The present invention relates to a downhole well pump assembly suited for pumping fluids within the well upwards through the well, string or tubing, towards the surface. Such pumps have been known for some time. However, challenges are still encountered as conditions in the well may be harsh and the costs associated with such pumps and their replacement or repair, are substantial.

Background

US patent application publication US2003042017 describes a submersible well pumping system which uses two diaphragm pumps. In this solution each of the two pump units have a pump chamber with walls constituted by a diaphragm, so that the volume within the pump chamber can be changed by supplying a hydraulic drive fluid with a reciprocating action. The reciprocating flow of drive fluid is controlled by a two state snap-acting valve, which in turn is controlled by a control valve which senses the differential pressure across the working diaphragm and generates a hydraulic signal to change the state of the two state snap acting valve.

Patent publication US3749526 discloses a pumping apparatus that comprises two tanks. Each tank is divided into two chambers by a bellows. Fluid is pumped by reciprocating the bellows in each tank.

US3524714 discloses a similar pump, which operates by reciprocating a bellows in a respective tank.

As the drive fluid is made to flow back and forth into a first and a second pump chamber, it is advantageous to avoid mechanical movements or rotations which change direction. Such change of direction may result in a loss of lubricating oil film on mechanical parts, and hence to increased wear of such parts.

Consequently, an object of the invention is to provide a downhole well pump, wherein its mechanical moving parts is not reciprocating, but are rather moved in a continuous, non-halting movement. This will contribute to maintaining the lubricating oil film on the mechanical parts, and thus enhance the lifetime of the pump. Another object of the invention is to enhance the lifetime of the pump units themselves, i.e. in addition to the drive fluid assembly which drives them. As mentioned above, conditions in a well bore may be harsh. For instance, the pump units may be exposed to acidic fluids, sand and wax and high temperatures, for instance in the area of 300° C.

The invention

According to a first aspect of the present invention, there is provided a downhole well pump assembly having a first pump unit and a second pump unit. Each pump unit has a compressible metal bellows arranged in a housing. The housing is connected to an inlet check valve and an outlet check valve. The assembly further has a drive fluid assembly with a first hydraulic drive line in

communication with the inner volume of the metal bellows of the first pump unit and a second hydraulic drive line in communication with the inner volume of the metal bellows of the second pump unit. The drive fluid assembly further comprises a drive fluid pump providing hydraulic fluid to the first and second hydraulic drive lines and which is mechanically connected to a drive motor that is powered through a power line. According to the first aspect of the present invention, a drive fluid distribution valve is arranged between the drive fluid pump and the first and second hydraulic drive lines. Moreover, the drive fluid

distribution valve has a drive fluid inlet, a drive fluid outlet, a first drive port and a second drive port. The drive fluid distribution valve is interchangeable between a first mode and a second mode. In the first mode the drive fluid inlet is in communication with the first drive port, and the drive fluid outlet is in

communication with the second drive port. In the second mode, the drive fluid inlet is in communication with the second drive port, and the drive fluid outlet is in communication with the first drive port.

The drive fluid pump and the drive motor can be arranged as one single component. The drive motor can be any appropriate type of motor, for instance an electric motor or a hydraulic motor, powered through an electric power line or a hydraulic power line, respectively. A gas/steam powered driver can also be used.

The drive fluid distribution valve is so configured, that it receives drive fluid through its drive fluid inlet, and distributes the drive fluid to either the first or the second drive port in an alternating fashion. Correspondingly, it exports drive fluid out through the drive fluid outlet, while receiving the drive fluid through either the first or the second drive port, also in an alternating fashion. Thus, the drive fluid distribution valve can receive the drive fluid through one single inlet, and export it through one single outlet, while alternating which drive port is guiding drive fluid to one of the pump units, and which drive port is receiving drive fluid from the other pump unit.

The drive fluid distribution valve can be in the form of a hydraulic sliding valve, where the position of the sliding valve body governs the mode (first or second mode) of the valve. This type of drive fluid distribution valve will need some sort of valve control means, such as electric actuation of the sliding valve body. As will appear in the following, however, advantageous embodiments may include another type of drive fluid distribution valve.

The housing of the pump unit(s) is advantageously cylindrical. Moreover, the first and second pump units, as well as the drive fluid assembly, are arranged in a row, thus forming a tubular shape. Such an arrangement of the downhole well pump assembly makes it suitable for being integrated or installed as a part of casing, liner, production/well tubing or in open hole. The downhole pump can be installed and operated using wire(line), umbilical, different pipes, coiled tubing, other tubing and in the open cavity of the well.

In an embodiment of the downhole well pump assembly according to the first aspect of the invention, the drive fluid pump has a rotating output which is functionally connected to the drive fluid distribution valve. In such an

embodiment, rotation of the rotating output will govern the changing of the drive fluid distribution valve between the first mode and the second mode. Advantageously, a reduction gear can be arranged functionally between the rotating output of the drive fluid pump, and the drive fluid distribution valve.

A bypass channel may be arranged between the first hydraulic drive line and the second hydraulic drive line. In some embodiments, the bypass channel can be integrated with the drive fluid distribution valve. In other embodiments, it may be arranged outside the drive fluid distribution valve, between the first and second hydraulic drive lines.

Moreover, the compressible bellows in the first and second pump units may comprise a collapse restriction means, wherein the collapse restriction means has a drive fluid valve member which is interchangeable between an open and a closed position.

