Power supply system for an offshore platform

Abstract

An offshore oil and gas platform has a power supply system with a cascaded arrangement for a black start. The power supply system includes a first power supply apparatus for providing power at a first energy level, an uninterruptible power supply arrangement configured to receive power from the first power supply apparatus, wherein the uninterruptible power supply is for powering at least one essential and/or safety critical component, and a second power supply apparatus for providing power at a second energy level to a main power distribution system, wherein the second energy level is higher than the first energy level, wherein the second power supply apparatus includes a power source and a high-power energy storage system capable of supplying power at the second energy level, and wherein the second power supply apparatus can receive and store energy from the first power supply apparatus.

Claims

1. A power supply system for an offshore oil and gas platform, the power supply system comprising: a first power supply apparatus for providing power at a first energy level; an uninterruptible power supply arrangement configured to receive power from the first power supply apparatus, wherein the uninterruptible power supply is for powering at least one essential and/or safety critical component of the oil and gas platform; a second power supply apparatus for providing power at a second energy level to a main power distribution system of the offshore platform, wherein the second energy level is higher than the first energy level, wherein the second power supply apparatus comprises a power source and a high-power energy storage system capable of supplying power at the second energy level, and wherein the second power supply apparatus can receive energy from the first power supply apparatus and can store energy from the first power supply apparatus in the high-power energy storage system; and a control system for controlling the first and second power supply apparatuses, wherein the control system is arranged to perform a black start routine to provide full power to the offshore platform via the main power distribution system after a shutdown of the power source in the second power supply apparatus, the black start routine comprising: using the first power supply apparatus to initiate the uninterruptible power supply and thereby power up the at least one essential and/or safety critical component; and then using the high-power energy storage system to power up the power source.

2. A power supply system as claimed in claim 1, wherein the power source within the second power supply apparatus comprises a gas turbine powered generator supplied with gas produced locally at the platform.

3. A power supply system as claimed in claim 1, wherein the power source within the second power supply apparatus is capable of supplying energy at a level higher than energy that can be supplied via the high-power energy storage system, and wherein the high-power energy storage system is capable of starting the power source within the second power supply apparatus.

4. A power supply system as claimed in claim 3, wherein the high-power energy storage system of the second power supply apparatus is arranged to receive and store energy from the power source during normal use of the offshore platform and the control system is arranged such that in the event of a black start, when there is not sufficient stored energy in the high-power energy storage system to power up the power source of the second power supply apparatus, then the black start routine includes charging the high-power energy storage system using the first power supply apparatus.

5. A power supply system as claimed in claim 4, wherein the first power supply apparatus has multiple redundant power sources including: a power cable for connection to a host installation, at least one solar energy generator, and/or at least one wind powered energy generator.

6. A power supply system as claimed in claim 5, wherein the first power supply has a power cable for connection to a host installation, the power cable comprising a DC fibre optic cable.

7. A power supply system as claimed in claim 1, wherein the first power supply apparatus includes a low-power energy storage system, wherein the low-power energy storage system is capable of supplying power at the first, lower, energy level and is charged by the power source(s) of the first power supply apparatus.

8. A power supply system as claimed in claim 1, wherein the uninterruptible power supply supplies power to all components deemed essential and/or safety critical in relation to powering up of the power source in the second power supply apparatus.

9. A power supply system as claimed in claim 8, wherein the uninterruptible power supply supplies power to a ventilation system and to a fire and gas (F&G) system, and wherein the second power supply apparatus requires ventilation in order to operate.

10. A power supply system as claimed in claim 8, comprising a communication system linked with the control system for use in remote control of the black start routine, wherein the uninterruptible power supply provides power for the communication system during the black start routine, such that once the uninterruptible power supply has been initiated then the communication system can be used in relation to remote control and/or remote monitoring of subsequent steps during the black start routine.

11. A power supply system as claimed in claim 10, wherein the power supply system has an umbilical for connecting the power supply to a remote host installation, with the umbilical including a wired communication connection for the communication system and a power cable to provide a power source for the first power supply apparatus.

12. A power supply system as claimed in claim 11, wherein the control system is arranged so that the remote host installation can use the umbilical connection to trigger the black start routine via the communication system and/or via a signal sent to the first power supply apparatus using other means.

