WO2017168008A2

WO2017168008A2 - Pump system

Info

Publication number: WO2017168008A2
Application number: PCT/EP2017/057845
Authority: WO
Inventors: Wilhelmus Hubertus Paulus Maria Heijnen
Original assignee: Yta B.V.
Priority date: 2016-03-29
Filing date: 2017-04-03
Publication date: 2017-10-05
Also published as: WO2017168008A3; GB201605195D0

Abstract

A fluid pump, for example being adapted to operate in a well bore, and a well bore tool are presented, the fluid pump comprising a pump housing comprising a cylinder, the cylinder having a first and a second chamber and a constriction between the first and the second chamber. The fluid pump further comprises a double action piston assembly arranged movably in the pump housing for pumping fluid, the double action piston assembly extending from the first chamber through the constriction into the second chamber.

Description

Pump System

Specification

Field of the invention

The invention is related to a pump system, for example for use in well bores especially for the Oil and Natural Gas Industry .

Background and Summary of the invention

Well bores are used in the petroleum and natural gas industry to produce hydrocarbons (production well) or to inject fluids, for example water, CO2 and/or Nitrogen

(injection well) . Typically, such fluids are injected to stimulate, i.e. to enhance the hydrocarbon recovery.

Lately, CO2 injection has been introduced to this to reduce the C02-concentration in the atmosphere in order to defeat global warming.

Typically, a well bore is lined with a steel pipe or steel tubing, generally referred to as casing or liner, and cemented in the overburden section to reduce the risk of unwanted evacuation of fluids from the overburden and/or the reservoir into the surface environment. For completion of the reservoir section at present several options are typically used, namely open hole completion, or using a liner with several formation packers for sealing off sections of the annulus around the steel liner, or using a steel liner which is cemented in place and access to the reservoir is gained by perforating the liner and cement in a later stage of the completion, or completion of the well with a liner in open hole which has predrilled holes in the liner to gain access to the reservoir. It should be noted that the holes can also be made in a later stage of the well life.

During the production or injection of fluids from a well bore in an earth formation the well bore can enlarge due to chemical reactions and/or an instability of the borehole. This may occur due to injection or production pressure changes and/or erosion which can take place e.g. in case of production from unstable geological formations such as turbidites known for their unpredictable sand face failure resulting in massive sand production leading to well failure. Furthermore, when injection processes are being used fractures can be generated resulting in undesired direct communication between the injection and production wells. On the other hand the well can collapse, for example caused by compaction, a process which happens when the pressure in the reservoir reduces, or by the use of

chemicals used to improve injectivity or productivity. The latter can cause a collapse of the annulus and therewith possibly block the access to the reservoir and, therewith, preventing injection or production. Also of importance may be a phenomenon which is called cross flow in the annulus. Cross flow in the annulus is the result of pressure

differences along the liner of the production or injection well in an un-cemented completion. The latter can lead to loss of production and/or loss of economic reserves.

As the total length from the reservoir to an access at the top end of the well bore may sum up to several hundred or even several thousand meters pumping fluids in our out the well bore is difficult and subject to continued development. In particular, said total length keeps increasing over the past decades.

It is an object of the invention to provide a novel fluid pump .

It is another object of the invention to provide a downhole tool having a fluid pump for pumping fluids in or out a well bore, thus a fluid pump which is able to work

satisfying in extreme conditions with high outside pressure levels .

Yet another object of the invention is to provide the fluid pump in such a way, that it is extremely compact and, at the same time, robust with respect to the type of fluid to be pumped.

The object of the invention is achieved by subject matter of the independent claims. Preferred embodiments of the invention are subject of the dependent claims.

A downhole tool is presented herein being adapted to operate in a well bore. For example, well bores can

comprise difficult environmental conditions such as a pressure up to 35 MPa or a temperature which could rise up to 1000 K, or, as development of well bore exploitation continues rapidly, even more. Such a well bore can have open hole sections and/or cased hole sections, and it can comprise an angle with respect to a vector towards the centre of the earth and/or gravity. The well bore fluid can consist of different portions or "phases" of fluid such as mainly water, oil and/or gas, but also other fluid portions (phases) and also particulate matter, e.g. sand particles, can be phases of the well bore fluid. It is particularly desired to be able to pump such difficult fluids, e.g. viscous fluids and/or fluids

containing particulate matter.

The proposed fluid pump is therefore in a greatly preferred embodiment adapted to operate in a well bore. This means thus, that the fluid pump of this embodiment is designed deployable into the well bore to operate from underground.

The fluid pump according to the invention comprises a pump housing comprising a cylinder. It might be possible to chain and/or combine several cylinders housing each one double action piston assembly. However, so far the design comprising one common cylinder seems most promising. The cylinder has a first and a second chamber and a

constriction between the first and the second chamber.

Particularly preferred, the first and second chamber are linked to each other, wherein the first and second chamber define parts of the inner volume of said cylinder. In an easy example, the first and the second chamber together occupy the total inner volume, wherein the constriction is arranged between the first and the second chamber within said cylinder. The constriction divides the total inner volume of the cylinder into two volumes, which is the first and the second chamber. Particularly preferred, the constriction is arranged centrically in the cylinder, the first and the second chamber comprising equal volumes. The constriction is arranged directly at the inner side of said cylinder and may be mounted thereto or formed in one piece when

manufacturing the cylinder. By way of example, the

constriction can be made in one piece with the cylinder by just adjusting the inner bore diameter, with which the cylinder is drilled into the pump housing. In another embodiment, the constriction can be formed by inserting a ring shaped inlay into the cylinder and fixing it thereto.

In the cylinder a double action piston assembly is arranged movably in the pump housing for pumping fluid. The double action piston assembly extends from the first chamber through the constriction into the second chamber.

