The present invention concerns a fluid lifting system to be placed in a fluid production well comprising:

- a fluid pump having a pump rotor, a rotation of the pump rotor around a longitudinal rotation axis generating pumping of the fluid through the fluid pump;

- a gas turbine comprising a turbine rotor having blades and a turbine stator defining a gas expansion chamber with the turbine rotor,

- a gas injection duct, configured to receive a gas flow from an external gas source and to introduce the gas flow in the gas expansion chamber to drive the turbine rotor in rotation, the turbine rotor and the pump rotor being mechanically coupled such that the rotation of the turbine rotor produced by gas injection from the gas injection duct drives in rotation the pump rotor.

The fluid is for example a multiphase fluid comprising various phases including liquid and gaseous hydrocarbons and/or water. The multiphase fluid may comprise a gas content which varies along time, for example a gas content pressure which progressively decreases with time.

During production, a change of phase composition of the produced fluid, in particular a decrease of the gas content may lead in some instances to an increase of pressure of the fluid column at the bottom of the well.

Indeed, the liquids conveyed in the fluid column in the well have a higher weight contribution when the gas flow rate is smaller due to higher liquid hold-up in the fluid column.

The productivity of the installation can thus be significantly affected. In some instances, below a critical gas flow rate, the liquid cannot any more be lifted by the gas. It then continuously accumulates in the fluid column, until the production eventually stops by installation self-killing.

If such an accumulation of liquid in the fluid column occurs, a potential stop of production can be avoided by creating an artificial lift of the produced liquid. The artificial lift can be carried out through gas lift or/and through pumping. Such solutions increase the production costs.

Gas lift is usually carried out by injecting gas from the annulus to the production tubing via a gas lift orifice. The injection of gas into the fluid column lightens the fluid column and enhances its circulation towards the surface of the well.

Similarly, a fluid pump at the bottom of the well is able to pump fluid to the surface. As indicated above, these two solutions are able to provide lift, but increase production costs. In order to alleviate this problem, WO 2015/065574 discloses a fluid lifting system in which the gas injected for gas lift is injected in a gas turbine mounted in series with the pump. The expansion of the gas in the gas turbine drives a rotor of the pump in rotation, which pumps the liquid upwards. At the same time, the gas expanded in the turbine is injected in the liquid column above the fluid lifting system to lighten the fluid column.

Such a solution is not entirely satisfactory. Indeed, variations of the composition of the fluid lifted by the fluid lifting system may in some instances completely change the pumping regimes of the pump.

When the fluid becomes denser, the load applied to the pump substantially increases, due to the pumped fluid composition itself and also due to the weight of the column located above the pump and applying on the pump.

If the gas injected in the gas turbine is constant, the pump thus tends to slow down and the pumping decreases.

On the contrary, if a gas pocket passes through the pump, the resistance it offers to the pump is much smaller, and the gas pocket will subsequently lighten the gas column applying on the pump, further reducing the load applied on the pump.

For a given gas injection flow rate to the gas turbine, the pump thus tends to rotate faster.

A control the gas flow provided to the gas turbine is therefore necessary. WO 2015/065574 mentions controlling the gas flow, apparently by using surface gas injection control valves.

Controlling the gas flow from the traditional surface gas injection equipment is nevertheless a tedious task. Moreover, such a solution is not energetically efficient, because the adjustment of the surface gas flow usually generates an isenthalpic expansion, which leads to thermal losses.

One aim of the invention is thus to provide a fluid lifting system, which is able to adapt its pumping capabilities to the nature of the fluid which is pumped, even if the fluid undergoes unpredictable or/and drastic changes in phase composition.

To this aim, the subject matter of the invention is a fluid lifting system of the above mentioned type, characterized by a self-operated gas controller, to automatically control the gas flow injected in the gas expansion chamber, the self-operated gas controller having a gas control member whose position is adjustable in response to a parameter representative of the pump load, the self-operated gas controller being carried by the fluid lifting system.

