Downhole power generation system

Abstract

A downhole power generation system (10) comprising a pressure chamber assembly (12) having a first movable element (14, 48, 49) which at least partially encloses a first variable volume chamber (V1A) and a second movable element (16, 48', 49') which at least partially encloses a second variable volume chamber (V1B), each movable element (14, 48, 49, 16, 48', 49') having an exterior surface and an interior surface, and the first and second variable volume chambers (V1A, V1B) being connected by a conduit (18) so that they together enclose a closed volume (V1) containing an incompressible fluid, the conduit (18) providing a path for flow of the incompressible fluid between the first variable volume chamber (V1A) and the second variable volume chamber (V1B) when the first and second movable elements (14, 48, 49, 16, 48', 49') move so that one of the first or second variable volume chamber (V1A, V1B) contracts and the other expands, the system further comprising a generator device (20) which is located in the conduit (18), and which is configured to use the flow of incompressible fluid along the conduit (18) to generate power.

Description

[0001] Downhole Power Generation System

[0002] The present invention relates to a downhole power generation system, particularly, but not exclusively for downhole electrical power generation.

[0003] BACKGROUND

[0004] Many tools and devices used downhole in boreholes in the oil and gas industry are electrically powered. These include sensors, telecommunications apparatus, actuators and valves. Typically, electrical power is supplied to such tools and devices by means of a battery or batteries, or a power cable run downhole from a location outside of the borehole. Both of these possibilities have disadvantages including, in the case of power cables, the cost and set-up time and power losses resulting from the length of the cables use, and in the case of batteries, the downhole space occupied by the batteries, limitations of battery life, and the cost and logistics of replacing spent batteries. As such, there is a need to provide means to generate the power required for such tools and devices in situ, at a downhole location.

[0005] It is known to use the flow of downhole fluid, for example fluid flowing along production tubing, to generate power. One example of a downhole power generation device harnessing downhole fluid flow in this way is disclosed in US 2023 / 0028913. The device disclosed in this document used the principle of electromagnetic induction to generate electrical power. It comprises a member which is located in the path of a downhole fluid flow, and which is configured to vibrate when exposed to fluid flow. The device also comprises a magnetic element and an electrically conductive element, one of which is positioned on the member and the other of which is positioned such that the electrically conductive element is located in a magnetic field produced by the magnetic element so that vibration of the member generates electrical power.

[0006] Downhole power generation devices which harness downhole fluid flow can, however, have a detrimental effect on this fluid flow. They could reduce the rate of fluid flow to below a desired value or even cause blockages in the pipe or tube along which the fluid is flowing. Moreover, downhole fluid is often corrosive and erosive, and corrosion or erosion of the power generation device caused by exposure to the downhole fluid can place significant restrictions on the longevity of such devices. Finally, such devices naturally rely on there being flow of downhole fluid - they will not generate power in a well which is not flowing.

[0007] The present application relates to an alternative downhole power generation system.

[0008] SUMMARY

[0009] According to a first aspect of the invention, we provide a downhole power generation system comprising a pressure chamber assembly comprising a first movable element at least partially enclosing a first variable volume chamber and a second movable element at least partially enclosing a second variable volume chamber, each movable element having an exterior surface and an interior surface, and the first and second variable volume chambers being connected by a conduit to form together a closed volume containing an incompressible fluid, the conduit forming a path for flow of the incompressible fluid between the first variable volume chamber and the second variable volume chamber when the first and second movable elements move so that one of the first or second variable volume chambers contracts and the other expands, and a generator device which is located in the conduit, and which is configured to be driven by flow of the incompressible fluid along the conduit to generate power.

[0010] The system may further comprise a housing having an interior, and which support the pressure chamber assembly so that the first variable volume chamber is located in the interior of the housing, and the housing forms a first housing volume in the interior of the housing around or adjacent the exterior surface of the first movable element. Fluid pressure in the first housing volume thus acts on the exterior surface of the first movable element.

