Operation of an Unmanned Productive Platform

Abstract

An unmanned production platform comprises apparatus for producing and processing hydrocarbons from a subsea reservoir. A storage vessel is provided in combination with and proximate to the platform, typically just outside the safety zone. The storage vessel provides storage for hydrocarbons produced at the platform and further provides a utility for use at the platform, such as chemical storage, liquid desiccant regeneration and/or seawater treatment. Typically, the unmanned production platform comprises no utilities and all utilities require for production are provided by the storage vessel.

Claims

1. An unmanned production platform in combination with and proximate to a storage vessel, wherein the platform comprises apparatus for producing and processing hydrocarbons from a subsea reservoir and the storage vessel provides storage for hydrocarbons produced thereby and further provides a utility for use at the platform.

2. The combination of claim 1, wherein the storage vessel is situated less than 2 km away from the platform, optionally less than 1 km away from the platform, and further optionally just outside of the safety zone of the platform.

3. The combination of claim 1, wherein the unmanned production platform is the only platform which the vessel is connected to.

4. The combination of claim 1, wherein the storage comprises an oil storage tank in fluid communication with the platform.

5. The combination of claim 1, wherein the apparatus for producing and processing hydrocarbons comprises separation apparatus for separating produced hydrocarbon into oil and gas components.

6. The combination of claim 5, wherein the separation apparatus additionally separates water from produced hydrocarbons.

7. The combination of claim 5 wherein the separation apparatus comprises multiple separation stages.

8. The combination of claim 1, further comprising subsea separation apparatus.

9. The combination of claim 1, wherein the vessel provides seawater treatment for seawater injection.

10. The combination of claim 1, wherein the vessel provides storage for chemicals used at the production platform.

11. The combination of claim 1, wherein the vessel provides a supply of liquid desiccant and desiccant regeneration.

12. The combination of claim 1, wherein the vessel provides sulphate removal apparatus.

13. The combination of claim 1, wherein the vessel comprises an electricity generator for supplying power to the platform.

14. The combination of claim 1, further comprising a shuttle tanker for collecting and transporting hydrocarbons stored on the storage vessel.

15. A method of producing hydrocarbons comprising the use of the combination of claim 1.

16. A hydrocarbon storage and utility vessel comprising an oil storage tank and providing one or more of the following utilities for use by a hydrocarbon production platform: a. chemical storage; b. liquid desiccant and desiccant regeneration; c. seawater treatment; and d. sulphate removal.

17. The hydrocarbon storage and utility vessel of claim 16, wherein the vessel additionally provides electricity generation for use by a hydrocarbon production platform.

18. The hydrocarbon storage and utility vessel of claim 16, wherein there is no hydrocarbon handling equipment (processing/production equipment) provided thereon.

19. The hydrocarbon storage and utility vessel of claim 16, wherein the chemical storage comprises storage for at least one of: corrosion inhibitors, hydrate inhibitors, emulsion breakers and hydrogen sulphide scavengers.

Description

[0044] An embodiment of the invention will now be described, by way of example only, and with reference to the accompanying drawings in which:

[0045] FIG. 1 is a perspective overview of an unmanned production platform and FUSO vessel according to an embodiment of the invention;

[0046] FIG. 2 is a view corresponding to FIG. 1 in which a shuttle tanker is additionally shown; and

[0047] FIG. 3 is a schematic view of the production and processing apparatus of the platform and FUSO vessel of FIG. 1.

[0048] As may be seen from FIG. 1, an unmanned production platform 1 is provided in the form of a floating spar buoy 2 with a superstructure 3 mounted thereon in a region of the sea 4 remote from a host platform (not shown). The platform is moored to the sea bed 5 by means of suitable catenary moorings 6. A Floating Utility, Storage and Offloading vessel (FUSO) 7 is located at the surface 8 nearby and is typically situated just outside of the safety zone of the platform 1.

[0049] A subsea separator 9 connected to a wellhead (not shown) via conduit 11 is provided at the seabed. The subsea separator 9 is connected to the platform 1 by means of two risers 10a, 10b. A further riser 10c connects the platform 1 to an additional wellhead (not shown). Utilities conduit 12 and hydrocarbon fluid conduit 13 interconnect the platform 1 with the FUSO vessel 7. A water conduit 14a also connects to the FUSO vessel 7 and interconnects the vessel 7 with injection wells (not shown). A similar water conduit 14b interconnects the platform 1 with the injection wells. The FUSO vessel 7 includes storage tanks (not shown) for receiving produced hydrocarbons from the platform 1 via the hydrocarbon fluid conduit 13 and provides various utilities to the platform 1 via the utilities conduit 12, as will be discussed further below. The FUSO vessel 7 further comprises a water treatment facility as described further below for providing water via the water conduit 14a to the injection wells.