13. A power supply system as claimed in claim 10, wherein once the uninterruptible power supply has been initiated via the black start routine then the remote host installation can communicate with the offshore platform by the communication system in order to control and/or monitor further progress of the black start routine.

14. A power supply system as claimed in claim 13, wherein the power supply system includes a monitoring system linked to the communication system to allow for remote monitoring of the power supply system, wherein the monitoring system includes one or more sensors such as cameras, pressure sensors, temperature sensors, and electricity meters such as voltmeters or ammeters in order to monitor aspects of the operation of the power supply system.

15. A power supply system as claimed in claim 14, wherein the control system is arranged to use the monitoring system during the black start routine in order to check for correct implementation of certain steps of the black start routine before subsequent steps are implemented.

16. A power supply system as claimed in claim 15, wherein the black start routine includes remotely monitoring the platform via the communication system to check for correct implementation of certain steps of the black start routine before subsequent steps are implemented.

17. An offshore oil and gas platform comprising a power supply system as claimed in claim 1.

18. A platform as claimed in claim 17, wherein the platform is an unmanned platform with no permanent personnel, wherein the unmanned platform has 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, no heli-deck and/or no lifeboat; and/or wherein the unmanned platform is arranged such that personnel are required to be present for fewer than 10,000 maintenance hours per year.

19. A method for supplying power for an offshore oil and gas platform, wherein the platform has a power supply system including: a first power supply apparatus for providing power at a first energy level; an uninterruptible power supply arrangement configured to receive power from the first power supply apparatus, wherein the uninterruptible power supply is for powering at least one essential and/or safety critical component of the oil and gas platform; a second power supply apparatus for providing power at a second energy level to a main power distribution system of the offshore platform, wherein the second energy level is higher than the first energy level, wherein the second power supply apparatus comprises a power source and a high-power energy storage system capable of supplying power at the second energy level, and wherein the second power supply apparatus can receive energy from the first power supply apparatus and can store energy from the first power supply apparatus in the high-power energy storage system; and a control system for controlling the first and second power supply apparatuses; and wherein the method comprises: using a black start routine to provide full power to the offshore platform via the main power distribution system after a shutdown of the power source in the second power supply apparatus, the black start routine comprising: using the first power supply apparatus to initiate the uninterruptible power supply and thereby power up the at least one essential and/or safety critical component; and then using the high-power energy storage system to power up the power source.

20. A method as claimed in claim 19, wherein the high-power energy storage system of the second power supply apparatus receives energy from the power source during normal use of the offshore platform and the method includes, when the platform is in operation, maintaining the high-power energy storage system in a state with sufficient stored energy for later use during a black start routine.

21. A method as claimed in claim 19, wherein the black start routine includes a step of checking the energy storage levels in the high-power energy storage system and, if there is not sufficient stored power for the high-power energy storage system to power up the power source after initiation of the uninterruptible power supply, the black start routine includes charging the high-power energy storage system using power from the first power supply apparatus until there is sufficient stored power for the high-power energy storage system to power up the power source of the second power supply apparatus.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Certain 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:

(2) FIG. 1 shows a layout for an offshore field development; and

(3) FIG. 2 is a diagram of an example power supply system for an offshore platform.

DETAILED DESCRIPTION

(4) An example is now described in the context of a possible field development as shown in FIG. 1, with this field development making use of a power supply system as described in FIG. 2. It will of course be appreciated that this is simply an example of one use for the power supply system of FIG. 2 and the power supply system of FIG. 2 could be used with other offshore platforms in other field developments with similar advantages being obtained.

(5) As shown in FIG. 1, a six-slot subsea production system (SPS) 12 is proposed at a first remote site, A, which is spaced apart from a second remote site, B, where it is proposed to locate an Unmanned Wellhead Platform (UWP) 14 and an Unmanned Processing Platform (UPP) 16.

(6) For the purposes of this example, the distance between remote site A and remote site B is approximately 12 km, while the distance from remote site B to the tie-in point at a host pipeline or host installation is approximately 34 km. The water depth both at remote site A and remote site B and in the host area is in the range of 100 to 110 metres, and the seabed bathymetry is in general flat with no major features or pockmarks.