[0011] The housing may be provided with a charging port which provides a conduit for flow of fluid into the first housing volume. In this case, the system may further comprise a removable plug which can be inserted into the charging port to block the charging port so that the first volume is closed, or a non-return valve which is provided in the charging port and arranged to allow flow of fluid into the first housing volume and to substantially prevent flow of fluid out of the first housing volume.

[0012] The first volume may contain a gas such as nitrogen or an inert gas. The housing may enclose a second housing volume around or adjacent the exterior surface of the second movable element, so that fluid pressure in the second housing volume acts on the exterior surface of the second movable element. In this case, the housing may be provided with an inlet port which provides a conduit for flow of fluid into the second volume. Furthermore, the housing may be provided with an outlet port which provides a conduit for flow of fluid out of the second volume.

[0013] One or both of the movable elements may comprise bellows.

[0014] One or both of the movable elements may comprise a piston and cylinder.

[0015] One or both of the movable elements may comprise a diaphragm.

[0016] The generator device may comprise a mechanical power generating device such as a turbine or piston. In this case, the system may further comprise an electrical power generator which is driven by the generator device. Alternatively, the system may comprise a compressor which is driven by the generator device.

[0017] The generator device may comprise an electrical power generation device.

[0018] According to a second aspect of the invention, we provide a hydrocarbon drilling or production system comprising a bore hole, a tubular extending down the borehole, there being an annular volume around the tubular and an interior volume inside the tubular, the system further comprising a downhole power generation system according to the first aspect of the invention, wherein the exterior surface of the second movable element is exposed to fluid pressure from either the annular volume or the interior volume of the tubular.

[0019] Fluid from either the annular volume or the interior volume of the tubular may be in direct contact with the exterior surface of the second movable element.

[0020] BRIEF DESCRIPTION OF THE DRAWINGS

[0021] These and other characteristics will become clear from the following description of illustrative embodiments, given as non-restrictive examples, with reference to the attached drawings, in which

[0022] FIGURE 1 is a schematic illustration of a first embodiment of downhole power generation device according to the first aspect of the invention, excluding the generator device, FIGURE 2 is a schematic illustration of the downhole power generation device shown in Figure 1 in which the generator device is shown.

[0023] FIGURE 3 is a schematic illustration of the downhole power generation device illustrated in Figure 2 in a first configuration,

[0024] FIGURE 4 is a schematic illustration of the downhole power generation device illustrated in Figure 2 in a second configuration,

[0025] FIGURE 5 is a schematic illustration of an alternative embodiment of downhole power generation device according to the first aspect of the invention,

[0026] FIGURE 6 is a schematic illustration of a further alternative embodiment of downhole power generation device according to the first aspect of the invention,

[0027] FIGURE 7 is a schematic illustration of a further alternative embodiment of downhole power generation device according to the first aspect of the invention,

[0028] FIGURE 8 is a schematic illustration of a further alternative embodiment of downhole power generation device according to the first aspect of the invention,

[0029] FIGURE 9 is a schematic illustration of a further alternative embodiment of downhole power generation device according to the first aspect of the invention,

[0030] FIGURE 10 is a schematic illustration of a further alternative embodiment of downhole power generation device according to the first aspect of the invention,

[0031] FIGURE 11 is a schematic illustration of a further alternative embodiment of downhole power generation device according to the first aspect of the invention, and

[0032] FIGURE 12 is a hydrocarbon drilling or production system according to the second aspect of the invention.

