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Patent Searching and Data


Title:
SUBSEA PETROLEUM RECOVERY
Document Type and Number:
WIPO Patent Application WO/2016/086260
Kind Code:
A1
Abstract:
An offshore facility (10) established for recovery of petroleum fluids from a stranded oil field (11). The offshore facility (10) provides for temporary storage of oil extracted from subsea oil production wells (13) and then subsequent off-loading of the stored oil to, for example, a shuttle tanker. The infrastructure (17) comprises a unit (31) providing a storage tank (33) and two riser towers (35). The storage tank (33) is located below water surface 21 and rests on the sea bed. The two riser towers (35) extend upwardly from the submerged storage tank (23) towards and above the water surface. A platform structure (61) is integrated with the two riser towers (35). The platform structure (61) comprises a platform (63) and a plurality of support legs (65) moveable between a raised condition and a lowered condition. The platform structure (61) is floated into position between the two riser towers (35), with the support legs (65) in the raised condition. The support legs (65) are then deployed through movement into the lowered condition to engage and rest upon the storage tank (33), thereby providing stable support for the platform structure (61).

Inventors:
BROWN PHILLIP GWYN (AU)
Application Number:
PCT/AU2015/000729
Publication Date:
June 09, 2016
Filing Date:
December 01, 2015
Export Citation:
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Assignee:
WORLEYPARSONS SERVICES PTY LTD (AU)
International Classes:
E02B17/00
Foreign References:
US3716993A1973-02-20
CA2248578A12000-03-23
US6164234A2000-12-26
US20130177358A12013-07-11
US3327780A1967-06-27
US4969776A1990-11-13
Attorney, Agent or Firm:
WRAYS PTY LTD (56 Ord StreetWest Perth, Western Australia 6005, AU)
Download PDF:
Claims:
CLAIMS

1 . A method of establishing an offshore facility for recovery of petroleum fluid from a subsea location, the method comprising: installing an installation comprising a storage tank and a riser tower, the storage tank being located below water surface and the riser tower extending upwardly towards the water surface; and installing a flowline between the installation and a subsea production well for conveying petroleum fluid from the well to the installation.

2. The method according to claim 1 , wherein the installation is installed at a location spaced from the subsea production well.

3. The method according to claim 1 , wherein the installation is installed at a location above a production well.

4. The method according to claim 1 , wherein installation is operable to service at least two subsea production wells, at least one of which is spaced from the installation and at least another of which is beneath the installation.

5. The method according to any one of the preceding claims, wherein the flowline provides a continuous flowline between the production well and the installation.

6. The method according to any one of the preceding claims, wherein the flowline has a delivery end section, and wherein the method further comprises drawing the delivery end section upwardly along the riser tower and connecting it in position.

7. The method according to claim 6, wherein the flowline is be drawn upwardly along the riser tower through a J-tube assembly.

8. The method according to any one of claims 1 to 5, wherein the flowline extends along the riser tower.

9. The method according to any one of the preceding claims, wherein the petroleum fluid from the flowline is delivered to a transfer facility or to the storage tank for temporary storage before being delivered to a transfer facility.

10. The method according to any one of the preceding claims, wherein the storage tank and the riser tower(s) are configured as a unit, and wherein the method further comprises transporting the unit to a site of installation and causing the unit to descend into the water, sinking the storage tank to a desired location.

1 1 . The method according to any one of the preceding claims, further comprising providing a platform structure at or adjacent the surface level of water at the installation site and integrating the platform structure with the riser tower(s).

12. The method according to claim 1 1 , wherein the platform structure comprises a platform and one or more support legs for supporting the platform structure at or adjacent water surface level, and wherein the method further comprises floating the platform structure into position at an installation site above the storage tank with the support leg(s) in a raised condition, and deploying the support leg(s) to a lowered condition to rest upon the storage tank.

13. The method according to claim 1 1 or 12, wherein there are two riser towers, wherein the method further comprises positioning the platform structure between the two riser towers and integrating the platform structure with each riser tower.

14. A method of establishing an offshore facility for recovery of petroleum fluid from a subsea location, the method comprising: installing an installation comprising a storage tank and a riser tower, the storage tank being located below water surface and the riser tower extending upwardly towards the water surface; and installing a flowline between the installation and a subsea production well for conveying petroleum fluid from the well to the installation, the flow line comprising a subsea pipeline.

15. A method of establishing an offshore facility for recovery of petroleum fluid from a subsea location, the method comprising: installing an installation comprising a storage tank and a riser tower, the storage tank being located below water surface and the riser tower extending upwardly towards the water surface; and establishing a subsea production well beneath the installation

16. A petroleum fluid recovery facility established at an offshore location using a method according to any one of the preceding claims.

17. A method of recovery of petroleum fluid from a subsea location comprising: establishing a subsea production well; installing an installation comprising a storage tank and a riser tower, the storage tank being located below water surface and the riser tower extending upwardly towards the water surface; and installing a flowline between the installation and the subsea production well for conveying petroleum fluid extracted from the well to the installation.

18. A method of recovery of petroleum fluid from a subsea location comprising: establishing a subsea production well; installing an installation comprising a storage tank and a riser tower, the storage tank being located below water surface and the riser tower extending upwardly towards the water surface; installing a flowline between the installation and the subsea production well for conveying petroleum fluid extracted from the well to the installation, the flow line comprising a subsea pipeline.

19. A method of recovery of petroleum fluid from a subsea location comprising: installing an installation comprising a storage tank and a riser tower, the storage tank being located below water surface and the riser tower extending upwardly towards the water surface; and establishing a subsea production well beneath the installation.

20. A petroleum fluid recovery facility installed at an offshore location for recovery of petroleum fluid using a recovery method according to 17, 18 or 19.

21 . A petroleum fluid recovery facility comprising an installation comprising a storage tank and a riser tower, the storage tank being located below water surface and the riser tower extending upwardly towards the water surface, a flowline between a subsea production well and the installation for conveying petroleum fluid from the well to the installation; the flowline having an intake end section and a delivery end section, the delivery end section rising upwardly along the riser tower, having been drawn upwardly along the riser tower.

22. A petroleum fluid recovery facility comprising an installation comprising a storage tank and a riser tower, the storage tank being located below water surface and the riser tower extending upwardly towards the water surface, and a subsea production well beneath the installation.