Particularly preferred, the double action piston assembly fits sealingly into the constriction. Thereby, when the double action piston assembly is mounted in the cylinder, the first chamber is sealingly separated from the second chamber by means of the double action piston assembly, for example by way of a piston rod of the double action piston assembly .

Such, the fluid pump can be described as a double action reciprocating plunger type pump.

Preferably the double action piston assembly comprises a first piston arranged in the first chamber, a second piston in the second chamber and a piston rod for directly

connecting the first piston with the second piston. In other words, two pistons are directly mounted to each other by said piston rod. The piston rod thus as a first function connects the first piston directly with the second piston, so that the whole double action piston assembly can perform a longitudinal movement in the cylinder in absence of relative movement between the first and the second piston. The distance between the first and the second piston is therefore affixed by the piston rod. The piston rod, as a second function, therein also seals - in cooperation with the constriction - the first chamber against the second chamber .

The double action piston assembly may be designed movable along the longitudinal extension direction of the pump housing, or the cylinder respectively, so that the double action piston assembly as a whole performs a longitudinal movement.

The pump housing may further comprise a first cylinder head and a second cylinder head, wherein the first cylinder head is arranged at a first end of the cylinder, and wherein the second cylinder head is arranged at a second end of the cylinder opposing the first end.

The first cylinder head may then comprise a first fluid channel for inflow and/or outflow of a pump fluid. The first fluid channel may be closable e.g. by means of a valve, so that fluid only flows into or out of the first chamber when the valve is opened.

Influx and/or outflux of the pump fluid into the cylinder, or into the first chamber respectively, can be performed e.g. by using two fluid channels per cylinder head, one fluid channel for influx and one fluid channel for outflux of the pump fluid. However, already one fluid channel would suffice, whereas on the other side more than two fluid channels can be utilized if improvements of the fluid flow of the pump fluid are to be expected.

A switchable valve, by way of example a three-way valve, can be utilized in communication with the fluid channel, for example mounted at or to the first cylinder head and/or to the second cylinder head, respectively.

In a simple embodiment, by using one fluid channel only, the three-way valve can thus distinguish or switch between inflow and outflow. However, usage of two fluid channels per cylinder head, wherein one fluid channel is used for pump fluid influx and the other fluid channel is used for pump fluid efflux, is preferred.

However, when using two fluid channels per cylinder head, also said three-way valves may be used. For example, with the three-way valve (one for each fluid channel) in this embodiment, the operative direction of the fluid pump can be reversed. Reversion of the operative direction of the fluid pump is especially preferred in the case, that additionally an influx filter is installed forward to the three-way valve, so that by reversed action of the fluid pump, flushing of the influx filter is possible. However, also the reversion of the operative direction allows for a two-way mode for the fluid pump, which is pumping fluids in both directions, if necessary.

The second cylinder head may comprise a second fluid channel for inflow and/or outflow of the pump fluid. The second cylinder head advantageously is designed similar or even identical to the first cylinder head. This allows for facilitation of production process of the fluid pump. The double action piston assembly is designed to perform, as a whole, a longitudinal movement in the cylinder. The cause for such longitudinal movement of the double action piston assembly is advantageously exposion to a pressure force .

The cylinder may further comprise an action fluid channel for providing action fluid into an action chamber. The action fluid channel advantageously is arranged at the inner surface of the cylinder, more advantageously in proximity to the constriction in the first chamber of the cylinder .

The action fluid can provide a pressure force for acting from the inside of the double action piston assembly on one side of the double action piston assembly, e.g. on the first piston. In other words, the action force for moving the first piston for executing the pump work is generated from the inside of the region, where the double action piston assembly is positioned in the cylinder. In

particular, the action fluid channel is arranged between the first piston and the constriction, which is also within the first chamber. This is true for all motion phases of the double action piston assembly, wherein the distance between the action fluid channel varies during movement of the first piston. The action volume is thus arranged between the first piston and the constriction. E.g., the action volume surrounds the part of the piston rod which is situated in the first chamber .

A second action fluid channel arranged between the second piston and the constriction can be implemented for

separately providing action fluid to a second action volume arranged between the second piston and the constriction. In other words, second action fluid channel and second action volume can be reversed left to right and otherwise the same with respect to the action fluid channel and the action fluid volume. The action volume can advantageously be designed such that, when action fluid is provided thereto through the action fluid channel, the action fluid of the action volume provides an action force on the first piston. The first piston can then be designed such, that in response to said action force the first piston can perform a longitudinal movement towards the first cylinder head. By such movement the first piston increases pressure in the pump fluid and/or pumps fluid out of the cylinder. The second action volume can be designed such that, when action fluid is provided thereto through the second action fluid channel, the action fluid of the second action volume provides an action force on the second piston. The second piston can then be designed such, that in response to said action force the second piston can perform a longitudinal movement towards the second cylinder head. The second piston thereby increases pressure in the pump fluid or pumps fluid out of the cylinder.

The action fluid together with the first action fluid channel and the second action fluid channel as well as the double action piston assembly interact such, that action fluid is provided alternatingly to the action volume or the second action volume such that the double action piston assembly performs an oscillating movement in the cylinder. For example, the action fluid channel and the second action fluid channel can be designed switchable by means of a respective valve.

Preferably, the action chamber at least partly surrounds the piston rod and/or the second action chamber at least partly surrounds the piston rod.

The double action piston assembly can further comprise a first pump surface in the first chamber and a second pump surface in the second chamber, the respective pump surface being designed for being in contact with the pump fluid.

For example, the first pump surface is the outer surface of the first piston, where the second pump surface is the outer surface of the second piston. The respective pump surface advantageously sealingly engages the inner surface of the cylinder. In other words, for example, the first piston and the second piston

precisely match the inner cylinder diameter so that

relative movement is allowed but flow of fluid between the pump chamber and the action fluid chamber - or the second pump chamber and the second action fluid chamber - is suppressed. Reduction of such cross-flow and thus increase of said sealing can be improved by usage of at least one piston ring.