[0033] DETAILED DESCRIPTION

[0034] The following description may use terms such as “horizontal”, “vertical”, “lateral”, “back and forth”, “up and down”,” upper”, “lower”, “inner”, “outer”, “forward”, “rear”, etc. These terms generally refer to the views and orientations as shown in the drawings and that are associated with a normal use of the invention. The terms are used for the reader’s convenience only and shall not be limiting. Figure 1 shows a downhole power generation system 10 comprising a pressure chamber assembly 12 comprising a first movable element 14 which at least partially encloses a first variable volume chamber V1A and a second movable element 16 which at least partially encloses a second variable volume chamber V1B, each movable element 14, 16 having an exterior surface and an interior surface. The first and second variable volume chambers V1A, V1B are connected by a conduit 18 together to form a closed interior volume V1 containing a non-compressible fluid. The interior surface of each movable element 14, 16 is in contact with the non- compressible fluid so that the pressure of the incompressible fluid acts on the movable elements 14, 16. The conduit 18 provides a path for flow of the non- compressible fluid between the first and second variable volume chambers V1A, V1 B when the first and second movable elements 14, 16 move so that one of the first or second variable volume chambers V1A, V1B contracts and the other expands. By virtue of filling the closed interior volume V1 with an incompressible fluid, such movement of the first and second movable elements 14, 16 is driven by a difference in pressure between the pressure of fluid acting on the exterior surface of the first movable element 14 and the pressure of fluid acting on the exterior surface of the second movable element 16.

[0035] In this embodiment the pressure chamber assembly 12 is a dual bellows assembly 12, and the first movable element is a first bellows 14 and the second movable element is a second bellows 16.

[0036] The downhole power generation system further includes a generator device 20 which is located in the conduit 18, and which is configured to use the flow of incompressible fluid along the conduit 18 to generate power. The generator device 20 is shown in Figure 2. The generator device 20 effectively divides the interior volume V1 of the dual bellows assembly 12 into the first variable volume chamber V1A enclosed by the first bellows 14, and the second variable volume chamber V1B enclosed by the second bellows 16.

[0037] The system 12 further comprise a housing 22 having an interior, and which supports the dual bellows assembly 12 so that the first bellows 14 is located in the interior of the housing 22 and the housing 22 form a first housing volume V2 in the interior of the housing 22 around the exterior surface of the first bellows 14. In this embodiment, one wall of the housing 22 provides a support 24, the first bellows extending from one side of the support 24 into the interior of the housing 22, whilst the second bellows 16 extends from the opposite side of the support 24 to the first bellows 14 at the exterior of the housing 22. The fluid pressure in the first housing volume V2 therefore acts on exterior surface of the first bellows 14, whilst the exterior surface of the second bellows 16 is exposed to ambient pressure.

[0038] The conduit 18 is fixed relative to the housing 22. In this embodiment, the conduit 18 extends through the support 24.

[0039] In this embodiment, the housing 22 is provided with a charging port 26 which provides a conduit for flow of fluid into the first housing volume V2, and a removable plug 28 which is inserted into the charging port 26 to block the charging port 26. The plug 28 engages with the housing 22 to provide a substantially fluid tight seal, so that the first housing volume V2 is therefore completely closed when the plug is in place.

[0040] The charging port 26 may be used to fill the first housing volume V2 with a gas such as nitrogen or an inert gas, and the plug 28 used to block the charging port 26 when the pressure of the gas in the first housing volume V2 has reached a desired level.

[0041] Whilst this embodiment, the charging port 26 is closed with a plug, it should be appreciated that this need not be the case, and any other suitable means for containing pressure in the first housing volume V2 may be used. For example, the charging port 26 may be closed using a non-return valve or check valve, which is arranged to allow flow of gas into the first housing volume V2, but prevents flow of gas out of the first housing volume V2, unless mechanically actuated to vent the first housing volume V2. Alternatively, once the first housing volume V2 is charged with the required pressure of gas, the charging port 26 may be permanently closed, for example using a welded closure element.