(7) Oil, gas and water from the reservoir of remote site A are produced to the SPS 12. The well fluid is transported through an insulated and heat traced pipe-in-pipe pipeline 18 to remote site B. The UPP subsea and topside facility 16 at remote site B is protected from the high well shut-in pressure by a subsea high-integrity pressure protection system (HIPPS) system 20. Oil, gas and water from the reservoir of remote site B are produced to the UWP 14. The UPP subsea and topside facility 16 is protected from the high well shut-in pressure by a topside HIPPS system 22 on the UWP 14. Injection of water for pressure support is planned for the reservoirs of both remote site A and remote site B via respective water injection pipelines 24, 26.

(8) Produced fluid from remote site A and remote site B is mixed upstream of a subsea separator 30. The subsea separator 30 is a three phase separator operating at approximately 40 bar initially. The temperature in the separator 30 is high (90° C.) and good separation is expected. Oil and water leaving the separator 30 is metered by a multiphase flow meter 32 and exported to a host 34. The receiving pressure at the host 34 will be kept at the same pressure as the subsea separator 30 to avoid flashing and multiphase flow in the export pipeline or inlet heater at the host 34. The oil is only partly stabilised in the subsea separator 30, and further stabilization to pipeline export specification is assumed at the host 34.

(9) The subsea separator 30 and pumps (not shown) are provided as a subsea separator and booster station (SSBS) 29, which is located as close to the UPP 16 as possible to minimise condensation and liquid traps in the gas piping from the separator 30 to the UPP 16. Gas at 40 bar is delivered from the separator 30 to the UPP 16 topside inlet cooler 36 through a dedicated riser 38. The inlet cooler 36 comprises a seawater-cooled shell and tube heat exchanger. TEG is injected into the gas for hydrate inhibition before cooling the gas to 20° C. in the seawater-cooled shell and tube inter stage cooler 36. Condensed water and hydrocarbons are removed in a downstream scrubber 37. Liquid from the scrubber 37 flows by gravitation back down to the subsea separator 30 through a dedicated riser 40. The gas from the scrubber 37 is then compressed to around 80 bar in a first stage compressor with a discharge temperature of around 80° C. The temperature should ideally be as low as possible to reduce the amount of glycol required for dehydration.

(10) An umbilical 50 connects the UPP 16 to the host 34. The umbilical provides remote control of the operations of the UPP 16, as well as of the operations of the SPS 12, UWP 14 and SSBS 29 via secondary umbilicals between the UPP16, the UWP 14 and the SSBS 29. The secondary umbilicals also supply any required power and chemicals required from the UPP 16 to the SPS 12, UWP 14 and SSBS 29. The umbilical 50 connecting to the host 34 includes a power cable 52, which can be integrated with the umbilical 50 or separate from the umbilical 50. In this example the power cable 52 is a fibre optic cable such as a DCFO type cable, and it may be used in relation to an on-board power supply system of the UPP 16 and/or UWP 14 as shown in FIG. 2.

(11) The power supply system of FIG. 2 can be installed for the UPP 16 and/or the UWP 14. Where the UPP 16 and the UWP 14 are in very close proximity, for example if they are connected by a bridge, then they may share a power supply system. On the other hand, when the UPP 16 and the UWP 14 are remote from one another then they may simply be coupled via an umbilical with a power cable for a low-power connection, such as a DCFO, and each of the UPP 16 and the UWP 14 can have its own power supply system as in FIG. 2. If there is no bridge but the UPP 16 and the UWP 14 are still close to one another, for example within a few hundred metres, then they may be coupled via a subsea power cable with a greater capacity such that some of the parts of the power supply system of FIG. 2 can be shared.

(12) As seen in FIG. 2 the power supply system includes a first power supply apparatus 60, a UPS and black start control system 62, and a main power distribution system 64. The main power distribution system 64 receives power from large batteries 66 providing a high-power energy storage system 66 and also receives power from a gas turbine 68. The gas turbine 68 is a main power source for a second power supply apparatus which includes the batteries 66 and the gas turbine 68 and supplies power to the main power distribution system 64. Optionally, the main power distribution system 64 can include a generator 70, which can have the function of supplying power to essential systems before start-up of the gas turbine 68. However, it is an advantage to avoid the use of a generator 70 since then there is no need for external supply of fuel since the gas turbine 68 can be powered by gas produced at the platform, which in this example is the UPP 16.

