Subsea equipment installation

Abstract

The invention relates to the drilling of subsurface oil and gas wells and the installation of subsurface equipment (11). A lifting vessel 7 brings heavy equipment such as Xmas trees or manifolds and wet parks this equipment (11) on the seafloor (5) during good weather when the significant wave height is low. The equipment (11), once it is underwater, has much lower weight and may easily be moved into place onto a wellhead (10) at an appropriate time using lower capacity lifting gear. The timing of this operation is much less sensitive to weather conditions because the equipment does not need to pass through the splash zone (sea surface). This makes for efficient use of expensive drilling rig time, and allows for acceleration of production of first wells on the template as critical heavy lifts could not else be done until rig has left the location. (FIG. 1).

Claims

1. A process for installing subsea equipment comprising a subsea Xmas tree or manifold in an installation region of seafloor, the process comprising: (a) wet parking the equipment on the seafloor in proximity to the installation region using a marine vessel with a crane, including lowering the equipment through the splash zone at a time when the significant wave height is less than 3 m; (b) subsequently repositioning the equipment into the installation region, wherein the equipment remains underwater throughout the repositioning operation; wherein, prior to step (b), a subsea template comprising a plurality of template slots is installed in the installation region and, also prior to step (b), a plurality of Xmas trees and/or manifolds are wet parked on a wet parking area of the seafloor adjacent the installation region, and wherein step (b) involves installing a plurality of Xmas trees and/or manifolds in respective template slots in the template, and further wherein a drilling rig crane is employed in step (b) to position the equipment in a first one of the said template slots whilst a drilling rig tower of the drilling rig performs a drilling operation in a second one of the said template slots.

2. The process according to claim 1, wherein preparing the wet parking area comprises installing a mud mat on the seafloor.

3. The process according to claim 1, wherein, prior to step (b), the buoyancy of the subsea equipment is increased.

4. The process according to claim 3, wherein the buoyancy of the subsea equipment is increased by (i) attaching buoyant members to the equipment, or (ii) inflating pre-attached inflatable buoyancy devices.

5. The process according claim 4, wherein compressed gas or air supplied by a hose from the surface or from temporary tanks is used to fill the inflatable buoyancy devices.

6. The process according to claim 1, wherein step (b) is performed using two or more cranes or other lifting or hauling devices at different locations simultaneously in order to move the subsea equipment laterally onto the installation region.

7. The process according to claim 1, wherein a time interval between steps (a) and (b) is up to 2 years.

8. The process according to claim 1, wherein there is a time interval of between 1 week and 2 years between the installation of a first and a second of the said manifolds and/or XMas trees.

9. The process according to claim 1, wherein the drilling rig is a jack-up rig and the water depth is from 20 to 200 m.

10. The process according to claim 9, wherein the water depth is from 30 to 150 m.

11. The process according to claim 9, wherein the water depth is from 30 to 100 m.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) A more complete understanding of the present invention and benefits thereof may be acquired by referring to the follow description taken in conjunction with the accompanying drawings in which:

(2) FIG. 1 is a schematic showing subsea equipment and lifting facilities which may be used in accordance with the invention, including a surface vessel having deposited subsea equipment on the seafloor;

(3) FIG. 2 is an illustration similar to FIG. 1 showing one possible combination of lifting equipment for maneuvering the equipment into place on a wellhead and also showing drilling being performed in parallel with lifting;

(4) FIG. 3 is an illustration similar to FIG. 2 showing the equipment in place on the wellhead/template; and

(5) FIG. 4 is a flow chart showing an exemplary sequence of steps for the method according to the invention.

DETAILED DESCRIPTION

(6) Turning now to the detailed description of the preferred arrangement or arrangements of the present invention, it should be understood that the inventive features and concepts may be manifested in other arrangements and that the scope of the invention is not limited to the embodiments described or illustrated. The scope of the invention is intended only to be limited by the scope of the claims that follow.

(7) As shown in FIG. 1 in highly schematic form, a jack-up rig 1 rests on the seafloor 5 with its legs 2 passing through the surface 4 of the sea. A high lifting capacity rig tower 3 is located on the jack-up 1. The rig derrick 3 (also called rig tower 3) is mounted on a cantilever structure 16 which, in FIG. 1, is not deployed but can be used to position the rig tower 3 such that it has a reach beyond the deck of the rig (see FIGS. 2 and 3). The jack-up 1 also has a rig crane 6 with a lower lifting capability than the tower 3.

