US20160053569A1

US20160053569A1 - Retrievable packer for operations in cased wells at high pressures

Info

Publication number: US20160053569A1
Application number: US14/689,514
Authority: US
Inventors: Gustavo Ignacio Carro
Original assignee: TACKER Srl
Current assignee: TACKER Srl
Priority date: 2014-08-20
Filing date: 2015-04-17
Publication date: 2016-02-25
Also published as: AR097407A1; MX2015003493A; CA2887968A1; CO7180035A1

Abstract

Retrievable packer for operations in wells cased by means of a casing pipe, the packer being applied in operations involving very high pressures, of up to about 15,000 psi, wherein the packer comprises a connecting head for being fixed to a service pipe, an upper mandrel threaded at a lower mandrel, a balancing liner holder concentrically arranged on the upper mandrel so as to form a space of hydraulic pressure between both, within which space one balancing liner is accommodated, designed to apply a downward force on an annular ledge of the upper mandrel, to offset upwards thrust forces that operate on the tool and the service pipe.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
This invention relates to a Packer, also known as gasket or “Packer” retrievable and usable in operations in wells, which is part of tools used in cased wells, such as oil, gas or water wells. More specifically, the invention primarily refers to a Packer, gasket or well packer, preferably for operations at high pressures, i.e. at pressures above 10,000 psi, which can be used with conventional tubing and/or coiled tubing alone or together with a retrievable plug.
2. Description of the Prior Art
Devices like that of the invention, well known in the art with the popular name “Packer”, are devices or tools currently used as retrievable sealing or packing elements and which are used in wells where it is required to perform works which should be restricted to one or more distinct areas, such as Operations of Acid Stimulation or Fracturing (“fracking”), Case-hardenings, Pressure Testing, etc. These known retrievable Packers (Packers or Gaskets), even when operated satisfactorily in most applications, have limitations when pressures involved in the service, such as case-hardening, fracking, etc., exceed values considered high, e.g. between 11,000 and 15,000 Psi. In such cases, the packer runs the risk of not remaining fixed in the workplace, with a high possibility of being detached, thus putting the entire system operation at risk.
A packer of this type, known and belonging to the applicant of this invention, is that one disclosed in U.S. Pat. No. 7,708,062 and which comprises a retrievable packer for operations in cased wells by means of a pipe or “casing”, such as oil, water, gas and similar fluids wells, where the packer is of the type used to temporarily or permanently seal the well by means of sealing cups which seal against said pipe, having the packer a set of piston holders for fixing within the pipe, and further comprising a continuous mandrel on which a valve body is placed which in turn carries mounted thereon at least one of said sealing cups, said valve body being mounted axially slidebly on the mandrel, between a closed position against a seal on the mandrel and an open position spaced from said seal, and being defined between said valve body and said mandrel a fluid flow passage sealable at said closed position of the valve body.
The packer of U.S. Pat. No. 7,708,062 always operates efficiently within pressure ranges that are below about 10,000 psi. Above this threshold the pistons can escape from the set of piston holders, being these pistons the ones that keep fixed and fastened the packer against casing under working pressures that push packer up within casing.
To understand this effect, it should be known that treatment services such as case-hardening, fracking, etc., are carried out by injecting a fluid at very high pressures within a pipe, known as “tubing”, which is inserted inside the cased well. At the lower end of this service pipe a packer is arranged, the packer operating to close and seal the annular space formed between the service pipe and the casing. Once the service pipe is lowered to the section of the well to be treated, the packer is triggered thus closing the above-mentioned annular space. Thus, the service pipe can inject service fluid to the section of the well which is only below the packer that seals the cased well in order to isolate the part of the casing above the packer from the part of the casing below the packer. One skilled in the art knows that this pressure below the packer will push up the packer and pipe together so the packer should have suitable fixing means to prevent the pipe from being thrown upwards. When the service or treatment involves very high pressures, this function becomes essential and is not satisfied by known packers in the art.
There are other types of packer, e.g. strain packers which work with an automatic anchoring arrangement by means of a guide generally simply called in the art as automatic cycling “J” guide or simply “J”, through which actuation pipe rises causing a plurality of clamps to expand over a cone so that, along with a drag block, they become an integral part with the friction pipe. Although this system could better resist upward thrusts, the drawback is that it is required to strain the coiled tubing to fix and pack the tool, limiting the ability of the pipe in terms of pressures of treatment or limiting tensile safety joints. When the pressure operation occurs inside the pipe, there occurs a shortening due to the expansion of the pipe, thus adding tension to the tool and reducing the service life due to fatigue. Furthermore, due to its construction, it does not allow packing tasks together with other tasks such as tool washing for removing sand and dirt before subsequent operations.
