The present invention relates to the field of well maintenance, in particular water well maintenance but is applicable to any type of extraction well, when it is necessary to intervene in a borehole so as to ensure a minimum production volume or an increment of production.

Document US7360596B2 describes an apparatus and method to regenerate permeability of a well by use of pressure pulses. However, this method generates particulate matters which pollute the surrounding liguid, so that pumping/cleaning/filtering operations are necessary in any case and especially when used in a water well, and all these steps lead to increase costs and time of such maintenance. In addition, the pulse generator is not protected against rocks or debris which could fall onto the pulse generator during use.

Document US9057232B2 describes an apparatus and method to regenerate permeability of a well by use of pressure pulses, with the use of packers to isolate specific portions of the well screen to regenerate. However, this document does not propose any efficient solution to treat the pollution nor to protect the pulse generator from being damaged/blocked into the well.

Document US2006137872A1 discloses method and device for intensifying the permeability of ground layers close to bore holes and filter bodies and filter layers in wells and other production wells. Document US7681654B1 discloses methods for isolating well bore portions for fracturing and the like. Document EP0778393A2 discloses method and apparatus for maintaining the performance of a water well and for cleaning and regenerating existing wells by means of ultrasonic waves. Document US2003079876A1 discloses method and system for regeneration of a membrane used to separate fluids in a wellbore. The present invention aims to address the above-mentioned drawbacks of the prior art, and to propose first a well regenerating apparatus and method which provide efficient regeneration of a well, and which also provide protection to the pulse generator from being damaged/blocked into the well.

In this aim, a first aspect of the invention relates to a well regenerating apparatus comprising: a treatment device, arranged to regenerate a well screen in a treatment zone of the well screen, at least an upper packer and a lower packer arranged to isolate the treatment zone between the upper packer and the lower packer, characterized in that the well regenerating apparatus comprises a sliding sleeve, moveable between:

- a lifting position in which the sliding sleeve is connected to both the upper packer and the lower packer,

- a treatment position, in which the sliding sleeve is disconnected at least from one of the upper packer and the lower packer, so as to allow the treatment device to face directly the well screen.

The well regenerating apparatus according to the above embodiment comprises two packers which are expandable to isolate or confine a specific treatment zone of the well. Typically, the packers are introduced and lifted towards the treatment zone in a retracted state, and are expanded when located at the desired depth, to form a transverse partition so as to close the well cross section. In addition, the well regenerating apparatus comprises a sliding sleeve (typically a tubular part or hollow part) which is attached to the two packers during the lifting of the packers through the borehole up or down. In the present disclosure, the lower packer is the one intended to be located at the deepest position (the closest to the bottom of the well) and the upper packer is the one intended to be located at the highest position (the closest to the surface of the well). At this stage, the sliding sleeve is in the lifting position, and provides mechanical linking between the two packers. Once the packers are deployed to isolate the treatment zone, the sliding sleeve is at least partially removed from the treatment zone. In other words, the sliding sleeve is detached from at least one of the packers and moved at least partially away out of the treatment zone (typically via a sliding or translation movement). Consequently, the treatment device can directly access or face the well screen to perform an efficient treatment I regeneration of the well screen, while being protected in the treatment zone by the two packers from foreign debris or material coming from the rest of the well. In particular, in the treatment position, sliding sleeve is disconnected from lower packer, so that the treatment device may face directly the well screen.

Typically, when the sliding sleeve is in the treatment position, the two packers are still secured or linked by wires.

In other words:

- in the lifting position, the sliding sleeve is fully crossing the treatment zone so that efficient and robust link is provided between the two packers, but meanwhile the sliding sleeve constitutes in a given extent a “screen” or “shield” between the treatment device and at least a part of the well screen to treat,

- in the treatment position, the packers are attached or in close fitment with the well screen, so that the sliding sleeve in lifting position providing mechanical link is not necessary anymore and the sliding sleeve can be at least partially removed to be placed in the treatment position, thereby removing the above mentioned “screen” or “shield” between the treatment device and at least a part of the well screen to treat: the treatment device can directly face all the well screen to treat, so that the treatment will be fully effective. In the treatment position, there is no central tubing or central element linking the upper and lower packers. Solely cables or wires are present to link and secure the two packers together. According to an embodiment, the well regenerating apparatus comprises at least one connector arranged to be reversibly set in:

- a connecting state in which the connector provides an attachment between the sliding sleeve and at least the upper packer,

- a disconnecting state in which the connector releases the attachment between the sliding sleeve and the upper packer.

