WO2017141027A1 - Improved subsea hydroelectric generation - Google Patents

Improved subsea hydroelectric generation Download PDF

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Publication number
WO2017141027A1
WO2017141027A1 PCT/GB2017/050392 GB2017050392W WO2017141027A1 WO 2017141027 A1 WO2017141027 A1 WO 2017141027A1 GB 2017050392 W GB2017050392 W GB 2017050392W WO 2017141027 A1 WO2017141027 A1 WO 2017141027A1
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WO
WIPO (PCT)
Prior art keywords
reservoir
generator
wellhead
generators
configuration
Prior art date
Application number
PCT/GB2017/050392
Other languages
French (fr)
Inventor
Margaret Rose LINDAHL
Original Assignee
Lindahl Margaret Rose
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Lindahl Margaret Rose filed Critical Lindahl Margaret Rose
Publication of WO2017141027A1 publication Critical patent/WO2017141027A1/en

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Classifications

    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B41/00—Equipment or details not covered by groups E21B15/00 - E21B40/00
    • E21B41/0085—Adaptations of electric power generating means for use in boreholes

Definitions

  • the present invention relates to a system for producing hydroelectric power from a depleted subsea oil and/or gas reservoir and associated method.
  • US Patent No. 8,638,004 (Badger) describes an apparatus and method for generating electricity from a liquid flowing in a generally vertical direction down a bore hole.
  • a turbine is disposed in a downhole location below a wellhead assembly. This requires the wellhead assembly to be at least partially opened, which can be very time consuming. In addition, it is difficult to access a turbine disposed in a wellhead assembly for replacement and/or maintenance of the turbine.
  • a hydroelectric system for generating electricity from an oil and/or gas reservoir.
  • the reservoir may be or comprise a subsea oil and/or gas reservoir.
  • the reservoir may be partially depleted or depleted.
  • the system may comprise a wellhead.
  • the wellhead may be coupled to the reservoir.
  • the wellhead may comprise a valve assembly.
  • the valve assembly may comprise a first configuration or position in which fluid flow into the reservoir is prevented.
  • the valve assembly may comprise a second configuration or position in which fluid flow into the reservoir is permitted.
  • the valve assembly may be operable, switchable or actuatable between the first and second configurations.
  • the system may comprise a generator, e.g. a hydroelectric generator.
  • the generator may be arranged on a seabed.
  • the generator may be arranged a structure.
  • the structure may be attached, fixed or secured to a seabed.
  • the structure may be configured to arrange the generator relative to the wellhead and/or support the generator.
  • the structure may be configured to secure or attached the generator to a seabed.
  • the structure may be or comprise a frame, housing and/or support or the like.
  • the generator may be coupled to the wellhead.
  • fluid When the valve assembly is operated from the first configuration into the second configuration fluid may be permitted to flow through the generator and into the reservoir, e.g. in use.
  • the generator may convert energy from the flow of fluid into the reservoir to generate electricity.
  • valve assembly When the valve assembly is in the second configuration, e.g. in use, flow of fluid into the reservoir may be due to a pressure differential, e.g. a hydrostatic pressure differential, between the reservoir and the surrounding body of fluid. Alternatively or additionally, when the valve assembly is in the second configuration, e.g. in use, flow of fluid into the reservoir may be due to gravity.
  • a pressure differential e.g. a hydrostatic pressure differential
  • the system may comprise a casing, tubing and/or conduit.
  • the wellhead may be coupled to the reservoir by the casing, tubing and/or conduit.
  • the casing, tubing and/or conduit may extend from the wellhead to the reservoir.
  • the casing, tubing and/or conduit may be suspended from the wellhead.
  • the system may comprise a wellbore.
  • the wellbore may couple the wellhead to the reservoir.
  • the wellbore may extend from the wellhead to the reservoir.
  • the casing, tubing and/or conduit may be provided or located in the wellbore.
  • the casing, tubing and/or conduit may be inserted into and/or installed in the wellbore, e.g. to replace a previous casing, tubing and/or conduit.
  • the fluid may flow from the generator down, along or through the wellbore and/or casing, tubing and/or conduit into the reservoir.
  • the system may comprise a plurality of generators.
  • Each generator of the plurality of generators may be arranged on the seabed.
  • Each generator of the plurality of generators may be coupled to the wellhead.
  • the plurality of generators may be arranged in series, e.g. such that fluid flows successively through the/each of generators before flowing into the reservoir, when the valve assembly is in the second configuration.
  • the plurality of generators may be coupled to the wellhead in a parallel arrangement, e.g. such that fluid flows simultaneously through each of the generators, when the valve assembly is in the second configuration.