The fluid lifting system according to the invention may comprise one or more of the following features, taken solely or according to any technical feasible combination: - the gas control member is movable with regards to a gas passage orifice connected to or within the gas injection duct, between a position of minimal or nil gas injection in the gas expansion chamber and a position of maximal gas injection in the gas expansion chamber, the gas control member being configured to move towards the position of maximal gas injection in response to an increased pump load, and to move towards the position of minimal or nil gas injection in response to a decreased pump load;

- the self-operated gas controller comprises a biasing member biasing the gas control member towards the position of maximal gas injection, the biasing member being directly connected to the gas control member or being connected to the gas control member through a link, advantageously a flexible link;

- the parameter representative of the pump load is a rotation speed of the pump rotor, the gas control member being configured to move towards the position of minimal or nil gas injection in response to an increase of the pump rotor rotation speed, the gas control member being configured to move towards the position of maximal gas injection in response to a decrease of the pump rotor rotation speed;

- the gas control member is jointly rotatable with the pump rotor, the movement of the gas control member being controlled by a centripetal force applying on the gas control member in response to a rotation speed of the pump rotor;

- the gas control member is movable in radial translation with regards to the pump rotor;

- the self-operated gas controller comprises at least an actuating coil, the gas control member being configured to move between the position of minimal or nil gas injection and the position of maximal gas injection under the effect of an electromagnetic field generated by the actuating coil, the intensity of the electromagnetic field being in response to the parameter representative of the pump load;

- the self-operated gas controller comprises a local current generator connected to the actuating coil the local current generator comprising at least a permanent magnet and at least a current generating coil rotatable with regards to the permanent magnet, one of the permanent magnet and of the current generating coil being jointly rotatable with the pump rotor;

- the parameter representative of the pump load is a pumped fluid pressure within the fluid pump, the gas control member being configured to move towards the position of minimal or nil gas injection in response to a decrease of the pumped fluid pressure, the gas control member being configured to move towards the position of maximal gas injection in response to an increase of the pumped fluid pressure; - the self-operated gas controller comprises a deformable pocket, placed in contact with the pumped fluid circulating in the fluid pump, the deformable pocket containing an actuating fluid actuating the gas control member to move the gas control member between the position of minimal or nil gas injection and the position of maximal gas injection;

- the turbine rotor is rotatable around the longitudinal rotation axis.

The invention also concerns a fluid production installation, comprising a fluid production well having:

- a production tubing inwardly defining an inner production canal and outwardly defining an outer annular space being connected to a gas source at the surface of the well, the production tubing delimiting a gas injection inlet extending between the outer annular space and the production canal,

- a fluid lifting system as defined above, the gas injection duct being connected to the gas injection inlet.

The invention also concerns a fluid lifting process, comprising the following steps:

- providing a fluid lifting system as defined above in a fluid production well;

- providing a gas flow from an external gas source to the gas injection duct, and introducing the gas flow in the gas expansion chamber to drive the turbine rotor in rotation around the longitudinal rotation axis,

- jointly driving the pump rotor with the turbine rotor to pump fluid through the intermediate fluid pumping space, the process comprising automatically controlling the gas flow injected in the gas expansion chamber with the self-operated gas controller, the gas control member adjusting its position in response to a parameter representative of the pump load.

The process according to the invention may comprise one or more of the following features, taken solely, or according to any technical feasible combination:

- the gas control member moves with regards to a gas passage orifice connected to or within the gas injection duct towards a position of maximal gas injection in the gas expansion chamber in response to an increased pump load, and moves towards a position of minimal or nil gas injection in the gas expansion chamber in response to a decreased pump load;

- the parameter representative of the pump load is a rotation speed of the pump rotor, the gas control member moving towards the position of minimal or nil gas injection in response to an increase of the pump rotor rotation speed, the gas control member moving towards the position of maximal gas injection in response to a decrease of the pump rotor rotation speed or wherein the parameter representative of the pump load is a pumped fluid pressure within the fluid pump, the gas control member moving towards the position of minimal or nil injection in response to a decrease of pumped fluid pressure, the gas control member moving towards the position of maximal gas injection in response to an increase of the pumped fluid pressure.

The invention will be better understood, based on the following description, given solely as an example, and made in reference to the appended drawings, in which:

- [Fig 1] Figure 1 is a schematic cross-section of the bottom part of a well equipped with a fluid lifting system according to the invention;

- [Fig 2] Figure 2 is a schematic functional view of the fluid lifting system according to the invention;

- [Fig 3] Figure 3 is a structural view of the fluid lifting system of figure 2.