[0050] FIG. 2 corresponds exactly to FIG. 1 except that it additionally shows a shuttle tanker 15 connected to FUSO vessel 7 by means of a flexible offloading conduit 16.

[0051] During operation, produced hydrocarbons pass from the wellhead, via the subsea separator, 9 and flow via risers 10a, 10b to the platform 1 for processing. Produced hydrocarbons similarly pass from the other wellhead via riser 10c to the platform 1 for processing. Processed hydrocarbons (e.g. separated and stabilised or semi-stabilised oil and/or gas) flow from the platform 1 to the FUSO vessel 7 via hydrocarbon fluid conduit 13 where they are stored pending transportation by a shuttle tanker.

[0052] Once the tanks on the FUSO vessel 7 approach being filled, a shuttle tanker 15 sails to the site of the FUSO vessel 7. Here, as shown in FIG. 2, it is connected via conduit 16 to the FUSO vessel 7 and hydrocarbon fluids are then transferred to the shuttle tanker 15. Once it is fully loaded, the shuttle tanker 15 sails to the host with its cargo of hydrocarbon fluid where it is unloaded. The shuttle tanker 15 may then return to the FUSO vessel 7 when required.

[0053] The FUSO vessel 7 also serves to provide various utilities to the production platform.

[0054] In the present embodiment, a first utility is the provision of electrical power. This is generated on board the FUSO vessel 7 using a gas motor powered by gas supplied by the platform. The electrical power is transmitted to the platform via a cable provided within the utilities conduit 12.

[0055] A second utility provided at the FUSO vessel 7 is the storage and processing of chemicals, such as glycols e.g. MEG and TEG used to dehydrate produced fluids. The processing of these fluids comprises regeneration of them to remove water absorbed from the hydrocarbon fluids, in the known manner. The FUSO vessel 7 may additionally provide storage and processing of emulsion inhibitors, other hydrate inhibitors, corrosion inhibitors and hydrogen sulphide scavengers. These fluids are transported via respective lines within the utilities conduit 12 to/from the platform 1.

[0056] A third utility provided at the FUSO vessel 7 is the provision of treated sea water for injection. It is known that sulphates found in sea water can cause problematic scale formation and so it is known to remove sulphates from the water before it is injected.

[0057] The FUSO vessel 7 draws sea water through an inlet port provided in its hull (not shown) and uses treatment apparatus known in the art to remove sulphates. The treated sea water is then transported via water conduit 14a to the injection wells at the sea bed.

[0058] The operation of the platform 1 and FUSO vessel 7 will now be described in more detail with reference to FIG. 3, which shows a schematic flow diagram. This diagram has four regions demarcated by dashed lines. These are platform superstructure 3, FUSO vessel 7, shuttle tanker 15 and subsea components 17.

[0059] Considering first the subsea components, a plurality of production wells 20 are connected via conduits to manifold 21, which in turn feeds subsea first-stage separator 9. The gas outlet from this is connected to gas riser 10a. The oil outlet is connected to oil pumps 24a feeding oil riser 10b and the water outlet connected to water pumps 24b feeds water riser 26. Each of these risers is connected to apparatus at the superstructure 3 of the platform 1 as will be described further below.

[0060] In addition, water injection wells 27 (not shown in FIG. 1) are provided at the seabed. These wells 27 are fed by the water conduits 14a, 14b from the FUSO vessel 7 and the UPP 1.

[0061] As discussed above, the FUSO vessel 7 provides both hydrocarbon (here oil) storage and various utilities.

[0062] Oil storage is provided by means of conventional storage tanks 30 on board the vessel. These are supplied by means of hydrocarbon conduit 13 from the platform 1.

[0063] TEG regeneration is provided using conventional apparatus at 32.

[0064] Chemical storage (e.g. storage of TEG) is provided at 33.

[0065] The conduits associated with oil storage (i.e. between conduit 13 and tanks 30) and TEG storage and regeneration are not shown in this figure for clarity.

[0066] Gas motor 34 is supplied by gas from the platform via line 35. The motor drives generator 36 and the electricity from generator 36 is transmitted to the platform via a subsea cable within the utilities conduit (see FIG. 1, 12).

