US20110232912A1

US20110232912A1 - System and method for hydraulically powering a seafloor pump for delivering produced fluid from a subsea well

Info

Publication number: US20110232912A1
Application number: US12/731,252
Authority: US
Inventors: Frank Close
Original assignee: Chevron USA Inc
Current assignee: Chevron USA Inc
Priority date: 2010-03-25
Filing date: 2010-03-25
Publication date: 2011-09-29

Abstract

A system and method for hydraulically powering a seafloor pump and thereby delivering produced fluid from a subsea well are provided. The system includes a power fluid source, such as a seawater source, which is located at a seasurface location of a sea, and a hydraulically-driven pump, which is located at a seafloor location. The pump is configured to receive a flow of produced fluid from a subsea well and deliver the produced fluid through a riser to a receiver at a seasurface location. One or more conduits that define a feed passage connect the source and the pump, and the source is configured to receive power fluid and provide a flow of the power fluid via the feed passage of the conduit to the pump. The pump is hydraulically operated by the flow of power fluid and delivers the produced fluid from the pump to the receiver.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
This invention relates to the operation of subsea pumps and, more particularly, to hydraulically powering a seafloor pump so that the pump delivers produced fluid from a subsea well.
2. Description of Related Art
In the production of fluids from a subsea hydrocarbon reservoir, the pressure in the reservoir may be insufficient to deliver the produced fluid from the wellbore and/or to a topside location. In some cases, a subsea pump can be used to deliver the fluids produced from such a reservoir through one or more pipes, such as a subsea flowline and a riser that extend from the subsea pump to a topside processing or storage facility at the surface of the sea. One conventional subsea pump is configured to be installed directly into the subsea well. These devices are typically designed and constructed with a high aspect ratio, i.e., to be tall with a small footprint so that the devices will fit into a wellbore of a relatively small diameter. Such an in-well pump can be disposed deeply in the subsea well and can increase the pressure of the produced fluid sufficiently to deliver the fluid out of the well and through a riser that extends from the subsea well to the topside facility. In-well pumps can be electrically or hydraulically powered. A typical hydraulic-powered, in-well pump is configured to mix the hydraulic fluid that powers the pump with the produced fluid, there typically being no space or delivery paths for separately delivering the fluids therefrom. Thus, a typical hydraulic-powered, in-well pump is configured to receive a hydraulic fluid for powering the pump, mix the hydraulic fluid with the produced fluid in the well, and deliver the mixture from the well. The fluids are then separated downstream, e.g., at the topside facility.
In other cases, produced fluids from subsea wells can be boosted by a subsea pump located outside the well, for example, an electric pump located on the seafloor. Such a pump can receive the produced fluid from the well, boost the pressure of the fluid, and thereby deliver the fluid to the topside facility. Power requirements for subsea pumps can be significant, requiring high electric power sources, and large electric cables, especially when such pumps are disposed in deepwater locations, 1000 feet or more below the sea surface.
A continued need exists for an improved system and method for powering a pump for delivering produced fluid from a subsea well. The system and method should be adaptable to deployment on the seafloor and to being powered hydraulically, such that the pump does not require significant electrical power and cabling associated with high electrical power requirements.