When the drive fluid valve member is in the open position, drive fluid may flow out of the bellows. However, when the drive fluid valve member is in the closed position, it shuts off the fluid flow out from the bellows. Thus, when in the closed position, the drive fluid valve member restricts the bellows from collapsing further.

In embodiments including the collapse restriction means, the drive fluid valve member can be arranged at a drive fluid inlet and outlet end of the compressible bellows, and a bellows closure flange can be arranged at the opposite end of the compressible bellows. An actuation member, connected to the bellows closure flange, can then protrude axially into compressible bellows and be configured to abut and thereby move the drive fluid valve member into the closed position upon movement of the bellows closure flange towards the drive fluid inlet and outlet end.

In some embodiments of the downhole well pump assembly according to the invention, the drive fluid distribution valve comprises a housing, a first distribution chamber communicating with the drive fluid outlet, a second distribution chamber communicating with the drive fluid inlet, a first drive channel arranged between the first drive port and the first and second distribution chambers, and a second drive channel arranged between the second drive port and the first and second distribution chambers. The drive fluid distribution valve can further comprise a rotatable first distribution member which is arranged between the first distribution chamber and the first and second drive channels and which has a distribution aperture, and a rotatable second distribution member which is arranged between the second distribution chamber and the first and second drive channels, and which has a distribution aperture. Each distribution aperture of the first distribution member and the second distribution member is then adapted to align with both and opposite first and second drive channels, depending on the rotational position of the first and second distribution members.

Thus, in such embodiments, each of the first and second distribution members can be rotated so that they provide fluid communication between one of the distribution chambers and one of the first or second drive channels. The first and second distribution members are mutually arranged in such way that while one distribution member provides fluid communication between the first distribution chamber and one of the drive channels, the other distribution member provides fluid communication between the second distribution chamber and the other drive channel. Hence, the position of the first and second distribution members, and their respective distribution apertures, governs the mode of the assembly, i.e. the first and second mode. The first and second drive channels alternate between being a drive fluid delivery channel and a drive fluid return channel.

In some embodiments, the first and second distribution members can be connected to a common shaft. The shaft can be connected to a reduction gear. Moreover, the reduction gear can be connected to the rotating output.

In a preferred embodiment, the bypass channel is a part of the fluid distribution valve. However, in other embodiments, the bypass channel can be a separate component that connects the first and second hydraulic drive lines in an external position with respect to the drive fluid distribution valve.

According to a second aspect of the present invention, there is provided a fluid distribution valve comprising a housing, a drive fluid inlet, a drive fluid outlet, a first drive port and a second drive port. According to the second aspect of the invention, the fluid distribution valve comprises a first distribution chamber in fluid communication with the drive fluid outlet, a second distribution chamber in fluid communication with the drive fluid inlet, a first drive channel arranged between the first drive port and the first and second distribution chambers, and a second drive channel between the second drive port and the first and second distribution chambers. The fluid distribution valve further has a rotatable first distribution member which is arranged between the first distribution chamber and the first and second drive channels and which has a distribution aperture, as well as a rotatable second distribution member which is arranged between the second distribution chamber and the first and second drive channels, and which also has a distribution aperture. Each distribution aperture of the first distribution member and the second distribution member is adapted to align with both and opposite first and second drive channels, depending on the rotational position of the first and second distribution members.

As the skilled reader will appreciate, the fluid distribution valve according to the second aspect of the invention may very well be a part of the downhole well pump assembly according to the first aspect of the invention.

In an embodiment of the second aspect of the invention, the first and second distribution members are arranged on opposite sides of a partition wall comprising a first partition wall bore and a second partition wall bore which constitute part of the first and second drive channels. Moreover, the first and second distribution members are connected to a common shaft which extends through the partition wall. The shaft and the distribution members can rotate together / co-rotate.

The fluid distribution valve may comprises a main body within which the following are arranged:

- the first and second distribution chamber;

- the partition wall;

- the first and second drive channels;

- an output channel and a first distribution chamber mouth which connect the first distribution chamber to the drive fluid output; - an input channel and a second distribution chamber mouth which connect the second distribution chamber to the drive fluid input.

Moreover, the fluid distribution valve may comprise a bypass channel which connects the first drive port with the second drive port.

The bypass channel is advantageously a channel which only offers a low flow rate. I.e. it should be a narrow channel, or a channel having a narrow flow restriction. By means of the bypass channel, some drive fluid may flow into and out of the fluid distribution valve even if there is no flow through the first and second drive ports. When, however a large flow exists through the drive ports, there will be some flow also through the bypass channel, which then may be construed as a leak. However, by arranging a flow through the first and second drive ports which is significantly larger than the possible flow through the bypass channel, this leak through the bypass channel can be made substantially insignificant.

As will be apparent from the detailed description of embodiment below, the distribution member, employed either in the first or second aspect of the invention, may advantageously be disc shaped.

According to a third aspect of the invention, there is provided a collapsible metal bellows which has a cylindrical shape, which is axially collapsible, and which at one axial end has a drive fluid inlet and outlet end and which at the opposite axial end has a bellows closure flange. It further comprises a collapse restriction means which at the drive fluid inlet and outlet end comprises a drive fluid valve member movable between an open valve position and a closed valve position, and which is biased towards the open valve position. At the opposite axial end it comprises an actuation member which protrudes with an axial distance into the metal bellows, and which upon axial movement of the bellows closure flange towards the drive fluid inlet and outlet end is configured to abut against and move the drive fluid valve member towards the closed valve position. In such an embodiment, the drive fluid valve member may have a valve member opening that constitutes fluid communication between the interior and exterior of the metal bellows, wherein the valve member opening is partially closed when the fluid valve member is in an intermediate valve position.