  • The/each generator may have or comprise a generator output for transferring electricity generated by the/each generator to a power terminal and/or power station, e.g. a subsea power terminal and/or power station, an offshore power terminal and/or power station or an onshore power terminal and/or power station.
  • the generator output of each/the generator may be coupled, connected or coupleable or connectable to the power terminal and/or power station.
  • the generator outputs of each of the generator of the plurality of generators may be coupled together to permit transfer of electricity generated from each generator to the power terminal and/or power station.
  • electricity generated by the/each generator may be transferred from the generator output to a power transmission system.
  • the system may include or comprise a plurality of wellheads.
  • Each wellhead of the plurality of wellheads may be coupled to a respective reservoir or a common reservoir.
  • At least one generator may be coupled to the plurality of wellheads.
  • At least one generator of the plurality of generators may be coupled to at least respective wellhead of the plurality of wellheads.
  • The/each generator may comprise or have a turbine.
  • the being turbine may be arranged in the/each generator, e.g. such that fluid flow through the/each generator may cause the turbine to rotate and/or generate electricity.
  • the valve assembly may be configured to control and/or adjust fluid flow into the reservoir. This may allow the generation of electricity to be controlled.
  • the valve assembly may comprise at least one valve.
  • the valve assembly may comprise a plurality of valve.
  • the at least one valve or the plurality of valves may be part of or comprised in the wellhead.
  • The/each valve of the plurality of valves may be operable, switchable or actuatable between the first and second configurations.
  • The/each valve may be configured to control and/or adjust fluid flow into the reservoir.
  • a method for generating electricity from an oil and/or gas reservoir may be or comprise a subsea reservoir.
  • the reservoir may be partially depleted or depleted.
  • the method may comprise locating at least one generator on a seabed or on a structure attached to a seabed.
  • the method may comprise coupling the generator to a wellhead.
  • the wellhead may be coupled to the reservoir.
  • the wellhead may comprise or have a valve assembly.
  • the valve assembly may comprise a first configuration in which fluid flow into the reservoir is prevented.
  • the valve assembly may have or comprise a second configuration in which fluid flow into the reservoir is permitted.
  • the method may comprise operating the valve assembly from the first configuration to the second configuration to permit flow of fluid through the generator and into the reservoir.
  • the generator may convert energy from the flow of fluid into the reservoir to generate electricity.
  • the method may comprise converting the fluid flow to electrical energy.
  • the method may comprise transmitting the electrical energy to a power terminal and/or power station.
  • the method may include or comprise controlling and/or adjusting the flow of fluid into the reservoir.
  • the step of controlling and/or adjusting the flow of fluid may permit the generation of electricity by the generator to be controlled.
  • the method may include or comprise coupling at least one generator to a plurality of wellheads.
  • Each wellhead may be coupled to a respective reservoir or common.
  • the method may include or comprise locating a plurality of generators on a seabed.
  • the method may include or comprise coupling of the plurality of generators to at least one wellhead.
  • the method may include or comprise coupling at least one generator of the plurality of generators to a respective wellhead, e.g. at least one wellhead of the plurality of wellheads.
  • Figure 1 depicts a schematic representation of a hydroelectric system in accordance with an embodiment of the present invention
  • Figure 2 depicts an alternative system to Figure 1 in which a plurality of generators are arranged in parallel;
  • Figure 3 depicts an alternative system to Figure 1 in which a plurality of generators are arranged in series;
  • Figure 4 depicts an alternative system to Figure 1 in which a generator is coupled to a plurality of wellheads
  • Figures 5(a) to 5(d) depict the stages of a method of generating hydroelectric power from a reservoir.
  • FIG. 1 depicts a hydroelectric system 5 for generating hydroelectric from a depleted subsea oil and/or gas reservoir 12.
  • the system 5 includes a wellhead 14, which is located on the sea bed 15 and coupled to a subsea reservoir 12 by a subsea wellbore 10.
  • the wellhead 14 is sealed or capped after oil and/or gas has been withdrawn from the reservoir to prevent sea water ingress into the reservoir 12.
  • the reservoir 12 is considered sufficiently deplete such that it cannot be considered a satisfactory hydrocarbon producer.
  • Figure 1 shows a hydroelectric generator 16, which includes a turbine 18.
  • the turbine 18 is horizontally arranged on the seabed 15.
  • the generator 16 is coupled to the wellhead 14.
  • the generator 16 is shown coupled to the wellhead by tubing 20.
  • the wellhead includes a valve assembly, which has a valve 22.
  • the valve 22 is connected to the generator by the tubing 20.
  • the valve 22 has a first configuration in which fluid flow into the reservoir 12 is prevented and a second configuration in which fluid flow into the reservoir 12 is permitted.