[0042] When the first housing volume V2 is filled with gas and closed, if the ambient pressure at the exterior of the housing 22 is the same as the pressure in the first housing volume V2, the first and second bellows 14, 16 adopt an equilibrium configuration illustrated in Figures 1 and 2. In this embodiment, when in the equilibrium position, the first and second bellows 14, 16 are extended by similar amounts, and the first bellows chamber V1 A and second bellows chamber V1 B contain a generally equal volume of incompressible fluid. If the ambient pressure increases so that it is higher than the pressure of the gas in the first housing volume V2, the second bellows 16 is compressed, and incompressible fluid is driven from the second bellows chamber V1 B, through the generator device and into the first bellows chamber V1A, causing the first bellows 14 to expand, as illustrated in Figure 3. Similarly, if the ambient pressure decreases so that it is lower than the pressure of the gas in the first housing volume V2, the first bellows 14 is compressed, incompressible fluid is driven from the first bellows chamber V1 A, through the generator device and into the second bellows chamber V1 B, causing the second bellows 16 to expand, as illustrated in Figure 4.

[0043] Varying the ambient pressure can thus be used to drive fluid through the generator device 20 to generate power.

[0044] The housing 22 may enclose a second housing volume V3 around the second bellows 16, as illustrated in Figure 5. In this case, the fluid pressure in the second housing volume V3 therefore acts on exterior surface of the second bellows 16.

[0045] In this embodiment, the support 24 separates the first housing volume V2 from the second housing volume V3. In this case, the housing 22 is provided with an inlet port 30 which provides a conduit for flow of fluid into the second volume and an outlet port 32 which provides a conduit for flow of fluid out of the second housing volume V3. It will be appreciated that, in this case, rather than ambient pressure, it will be the pressure in the second housing volume V3 relative to the pressure in the first housing volume V2 that will cause the system to operate as described in relation to Figures 3 and 4 above. In other words, varying the pressure in the second housing volume V3 can be used to drive fluid through the generator device 20 to generate power.

[0046] In one embodiment, the generator device 20 is configured to use to the flow of incompressible fluid to generate mechanical power. For example, it may comprise a turbine or piston. It may further comprise an electro-magnetic generator which provided in the same unit in the interior of the dual bellows assembly 12, and which is driven by the turbine (or other mechanical power generating device) to generate electricity.

[0047] Alternatively, the generator device 20 may comprise an electrical generator which uses flow of fluid to generate electricity without the use of a turbine, such as the downhole power generation device disclosed in US 2023 / 0028913, or the water current power generating device disclosed in US 2012 / 248779.

[0048] In this case, the generator device 20 may be connected directly to the equipment requiring electrical power 34 (tool, actuator, valve, sensor etc.) by an electrical power cable. Alternatively, or additionally the generator device 20 may be connected directly to a battery 36, so that the electrical energy generated by the generator device 20 charges the battery. The equipment 34 may, in this case, draw power from the battery.

[0049] Where the generator device 20 comprises a turbine, piston or other mechanical power generating device, the system may further comprise a separate electrical power generator 38 which is driven by the generator device 20 via a drive shaft 40, as illustrated in Figure 7. The electrical power generator 38 could be a conventional electro-magnetic generator. Alternatively, the system may comprise a compressor 42 which is driven by the generator device 20, the compressor 42 being configured to drive fluid into compressed fluid reservoir. In a further alternative embodiment, the mechanical power generated by the generator device 20 could be used to drive movement hydraulic or pneumatic fluid to power hydraulically or pneumatically operated equipment.

[0050] By locating the generator device 20 in the dual bellows assembly 12, in which it is in contact only with the clean incompressible fluid sealed in the dual bellows assembly 12. The power generation system 10 can thus be used in a downhole environment without the generator device 20 coming into contact with any downhole fluids such as hydrocarbon formation fluids. Corrosion I erosion of the generator device 20 by the downhole fluids may thus be avoided.

[0051] It should be appreciated that the invention is not restricted to the use of a dual bellows assembly 12. The first and second bellows 14, 16 each merely provide a chamber which has a variable volume and which is configured to hold the incompressible fluid, and any other means for providing such a chamber may be used. For example, one or both of the variable volume chambers V1A, V1 B may be formed by a piston and cylinder arrangement, or a diaphragm.