Examples of embodiment

While the various aspects of the invention have been discussed in general terms above, a non-limiting example of embodiment will be discussed in the following with reference to the appending drawings, in which

Fig. 1 is a perspective view of a downhole pump assembly according to the invention;

Fig. 2 is a schematic diagram illustrating elements of the pump assembly;

Fig. 3 is a schematic illustration of a fluid distribution valve, here in form of a hydraulic slide valve;

Fig. 4 is a cross section view through a pumping section comprising two pump units;

Fig. 5 is a schematic diagram of the function of the pumping section;

Fig. 6 and Fig. 7 are cross section views of a pump unit, having an expanded and a collapsed metal bellows, respectively;

Fig. 8 is a cross section view of a drive fluid assembly;

Fig. 9 is a cross section, perspective view of a main end body which is

configured for connection to an axial end of the metal bellows;

Fig. 10 is a cross section side view through the components shown in Fig. 9;

Fig. 11 is a cross section view through a drive fluid valve member;

Fig. 12 another cross section, perspective view according to Fig. 9, however with the drive fluid valve member in a closed state;

Fig. 13 is a perspective view of a fluid distribution valve according to the second aspect of the invention;

Fig. 14 is a perspective, cross section view through the fluid distribution valve shown in Fig. 13;

Fig. 15 is a side cross section view of the fluid distribution valve;

Fig. 16 is a side cross section view of the fluid distribution valve along a different plane; Fig. 17 is a side view of the fluid distribution valve, with indication of the cross section view planes;

Fig. 18 is a separate perspective view of a distribution member in the form of a distribution disc;

Fig. 19 is a perspective view of two distribution discs mounted on a common shaft;

Fig. 20 is a side view of the two distribution discs and the shaft shown in Fig. 19; Fig. 21 is a cross section top view through the fluid distribution valve;

Fig. 22 is another cross section side view of the fluid distribution valve;

Fig. 23 is another cross section top view of the fluid distribution valve; and Fig. 24 is a schematic view of an alternative embodiment according to the

invention.

Fig. 1 is a perspective view showing an example of a downhole well pump assembly 1 according to the invention. The assembly has a pumping section 3, which contains two pump units, and a drive fluid assembly 5, which is configured to provide pressurized hydraulic drive fluid to the pumping section 3.

As can be appreciated from Fig. 1 , the downhole well pump assembly 1 has a tubular, elongated configuration. It is well suited for being integrated or installed in a casing, production tubing, or an open hole (not shown) (i.e. a well). This being said, one can also imagine the pump assembly being suspended on a wire or an umbilical.

Fig. 2 is a schematic representation of the various components of the pump assembly 1. The pumping section 3 has a first pump unit 7a and a second pump unit 7b, which in Fig. 2 are represented by bellows (which will be discussed below). First and second pump units 7a, 7b are connected to a hydraulic drive line, namely a first hydraulic drive line 9a or a second hydraulic drive line 9b, respectively. When in use, drive fluid is flown into and out of the pump units 7a, 7b (i.e. the bellows) through the hydraulic drive lines 9a, 9b.

The hydraulic drive lines 9a, 9b connect to a drive fluid distribution valve 11. In this embodiment, the drive fluid distribution valve is in the form of a continuous rotating distribution valve 11 (CRDV). The operation of the CRDV 11 will be thoroughly discussed further below. However, its function may be compared with the slide valve 211 depicted in Fig. 3. The CRDV 11 will, in the setup shown in Fig. 2, receive the hydraulic drive fluid through its inlet line 13, and the hydraulic drive fluid will exit through its outlet line 15. As illustrated with the sliding valve 211 in Fig. 3, it has two functional modes. In a first mode, the received drive fluid will be guided to the first hydraulic drive line 9a, while it receives drive fluid from the second hydraulic drive line 9b. In the second mode, it will guide the drive fluid to the second hydraulic drive line 9b, while receiving drive fluid from the first drive line 9a. As illustrated with the sliding valve in Fig. 3, the two modes are determined by the position of the sliding valve. With such a sliding valve 211 , the position (mode) of the valve body may typically be controlled with an electric control means 219, schematically illustrated in Fig. 3.

In the schematic illustration of Fig. 2, the inlet line 13 and the outlet line 15 both extend between the CRDV 11 and a drive fluid pump 17. The drive fluid pump 17 delivers pressurized hydraulic drive fluid to the inlet line 13. Delivered drive fluid is guided into one of the pump units 7a, 7b. Which of the two pump units 7a, 7b which receives the drive fluid, is governed by the current mode of the CRDV 11 (i.e. which one of the two possible modes). Drive fluid returning to the drive fluid pump 17, flows through the outlet line 15.

Notably, since the flow direction out from and into the drive fluid pump 17 never changes, the drive fluid pump 17 can run continuously without changing its direction. In this embodiment, the drive fluid pump 17 is a rotating positive displacement hydraulic pump.