Such connector provides the capacity to repeatedly attach I detach the sliding sleeve and at least the upper packer as many times required to treat several treatment zones in the well.

According to an embodiment:

- in the connecting state, the connector blocks at least five degrees of freedom and preferably six degrees of freedom between the sliding sleeve and at least the upper packer,

- in the disconnecting state, the connector releases at least one degree of freedom between the sliding sleeve and at least the upper packer, so that the upper packer can provide a sliding joint to the sliding sleeve, and preferably a sliding pivot joint.

In other words, in the connecting state, there is no free relative rotation between sliding sleeve and at least the upper packer so that a movement of the sliding sleeve is fully transmitted to the upper packer, and in the disconnecting state, relative movement such as translation I rotation is authorized between sliding sleeve and upper packer.

According to an embodiment, the lower packer is engaged via a secondary connector with the sliding sleeve when the sliding sleeve is in the lifting position, and the lower packer is fully disengaged I separated from the sliding sleeve when the sliding sleeve is in the treatment position.

According to an embodiment, said connector comprises:

- at least one cam track provided on one of the upper packer or the sliding sleeve,

- at least one protrusion provided on the other of the upper packer or the sliding sleeve and arranged to travel along the cam track, and wherein the cam track comprises:

- a locking portion for receiving the protrusion, so as to attach the sliding sleeve to the upper packer,

- an open end portion for releasing the protrusion, so as to detach the sliding sleeve from the upper packer.

Such cam track provides a secured engagement, as it typically requires to the protrusion an axial movement to leave the locking portion, a rotational movement to reach the open end portion, and an axial movement to leave the open end portion. As an example, to get the connector into disconnecting state, lowering 50 mm sliding sleeve, plus 70 degrees to the right of rotation, plus 120 mm of vertical lift must be applied to allow fully rotation movement and vertical movement inside of treatment window.

According to an embodiment, the well regenerating apparatus comprises a tubing string arranged for linking the upper packer to a hoisting or lifting equipment located at surface, wherein the sliding sleeve is attached to the tubing string or is part of the tubing string so as to form a distal part of the tubing string. In other words, the sliding sleeve is the terminal part or deepest part of the tubing string, which facilitates to impart the movement of the sliding sleeve between the lifting position and the treatment position and vice versa: an equipment located at the surface of the well can easily be used to move the sliding sleeve by an action onto the tubing string. In the present disclosure, surface means the ground level, from where typically operators organize and control the maintenance, which is often an open air site.

According to an embodiment, the well regenerating apparatus comprises at least one air supply connector:

- connected to the sliding sleeve and/or to the tubing string,

- located above the upper packer so as to generate an air lift in the sliding sleeve and in the tubing string, at least when the sliding sleeve is in the treatment position. The use of the tubing string terminated by the sliding sleeve to drain the liquid in the treatment zone with air lift avoids any additional piping between the surface and the treatment zone. The tubing string, communicating with the sliding sleeve advantageously provides a direct channel to pump the liquid in the treatment zone, so that the limited amount of contaminated liquid can be easily and safely pumped up to the surface. This avoids to fully drain of filter the well. Preferably, the air supply connector is located on the tubing string, few meters above the sliding sleeve.

According to an embodiment, the well regenerating apparatus comprises at least one permanent link such as a metallic cable, attached to both the upper packer and the lower packer. Such metallic cable or wire provides a safety link which allows to remove the two packers, even if the sliding sleeve in the treatment position or tubing string is solely attached or linked to the upper packer.

According to an embodiment, the well regenerating apparatus comprises an inspection device, arranged to inspect the well screen in the treatment zone.

According to an embodiment, the well regenerating apparatus comprises a main lifting unit, arranged to move downwardly and/or upwardly and/or in rotation the sliding sleeve.