- [Fig .4] Figure 4 is a schematic view of a first embodiment of the self-operated gas controller in the fluid lifting system according to the invention;

- [Fig.5] Figure 5 is a view similar to figure 4, of a second embodiment of the selfoperated gas controller;

- [Fig.6] Figure 6 is a view similar to figure 3 of a variant of fluid lifting system according to the invention;

- [Fig.7] Figure 7 is a view similar to figure 4 of another embodiment of the selfoperated gas controller of the fluid lifting system of figure 6;

- [Fig.8] Figure 8 is a view of a variant of a fluid lifting system according to the invention.

In the following description, the terms “upper”, “upwards”, “upwardly”, “uphole”, “lower”, “downwards”, “downwardly”, “downhole” are given relative to their orientation from the top of the installation to the bottom of the installation.

The terms “inward”, “inside”, “outward”, “outside” are given relative to a local central axis of the installation. The term “inside” generally means closer or oriented towards the central axis, whereas the term ’’outside” generally means further away or oriented away from the central axis.

A first fluid production installation 10 according to the invention is shown partially in figure 1.

The fluid production installation 10 comprises at least one well 12 bored in a subsoil 14, an outer casing 19, and a production tubing 18 inserted in the casing 19.

The fluid production installation 10 further comprises a downhole fluid lifting system 20 according to the invention. It comprises a surface gas source 22 connected to an annular space 24 between the casing 19 and the production tubing 18 to feed gas to the fluid lifting system 20 through the annular space 24.

In the region shown in figure 1 , the well 12 extends along a local central axis A-A’ which is here shown vertical. In a variant, the well 12 has inclined regions, and/or horizontal regions.

The well 12 extends from the surface of the subsoil 14 (not shown), which can be located on the ground or at the bottom of a body of water, to a lower formation including a fluid reservoir 28. As known in the art, the well 12 is closed by a wellhead (not shown) located at the top of the well 12.

The casing 19 lines the well 12. In this example, the casing 19 comprises an assembly of cylindrical metal strings, which are advantageously held in place with cement.

The casing 19 or an alternative lower liner (not shown) is in communication with the reservoir geological formation 28 containing hydrocarbons and/or water. Thus, a multiphase fluid stream, which can comprise hydrocarbons, is produced through perforations 27 emerging in the well 12, downhole of the lower end of the production tubing 18.

In this example, the reservoir geological formation 28 produces gas in particular, hydrocarbons such as methane. It also produces liquids, for example water and/or liquid hydrocarbons called oil or condensates.

The multiphase fluid stream produced from the reservoir 28 is under pressure, for example at a pressure greater than 10 bars. Preferentially, the liquid is dispersed in the gas in the form of droplets (“mist flow”), or at intervals in the form of liquid pockets, (“slug flow”). In variant, the gas is dispersed in the liquid, in the form of droplets or in the form of gas pockets.

The production tubing 18 is surrounded at its lower end with an annular outer packer 30, interposed between the casing 19 and the production tubing 18.

The packer 30 seals the annular space 24 at the bottom of the production tubing 18. Hence, the fluid produced from the reservoir 18 necessarily flows to the production tubing 18 without entering the annular space 24 uphole of the outer packer 30.

The production tubing 18 defines an internal production canal 32, which extends from the bottom of the production tubing 18, in the vicinity of the reservoir 28, to the wellhead at the surface. The annular space 24 is radially delimited towards the axis A-A' by the production tubing 18.

The production tubing 18 delimits at least a radial gas injection inlet 34 which extends through the production tubing 18 to connect the annular space 24 to the internal production canal 32. The gas injection inlet 34 allows feeding gas received from the gas source 22 through the annular space 24 to the fluid lifting system 20 located in the internal production canal 32, as will be described below.

As shown in figure 2, the fluid lifting system 20 is anchored in the production canal 32 at a longitudinal position facing the gas injection inlet 34.

The fluid lifting system 20 comprises a fluid pump 40, to pump the multiphase fluid flowing upwardly in the internal production canal 32, and a gas turbine 42 coaxially connected to the fluid pump 40, and driving the fluid pump 40 in rotation.

The fluid lifting system 20 further comprises an anchoring system 44 to longitudinally anchor the gas turbine 42 in the production tubing 18, and a sealing system 46 to guide the gas received from the gas injection inlet 34 exclusively to the gas turbine 42.