23. A petroleum fluid recovery facility comprising an installation comprising a storage tank and two riser towers, the storage tank being located below water surface and the two riser towers extending upwardly towards the water surface, each riser tower having a J-tube assembly, a flowline and/or umbilical associated with each riser tower, the flowline being disposed between a subsea production well and the installation for conveying petroleum fluid from the well to the installation; the flowline and/or umbilical rising upwardly along the respective riser tower through the respective J-tube assembly.

24. A petroleum fluid recovery facility comprising an installation comprising a storage tank and two riser towers, the storage tank being located below water surface and the two riser towers extending upwardly towards the water surface, each riser tower having a J-tube assembly for receiving a flowline and/or umbilical, a platform structure at or adjacent the surface level of water at the installation site, the platform structure comprising a platform and a plurality of support legs for supporting the platform at or adjacent water surface level, the platform structure being positioned between the two riser towers and the support legs standing on the storage tank, and a structural connection between the platform structure and the riser towers to provide an integrated facility .

25. An apparatus comprising a storage tank and a riser tower upstanding from the storage tank, the riser tower having a pathway along which a flowline and/or an umbilical can be drawn upwardly to an upper location.

26. A petroleum fluid recovery facility comprising an installation comprising a storage tank and two riser towers, the storage tank being located below water surface and the two riser towers extending upwardly towards the water surface, at least one riser tower having pathway such as a conduit through which a drilling operation can be performed for establishing a subsea production well beneath the installation.

27. A petroleum fluid recovery facility comprising an installation comprising a storage tank and two riser towers, the storage tank being located below water surface and the two riser towers extending upwardly towards the water surface, and a platform structure comprising a platform and a plurality of support legs moveable between a raised condition and a lowered condition, whereby in the lowered condition the support legs rest upon the storage tank, the platform being integrated with the two riser towers by being connected thereto.

28. Apparatus comprising a storage tank and a riser tower upstanding from the storage tank, the riser tower having a pathway through which a drilling operation can be performed for establishing a subsea production well beneath the apparatus

29. A platform structure comprising a platform and a plurality of support legs, the support legs being moveable between a raised condition and a lowered condition, whereby in the raised condition the platform structure can be floated in water to an installation site and in a lowered condition the support legs can rest upon a previously installed submerged structure comprising a storage tank and a riser tower, the platform providing a topside facility when the support legs are in the lowered condition and resting upon the submerged structure whereby the topside facility is supported in position above the submerged structure.

Description:
SUBSEA PETROLEUM RECOVERY

TECHNICAL FIELD

[0001] This invention relates to recovery of petroleum fluids from subsea locations. More particularly, the invention concerns a localised facility for, and a localised method of, recovery of petroleum fluids from subsea reservoirs which are considered to be an uneconomic distance from any existing infrastructure.

BACKGROUND ART

[0002] The invention has been devised particularly, although not necessarily solely, for the recovery of petroleum fluid in the form of oil from so-called "stranded oil" fields, where oil reservoirs have been identified but are difficult to access due to their location. Often such reservoirs are at offshore locations remote from an onshore delivery point, making construction of a pipeline to the onshore delivery point prohibitively expensive.

[0003] It would be advantageous to provide a facility which provides offshore storage for petroleum fluid extracted from such a reservoir and periodically offloading the petroleum fluid to a transfer facility (such as a shuttle tanker).

[0004] It is against this background and the problems and difficulties associated therewith that the present invention has been developed.

SUMMARY OF INVENTION

[0005] According to a first aspect of the invention there is provided a method of establishing an offshore facility for recovery of petroleum fluid from a subsea location, the method comprising: installing an installation comprising a storage tank and a riser tower, the storage tank being located below water surface and the riser tower extending upwardly towards the water surface; and installing a flowline between the installation and a subsea production well for conveying petroleum fluid from the well to the installation

[0006] In a first arrangement, the installation may be installed at a location spaced from the subsea production well. [0007] With this first arrangement, the installation would typically be installed after establishment of the subsea production well, although this need not necessarily be so as it may be installed at some other time such as before or during establishment of the subsea production well.

[0008] In a second arrangement, the installation may be installed at a location above a production well.

[0009] With this second arrangement, the installation would typically be installed before establishment of the subsea production well, although this need not necessarily be so as it may be installed at some other time such as during establishment of the subsea production well. Typically, the subsea production well would be established using a drilling process performed from the installation. The installation is at a location above a production well in the sense that the drilling operation can be performed into the seabed beneath the installation to establish the subsea production well.

[0010] In a third arrangement, the installation may service at least two subsea production wells, at least one of which is spaced from the installation and at least another of which is beneath the installation.

[0011] In each arrangement, the installation is typically installed on the sea bed.

[0012] With each arrangement, the flowline may provide a continuous flowline between the production well and the installation. This may be advantageous in that it avoids intermediate subsea connections in the flowline at the installation which may provide a vulnerability to leakage.

[0013] In the first arrangement, the flowline typically comprises a subsea pipeline.

[0014] The flowline may have a delivery end section, the delivery end section being drawn upwardly along the riser tower and connected in position.

[0015] The flowline may extend between the installation and the subsea production well, or between the installation and a plurality of production wells. In the latter case, the flowline may be connected to various production wells by way of intervening branch lines between the flowline and the production wells. [0016] This may also apply to the third arrangement for the case of a subsea production well(s) spaced from the installation.

[0017] The riser tower may accommodate more than one flowline, thereby increasing the number of production wells that can be serviced by the installation.

[0018] In the first arrangement (and third arrangement as the case may be), the flowline may be drawn upwardly along the riser tower through a J-tube assembly.

[0019] One or more umbilicals may also be installed in the J-tube assembly.

[0020] Where the riser tower is adapted to accommodate more than one flowline and/or umbilical, there may be a J-tube assembly corresponding to each flowline and/or umbilical, with the end section of each such flowline and/or umbilical being drawn upwardly along the respective J-tube assembly in the riser tower. In other words, the raiser tower may have a plurality of J-tube assemblies. Alternatively, one J-tube assembly may accommodate several flowlines and/or umbilicals.

[0021] In the second arrangement (and third arrangement as the case may be), the flowline extends along the riser tower.

[0022] The flowline may extend along the riser tower through a pathway. The pathway may be defined by a conduit. The flow line may comprise a conductor pipe installed in the pathway as part of the process in establishment of the subsea production well.