  • the valve 22 is operable between the first and second configurations to adjust the flow of seawater into the reservoir 12.
  • the valve 22 may be operated from the first configuration into second configuration by an external actuation arrangement (not shown), which may be coupled to a vessel, floating platform or an offshore platform
  • an external actuation arrangement not shown
  • sea water flows through the generator 16 into the reservoir 12, thereby rotating the turbine 18 of the generator 16.
  • the arrows depict the flow of sea water through the system 5. It will be appreciated that when the valve is in the second configuration, seawater passes through the generator 16 and into the tubing 20. From the tubing 20, the seawater flows through a part of the wellhead 14 into the reservoir 12 via the wellbore 10.
  • Electricity is thus generated by the turbine 18 and is transferred via a general output, which may be in the form of a conductor 24.
  • the conductor 24 connects the generator 16 to a power transmission system 26, which in this embodiment is located on an onshore location 27.
  • valve 22 When the valve 22 is in the second configuration, in use, flow of seawater into the reservoir 12 is due to a hydrostatic pressure differential between the reservoir 12 and the surrounding body of seawater, primarily due to gravity.
  • FIG 2 shows a system 5 similar to that shown in Figure 1 , except that three generators 16a, 16b, 16c are shown coupled to the wellhead 14. It will be appreciated that in other embodiments more or less than three generators may be coupled to the wellhead 14.
  • the output of each generator 16a, 16b, 16c is transferred to a power transmission system (not shown) by respective conductors 24a, 24b, 24b.
  • the generators 16a, 16b, 16c are coupled to the wellhead 14 in a parallel arrangement such that sea water can flow simultaneously through each of the generators 16a, 16b, 16c, when the valve 22 is in the second configuration.
  • the system shown in Figure 3 is similar to that shown in Figure 1 , except that two generators 16a, 16b are coupled to the wellhead 14.
  • the output of each generator 16a, 16b is transferred to a power transmission system (not shown) by respective conductors 24a, 24b, 24b.
  • the two generators 16a, 16b are shown as being coupled to the wellhead 114 in series such that seawater can flow successively through the generators 16a, 16b before flowing into the reservoir, when the valve 22 is in the second configuration.
  • a portion 20a of the tubing couples a first generator 16a to the wellhead 14.
  • a second portion 20b of the tubing connects a second generator 16b to the first generator 16a. In use, seawater passes through the second generator 16 before encountering the first generator 16a.
  • FIG. 4 depicts a plurality of wellheads located on the sea bed 15.
  • three wellheads 14a, 14b, 14c are shown. It will be appreciated that in other embodiments more or less than three wellheads may be provided.
  • Each wellhead 14a, 14b, 14c is coupled to a respective reservoir 12a, 12b, 12c by a respective wellbore 10a, 10b, 10c. It will be appreciated that in other embodiments the all or some of the wellheads 14a, 14b, 14c may be coupled to a common reservoir (not shown).
  • Each wellhead 14a, 14b, 14c has a respective valve 22a, 22b, 22c.
  • a single generator 16 is coupled to the three wellheads 14a, 14b, 14c, for examples, by tubing 20a, 20b, 20c.
  • Figures 5(a) to 5(d) illustrate the stages of a method for generating hydroelectric power from the reservoir 12, e.g. by using the system 5.
  • the generator 16 is shown as being arranged on a frame 17, which is attached to the seabed 15.
  • Figure 5(a) shows an existing wellhead 14, which is coupled to the depleted reservoir 12 by wellbore 10.
  • the wellhead 14 is associated with an offshore platform 28, which is extends above the sea level 30.
  • electricity generated by the generator 16 may be transferred to the offshore platform 28 via a conductor 24 (not shown).
  • Figure 5(b) shows the generator 16 arranged on the seabed 15 and coupled to the wellhead 14 by tubing 20.
  • the valve (not shown in the interest of clarity) is in the first configuration and flow of seawater into the reservoir 12 is prevented.
  • the system utilises the existence of depleted subsea oil and gas reservoirs to generate hydroelectricity by arranging hydroelectric generators on the seabed and coupling the generators to the wellhead. Valves in the wellhead can be operated to control the flow of sea water through the wellbores and thus power from the hydroelectric turbines. This facilitates installation of the system. By arranging the generator(s) on the seabed, the wellhead does not required to be opened, which facilitates replacement and/or maintenance of the generator/turbine.
  • the generator can be coupled to a wellhead that already exist and no further drilling or modification of the wellbore may be required.
  • the above described system and method could provide a viable source of electric power for local communities as well as for replenishing national power requirements.