In the particular example of figures 2 and 3, the gas turbine is an outer gas turbine 42 and the fluid pump is an inner fluid pump 40 received in the outer gas turbine 42. The gas turbine 42 and the fluid pump 40 longitudinally overlap over the whole length of the outer gas turbine 42, in projection on the axis A-A’. In this example, the inner fluid pump 40 is totally received at the center of the outer gas turbine 42.

In a variant, which will be described below in view of figure 6, the gas turbine 42 is located downstream of the fluid pump 40, without longitudinal overlap between the fluid pump 40 and the gas turbine 42 in projection on the axis A-A’.

In reference to figure 3, the gas turbine 42 comprises, in a radial direction towards the axis A-A’, an outer turbine stator 50, fixed to the production tubing 18 via the anchoring system 44, and a turbine rotor 52 rotatably mounted into the turbine stator 50 about a rotation axis A-A’ which corresponds to the center longitudinal axis A-A’ of the production tubing 18.

The gas turbine 42 further comprises a gas injection duct 54, to feed the turbine rotor 52 with gas from the gas injection inlet 34.

The turbine stator 50 comprises a sleeve 56 defining an outer wall of the gas turbine. The sleeve 56 inwardly delimits, with the turbine rotor 52, a gas expansion chamber 58 receiving gas from the gas injection duct 54 to drive the turbine rotor 52 in rotation.

The turbine rotor 52 comprises for example a rotating hub 60, and rotating blades 62 protruding from the hub 60 towards the sleeve 56 in the expansion chamber 58. The expansion of gas received from the gas injection inlet 34 in the expansion chamber 58 acts on the rotating blades 62 to jointly drive the blades 62 and the hub 60 of the turbine rotor 52 in rotation around the axis A-A’ with regards to the turbine stator 50.

The pump 40 comprises a pump rotor 70, mechanically connected to the turbine rotor 52 to be driven in rotation by the turbine rotor 52, and a pump stator 72, here placed at the center of the pump rotor 70, to guide in rotation the pump rotor 70 about the axis A-A’. The pump rotor 70 comprises an impeller 74 having vanes protruding towards the pump stator 72 in the intermediate fluid pumping space 76 defined between the pump rotor 70 and the pump stator 72.

The intermediate fluid pumping space 76 opens downwardly and upwardly in the internal production canal 32 to allow intake of fluid from the internal production canal 32, downhole of the fluid lifting system 20, and ejection of pumped fluid uphole of the fluid lifting system 20, after having being pumped by the pump rotor 70.

The pump rotor 70 is mounted rotatable about the axis A-A’ with regards to the pump stator 72.

In the example shown in figure 3, the pump rotor 70 is directly mechanically connected to the turbine rotor 52, such that a rotation of the turbine rotor 52 at a given angular rotation speed around the axis A-A’ provides a joint rotation of the pump rotor 70 at the same angular rotation speed around the rotation axis A-A’.

In a variant, shown in dotted line in figure 3, a mechanical decoupler 68 is provided between the turbine rotor 52 and the pump rotor 70.

The mechanical decoupler 68 for example comprises a non-Newtonian fluid to adjust the decoupling based on the angular rotation speed of the pump rotor 70 as a function of the turbine rotor 52 speed. Alternatively, the mechanical decoupler 68 comprises an epicyclical gear, non-Newtonian fluid or a magnetic coupler having magnets. Preferentially, the mechanical decoupler 68 comprises at least a bearing 79 to maintain the turbine rotor 52 and the pump rotor 70 well centered and to support rotation.

Generally, the mechanical decoupler 68 allows the pump rotor 70 to be driven in rotation at a second given angular rotation speed, when the turbine rotor 52 is driven in rotation at a first given angular rotation speed. The second given angular rotation speed is for example greater or lower than the first given angular rotation speed. Advantageously, the mechanical decoupler 68 comprises a gearbox (not shown) able to modify the ratio of the second given angular speed to the first given angular speed.

In any case, the pump rotor 70 is driven in rotation around axis A-A’ exclusively by the turbine rotor 52, without provision of rotative drive by a hydraulic or electric motor.

In this example, the pump stator 72 extends in the middle of the pump rotor 70, along the axis A-A’. It comprises a cylindrical base, and arms (not shown) connecting to the turbine stator 50. The arms define between them through openings for fluid to flow through.