SUMMARY OF THE INVENTION

The embodiments of the present invention generally provide a system and method for hydraulically powering a seafloor pump for delivering produced fluid from a subsea well. According to one embodiment of the present invention, the system includes a power fluid source, which is located at a first seasurface location of a sea, and a hydraulic pump located at a seafloor location. The pump is configured to receive a flow of produced fluid from a subsea well and deliver the produced fluid through a riser to a receiver at a second seasurface location. At least one conduit defines a feed passage connecting the source and the pump. The source is configured to receive a power fluid, such as seawater, and provide a flow of the seawater or other power fluid via the feed passage of the conduit to the pump to thereby hydraulically operate the pump and deliver the produced fluid from the pump to the receiver. The first and second seasurface locations can be the same. For example, in some cases, the source and the receiver can be collocated on the same topside structure. Alternatively, the two locations can be remote from one another, e.g., with the source and receiver at different topside structures.
In one open-loop configuration, the source is configured to receive the power fluid, e.g., seawater from the sea, at the seasurface location, and the pump is configured to discharge the flow of seawater to the sea at the seafloor location. In a closed-loop configuration, the at least one conduit defines a return passage that connects the pump to the source, and the source is configured to deliver the flow of the power fluid to the pump via the feed passage and return the flow of power fluid to the source via the return passage. In another closed-loop configuration, the pump is configured to deliver the produced fluid and the flow of power fluid as a mixed stream to the receiver via the riser, and, the receiver can be a separator that is configured to separate the power fluid from the produced fluid.
The source can be, or include, a pump that is configured to increase the pressure of the power fluid to thereby provide the flow of the power fluid. For example, the source can include a pump that is electrically or hydraulically powered. In cases where the power fluid includes seawater, the system can also include a seawater treatment device at the first seasurface location. The seawater treatment device can be configured to receive the flow of seawater from the sea, process the seawater, and provide the flow of the seawater to the source. The conduit through which the power fluid is delivered to the seafloor pump can be a riser, umbilical, or other conduit and, in some cases, can define a plurality of connections between the first seasurface location and the seafloor location. For example, the conduit can also include electrical connections between the two devices for transmitting electrical communication signals, fiber optic connections for transmitting optical communication signals, other fluid connections, and the like.
According to another embodiment of the present invention, the method includes hydraulically powering a seafloor pump for delivering produced fluid from a subsea well. The method includes delivering a pressurized flow of power fluid, such as seawater, from a source at a first seasurface location of a sea via a feed passage of a conduit to a hydraulic pump located at a seafloor location, receiving by the hydraulic pump a flow of produced fluid from a subsea well, and hydraulically operating the pump by the flow of power fluid such that the pump delivers the produced fluid through a riser to a receiver at a second seasurface location.
For example, delivering the pressurized flow of power fluid from the source to the pump can include operating a pump at the first seasurface location to increase the pressure of the power fluid at the first seasurface location. The pump can be electrically or hydraulically powered. The flow of power fluid can be received from the sea, processed, and provided to the source. The source can deliver the pressurized flow of power fluid from a topside structure, and the pump can deliver the produced fluid through a riser to the receiver located on the topside structure. In some cases, the source can deliver the pressurized flow of power fluid to the pump via a riser, umbilical, or other conduit that defines a plurality of connections between the first seasurface location and the seafloor location.
In some cases, the source receives the seawater from the sea at the seasurface location as the power fluid, and the pump discharges the flow of seawater to the sea at the seafloor location. In other cases, the produced fluid and the flow of seawater or other power fluid is delivered by the seafloor pump as a mixed stream to the receiver via the riser, and the power fluid can be separated from the produced fluid in the receiver. Alternatively, the flow of power fluid can be returned from the seafloor pump to the seasurface location separately from the produced fluid via a return passage that is separate from the riser.
As described further below, the system and method can power the seafloor pump for delivering the produced fluid from the subsea well. The seafloor pump can be deployed on the seafloor. The seafloor pump does not need to be deployed in, or designed to fit into, the wellbore. Further, the seafloor pump can be powered hydraulically so that the pump does not require the provision of significant electrical power and cabling for its subsea operation. In some cases, the reliability of the seafloor pump can improve upon conventional in-well pumps that are designed for, and deployed in, subsea wells. In addition, the seafloor pump can be more easily accessible than in-well pumps and can facilitate maintenance, repair, or replacement. For example, if the seafloor pump breaks or otherwise fails, it can be configured to be repaired or replaced more easily than an in-well pump. The seafloor pump can also improve upon the reliability of conventional electric pumps that are disposed on the seafloor.

BRIEF DESCRIPTION OF THE DRAWINGS

Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:

FIG. 1 is a schematic view illustrating a system for hydraulically powering a seafloor pump for delivering produced fluid from a subsea well according to one embodiment of the present invention;

FIG. 2 is a schematic view illustrating a system for hydraulically powering a seafloor pump for delivering produced fluid from a subsea well according to another embodiment of the present invention;

FIG. 3 is a schematic view illustrating a system for hydraulically powering a seafloor pump for delivering produced fluid from a subsea well according to another embodiment of the present invention; and

FIG. 4 is a cross-sectional view illustrating a pipe-in-pipe structure of a riser for communicating produced fluid and power fluid.