[0023] The pathway has a bottom end section which, in use, opens onto the seabed.

[0024] Typically, the conduit extends through the storage tank to open onto the seabed.

[0025] Preferably, the riser tower extends upwardly to a location above the water surface.

[0026] There may be more than one riser tower. This may increase the number of production wells that can be serviced by the installation. In an embodiment, there are two riser towers.. [0027] Petroleum fluid from the subsea production well(s) may be conveyed along the flowline to the installation from which it can be subsequently transported.

[0028] At the installation, the petroleum fluid from the flowline may be delivered to a transfer facility (such as a shuttle tanker) or to the storage tank for temporary storage before being delivered to a transfer facility.

[0029] The storage tank and the riser tower(s) may be configured as a unit which is transported to the site of installation and caused to descend into the water, sinking the storage tank to its desired location, typically on the sea bed.

[0030] The installation may further comprise a platform structure at or adjacent the surface level of water at the installation site. The platform structure may include a connection point to which the delivery end section of the flowline is connected.

[0031] In the second arrangement (and the third arrangement as the case may be), the connection point may comprise a well head such as a "dry" production tree unit.

[0032] The petroleum fluid may be subjected to one or more processing stages before delivery to the transfer facility or the storage tank. Such processing stages may be performed to remove unwanted components from the petroleum fluids; for example, gas, water and other contaminants.

[0033] The processing may be performed on the platform structure.

[0034] Preferably, the installation is installed on the seabed. More particularly, the storage tank is installed on the seabed.

[0035] Preferably, the platform structure comprises a platform and one or more support legs for supporting the platform structure at or adjacent water surface level. Preferably, there is a plurality of support legs, typically at least three (and usually three or four).

[0036] The support leg or legs may be adapted to stand on the storage tank.

[0037] The storage tank may be reinforced to accommodate loadings imposed thereon through the support leg or legs of the platform structure. [0038] Each support leg may comprise a foot, and the storage tank may have a counterpart pad adapted to receive the foot.

[0039] The support leg(s) may be moveable between raised and lowered conditions.

[0040] The platform structure may be configured as a jack-up assembly facilitating movement of the support leg(s) between the raised and lowered conditions

[0041] The platform structure may be floated into position at the installation site above the storage tank with the support leg(s) in the raised condition, and the support leg(s) then deployed to the lowered condition to rest upon the storage tank.

[0042] The platform structure may be integrated with the riser tower, or each riser tower, once the support legs are resting upon the storage tank. The integration may comprise a structural connection between the platform structure and the riser tower(s), thereby providing an integrated facility. The integration may, more particularly, comprise mechanically coupling the platform structure to the riser tower(s).

[0043] In an embodiment where there are two riser towers, the platform structure may be positioned between the two riser towers, with the platform structure integrated with each riser tower.

[0044] The platform may comprise a topside installation.

[0045] The top side installation may incorporate a receiver system for receiving petroleum fluids from the subsea production well, the flowline(s) being fluidly connected to the receiving system.

[0046] From the receiving system, the petroleum fluid may be delivered to the transfer facility or the storage tank for temporary storage.

[0047] The topside installation may incorporate an offloading system for offloading petroleum fluid to the transfer facility (such as, for example, a shuttle tanker). Typically, there are two or more offloading systems.

[0048] The offloading system(s) may be arranged to deliver petroleum fluid stored in the storage tank to the transfer facility. Further, in circumstances where the transfer facility (a shuttle tanker, for example) is moored, berthed or otherwise located at the installation site and available to receive the petroleum fluid, the offloading system may be arranged to deliver petroleum fluid being received at the time from the production well(s) directly to the transfer facility, without the petroleum fluid going to the storage tank.

[0049] In the first arrangement (and the third arrangement as the case may be), the flowline may be delivered to the installation site on a reel and laid onto the sea floor.

[0050] The end of the flowline which is drawn upwardly through the riser tower may be deployed first, and the remainder of the flowline then progressively deployed as the leading end of the flowline is drawn to, and upwardly along, the riser tower.

[0051] The unit comprising the storage tank and the riser tower(s) may have two buoyancy conditions, one being a positive buoyancy condition to permit the unit to be floated along a water surface to an installation site and the other being a controlled negative buoyancy condition permitting the unit to descend in the water, submerging the storage tank, typically to a location at which is rests on the sea bed.

[0052] The unit comprising the storage tank and the riser tower(s) may have provision for addition of ballasting material to establish the controlled negative buoyancy condition to cause it to descend into the water. Accordingly, the method may further include the step of introducing the ballasting materials into the unit. The ballasting material may comprise any suitable material or materials, including for example water or other pumpable liquid.

[0053] The storage tank may define one or more storage chambers for receiving and temporarily containing petroleum fluid awaiting withdrawal and offloading to a transfer facility.

[0054] The provision for addition of ballasting material to provide the unit with the controlled negative buoyancy condition may comprise one or ballast compartments integrated with the storage tank to receive the ballasting material.

[0055] The method may further comprise re-deployment of the platform structure at a later time, such as when the production well(s) are no longer considered to be viable. [0056] The method may also further comprise re-deployment of the unit comprising the storage tank and the riser tower(s).

[0057] According to a second aspect of the invention there is provided a method of establishing an offshore facility for recovery of petroleum fluid from a subsea location, the method comprising: installing an installation comprising a storage tank and a riser tower, the storage tank being located below water surface and the riser tower extending upwardly towards the water surface; and installing a flowline between the installation and a subsea production well for conveying petroleum fluid from the well to the installation, the flow line comprising a subsea pipeline.

[0058] According to a third aspect of the invention there is provided a method of establishing an offshore facility for recovery of petroleum fluid from a subsea location, the method comprising: installing an installation comprising a storage tank and a riser tower, the storage tank being located below water surface and the riser tower extending upwardly towards the water surface; and establishing a subsea production well beneath the installation.

[0059] Preferably, the method according to the third aspect of the invention comprises establishing the production well by a drilling operations comprising passing a conductor pipe through the riser tower.

[0060] The conductor pipe may be passed through a conduit within the riser tower.

[0061] According to fourth aspect of the invention there is provided a petroleum fluid recovery facility established at an offshore location using a method according to the first, second or third aspect of the invention.