The fluid pump can thus comprise a respective piston sealing member arranged radially on the first and/or second piston for sealing the action volume against the pump volume. This is, by way of example, said piston ring.

Particularly preferred, the action fluid comprises a higher pressure with respect to the pressure of the pump fluid, also when compressed by the first or second piston. Thus, a positive pressure difference against said sealing, e.g. piston rings, is provided from the backside of the first or second piston, so that flow of pump fluid into the action chamber or the second action chamber is prevented.

The respective pump surface thus limits the respective pump volume (which is the pump chamber) in the first and the second chamber. The absolute volume of the first pump chamber together with the second pump chamber stays constant, also the volume of the action fluid chamber together with the second action fluid chamber stays constant, whereas each volume changes, during action, periodically due to the movement of the double action piston assembly.

The first piston comprises, at its other side, an action surface, wherein the action fluid acts on the action surface of the piston thereby translationally moving the first piston and such the double action piston assembly towards the first cylinder head, when action fluid flows into the action chamber. Thus, the second piston can also comprise an action

surface, wherein the action fluid acts on the action surface of the second piston thereby translationally moving the second piston and such the double action piston

assembly towards the second cylinder head, when action fluid flows into the second action chamber.

The respective action surface of the respective first or second piston thus limits the respective action volume in the first and/or the second chamber.

In the fluid pump, the piston rod may be designed having an outer diameter equally or close to equal the inner diameter of said constriction.

The constriction can thus comprise a sliding support for the piston rod or even may be designed as the sliding support for the piston rod. As thus, the constriction can have any inner diameter which is smaller than the diameter of the cylinder. For example, the constriction can have an inner diameter which equals to about 0,99 to 0,9 times the inner diameter of the cylinder. The piston rod thus can have an outer diameter which almost resembles the inner diameter of the constriction.

The fluid pump can comprise an action fluid reservoir. The action fluid reservoir then is connected to the action fluid channel and/or to the second action fluid channel. The action fluid reservoir may be housed within a common fluid pump housing, however may also be separated. The fluid pump can further comprise a feed unit for

providing the action fluid to the action chamber. In other words, the feed unit will be situated between the action fluid reservoir and the action fluid channel and/or the second action fluid channel.

The feed unit may comprise a compressor unit and/or an action fluid pump for providing a pressure level to the action fluid which is higher with respect to the pump fluid to be pumped by the fluid pump.

The pressure level provided by the feed unit can be

selected adjustable.

For example, the pressure level provided by the feed unit to the action fluid is 10 bar or more higher than the pressure level of the pump fluid. In combination with the flexible action fluid reservoir, the feed unit only needs to provide excess pressure exceeding the surrounding pressure level. In the case of a downhole tool, such surrounding pressure level may reach levels up to 1000 Bar or more. The excess pressure provided by the feed unit can also be 100 bar or more or 1000 bar or more higher than the pressure level of the pump fluid.

In principal, the pressure excess of the action fluid, which is provided by the feed unit, can be evaluated by the ratio of the volume of the action chamber to the pump chamber, and/or by ratio of the outer diameter of the piston rod to the inner diameter of the cylinder. The smaller the action chamber is compared to the pump chamber, the higher the pressure excess can be selected. In other words, a pressure transmission ratio can be defined between the pressure of the action fluid and the pump fluid. By way of example, the pressure transmission ratio depends also on the oscillation frequency of the fluid pump.

Oscillation frequency of the fluid pump may be selected depending on the surrounding pressure level, on the size of the fluid pump, on the fluid to be pumped, and the like. For example, the cycle period of the double action piston assembly in the fluid pump for use in a downhole tool may be in the range of 30 seconds or more, 60 seconds or more or even 90 seconds or more. Preferably, the action fluid reservoir comprises a flexible reservoir casing which is open to pressure level of the surrounding, so that the action fluid reservoir is pressure compensated. By way of example, this is of specific

interest when the fluid pump is utilized in conditions having rather high surrounding pressure levels, for example of 100 Bar or more, or 500 Bar or more. The flexible reservoir casing this imposes the pressure level of the surrounding on the action fluid reservoir, so that the action fluid is pressurized to the outside pressure level. The flexible reservoir casing can be embodied, by way of a simple example, by a bag, or, by way of another example, by a casing which comprises a pressure opening to the

surrounding, wherein the opening is close to the fluid but lets the pressure pass through to the action fluid

reservoir. Thus, the feed unit for the action fluid does only need to provide the excess pressure level to the action fluid.

Furtheron, an inlet filter can be provided in the fluid pump at the first and/or second pump fluid channel. Thus, filtration of the pump fluid is provided, which allows for cleaning of pump fluids. In operation situations where a high load with particulate matter is observed, or just when the inlet filter is filled, the fluid pump can be

advantageously driven in an inverse mode. This can, by way of example, be performed when said three-way valves are utilized.

A respective fluid brake nose can be provided at the first and/or the second cylinder head. With other words, a first fluid brake nose can be provided at the first cylinder head. For example, the fluid brake nose stops the moving double action piston assembly just before reaching the cylinder head. In other words, the fluid brake nose

generates a braking force on the double action piston assembly, e.g. on the first piston's pump surface,

counteracting the driving force of the action fluid.

For detection of proper position of the double action piston assembly, e.g. of the first piston, further a pump stroke sensor can be comprised in the fluid pump.

Further improving the invention, the first piston and/or the second piston and/or the piston rod can be made at least partly hollow for reducing weight of the double action piston assembly. A downhole tool, comprising a fluid pump for pumping fluid to the surface and/or into the well, e.g. for pumping well bore fluid out of the well bore or for pumping e.g.

polymers, carbon dioxide or water into the well, is also presented. The downhole tool may comprise the fluid pump being designed, for example, as depicted above. The

downhole tool advantageously comprises an elongated, cylindrical section comprising the cylinder. Said

cylindrical section may be the cylinder itself, so that the cylinder in this embodiment is part of the housing of the downhole tool.