DETAILED DESCRIPTION OF THE INVENTION

The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. Indeed, this invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout.
Referring now to the drawings and, in particular, to FIG. 1, there is shown a system 10 for powering a subsea pump 12 according to one embodiment of the present invention. Generally, the system 10 can be used to hydraulically power a subsea pump 12 that is configured to deliver produced fluid from a subsea well 14. As illustrated, the subsea well 14 includes a wellbore 16 that extends downward from the seafloor or seabed 18 and provides a path of communication between a subterranean hydrocarbon reservoir 20 under the seafloor 18 and subsea well equipment 22 associated with the operation of the well 14, such as a subsea Christmas tree, i.e., an assembly of valves, spools, and fittings, used for controlling the operations of the subsea well 14.
The produced fluid that is delivered from the wellbore 16 via the subsea well equipment 22 typically includes a hydrocarbon and can include a mixture of materials and/or phases. For example, the produced fluid can include oil, water, natural gas, other fluids, solid particulates, and the like. The produced fluid is typically delivered via a riser 24 to a topside facility 26. The riser 24 can extend directly from the pump 12 to the topside facility 26, or the riser 24 can be connected to the pump 12 by a subsea flowline 25. The produced fluid can be refined, treated, or otherwise processed at the topside facility 26 and/or at a remote processing facility, to produce hydrocarbon products.
The subsea pump 12 is a hydraulic, seafloor pump, i.e., a hydraulically-operated pump that is located at a seafloor location 28. By “seafloor location,” it is meant that the pump 12 is resting on the seafloor 18 and/or a foundation in the seafloor 18, but that the pump 12 is not disposed within the well 14. The subsea pump 12 includes a pumping mechanism and a motor, which is hydraulically powered. The seafloor pump 12 is configured to receive the flow of produced fluid from the subsea well 14 and is typically located proximate to at least one subsea well 14. In some cases, the pump 12 may be configured to receive produced fluids from two or more subsea wells 14. For example, the flow of produced fluids from one or multiple subsea wells 14 can be delivered via one or more subsea flowlines 30 to the seafloor location 28 of the seafloor pump 12, and the pump 12 can deliver the produced fluids from the multiple wells 14 as a mixture.
The seafloor pump 12 is a hydraulically powered by a hydraulic source 32 located at a seasurface location 34. By “seasurface location,” it is meant that the hydraulic source 32 is located on a structure at the seasurface 36, the structure typically being configured in a floating or moored configuration, though structures fixed to the seafloor can be used in relatively shallow applications. As illustrated in FIG. 1, the hydraulic source 32 can be located on the topside facility 26. That is, the seasurface location 34 of the hydraulic source 32 can be the same as the seasurface location 34 where the produced fluid is received from the seafloor pump 12. Alternatively, in other cases, the hydraulic source 32 can be located at a remote facility. In either case, the hydraulic source 32 can be configured to power one or more of the seafloor pumps 12.
In the embodiment illustrated in FIG. 1, the hydraulic power fluid source 32 is a seawater source that is configured to provide a flow of pressurized seawater. For example, the seawater source 32 shown is configured to receive seawater via an input pipe 38 that extends into the sea 40. The hydraulic source 32 includes one or more pumps that are configured to increase the pressure of the seawater or other hydraulic fluid and provide a flow of the pressurized fluid. As indicated in FIG. 1, the flow of pressurized seawater is communicated to the seafloor pump 12 via a conduit. The conduit is typically a riser (optionally, in combination with flowline or other subsea pipe) that defines at least one internal passage 42 for communication, i.e., a feed passage through which the pressurized seawater from the source 32 can be delivered to the seafloor pump 12. In some cases, the conduit can be defined by other structures, such as an umbilical.
The system 10 can include a seawater treatment device 44, typically located at the same seasurface location 34 as the source 32. The seawater treatment device 44 is configured to receive the flow of seawater from the sea or a well, process the seawater, and provide the flow of the seawater to the source 32. For example, the seawater treatment device 44 can be disposed on the topside facility 26 and can be configured to draw seawater from the sea 40 via the input pipe 38, process the seawater, and deliver the seawater to the source 32. The seawater treatment device can include filters for removing materials from the seawater, chemical injectors for chemically treating the seawater (such as by adding oxygen scavengers, biocides, and the like), and other processing equipment that is configured to provide a flow of seawater that is sufficiently treated so that it can be pumped by the source 32 and delivered to the seafloor pump 12 for powering the pump 12.