In addition to the inlet line 13 and the outlet line 15, there is also a gear 19 arranged between the drive fluid pump 17 and the CRDV 11. The gear 19 connects to a (not shown) rotating part of the drive fluid pump 17. Also, it connects to a rotating part of the CRDV 11. The gear 19 governs changing of the modes of the CRDV 11. For instance, the CRDV 11 may change mode for every 50 ^th revolution in the drive fluid pump 17. Thus, the gear 19 does not transmit power used for pumping, but rather governs the mode of the CRDV 11 , and hence the flow direction within the two hydraulic drive lines 9a, 9b.

Functionally arranged between the two hydraulic drive lines 9a, 9b, there is also a bypass channel 21. The bypass channel 21 has only a small flow aperture and will substantially not affect the pumping during normal pumping speed. The function and object of the bypass channel 21 will be explained further below, together with discussion of the CRDV 11.

The drive fluid pump 17 is powered by a drive motor 23. The drive motor 23 can advantageously be a hydraulic motor powered by hydraulic fluid through a hydraulic power line 25. When in use downhole, the hydraulic power line 25 typically extends upwardly through the well bore, towards the surface. A hydraulic return line 27 is also arranged. Instead of a hydraulic drive motor 23, another type of motor could also be used for powering the drive fluid pump 17, such as an electric motor. For some embodiments, one could omit the return line 27, and dump the fluid delivered through the power line to the environment. For instance, if using a steam/gas turbine as a drive motor 23, one may be able to dump steam/gas into certain types of wells.

In this embodiment, the rotational connection between the drive motor 23 and the drive fluid pump 17 is a magnetic coupling 29. In this manner, one is able to separate the drive fluid pump 17 and the drive motor 23 in separate chambers. Flowever, it would also be possible to connect them with a rotating shaft extending between the drive fluid pump 17 and the drive motor 23.

The pumping section 3 and the drive fluid assembly 5 shown assembled together in Fig. 1 , are shown separately with cross section views in Fig. 4 and Fig. 8. The pumping section 3 has a first pump unit 7a and a second pump unit 7b. Each pump unit 7a, 7b has a metal bellows 31 arranged in a pump chamber 33. The pump chamber 33 is arranged within a pump housing 35. Moreover, the pump chamber 33 communicates with the outside of the pump housing 35 through an inlet check valve 37 and an outlet check valve 39. Each check valve 37, 39 have a closing member 41 which is adapted to move into and out of abutment with a valve seat 43. The closing member 41 is biased against the valve seat 43 with a check valve spring 45, and opens only upon a certain pressure drop over the valve 37, 39 (in one direction only).

Arranged in parallel with both pump units 7a, 7b are bypass channels 40. One bypass channel which is adjacent the first pump unit 7a, communicates with the inlet check valve of the second pump unit 7b. The other bypass channel 40, being adjacent the second pump unit 7b, communicates with the outlet check valve 39 of the first pump unit 7a (i.e. guiding pumped fluid exiting the first pump unit 7a).

The inlet and outlet check valves 37, 39 are arranged at opposite ends of the pump chamber 33 which in this embodiment has a cylindrical configuration.

Between the inlet check valve 37 and the outlet check valve 39, the bellows 31 is arranged. The bellows 31 is advantageously a metal bellows which may endure a large number of cycles before being worn out.

The function of the two pump units 7a, 7b shown in the pumping section 3 in Fig. 4 is illustrated with the schematic diagram in Fig. 5. Flere the check valves 37, 39 are illustrated with a ball being the closing member 41 , which close against the valve seat 43. It will be understood that by inflating and collapsing the bellows 31 , each pump unit will force out (pump out) the pumped fluid, and receive more fluid to be pumped, respectively. Indeed, in order to achieve the pumping function, only one pump unit 7a, 7b would suffice. In the shown embodiment, the downhole well pump assembly 1 has two pump units 7a, 7b. In other

embodiments, one could imagine three, four, or even more pump units in the same assembly.

Fig. 6 and Fig. 7 illustrate the pump unit 7a in more detail. In Fig. 6, the bellows 31 is in an expanded mode. In this position, it is ready to be collapsed. When collapsing, drive fluid within the bellows 31 is flown out from the bellows 31. The pumped fluid, such as hydrocarbon-containing fluid from a hydrocarbon reservoir, will then fill the pump chamber 33. That is, as the bellows 31 collapses, the pressure in the pumped fluid outside the pump housing 35 will open the inlet check valve 37, and thereby enter the pump chamber 33. The pumped fluid may flow through a not shown inlet opening in an end flange 47, in association with the valve seat 43. This continues until the bellows 31 has reached its collapsed mode. This collapsed mode is shown in Fig. 7.

Thus, when in the collapsed mode, shown in Fig. 7, the bellows 31 is ready to be filled with drive fluid, thereby moving it back towards the expanded mode. Drive fluid is flown into the bellows 31 with sufficient pressure to force the pumped fluid out through the outlet check valve 39.

Notably, there is some space between the outer portion of the bellows 31 and the inner face of the pump housing 33, through which the pumped fluid may flow.

Contrary to the pumped fluid, which enters and leaves the pump chamber 33 at different positions (different check valves 37, 39), the drive fluid enters and leaves the bellows 31 through the same drive fluid channel 49. The drive fluid channel 49 is connected to one of the hydraulic drive lines 9a, 9b schematically shown in Fig. 2.