[0062] According to a fifth aspect of the invention there is provided a method of recovery of petroleum fluid from a subsea location comprising: establishing a subsea production well; installing an installation comprising a storage tank and a riser tower, the storage tank being located below water surface and the riser tower extending upwardly towards the water surface; and installing a flowline between the installation and the subsea production well for conveying petroleum fluid extracted from the well to the installation [0063] The method according to the fifth aspect of the invention may have any one or more features, as appropriate, of the method according to the first, second or third aspect of the invention.

[0064] According to a sixth aspect of the invention there is provided a method of recovery of petroleum fluid from a subsea location comprising: establishing a subsea production well; installing an installation comprising a storage tank and a riser tower, the storage tank being located below water surface and the riser tower extending upwardly towards the water surface; installing a flowline between the installation and the subsea production well for conveying petroleum fluid extracted from the well to the installation, the flow line comprising a subsea pipeline.

[0065] According to a seventh aspect of the invention there is provided a method of recovery of petroleum fluid from a subsea location comprising: installing an installation comprising a storage tank and a riser tower, the storage tank being located below water surface and the riser tower extending upwardly towards the water surface; and establishing a subsea production well beneath the installation.

[0066] Preferably, the method according to the seventh aspect of the invention comprises establishing the production well by a drilling operation comprising passing a conductor pipe through the riser tower.

[0067] The conductor pipe may be passed through a conduit within the riser tower.

[0068] According to an eighth aspect of the invention there is provided a petroleum fluid recovery facility installed at an offshore location for recovery of petroleum fluid using a recovery method according to the fifth, sixth or seventh aspect of the invention. The petroleum fluid recovery facility provides a system for recovery of petroleum fluids from subsea reservoirs.

[0069] According to a ninth aspect of the invention, there is provided a petroleum fluid recovery facility comprising an installation comprising a storage tank and a riser tower, the storage tank being located below water surface and the riser tower extending upwardly towards the water surface, a flowline between a subsea production well and the installation for conveying petroleum fluid from the well to the installation; the flowline having an intake end section and a delivery end section, the delivery end section rising upwardly along the riser tower, having been drawn upwardly along the riser tower. [0070] Preferably, the riser tower includes a J-tube assembly along which the delivery end section of the flowline was drawn upwardly.

[0071] According to a tenth aspect of the invention, there is provided a petroleum fluid recovery facility comprising an installation comprising a storage tank and a riser tower, the storage tank being located below water surface and the riser tower extending upwardly towards the water surface, and a subsea production well beneath the installation.

[0072] Preferably, the petroleum fluid recovery facility according to the tenth aspect of the invention further comprises a flowline between a subsea production well and the installation for conveying petroleum fluid from the well to the installation, the flowline extending upwardly along the riser tower.

[0073] The recovery facility according to the ninth or tenth aspect of the invention may have any one or more features, as appropriate, of the installation as described in relation to the earlier aspects of the invention.

[0074] By way of example, the recovery facility according to the ninth or tenth aspect of the invention may further comprise a platform structure at or adjacent water surface level. The platform structure may include a connection point(s) to which the delivery end section(s) of the flowline or respective flowlines are connected. The platform structure may comprise a platform and one or more support legs for supporting the platform at or adjacent surface level. The support leg(s) may be adapted to stand on the storage tank. The storage tank may be reinforced to accommodate loadings imposed thereon through the support leg(s) of the platform structure. Each support leg may comprise a foot, and the storage tank may have a counterpart pad adapted to receive the foot. The support leg(s) may be moveable between raised and lowered conditions. The platform structure may be integrated with the riser tower, or each riser tower, with the support leg(s) resting upon the storage tank. The integration may comprise mechanically coupling the platform structure to the riser towers, thereby to provide an integrated facility. The facility may comprise are two riser towers, and the platform structure may be positioned between the two riser towers, with the platform structure integrated with each riser tower. The unit comprising the storage tank and the riser tower(s) may have provision for addition of ballasting material to establish a controlled negative buoyancy condition to cause it to descend into the water. [0075] According to an eleventh aspect of the invention, there is provided a petroleum fluid recovery facility comprising an installation comprising a storage tank and two riser towers, the storage tank being located below water surface and the two riser towers extending upwardly towards the water surface, each riser tower having a J-tube assembly, a flowline and/or umbilical associated with each riser tower, the flowline being disposed between a subsea production well and the installation for conveying petroleum fluid from the well to the installation; the flowline and/or umbilical rising upwardly along the respective riser tower through the respective J-tube assembly.

[0076] According to a twelfth aspect of the invention, there is provided a petroleum fluid recovery facility comprising an installation comprising a storage tank and two riser towers, the storage tank being located below water surface and the two riser towers extending upwardly towards the water surface, each riser tower having a J-tube assembly for receiving a flowline and/or umbilical, a platform structure at or adjacent the surface level of water at the installation site, the platform structure comprising a platform and a plurality of support legs for supporting the platform at or adjacent water surface level, the platform structure being positioned between the two riser towers and the support legs standing on the storage tank, and a structural connection between the platform structure and the riser towers to provide an integrated facility .

[0077] According to a thirteenth aspect of the invention, there is provided a petroleum fluid recovery facility comprising an installation comprising a storage tank and two riser towers, the storage tank being located below water surface and the two riser towers extending upwardly towards the water surface, at least one riser tower having pathway such as a conduit through which a drilling operation can be performed for establishing a subsea production well beneath the installation.

[0078] According to a fourteenth aspect of the invention, there is provided a petroleum fluid recovery facility comprising an installation comprising a storage tank and two riser towers, the storage tank being located below water surface and the two riser towers extending upwardly towards the water surface, and a platform structure comprising a platform and a plurality of support legs moveable between a raised condition and a lowered condition, whereby in the lowered condition the support legs rest upon the storage tank, the platform being integrated with the two riser towers by being connected thereto. [0079] Preferably, the platform is detachably connected to the two riser towers

[0080] According to a fifteenth aspect of the invention, there is provided apparatus comprising a storage tank and a riser tower upstanding from the storage tank, the riser tower having a pathway along which a flowline and/or an umbilical can be drawn upwardly to an upper location.