In other cases, the hydraulic source 32 is configured to provide other hydraulic power fluids, which can include seawater, produced fluids, chemicals, polymers, lubricants, and the like, or mixtures of such fluids. If the power fluid includes produced fluid, the produced fluid can be received from the one or more wells 14. For example, water or other fluids can be separated at the topside facility 26 from the produced fluid that is delivered through the riser 24, and the water or other fluids can be provided to the source 32 to be used as the power fluid. Alternatively, the produced fluid can be water from an aquifer well.
The system 10 can be configured to operate in an open- or closed-loop configuration. In particular, FIG. 1 illustrates an open-loop configuration of the system 10. In this embodiment of FIG. 1, the seafloor pump 12 is configured to be operated by the flow of the seawater, or other power fluid, from the hydraulic source 32. As the source 32 delivers a continuous flow of the power fluid to and through the pump, the pressure of the power fluid is reduced in the seafloor pump 12 as the power fluid powers the pump 12 to deliver the produced fluids to the topside facility 26. The flow of power fluid, in this case seawater, is then discharged from the seafloor pump 12 to the sea 40 at the seafloor location 28. Thus, while the source 32 and pump 12 are operating, the system 10 can continuously draw seawater from the sea 40 at the seasurface location 34 and discharge the treated seawater back to the sea 40 at the seafloor location 28.
FIG. 2 shows another embodiment, in which the system 10 is configured to operate in a closed-loop configuration. As shown, the seafloor pump 12 is connected to the hydraulic source 32 by a second passage 46, i.e., a return passage, so that source 32 can deliver the hydraulic power fluid to the pump 12 via the first, feed passage 42, and the hydraulic fluid can then return to the source 32 via the second, return passage 46. In this way, the hydraulic fluid can be reused, flowing repeatedly between the source 32 at the seasurface location 34 and the pump 12 at the seafloor location 28. The feed and return passages 42, 46 can be part of a single riser or other conduit. For example, the two passages 42, 46 can be defined by a single pipe, two or more concentric pipes, or other conduits or structures that define multiple, separate fluid passages. Alternatively, the passages 42, 46 can be separate tubular structures, e.g., two separate pipes or other conduits, which can be located together or apart from one another.
By “closed-loop,” it is meant that the system 10 can operate by re-using the same hydraulic fluid repeatedly such that little or no new fluid must be added to the system 10 during operation. The system 10 can still include an input pipe 38 and/or other equipment for receiving additional fluid, as some addition or replacement of fluid may be required during operation.
FIG. 3 illustrates another closed-loop configuration of the system 10. In this case, the seawater or other power fluid is delivered from the source 32 to the seafloor pump 12 via the feed passage 42. After flowing through the pump 12, the hydraulic fluid is delivered via a connector 48 to line 30 so that it joins the flow of the produced fluid entering the pump 12. The hydraulic fluid can be mixed with the produced fluid before the produced fluid is pumped by the pump 12 as indicated in FIG. 3. Alternatively, e.g., if the hydraulic fluid exiting the pump 12 is at a relatively high pressure with respect to the produced fluid entering the pump 12, the connector 48 can extend to the flowline 25 or riser 24 instead of the line 30, so that the hydraulic fluid is mixed with the produced fluid after the produced fluid has passed through the pump 12.
The seafloor pump 12 delivers the produced fluid through the flowline 25 and riser 24 to a receiver 50, which is typically located at the topside facility 26. The receiver 50 can include a separator that is configured to separate the produced fluid and/or a pressure/flow regulation device with valves, a fluid accumulation vessel, or the like for maintaining a consistent flow of the produced fluid. In the embodiment of FIG. 3, the produced fluid and the hydraulic fluid are delivered by the pump 12 as a mixed stream via the flowline 25 and riser 24 to the receiver 50, and the receiver 50 can include a separator that removes the seawater or other power fluid from the produced fluid. The hydraulic fluid can then be discharged from the receiver 50, e.g., to be released to the sea 40 or returned to the hydraulic source 32 for re-use. In any case, the receiver 50 can also be configured to perform other separation of the produced fluid, e.g., to separate the phases of the fluid and/or to remove water, gases, or solids from the hydrocarbons.
The hydraulic source 32 can include one or more electric or hydraulic pumps and, in some cases, a reservoir or other pressure storage device. The source 32 is typically configured to provide the flow of the hydraulic fluid to the pump 12 in a continuous flow, i.e., so that the seafloor pump 12 can operate continuously, thereby providing a continuous flow of the produced fluid from the well 14 to the topside facility 26. The source 32 can be powered by a power device that is located on the topside facility 26 or remotely. For example, if the source 32 is an electric or hydraulic motor, the power device can be an electrical or hydraulic power generation device located on the topside facility 26 that provides the necessary energy for operating the source 32.