The downhole tool may comprise a top connection having an electrical power connector. Power can be delivered, by way of example, through cables connected directly to the downhole tool, or as a second example, by means of an inductive power coupling.

The downhole tool may further comprise a separated

electronics section for housing pump electronics.

The downhole tool may also further comprise a separated reservoir section for storage of the action fluid. Preferably, the separated reservoir section comprises a flexible reservoir casing which is open to pressure level of the surrounding, so that the action fluid reservoir comprises a variable size. In other words, the separated reservoir section may accommodate the flexible action fluid reservoir casing. The downhole tool can comprise an action fluid pump

section, the action fluid pump section comprising an action fluid pump for compressing and pumping the action fluid to the action chamber and/or the second action chamber.

The downhole tool can further comprise an inlet filter section flangeable to the fluid pump. The inlet filter section can comprise the inlet filter. A method for pumping a pump fluid is defined, comprising several steps. Said pump fluid is provided to a first pump chamber of a fluid pump. The fluid pump can be designed self-priming for this case. A pressure level is provided to an action fluid and said action fluid is fed to an action chamber in the fluid pump.

With the action fluid a double action piston assembly is driven to perform a movement to shrinken the volume of said pump chamber. Thereby, the pressure level in the pump chamber is raised and/or said pump fluid is driven out through a first pump fluid channel.

At the same time, the volume of a second pump chamber in the fluid pump is increased through movement of the double action piston assembly. In other words, the same double action piston assembly acts on the first pump chamber as well as on the second pump chamber at the same time through its movement.

Thereafter, feeding of said action fluid to the action chamber is stopped and more action fluid is fed to a second action chamber in the fluid pump. Advantageously, feeding of said action fluid to the action chamber is stopped due to a stop signal obtained from a sensor. With the action fluid, a second piston of said double action piston assembly is driven to perform a movement to shrinken the volume of the second pump chamber. Thereby, the pressure level in the pump chamber is raised and said pump fluid is driven out from the pump chamber through a second pump fluid channel.

The pump chamber, the second pump chamber, the action chamber and the second action chamber are housed in a common cylinder of the fluid pump.

The pump chamber and the second pump chamber share a common volume in the common cylinder, so that, when the volume of the pump chamber decreases by movement of the double action piston assembly, automatically the volume of the second pump chamber increases and vice versa. In other words, the total volume taken by the pump chamber and the second pump chamber stays constant.

Advantageously, the action chamber and the second action chamber share a common volume in the common cylinder, so that, when the volume of the action chamber decreases by movement of the double action piston assembly,

automatically the volume of the second action chamber increases and vice versa. Further preferred, the action chamber and the second action chamber are separated by a constriction. The action fluid may drive the double action piston

assembly by pressure, wherein the pressure of the action fluid rests against a piston rod of the double action piston assembly on the one side, against a cylinder inner wall on a second side, against the constriction on a third side and against an action surface of a movable first cylinder on a fourth side, to perform the movement to shrinken the volume of said pump chamber. The downhole tool may comprise an elongated housing divided into several sections. The Downhole tool being adapted to operate in a well bore can comprise a segmented housing. The segmented housing has at least a first and a second tube segment forming part of the segmented housing.

The invention is described in more detail and in view of preferred embodiments hereinafter. Reference is made to the attached drawings wherein like numerals have been applied to like or similar components.

Brief Description of the Figures

It is shown in a schematic cross-sectional view of an earth formation with a downhole tool in a well bore; another schematic cross-sectional view of an earth formation with a downhole tool in a well bore having a horizontal section partly covered by a liner;

a first embodiment of a fluid pump;

a further embodiment of a fluid pump, showing in a different movement phase; Fig. 5 a further embodiment of a fluid pump, showing in a different movement phase;

Fig. 6 a further embodiment of a fluid pump, showing in a different movement phase;

Fig. 7 a cross-sectional drawing of a fluid pump;

Fig. 8 a cross-sectional drawing of another embodiment of the fluid pump;

Fig. 9 cross-sectional drawing of a further embodiment of the fluid pump;

Fig. 10 a detail of Fig. 9;

Fig. 11 a top view of a fluid pump;

Fig. 12 a schematical drawing of a downhole tool having a fluid pump;

Fig. 13 a schematical drawing of a reservoir section of a downhole tool;

Fig. 14 a schematical drawing of a feed section of a

downhole tool.

Detailed Description of the Invention

In Fig. 1 a well bore 2 is drilled in an earth formation 4 to exploit natural resources like oil or gas. The well bore 2 continuously extends from the extraction facility 9 at or near the surface 6 to a reservoir 8 of the well bore 2 situated distal from the wellhead 10 at the extraction facility 9.

A casing/liner 12 in the form of an elongated steel pipe or steel tubing is located within the well bore 2 and

extending from the wellhead 10 to an underground section of the well bore 2. The reservoir 8 and/or the casing/liner 12 are typically filled with a fluid 16, 17, 18, respectively. The fluids 16, 17, 18 are e.g. oil or gas in case of a production well or water, CO2 or nitrogen in case of an injection well. A downhole tool 20 is located within the casing or liner 12. Advantageously, the downhole tool 20 operates

autonomously having internal power storage 92 (see e.g. Fig. 2) and thus needs not be powered or wired externally. To sum up, the downhole tool 20 can be operated quite freely in the well bore 2 and particularly needs not to be cable linked to the surface.

The downhole tool 20 may additionally be a movable downhole tool 20 being moved by moving means 21, generally known to the skilled person, within the casing or liner 12 to any desired position in the casing or liner 12.

The diameter of the housing 28 can be chosen e.g. with respect to the well bore diameter the downhole tool shall be used for, and may comprise in an example an outer diameter of 73mm and an inner diameter of 55 mm, resulting in a housing thickness of about 18 mm. However, the outer diameter of the housing 28 lies preferably in a range in between 50 mm to 90 mm.