According to an embodiment, the well regenerating apparatus comprises a secondary lifting unit, arranged to move downwardly or upwardly the treatment device in the sliding sleeve. The channel provided by the sliding sleeve and tubing string allows to lift up or down the treatment device safely through the interior side of the tubing string I sliding sleeve: there is no risk of impact I blockage even if foreign material (rocks, damaged parts of the well casing or screen... ) fall from above the treatment zone, as the treatment device is supplied through the internal channel of the sliding sleeve and tubing string.

According to an embodiment, the secondary lifting unit is arranged to move downwardly or upwardly the inspection device in the sliding sleeve. There is no need to remove the full well regenerating apparatus: as the sliding sleeve is in the treatment position, the inspection device can easily inspect the well screen before/after treatment and via the internal space of tubing string and as clear water has (immediately) replaced the contaminated liquid.

According to an embodiment, the treatment device is arranged to generate any physical or chemical treatment to develop/treat the well.

According to a particular embodiment, the treatment device is arranged to generate impulse waves or shock waves or pressure waves in the treatment zone.

According to a particular embodiment, the treatment device is arranged to inject a treatment fluid into the treatment zone.

According to an embodiment, the upper packer and/or the lower packer are expandable or inflatable so as to be reversibly set in:

- a retracted state in which the upper packer and/or the lower packer are freely insertable into the well,

- an expanded state in which the upper packer and/or the lower packer are in contact with a well wall, such as the well screen.

According to an embodiment, the upper packer and/or the lower packer in the retracted state present an external dimension or diameter within ±30% and preferably ±20% of the external dimension or diameter of the tubing string.

According to an embodiment, the upper packer and/or the lower packer comprise a moving adaptor or sleeve arranged to compensate longitudinal shortening of rubber envelope during lateral expansion.

According to an embodiment, the well regenerating apparatus comprises a pressure control unit, arranged to control and adjust an inflating pressure of an inflation fluid fed to the upper packer and/or the lower packer, so as to set a maximum allowed difference of pressure between the treatment zone and the rest of the well, when the upper packer and/or the lower packer are in the expanded state. The packers are inflated at a given pressure to ensure isolation of the treatment zone, but when air lift is generated in the tubing string, it might be necessary to allow liquid income into the treatment zone to avoid collapsing of the well screen or casing. In this aim, the pressure in the packers is set so that above a given difference of pressure between the treatment zone and rest of the well, the packers will become leaky and will allow liquid to enter the treatment zone.

According to an additional or alternative embodiment, the well regenerating apparatus comprises a pressure control unit, arranged to control and adjust a contact pressure between the well wall and the upper packer and/or the lower packer, so as to set a maximum allowed difference of pressure between the treatment zone and the rest of the well, when the upper packer and/or the lower packer are in the expanded state.

According to an embodiment, the pressure control unit is arranged to be located at the surface, and a feed hose is provided between the pressure control unit and at least the upper packer.

According to an embodiment, the sliding sleeve is made of unitary pieces of tube, so as to provide a capacity of adjusting a height or length of the treatment zone. In other words, the unitary pieces of tube are provided with a given length (such as 1 m) and can be connected/disconnected before lifting in the well so as to define an adequate treatment zone, in relation to a preliminary inspection for example. In practice, the length of the window treatment is adjusted taking into account well characteristics and clogging situation. It can be defined from 1 m to whatever the distance is considered to proceed with the process.

Another aspect of the invention relates to a method for regenerating a well, comprising the steps of:

- introducing in the well at least an upper packer and a lower packer,

- isolating a treatment zone of a well screen between the upper packer and the lower packer,

- introducing in the well a treatment device arranged to regenerate a well screen in a treatment zone,

- moving a sliding sleeve between:

- a lifting position in which the sliding sleeve is connected to both the upper packer and the lower packer,

- a treatment position, in which the sliding sleeve is disconnected at least from one of the upper packer and the lower packer, so as to allow the treatment device to face directly the well screen, wherein the step of introducing and locating the treatment device in the treatment zone and the step of moving the sliding sleeve can be performed in any order. The packers are introduced into the well until they reach the treatment zone while the sliding sleeve is in the lifting position, providing robust and reliable mechanical link between the two packers. Once the packers are isolating the treatment zone, typically after expansion, the sliding sleeve can be partially removed out of the treatment zone to go in the treatment zone, so that the treatment device can be efficiently used in the treatment zone, free of the sliding sleeve. In particular, in the treatment position, sliding sleeve is disconnected from lower packer, so that the treatment device may face directly the well screen.