(8) A specialized high capacity lifting vessel 7 is shown, on which is mounted a high capacity crane 8. On the seafloor is a drilling template 9 which has previously been placed into position at a planned drilling location, either using methods in accordance with the invention or not. A well has been drilled through the template 9 and a wellhead 10 has already been installed. The template 9 has lifting/hauling points 12.

(9) Also located on the seafloor in proximity to the template 9 is a heavy piece of equipment 11 which needs to be mounted on the wellhead 10. The equipment 11 could be a manifold or a Xmas tree or both. The equipment includes one or more lifting/hauling points 12 which may be permanent or temporary. Buoyancy tanks 13 are attached on each side, or above, of the equipment 11; these were installed before or after lowering the equipment to the seafloor, possibly only inflated/made buoyant after being placed in the sea, to reduce the size and weight of the equipment for further maneuvering operations. The buoyancy elements may be inflated using high pressure air/gas, at sufficient pressure to fill the buoyancy elements as the water depth hydrostatic pressure is significantly less. The gas is supplied from a pressurized tank 20 on the seafloor via a high pressure line 21. Alternatively, the pressurized gas may be supplied from the surface. The equipment 11 rests on a mud mat 14 on the seafloor 5. A seafloor-mounted winch 15 is located nearby.

(10) In a first embodiment of the invention, the subsea template, having a mass of 100 metric tonnes (100,000 kg) is transported by the vessel 7 to an intended drilling location, in the Summer during a period of good weather. The conditions include a significant wave height of 1 meter, which is calm enough to allow the vessel 7 to lower the template 9 through the surface 4 of the sea (the splash zone) using its crane 8 and attachment points 12 on the template. The template may either be lowered directly onto a site prepared for drilling, or it may be parked on the seafloor nearby until it is needed, and then maneuvered into position using any combination of the surface vessel crane 8, rig crane 6 and seafloor winch 15. The rig tower 3 may also be used. Once the template has been placed on the seafloor, its effective weight is much less which means that it is not normally necessary to employ the rig tower 3 or such a high capacity surface vessel crane as was used to locate it initially. Thus, the relatively low capacity rig crane 6 may be used together with one or more seafloor winches 15 or a lower capacity lifting vessel. Furthermore, the process of moving the template into position is much less weather dependent than the initial lowering operation and so there is more flexibility about when this process is carried out. Once in position, the template 9 is securely anchored to the seafloor 5.

(11) A Xmas tree or manifold (equipment 11) will not be required until a well has been drilled through the template 9 and wellhead 10 installed using the drilling rig 1. However, while the weather conditions are good, the equipment 11 can be wet parked. The equipment may comprise a heavy manifold or Xmas tree with masses of 100 and 70 metric tonnes respectively. The high capacity surface vessel crane 8 may wet park the equipment 11 on the seafloor 5 during good weather conditions when the significant wave height is 1 m. The equipment 11 may then be left until the rig 1 has finished drilling operations.

(12) When drilling has been completed, the equipment 11 may then be installed on a wellhead 10. With the equipment underwater its effective weight is reduced and so it may be handled by lower capacity lifting/hauling equipment. Weight may be further reduced by adding buoyancy tanks 13. Also, the timing of this operation is not as sensitive to weather as the operation of lowering the equipment though the splash zone.

(13) Commonly, a template may have 4 or more slots for drilling. Each well requires a Xmas tree and manifold. By parking all the necessary Xmas trees and manifolds in advance during good weather, it becomes possible to bring one or more of the wells online pending drilling and completion of the others.

(14) FIG. 2 shows the drilling rig tower 3 deployed on cantilever structure 16. A drill string 17 is shown performing operations in a well, with wellhead 10. The other of the two illustrated wellheads 10 is ready to receive a Xmas tree/manifold.

(15) FIG. 2 shows various lifting equipment attached to the parked Xmas tree/manifold 11 ready to move it into position. This is only one example and there are many other possibilities. A relatively low capacity lifting vessel 18 (in comparison to the vessel 7 of FIG. 1) is shown with its crane 19 attached to the equipment 11. The rig crane 6 has its cable running through a lifting point/pulley 12 on the template and a similar point on the deployed cantilever structure 16, and then attached to the equipment 11. The seafloor winch 15 has a cable attached to a hauling point 12 on the subsea equipment 11.

(16) Using all three pieces of lifting/hauling equipment, the Xmas tree/manifold may be lifted and moved laterally into position on the wellhead 10. During this operation, the rig tower 3 and drill string 17 can be employed on the other well.

(17) FIG. 3 shows the equipment 11 in position. The lifting equipment is still attached to show how the various cables have moved during the operation. The buoyancy tanks 13 have been removed at this stage. The rig tower 3 and drill string 17 continue to operate on the other wellhead 10.