It is also known the so-called cup packer which comprises a piston holder and cup packing elements and plugs. This type of packer has the limitation that it can not move fluids by direct pathway before treatment, since the first reaction of this tool is to seal by pressure differential because cups are in constant contact with the pipe. To overcome this drawback an additional passage valve has to be added which has the disadvantage that more threads are added to the series and the valve is deficient when performing treatments with sand, in fracking operations, because it is contaminated with sand and locked thus preventing subsequent operations.
By virtue of the foregoing, it would be desirable to have a new well packer that may have advantages in terms of simplicity for tasks of washing, injecting fluid by direct pathway, etc. and withstand high pressures, for example above 11,000 psi.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide a new packer capable of solving the above drawbacks, being a packer or gasket which combines in a novel manner elements of support, fixation and sealing as well as valve and pressure equalization elements between the annular pathway, namely the ring space or annular gap, and the direct pathway, namely the path inside the tubing, also called simply “direct”, a novel result that has to do with greater securing reliability, simplicity in the sealing operation, washing effectiveness and operational automaticity.
It is still another object of this invention, to provide a well packer, which can be used alone or in conjunction with a blanking plug of the type known in the art, being a packer that works by hydraulic anchoring without requiring strains or weights, wherein the tool or packer is anchored to the pipe, being able to leave the pipe neutral, with weight or strain interchangeably to perform the pressing operations, thus relieving strains on the pipe.
It is another object of this invention to provide a well packer that may make it possible to fix, anchor and release the tool several times, with the possibility of releasing the packer and subsequently cleaning it in the case of premature or non-required sanding without any inconvenient since it is enough to stop pressure through the pipe and pump through the annular gap so that clean fluid can pass behind the packer and clean from the bottom tip thereof towards direct pathway. Thus a cleaning operation is effectively carried out and then the pistons go back to their housings, so that the packer is ready to perform another operation or is ready to be installed in another section of the casing.
It is further another object of this invention to provide a retrievable well packer which does not require strain to be fixed, which works hydraulically, with internal pressure and a set of seal which contact a lip of a set of balancing sleeves reinforcing the load on an upper mandrel in order to keep the whole set fixed on a reliable basis against the casing pipe despite high pressures applied between a lower section of the well, below the section sealed by the packer, and an upper section of the well, above the packer.
It is yet another object of this invention to provide a retrievable well packer that may allow fluid displacement by direct pathway, i.e. inside the pipe that carries it, to make movements of components and their fixings, wherein it has a set of integral upper mandrel and a lower mandrel that allow and facilitate the washing operation of the tool, for instance sand washing, direct circulation, reverse circulation, cement wash, etc. which is performed from the bottom, and in the event that the packer may be used in conjunction with a retrievable plug, it allows circulation through an inner “fishing” tool thus allowing full cleaning of the tool.
It is another object of this invention to provide a retrievable packer for operations in wells encased by means of a casing pipe, where the packer is one of the type employed to temporarily or permanently seal the annular space between the casing pipe of the well and a service pipe which is inserted into the casing for operations of treatment of one or more sections of the cased well, the packer comprising:
a head for connection to the service pipe,
an upper mandrel,
a lower mandrel threaded to the upper mandrel,
pistons and clamps for fixing the packer against the casing pipe, arranged to resist the upward and downward forces, respectively,
a set of rubber gaskets to seal said annular space,
a balancing sleeve holder concentrically arranged one such upper mandrel whereby a hydraulic pressure space is defined between the balancing sleeve holder and the upper mandrel,
at least one balancing sleeve arranged in said hydraulic pressure space,
an annular ledge of the upper mandrel, aligned with and arranged below said at least one balancing sleeve, and wherein said pistons and clamps respectively comprise a piston holder body and a set of clamps.
The above and other objects, features and advantages of this invention will be better understood when taken in connection with the accompanying drawings and description.