[0052] Figure 8 illustrates an embodiment of power generation system 10’ in which the first movable element is piston 48 which is movable in a cylinder, which in this example is formed by the housing 22, and the second movable element 16 is a bellows. The piston 48 is in sealing engagement with the interior surface of the housing 22 and is movable within the housing 22. As such, the piston 48 divides the interior of the housing 22 into the first housing volume V2 and the first variable volume chamber V1A. The piston 48 has an interior surface which is in contact with the incompressible fluid in the first variable volume chamber V1 A, and therefore acted on by fluid pressure of the incompressible fluid, and an exterior surface which is in contact with the fluid in the first housing volume V2, and acted on by the fluid pressure in the first housing volume V2.

[0053] The second variable volume chamber V1 B is formed by the bellows 16 just as in the embodiments described above in relation to Figures 1 - 4 and 6. This embodiment of power generation system 10’ operates in the same way as the embodiments described above in relation to figures 1 - 4 and 6 above, except that variations in the pressure in the first housing volume V2 relative to the pressure around the bellows 16 causes the bellows 16 to expand or contract and the piston 48 to move within the housing 22 to vary the volume of the first variable volume chamber V1A and drive non-compressible fluid through the generator device 20.

[0054] Figure 9 illustrates a further alternative embodiment of power generation system 10” in which the first and second movable elements are pistons 48, 48’, each of which are movable in a cylinder, which in this example are formed by the housing 22. Again, each piston 48, 48’ is in sealing engagement with the interior surface of the housing 22 and is movable within the housing 22. A first one of the pistons 48 is located on one side of the support 24 and divides the interior of the housing 22 into the first housing volume V2 and the first variable volume chamber V1A, whilst the other piston 48’ is located on the other side of the support 24 and divides the interior of the housing 22 into the second housing volume V3 and the second variable volume chamber V1 B. Each piston 48, 48’ has an interior surface which is in contact with the incompressible fluid in the closed interior volume V1, and therefore acted on by fluid pressure of the incompressible fluid, and an exterior surface which is in contact with the fluid in the first housing volume V2 or second hosing volume V3 respectively, and acted on by the fluid pressure in the first I second housing volume V2 / V3. This embodiment of power generation system 10’ operates in the same way as the embodiments described above in relation to figures 5, and 7 above, except that variations in the pressure in the first housing volume V2 in the second housing volume V3 causes the pistons 48, 48’ to move within the housing 22 to vary the volume of the first variable volume chamber V1A and second variable volume chamber V1B and drive non-compressible fluid through the generator device 20.

[0055] Whilst in these embodiments, the or each piston 48, 48’ engages with the housing 22 so that the housing 22 act as a cylinder, it will be appreciated that one or both of the pistons 48, 48’ could equally be provided in a separate cylinder which is located in the housing 22 and supported on the support 24. Such a cylinder would be open ended or contain a conduit to facilitate fluid pressure communication between the respective housing volume V21 V3 and exterior surface of the piston 48, 48’

[0056] Figure 10 illustrates a further alternative embodiment of power generation system 10’” in which the first movable element comprises a diaphragm 49 which divides the interior of the housing 22 into the first housing volume V2 and the first variable volume chamber V1 A, and the second movable element comprises bellows 16. The diaphragm 49 has an interior surface which is in contact with the incompressible fluid in the first variable volume chamber V1A, and therefore acted on by fluid pressure of the incompressible fluid, and an exterior surface which is in contact with the fluid in the first housing volume V2, and acted on by the fluid pressure in the first housing volume V2.

[0057] The second variable volume chamber V1 B is formed by a bellows 16 just as in the embodiments described above in relation to Figures 1 - 4 and 6. This embodiment of power generation system 10’ operates in the same way as the embodiments described above in relation to figures 1 - 4 and 6 above, except that variations in the pressure in the first housing volume V2 relative to the pressure around the bellows 16 causes the bellows 16 to expand or contract and the diaphragm 49 to move within the housing 22 to vary the volume of the first variable volume chamber V1 A and drive non-compressible fluid through the generator device 20.