According to an embodiment, the treatment device is introduced and located in the treatment zone by a step of passing the treatment device through the sliding sleeve. This step of supplying the treatment device through the sliding sleeve provides full protection against collisions or blockages due to fallen rocks, debris around the sliding sleeve I tubing string.

According to an embodiment, the method for regenerating a well comprises, before the step of moving the sliding sleeve, a step of expanding the upper packer and/or the lower packer until contact of at least a portion of said upper packer and/or lower packer with a well wall, such as the well screen. According to an embodiment, the method for regenerating a well comprises a step of regenerating the well screen, by generating with the treatment device impulse waves or shock waves or pressure waves in the treatment zone, and/or any physical or chemical process to treat the well screen.

According to an embodiment, the method for regenerating a well comprises a step of inspecting the well screen in the treatment zone, by a step of passing an inspection device through the sliding sleeve.

According to an embodiment, the method for regenerating a well comprises a step of pumping liquid in the treatment zone, with a step of generating a pumping flow with an air lift created in a tubing string connected to the sliding sleeve, so that the pumping flow passes through the sliding sleeve.

According to an embodiment, the method for regenerating a well comprises a step to inject or pump additives and/or chemicals pumped from surface through air supply connector (and air-lift pipe) and sliding sleeve to increase the regeneration capacity of the process. So the flow through air supply connector (and air-lift pipe) may be from the well to the surface or to the treatment zone (aquifer formation) through the air-lift pipe and screen area. Flow may work in two ways in order to get maximum efficiency

According to an embodiment, the method for regenerating a well comprises a step of allowing a leaking flow to pass into the treatment zone from the rest of the well, by a step of adjusting a contact pressure between the well wall and the upper packer and/or the lower packer so as to set a maximum allowed difference of pressure between the treatment zone and the rest of the well.

According to an embodiment, the method for regenerating a well comprises a step of injecting chemical and/or additive substance into the treatment zone through the sliding sleeve. The additional chemical or additive can enhance the treatment process and is easily provided from the surface through the tubing string and sliding sleeve.

Other features and advantages of the present invention will appear more clearly from the following detailed description of particular non -limitative examples of the invention, illustrated by the appended drawings where:

- figure 1 represents a simplified sketch of a well partially filled of liquid, and comprising a well screen needing maintenance to be regenerated ;

- figure 2 represents the well of figure 1 , to show the installation of a well regenerating apparatus comprising two packers in a deflated state and being lifted down into the well ;

- figure 3 represents the well of figure 2, with the well regenerating apparatus with the packers located in a treatment zone, and being in an inflated state, a sliding sleeve being coupled to the two packers, in a lifting position ;

- figure 4 represents the well of figure 3, with the well regenerating apparatus having the sliding sleeve in a treatment position, lifted up compared to figure 3 ;

- figure 5 represents the well of figure 4, with a treatment device of the well regenerating apparatus positioned in the treatment zone between the two packers ;

- figure 6 represents the well of figure 5, during a step of treatment and/or pumping liquid from the treatment zone ;

- figure 7 represents a connector arranged to provide a removable or reversible attachment between the sliding sleeve and at least a packer, in particular an upper packer.

Figure 1 represents a well drilled in ground 10. Ground 10 is composed of layers 11 and 12, the layer 11 in this example being saturated with liquid L. Liquid L is typically water but the disclosure is not limited to water. The well comprises a well screen WS which is porous to allow liquid L to pass from the saturated zones 11 to the wellbore, for collection and pumping via a pumping tube PT and a pump P. Of course, figure 1 is very simplified, and the well might comprise cemented area, or gravel pack...

During production, sand, fine particles, mud or corrosion might generate clogged areas CA of the well screen WS and reduce its porosity (capacity to let the liquid pass through the well screen WS), so that production volumes are affected.

For this reason it might be required to regenerate the well screen (to remove and clean the foreign material accumulated in the well screen WS), and the present disclosure proposes an advantageous method and apparatus for regenerating the well screen WS of the well.