Fig. 2 shows another earth formation with a down-hole tool 20 positioned in a horizontal portion of the casing/liner 12. The liner 12 in this embodiment only partly covers the well bore 2. The down-hole tool 20 comprises a power supply 92. Fig. 3 shows a first embodiment of the fluid pump having a double action piston assembly 50 with a first piston 52, a piston rod 54, and a second piston 56. The double action pump assembly 50 is mounted movably along a longitudinal axis 78 of the fluid pump 40.

In the embodiment depicted in Fig. 3, the fluid pump 40 is in a first stroke, where the double action piston assembly 50 moves towards the first cylinder head 80 to pump out pump fluid out of the pump chamber 46. The pump fluid can, for example, be pumped through the pump fluid outlet 72.

The double action pump assembly 50 is driven by action fluid which is led into the action chamber 60, for example through the action fluid channel 62. The action chamber 60 is adjacent to the constriction 44, which separates - in cooperation with the piston rod 54 - the first chamber 41 from the second chamber 43. While action fluid is led into the action chamber 60, more action fluid is pumped out of a second action chamber 66 by the double action pump assembly 50, in particular by a second piston 56 which is connected to the first piston 52 by the piston rod 54. The action fluid can be pumped out, by example, through a second action fluid channel 64.

The moving double action pump assembly 50 shrinkens in said first strike the first pump chamber 46 for pumping out the pump fluid. At the same time, the moving double action pump assembly 50 enlargens, in the first strike, the second pump chamber 48. By enlargement of the second pump chamber 48 an underpressure may be generated in the second pump chamber 48, which allows for generation of influx of pump fluid into the second pump chamber 48, for example through the pump fluid channel 76.

The double action piston assembly 50 comprises a first pump surface 53, a second pump surface 55, a first action surface 61 and a second action surface 63.

When the double action piston assembly 50 has reached a first dead center position at the end of the first strike, where the distance between the double action piston

assembly 50 and the first cylinder head 80 is minimal, a second stroke is initiated, which is illustrated by Fig. 4. Action fluid is injected into the second action chamber 66, which surrounds at least partly the piston rod 54 and which is arranged in the second chamber 43. The action fluid is set under pressure and thus acts on the second piston 56 to force a movement of the double action piston assembly 50 along the longitudinal axis 78 towards the second cylinder head 81. At the same time, through movement of the double action piston assembly 50 towards the second cylinder head 81, the action fluid in the first action chamber 60 is forced to leave the first action chamber 60. Also at the same time, through movement of said double action piston assembly 50, also further pump fluid is forced to enter the first pump chamber 46. Also at the sime time, pump fluid is forced, by the double action piston assembly 50, to leave the second pump chamber 48 while the double action piston assembly 50 moves towards the second cylinder head 81. The constriction 44 sealingly circumferes the piston rod 54 for dividing the cylinder 42 into two parts, where the double action piston assembly 50 can move longitudinally along the longitudinal axis 78 in the cylinder 42.

The double action piston assembly 50 is assembled, as the constriction 44 has a smaller diameter than the pistons 52, 56, if the cylinder 45 is made from one piece. If, however, the cylinder is made of at least two pieces, where the constriction 44 is one piece, the double action piston assembly 50 can also be made in single piece, the cylinder 45 being mounted around the assembly 50.

Fig. 5 depicts a third movement phase of the fluid pump 40, where the double action piston assembly 50 is at its left dead center position, which is the closest position of the double action piston assembly 50 to the second cylinder head 81. At the dead center position of the double action piston assembly 50, the fluid flow of the action fluid in or out the action chamber 60, in or out the second action chamber 66, in or out the pump chamber 46 and in or out the second pump chamber 48 is reversed. The meaning of reversed does include, that the respective fluid does not

necessarily have to flow through the same channel, for example when using separated input channels 70, 74 and output channels 72, 76.

Fig. 6 depicts a further embodiment of the fluid pump 40, wherein all fluid channels can be operated in dual ways. By reversing fluid flow in or out the pump chamber 46 or second pump chamber 48, in other words by reversing fluid flow through at least one of the individual fluid channels 70, 72, 74, 76, the effective direction of the fluid pump 40 can be reversed. Fig. 7 shows a schematical drawing of a fluid pump 40. The double action piston assembly 50 is designed to perform longitudinal motion along the longitudinal axis 78 of the cylinder 45 inside said cylinder 45. In the embodiment depicted in Fig. 7 the double action piston assembly 50 is in one of the dead center positions, e.g. the right or the first dead center position, whereas directions are only indicative. The first piston 52, as well as the piston rod 54 and the second piston 56 are made hollow to reduce weight. In the embodiment depicted, the double action piston assembly 50 comprises a sensor activator 82, which is in a simple case a magnet screwed to the pump side of the first piston 52. The sensor activator can induce a signal at the pump stroke sensor 86. For example, by means of the signal of the pump stroke sensor 86 the position of the double action piston assembly 50 can be determined, e.g. in each dead center position or when approaching the dead center position, so that the fluid flow of the action fluid can be shifted, so that the respective other action chamber 60, 66 is provided with action fluid and thus the movement direction of the double action piston assembly 50 is reversed. A fluid brake nose 85 is positioned at the leading edge of the second piston 56. The fluid brake nose 85 is made to approach a fluid brake void 82, wherein a fluid force is generated which brakes the second piston 56 prior to hitting the second cylinder head 81. Thus the oscillating movement of the double action piston assembly 50 may be performed without direct contact of the participating parts to each other, especially without the piston 52 or the second piston 56 hitting the first or second cylinder head 80, 81.