[0058] Figure 11 illustrates a further alternative embodiment of power generation system 10”” in which the first and second movable elements are both diaphragms 49, 49’. A first one of the diaphragms 49 is located on one side of the support 24 and divides the interior of the housing 22 into the first housing volume V2 and the first variable volume chamber V1 A, whilst the other diaphragm 49’ is located on the other side of the support 24 and divides the interior of the housing 22 into the second housing volume V3 and the second variable volume chamber V1 B. Each diaphragm 49, 49’ has an interior surface which is in contact with the incompressible fluid in the closed interior volume V1, and therefore acted on by fluid pressure of the incompressible fluid, and an exterior surface which is in contact with the fluid in the first housing volume V2 or second hosing volume V3 respectively, and acted on by the fluid pressure in the first I second housing volume V21 V3.

[0059] This embodiment of power generation system 10’ operates in the same way as the embodiments described above in relation to figures 5, and 7 above, except that variations in the pressure in the first housing volume V2 in the second housing volume V3 causes the diaphragms 49, 49’ to move within the housing 22 to vary the volume of the first variable volume chamber V1A and second variable volume chamber V1 B and drive non-compressible fluid through the generator device 20. It will be appreciated that it would equally be possible for one of the diaphragms 49, 49’ to be replaced with a piston.

[0060] Any of the downhole power generation systems 10, 10’, 10”, 10’”, 10”” described above may be used in a hydrocarbon drilling or production system 50 comprising a bore hole 52, and a tubular 54 extending down the borehole, there being an annular volume 56 around the tubular (hereinafter referred to as the annulus) and an interior volume 58 inside the tubular 54. Such a system is illustrated schematically in Figure 8. The downhole power generation system 10, 10’, 10”, 10’”, 10”” could be located in the annulus 56 so that the exterior surface of the second bellows 16 is in exposed to fluid pressure in the annulus 56. The downhole power generation system 10, 10’, 10”, 10’”, 10”” may thus be operated to generate power by increasing or decreasing the annulus pressure relative to the pressure of the gas in the first housing volume V2. Alternatively, the downhole generation device 10, 10’, 10”, 10’”, 10”” may be located in the interior volume 58 of the tubular 54, so that the exterior surface of the second bellows 16 is exposed to fluid pressure in the interior volume 58 of the tubular 54. In this case, the downhole power generation system 10, 10’, 10”, 10’”, 10”” may thus be operated to generate power by increasing or decreasing the pressure inside the tubular relative to the pressure of the gas in the first housing volume V2. Where the second variable volume chamber is located in a second housing volume V3, as illustrated in Figures 5, 7, 9 and 11, the downhole power generation system 10, 10”, 10”” need not be located in the annulus 56 or the interior 58 of the tubular 54 to operate in this way. In this case, a conduit could be provided between the inlet port 30 and the annulus 56 / interior 58 of the tubular 54, so that the second housing volume V3 is in communication with the annulus I tubular interior pressure, and the annulus I tubular interior pressure acts on the second movable element 16, 48’, 49’.

[0061] In these embodiments, the exterior surface of the second movable element 16, 48, 48’ is in direct contact with the fluid in the annulus 56 or interior 58 of the tubular 54, but this need not be the case. Pressure communication means such as a further piston, bellows or diaphragm may be used to communicate the annulus I tubular pressure to the exterior surface of the second movable element 16, 48’, 49’.

[0062] The downhole power generation system 10 may be located in a side pocket 60 of a side pocket mandrel of the tubular 54, as illustrated in Figure 8.

[0063] As the downhole power generation device 10 is operated to generate power by changes in fluid pressure, it can be used to generate power when there is no fluid flow along the bore hole 52.

[0064] The invention is not limited by the embodiments described above; reference should be had to the appended claims.