  • This type of energy may be regarded as "green” as it is simply using sea water to generate electricity and no fossil fuels are required. Additionally, by allowing seawater to flow into the reservoir due to the pressure differential between the reservoir and the surrounding body of seawater and/or gravity, no additional energy may be required and an effective barrier to the escape of any remaining hydrocarbons is achieved.
  • the reservoir 12 has been described above as being depleted, it will be appreciated that in other embodiments the reservoir may be partially depleted or may contain a fluid that has a density lower than the density of the surrounding body of seawater.
  • the power transmission system 26 may be located on a vessel, floating platform or an offshore platform instead of being located on an onshore location.
  • the electricity generated by the/each generator may be transferred to a power terminal and/or power station.
  • the power station and/or terminal may be located on a vessel, floating platform or an offshore platform instead of being located on an onshore location.
  • the conductor is coupled to a power aggregation station on the seabed and/or a main power conductor may be coupled to a floating vessel, offshore terminal and/or power station or to an onshore terminal and/or power station.
  • the conductors of each of the generators may be coupled together. This may facilitate or allow the conductors of each of the generators to be coupled to a main power conductor, a power aggregation station on the seabed, and/or a power station and/or terminal on a vessel, on an offshore platform and/or on an onshore location.
  • the wellbore may include a casing, tubing and/or conduit, which may couple the wellhead to the reservoir.
  • the casing, tubing and/or conduit may extend from the wellhead to the reservoir.
  • the casing, tubing and/or conduit may be suspended from the wellhead.
  • the casing, tubing and/or conduit may be inserted into the wellbore, e.g. to replace a previous casing, tubing and/or conduit.
  • a single generator was described above in relation to Figure 4 as being coupled to a plurality of wellheads, it will appreciated that more than one generator may be coupled to the plurality of wellheads, e.g. in series or in a parallel arrangement. Alternatively, a generator is coupled to each wellhead of the plurality of wellheads.
  • the generator has been described above as being arranged on a frame attached to the seabed. It will be appreciated that in other embodiments, the generator may be arranged on or in any other structure suitable for supporting the generator and/or securing the generator to the seabed. For example, the generator may be arranged on or in a support and/or housing or the like.

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Abstract

A hydroelectric system for generating electricity from a depleted or partially depleted subsea oil and/or gas reservoir. The system includes a wellhead coupled to the reservoir. The wellhead has a valve assembly, which has a first configuration in which fluid flow into the reservoir is prevented and a second configuration in which fluid flow into the reservoir is permitted. The system further comprises a generator arranged on a seabed or on a structure attached to a seabed, the generator being coupled to the wellhead. When the valve assembly is operated from the first configuration to the second configuration,fluid is permitted to flow through the generator and into the reservoir, wherein the generator converts energy from the flow of fluid into the reservoir to generate electricity.

Description

Improved Subsea Hydroelectric Generation
FIELD
The present invention relates to a system for producing hydroelectric power from a depleted subsea oil and/or gas reservoir and associated method.
BACKGROUND
There are many thousands of subsea oil and gas wells. Many of these wells have reached the end of their productive life and are depleted. In order for reservoir fluid, such as oil and gas, to be removed from the well this has to be done using a well production system and in all such well production systems there is a wellhead through which the well can be completed and production initiated. At the end of a well's life, the well is shut down and valves in the wellhead are closed and the production tubing removed so that on the seabed above the depleted reservoir sits the wellhead. In the subsea formations beneath the wellhead there are large low pressure cavities left by the removal of the oil and gas.
US Patent No. 8,638,004 (Badger) describes an apparatus and method for generating electricity from a liquid flowing in a generally vertical direction down a bore hole. A turbine is disposed in a downhole location below a wellhead assembly. This requires the wellhead assembly to be at least partially opened, which can be very time consuming. In addition, it is difficult to access a turbine disposed in a wellhead assembly for replacement and/or maintenance of the turbine.
It is an object of at least one embodiment/aspect of the present invention to obviate or at least mitigate at least one of the problems of the prior art.
SUMMARY
According to a first aspect of the present invention there is provided a hydroelectric system for generating electricity from an oil and/or gas reservoir. The reservoir may be or comprise a subsea oil and/or gas reservoir. The reservoir may be partially depleted or depleted.
The system may comprise a wellhead. The wellhead may be coupled to the reservoir. The wellhead may comprise a valve assembly. The valve assembly may comprise a first configuration or position in which fluid flow into the reservoir is prevented. The valve assembly may comprise a second configuration or position in which fluid flow into the reservoir is permitted. The valve assembly may be operable, switchable or actuatable between the first and second configurations.