[0081] Preferably, the pathway is defined by a J tube assembly

[0082] According to a sixteenth aspect of the invention, there is provided apparatus comprising a storage tank and a riser tower upstanding from the storage tank, the riser tower having a pathway through which a drilling operation can be performed for establishing a subsea production well beneath the apparatus.

[0083] Preferably, the pathway is defined by a conduit.

[0084] The apparatus according to the fifteenth or sixteenth aspect of the invention may have two riser towers.

[0085] The apparatus according to the fifteenth or sixteenth aspect of the invention may have two buoyancy conditions, one being a positive buoyancy condition to permit the apparatus to be floated along a water surface to an installation site and the other being a controlled negative buoyancy condition permitting the storage tank to descend within the water to a desired location, typically on the sea floor.

[0086] The apparatus according to the fifteenth or sixteenth aspect of the invention may have provision for addition of ballasting material to establish the controlled negative buoyancy condition. The ballasting material may comprise any suitable material or materials, including for example water or other pumpable liquid.

[0087] The storage tank may be configured to support a structure installed above the storage tank.

[0088] The storage tank may support the structure by receiving and supporting legs of the structure.

[0089] According to a seventeenth aspect of the invention, there is provided a platform structure comprising a platform and a plurality of support legs, the support legs being moveable between a raised condition and a lowered condition, whereby in the raised condition the platform structure can be floated in water to an installation site, and in a lowered condition the support legs can rest upon a previously installed submerged structure comprising a storage tank and a riser tower, the platform providing a topside facility when the support legs are in the lowered condition and resting upon the submerged structure whereby the topside facility is supported in position above the submerged structure.

[0090] Preferably, the plurality of support legs comprises at least three support legs (and usually three or four).

BRIEF DESCRIPTION OF THE DRAWINGS

[0091] Further features of the present invention are more fully described in the following description of several non-limiting embodiments thereof. This description is included solely for the purposes of exemplifying the present invention. It should not be understood as a restriction on the broad summary, disclosure or description of the invention as set out above. The description will be made with reference to the accompanying drawings in which:

Figure 1 is a schematic side view of a first embodiment of a facility according to the invention in position to receive petroleum fluid in the form of crude oil from several subsea oil wells;

Figure 2 is a schematic side view showing a first stage in a process for installation of the facility, the first stage involving drilling of a subsea oil well;

Figure 3 is a schematic side view of a second stage in the installation process, involving floating of a structure into position at an installation location;

Figure 4 is a schematic side of a third stage in the installation process, involving submerging of the structure to rest upon the seabed; Figure 5 is a schematic side view of a fourth stage of the installation process, involving floating of a jack-up assembly to the installation site and positioning it above the submerged structure;

Figure 6 is a schematic side view of a fifth stage of the installation process, involving lowering of support legs from the jack-up assembly to rest upon the submerged structure;

Figure 7 is a schematic side view of a sixth stage in the installation process, involving mechanically coupling the jack-up assembly and the submerged structure together to provide an integrated structure;

Figure 8 is a schematic side view of a seventh stage of the installation process, involving installation of a flowline between the integrated structure and the oil wells;

Figure 9 is a schematic side view of the completion of the installation process, which corresponds to the arrangement shown in figure 1 ; and

Figure 10 is a schematic side view of a second embodiment of a facility according to the invention.

[0092] In the drawings like structures are referred to by like numerals throughout the various views. The drawings shown are not necessarily to scale, with emphasis instead generally being placed upon illustrating the principles of the present invention.

[0093] The figures depict embodiments of the invention. The embodiments illustrates certain configurations; however, it is to be appreciated that the invention can take the form of many configurations, as would be obvious to a person skilled in the art, whilst still embodying the present invention. These configurations are to be considered within the scope of this invention.

DESCRIPTION OF EMBODIMENTS

[0094] Using the systems and methods according to the invention, an offshore facility 10 can be established for recovery of petroleum fluids from subsea reservoirs. In the embodiments described and illustrated, the offshore facility 10 has been established for the recovery of oil from a stranded oil field 11 , where a reservoir has been identified but is difficult to access due to its location. One or more subsea oil production wells 13 are established at a production site 15 for extraction of oil from the stranded oil field 1 1 . The offshore facility 10 provides for temporary storage of oil extracted from the subsea oil production wells 13 and then subsequent off-loading of the stored oil to a transfer facility, such as for example a shuttle tanker.

[0095] In the first embodiment, which is shown in Figures 1 to 9, infrastructure 17 associated with the facility 10 is installed at an installation site 19 located away from the production site 15. In the arrangement depicted, the production site 15 is at a deepwater location, such as for example at a depth of say some 50m to 2000m below sea level, and the infrastructure 17 associated with the facility 10 is installed at an installation site 19 in shallower waters, such as for example at a depth of say some 50m to 120m below sea level. It is the shallower water environment at the installation site 19 that permits installation of the infrastructure 17, as will be described in more detail later. The depths referred to above are indicative depths only and are provided merely as typical examples. The offshore facility 10 can be established at any appropriate location and depth, as would be understood by a person skilled in the art.

[0096] In the drawings, sea level is depicted by a line representing the water surface and identified by reference numeral 21 and the sea bed is depicted by a line identified by reference numeral 23.

[0097] The infrastructure 17 at the installation site 19 is connected to the subsea oil wells 13 at the production site 15 by way of flowlines in the form of subsea pipelines 25. In this embodiment, there is a pipeline 25 extending between each subsea oil well 13 and the infrastructure 17, although only one such pipeline can be seen in most of the drawings. Each subsea oil well 13 may have a "wet" production tree unit (not shown) situated on the seabed 23, as would be understood by a person skilled in the art. There may also be umbilicals, as would be understood by a person skilled in the art.

[0098] Each subsea pipeline 25 has an intake end section 27 and a delivery end section 29.

[0099] The infrastructure 17 comprises an installation 30 comprising a unit 31 providing a storage tank 33 and two riser towers 35. The storage tank 33 is located below water surface 21 and has a base section 36 which rests on the sea bed 23. The two riser towers 35 extend upwardly from the submerged storage tank 23 towards and above the water surface 21 . The riser towers 35 are typically framework structures but may be of any suitable construction, as would be understood by a person skilled in the art.

[00100] The storage tank 33 comprises a body 37 which incorporates the base section 36 and also a top section 38. The top section 38 includes pads 39 to support a further part of the installation 30, as will be described in more detail later. The body 37 is reinforced to accommodate loadings imposed upon it through the pads 39.