BRIEF DESCRIPTION OF DRAWINGS

The present invention is illustrated by way of example in the following drawings wherein:

FIGS. 1A to 1C show a vertical semi-section profile view of a preferred embodiment of the packer of this invention as a way of example;

FIG. 2 is a cross section along section line A-A indicated in FIG. 1A, and

FIG. 3 is a schematic view of a “J” guide, being released in the clockwise rotation, which can be used in the packer of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now referring in detail to the invention, the same refers to a retrievable packer or gasket, as illustrated in FIGS. 1A to 1C, 2 and 3, being a tool employed, for example, to seal and isolate, temporarily or permanently, desired sections or areas of the well, thus allowing to perform various operations; especially operations of stimulation, fracking, injection of acids and others, case-hardening, pressure resting, various treatments, etc.
A packer is a popular tool employed in the oil industry for temporary sealing a section of a extraction well and basically comprises a set of components arranged along one or more tubular parts where there are gripping or anchoring and sealing means which function, once the tool is arranged at the desired depth or section of the well, is to fix the packer in position and seal it against the walls of the casing. The packer, generally, is placed at the lower end of a series of sections and tools formed by a plurality of pipe sections forming the pipe for operations or services. The casing pipe, or simply the casing, and the service pipe will not be illustrated herein as they are well known in the art and do not form part of the invention.
The retrievable packer of this invention has preferably been developed for use in high pressure service, e.g. more than 10,000 psi, and more preferably at 15,000 psi or more, in wells encased by means of one casing. The packer consists of an upper head 1 in which the lower end of a service pipe is threaded, which is well known in the art. The head 1 in turn is linked by a thread sealed by seal 2 to an upper mandrel 5 which has an annular protrusion or ledge 15, having a shape of star-shape protrusion 15, see FIGS. 1A and 2, and at its lower end it is connected by a thread to a lower mandrel 47 which has a “J” bolt or “pin” 40 to which reference will be made later. Head 1, upper mandrel 5 and lower mandrel 47 are therefore an integral assembly that behaves as a single piece.
Upper head 1 includes an equalization seal 4 held and protected by a seal holder nut 3 which is threaded to upper head 1 and which has a step 3A, with seal 4 intended to hydraulically seal against a lip 6 to which reference will be made later. There is a plurality of components concentrically arranged to cover mandrel 5 and mandrel 47, which will maintain, during operation of the packer, a plurality of axial relative movements with respect to mandrels 5 and 47.
Starting from the top, there is a balancing sleeve holder 7 which accommodates at least one upper balancing sleeve 9 and, preferably, also a lower balancing sleeve 13, being both hydraulically operated and aligned with star-shaped end or ledge 15, designed to mechanically act on the star-shaped ledge 15 integrated into upper mandrel 5. Then there is a connecting sleeve 11 threadably connected to the balancing sleeve holder 7, so that balancing sleeves 9 and 13 are arranged inside the sleeve holder 7 and the connecting sleeve 11, as best seen in FIG. 1A. The balancing sleeve holder 7 has at least one balancing hole 10A below seals 8 of the upper end of the upper balancing sleeve 9 and abuts against a middle portion of said connecting sleeve 11.
Upper balancing sleeve 9 has on its upper end at least one seal of said seals 8, which seal seals against one interior wall of the balancing sleeve holder 7, while a lower end of sleeve 9 includes a hole 9A and abuts against an upper end of the lower balancing sleeve 13. On its turn, said lower balancing sleeve 13 has on its upper end, one larger section shoulder 13A on which the lower end of the sleeve 9 and a portion of the connecting sleeve 11 abut, while its lower end abuts on such star-shaped ledge 15. Moreover, said lower balancing sleeve 13 is provided with at least one seal 12 which seals against one interior wall of connecting sleeve 11. Wherein, said connecting sleeve 11 is provided with at least one balancing hole 14A below such seals 12 of the upper end of the lower balancing sleeve 13, and has, on its upper end, at least one seal 10 which seals against one middle portion of upper balancing sleeve 9, while its lower end is connected to a piston body holding ring 17, which ring 17 partly holds a piston holder body 16 which is provided on its upper end with at least a seal 14 which seals against lower balancing sleeve 13. In this way, a chamber 7A between such seals 8 and 10, and a chamber 11A between such seals 12 and 14, are defined.
On its turn, such piston holder body 16 is arranged between said lower balancing sleeve 13, star-shaped ledge 15, and said connecting sleeve 11, and ring 17. A strip 18 is the end of the run of piston 19 and is supported by upper 17 and lower 24 holding rings and additionally, between pistons 19, by screws 21, housing four sets of securing pistons 19, each securing piston 19 having a pair of tungsten inserts 20 and comprising a piston 19 mounted radially extendable within a corresponding housing of piston holder body 16, such housing being open towards the interior of piston holder body 16 and in communication with the circulating pressurized fluid inside the same. It is noteworthy that, each piston 19 is connected to a pair of springs 23 which are housed in respective seals or springs holder 22 arranged in such housing and which make it possible that the piston 19 leave or enter depending on the side hydraulic pressure acts, by direct or annular pathway, that is through the interior of the tubing. Likewise, such piston holder body 16 holds, by a thread sealed by at least a seal 25, at least one rubber gasket holder sleeve 27 provided with respective sets of rubber gaskets comprising each, at least four annular rubber gaskets 28 separated between each other by respective separating rings 29 and which are axially arranged one below the other. Wherein, said four rubber annular gaskets 28 comprise two end gaskets of a certain hardness and two internal gaskets of different hardness, which are arranged between an upper ring 26 and a lower ring 30 that is supportive of one sleeve joint 31 connecting to clamp holder cone 32 which has an inclined plane 33 on which a set of clamps 34 moves, which are provided with respective tungsten pellets 35.
Next and concentrically arranged on an lower section of such upper mandrel 5, a clamp holder ring 38 is arranged, on which such set of clamps 34 is secured, and which has fixed thereto a screw 36 limiting movement for each of the clamps 34 and a holding screw 37 of the clamp holder, which is an option to the assembly of the tool.
Also, such clamp holder ring 38 holds a J guide sleeve 39 bearing on its carved inner wall one J-shaped guide 48 within which such pin 40 of the J guide guidably slides which is part of such lower mandrel 47, which way of being driven shall be described later. On the other hand, following the J sleeve 39 and concentrically arranged on such lower mandrel 47, a drag block 43 is arranged which is mounted in a radially and elastically compressible way thanks to the arrangement of respective compression springs 45, such drag block 43 being secured to said sleeve J 39 by an upper drag block locking ring 42, with its holding screw 41, and a lower drag block locking ring 46. Such upper 42 and lower 46 drag block locking rings allow to support sealing of packing and centering in the encased well. The drag block has tungsten pellets 44 which improve the wear resistance.
Now, reference to the use and operation of the inventive packer will be made.