The system may comprise a generator, e.g. a hydroelectric generator. The generator may be arranged on a seabed. The generator may be arranged a structure. The structure may be attached, fixed or secured to a seabed. The structure may be configured to arrange the generator relative to the wellhead and/or support the generator. The structure may be configured to secure or attached the generator to a seabed. For example, the structure may be or comprise a frame, housing and/or support or the like.
The generator may be coupled to the wellhead. When the valve assembly is operated from the first configuration into the second configuration fluid may be permitted to flow through the generator and into the reservoir, e.g. in use. The generator may convert energy from the flow of fluid into the reservoir to generate electricity.
When the valve assembly is in the second configuration, e.g. in use, flow of fluid into the reservoir may be due to a pressure differential, e.g. a hydrostatic pressure differential, between the reservoir and the surrounding body of fluid. Alternatively or additionally, when the valve assembly is in the second configuration, e.g. in use, flow of fluid into the reservoir may be due to gravity.
The system may comprise a casing, tubing and/or conduit. The wellhead may be coupled to the reservoir by the casing, tubing and/or conduit. The casing, tubing and/or conduit may extend from the wellhead to the reservoir. The casing, tubing and/or conduit may be suspended from the wellhead.
The system may comprise a wellbore. The wellbore may couple the wellhead to the reservoir. The wellbore may extend from the wellhead to the reservoir. The casing, tubing and/or conduit may be provided or located in the wellbore. The casing, tubing and/or conduit may be inserted into and/or installed in the wellbore, e.g. to replace a previous casing, tubing and/or conduit. For example, in use, when the valve is in the second configuration, the fluid may flow from the generator down, along or through the wellbore and/or casing, tubing and/or conduit into the reservoir.
The system may comprise a plurality of generators. Each generator of the plurality of generators may be arranged on the seabed. Each generator of the plurality of generators may be coupled to the wellhead. The plurality of generators may be arranged in series, e.g. such that fluid flows successively through the/each of generators before flowing into the reservoir, when the valve assembly is in the second configuration.
The plurality of generators may be coupled to the wellhead in a parallel arrangement, e.g. such that fluid flows simultaneously through each of the generators, when the valve assembly is in the second configuration.
The/each generator may have or comprise a generator output for transferring electricity generated by the/each generator to a power terminal and/or power station, e.g. a subsea power terminal and/or power station, an offshore power terminal and/or power station or an onshore power terminal and/or power station. The generator output of each/the generator may be coupled, connected or coupleable or connectable to the power terminal and/or power station. The generator outputs of each of the generator of the plurality of generators may be coupled together to permit transfer of electricity generated from each generator to the power terminal and/or power station.
Alternatively or additionally, electricity generated by the/each generator may be transferred from the generator output to a power transmission system.
The system may include or comprise a plurality of wellheads. Each wellhead of the plurality of wellheads may be coupled to a respective reservoir or a common reservoir. At least one generator may be coupled to the plurality of wellheads.
At least one generator of the plurality of generators may be coupled to at least respective wellhead of the plurality of wellheads.
The/each generator may comprise or have a turbine. The being turbine may be arranged in the/each generator, e.g. such that fluid flow through the/each generator may cause the turbine to rotate and/or generate electricity.
The valve assembly may be configured to control and/or adjust fluid flow into the reservoir. This may allow the generation of electricity to be controlled.
The valve assembly may comprise at least one valve. The valve assembly may comprise a plurality of valve. The at least one valve or the plurality of valves may be part of or comprised in the wellhead.
The/each valve of the plurality of valves may be operable, switchable or actuatable between the first and second configurations. The/each valve may be configured to control and/or adjust fluid flow into the reservoir.
According to a second aspect of the present invention there is provided a method for generating electricity from an oil and/or gas reservoir. The reservoir may be or comprise a subsea reservoir. The reservoir may be partially depleted or depleted. The method may comprise locating at least one generator on a seabed or on a structure attached to a seabed.
The method may comprise coupling the generator to a wellhead. The wellhead may be coupled to the reservoir. The wellhead may comprise or have a valve assembly. The valve assembly may comprise a first configuration in which fluid flow into the reservoir is prevented. The valve assembly may have or comprise a second configuration in which fluid flow into the reservoir is permitted.
The method may comprise operating the valve assembly from the first configuration to the second configuration to permit flow of fluid through the generator and into the reservoir. The generator may convert energy from the flow of fluid into the reservoir to generate electricity.
The method may comprise converting the fluid flow to electrical energy.
The method may comprise transmitting the electrical energy to a power terminal and/or power station.
The method may include or comprise controlling and/or adjusting the flow of fluid into the reservoir. The step of controlling and/or adjusting the flow of fluid may permit the generation of electricity by the generator to be controlled.