Fig. 8 shows a further embodiment of the fluid pump 40. Additional valves 93, 94, 96, 98 are installed at the pump fluid channels 70, 72, 74, 76 of this embodiment of the fluid pump 40. Further, action fluid lines 102, 104 are installed for supplying action fluid to the action chamber 60 and the second action chamber 66. The fluid pump 40 is housed in a downhole tool pump section 200. In other words, the fluid pump 40 is part of a downhole tool 20.

Fig. 9 shows a sectional drawing of another embodiment of a fluid pump 40. The section Z depicts the square, which shows a more detailed drawing in Fig. 10. Action fluid inlets 62, 64 is shown in more detail.

Fig. 10 shows a sectional drawing of a part of Fig. 9 depicted by line Z. The second piston 56 comprises two piston rings 58 for sealing the second action chamber 66 against the second pump chamber 48. The diameter Dl of the second piston 56 is only slightly larger than the diameter D2 of the constriction 44. Thus, advantageously either the pressure ratio between the action fluid and the pump fluid is high or the pump velocity is rather slow. The piston rod 54 has a hollow section 59.

The second piston 56 accesses into the piston rod 54 for secure fixation of the double action piston assembly 50.

Fig. 11 gives a sideview on further embodiment of a fluid pump 40. The first and the second cylinder head 80, 81 are mounted on both sides of the fluid pump 40. The

constriction 44 in this embodiment is a fitting, whereas two half pieces of the cylinder are mounted laterally to said constriction 44 to form, altogether, the cylinder and/or the pump housing 42 of the fluid pump 40.

Fig. 12 shows a schematic embodiment of a downhole tool 20 having a fluid pump 40. The fluid pump 40 is arranged in the downhole tool fluid pump section 200.

A downhole tool top connector section 240 is used for establishing connection to outer line, e.g. for a power link connection. Adjacent to the top connector section 240 a downhole tool electronics section 230 houses the downhole tool electronics, such as a pump control system.

The downhole tool electronics in the electronics section 230, by way of example, may perform at least one of the following tasks:

- Communicate with the surface through the power supply line

- accept signals/data from the surface

- transmit signals/data to the surface

- control the valves and the electric motor connected to the oil pump

- measure the inlet and outlet pressures as well as the down-hole pressure, based on this filter blockage can be detected, as well as obstructions in the inlet and outlet

- measure the E-motor power consumption as well as the E-motor temperature. The power, temperature (well bore and motor) in combination with the measured pressures as a function of time will indicate any problem related to the pump and the inflow performance of the well

- automatically control the fluid pump (6), using the valves, allowing back-flushing the filter (7) in case of blockage and or inlet pressure increase

- enable re-programming of the PLC from the surface to adjust to changing production/injection behavior.

A downhole tool reservoir section 220 provides shelter for the flexible action fluid reservoir 225 (see e.g. Fig. 13) .

Next to the fluid pump section 200 a downhole tool feed section 210 is arranged, where the action fluid is fed to the fluid pump 40 by means of the feed section 210. A filter section 250 houses at least one input filter for filtration of the pump fluid to be pumped by the fluid pump 40.

Inlet filters can be selected, such that no particles bigger than a such that no particles bigger than a

predefined size will pass the filter. In a flowing well there are always particles part of a well stream. Even when we use tap water to inject into a well there will be particles in that injection stream.

The particles could be pumped up into the annulus or pipe to the surface, but as soon as the pump would stop,

particles would sink to the bottom of the annulus or pipe, potentially blocking the annulus or pipe. So they need to be stopped by the filter. The filter however could be blocked by these particles and therewith reduce the pump efficiency or even stop the pump. In that case the pump can be reversed so that fluid is being pumped into the filter 'blowing' the particles away, which than will 'sink' to the bottom of the well. As a result the pump will be unblocked.

Fig. 13 shows a cross-sectional view of a downhole tool reservoir section 220, having an action fluid reservoir 225 being open to the surrounding well bore fluid 16, 17, 18 so that part of the well bore fluid 16, 17, 18 can enter the downhole tool reservoir section 220 and thus deliver the surrounding pressure level to the action fluid reservoir 225. The action fluid thus is - before the feed section 210 - in equilibrium pressure to the surrounding pressure level .

The function of the action fluid reservoir 225 is to get the well bore pressure transferred to the action fluid

(oil) required for the action fluid (oil) used to drive the pump .

Additionally, minimal oil losses in the oil driven piston of the down-hole pump cannot be prevented. The oil filled flexible chamber acts also as an oil reservoir compensating for eventual oil losses.

Fig. 14 shows a cross-sectional view of a downhole tool feed section 210, having an electro motor 212 driving an action fluid pump 216 via a gear section 214. The action fluid is fed via action fluid lines 102, 104 to either fluid pump section 41, 43, whereas the valve section 218 distributes the action fluid accordingly.

It will be appreciated that the features defined herein in accordance with any aspect of the present invention or in relation to any specific embodiment of the invention may be utilized, either alone or in combination with any other feature or aspect of the invention or embodiment. In particular, the present invention is intended to cover a fluid pump and/or a downhole tool configured to include any feature described herein. It will be generally appreciated that any feature disclosed herein may be an essential feature of the invention alone, even if disclosed in combination with other features, irrespective of whether disclosed in the description, the claims and/or the

drawings .

It will be further appreciated that the above-described embodiments of the invention have been set forth solely by way of example and illustration of the principles thereof and that further modifications and alterations may be made therein without thereby departing from the scope of the invention .

