Apparatus and Method

Abstract

Apparatus and method for processing of production fluids from a subsea oil or gas well, in order to recover hydrocarbons from the well. In an embodiment, the apparatus is a column stabilised structure having an interconnected array of three columns, with the upper portion protruding above the surface of the sea. The apparatus described has processing facilities in a lower portion of a first column, power generation facilities in a lower portion of a second column and service and utilities in a lower portion of a third column. Further facilities equipment and storage tanks can be located in the columns.

Claims

1. An apparatus for processing of production fluids from a subsea well, the apparatus being a column stabilised submerged structure comprising an interconnected array of at least three columns, each column comprising an upper portion and a lower portion, the lower portion comprising at least one compartment, and wherein said at least one compartment incorporates facilitating equipment, the facilitating equipment comprising processing equipment for processing of production fluids from the subsea well in at least one column.

2. The apparatus according to claim 1 wherein the apparatus is unmanned.

3. The apparatus according to claim 1 wherein the production fluids comprise hydrocarbons and the processing equipment is adapted to separate the hydrocarbons from other components of the production fluids.

4. The apparatus according to claim 1 wherein the lower portions of the columns incorporating the facilitating equipment are submerged beneath the waterline when the interconnected array is fully installed.

5. The apparatus according to claim 1 wherein the majority of the total mass of the apparatus is in the lower portions of the columns.

6. The apparatus according to claim 1 wherein the columns pierce the surface of the sea so that the upper portion of each column is above the sea surface.

7. The apparatus according to claim 1 wherein the facilitating equipment comprises one or more from a group comprising: water treatment facilities, injection facilities, gas compression apparatus, oil metering and export, power generation and distribution equipment, and service equipment, utilities equipment, HVAC, control system, telecommunications system, firefighting system; crew facilities, a control room, refuge space, workshops, and life-saving equipment.

8. The apparatus according to claim 7 wherein the lower portion in at least one column also includes one or more fluid storage chambers wherein the one or more fluid storage containers contain fluid selected from a group comprising: oil, fuel, chemical, potable water, and water ballast.

9. The apparatus according to claim 7 wherein the processing equipment is located in the lower portion of a first column, power generation equipment is located in the lower portion of a second column, and service and utilities functions are located in a third column.

10. The apparatus according to claim 9 wherein at least one column includes a HVAC system and the heat generated from power generation and processing is directed via the HVAC system to provide heating for the services and utilities functions in the third column.

11. The apparatus according to claim 9 wherein at least one column includes a HVAC system and the heat generated from power generation and processing is directed via the HVAC system to minimise build-up of ice and/or snow on the apparatus located above the sea surface.

12. The apparatus according to claim 1 wherein each column of the interconnected array is connected to at least two other columns.

13. The apparatus according to claim 12 wherein the columns are interconnected above the surface of the sea by structural braces.

14. The apparatus according to claim 12 wherein the columns are interconnected below the sea surface by structural braces.

15. The apparatus according to claim 1 wherein offloading of processed fluids to a tanker is performed directly from the apparatus via a hose reel contained within one of the columns.

16. (canceled)

17. The apparatus according to claim 1 wherein a subsea storage tank is supported by the columns in a central section of the interconnected array between the columns.

18. The apparatus according to claim 17 wherein the subsea storage tank is secured to the interconnected array during transport of the apparatus to a deployment location and the subsea storage tank is released and lowered to the seabed once the interconnected array has reached the deployment site.

19. The apparatus according to claim 1 wherein the interconnected array is configured to have chain lockers in at least one of the upper portions, wherein the chain lockers are used to pre-connect and store chain prior to load-out of the apparatus.

20. The apparatus according to claim 1 wherein the apparatus includes mooring lines for mooring the interconnected array, the mooring lines being in sections and when laid straight on the seabed a free end of each mooring line is the same distance from a target array location.

21. (canceled)

22. The apparatus according to claim 1 wherein an additional power generation source is located on the apparatus, selected from a group comprising: wind turbine, wave energy device and solar energy device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In the accompanying drawings:

[0044] FIG. 1a shows a side view of a first example of apparatus for processing of production fluids from a subsea well comprising an interconnected array having three columns;

[0045] FIG. 1b shows a plan view of the array of FIG. 1a;

[0046] FIG. 1c shows a cross-sectional view of each column of the array of FIG. 1a;

[0047] FIG. 2a shows a plan view of a second example of an interconnected array having four columns;

[0048] FIG. 2b shows a plan view of a third example of an interconnected array with five columns;

[0049] FIG. 2c shows a plan view of a fourth example of an interconnected array with six columns;