The method may include or comprise coupling at least one generator to a plurality of wellheads. Each wellhead may be coupled to a respective reservoir or common.
The method may include or comprise locating a plurality of generators on a seabed. The method may include or comprise coupling of the plurality of generators to at least one wellhead.
The method may include or comprise coupling at least one generator of the plurality of generators to a respective wellhead, e.g. at least one wellhead of the plurality of wellheads.
Any of the features defined in the first aspect may be applied to and/or used in the second aspect.
It should be understood that the features defined above in accordance with any aspect of the present invention or below in relation to any specific embodiment of the invention may be utilised, either alone or in combination with any other defined feature, in any other aspect or embodiment of the invention BRIEF DESCRIPTION OF DRAWINGS
These and other aspects of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:
Figure 1 depicts a schematic representation of a hydroelectric system in accordance with an embodiment of the present invention;
Figure 2 depicts an alternative system to Figure 1 in which a plurality of generators are arranged in parallel;
Figure 3 depicts an alternative system to Figure 1 in which a plurality of generators are arranged in series;
Figure 4 depicts an alternative system to Figure 1 in which a generator is coupled to a plurality of wellheads; and
Figures 5(a) to 5(d) depict the stages of a method of generating hydroelectric power from a reservoir. DETAILED DESCRIPTION OF DRAWINGS
Reference in first made to Figure 1 of the drawings which depicts a hydroelectric system 5 for generating hydroelectric from a depleted subsea oil and/or gas reservoir 12. The system 5 includes a wellhead 14, which is located on the sea bed 15 and coupled to a subsea reservoir 12 by a subsea wellbore 10. The wellhead 14 is sealed or capped after oil and/or gas has been withdrawn from the reservoir to prevent sea water ingress into the reservoir 12. The reservoir 12 is considered sufficiently deplete such that it cannot be considered a satisfactory hydrocarbon producer. Figure 1 shows a hydroelectric generator 16, which includes a turbine 18. In this embodiment, the turbine 18 is horizontally arranged on the seabed 15. The generator 16 is coupled to the wellhead 14. Here, the generator 16 is shown coupled to the wellhead by tubing 20.
The wellhead includes a valve assembly, which has a valve 22. In this embodiment, the valve 22 is connected to the generator by the tubing 20. The valve 22 has a first configuration in which fluid flow into the reservoir 12 is prevented and a second configuration in which fluid flow into the reservoir 12 is permitted. The valve 22 is operable between the first and second configurations to adjust the flow of seawater into the reservoir 12. For example, the valve 22 may be operated from the first configuration into second configuration by an external actuation arrangement (not shown), which may be coupled to a vessel, floating platform or an offshore platform In use, when the valve 22 is in the second configuration, sea water flows through the generator 16 into the reservoir 12, thereby rotating the turbine 18 of the generator 16. In Figure 1 the arrows depict the flow of sea water through the system 5. It will be appreciated that when the valve is in the second configuration, seawater passes through the generator 16 and into the tubing 20. From the tubing 20, the seawater flows through a part of the wellhead 14 into the reservoir 12 via the wellbore 10.
Electricity is thus generated by the turbine 18 and is transferred via a general output, which may be in the form of a conductor 24. The conductor 24 connects the generator 16 to a power transmission system 26, which in this embodiment is located on an onshore location 27.
When the valve 22 is in the second configuration, in use, flow of seawater into the reservoir 12 is due to a hydrostatic pressure differential between the reservoir 12 and the surrounding body of seawater, primarily due to gravity.
Reference is now made to Figure 2, which shows a system 5 similar to that shown in Figure 1 , except that three generators 16a, 16b, 16c are shown coupled to the wellhead 14. It will be appreciated that in other embodiments more or less than three generators may be coupled to the wellhead 14. The output of each generator 16a, 16b, 16c is transferred to a power transmission system (not shown) by respective conductors 24a, 24b, 24b. The generators 16a, 16b, 16c are coupled to the wellhead 14 in a parallel arrangement such that sea water can flow simultaneously through each of the generators 16a, 16b, 16c, when the valve 22 is in the second configuration.