The anchoring system 44 comprises at least an anchor 80 protruding radially from the sleeve 56 of the turbine stator 50 to attach to the production tubing 18. The production tubing 18 preferably comprises a corresponding housing receiving the anchor 80. The anchor 80 radially spaces the turbine stator 50 from the production tubing 18 such that a peripheral space 82 is defined around the turbine stator 50, between the turbine stator 50 and the production tubing 18.

The sealing system 46 comprises at least an upper seal 84 to tightly close the peripheral space 82 in the uphole direction and at least a lower seal 86 to tightly close the peripheral space 82 in a downhole direction.

Hence, the peripheral space 82 exclusively communicates with the gas injection inlet 34 on the one side and with the gas injection duct 54 on the other side. Gas from the source flowing from the annular space 24 through the gas injection inlet 34 directly and exclusively flows to the expansion chamber 58 through the gas injection duct 54.

In a preferred embodiment, the hub 60 of the turbine rotor 52, the mechanical decoupler 68 if present and the pump rotor 70 define at least a radial gas through passage connecting the expansion chamber 58 to the intermediate fluid pumping space 76.

Preferably, the impeller 74 vanes define through longitudinal through holes 75, through which gas flowing from the radial passages is evacuated and mixed.

Thus, the gas expanded in the intermediate chamber 58 is evacuated through the radial through passages to the intermediate fluid pumping space 76 and mixes with the fluid pumped in the intermediate fluid pumping space 76. Further mixing and gas lift effect is advantageously provided by the gas passage through the holes 75 made in the vanes of the impeller 74. A jet pump effect occurs which increases the gas injection speed.

According to the invention, the downhole fluid lifting system 20 comprises a selfoperated gas controller 90, an example of which is shown on figure 4. The self-operated gas controller 90 is able to automatically control the gas flow provided to the expansion chamber 58 of the gas turbine 42 in response to at least a parameter dependent on the load applied on the fluid pump 40, in particular on the fluid pump rotor 70.

The load applied on the fluid pump 40 generally results from the phase composition of the fluid pumped in the fluid pump. The gas hold-up in the multiphase fluid advantageously affects the viscosity of the multiphase fluid having a direct effect on the applied load.

The load applied on the fluid pump is also dependent on the weight of the fluid column extending above the fluid lifting system 20, uphole of the fluid lifting system 20.

The at least one parameter dependent on the load applied on the pump is for example a rotation speed of the pump rotor 70. For a given gas injection rate in the gas expansion chamber 58 of the gas turbine 42, the rotation speed directly depends on the load applied to the fluid pump 40, as defined above. The pump rotor 70 therefore acts as a sensor of the load applied by the fluid pumped by the pump 40, its rotation speed being representative of such a load.

Preferentially, the self-operated gas controller 90 is configured to increase the amount of gas delivered from the gas injection duct 54 to the gas expansion chamber 58 in response to a decreasing rotation speed representative of an increase in load. It is configured to decrease the quantity of gas provided from the gas injection duct 54 to the gas expansion chamber 58, in response to an increasing rotation speed, representative of a decreasing load.

The gas controller 90 may be operating purely mechanically as in the example of figure 4, i.e. without active components powered to measure rotation speed and without electrically powered actuator to regulate the amount of gas delivered from the gas injection in response to the rotation speed. In a variant, the gas controller 90 may operate electronically, e.g. with an electronic sensor measuring rotation speed and an active electric or hydraulic actuator regulating the amount of gas delivered from the gas injection in response to the rotation speed.

In the example of figure 4, the self-operated gas controller 90 comprises at least a mobile gas control member 92, mounted mobile with regards to a gas passage orifice 93, through which gas flowing from the gas injection duct 54 flows towards the gas expansion chamber 58.

The gas passage orifice 93 may be located at a location fixed in rotation, or may be located at a location which jointly rotates with the pump rotor 70 and with the turbine rotor 52. In the example of figure 4, the gas passage orifice 93 is located at a location which rotates jointly with the pump rotor 70.

The gas control member 92 is movable with regards to the gas passage orifice 93, between a position of minimal or nil gas injection and a position of maximal gas injection.

The self-operated gas controller 90 moreover advantageously comprises a biasing member 94 configured to permanently bias the gas control member 92 towards the position of maximal gas injection.

The number of gas passage orifices 93 and of corresponding gas control members 92 is equal to one or greater than one.