[0050] FIG. 3a shows a side view of an interconnected array with three columns during the mooring procedure, having chain lockers for storing chain that is pre-connected to the array;

[0051] FIG. 3b shows a plan view of the configuration of FIG. 3a;

[0052] FIG. 4a shows a side view of an interconnected array substantially in line with FIG. 1, with a typical arrangement for dynamic flexible risers;

[0053] FIG. 4b is a plan view of the configuration shown in FIG. 4a;

[0054] FIG. 5a shows a side view of an interconnected array with three columns, the array comprising a tank or subsea structure that is ready to deploy onto a landing site;

[0055] FIG. 5b shows a plan view of the array and subsea structure of FIG. 5a;

[0056] FIG. 5c shows a side view of the subsea structure beginning to be lowered to the landing site using winches on board the array;

[0057] FIG. 5d shows a side view of the subsea structure having been landed on the seabed;

[0058] FIG. 6a shows a side view of a hydrocarbon offloading configuration with an array substantially in line with FIG. 2a;

[0059] FIG. 6b shows a plan view of the configuration of FIG. 6a, showing two possible positions for the hose reel;

[0060] FIG. 7 shows a side view of an interconnected array substantially in line with FIG. 1, with storage tanks underneath each column;

[0061] FIG. 8a shows a side view of an interconnected array with three columns, with a drilling derrick and covered over main deck;

[0062] FIG. 8b shows a plan view of the array and derrick of FIG. 8a;

[0063] FIG. 9a shows a side view of an interconnected array having four columns with a wind turbine connected to the array in a central location and a wave energy device incorporated within one of the columns;

[0064] FIG. 9b shows a plan view of the array and centrally-installed wind turbine of FIG. 9a;

[0065] FIG. 9c shows an alternative installation site for the wind turbine on top of one of the columns of the array.

DETAILED DESCRIPTION

[0066] Referring to the drawings, an example of apparatus for processing of production fluids from a subsea well comprising a facility in the form of an interconnected array 1 with three columns 10, 20, 30 is shown in FIGS. 1a-1c. This configuration of columns provides good column stabilisation in all directions. Alternatively, a greater number of columns may be used as illustrated in FIGS. 2a-2c.

[0067] Each column 10, 20, 30 has an upper portion 10u, 20u, 30u and a lower portion 101, 201, 301. The upper portions 10u, 20u, 30u comprise a portion of a long vertical neck section 10n, 20n, 30n, and refer to the part of the neck that is above the surface of the sea. The upper portions 10u, 20u, 30u extend above the sea surface to a height that is above the highest anticipated wave crest at the deployment site.

[0068] The lower portions 101, 201, 301 of the columns 10, 20, 30 comprise a submerged portion of the neck 10n, 20n, 30n, and a larger diameter section that is well below the surface of the sea, and thus at reduced risk of an impact with the keel of a passing vessel.

[0069] The dimensions (e.g. diameters and relative heights) of the upper 10u, 20u, 30u and lower portions 101, 201, 301 of the columns 10, 20, 30 may optionally be the same, or may optionally vary according to the functional requirement of what is contained within the columns 10, 20, 30 and to optimise the hydrodynamic behaviour of the overall array 1. The columns 10, 20, 30 are held structurally together typically by braces 7, 8, 9. An example configuration for the bracing is illustrated in the Figures, but other configurations may be used.

[0070] Access from one column 10, 20, 30 to another is via a walkway 5 above the water line, or via a series of watertight and blast-proof doors in the lower braces 8. Stores and equipment can be lifted onto the platform 3 by either the vessel's crane or the crane 15 located on column 10.

[0071] The array 1 is moored in position by mooring lines 4. The mooring lines 4 are typically installed to an outer surface of each column, however, in some configurations of the array it is not necessary to attach mooring lines to every column.

[0072] In the example shown in FIG. 1a, the majority of the displaced volume of the array 1 is below the water line. The service and utilities column 10 is the normal point of access and egress to the array 1 either via access walkway from a vessel onto the platform 3, or via a smaller vessel and the ladder 11. The upper section 10u of column 10 contains the control room, crane 15, and telecommunications and radar mast 16. The overall height of this section 10u is greater than the upper sections 20u, 30u of the other two columns 20, 30, in order to maximise the height of the telecommunications and radar mast 16, and enable and enhance transmission and receipt of signals.