The seafloor pump 12 can include any of a variety of hydraulic-powered pumping technologies. For example, the seafloor pump 12 can include one or more centrifugal or rotary pumping devices such as helico-axial pumping mechanisms. The seafloor pump 12 can include one stage or a plurality of stages. Further, it is appreciated that the system 10 can include one pump 12 or multiple pumps 12. If multiple pumps 12 are used in a single system 10, the pumps 12 can be configured in series and/or parallel configurations. For example, if a single pump 12 cannot handle the volume of produced fluid that is being delivered from a well 14 or group of wells 14, a plurality of the pumps 12 can be configured in parallel to provide the necessary pumping capacity. If a single pump 12 cannot provide the necessary boost in pressure to the produced fluid to deliver the fluid to the seasurface location 34, a plurality of the pumps 12 can be configured in series to provide incremental increases in pressure as needed. The pumps 12 can be located in close proximity to one another, or the pumps 12 can be located at successive positions (e.g., miles apart) along the length of the subsea flowline 25 so that each pump 12 provides the necessary pressure increase to move the produced fluid along a subsea distance to the next successive pump 12. In any case, the pumps 12 can be powered by hydraulic fluid that is provided by one or more sources 32 and/or via one or more feed passages 42. Further, the system 10 can include other pumps, such as hydraulically operated in-well pumps, electrically operated seafloor pumps, and the like. Thus, the seafloor pump 12 can be the primary (or only) lifting pump in some systems 10, while in other the systems 10 the seafloor pump 12 can act as a booster pump that operates in combination with other subsea pumps.
In some cases, one or both of the fluid passages 42, 46 can be provided by pipe-in-pipe or tube-in-tube structures. For example, a pipe-in-pipe structure can include a first pipe disposed inside of another pipe of greater diameter, with an annular space defined between the outer diameter of the first pipe and the inner diameter of the second pipe. The passage inside the first pipe and the annular space can each define a separate passage for feeding or returning the hydraulic fluid or otherwise communicating fluids between the seasurface and seafloor locations 34, 28. For example, one of the passage inside the first pipe and the annular space can define the feed passage 42, and the other of the passage inside the first pipe and the annular space can define the return passage 46. Alternatively, one of the passage inside the first pipe and the annular space can define the feed passage 42 or the return passage 46, and the other one of the passage inside the first pipe and the annular space can define a passage for another fluid. For example, in any of the embodiments of FIGS. 1-3, the flowline 25 and/or the riser 24 can be a pipe-in-pipe structure, as shown in FIG. 4, that defines an inner passage 52 within an inner pipe 54 and an annular passage 56 between the inner pipe 54 and an outer pipe 58. Either of the inner passage 52 or the annular passage 56 can be used to communicate the produced fluid, and the other one of the inner passage 52 and the annular passage 56 can define the feed passage 42. In this way, the hydraulic fluid within the feed passage 42 can be kept in thermal communication with the produced fluid in the flowline 25 and/or riser 24 so that the hydraulic fluid heats the produced fluid to facilitate the flow of the produced fluid through the flowline 25 and/or riser 24. In fact, in some cases, the hydraulic fluid can be heated, e.g., at the source 32, to provide thermal energy to the produced fluid. Heating of the produced fluid in this manner can provide flow assurance, especially in cases where the produced fluid is flowing through a cold environment that typically exists at deep water depths.
It is appreciated that the system 10 can be newly deployed, or an existing system can be retrofitted to the configurations described above. For example, in some conventional systems for operating subsea wells, a topside water injection pump is used to inject water from the topside location through a riser (and, optionally, a subsea flowline) and through a subsea tree into the well for a water injection or flooding operation. The topside pump that is used for such a water injection operation can reconfigured for use as the source 32 that provides water or another power fluid to the seafloor pump 12. For example, a conventional system can be retrofitted by deploying the seafloor pump 12 and connecting the seafloor pump 12 to the riser or flowline connected to the water injection pump. The seafloor pump 12 can also be connected to the riser 24 and/or flowline 25 carrying the produced fluid. Thus, the flow of fluid from the source 32 (formerly used as a water injection pump) can be used to power the seafloor pump 12 to deliver the produced fluids to the topside facility 26.
Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