List of reference signs:

2 Well bore

4 earth formation

6 surface

8 reservoir

9 extraction facility

10 well head

12 casing/ liner

16 wellbore fluid

17 wellbore fluid, sideflow

18 fluid flow in the annulus

20 downhole tool

21 moving means

40 fluid pump

41 first chamber

42 pump housing

43 second chamber

44 constriction

45 cylinder

46 pump chamber

48 second pump chamber

50 double action piston assembly

52 first piston

53 first pump surface

54 piston rod

55 second pump surface

56 second piston

58 piston ring

59 hollow section

60 action chamber

61 first action surface

62 first action fluid channel 63 second action surface

64 second action fluid channel

66 second action chamber

70 fluid channel of the first fluid chamber (inlet)

72 fluid channel of the first fluid chamber (outlet )

74 fluid channel of the second fluid chamber (inlet)

76 fluid channel of the second fluid chamber (outlet)

78 longitudinal fluid pump axis

80 first cylinder head

81 second cylinder head

82 sensor activator (magnet)

84 fluid brake void

85 fluid brake nose

86 pump stroke sensor

92 power supply

93 valve

94 valve

96 valve

98 valve

102 action fluid line

104 action fluid line

200 downhole tool pump section

210 downhole tool pump feed section

212 electro motor

214 gear section

216 action fluid pump

218 valve section

220 downhole tool reservoir section

222 reservoir filter

225 flexible action fluid reservoir

227 reservoir connector

230 downhole tool electronics section downhole tool top connector section downhole tool filter section

Claims

What is claimed:

Fluid pump (40), for example being adapted to operate in a well bore (2), comprising:

^■ a pump housing (42) comprising a cylinder (45),

^■ the cylinder (45) having a first (41) and a second chamber (43) and

^■ a constriction (44) between the first (41) and the second chamber (43) ,

^■ a double action piston assembly (50) arranged

movably in the pump housing (42) for pumping fluid, the double action piston assembly (50) extending from the first chamber (41) through the constriction (44) into the second chamber (43) .

Fluid pump (40) according to the preceding claim, the double action piston assembly (50) comprising a first piston (52) arranged in the first chamber (41), a second piston (56) in the second chamber (43) and a piston rod (54) for directly connecting the first piston (52) with the second piston (56) .

Fluid pump (40) according to any of the preceding claims ,

wherein the double action piston assembly (50) is designed movable along the longitudinal extension direction (78) of the pump housing (42), so that the double action piston assembly (50) as a whole performs longitudinal movement.

Fluid pump (40) according to any of the preceding claims , the pump housing (42) further comprising a first cylinder head (80) and a second cylinder head (81), wherein the first cylinder head (80) is arranged at a first end of the cylinder (45) , and

wherein the second cylinder head (81) is arranged at a second end of the cylinder (45) opposing the first end .

Fluid pump (40) according to the preceding claim,

the first cylinder head (80) comprising a first fluid channel (70) for inflow and/or outflow of a pump fluid, the second cylinder head (81) comprising a second fluid channel (74) for inflow and/or outflow of the pump fluid.

Fluid pump (40) according to any of the preceding claims ,

wherein the double action piston assembly (50) is designed to perform, as a whole, a longitudinal

movement in the cylinder (45) when exposed to pressure.

Fluid pump (40) according to any of the preceding claims ,

the cylinder (45) further comprising an action fluid channel (62, 64) for providing action fluid into an action chamber (60),

wherein the action fluid provides a pressure force for acting from the inside of the double action piston assembly (50) on one side of the double action piston assembly (50), e.g. on the first piston (52).

8. Fluid pump (40) according to the preceding claim, wherein the action fluid channel (62, 64) is arranged between the first piston (52) and the constriction (44) and

wherein the action chamber (60) is arranged between the first piston (52) and the constriction (44) .

Fluid pump according to claim 7 or 8,

further comprising a second action fluid channel (64) arranged between the second piston (56) and the

constriction (44) for separately providing action fluid to a second action chamber (66) arranged between the second piston (56) and the constriction (44) .

Fluid pump (40) according to any of the preceding claims ,

wherein the action chamber (60) is designed such that, when action fluid is provided thereto through the action fluid channel (62), the action fluid of the action chamber (60) provides an action force on the first piston (52), and

wherein the first piston (52) is designed such, that in response to said action force the first piston (52) can perform a longitudinal movement towards the first cylinder head (80) .

Fluid pump (40) according to any of the preceding claims ,

wherein the second action chamber (66) is designed such that, when action fluid is provided thereto through the second action fluid channel (64), the action fluid of the second action chamber (66) provides an action force on the second piston (56) , and

wherein the second piston (56) is designed such, that in response to said action force the second piston (56) performs a longitudinal movement towards the second cylinder head (81) .

12. Fluid pump (40) according to any of the preceding

claims ,

wherein the first action fluid channel (62), the second action fluid channel (64) and the double action piston assembly (50) interact such, that action fluid is provided alternatingly to the action chamber (60) or the second action chamber (66) such that the double action piston assembly (50) performs an oscillating movement in the cylinder (45) .

. Fluid pump (40) according to one of the preceding

claims ,

wherein the action chamber (60) at least partly surrounds the piston rod (54) and/or

wherein the second action chamber (66) at least partly surrounds the piston rod (54) .

14. Fluid pump (40) according to one of the preceding

claims,

the double action piston assembly (50) comprising a first pump surface (53) in the first chamber (41) and a second pump surface (55) in the second chamber (43) , the respective pump surface (53, 55) being designed for being in contact with the pump fluid. Fluid pump (40) according to the preceding claim, the respective pump surface (53, 55) sealingly engaging with a circumference of the respective pump surface (53, 55) the inner surface of the cylinder (45) ,

the respective pump surface (53, 55) limiting a respective pump chamber (46, 48) in the first (41) and the second chamber (43) , and

the respective pump surface (53, 55) further limiting the respective action chamber (60, 66) in the first (41) and/or the second chamber (43) .

Fluid pump (40) according to one of the preceding claims ,

the first piston (52) comprising a first action surface (61), the fluid pump (40) being designed such, that the action fluid can act on the action surface (61) of the piston (52) thereby translationally moving the first piston (52) and such the double action piston assembly (50) towards the first cylinder head (80) and/or

the second piston (56) comprising a second action surface (63), the fluid pump (40) being designed such, that the action fluid can act on the action surface (63) of the second piston (56) thereby translationally moving the second piston (56) and such the double action piston assembly (50) towards the second cylinder head (81) .