When the gas passage orifices 93 are more than one, they are preferably angularly distributed around the axis A-A’, as well as the corresponding gas control members 92 and biasing members 94.

In the example of figure 4, each gas control member 92 is movable in radial translation between the position of minimal or nil gas injection and the position of maximal gas injection. In the position of maximal injection, the gas control member 92 is located closer to the axis A-A’ than in the position of minimal or nil gas injection.

In figure 4, each gas control member 92 is rotatable around the axis A-A’ jointly with the pump rotor 70 and the turbine rotor 52. It is therefore subjected to a centripetal force, which automatically induces a specific position of the gas control member 92 in response to a specific rotation speed of the pump rotor 70.

Hence, the gas control member 92 and the biasing member 94 are thus able to control the gas injection through the gas passage orifice 93, in direct response to the rotation speed of the pump rotor 70 and thus, in response to the load applied on the pump. This is done purely mechanically, without active components powered by a source of electrical energy.

The operation of the fluid lifting system 20 to enhance fluid production in the installation 10 will now be described.

In production, fluid from the reservoir 28 enters the well 12 and flows up in the production tubing 18, downhole of the fluid lifting system 20.

At the same time, gas from the gas source 22 is injected in the well annular space 24 and flows downhole to the gas injection inlet 34. The gas enters the peripheral space 82 around the turbine stator 50 and is confined longitudinally in the peripheral space 82 by the seals 84, 86 of the sealing system 46.

The gas thus flows to the gas injection duct 54, and enters the expansion chamber 58. In the expansion chamber 58, the gas expands and interacts with the blades 62 to drive the turbine rotor 52 in rotation around the rotation axis A-A’.

The rotation of the turbine rotor 52 jointly drives in rotation the pump rotor 70 around the pump stator 72.

Fluid flowing downhole of the fluid lifting system 20 thus enters the intermediate fluid pumping space 76 and is pumped uphole, to be ejected from the fluid lifting system 20 towards the surface.

Preferably, the gas which has expanded in the chamber 58 flows into the intermediate fluid pumping space 76 through the or each radial passage and mixes with the pumped fluid. A jet effect is advantageously generated, as the gas circulates into the through holes 75 made in the vanes of the impeller 74.

As mentioned above, each gas control member 92 rotates around the axis A-A’ jointly with the pump rotor 70 and the turbine rotor 52. It is therefore subjected to a centripetal force, which automatically induces a specific position of the gas control member 92, between the position of minimal or nil gas injection and the position of maximal injection, in response to a specific rotation speed of the pump rotor 70. The gas control member 92 and the biasing member 94 thus control the gas injection, in direct response to the rotation speed of the pump rotor 70 and thus, in response to the load applied on the pump.

In particular, when the load applied on the pump 40 increases, leading to a decrease in the rotation speed of the pump rotor 70, the centripetal force decreases, leading to a bias of the gas control member 92 towards the position of maximal injection by the biasing member 94. The gas flow rate injected in the expansion chamber 58 hence increases.

On the contrary, when the load applied on the pump 40 decreases, increasing the rotation speed of the pump rotor 70, the centripetal force increases, leading to movement of the gas control member 92 towards the position of minimal or nil gas injection against the bias of the biasing member 94. The gas flow rate injected in the expansion chamber 58 hence decreases.

A self-control of the gas flow injected in the gas expansion chamber 58 is thus obtained without needing active control means or a control signal from the surface. The control of the gas injection within the gas expansion chamber 58 is purely mechanical and is directly in response to the turbine rotor 52 and the pump rotor 70 rotation speed.

A variant of the downhole fluid lifting system 20 is illustrated in figure 5. In this variant, the gas control member 92 is moved between its position of maximal gas injection and its position of minimal or nil gas injection by an electromagnetic force whose intensity depends on the rotation speed of the pump rotor 70. Preferably, the gas control member 92 is fixed in rotation around the axis A-A’.

The self-operated gas controller 90 comprises for each gas control member 92, an actuating coil 96 actuating the gas control member 92, and a local current generator 98 to generate an electric current to power the actuating coil 96, the intensity of the electric current being in response to the rotation speed of the pump rotor 70.

The local generator 98 for example comprises a permanent magnet 100 borne by one of the pump stator 72 or of the pump rotor 70 and a current generating coil 102, borne by the other of the pump stator 72 and the pump rotor 70.