Typical methods to remove the foreign material which plugs or blocks the well screen WS are either mechanical treatments (with generation of pressure waves or shock wave or pulse waves or any other physical process) or chemical treatments (with injection in vicinity of the clogged area of a chemical substance (such as acid) arranged to remove or transform or dissolve the foreign material.

Figure 2 represents the well of figure 1 where the regular production equipment's (pump P and pumping tube PT) have been removed to facilitate the regeneration maintenance.

In this aim, a well regenerating apparatus is introduced in the well with a crane CA comprising a main lifting unit 61 and attached to a truck, and comprises notably:

- a tubing string 50 made of unitary tubing string tubes 51 ,

- an upper packer 31 ,

- a sliding sleeve 20 made of unitary sliding sleeve tubes 22,

- a lower packer 32.

The equipment is lifted down in the well by assembling progressively the unitary tubing string tubes 51 from the top portion of the tubing string 50 located at the surface, so as to position the upper packer 31 , sliding sleeve 20 and lower packer 32 at the level of the deepest clogged area CA, as shown figure 2.

The unitary tubing string tubes 51 can be screwed together, via threaded ends, to form the tubing string 50, and the unitary sliding sleeve tubes 22 can be screwed together as well, via threaded ends, to form the sliding sleeve 20, also screwed to the tubing string 50. Other assembly techniques are possible, such as fast interlock joints, spring locking joints...

Preliminary inspection (with a camera) can be made to determine the height of this deepest clogged area CA, so as to adjust, before introduction of the well regenerating apparatus into the well, the quantity of unitary sliding sleeve tubes 22, to make sure that the upper packer 31 is located a bit above the deepest clogged area CA and the lower packer 32 is located a bit below the deepest clogged area CA.

The upper packer 31 and lower packer 32 are expandable so as to be set in a deflated state as shown figure 2, and might be set in an inflated state as will be shown figure 3, 4, 5 and 6. Pneumatic or hydraulic packers, comprising rubber vessels can be typically used, but one can consider to use any other solution to expand I retract the upper packer 31 and lower packer 32.

While the tubing string 50 is lifted down in the wellbore, a packer hose

33 and an air lift hose 52 are deployed in the well, outside of the tubing string 50 and unitary tubing string tubes 51 .

The upper packer 31 and lower packer 32 are attached together via metallic cables 37 for securing the packers together, as shown figure 7, and a secondary hose 34 is joining the upper packer 31 and lower packer 32 for distributing inflating pressure I fluid to the lower packer 32. Secondary hose

34 might be directly connected to the packer hose 33, or via a pressure regulator to set specific pressure in lower packer 32. As an example, if the well casing ranges from approx. 205 mm to 305 mm (approx, from 8" to 12"), the internal diameter of the tubing string and/or the sliding sleeve might be approx. 80 mm (approx. 3").

As an example, if the well casing ranges from approx. 305 mm to 405 mm (approx, from 12" to 16"), the internal diameter of the tubing string and/or the sliding sleeve might be approx. 100 mm (approx. 4").

As an example, if the well casing ranges from approx. 405 mm to 505 mm (approx, from 16" to 20"), the internal diameter of the tubing string and/or the sliding sleeve might be approx. 120 mm (approx. 5").

The upper packer 31 and lower packer 32 can also be attached/detached to/from the sliding sleeve 20, and figure 7 shows an example of reversible connection between the parts.

The upper packer 31 is attached to the sliding sleeve via a connector 35 comprising:

- one cam track 35a provided on one of the upper packer 31 or the sliding sleeve 20,

- one protrusion 35b provided on the other of the upper packer 31 or the sliding sleeve 20 and arranged to travel along the cam track 35a, and wherein the cam track 35a comprises:

- a locking portion where the protrusion 35b is shown on figure 7, so as to attach the sliding sleeve 20 to the upper packer 31 (for vertical travel I lifting in the wellbore when the packers are in the retracted or deflated state)

- an open end portion (located on the left side on figure 7) for releasing the protrusion 35b, so as to detach the sliding sleeve 20 from the upper packer 31 , typically in the inflated state.