[00101] The body 37 also incorporates one or more storage chambers (not shown) for receiving and temporarily containing oil extracted from the subsea oil production wells 13. This provides temporary storage for the extracted oil, pending withdrawal and offloading to a transfer facility (a shuttle tanker, for example).

[00102] The one or more storage chambers (not shown) would typically have sufficient storage capacity to accommodate a quantity of oil extracted during a typical time period between offloading stages. During an offloading stage, oil stored with the storage tank 33, and optionally also further oil delivered to the installation 30 during the offloading stage, would be offloaded onto the transfer facility (shuttle tanker). During intervening time periods (between offloading stages), when there is no transfer facility (shuttle tanker) available or in a condition to receive offloaded oil, oil extracted from the subsea oil production wells 13 would be delivered to the storage tank 33, with oil progressively accumulating in the storage tank 33, pending subsequently withdrawal and offloading at the next, or a later, offloading stage.

[00103] The unit 31 also incorporates one or ballast compartments (not shown) for receiving ballasting material, such as for example water or other pumpable liquid. Typically, the ballast compartments are incorporated in the body 37. However, other arrangements are of course possible; for example, the one or ballast compartments may be associated with one or more of the riser towers 35.

[00104] The unit 31 has two buoyancy conditions, one being a positive buoyancy condition to permit the unit to be floated along the water surface 21 to installation site 19 and the other being a controlled negative buoyancy condition permitting the unit 31 to descend in the water, submerging the storage tank 33 so that the base section 36 rests on the sea bed 23. The unit 31 is constructed to inherently have the positive buoyancy condition, and the negative buoyancy condition is attained through addition of ballasting material to the ballast compartments at the installation site 19. The negative buoyancy condition is controlled in the sense that the buoyancy of the unit 31 is changed from positive to negative, and the extent and rate of change to negative buoyancy, is controlled to assist in regulating descent of the unit 31 to descend in the water.

[00105] The riser towers 35 also contribute to the buoyancy of the unit 31 , particularly during the descent of the unit.

[00106] Once the facility 10 is operational, the unit 31 would always have sufficient quantities of ballasting material and/or oil to provide sufficient weight for stability purposes.

[00107] Each riser tower 35 incorporates a J-tube assembly 41 corresponding to each pipeline 25. The J-tube assembly 41 of each riser tower 35 may also accommodate one or more umbilicals. Each riser tower 35 may be provided a plurality of J-tube assemblies accommodating the respective pipeline and various umbilicals.

[00108] The J-tube assemblies 41 are of known kind, each having an upper section terminating at an upper exit end 43 and a lower section terminating at a lower entry end 47. The J-tube assembly 41 extends along the riser tower 35, with the upper exit end 43 being above sea level 21 and the lower entry end 47 located at or adjacent the sea bed 23. More particularly, the lower section of the J-tube assembly 41 bends near the sea bed 23 and extends a short distance laterally in an outward direction to terminate at the lower entry end 47. The entry end 47 may be of flared configuration to provide what is known as a bell mouth.

[00109] Each pipeline 25 rests on the seabed 23, with the delivery end section 29 extending through the lower entry end 47 and upwardly along the respective J-tube assembly 41 to the exit end 43 from which it extends to a connection point (not shown) at which is connected in position, as will be described further later.

[00110] The installation 30 further comprises a platform structure 61 at or adjacent the water surface 21 at the installation site 19.

[0011 1] The platform structure 61 comprises a platform 63 and a plurality of support legs 65 for supporting the platform structure in position. In the embodiment shown, there would be a minimum of three support legs 65 and sometimes four support legs. [00112] The support legs 65 are adapted to stand on the storage tank 33 to support the platform 63 in position. Specifically, the support legs 65 have feet 67 adapted to respectively engage the pads 39 provided on the top section 38 of the body 37 of the storage tank 33. With this arrangement, the platform structure 61 constitutes said further part of the installation 30 referred to above.

[00113] The platform structure 61 is constructed as a jack-up assembly, as would be understood by a person skilled in the art, with the support legs 65 being selectively movable between raised and lowered conditions.

[00114] The platform structure 61 is floated into position at the installation site 19, between the two riser towers 35 and above the storage tank 33 with the support legs 65 in the raised condition. The support legs 65 are then deployed through movement into the lowered condition to engage and rest upon the storage tank 33, thereby providing stable support for the platform structure 61 . The support legs 65 may be locked in the lowered condition in any appropriate way, as would be understood by a person skilled in the art.

[00115] The platform structure 61 is then integrated with the riser towers 35. The integration may comprise a structural connection between the platform 63 and the riser towers 35, thereby providing an integrated facility. The structural connection is provided by mechanically coupling each riser tower 35 and the adjacent portion of the platform 63. In the arrangement shown, the coupling between the platform 63 and the riser towers 35 is provided by way of a detachable connection system 67 between each riser tower 35 and the adjacent portion of the platform 63.

[00116] The platform 63 is fitted with a topside installation 71 .

[00117] The topside installation 71 incorporates a receiver system 73 for receiving extracted oil from the subsea production wells 13. The receiver system 73 incorporates the connection point (not shown) at which the delivery end section 29 of the pipeline 25 is connected in position, as previously described.

[00118] From the receiving system 73, oil extracted from the production wells 13 via the pipelines 25 is directed to the storage tank 33 for temporary storage. [00119] The topside installation 71 also incorporates an offloading system 75 for offloading extracted oil to the transfer facility (such as, for example, a shuttle tanker).

[00120] The offloading system 75 is arranged to deliver oil stored in the storage tank 33 to the transfer facility (shuttle tanker). During an offloading stage, oil stored with the storage tank 33, and optionally also any further oil extracted from the subsea oil production wells 13 and delivered to the installation 30 during the offloading stage, would be offloaded onto the transfer facility (shuttle tanker). During intervening time periods between offloading stages, when there is no transfer facility (shuttle tanker) available or in a condition to receive offloaded oil, oil extracted from the subsea oil production wells 13 would be delivered to the storage tank 33, with oil progressively accumulating in the storage tank 33, pending subsequently withdrawal and offloading at the next, or a later, offloading stage.