Fluid pump (40) according to one of the preceding claims ,

further comprising a respective piston sealing member (58) arranged radially on the first (52) and/or second piston (56) for sealing the respective action chamber (60, 66) against the respective pump chamber (46, 48).

Fluid pump (40) according to one of the preceding claims ,

wherein the piston rod (54) is designed having an outer diameter equally or close to equal the inner diameter of said constriction (44) .

Fluid pump (40) according to one of the preceding claims ,

wherein the constriction (44) comprises a sliding support for the piston rod (54) or is designed as the sliding support for the piston rod (54) .

Fluid pump (40) according to one of the preceding claims ,

the fluid pump (40) further comprising an action fluid reservoir (225) and/or

the fluid pump (40) further comprising a feed unit (210) for providing the action fluid to the respective action chamber (60, 66) . 21. Fluid pump (40) according to the preceding claim,

wherein the feed unit (210) comprises a compressor unit and/or an action fluid pump (216) for providing a pressure level to the action fluid which is higher with respect to the pump fluid to be pumped by the fluid pump (40) .

22. Fluid pump (40) according to the preceding claim, wherein the pressure level provided by the feed unit (210) is adjustable. 23. Fluid pump (40) according to any of the claims 20, 21 or 22 ,

wherein the pressure level provided by the feed unit (210) to the action fluid is 10 bar or more higher than the pressure level of the pump fluid.

24. Fluid pump (40) according to any of the claims 20 to 23,

wherein the action fluid reservoir (225) comprises a flexible reservoir casing which is open to pressure level of the surrounding, so that the action fluid reservoir (225) is pressure compensated.

25. Fluid pump (40) according to any of the preceding

claims ,

further comprising an inlet filter (250) at the first and/or second pump fluid channel (70, 72, 74, 76) for filtration of the pump fluid.

26. Fluid pump (40) according to any of the preceding

claims,

further comprising a respective fluid brake nose (85) at the first and/or the second cylinder head (80, 81) .

27. Fluid pump (40) according to any of the preceding

claims,

further comprising a pump stroke sensor (86) .

28. Fluid pump (40) according to any of the preceding claims ,

wherein the first piston (52) and/or the second piston (56) and/or the piston rod (54) is made at least partly hollow (59) for reducing weight of the double action piston assembly (50).

29. Downhole tool (20), comprising a fluid pump (40) for pumping fluid to the surface and/or into the well, e.g. for pumping well bore fluid (16, 17, 18), wherein the fluid pump (40) is designed, for example, according to any of the preceding claims.

30. Downhole tool (20) according to the preceding claim, comprising a top connection (240) having an

electrical power connector.

31. Downhole tool (20) according to any of claims 29 to 30, the downhole tool further comprising a separated electronics section (230) for housing pump electronics.

32. Downhole tool (20) according to any of claims 29 to 31, the downhole tool (20) further comprising a separated reservoir section (220) for storage of the action fluid.

33. Downhole tool (20) according to the preceding claim, wherein the separated reservoir (225) comprises a flexible reservoir casing which is open to pressure level of the surrounding, so that the action fluid reservoir (225) comprises a variable size. Downhole tool (20) according to any of claims 29 to 33, the downhole tool (20) comprising an action fluid pump section (210),

the action fluid pump section (210) comprising an action fluid pump (216) for compressing and pumping the action fluid to the action chamber (60) and/or the second action chamber (66) .

Downhole tool (20) according to any of the claims 29 to 34,

further comprising an inlet filter section (250) flangeable to the fluid pump (40) .

Method for pumping a pump fluid, comprising the

following steps:

providing said pump fluid to a first pump chamber (46) of a fluid pump (40),

providing a pressure level to an action fluid, feeding said action fluid to an action chamber (60) in the fluid pump (40),

with the action fluid driving a double action piston assembly (50) to perform a movement to shrinken the volume of said pump chamber (46),

thereby raising the pressure level in the pump chamber (46) and driving out said pump fluid through a first pump fluid channel (70),

at the same time increasing volume of a second pump chamber (48) in the fluid pump (40) through movement of the double action piston assembly (50),

thereafter stopping feeding said action fluid to the action chamber (60) and feeding more action fluid to a second action chamber (66) in the fluid pump (40), with the action fluid driving a second piston (56) of said double action piston assembly (50) to perform a movement to shrinken the volume of the second pump chamber (48),

thereby raising the pressure level in the second pump chamber (48) and driving out said pump fluid from the second pump chamber (48) through a second pump fluid channel (74) . 37. Method for pumping fluid according to the preceding

claim,

wherein the pump chamber (46), the second pump chamber (48), the action chamber (60) and the second action chamber (66) are housed in a common cylinder (45), and

wherein the pump chamber (46) and the second pump chamber (48) share a common volume in the common cylinder (45) , so that, when the volume of the pump chamber (46) decreases by movement of the double action piston assembly (50), automatically the volume of the second pump chamber (48) increases and vice versa.

38. Method for pumping fluid according to the preceding

claim,

wherein the action chamber (60) and the second action chamber (66) share a common volume in the common cylinder (45) , so that, when the volume of the action chamber (60) decreases by movement of the double action piston assembly (50), automatically the volume of the second action chamber (66) increases and vice versa.

39. Method for pumping fluid according to any of claims 36 to 38,

wherein the action chamber (60) and the second action chamber (66) are separated by a constriction (44) .

40. Method for pumping fluid according to any of claims 36 to 39,

wherein the action fluid drives the double action piston assembly (50) by pressure,

wherein the pressure of the action fluid rests against a piston rod (54) of the double action piston assembly (50) on the one side, against a cylinder inner wall on a second side, against the constriction (44) on a third side and against an action surface (61) of a movable first cylinder (52) on a fourth side, to perform the movement to shrinken the volume of said pump chamber (46) .