OFFSHORE HYDROCARBON PROCESSING FACILITY AND METHOD OF OPERATION

Abstract

An offshore hydrocarbon processing facility (2) comprises an offshore floating structure (8) and a submerged floating riser deck (10). The submerged floating riser deck is operatively connected to a subsea hydrocarbon riser (12). Hydrocarbon processing equipment (26) is disposed on the submerged floating riser deck. The offshore floating structure (8) may be connected to the submerged floating riser deck (10) using a riser (16) that can be disconnected if there is inclement weather.

Claims

1. An offshore hydrocarbon processing facility comprising: an offshore floating structure; a submerged floating riser deck operatively connected to a subsea hydrocarbon riser; and hydrocarbon processing equipment disposed on the submerged floating riser deck.

2. An offshore hydrocarbon processing facility according to claim 1, wherein the submerged floating riser deck floats suspended from the offshore floating structure.

3. An offshore hydrocarbon processing facility according to claim 1 or 2, comprising a riser arranged for disconnectable connection between the offshore floating structure and the submerged floating riser deck.

4. An offshore hydrocarbon processing facility according to claim 1, 2 or 3, wherein the hydrocarbon processing equipment is entirely disposed on the submerged floating riser deck.

5. An offshore hydrocarbon processing facility as claimed in any preceding claim, wherein the offshore hydrocarbon processing facility is an unmanned hydrocarbon processing facility, comprising at least one of: no permanent personnel; no provision of facilities for personnel to stay on the offshore hydrocarbon processing facility, for example there may be no shelters for personnel, no toilet facilities, no drinking water, no personnel operated communications equipment and/or no lifeboat; and/or a requirement that personnel be present for fewer than 10,000 maintenance hours per year.

6. An offshore hydrocarbon processing facility as claimed in any preceding claim, wherein the offshore floating structure is an unmanned structure and/or an unmanned production structure, comprising at least one of: no permanent personnel; no provision of facilities for personnel to stay on the platform, for example there may be no shelters for personnel, no toilet facilities, no drinking water, no personnel operated communications equipment and/or no lifeboat; and/or a requirement that personnel be present for fewer than 10,000 maintenance hours per year.

7. An offshore hydrocarbon processing facility as claimed in claim 1, wherein the offshore floating structure further comprises topside processing equipment located on the offshore floating structure, arranged to produce at least one of a hydrocarbon liquid product, a hydrocarbon semi-stable liquid product and a liquefied gas product.

8. An offshore hydrocarbon processing facility as claimed in claim 7, wherein the facility is configured such that a hydrocarbon fluid to be processed is processed first by the subsea equipment and then by the topside equipment.

9. An offshore hydrocarbon processing facility as claimed in any preceding claim, wherein the offshore floating structure is horizontally offset from the submerged floating riser deck, such that the two are not vertically aligned.

10. An offshore hydrocarbon processing facility as claimed in any preceding claim, wherein the submerged floating riser deck is arranged to separate liquid hydrocarbons, flash the separated liquid hydrocarbons and store the flashed hydrocarbons at the submerged floating riser deck.

11. An offshore hydrocarbon processing facility as claimed in any preceding claim further comprising a buoy, wherein the submerged floating riser deck is operatively connected to the buoy for offload of hydrocarbon products to a floating vessel.

12. A method of operating the offshore hydrocarbon processing facility of any of claims 1 to 11, comprising: receiving hydrocarbons at the submerged floating riser deck from the subsea hydrocarbon riser; and processing the hydrocarbons using the hydrocarbon processing equipment.

13. A method of operating the offshore hydrocarbon processing facility as claimed in claim 12, comprising disconnectably connecting the submerged floating riser deck to the offshore floating platform using a riser for transfer of hydrocarbons between them.

14. A method of operating the offshore hydrocarbon processing facility as claimed in claim 12 or 13, comprising: fluidly connecting the submerged floating riser deck to a floating vessel for transfer of hydrocarbons from the submerged floating riser deck to the floating vessel; and/or fluidly connecting the submerged floating riser deck to a pipeline for transfer of hydrocarbons from the submerged floating riser deck via the pipeline.

15. A method of operating the offshore hydrocarbon processing facility as claimed in claim 12, 13 or 14, comprising: fluidly connecting the submerged floating riser deck to a buoy; and transferring hydrocarbons from the buoy to a floating vessel.

16. A method of using the offshore hydrocarbon processing facility as claimed in any of claims 12 to 15, comprising: separating and flashing liquid hydrocarbons at the submerged floating riser deck; and storing the flashed hydrocarbons in storage tanks at the submerged floating riser deck.

Description

[0042] Certain preferred embodiments of the present invention will now be described in greater detail by way of example only and with reference to the accompanying drawings, in which:

[0043] FIG. 1 shows an offshore hydrocarbon processing facility where an offshore floating structure includes a platform with decks; and

[0044] FIG. 2 shows another offshore hydrocarbon processing facility where an offshore floating structure is a spar buoy.