[0073] Column 20 contains the power generation equipment for the array 1 and is used to generate the required electrical power for facility and subsea functions. Any exhaust gases produced as a result of the power generation process are vented from the array 1 through exhaust tubes 25, on the uppermost surface of the column neck 20n. Column 30 contains the processing area for the processing of, for example, hydrocarbon fluids, gases, solids and water. Excess gases that may be produced from the processing of production fluids are either sent to the power generator in column 20 for use as fuel, or vented via the flare 35 above the processing column 30. Subject to the design of the facility, the gas may be exported via one or more dynamic risers 38. The dynamic risers are typically hung off the column 30 on a support structure 37, connected to one side of the column 30.

[0074] The fluids and gases to be processed along with any electrical or hydraulic controls and electrical power may be transferred to the subsea via the dynamic flexible risers and umbilicals 38.

[0075] FIG. 1c shows a cross-sectional view of the columns 10, 20, 30. The location and arrangement of functions and equipment described herein are exemplary and may be changed based on the required functionality of the array 1. For example, if it is required to store processed oil for an extended period of time, more space may be given over for fluid storage.

[0076] In FIG. 1c, the processing area 32 has an access trunk 33a directly above it, which allows personnel to access the processing area 32 and other sections of the column 30 to install, maintain, or replace equipment. The power generation area 22 of column 20 similarly has an access trunk 23a above.

[0077] The service and utilities column 10 holds the main controls and telecommunications area 19, which is located well above the water line. The controls and telecommunications area 19 contains the control room, workshop, office and refuge for personnel working on the array 1, and is the principal area where personnel gain access to and egress from the facility. Below this area 19 there is an access shaft 13a to the utilities area 12, which in a typical configuration includes HVAC and fire control systems, but may also be used for supplementary functions such as e.g. water cleaning, or oil metering, as required.

[0078] The areas 13s, 23s, 33s surrounding the access trunks 13a, 23a, 33a are void spaces. The dimensions of the spaces 13s, 23s, 33s are optionally selected to provide sufficient buoyancy to support the upper portion of the columns above the waterline, and optionally act as a buffer in the event of vessel impact with the column 10, 20, 30. The spaces 13s, 23s, 33s around the processing 32, power generation 22 and utilities 11 areas are used for storage of water ballast, fuel, chemicals and potable water as required and are typically below the keel of passing vessels.

[0079] FIGS. 2a-2c show some further examples of configurations of the array 1 with increasing numbers of columns, and the reference numbers for each separate and subsequent example have been increased by 100.

[0080] FIG. 2a shows an array 100 having four columns 110, 120, 130, 140 interconnected by braces 107 and others (not shown). The four column arrangement 100 may use the additional column 140 to further sub-divide the functions of the facility, but equally may be used for storage of fuel, ballast, processed oils, chemicals or a combination thereof. Alternatively, the additional column 140 can be used to provide additional processing or power generation capacity. This configuration allows greater separation between the services and utilities column 110 and the processing column 130, which in some cases can allow greater stability of the array.

[0081] The five-column configuration 200, shown in FIG. 2b, is typically a pentagonal configuration, and allows further separation between the processing column 230 and the service/utilities column 210.

[0082] The six-column configuration 300 in FIG. 2c offers a more symmetrical arrangement of columns, and does not require mooring lines 304 to be connected to every column 310, 320, 330, 340, 350, 360. This configuration may be strengthened against flexing under wave loading by including cross braces 306 for additional resistance. This configuration could allow direct access for personnel via the cross-braces 306 to the processing column 330. Due to the addition of three further columns 340, 350, 360 over the array 1 shown in FIGS. 1a-1c, this configuration may be used to store increased volumes of oil.

[0083] FIGS. 3a and 3b shows the array 1 nearing completion of the mooring operation at the installation site, with eight out of nine mooring lines 4 connected. The last mooring line is within a chain locker 36 and is pre-connected to the outside surface of column 30, with the other free end being accessible at the top of the chain locker 36. The free end is lifted out of the locker 36 to allow connection to a pre-installed mooring line on the seabed. By using this method there does not need to be personnel on board the facility for the mooring hook-up. This configuration increases the stability of the facility during towing by having the weight of the chain low down in the structure. This configuration also allows the connection between the top of the mooring line and the facility to be performed in sheltered water or alongside in port.

[0084] FIGS. 4a and 4b shows an example of a typical arrangement of dynamic flexible risers, umbilicals, and power cables connecting to the columns 10, 20, 30. Production fluids and water are transported through risers 38 and brought onboard the facility through a bulkhead towards the base of the processing column 30. A control umbilical 18 passes through the base of the service/utility column 10 in an I-tube and is hung-off well above the water line. This allows the individual cables and hoses to be attached in a dry environment. Similarly, a power cable 28 is brought up through the bottom of the power generation column 20 inside an I-tube and hung-off at a similar elevation as the control umbilical 18. This configuration ensures that the functions which are sensitive to water ingress are connected in a dry, controlled, and sheltered environment.