(13) In this example there are two batteries 66 rated at 500 kWh allowing for 1000 kWh for the second power supply apparatus when powered by the batteries 66 alone. The gas turbine 68 is rated at 25 MW and generator, where present, might be 5 MW. The main power distribution system 64 operates at various voltages, which in this example include: a 400 V rail 72 for emergency power, which may be supplied from the first power supply apparatus 60; a 400 V rail 74 for main power, which can be from the batteries 66; a 690 V rail 78 for main power, which can also be the voltage from the generator if present; and a 6.6 kV rail 80 for main power, which is the voltage supplied from the gas turbine 68. A transformer 76 is included in the main power distribution system 64 for conversion between the various voltages. There may also be an added transformer such as the transformer 82 in this example for dedicated supply of electricity to high-power loads such as a high pressure gas compressor 84, which might be rated at 5.2 MW.

(14) The main power 6.6 kV rail 80 supplies power to various high-power loads 86 at the platform such as low pressure gas compressors and pumps, which might be rated in the range 1-3 MW. The loads supplied by higher voltages would typically be connected using variable speed drives (VSD) 88. The main power 690 V rail 78 can supply electricity to power lower rated loads 90, typically in the kW range, such as heating and cooling systems and materials handling, for example the platforms main crane. If a diesel generator 70 is present then the 690 V supply might also power a pre-warming system 92. The pre-warming system 92 can be arranged to receive power from the batteries 66 during a start-up phase.

(15) The first power supply apparatus 60 can receive power from the umbilical power cable 52 and it also has a solar energy converter 94 as well as a wind turbine 96. The various power sources 52, 94, 96 are connected via respective converters/regulators 98, 100, 102 to a main voltage rail 104 of the first power supply apparatus 60. A solar energy regulator 98 and wind turbine regulator 100 may be selected as appropriate based on the specifications of the solar energy converter 94 and the wind turbine 96. Typically they may produce outputs in the range 30-60 kW. When the umbilical power cable 52 is a DCFO then it would be connected to the main rail 104 via a DC/AC converter with a 100 kW output. The first power supply apparatus 60 further includes batteries 106. These batteries 106 form a low-power energy storage system 106 with a considerably lower energy capacity and energy output capacity than the high-power energy storage system 66 of the second power supply apparatus. Typically, there may be a factor of 10 difference, as in this case where the high-power energy storage system 66 can output 1000 kWh in total whereas the low-power energy storage system 106 can output 100 kWh. Thus, the power supply system of FIG. 2 has a cascaded arrangement in relation to the energy storage systems as well as in relation to other aspects of the first power supply apparatus 60 as compared to the second power supply apparatus 66, 68, 70.

(16) The two energy storage systems 106, 66 can form the basis for an uninterruptible power supply of the offshore platform, although it will be appreciated that there will be situations where one or both of these energy storage systems 106, 66 are depleted. In the event of a small power outage, for example if the gas turbine 68 is turned off for a small period time, then typically the high-power energy storage system 66 would provide the main basis for the uninterruptible power supply. If there were a longer shutdown of the power sources in the second power supply apparatus then high-power energy storage system 66 may become depleted and in this case the first power supply apparatus with the low-power energy storage system 106 can become the main basis for the uninterruptible power supply. It will be noted that the power cable 52 as well as the solar energy converter 94 and the wind turbine 96 may also provide power for the uninterruptible power supply, as well as supplying energy to be stored in the batteries 106 for the low-power energy storage system 106.

(17) The first power supply apparatus 60 thus supplies power to the UPS and black start control system 62 in an emergency or similar where the turbine 68 (and optionally the generator 70) is not operational. This provides redundancy in situations where the high-power energy storage system 66 can also supply power for the UPS. It also allows for a remotely controlled and unmanned start up sequence in situations where the high-power energy storage system 66 is depleted and where the low-power energy storage system may also be depleted. This is carried out in a black start routine as follows.

(18) First, a signal is received to initiate the black start routine. This may be a signal from the host 34 via the umbilical 50 or power cable 52, or it may be a wireless signal from the host 34 or from elsewhere. When the black start routine begins then the first power supply apparatus 60 supplies power to the UPS and black start control system 62. This may be done immediately if there is a sufficient power supply via the power cable 52 and/or from the batteries 106. Alternatively there may be a charging period where sufficient power is built up in the batteries 106 via charging from one or more of the power cable 52, the solar energy converter 98 or the wind turbine 100. It should be noted that the power cable 52, the solar energy converter 98 and/or the wind turbine 100 can be used to constantly maintain charge in the batteries 106 during periods of shut down for the main power distribution system so that the batteries 106 are ready to supply power to the UPS and black start control system 62 when the signal is received to initiate the black start routine.