Fig. 8 depicts a cross section view through the drive fluid assembly 5. Connected to the hydraulic power line 25 and the hydraulic return line 27 (cf. Fig. 2) is the drive motor 23. The drive motor 23 is driven by hydraulic fluid and rotates the drive fluid pump 17. In this embodiment, a magnetic coupling 29 connects the drive motor 23 to the drive fluid pump 17. Corresponding to the pump units 7a,

7b, the drive fluid assembly 5 also has a bypass channel 40, through which pumped fluid may flow. A rotating output 16 of the drive fluid pump 17 is connected to a reduction gear 19, which further connects to the continuous rotating distribution valve 11 (CRDV). The functional equipment of the drive fluid assembly 5 is mounted within a drive fluid assembly housing 30.

The drive motor 23, magnetic coupling 29, the reduction gear 19 and the drive fluid pump 17 can be conventional equipment and will need no further description herein, as such equipment is known to the skilled person. For many types of bellows, and in particular the metal bellows 31 of the type discussed in this embodiment, it is imperative that the pressure drop over the bellows walls is small. They are not designed to endure any significant pressure drops. Thus, the pressure of the drive fluid within the bellows 31 should be substantially the same as the pressure in the pumped fluid within the pump chamber 33, outside the bellows.

Also, such bellows, of the type shown in this embodiment, should not be totally collapsed. That is, the collapsing of the bellows should stop before reaching the maximum degree of collapsing. Prevention of such maximum collapsing increases the lifetime of such bellows.

These two requirements can be met by proper control of the drive fluid flow into and out of the bellows 31.

The disclosed pump units 7a, 7b are however, in addition to such proper control of the drive fluid (which will be discussed below), provided with a collapse restriction means 50.

For the discussion of the collapse restriction means 50, reference is now made to Fig. 9. In this perspective cross section view, the outlet check valve 39, as well as adjacent components, are shown. The drive fluid channel 49 (of. also Fig. 6 and Fig. 7) extends through a portion of a main end body 51. The main end body 51 is arranged in association with the outlet check valve 39, and is permanently fixed to one axial end of the bellows 31 (of. Fig. 6 and Fig. 7). As a part of the drive fluid channel 49, there is a drive fluid valve bore 53. At an end of the drive fluid valve bore 53, there is a drive fluid valve member 55 which is biased with a drive fluid valve spring 57 towards an open valve position. This open valve position is shown in Fig. 9.

The drive fluid valve member 55 is a substantially cup-shaped member having a collar 59 at its open end. The collar 59 is adapted to abut against an abutment shoulder 61 of a drive fluid valve disk 63, when in the open valve position (Fig. 9). When the collar 59 abuts against the abutment shoulder 61 , the drive fluid valve member 55 protrudes through a drive fluid valve aperture 65 in the drive fluid valve disk 63. When in this position, valve member openings 67 are positioned within the bellows 31 , so that drive fluid may flow into or out of the bellows 31 through the valve member openings 67. The valve member openings 67 are positioned in the wall of the drive fluid valve member 55. As a skilled person will appreciate, only one valve member opening would 67 suffice.

Reference is now made to the cross section view of Fig. 10, showing the same components as in Fig. 9. In the situation shown in Fig. 10, the drive fluid valve member 55 has been moved further into the drive fluid valve bore 53, thereby compressing the drive fluid valve spring 57. When in this position, which may be termed an intermediate valve position, only a portion of the valve member openings 67 are exposed against the inner compartment of the bellows 31 . As a result, the effective area of the valve member openings 67 is reduced, and the flow rate of drive fluid into or out from the bellows 31 is reduced.

In the shown embodiment, the valve member openings 67 have a tapered or triangular shape, wherein the narrower portion is the last portion being closed when the drive fluid valve closes, and the first portion being opened when the drive fluid valve opens.

Fig. 1 1 is a cross section showing only a portion of the main end body 51 . In the situation shown in Fig. 1 1 , the drive fluid valve member 55 has been moved all the way to the closed position. In this closed position, there is no communication between the valve member openings 67 and the interior of the bellows 31 .

Flence, no drive fluid can out from the bellows through the drive fluid channel 49. Fig. 12 depicts the same closed situation as in Fig. 1 1 with a perspective cross section view corresponding to Fig. 9. Notably, the drive fluid valve spring 57 has been collapsed within the drive fluid valve bore 53. Also, the closed end face 69 of the drive fluid valve member 55 is flush with the drive fluid valve disk 63. The outer circumferential face of the drive fluid valve member 55 seals against the radially inwardly facing surface of the drive fluid valve aperture 65. The manner in which the drive fluid valve member 55 is, or may be, moved down into or towards the closed position (Fig. 11 and Fig. 12), will now be discussed with reference to Fig. 6 and Fig. 7. The axial end of the bellows 31 which is opposite of the outlet check valve 39, is attached to a bellows closure flange 71. The bellows closure flange 71 is arranged opposite a drive fluid inlet end and outlet 72 of the bellows 31. The bellows closure flange 71 fulfils two main objects. First of all, it closes the axial end of the bellows 31. Also however, it is adapted to force the drive fluid valve member 55 towards and/or into the closed position (Fig. 11 and Fig. 12). The bellows closure flange 71 has an actuation member 73 which protrudes an axial distance into the bellows 31.

In the situation shown in Fig. 7, the bellows 31 has been collapsed to a correct collapsing position. Thus, the bellows 31 is not fully collapsed and could be further collapsed. Flowever, as discussed above, in order to enhance the lifetime of the bellows 31 , it is an object to avoid collapsing the bellows beyond a certain degree or beyond a certain level. For instance, it may be advantageous to only flow out 70 % of the volume which is contained in the bellows 31 when in the expanded position (Fig. 6).