[00121] In the arrangement shown, the pipelines 25 are installed between the installation 30 and the subsea production wells 13 for conveying extracted oil from the wells to the installation, with the delivery end section 29 of each pipeline extending upwardly along one of the riser towers 35; specifically, riser tower 35a. There may, however, only be one production well 13, in which case there might only be one pipeline 25. Additionally, or alternatively, there may be one or more other pipelines (also not shown) connected to the installation 30 and extending upwardly along the other riser tower 35b, thereby also increasing the number of production wells that can be serviced by the installation.

[00122] The manner in which the offshore facility 10 is established for the recovery of oil from a stranded oil field 1 1 will now be described with reference to Figures 2 to 9 of the drawings.

[00123] Referring to Figure 2, there is shown a drill vessel 81 above the stranded oil field 11 in operation drilling oil production well 13 at the intended production site 15.

[00124] Referring to Figure 3, there is shown a first stage of establishment of the infrastructure 17 at the installation site 19. As depicted schematically in the drawings, the production site 15 is at a deep water location and the installation site 19 is at a shallow water location. It is the shallower water environment at the installation site 19 that permits installation of the infrastructure 17. This first stage involves towing or otherwise transporting the unit 31 to the installation site 19, typically by floatation with the unit being in a positive buoyancy condition, as is depicted in Figure 3.

[00125] Referring to Figure 4, there is shown a second stage of establishment of the infrastructure 17 at the installation site 19. This second stage involves partially sinking the unit 31 , submerging the storage tank 33 to the bottom with the base section 36 resting on the sea bed 23 and the two riser towers 35 extending upwardly from the submerged storage tank 23 towards and above the water surface 21 . The unit 31 is caused to sink in a controlled and systematic manner at the installation site 19 by changing its buoyancy condition from positive to negative, through the addition of ballasting material to the unit 31 .

[00126] Referring to Figure 5, there is shown a third stage of establishment of the infrastructure 17 at the installation site 19. This stage involves floating the platform structure 61 into position at the installation site 19. More particularly, the platform structure 61 , with the support legs 65 in the raised condition, is floated into position between the two riser towers 35 and above the storage tank 33.

[00127] Referring to Figure 6, there is shown a fourth stage of establishment of the infrastructure 17 at the installation site 19. This stage involves deployment of the support legs 65 through movement into the lowered condition to engage and rest upon the storage tank 33. Specifically, the feet 67 of the support legs 65 engage the pads 39 on the top section 38 of the body 37 of the storage tank 33. In this way, the support legs 65 stand on the storage tank 33 to support the platform 63 in position, thereby providing stable support for the platform structure 61 . The support legs 65 may be locked in the lowered condition.

[00128] Referring to Figure 7, there is shown a fifth stage of establishment of the infrastructure 17 at the installation site 19. This stage involves integration of the platform structure 61 with the unit 31 . The integration comprises a structural connection between the platform 63 to the riser towers 35 by way of detachable connection system 67 between each riser tower 35 and the adjacent portion of the platform 63, thereby to provide an integrated facility.

[00129] Referring to Figure 8, there is shown a stage involving installation of pipelines 25 between the oil production wells 13 and the installation 30. Each pipeline 25 is layed from a lay vessel 89 of known kind, as would be well understood by a person skilled in the art. Each pipeline 25 is delivered to the installation site 19 in roll form on a reel 91 carried on the lay vessel 89. In this drawing, there are two pipelines 25 depicted, one pipeline 25a shown already in position between a respective oil production well 13 and the installation 30, and the other pipeline 25b shown in the process of being layed.

[00130] The delivery end section 29 of the pipeline 25b is deployed from the lay vessel 89 and connected to a pull line 93 extending through the respective J-tube assembly 41 designated for the pipeline. As the pipeline 25b is deployed from the lay vessel 89, the pull line 93 is hauled upwardly along the J-tube assembly 41 , thereby pulling the delivery end section 29 of the pipeline 25b into the lower entry end 47 located at or adjacent the sea bed 23 and upwardly along the J-tube assembly to the upper exit end 43. At the upper exit end 43 of the J-tube assembly 41 , the delivery end section 29 of the pipeline 25b leaves the J-tube assembly and is directed to the receiver system 73 at which the delivery end section 29 of the pipeline 25b is connected to the connection point (not shown).

[00131] The remainder of the pipeline 25b is then layed from the lay vessel 89 upon the seabed 23 so as to extend to the respective production well 13. The intake end section 27 of the pipeline 25b is then connected to the production well 13.

[00132] With this arrangement, each pipeline 25 provides a continuous flowline between the respective production well 13 and the connection point (not shown) at the receiver system 73. This may be advantageous in that it avoids a need for intermediate subsea connections in the flowline at the installation 30, the presence of which may provide a vulnerability to leakage.

[00133] Other pipelines 25 as well as umbilicals associated with the installation 30 may be installed in a similar manner.

[00134] Referring to Figure 9, there is shown the completed installation 30 and the facility 10 in operation.

[00135] In operation, oil extracted from the oil production wells 13 flows along the respective pipelines 25 to the installation 30, at which the extracted oil is directed to the storage tank 33 for temporary storage. In the arrangement shown in Figure 9, there are two shuttle tankers 95 depicted at the facility 10, each being loaded with oil from the production wells 13. [00136] The offloading system 75 delivers a load of oil stored in the storage tank 33 to shuttle tanker(s) 95. During an offloading stage, oil stored with the storage tank 33, and optionally also further oil delivered to the installation 30 during the offloading stage, would be offloaded onto the shuttle tanker(s) 95. During intervening time periods between offloading stages, when there is no shuttle tanker at the facility 10 available or in a condition to receive offloaded oil, oil extracted from the subsea oil production wells 13 is delivered to the storage tank 33, with oil progressively accumulating in the storage tank 33, pending subsequently withdrawal and offloading at the next, or a later, offloading stage.

[00137] When the oil production wells 13 are no longer considered to be viable, the facility 10 can be abandoned. The abandonment may involve removal of the platform structure 61 and possibly re-deployment at another location. The abandonment may also involve removal of the unit 31 , and possibly re-deployment at another location. Removal of the unit 31 involves discharging the ballasting material to return the unit 31 to a positive buoyancy condition so that the unit can return to the water surface 21 , permitting it to be towed away.

[00138] Referring now to Figure 10 of the drawings, there is shown a second embodiment of the production facility 10. The second embodiment is similar in many respects to the first embodiment and similar reference numerals are used to denote similar parts.