In the present case, the permanent magnet 100 is preferably borne by the pump stator 72, the current generating coil 102 being borne by the pump rotor 70.

The self-operated gas controller 90 further comprises an electric conduction path electrically connecting the current generating coil 102 to the actuating coil 96 associated to each gas control member 92.

Thus, in response to a given rotation speed, the relative rotation between the current generating coil 102 and the permanent magnet 100 leads to the generation of a current whose intensity depends on the rotation speed. The current is transmitted to the actuating coil 96 to generate an electromagnetic field whose intensity depends on the intensity of the generated current and thus of the rotation speed.

Depending on the intensity of the electromagnetic field, the position of the gas control member 92 adjusts between the position of maximal gas injection and the position of minimal or nil gas injection.

When the load applied to the pump rotor 70 increases, the rotation speed of the pump rotor 70 decreases, leading to a decrease of the intensity of the current generated in the current generating coil 102. This leads to a lesser intensity of the current transmitted to the actuating coil 96 and thus to an electromagnetic field of lesser value, moving the gas control member 92 towards the position of maximal injection under the bias of the biasing member 94.

On the contrary, if the load applied on the pump rotor 70 decreases, the rotation speed of the pump rotor 70 increases, leading to an increase of the intensity of the current generated in the current generating coil 102. This leads to a higher intensity of the current transmitted to the actuating coil 96 and thus to an electromagnetic field of greater value, moving the gas control member 92 towards the position of minimal or nil injection against the bias of the biasing member 94

Another example of a downhole fluid lifting system 20 according to the invention is shown in figure 6.

Contrary to the downhole fluid lifting system 20 of figure 3, the gas turbine 42 is arranged adjacent to the fluid pump 40.

In this example, the gas turbine 42 is located uphole of the fluid pump 40. The pump rotor 70, and the turbine rotor 52 are still coupled in rotation about the longitudinal axis A- A’. In this example, the turbine rotor 52 and the pump rotor 70 share a common shaft rotatable around the axis A-A’.

Contrary to the fluid lifting system 20 disclosed in figure 3, the pump stator 72 is located outside of the pump rotor 70 in a downhole extension of the turbine stator 50.

The intermediate fluid pumping space 76 emerges uphole, in an axial through passage 120 delimited in the turbine stator 50, outside of the sleeve 56. The axial through passage 120 preferentially has an annular shape.

The gas injection duct 54 crosses the axial through passage 120 to reach the gas expansion chamber 58 located inside the sleeve 56.

The turbine rotor blades 62 protrude radially away of the axis A-A’ from the turbine rotor 52 in the gas expansion chamber 58. Furthermore, in this example, the gas injection duct 94 comprises an axial region 122, emerging upwardly into the gas expansion chamber 58.

Advantageously, the gas expansion chamber 58 and the axial through passage 120 both emerge uphole in a mixing chamber 124 located downstream of the turbine stator 72.

In the particular embodiment of figure 7, the turbine rotor 52 also defines an internal gas derivation canal 126 which also emerges in the mixing chamber 124 without passing through the gas expansion chamber 58.

The gas passage orifice 93 is defined between the axial region 122 of the gas injection duct 54, and the internal gas derivation canal 126.

In this example, the gas control member 92 is mounted pivoting around an axis B-B’ perpendicular and apart from the rotation axis A-A’, between the position of maximal injection in the gas expansion chamber 58, in which the passage of gas through the internal gas derivation canal 126 is minimized or nil and the position of minimal or nil gas injection in the gas expansion chamber 58, in which the passage of gas through the internal gas derivation canal 126 is maximal.

The pivotal of the gas control member 92 is driven by the centripetal force applying on the gas control member 92 during its joint rotation with the turbine rotor 52 and with the pump rotor 70.

In this particular example, the self-operated gas controller 90 comprises a supporting rod 130 supporting the biasing member 94 and a flexible link 132 connecting the biasing member 94 to the gas control member 92.

The supporting rod 130 extends for example along the axis A-A’ in the gas derivation canal 126. It comprises an upper stop 134 on which an end of the biasing member 94 is fixed. A free end of the biasing member 94 is connected to the gas control member 92 via the link 132.