[0067] Seawater treatment unit 37 removes sulphates from seawater as discussed above. Treated water from that unit is pumped by seawater injection pumps 38 via water conduit 14a to injection wells 27 at the sea bed.

[0068] Shuttle tanker 15 comprises oil storage tanks (not shown). These are connected via conduit 40 and valves 41 which are connectable to a flexible conduit 16, which leads to the oil storage tanks 30 of the FUSO vessel. The connectable arrangement allows for the shuttle tanker to be moored close to the FUSO vessel for side-by-side offloading in the known manner.

[0069] The superstructure 3 of the platform 1 provides the hydrocarbon processing apparatus, in particular the further separation of the produced fluid into its components (oil, water, gas) following the first stage separation carried out subsea. (As is well known in the art, a single stage of separation will not completely separate the fluids and so references to the flow of a specific fluid from a separator refers to a flow that is primarily of that fluid, but which may contain other components).

[0070] It will be appreciated that the specific details of the separation apparatus shown in FIG. 3 are not critical to a proper understanding of the invention described herein and so the discussion below focuses on the main components.

[0071] Oil (i.e. oil-rich fluid) from riser 10b flows to second stage separator 50. The oil component of this then passes to third (and final) stage separator 51, with the oil from the outlet of the final stage flowing via pump 52 and oil transfer riser 13 to the oil storage tanks 30 on the FUSO vessel 7.

[0072] Gas from the first stage separator 9 flows via riser 10a to gas cooler 53 and then to first stage scrubber 54. The gas from the outlet of scrubber 54 is split into two flow paths. The first of these flows via line 35 to the gas motor 34 on board the FUSO vessel 7 (used to drive electricity generator 36). The remaining portion flows to first stage gas compressor 55 and then via dehydration inlet cooler 56, dehydration unit 57 and gas scrubber 58 to export gas compressor 59. The gas from the compressor 59 then flows via gas export riser 60 to a gas export pipeline 61 on the sea bed. This is used to transport gas to an onshore facility or to a host vessel. It will be appreciated that in some cases it will not be economically viable to provide a gas transport pipeline and so in alternative embodiments, gas that is not used for fuel at the FUSO vessel 7 may be re-injected or flared.

[0073] Water from water riser 26 is fed via compact floatation unit 62 and walnut shell filter 63 to cooler 64 and water pumps 65 before flowing along water conduit 14b to the injection wells 27 at the sea bed. Any hydrocarbons removed from the water at the compact floatation unit 62 and walnut shell filter 63 are sent to the second 50 and/or third 51 stage separator.

[0074] It will be noted that in this embodiment, the injection water is provided both from the platform 1 (i.e. separated water for reinjection) and from the seawater treatment unit at the FUSO vessel 7. In alternative embodiments, the injection water may be provided from only one of these sources. Additionally and/or alternatively, the water separated at the platform 1 may be passed to the FUSO vessel 7 for treatment prior to injection at the wells 27. As such, the compact floatation unit 62 and walnut shell filter 63 may be provided on the FUSO vessel 7.

[0075] In addition to the flows described above, the flows of separated gas and water from the second 50 and third 51 stage separators need to be considered.

[0076] Gas from the second stage separator 50 flows via third stage cooler 66 and scrubber 67 to third stage compressor 68 before joining the flow of gas from the first stage separator 22 upstream of cooler 53.

[0077] Gas from the third (final) separator 51 flows via first stage cooler 69, scrubber 70, compressor 71, second stage cooler 72, scrubber 73 and second stage compressor 74 before joining the flow of gas from second stage separator 50 upstream of the third stage cooler 66.

[0078] It will also be noted from the figure that oil removed from the gas at scrubbers 58, 54 and 73 is returned to the previous scrubber, with oil from scrubber 70 being routed via pump 75 to join the oil flowing from second stage separator 50 to third (final) separator 51.

[0079] Finally, water from second stage separator 50 joins the flow of water from riser 26 upstream of CFU 62.

[0080] Thus, in this embodiment it will be seen that the produced fluid is fully separated and processed at the platform itself, with the oil component then being stored in tanks 30 on board the FUSO vessel 7 prior to loading on board shuttle tanker 15 for transportation to a host.

[0081] In addition, the FUSO vessel 7 provides utilities, which would conventionally be provided on board the platform 1, including chemical (e.g. TEG) storage 33, TEG regeneration 32, injection water provision and treatment 37 and 38, and electricity generation 34 and 36.