[00139] This second embodiment is particularly, although not necessarily solely, suitable for establishing a production site 15 in relatively shallower waters.

[00140] In this second embodiment, infrastructure 17 associated with the facility 10 is installed at an installation site 19 directly above the production site 15. Indeed, the infrastructure 17 is likely to be installed prior to the oil production well(s) 13 being drilled to establish the production site 15, as will be explained.

[00141] In this second embodiment, the unit 31 provides storage tank 33 and two riser towers 35, as was the case with the first embodiment. The storage tank 33 is located below water surface 21 and has a base section 36 which rests on the sea bed 23. The two riser towers 35 extend upwardly from the submerged storage tank 23 towards and above the water surface 21 . The riser towers 35 are typically framework structures but may be of any suitable construction, as would be understood by a person skilled in art.

[00142] At least one of the riser towers 35 has a pathway 101 defined by, for example a conduit 103, through which a drilling operation can be performed for establishing a respective one of the subsea production wells 13 beneath the installation. The pathway 101 extends downwardly through the unit 31 to open onto the seabed 23 when the unit 31 is resting on the seabed.

[00143] In the arrangement illustrated, both riser towers 35 have pathways 101 .

[00144] In this embodiment, the conduits 103 extend downwardly from the tops of the respective riser towers 35 to open onto the seabed 23 when the unit 31 is resting on the seabed. In other words, the conduits 103 run straight from the tops of the riser towers 35 to the bottom of the unit 31 . In the arrangement shown, the conduits 103 extent through the tank 33 to open onto the base section 36.

[00145] The unit 31 is installed in position, with the base section 36 resting on the sea bed 23 and the two riser towers 35 extending upwardly from the submerged storage tank 23 towards and above the water surface 21 , in a manner similar to that described in relation to the first embodiment.

[00146] The platform structure 61 is then positioned at the installation site 19 and integrated with the unit 31 , again in a manner similar to that described in relation to the first embodiment.

[00147] A drilling operation can then be performed through each conduit 103 into the seabed 23 to establish a subsea production well 13 below the respective riser tower 35. As part of this process, a conductor pipe 105 is installed in each conduit 103. The drilling operation is performed via the conductor pipe 105, as would be understood by a person skilled in the art. The conduit 103 thus provides a support pipe for the conductor pipe 105.

[00148] In this embodiment, the conduits 103 are each 36 inches in diameter and the conductor pipes 105 are 30 inches in diameter. These are indicative sizes (diameters) only and are provided merely as typical examples. The conduits 103 and conductor pipes 105 can, of course, be of any appropriate sizes suitable for the intended purpose, as would be understood by a person skilled in the art.

[00149] The drilling operation is performed using a drilling unit 106.

[00150] A connection point 107 is then installed at the upper end of each conductor pipe 105 as part of the topside installation 71 on platform 63. In this embodiment, the connection point 107 comprises a "dry" production tree unit 109, typically of known kind as would be understood by a person skilled in the art. With this arrangement, the "dry" production tree units 109 are located at the top of the conductor pipes 105 (above the water surface 21 ). This is in contrast to the arrangement in the first embodiment which involves "wet" production tree units situated on the seabed some distance from the installation 30.

[00151] For the purpose of illustration, the arrangement depicted in Figure 10 shows conductor pipe 105 in position in, and supported by, conduit 103a within riser tower 35a, and the associated "dry" production tree unit 109 installed in position. Further, the arrangement depicted in Figure 10 also shows drilling unit 106 in position for a drilling operation through conduit 103b within riser tower 35b.

[00152] Each conductor pipe 105 constitutes at least part of the respective flowline 25 between the subsea production well 13 and the installation 30 above the production site 15.

[00153] While not shown in Figure 10, the unit 31 of this second embodiment may also have one or more J-tubes in one or both riser towers 35 to allow servicing of additional production wells in the manner of the first embodiment. In this way, infrastructure 17 associated with the facility 10 of this second embodiment may service at least two subsea production wells 13, at least one of which is beneath the installation site 19 and at least another of which is spaced away from the installation site 19.

[00154] It should be appreciated that in this second embodiment the production site 15 and associated subsea production wells 13 need not necessarily be directly (vertically) below the installation 30. In circumstances where, for example, the drilling process through the conduits 103 involves directional drilling having a horizontal component, it may be that the production wells 13 are horizontally offset from the installation 30 but nevertheless ultimately connected to the installation 30 by way of flowlines (pipelines 25) passing through the conduits 103. With such an arrangement, the subsea wells 13 would still be established beneath the installation 30 in the sense that the drilling process and the flowlines (pipelines 25) extend into the seabed 23 at a location underneath the installation 30.

[00155] From the foregoing, it is evident that the present embodiments each provides for the establishment of an offshore facility for the recovery of oil from a stranded oil field, where a reservoir has been identified but is difficult to access due to its location. One or more subsea oil production wells are established at a production site for extraction of oil from the stranded oil field, and the offshore facility provides for temporary storage of oil extracted from the subsea oil production wells and then subsequent off-loading of the stored oil to a transfer facility, such as a shuttle tanker.

[00156] Modifications and variations such as would be apparent to the skilled addressee are considered to fall within the scope of the present invention.

[00157] The present disclosure is provided to explain in an enabling fashion the best modes of making and using various embodiments in accordance with the present invention. The disclosure is further offered to enhance an understanding and appreciation for the invention principles and advantages thereof, rather than to limit in any manner the invention. While a preferred embodiment of the invention has been described and illustrated, it is clear that the invention is not so limited. Numerous modifications, changes, variations, substitutions, and equivalents will occur to those skilled in the art having the benefit of this disclosure without departing from the spirit and scope of the present invention as defined by the following claims.

[00158] Reference to positional descriptions, such as "upper", "lower", "top" and "bottom", are to be taken in context of the embodiments depicted in the drawings, and are not to be taken as limiting the invention to the literal interpretation of the term but rather as would be understood by the skilled addressee.

[00159] Additionally, where the terms "system", "device", and "apparatus" are used in the context of the invention, they are to be understood as including reference to any group of functionally related or interacting, interrelated, interdependent or associated components or elements that may be located in proximity to, separate from, integrated with, or discrete from, each other. [00160] Throughout this specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.