As shown in figure 7, when the rotation speed of the pump rotor 70 and of the turbine rotor 52 is minimal or nil, the biasing member 94 pulls on the flexible link 132 to maintain the gas control member 92 in its position of maximum gas injection in the gas expansion chamber 58.

When the rotation speed of the pump rotor 70 increases, in response to a lower load, the rotation speed of the turbine rotor 52 increases accordingly, and the gas control member 92 pivots away from the axis A-A’ under the effect of the centripetal force. This drives the gas control member 92 towards its position of minimum or nil gas injection in the gas expansion chamber 58. Part of the gas supplied to the gas injection duct 54 is lead to the internal derivation canal 126, without passing to the gas expansion chamber 58 through the axial region 122. Thus, the flow rate of gas injected in the gas expansion chamber 58 decreases.

The pivotal of the gas control member 92 pulls on the free end of the biasing member 94, extending the length of the biasing member 94 as shown in dotted lines.

On the contrary, when the load on the pump rotor 70 increases, the rotation speed of the pump rotor 70 decreases, leading to a lesser centripetal force on the gas control member 92.

The gas control member 92 is biased back towards its position of maximal injection by the return movement of the free end of the biasing member 94, transmitted via the flexible link 132.

In another variant, shown in figure 8, the gas control member 92 is located directly into a gas passage orifice 93 defined in the gas injection duct 54, upstream of the axial region 122.

In the position of minimal or nil gas injection, the gas control member 92 at least partially closes the gas injection duct 54. In the position of maximal gas injection, the gas control member 92 moves away from the gas injection duct 54, freeing the gas passage orifice 93.

In this example, the self-operated gas controller 90 comprises a hydraulic jack 140 having a cylindrical chamber 142, a plunger 144 received in the cylindrical chamber 142, and a stem 146, connecting the plunger 144 to the gas control member 92.

The biasing member 94 is interposed in a first region 147A of the chamber 142 on a side of the plunger 144 in contact with the stem 146.

The self-operated gas controller 90 further comprises a closed deformable pocket 150 containing an actuating fluid, communicating with a second region 147B of the chamber 142 delimited by another side of the plunger 144.

The closed deformable pocket 150 is inserted in the intermediate fluid pumping space 76 or downstream of it, in the axial through passage 120.

The closed deformable pocket 150 is sensitive to the pressure present in the intermediate fluid pumping space 76, which is representative of the load applied on the pump rotor 70.

Thus, when the load applied on the pump rotor 70 increases, due to an increase of the pressure applying on the pump rotor 70, the pressure also applies on the closed deformable pocket 150. The fluid contained in the closed deformable pocket 150 flows to the second region 147B of the internal chamber 142 to push the plunger 144 against the biasing force of the biasing member 94.

This moves the stem 146 and thereby the gas control member 92 towards its position of maximal gas injection.

The quantity of gas injected to the gas expansion chamber 58 through the gas injection duct 54 therefore increases.

On the contrary, when the load applied on the pump rotor 70 decreases, in particular due to a decrease of pressure in the intermediate fluid pumping space 76, the pressure applying on the closed deformable pocket 150 decreases. The biasing member 94 pushes the fluid present in the second region 147B of the chamber 142 towards the closed pocket 150.

This leads to moving the gas control member 92 towards the position of minimal or nil injection, via the stem 146.

The downhole fluid lifting systems 20 according to the invention are therefore able to self-operate downhole, without having to control the gas flow from the surface, and without providing a control signal or a control power to the fluid lifting system 20.

The control of the gas flow injected in the gas expansion chamber 58 is totally automatic and is directly in response to the load applied on the pump rotor 70, either based on the rotation speed of the pump rotor 70, or on the pressure present in the intermediate fluid pumping space 76 or downstream.

The control parameters can be easily adjusted by choosing appropriate dimensions and stiffness of the biasing member 94.

The fluid lifting system 20 according to the invention is therefore simple and very reliable to operate downhole, without having to pilot it from the surface.

Using the fluid lifting system 20 according to the invention thus increases the productivity of the fluid production installation 10 by adapting to produced fluids which have no constant phase composition, including sludge or bubble regimes.

Energy losses in the fluid production installation 10 are significantly decreased in comparison with traditional gas lift solutions, in which the gas is limited in flow rate into the gas lift valve at the bottom of the well and by the flow control valve at the head of the tubing.