reached the tower can be removed. Situated on the underside of the drill string is a well head to which the drill string is attached. A so-called christmas tree (or simply tree) 9 is placed over the well head. Tree 9 comprises a number of valves with which the flow rate of the product flowing out of the well (gas, oil and so on) can be regulated. Tree 9 can also fulfil other functions such as for instance providing injection points for chemicals, providing means for performing well intervention operations, and providing pressure valves, measuring equipment and so on.
[0034] When well intervention operations are being performed the tree 9 which is present is used as connecting member for a riser 6. Such a riser 6 connects jack-up platform 1, and more particularly the well intervention equipment present in frame 3, to christmas tree 9 or to a well head. Riser 6 is constructed from work deck 21 of platform 1 from a number of mutually connecting steel pipe parts with a diameter in the order of magnitude of for instance 15-20 cm. In order to enable connection of riser 6 to tree 9, tree 9 is provided with a tree running tool (TRT) 8 which forms the interface between christmas tree 9 and well intervention operators. The settings of tree 9 can for instance be determined using the TRT 8 in order to guarantee the safety of the well intervention operations. Riser 6 is provided on the upper side with a flowhead 4 which regulates, among other things, the flow rate of well intervention liquids.
[0035] Equipment which can be employed for well plug and abandonment comprises for instance:
- pumps and storage tanks for filling a borehole with concrete/grout/CO2. These can be placed on the deck of the jack-up platform or are located on a horizontal floor 12 or 13 of frame 3;
- a crane 27 for lifting the borehole components;
- clamps for holding the borehole casings. These clamps are generally located on a horizontal floor 12 or 13 of frame 3;
- a cutting tool for cutting through the borehole casings. This tool is preferably placed just above the clamps.
[0036] Suitable equipment for lifespan extension comprises for instance:
- at least one wire line and slick line reel and guides for guiding these wires in a riser; and
- a coiled tubing reel and injector.
[0037] By way of example an upper horizontal floor 12 of frame 3 comprises a coiled tubing injector unit 5 which is fixed to frame parts 34. Situated on the upper floor 12 of the work deck part 31 is a coiled tubing reel 10 from which can be unrolled a flexible, generally metal tube 50 (coiled tubing) which is shot via a support structure 51 with the coiled tubing injector unit 5 into a riser 6 to depths of 4000-5000 m and more. The upper floor can further be provided with pump means (not shown) with which liquids can be pumped via tube 50 to a well. Pumping for instance scale-reducing liquids and methanol prevents scale forming in the borehole casing. Saline liquids (brine) or steam can also be injected for maintenance of a borehole. A flexible tube 50 can also be used as production tube in almost depleted wells.
[0038] Coiled tubing 50 is generally provided on the underside with a bottom hole assembly (BHA) (not shown). Suitable BHA for instance comprise a nozzle for pumping chemicals or cement through tube 50 but, depending on the purpose, can also comprise a number of logging instruments placed in series. Coiled tubing can also be used as a cheaper alternative to workover operations. A BHA can also be used to break open an oil well, wherein a liquid is pumped under high pressure into tube 50 in order to break the bedrock and to allow product (oil or gas) to flow.
[0039] Means for supporting wires or wire lines (wire line tools) can also be attached to the upper frame floor 12. Diverse (measuring) equipment can be lowered from frame 3 into the well using wire lines. Wire lines comprise electrical cabling with which diverse data relating to the state of the well can be transmitted, for instance for the purpose of logging the well. Other equipment, intended for instance to remove well plugs, can also be lowered from frame 3 using slick lines (not shown). The wire (and slick) lines are connected via winches to frame 3 and can be lengthened or shortened using the winches. Guide wires 7 can be provided to guide equipment to the underwater bottom therewith.
[0040] The upper frame floor 12 preferably further supports a Blow Out Preventer (BOP) (not shown). A BOP comprises a valve which reacts to excessive pressures and flow in a drill string during drilling into a well resemoir. A BOP hereby prevents drill string components, and also well intervention liquids for instance, being blown out of the drill shaft with great force.
[0041] A middle floor 13 extends substantially in the plane of work deck 21 of platform 1 and comprises a riser constructing apparatus which is connected to frame parts 34. The riser constructing apparatus comprises for instance flowhead 4. A diver can if desired be launched at the height of the middle floor, for instance using a launching frame (not shown). Such a launching frame comprises for instance an A-frame which is pivotally connected to a floor and which is provided with a top tackle to which a cage for a diver can be attached and lowered. A remote-controlled robot or Remote Operated Vehicle (ROV) can for instance also be attached to and lowered from the top tackle.
[0042] A lowest floor 14 of protruding part 32 of frame 3 preferably comprises a riser ring tensioner 60 which is connected to frame parts 34. Ring tensioner 60 ensures that riser 6 is tensioned at the position of work deck 21. Movements of riser 6 resulting from wind load and wave movements are hereby largely prevented.