In a preferred embodiment, only the upper packer 31 is attached to the sliding sleeve 20 by a connector 35, no connector being provided at the lower packer 32 level. However, the lower packer 32 might be attached to the sliding sleeve 20 via another connector 36 comprising:

- one secondary cam track 36a provided on one of the lower packer 32 or the sliding sleeve 20,

- one secondary protrusion 36b provided on the other of the lower packer 32 or the sliding sleeve 20 and arranged to travel in the secondary cam track 36a, and wherein the secondary cam track 36a comprises an open end portion (located on the left side on figure 7) for releasing the secondary protrusion 36b, so as to detach the sliding sleeve 20 from the lower packer 32.

One should notice that in this configuration on figure 7, as the packers are attached to the sliding sleeve 20, the length of metallic cables 37 and secondary hose 34 is longer than the distance between the packers.

When tubing string 50 is fully deployed and lifted in the wellbore as shown figure 2, the packers might be expanded, as shown figure 3. At this stage, pressure is supplied to the upper packer 31 and lower packer 32 via the packer hose 33 to the upper packer 31 and secondary hose 34 to the lower packer 32.

As a consequence of pressure supply, the upper packer 31 and lower packer 32 expand (their outer diameter increases), until their outer surface contacts the well screen WS, as shown figure 3. At the end of the expansion step, the deepest clogged area CA is confined or isolated from the rest of the well. That is to say that liquid L located between the upper packer 31 and lower packer 32 cannot (or very little) flow above the upper packer 31 or below the lower packer 32.

As will be further explained in relation to figure 6, the upper packer 31 and lower packer 32 are inflated with a given pressure, which is determined in relation to the depth of the clogged area CA to treat (the height of the liquid column is a parameter to consider to determine the pressure of inflation of the packers, as will be explained in relation to figure 6). In summary, in the situation of figure 3, the well regenerating apparatus (the upper packer 31 , lower packer 32, sliding sleeve 20) is positioned in the wellbore in regards to the clogged area CA to treat, and the upper packer 31 , lower packer 32 isolate the liquid in this treatment zone and are mechanically linked together by the sliding sleeve 20.

Then, as the upper packer 31 and lower packer 32 are in the expanded or inflated state, in firm contact with the well screen WS, it is possible and proposed to remove at least partially the sliding sleeve 20 from the treatment zone.

This requires to disconnect the sliding sleeve 20 from the packers, and as shown by the arrows drafted at the level of the truck in figure 3:

- at a step A, the tubing string 50 and sliding sleeve 20 are lifted down or vertically translated for a small distance downward (so that protrusion 35b (embarked on sliding sleeve 20) of figure 7 travels to the horizontal and lower portion of cam track 35a),

- at a step B, the tubing string 50 and sliding sleeve 20 are rotated versus the packers (so that protrusion 35b and secondary protrusion 36b of figure 7 travel to be aligned respectively with the open end portion of cam track 35a and open end portion of secondary cam track 36a) so as to unlock the sliding sleeve 20 from the packers.

Figure 4 shows a step C of removal or upward movement of the sliding sleeve 20, with a upward arrow drafted at the level of the truck. Indeed, after step B of rotation, the protrusion 35b and secondary protrusion 36b are aligned with the open end portion of the cam tracks 35a, 36a, so that vertical translation or lift is possible so as to remove, as shown, the sliding sleeve 20 from the treatment zone defined between the packers. In other words the sliding sleeve has been moved from a lifting position (in which sliding sleeve 20 is located between the upper packer 31 and lower packer 32, see figure 2 and 3) to a treatment position (in which sliding sleeve 20 is partially of fully removed from the zone between the upper packer 31 and lower packer 32, see figure 4, 5 and 6).

Therefore, when the sliding sleeve 20 has been moved away from the lifting position to the treatment position, one can say that a window has been opened in the treatment zone.

As also shown figure 4, a treatment device 41 can be inserted inside the tubing string 50, and lifted down via a treatment line 42 and secondary lifting unit 62 attached to the crane CA. this operation can be realized before, in parallel or after the disconnection/movement of the sliding sleeve 20.

In summary, in the configuration of figure 4, the well regenerating apparatus, after steps A, B and C of figures 3 and 4, has been set in a configuration where the treatment zone is free of any central tube, as the sliding sleeve 20 is not anymore located between the upper packer 31 and lower packer 32. There is not anymore any central link or tube joining the two packers, which remain in position because of the pressure applied to the external membrane contacting the well screen WS.