[0045] FIG. 1 shows an offshore hydrocarbon processing facility 2, located offshore, comprising an offshore floating structure 8 (designed to be unmanned as discussed above) and a submerged floating riser deck 10. The offshore floating structure 8 is a platform with decks that may hold equipment as required for the intended use of the offshore facility 2, The submerged floating riser deck 10 is operatively connected to a number of subsea hydrocarbon risers 12, through which hydrocarbons can flow from the seabed 4, The hydrocarbon risers 12 may be steel catenary risers, supported by buoyancy aids 14. The submerged floating riser deck 10 comprises hydrocarbon processing equipment 26 for processing hydrocarbons received via the hydrocarbon risers 12. The submerged floating riser deck 10 is submerged, i.e. fully below sea level 6, but remains floating through the use of buoyancy aids 18 and/or through suspension from the offshore floating structure 8. The platform 8 can be secured to the seabed via a catenary mooring system (not shown).

[0046] Floating near the surface of the sea (sea level 6) and at least partially protruding above the surface of the sea level 6 is the offshore floating platform 8, which has hydrocarbon processing equipment 24. The offshore floating platform 8 is connected to the submerged floating riser deck 10 via several risers 16. The risers 16 can be disconnected from the offshore floating platform 8 in case of inclement surface conditions.

[0047] FIGS. 2, 3 and 4 show another hydrocarbon processing facility where the offshore floating structure 8 is a spar buoy 8. In this example the spar buoy 8 floats due to its own buoyancy and the submerged floating riser deck 10 is suspended from the spar buoy 8 via a cable suspension system 32. The submerged floating riser deck 10 is fully supported by the cable suspension system 32 and does not need any additional positive buoyancy elements. The spar buoy 8 is moored via catenary mooring cables 30 and hydrocarbons are transported between the seabed 4, the submerged floating riser deck 10 and the spar buoy (offshore floating structure) 8 via catenary hydrocarbon risers 12 and disconnectable risers 16 in a similar way to FIG. 1. The catenary risers 12 are supported by buoyancy aids 14.

[0048] FIGS. 2 and 3 show an example of this spar buoy system at a realistic scale and also include vessels servicing the offshore facility 2, along with subsea structures to which the offshore facility is connected. FIG. 4 shows a similar system in a more schematic arrangement similar to FIG. 1, with the scale distorted and the catenary mooring cables 30 omitted from the drawing.

[0049] In relation to the offshore facilities 2 of both of FIG. 1 and FIG. 2 the hydrocarbon processing facility 2 has a buoy 20 connected to the offshore floating platform 8 for transferring gas or pressured and cooled gas therefrom to a tanker, floating vessel or the like which can connect to the buoy 20.

[0050] The hydrocarbon processing facility 2 also has a buoy 22 connected to the submerged floating riser deck 10 for transferring semi-stable liquid therefrom to a tanker, floating vessel 34 or the like, as shown in FIG. 2, which can connect to the buoy 22.

[0051] In operation, hydrocarbons flow from the seabed 4 through the risers 12 to the submerged floating riser deck 10. Here, the hydrocarbons may be fully processed, partially processed or not processed at all. Any processing is carried out by the hydrocarbon processing equipment 26. One or more storage tanks at the submerged floating riser deck 10 can be used for storage of fully processed, part processed or unprocessed hydrocarbons. In the exemplary diagram shown in the Figures, the hydrocarbons can be processed out by the hydrocarbon processing equipment 26 at the subsea riser deck 10 to produce two products, namely a gaseous product and a semi-stable liquid product. The former is transferred to the offshore floating structure 8 via the disconnectable risers 16, while the latter is transferred to the semi-stable liquid buoy 22. The semi-stable liquid product may comprise any or all of water, oil condensate, LPG and NGL.

[0052] At the offshore floating structure 8, the received gas product is optionally processed using hydrocarbon processing equipment 24. The processing may include drying and/or cooling and pressurising. The final product, which may be liquefied, is transferred to buoy 20. Alternatively, the offshore facility 2 may be arranged so that all of the required processing is done at the submerged riser deck 10 with no processing equipment on the offshore floating structure 8. This can allow the offshore floating structure 8 to be a smaller floating platform such as the spar buoy 8 of FIG. 2.

[0053] Tankers, other floating vessels and the like can connect to buoys 20 and 22 to be loaded with the gas and semi-stable liquid products respectively.

[0054] In the case of inclement weather conditions at sea level 6, such as wind, waves, hurricanes, tropical monsoons, precipitation, icebergs, ice floes or other conditions deemed to be harmful to the riser 16, the riser 16 can be disconnected from the offshore floating structure 8 for the duration of the harmful conditions, and can be reconnected once these conditions pass.

[0055] Any maintenance work which needs to be carried out on the submerged hydrocarbon processing equipment 26 can be done more easily than in the prior art where the equipment is at the sea bed, since the hydrocarbon processing equipment 26 is not as deep underwater as the sea bed 4.

[0056] In some embodiments the offshore floating structure does not have any role in processing the hydrocarbons that are processed at the submerged floating riser deck. For example, the spar buoy Thus, hydrocarbons may be processed at the submerged riser deck and transferred elsewhere, via the offshore floating structure or via other means such as the buoys, without any processing aboard the floating structure.