Still referring to Fig. 7, if the bellows 31 would have been collapsed further, the actuation member 73 of the bellows closure flange 71 would abut against the drive fluid valve member 55, and move the drive fluid valve member 55 towards the closed position. As an effect of this movement, as discussed above, the effective area of the valve member openings 67 would decrease, and the collapsing rate would also decrease. If collapsing the bellows 31 even further, the actuation member 73 would move the drive fluid valve member 55 all the way to the closed position, thereby preventing further collapsing of the bellows 31.

In the shown embodiment, the actuation member 73 has the shape of a cup. In the expanded position, as shown in Fig. 6, the cup shape of the actuation member 73 accommodates a portion of the structure that supports the check valve spring 45 of the inlet check valve 37. Flowever, as will be understood by the person skilled in the art, the actuation member 73 may also exhibit other configurations which would be suited for abutting against the drive fluid valve member 55.

As a result of the collapse restriction means 50, it is not possible to collapse the bellows 31 beyond a predetermined degree of collapse. Such degree can easily be chosen by appropriate dimensioning of the actuation member 73 of the bellows closure flange 71 , and/or the drive fluid valve member 55. In practical use, it is however an object to control the flow of drive fluid in such manner that the collapse restriction means 50 does not come into use.

As discussed above, the collapse restriction means 50 will restrict the bellows 31 from collapsing excessively. When being used with the downhole well pump assembly 1 , as schematically depicted in Fig. 2, it will also restrict the bellows 31 from becoming excessively inflated. This is because the assembly 1 contains a given amount of drive fluid. Indeed, drive fluid inflated in one bellows 31 is delivered from a collapsing other bellows 31. Thus, when the bellows 31 which is collapsing is refrained from collapsing further, it cannot give out more drive fluid for inflating the other bellows 31.

In the shown embodiment (Fig. 9 to Fig. 12), the valve member opening 67 has a triangular shape, with a narrow portion being the last portion to closed off when the opening closes. Other shapes are however also possible, for instance a rectangular shape or a circular shape. Since the velocity, with which the drive fluid valve member 55 and thus the valve member opening 67 is closed, depends on the available flow-through aperture of the valve member opening 67, this velocity will decelerate when the drive fluid valve member 55 is moved towards the closed position.

In the following, the continuous rotating distribution valve 11 (CRDV) will be discussed. Fig. 13 depicts the CRDV 11 with a perspective view. The CRDV 11 has an input section 101 and an output section 103. At the input section 101 , the reduction gear 19 is arranged. The reduction gear 19 has a rotating output, as well as a rotating input which connects to a rotating output 16 of the drive fluid pump 17 (cf. Fig. 8). At the input section 101 are also arranged a drive fluid inlet 113 and a drive fluid outlet 115. When used with the embodiment discussed above (e.g. as shown in Fig. 1 to Fig. 8) the drive fluid inlet 113 and drive fluid outlet 115 are connected to the inlet line 13 and outlet line 15, respectively (of.

Fig. 2). At the output section 103, the CRDV 11 has two drive ports, namely a first drive port 109a and a second drive port 109b. When used in the above embodiment of the downhole well pump assembly 1 , the first and second drive ports 109a, 109b connect to the first and second hydraulic drive lines 9a, 9b, respectively (Fig. 2). Thus, the drive ports 109a, 109b are then functionally connected to the interior of the metal bellows 31. Moreover, the inlet line 13 from the drive fluid pump 17 will communicate with one of the metal bellows 31 , while the outlet line 15 of the drive fluid pump 17 will communicate with the other one of the metal bellows 31.

The reduction gear 19 may be of various types and will be chosen by the skilled person according to needs. As reduction gears are well known to the skilled person, its function will not be discussed herein. For simplicity, the reduction gear 19 is in the drawings merely shown as a single piece.

Fig. 14 is a perspective cross section view through the CRDV 11 , while Fig. 15 is a cross section side view through the CRDV 11. The CRDV 11 has a main body 105. The main body 105 has been manufactured from a solid metal cylinder.

From each axial end of the main body 105, a first distribution chamber 107 and a second distribution chamber 111 has been machined. Between the first and second distribution chambers 107, 111 , a partition wall 117 remains. Through the partition wall 117, a first and second axially directed partition wall bores 119a, 119b are drilled. The first and second partition wall bores 119a, 119b constitute part of respective first and second drive channels 121 a, 121 b. The first and second drive channels 121 a, 121 b lead to respective first and second drive ports 109a, 109b, and are able to connect the first and second distribution chambers 107, 111 to the drive ports 109a, 109b. When used with the pumping section 3, as discussed above, the first and second drive channels 121 a, 121 b thus lead to the metal bellows 31. As seen in Fig. 14 and in Fig. 15, arranged at the input section 101 , an input section flange 123 is attached to the main body 105. Correspondingly, an output section flange 125 is attached at the output section 103. The output and input section flanges 123, 125 close the first and second distribution chambers 107, 111 , respectively.

Referring now to Fig. 16, which is a cross section view through the CRDV 11 along the plane R-R indicated in Fig. 17. The first and second drive ports 109a, 109b are arranged in the output section flange 125. The drive ports 109a, 109b mate with axially extending drive channel bores 127 in the main body 105.