(19) When sufficient power is available from the first power supply apparatus then the control system 62 brings the UPS into operation and powers up essential and safety critical components including a ventilation system 108, a fire and gas (F&G) system 110, and a communications system 112. The ventilation system 108 provides ventilation required for safe operation of the second power supply apparatus, such as for safe use of the high-power energy storage system 66 and/or the turbine 68. Ventilation is required in many areas on an offshore oil and gas platform in order that potentially hazardous build-up of flammable hydrocarbons is dispersed. The ventilation may also be required for other equipment on the platform when the platform is fully operational. The F&G system may have features typical for known F&G systems on board similar offshore platforms. The communications system 112 can be a wired and/or wireless system and is primarily for communications with the host 34. A wired communication link with the host 34 may be provided via the umbilical 50. The communications system 112 can provide the host 34 with data from monitoring systems on the platform and allow for remote control and remote monitoring of the black start routine, amongst other things. The UPS may also provide power to other emergency equipment 114 such as an emergency crane.

(20) With the UPS online and each of the ventilation system 108, fire and gas (F&G) system 110, and communications system 112 operational then the control system 62 can monitor the platform and/or the power supply system to ensure that it is appropriate to move to the next phase of the black start routine. The same monitoring may additionally or alternatively be carried out remotely at the host 34, or elsewhere. For example, it may be necessary to wait for a certain level of ventilation or to allow for a certain time of ventilation before aspects of the second power supply apparatus 66, 68 are used. There may be a requirement for the F&G system to confirm that the platform is safe and/or that it is within certain parameters detected by the F&G system. Various sensors such as cameras, pressure sensors, temperature sensors, and electricity meters such as voltmeters or ammeters may be used in order to monitor aspects of the operation of the power supply system and more generally of the other equipment on the platform. The status of the high power energy storage system 66 may also be checked to ensure that sufficient power is available. If the high-power batteries 66 require charging then power can be supplied via the 400 V emergency power supply rail 72 in order to charge the high-power batteries 66.

(21) Once all required safety and operational criteria are met, and when the high-power batteries 66 have sufficient power available, then the black start routine moves to the next phase. This involves the use of the high-power batteries 66 to power up the gas turbine 68, or the generator 70 where a generator is present. A power-up routine for the generator 70 can include pre-warming with the pre-warmer 92 powered by the batteries 66. Where the batteries 66 start the gas turbine 68 then there may be a pre-warming phase before ignition. The high-power energy storage system 66 may also include or be augmented by a compressed air energy storage system for use in starting the turbine 68. Where compressed air is used then this can be kept at a suitable capacity during normal operation of the platform, and if the compressed air store is depleted then it may be recharged during the black start routine. This may be done using power from the high power batteries 66, for example. Gas to power the gas turbine 68 during start-up can be produced gas or gas stored on the platform for the purpose of starting the turbine 68 during black start, when gas production may not be available. In cases where produced gas is used then the black start routine may include activation of a gas supply using power from the UPS and/or the high-power energy storage system 66. The activation of the gas supply may include any suitable sequence of steps, such as opening of valves and so on, as may be used in other situations where produced gas is required for a gas turbine 68 as the main power source on a platform.

(22) When the gas turbine 68 is operational then it may be used to supply power to all of the equipment on the platform 14, 16 via the main power distribution system 64. There may be a staged start up sequence for this equipment in order to ensure correct operation of the equipment and also to avoid excessive load on the turbine 68. When the platform 14, 16 is in normal operation then the high-power energy storage system 66 may be recharged via the main power distribution system 64 and the low-power energy storage system 106 may be recharged via one or more of the power source(s) of the first power supply apparatus 60.

(23) It should be apparent that the foregoing relates only to the preferred embodiments of the present application and the resultant patent. Numerous changes and modification may be made herein by one of ordinary skill in the art without departing from the general spirit and scope of the invention as defined by the following claims and the equivalents thereof.