[0085] FIGS. 5a-5d show deployment of a subsea storage tank 40 using winches connected via winch lines 41. The storage tank 40 is likely to be fully submerged during transport and installation, and hence the tension in the winch lines 41 can be controlled using adjustment of the amount of ballast on the tank 40. During transit, the tank 40 is secured in place by guides (not shown) that are located between the columns 10, 20, 30 of the array 1.

[0086] Upon arrival at the offshore site the array 1 may be moored, either at its final location or above the planned location of the storage tank 40. Winches on the array 1 may be used to control the lowering of the tank 40 onto the seabed, by releasing the seafastening arrangement and then lowering the tank 40, using the winches to control the angle of the tank 40 via the winch lines 41. Once the tank 40 is on the seabed the winch lines 41 may be disconnected and the subsea tank 40 will be fully ballasted to its operational weight.

[0087] When the tank 40 is to be recovered, the installation procedure may be carried out in reverse. The tank 40 is deballasted and winched from the seabed to the array 1, and the array 1 and tank 40 are then towed to port together. The subsea tank 40 may be lowered underneath the array 1 in sheltered water in order to separate the tank 40 from the array 1.

[0088] FIGS. 6a and 6b show a direct offloading configuration from an example of an array with four columns, using a hose reel 161 which transports fluid to or from the facility to a tanker 160 via a hose section 162. The hose section 162 may be in a catenary configuration as illustrated, or it may be floating on the surface of the sea. The hose reel 161 may be in two positions, the first being on top of a column (in this example column 140), or being installed on a brace 107. The hose reel 161 may optionally be contained within the column 140 to protect it from the environment, and for security purposes.

[0089] The tanker 160 may be moored to one or more columns of the array via one or more mooring lines 164. The mooring line or lines 164 may be individual lines, or alternatively may be in a bridle arrangement as shown in FIG. 6b. Alternatively, if the tanker 160 is dynamically positioned, mooring may not be necessary.

[0090] The oil which is to be offloaded to the tanker 160 may be extracted from a subsea storage tank (not shown) via flexible risers 138, or may be provided by storage tanks on, or within, the array itself.

[0091] FIG. 7 shows an alternative configuration of the array 401, with three columns, where the columns 410, 420, 430 have additional tanks 470 under one or more of the columns 410, 420, 430, which may be used to enhance the stabilisation of oil, and/or provide storage for the oil. The inner chamber of the tank 470 may be segmented, or may contain baffles 477 to restrict movement or sloshing of oil, for example as a result of wave impacts, and potential destabilisation of the array 401 as a result. The oil would typically enter and exit the tank 470 via a connection 476, and water ballast levels may be adjusted via pipe 475. In an alternative arrangement, the water ballast may be held in a separate tank to prevent mixing of oil and water. The tanks 470 may be an integral part of the column (as shown for columns 410 and 420), or may be detachable as shown for column 430, where clamping devices 474 connect the tank 470 to the base of the column 430.

[0092] FIG. 8 shows an example of the array 1 with a covered-over main deck 82, onto which a drilling derrick 80 has been installed. This configuration allows the array 1 to either perform intervention on a well, such as retrieval of an electric submersible pump, or alternatively have dry trees. This allows the process fluid to rise vertically and directly onto the facility. In this example, the array 1 may require additional modules and functions to be added to permit either part- or fully-manned operation, such as accommodation blocks. However, the processing function is unaffected by the installation of the derrick, and this procedure may continue without requiring manual intervention, i.e. in unmanned examples.

[0093] FIGS. 9a and 9b show an example of the array having four columns 110, 120, 130, 140, with a wind turbine 150 installed at a central position equidistant from all four columns 110, 120, 130, 140. The wind turbine 150 is used to provide additional power generation capacity, thus reducing the fuel consumption of the array. Should excess power be produced, it can optionally be exported to an electrical grid. FIG. 9c shows an alternative installation location for the wind turbine 150 on top of one of the columns.

[0094] Wave devices also may also be attached or incorporated within the facility and used to supplement power requirements, or create excess energy that can be exported. One example of such a device is illustrated in FIG. 9a, installed on a column. There is a wide variety of different types of device that could be used and one typical Oscillating Water Column (OWC) system 190 is illustrated. In this example, the OWC system 190 is installed within the void space in the upper part of one of the columns, comprising an open input 193 below the water line, moving into a vertical tube 194 and through an OWC device 195. Typically, an OWC system 190 may be located on one column facing the dominant wave direction; however more than one OWC system may be attached to each column, or alternatively OWC systems could be installed on more than one column.