Moreover, between the outer face of the main body 105 and the partition wall bores 119a, 119b, there are drilled two cross bores 129. The respective cross bores 129 connect the respective partition wall bores 119a, 119b (cf. Fig. 14 and Fig. 15) and the drive channel bores 127. Thus, each of the first and second drive channels 121 a, 121 b, which extend between the first and second distribution chambers 107, 111 and the first and second drive ports 109a, 109b, comprises a first or second partition wall bore 119a, 119b, one drive channel bore 127, and one cross bore 129. The cross bores 129, which are drilled in a direction crosswise to the axial direction, are blinded off at the external face of the main body with a blinding arrangement 131.

It is still referred to Fig. 16, showing the two drive channel bores 127 that connect to the respective drive ports 109a, 109b. Through a part of the main body 105, a bypass channel bore 133 connects the two drive channel bores 127 and this the two drive ports 109a, 109b. Within the bypass channel bore 133 is the bypass channel 21 (cf. also the schematic illustration of Fig. 2). Advantageously, the bypass channel 21 can be constituted by a threaded piece which the operator can install according to desired flow through it. At the outer perimeter of the main body 105, the bypass channel bore 133 is blinded off with a bypass channel bore blinding arrangement 135 (also shown in Fig. 13).

Flence, the first and second drive ports 109a, 109b each communicates with a respective first or second partition wall bore 119a, 119b (cf. Fig. 15). In the situation shown in Fig. 15, the first drive port 109a communicates with the first distribution chamber 107. The second drive port 109b communicates with the second distribution chamber 111. Between both partition wall bores 119a, 119b and the first distribution chamber 107, there is arranged a first distribution member, here in the form of a first distribution disc 137. The first distribution disc 137 comprises a distribution aperture 139 extending through the first distribution disc 137. In the shown position (Fig. 15), the distribution aperture 139 of the first distribution disc 137 connects the first distribution chamber 137 to the first partition wall bore 119a. Moreover, the first distribution disc 137 closes communication between the first distribution chamber 107 and the second partition wall bore 119b.

Correspondingly, on the opposite side of the partition wall 117, a second distribution member, here in the form of a second distribution disc 141 , having also a distribution aperture 139, is arranged. The second distribution disc 141 is positioned in such way that it closes off communication between the second distribution chamber 111 and the first partition wall bore 119a. However, the second distribution chamber 111 communicates with the second partition wall bore 119b through the distribution aperture 139 of the second distribution disc 141.

Fig. 18 illustrates the first distribution disc 137 (which can be identical to the second distribution disc 141 ), separated from the CRDV 11. Centrally arranged in the first distribution disc 137 it has a central bore 143. The central bore 143 is arranged to receive a disc shaft 145 which extend through the partition wall 117. As can be seen in Fig. 14 and Fig. 15, both the first and the second distribution discs 137, 141 connects to the disc shaft 145. The disc shaft 145 connects to the gear 19, and hence rotates the first and second distribution discs 137, 141 when the drive fluid pump 17 is operated.

It will be appreciated by the skilled person, that the CRDV 11 also may be used in other applications than the one shown herein. In such applications, the disc shaft 145 may connect to and be rotated by other components. Advantageously, the first and second distribution discs 137, 141 connect to the disc shaft 145 with a spline connection. Thus, they may move somewhat in the axial direction, with respect to the disc shaft 145. Belleville springs 147 are arranged between respective distribution discs 137, 141 and input and output section flanges 123, 125, as illustrated in Fig. 14 and Fig. 15. A spring disc 149 is interposed between the Belleville spring 147 and the distribution disc 137, 141. The spring discs 149 transfers biasing force from the Belleville springs 147 onto the distribution discs 137, 141. In this way, the distribution discs 137, 141 are biased towards the partition wall 117.

Fig. 19 and Fig. 20 depict the first and second distribution discs 137, 141 arranged on the disc shaft 145. When in operation, these three components rotate together.

Fig. 21 is a cross section through the CRDV 11 along a plane perpendicular to its axial direction. In the position shown in Fig. 21 , the distribution aperture 139 of the first distribution disc 137 is partially aligned with the second partition wall bore 119b.

Referring again to Fig. 15, the first distribution chamber 107 communicates with the drive fluid outlet 115 via a first distribution chamber mouth 151. The first distribution chamber mouth 151 and the drive fluid outlet 115 are connected with an output channel 153 extending in an axial direction through a part of the main body 105. Similarly, in the second distribution chamber 111 there is a second distribution chamber mouth 155. The second distribution chamber mouth 155 communicates with the drive fluid inlet 113 via an input channel 157.

Corresponding to the output channel 153, the input channel 157 extends in an axial direction through a part of the main body 105. More precisely, it extends from the drive fluid inlet 113 to the second distribution chamber mouth 155.

The cross section of Fig. 21 depicts the output channel 153 and the input channel 157 within the main body 105. Also shown in Fig. 21 is the interface between the output channel 153 and the first distribution chamber mouth 151. Thus, in the embodiment discussed above, such as with reference to Fig. 2, the inlet line 13 communicates with the second distribution chamber 111. Moreover, the outlet line 15 communicates with the first distribution chamber 107.

Hence, when the first distribution disc 137 and the second distribution disc 141 are in the position shown in Fig. 15, drive fluid will be pumped (by the drive fluid pump 17) into the second distribution chamber 111 , and further through the distribution aperture 139 of the second distribution disc 141 , and into the second drive port 109b. Correspondingly, drive fluid will flow from the first drive port 109a and into the first distribution chamber 107, and out through the drive fluid outlet 115.