Claims

CLAIMS1. A downhole power generation system (10) comprising a pressure chamber assembly (12) having a first movable element (14, 48, 49) which at least partially encloses a first variable volume chamber (V1A) and a second movable element (16, 48’, 49’) which at least partially encloses a second variable volume chamber (V1B), each movable element (14, 48, 49, 16, 48’, 49’) having an exterior surface and an interior surface, and the first and second variable volume chambers (V1A, V1B) being connected by a conduit (18) so that they together enclose a closed volume (V1) containing an incompressible fluid, the conduit (18) providing a path for flow of the incompressible fluid between the first variable volume chamber (V1A) and the second variable volume chamber (V1 B) when the first and second movable elements (14, 48, 49, 16, 48’, 49’) move so that one of the first or second variable volume chamber (V1A, V1B) contracts and the other expands, the system further comprising a generator device (20) which is located in the conduit (18), and which is configured to be driven by flow of the incompressible fluid along the conduit (18) to generate power.

2. The downhole power generation system (10) of claim 1 further comprising a housing (22) having an interior, and which support the pressure chamber assembly (12) so that the first variable volume chamber (V1A) is located in the interior of the housing (22) and the housing (22) forms a first housing volume (V2) in the interior of the housing (22) around or adjacent the exterior surface of the first movable element (14, 48, 49) and pressure of fluid in the first housing volume (V2) acts on the exterior surface of the first movable element (14, 48, 49).

3. The downhole power generation system (10) of claim 2 wherein the housing (22) is provided with a charging port (26) which provides a conduit for flow of fluid into the first housing volume (V2)4. The downhole power generation system (10) of claim 3 wherein the system further comprises a removable plug (28) which can be inserted into the charging port to block the charging port (26) so that the first housing volume (V2) is closed, or a non-return valve which is provided in the charging port (26) and arranged to allow flow of fluid into the first housing volume (V2) and to substantially prevent flow of fluid out of the first housing volume (V2).

5. The downhole power generation system (10) of any one of claims 2 - 4 wherein the housing (22) encloses a second housing volume (V3) around or adjacent the exterior surface of the second movable element (16, 48’, 49’) so that pressure of fluid in the second housing volume (V4) acts on the exterior surface of the second movable element (16, 48’, 49’).

6. The downhole power generation system (10) of claim 5 wherein the housing (22) is provided with an inlet port (30) which provides a conduit for flow of fluid into the second housing volume (V3).

7. The downhole power generation system (10) of claim 6 wherein the housing (22) is provided with an outlet port (32) which provides a conduit for flow of fluid out of the second housing volume (V3).

8. The downhole power generation system (10) of any preceding claim wherein one or both of the movable elements (14, 16) comprise(s) bellows.

9. The downhole power generation system (10) of any one of claims 1-8 wherein one or both of the movable elements (48, 48’) comprise(s) a piston and cylinder.

10. The downhole power generation system (10) of any one of claims 1-8 wherein one or both of the movable elements (49, 49’) comprise(s) a diaphragm.

11. The downhole power generation system (10) of any preceding claim wherein the generator device (20) comprises a mechanical power generating device.

12. The downhole power generation system (10) of claim 9 wherein the system further comprises an electrical power generator (38) which is driven by the generator device (20).

13. The downhole power generation system (10) of claim 9 or 10 wherein the system comprises a compressor (42) which is driven by the generator device (20).

14. The downhole power generation system (10) of any one of claims 1 to 8 wherein the generator device (20) comprise an electrical power generation device.

15. A hydrocarbon drilling or production system (50) comprising a bore hole (52), a tubular (54) extending down the bore hole (52), there being an annular volume (56) around the tubular (54) and an interior volume (58) inside the tubular (54), the system further comprising a downhole power generation system (10) according to any preceding claim, wherein the exterior surfaceof the second movable element (16, 48’, 49’) is exposed to fluid pressure from either the annular volume (56) or the interior volume (58) of the tubular (54).

16. A hydrocarbon drilling or production system (50) according to claim 15 wherein in fluid from either the annular volume (56) or the interior volume(58) of the tubular (54) is in direct contact with the exterior surface of the second movable element (16, 48’, 49’).

Images