The system shown in Figure 3 is similar to that shown in Figure 1 , except that two generators 16a, 16b are coupled to the wellhead 14. The output of each generator 16a, 16b is transferred to a power transmission system (not shown) by respective conductors 24a, 24b, 24b. In Figure 3, the two generators 16a, 16b are shown as being coupled to the wellhead 114 in series such that seawater can flow successively through the generators 16a, 16b before flowing into the reservoir, when the valve 22 is in the second configuration. A portion 20a of the tubing couples a first generator 16a to the wellhead 14. A second portion 20b of the tubing connects a second generator 16b to the first generator 16a. In use, seawater passes through the second generator 16 before encountering the first generator 16a. This arrangement allows energy to be extracted from the seawater in stages by respective conductors 24a, 24b of the first and second generators 16a, 16b. Reference is now made to Figure 4 of the drawings which depicts a plurality of wellheads located on the sea bed 15. In Figure 3 three wellheads 14a, 14b, 14c are shown. It will be appreciated that in other embodiments more or less than three wellheads may be provided. Each wellhead 14a, 14b, 14c is coupled to a respective reservoir 12a, 12b, 12c by a respective wellbore 10a, 10b, 10c. It will be appreciated that in other embodiments the all or some of the wellheads 14a, 14b, 14c may be coupled to a common reservoir (not shown). Each wellhead 14a, 14b, 14c has a respective valve 22a, 22b, 22c. In this embodiment a single generator 16 is coupled to the three wellheads 14a, 14b, 14c, for examples, by tubing 20a, 20b, 20c. By coupling a single generator 16 to a plurality of wellheads, the costs for installing the system may be reduced.
Figures 5(a) to 5(d) illustrate the stages of a method for generating hydroelectric power from the reservoir 12, e.g. by using the system 5. In Figures 5(b) to 5(d) the generator 16 is shown as being arranged on a frame 17, which is attached to the seabed 15.
Figure 5(a) shows an existing wellhead 14, which is coupled to the depleted reservoir 12 by wellbore 10. In this embodiment, the wellhead 14 is associated with an offshore platform 28, which is extends above the sea level 30. for example, electricity generated by the generator 16 may be transferred to the offshore platform 28 via a conductor 24 (not shown).
Figure 5(b) shows the generator 16 arranged on the seabed 15 and coupled to the wellhead 14 by tubing 20. In Figure 5(b), the valve (not shown in the interest of clarity) is in the first configuration and flow of seawater into the reservoir 12 is prevented.
In Figures 5(c) and 5(d), the valve has been operated into the second configuration and seawater is permitted to flow into the reservoir 12 via the wellbore 10. The seawater flows through the generator 16, which causes the turbine 18 to rotate and generate electricity, which can be transferred to the platform 28, for example, by a conductor (not shown). In Figure 5 (d), the reservoir 12 is partially filled with seawater.
In this way the system utilises the existence of depleted subsea oil and gas reservoirs to generate hydroelectricity by arranging hydroelectric generators on the seabed and coupling the generators to the wellhead. Valves in the wellhead can be operated to control the flow of sea water through the wellbores and thus power from the hydroelectric turbines. This facilitates installation of the system. By arranging the generator(s) on the seabed, the wellhead does not required to be opened, which facilitates replacement and/or maintenance of the generator/turbine.
It is envisaged that with this invention, many thousands of disused oil and gas wells could provide sufficient electricity for many years to come and would help to mitigate any energy shortage. For example, in the UK sector of the southern North Sea there are many thousands of disused gas wells. The southern North Sea is shallow, which facilitates the arrangement hydroelectric generators on the seabed, as described above.
By using existing structures that are in place, the above system and method could be rapidly implemented. For example, the generator can be coupled to a wellhead that already exist and no further drilling or modification of the wellbore may be required.
The above described system and method could provide a viable source of electric power for local communities as well as for replenishing national power requirements. This type of energy may be regarded as "green" as it is simply using sea water to generate electricity and no fossil fuels are required. Additionally, by allowing seawater to flow into the reservoir due to the pressure differential between the reservoir and the surrounding body of seawater and/or gravity, no additional energy may be required and an effective barrier to the escape of any remaining hydrocarbons is achieved.
It should be understood that the embodiments described herein are merely exemplary and that various modifications may be made thereto without departing from the scope of the invention.
Although the reservoir 12 has been described above as being depleted, it will be appreciated that in other embodiments the reservoir may be partially depleted or may contain a fluid that has a density lower than the density of the surrounding body of seawater.
It will be appreciated that in other embodiments more or less than three generators may be coupled to the wellhead 14.
For example, the power transmission system 26 may be located on a vessel, floating platform or an offshore platform instead of being located on an onshore location.
Alternatively or additionally, the electricity generated by the/each generator may be transferred to a power terminal and/or power station. The power station and/or terminal may be located on a vessel, floating platform or an offshore platform instead of being located on an onshore location.
Alternatively or additionally, the conductor is coupled to a power aggregation station on the seabed and/or a main power conductor may be coupled to a floating vessel, offshore terminal and/or power station or to an onshore terminal and/or power station.
When a plurality of generators is arranged on the seabed, the conductors of each of the generators may be coupled together. This may facilitate or allow the conductors of each of the generators to be coupled to a main power conductor, a power aggregation station on the seabed, and/or a power station and/or terminal on a vessel, on an offshore platform and/or on an onshore location.