When the disc shaft 145, along with the first and second distribution discs 137, 141 rotates 180 degrees, the flow directions through the two drive ports 109 will have been changed. The pumped drive fluid will then be pumped out of the CRDV 11 through the first drive port 109a, while drive fluid will enter the CRDV 11 through the second drive port 109b.

The configuration of the distribution aperture 139 in the first distribution disc 137 and in the second distribution disc 141 , is preferably such that there always will be a some flow through the CRDV 11. That is, the first and second distribution discs 137, 141 are partly open simultaneously, when switching between the first and second modes.

Fig. 22 is a cross section view of the CRDV 11 , along the plane U-U indicated in Fig. 17.

Fig. 23 is another cross section view through the CRDV 11 , along the plane T-T in Fig. 17. In this view, the cross bores 129 are illustrated, extending in a direction crosswise to the axial direction.

As appears particularly from Fig. 21 and Fig. 23, the main body of the CRDV 11 has a cylindrical shape with a circular cross section. Moreover, the disc shaft 145 is arranged somewhat displaced with respect to the center axis of the main body 105. The first and second distribution chambers 101 , 111 are also eccentrically arranged within the main body 105. This makes space available within the main body 105 to accommodate the input channel 157, output channel 153, and the drive channel bores 127 (cf. Fig. 16).

Referring again to the schematic illustration of Fig. 2. The drive fluid pump 17 can be continuously run, pumping drive fluid from the outlet line 15 to the inlet line 13. As discussed, the direction of flow into and out from the drive fluid pump 17 is not changed. By means of the CRDV 11 , which was discussed above, drive fluid is pumped from a first pump unit 7a and into a second pump unit 7b a first mode, while from the second pump unit 7b and into the first pump unit 7a when in a second mode. Thus, there is no need for an additional reservoir of pump fluid, as the bellows 31 (pump units) function as pump fluid reservoirs for each other.

By knowing the pumped volume out from the drive fluid pump 17 per revolution of the drive fluid pump 17, one can make sure that a correct volume of drive fluid is pumped into and flown out from each pump unit 7a, 7b by appropriate use or design of the gear 19 and the CRDV 11.

As an example, a drive fluid volume of 5 liters shall be pumped into the first pump unit 7a. Then, 5 liters shall be flown out from the second pump unit 7b. If the drive fluid pump 17 feeds out 0,1 liters per revolution, the drive fluid pump 17 shall rotate 50 revolutions for filling the first pump unit 7a, and empty the second pump unit 7b. The gear 19 should then be a reduction gear, so designed that the disc shaft 145 (cf. Fig. 14 and Fig. 15) of the CRDV 11 will rotate 180 degrees as the drive fluid pump 17 rotates 50 rounds. Then, by further, continuous rotation of the disc shaft 145, the CRDV 11 changes mode (alters the direction of the drive fluid through the hydraulic drive lines 9a, 9b).

Notably, the repeated pumping into and out of the two bellows 31 or pump units 7a, 7b, is achieved without usage of electrical controls. The operator may simply pump hydraulic power fluid through the hydraulic power line 25 (Fig. 2). Before starting normal operation of the downhole well pump assembly 1 , the operator may not know if the position of the CRDV 11 is correct with respect to the filling level of the two bellows 31 (pump units 7a, 7b). If the drive unit pump 17 is started with normal speed while the two bellows 31 are not in the correct filling modes, the bellows 31 could be harmed. (A precaution means against excessive collapsing is however represented by the collapse restriction means 50 discussed above.) In order to avoid a situation where drive fluid is pumped into an already fully expanded bellows 31 , the operator may run the drive fluid pump 17 very slowly during a startup phase. Such slow running of the drive fluid pump 17 will ensure that drive fluid, instead of entering an already expanded bellows 31 (pump unit 7a, 7b), will flow through the bypass channel 21 (of. Fig. 2 and Fig.

16). Such a startup phase will protect the bellows 31 from excessive inflation and excessive deflation. By running the drive motor 23, the drive fluid pump 17, and thereby the CRDV 11 in this slow pace, in the startup phase, the position or mode of the CRDV 11 will be aligned with the mode (inflated or deflated / expanded or collapsed) of the bellows 31. Thereafter, the drive fluid pump 17 can be run with normal, i.e. quicker, speed in order to commence pumping of the fluid which shall be pumped by the downhole well pump assembly 1. When running the drive fluid pump 17 with the normal pumping speed, some drive fluid will escape through the bypass channel 21. Flowever, this amount can be made sufficiently small to ensure a sufficient efficiency of the downhole well pump assembly 1. Moreover, if - for some reason - the CRDV 11 should not balance the fluid amounts to the two bellows 31 , this will be adjusted by some flow through the bypass channel 21. For instance, if the CRDV 11 repeatedly delivers more drive fluid to the first pump unit 7a, and less to the second pump unit 7b, this will be compensated for by some flow through the bypass channel 21.

Fig. 24 depicts a schematic view of an alternative embodiment according to the invention. In this embodiment, the downhole well pump assembly 1 has four pump units 7a, 7b, 7b wherein two and two bellows (i.e. two pairs of bellows) are placed in a common pump cavity. The four pump units 7 may typically be arranged in a row, such as the two pump units shown in Fig. 1 and in Fig. 4. By including more pump units 7, the pumping volume per cycle can be increased. Some embodiments may include more than one pump assemblies according to the invention. I.e. one can for instance have two or more downhole well pump assemblies 1 (of. Fig. 1 ) arranged in series inside one well.