(18) FIG. 4 shows an exemplary sequence of steps: first, prepare the seafloor (step 20); second, during the Summer and using a specialized lifting vessel, install the template and wet park VXTs (vertical Xmas trees) and manifold adjacent the template (step 21); third, at a convenient time move in the jack-up rig and drill the first well (step 22); fourth, attach any buoyancy required (step 23); fifth, commence drilling a second well in the template whilst using a rig crane on the rig to position, or help position, a VXT or a manifold on the wellhead of the first drilled well (step 24).

(19) In this example, the manifold is installed before the VXTs, so whilst the second slot is being drilled the manifold is moved into place followed by the first VXT. Depending on the design of the equipment, the manifold may be installed after the VXTs, in which case only the first VXT is installed in parallel with the drilling of the second slot and the manifold would be installed at the end of the procedure.

(20) Obviously, step 24 can be repeated until all slots in the template have been drilled and the manifold and all VXTs placed.

(21) Depending on the weight of the equipment and the starting and finishing positions, it may be possible to perform the maneuvering operation with different combinations of equipment, e.g. no lifting vessel and/or more than one seafloor winch. The rig tower itself could be employed to lift, but normally this would not be done because this would take the rig tower away from other well drilling and preparation operations which only it can perform.

(22) As can be seen from the above description of a specific example, the advance wet parking of the heavy equipment and the reduction of the load using buoyancy elements allows a rig crane or rig draw work to pick up the parked equipment from seafloor. In the described method, lift may be provided by a combination of a crane with another lifting point or device. In this way, sufficient lift may be provided for the lift and installation move from the parked position onto the planned position on the well template or wellhead. A buoyancy device suitable for this purpose may be, for example, a submerged tank to be filled with air before the lift and emptied after the lift. Alternatively, buoyancy elements may be attached t the modules when parked, and then carefully released after installation.

(23) At a time when the weather is acceptable, the transport crane vessel can move to a position above the planned wet parking area on the seafloor. This area may be next to the rig operating on a template/well(s). A mud mat with the necessary strength may first be installed on the seafloor, and buoyancy elements/equipment also placed on the seafloor. The manifold and Xmas tree and other heavy equipment may then be placed on the mud mat(s). During installation or after landing on the mud mat, buoyancy elements/equipment of sufficient capacity to allow for the use of a surface crane are installed/added/inflated.

(24) The transport vessel may then be moved away. When ready for installation the rig crane may lower its crane hook and lifting gear into the sea above the equipment to be installed. An ROV may attach the lifting gear to the equipment. The lifting gear may comprise either only a crane hook for direct installation, or as required an additional hook(s) may be provided for one or more additional lifting device(s) on surface to enable the equipment may be lifted only slightly and moved laterally to the final intended installation point on the template, well or other position under the rig.

(25) During the lateral movement, the load transfer happens as the surface crane moves, or when hoisting the next lifting device to a point where the next secondary lifting device has taken the full load, and the crane load is zero and thereafter its hook released from the equipment. In its final installation position, the equipment is lowered down and installed and hooked up on to the well or template or set on the seafloor in the final position. In this final position the last hooks(s) are released. The buoyancy elements/equipment is thereafter controlled by deflating or removing/detaching it.

(26) Avoiding the possible weather delays during rig move phase, and later equipment installation (impacting first oil) is a big advantage. Running the subsea equipment through the sea surface/splash zone when the average wave height is low reduces uncertainties for installation. Early installation with the rig also enables single wells in a template to be put on production earlier as the rig does not have to complete the operation and can be moved away before wells are completed. Another direct improvement on early installation is the ability of secondary well intervention to repair of intervene on the producing well whilst the rig is in place rather having to call in the rig later if unforeseen repair is required.

(27) In closing, it should be noted that the discussion of any reference is not an admission that it is prior art to the present invention, especially any reference that may have a publication date after the priority date of this application. At the same time, each and every claim below is hereby incorporated into this detailed description or specification as a additional embodiments of the present invention.

(28) Although the systems and processes described herein have been described in detail, it should be understood that various changes, substitutions, and alterations can be made without departing from the scope of the invention as defined by the following claims. Those skilled in the art may be able to study the preferred embodiments and identify other ways to practice the invention that are not exactly as described herein. It is the intent of the inventors that variations and equivalents of the invention are within the scope of the claims while the description, abstract and drawings are not to be used to limit the scope of the invention. The invention is specifically intended to be as broad as the claims below and their equivalents.