It will be appreciated that in some embodiments, the wellbore may include a casing, tubing and/or conduit, which may couple the wellhead to the reservoir. The casing, tubing and/or conduit may extend from the wellhead to the reservoir. The casing, tubing and/or conduit may be suspended from the wellhead. The casing, tubing and/or conduit may be inserted into the wellbore, e.g. to replace a previous casing, tubing and/or conduit.
Although the above embodiments have been described with two or three generators, it will be appreciated that in other embodiments more or less than two or three generators may be used.
Although a single generator was described above in relation to Figure 4 as being coupled to a plurality of wellheads, it will appreciated that more than one generator may be coupled to the plurality of wellheads, e.g. in series or in a parallel arrangement. Alternatively, a generator is coupled to each wellhead of the plurality of wellheads.
The generator has been described above as being arranged on a frame attached to the seabed. It will be appreciated that in other embodiments, the generator may be arranged on or in any other structure suitable for supporting the generator and/or securing the generator to the seabed. For example, the generator may be arranged on or in a support and/or housing or the like.

Claims

1. A hydroelectric system for generating electricity from a depleted or partially depleted subsea oil and/or gas reservoir, the system comprising
a wellhead coupled to the reservoir, the wellhead having a valve assembly, which has a first configuration in which fluid flow into the reservoir is prevented and a second configuration in which fluid flow into the reservoir is permitted,
a generator arranged on a seabed or on a structure attached to a seabed, the generator being coupled to the wellhead, wherein when the valve assembly is operated from the first configuration to the second configuration fluid is permitted to flow through the generator and into the reservoir, and wherein the generator converts energy from the flow of fluid into the reservoir to generate electricity.
2. The system according to claim 1 , wherein the system includes a wellbore, which extends from the wellhead to the reservoir and couples the wellhead to the reservoir.
3. The system according to claim 2, wherein a casing, tubing and/or conduit is provided or located in the wellbore.
4. The system according to any preceding claim, wherein the system comprise a plurality of generators, each generator of the plurality of generators being arranged on the seabed.
5. The system according to claim 5, wherein each generator of the plurality of generators is coupled to the wellhead.
6. The system according to claim 4 or 5, wherein the plurality of generators is coupled to the wellhead, the plurality of generators being arranged in series such that fluid flows successively through each of the generators before flowing into the reservoir, when the valve assembly is in the second configuration.
7. The system according to claim 4 or 5, wherein the plurality of generators is coupled to the wellhead in a parallel arrangement such that fluid flows simultaneously through each of the generators, when the valve assembly is in the second configuration.
8. The system according to any preceding claim, wherein the/each generator has a generator output for transferring electricity generated by the/each generator to a power terminal.
9. The system according to any preceding claim, wherein the system includes a plurality of wellheads, each wellhead of the plurality of wellheads being coupled to a respective reservoir or a common reservoir.
10. The system according to claim 9, wherein at least one generator is coupled to the plurality of wellheads.
1 1. The system according to any preceding claim, wherein the/each generator has a turbine, the being turbine being arranged in the generator such that fluid flow through the generator causes the turbine to rotate and/or generate electricity.
12. The system according to any preceding claim, wherein the valve assembly is configured to control and/or adjust fluid flow into the reservoir to allow the generation of electricity to be controlled.
13. A method for generating electricity from a depleted or partially depleted subsea oil and/or gas reservoir, the method comprising
locating at least one generator on a seabed or on a structure attached to a seabed;
coupling the generator to a wellhead, the wellhead being coupled to the subsea reservoir and having a valve assembly with a first configuration in which fluid flow into the reservoir is prevented and a second configuration in which fluid flow into the reservoir is permitted;
operating the valve assembly from the first configuration to the second configuration to permit flow of fluid through the generator and into the reservoir;
converting the fluid flow to electrical energy; and
transmitting the electrical energy to a power terminal.
14. The method according to claim 13, wherein the method includes controlling and/or adjusting the flow of fluid into the reservoir.
15. The method according to claim 13 or 14, wherein the method includes coupling at least one generator to a plurality of wellheads, each wellhead may be coupled to a respective reservoir or common reservoir.
16. The method according to any one of claims 13 to 15, wherein the method includes locating a plurality of generators on a seabed.
17. The method according to claim 16, wherein the method includes coupling the plurality of generators to at least one wellhead.
18. The method according to claim 17, wherein the method includes coupling at least one generator of the plurality of generators to a respective wellhead.
PCT/GB2017/050392 2016-02-16 2017-02-15 Improved subsea hydroelectric generation WO2017141027A1 (en)

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