Figure 5 shows the well regenerating apparatus operated to treat the well screen WS. Indeed, the secondary lifting unit 62 has lifted the treatment device 41 down to the treatment zone, i.e. between the upper packer 31 and lower packer 32, via treatment line 42, and the treatment device 41 can be controlled to treat the clogged area CA. The treatment will be efficient, as the treatment device 41 directly faces the well screen WS (there is no wall I no sliding sleeve 20 between the treatment device 41 and the well screen WS)

One should note that the treatment device 41 is travelling inside the tubing string 50 and sliding sleeve 20, so that it is fully protected during all travel in the wellbore. Even if debris or rocks or foreign material fall from the well wall, such obstacles will remain outside the internal channel (tubing string 50) and the treatment device 41 can be safely and reliably positioned in the treatment zone. In detail in this example, the treatment device 41 is a pulse generator supplied in energy via the treatment line 42 to generate pressure or shock or pulse waves in the liquid L, so that the particles, corrosion, fines, mud will be detached from the well screen WS. However, other treatment methods can be used, such as chemical treatments for example. One should note on figure 5 that the deepest clogged area has disappeared, and that liquid L in the treatment zone is now mixed with particles I foreign material.

After or during this step of treatment, another advantage provided by the well regenerating apparatus is that only the liquid located in the treatment zone is polluted by the material removed from the well screen. Also, it is proposed to pump only this polluted liquid so as to minimize the operating time and liquid to waste.

In this aim, as the treatment zone is in direct communication with internal channel of the tubing string 50 and sliding sleeve 20, an air lift can be advantageously generated in the tubing string 50 and sliding sleeve 20 with air supply provided by the air lift hose 52. As shown figure 6 an upward movement I pumping of liquid L located in the treatment zone is generated in the tubing string 50 and sliding sleeve 20.

Liquid L is easily supplied from the saturated layer 11 , as the well screen WS is now regenerated. However, if flow from the saturated layer 11 is not sufficient to compensate the air lift flow, liquid L can be supplied from the rest of the well. In this aim, it is proposed to accurately set the pressure in the upper packer 31 and/or in the lower packer 32 so as to allow leaks into the treatment zone. Indeed if the flow from the saturated layer 11 is not sufficient to compensate the air lift flow, pressure in liquid located in the treatment zone will be lower than the hydrostatic pressure in liquid located just above the upper packer 31 and/or than the hydrostatic pressure in liquid located just below the lower packer 32.

It is proposed to inflate the upper packer 31 and/or the lower packer 32 with a pressure not exceeding a maximum pressure being calculated to be a bit greater than the hydrostatic pressure of liquid located just above the upper packer 31 and/or of the liquid located just below the lower packer 32. In any case, the maximum pressure packer may be inflated is a function of rubber element manufacturer or type of packer used.

Maximum depression or maximum differential pressure between the treatment zone located between the packers in relation with the rest of the well might be a function of the following well characteristics:

Type of casing (pvc, steel, stainless steel, etc) ;

Type of screen area (louver, wired, bridge, drilled, slotted, etc) ;

Screen situation. Corrosion, aged, deformed, damaged, etc. ;

Grade of screen clogging ;

Flow of the well ;

And the differential pressure might be a function of the packer characteristics (rubber thickness, kind... ).

As a non limitative example, it is proposed to have :

Pup = Phi + ki, with

- Pup is the inflating pressure supplied to the upper packer 31 ,

- Phi is the hydrostatic pressure of liquid located just above the upper packer 31 (might be measured, or calculated as a function of the liquid column height and liquid density or weight),

- ki is the maximum allowable pressure difference, with for example:

2 bars < ki < 8 bars with for example a preferred value of 5 bars for a well casing of 205 mm, in PVC, when all pressures are in bars ;

5 bars < ki < 15 bars with for example a preferred value of 10 bars for a well casing of 305 mm, in steel, when all pressures are in bars.