[0043] Frame 3 according to the invention has the great advantage that it provides a plurality of floors (12, 13, 14) and, owing to the construction by means of frame parts (33, 34), is still readily accessible for an apparatus to be arranged in the (protruding part 32 of) frame 3. An embodiment wherein a horizontal floor (12, 13, 14) of frame 3 can be opened has further advantages in this respect. This is possible for instance by embodying a relevant floor pivotally to the rest of frame 3 so that it can be folded aside.
[0044] A method for performing well interventions offshore can be performed in efficient manner with the device according to the invention.
[0045] Jack-up platform 1 of the device is for this purpose positioned in the immediate vicinity of a well in which intervention is to take place and frame 3 is moved in a horizontal plane relative to the work deck until operative part 32 of frame 3 is aligned with the borehole. A diver can then be launched from frame 3 in order to make connections between frame 3 and a Christmas tree 9 of the borehole. Equipment required for the well intervention can be carried downward here via guide wires 7. From frame 3 diverse liquids suitable for the intervention can then be injected or (conversely) brought up through the coiled tubing 50 shot downward into the constructed riser 6. Following the intervention, platform 1 can be easily uncoupled from the borehole and navigated to another borehole.
[0046] As shown in figure 6, the device according to the invention is also advantageously applied in a method for performing well interventions offshore above an existing production platform. The existing production platform comprises a jacket foundation 61 which extends partially under water and on which is placed a processing platform 60 which lies above water level 17. Borehole casings 62 extend from a well under ground surface 15 to a position above processing platform 60 and can be easily reached with frame 3 by displacing this frame 3 in a horizontal plane.
1. Device for performing well interventions offshore, comprising a jack-up platform which
comprises a height-adjustable horizontal work deck which is supported by vertical
legs supporting on an underwater bottom; a frame of frame parts connected rigidly
to each other which is configured to support well intervention equipment and comprises
for this purpose at least two horizontal frame floors of mutually connected frame
floor parts; wherein the frame is connected with a work deck part to the work deck
for movement in horizontal directions over the work deck, and wherein the frame protrudes
with an operative part beyond a side edge of the work deck.
2. Device as claimed in claim 1, wherein the work deck has a thickness and the protruding
part of the frame extends vertically along the work deck in the thickness direction
thereof.
3. Device as claimed in claim 1 or 2, wherein the protruding part of the frame has more
horizontal frame floors of mutually connected frame floor parts than the work deck
part.
4. Device as claimed in any of the foregoing claims, wherein the frame has a width and
the protruding part of the frame comprises a horizontal frame floor extending beyond
the width.
5. Device as claimed in any of the foregoing claims, wherein the work deck part of the
frame comprises two horizontal floors and the protruding part of the frame comprises
three horizontal floors.
6. Device as claimed in any of the foregoing claims, wherein an upper horizontal floor
of the frame comprises a coiled tubing injector which is connected to frame parts.
7. Device as claimed in any of the foregoing claims, wherein a middle floor extends in
the plane of the work deck of the platform and comprises a riser constructing apparatus
which is connected to frame parts.
8. Device as claimed in any of the foregoing claims, wherein a lowest floor of the protruding
part of the frame comprises a riser ring tensioner which is connected to frame parts.
9. Device as claimed in any of the foregoing claims, wherein a horizontal floor of the
frame can be opened.
10. Device as claimed in any of the foregoing claims, wherein the side edge of the work
deck comprises a support rail.
11. Device as claimed in any of the foregoing claims, wherein the work deck comprises
a skidding beam which lies at a distance from and substantially parallel to the support
rail and to which the work deck part of the frame is connected movably over the work
deck in a direction running substantially parallel to the side edge.
12. Device as claimed in any of the foregoing claims, wherein the work deck comprises
horizontal skidding beams which run substantially perpendicularly of the support rail
and to which the work deck part of the frame is connected movably over the work deck
in a direction running substantially perpendicularly of the side edge.
13. Device as claimed in any of the foregoing claims, wherein the jack-up platform comprises
bulkheads under the work deck which preferably run along the underside of the skidding
beams.
14. Device as claimed in any of the foregoing claims, wherein the jack-up platform comprises
four or more legs with a diameter of a maximum of 4 m.
15. Method for performing well interventions offshore making use of a device as claimed
in any of the foregoing claims.
16. Method as claimed in claim 15, wherein the jack-up platform is positioned in the immediate
vicinity of a well in which intervention is to take place and the frame is moved relative
to the work deck until the operative part of the frame is aligned with the borehole.
17. Method as claimed in claim 15 or 16, wherein the jack-up platform is positioned in
the immediate vicinity of a plurality of wells of an existing production platform
in which intervention is to take place and the frame is moved relative to the work
deck until the operative part of the frame is aligned with one of the boreholes.