1. A system for hydraulically powering a seafloor pump for delivering produced fluid from a subsea well, the system comprising:

a power fluid source located at a first seasurface location of a sea;

a hydraulic pump located at a seafloor location, the pump configured to receive a flow of produced fluid from a subsea well and deliver the produced fluid through a riser to a receiver at a second seasurface location; and

at least one conduit defining a feed passage connecting the source and the pump,

wherein the source is configured to receive power fluid and provide a flow of the power fluid via the feed passage of the conduit to the pump to thereby hydraulically operate the pump and deliver the produced fluid from the pump to the receiver.

2. A system according to claim 1 wherein the source is configured to receive seawater from the sea as the power fluid at the seasurface location and the pump is configured to discharge the flow of seawater to the sea at the seafloor location.

3. A system according to claim 1 wherein the at least one conduit further comprises a return passage connecting the pump to the source and wherein the source is configured to deliver the flow of power fluid to the pump via the feed passage and return the flow of power fluid to the source via the return passage.

4. A system according to claim 1 wherein the pump is configured to deliver the produced fluid and the flow of power fluid as a mixed stream to the receiver via the riser.

5. A system according to claim 4 wherein the receiver is a separator configured to separate the power fluid from the produced fluid.

6. A system according to claim 1, further comprising a seawater treatment device at the first seasurface location, the seawater treatment device configured to receive a flow of seawater from the sea as the power fluid, process the seawater, and provide the flow of the seawater to the source as the power fluid.

7. A system according to claim 1 wherein the source is a pump configured to increase the pressure of the power fluid to thereby provide the flow of the power fluid, the pump being powered by at least one of the group consisting of electric and hydraulic power.

8. A system according to claim 1 wherein the source and the receiver are collocated on a topside structure.

9. A method for hydraulically powering a seafloor pump for delivering produced fluid from a subsea well, the method comprising:

delivering a pressurized flow of power fluid from a source at a first seasurface location of a sea via a feed passage of a conduit to a hydraulic pump located at a seafloor location;

receiving by the hydraulic pump a flow of produced fluid from a subsea well; and

hydraulically operating the pump by the flow of power fluid such that the pump delivers the produced fluid through a riser to a receiver at a second seasurface location.

10. A method according to claim 9 wherein the source receives seawater from the sea at the seasurface location as the power fluid and the pump discharges the flow of seawater to the sea at the seafloor location.

11. A method according to claim 9, further comprising returning the flow of power fluid from the pump to the source via a return passage separately from the produced fluid.

12. A method according to claim 9, further comprising delivering the produced fluid and the flow of power fluid as a mixed stream to the receiver via the riser.

13. A method according to claim 12, further comprising separating the power fluid from the produced fluid in the receiver.

14. A method according to claim 9, further comprising receiving a flow of seawater from the sea as the power fluid, processing the seawater, and providing the flow of the processed seawater to the source.

15. A method according to claim 9 wherein delivering the pressurized flow of power fluid from the source to the pump comprises operating a pump at the first seasurface location to increase the pressure of the power fluid at the first seasurface location, the pump being powered by at least one of the group consisting of electric and hydraulic power.

16. A method according to claim 9 wherein the source delivers the pressurized flow of power fluid from a topside structure and the pump delivers the produced fluid through the riser to the receiver located on the topside structure.