As a non limitative example, it can be also proposed to have : Pip ⁼ Ph2 + k2, with

- Pip is the inflating pressure supplied to the lower packer 32, - Ph2 is the hydrostatic pressure of liquid located just below the lower packer 32 (might be measured, or calculated as a function of the liquid column height and liquid density or weight),

- k2 is the maximum allowable pressure difference, with for example: 2 bars < k2 8 bars with for example a preferred value of 5 bars for a well casing of 205 mm, in PVC, when all pressures are in bars ;

5 bars < k2 15 bars with for example a preferred value of 10 bars for a well casing of 305 mm, in steel, when all pressures are in bars.

As an alternative, it might be proposed to set the same inflating pressure in the two packers (and actual pressure inside packers will be slightly different, the difference being caused by the altitude difference and liquid column height).

This embodiment allows liquid L from the rest of the well to enter the treatment zone in case the saturated layer 11 cannot supply enough liquid to compensate the air lift pumping. In addition, this protects the well screen or well casing to be damaged/collapsed by a too high difference of pressure between outer part of casing and treatment zone.

The inflating pressure in the packers might be adjusted from the surface during the maintenance, with for example a pressure control unit operated by a user. Inflating pressure in packer is regulated from surface in a continuous mode and it may be modified according to obtained results.

As shown figure 6, the polluted liquid PL from the treatment zone is pumped to the surface via the tubing string 50 to be collected in a reservoir 71 , and a pumping device 72 can be used to assist this operation. This operation might be simultaneous to the treatment operated by the treatment device.

The treatment device 41 is still located in the treatment zone at this stage, but it might be independently lifted up if necessary. It is also possible to take advantage of the secondary lifting unit 62 to lift an inspection device (such as a camera) to check if the well screen WS in the treatment zone is in the expected state I shape, when the liquid L has be renewed and is clear enough for visual I camera inspection.

Once the deepest clogged area is treated, the well screen WS is regenerated and the well regenerating apparatus can be removed to treat another clogged area. In summary:

- the air lift is stopped, reservoir 71 is disconnected from the tubing string 50,

- the treatment device 41 and/or inspection device are removed from the tubing string 50,

- the sliding sleeve 20 is moved from the treatment position of figures 4, 5, 6 into the lifting position of figure 2, 3 (via the tubing string 50 and steps C, B, A),

- the packers are deflated so as to be set back in the deflated I retracted state,

- the tubing string and well regenerating apparatus are lifted up to the second clogged area CA, via the main lifting unit 61 (and by removing unitary tubing string tubes 51 ).

One should note the following:

- in case the coupling between the lower packer 32 and sliding sleeve 20 is difficult I impossible, the metallic wires 37 allow to still lift up the system,

- in case the coupling between the upper packer 31 and sliding sleeve 20 is difficult I impossible, or if the sliding sleeve is in the treatment position, one can implement a stopper (a stop collar or shoulder on the sliding sleeve for example) in the bottom part of the sliding sleeve to abut the upper packer 31 and still lift up the system,

- the quantity of unitary sliding sleeve tubes 22 can be adjusted between two treatments,

- a production test can be implemented via the air lift (or regular pumping equipment) to check the capacity of production volume of a given part of the well screen, after treatment and before moving back the sliding sleeve 20 in the lifting position. In summary, the well regenerating apparatus provides the below advantages:

- the height of the treatment zone is easily tunable before lifting all the system down into the well, with the unitary sliding sleeve tubes 22,

- the treatment device 41 faces directly the well screen WS to treat when the sliding sleeve 20 has been moved into the treatment position (out of the treatment zone),

- the treatment device 41 is safely and independently travelled from surface to the treatment zone via the internal channel of the tubing string 50 I sliding sleeve 20, and vice versa,

- the liquid L of the treatment zone contaminated during I after treatment is not spread into the rest of the well but is safely contained in the treatment zone thanks to the upper packer 31 and lower packer 32 inflated and in contact with the well screen,

- the liquid L of the treatment zone contaminated during I after treatment is safely and easily pumped to the surface via the air lift generated into tubing string 501 sliding sleeve 20,

- the well screen is protected from pressure damage even if the saturated layer 11 cannot supply liquid to compensate the air lift, thanks to the pressure management of the packers,

- the secondary lifting unit can easily lift the treatment device and/or an inspection device to fully treat the treatment zone.

It is of course understood that obvious improvements and/or modifications for one skilled in the art may be implemented, still being under the scope of the invention.