Packer Operation:

Tool Securing and Packing
Once the upper head 1 of the packer is threaded to the pipe, commonly called “tubing”, there proceeds the operation of deepening the tool to the area required for operation. It should be remembered that the function of the packer is to seal the annular space or gap between the service pipe and the casing pipe to isolate a lower section, where pressurized fluid shall be injected, from an upper section where it is not desired than this pressure has access, at least during the carrying out of the service.
At all times during the down movement or insertion of the tool into the well drag blocks 43 are expanded against the pipe forcing the assembly upwards. The assembly formed by the upper head 1, the upper mandrel 5 and the lower mandrel 47, which includes the “pin” or bolt of the J guide is an integral assembly, i.e. it behaves as a single piece.
According to FIG. 3, when packer reaches the section or depth where it should be sealed, the pipe (not shown) is lifted whereby it is pulled upwards from the head 1, so that bolt 40, being part of the lower mandrel 47, ascends along the J1 section of the J guide. Thus, head 1 is rotated counterclockwise, i.e. to the right, according to Figure, along the J2 section of the J guide. Then, taking advantage of the weight of the whole assembly of pipe sections, that is the string, plus some additional load if necessary, the set of upper 5 and lower 47 mandrel is lowered so that the pin 40 is downwardly moved along the J3 section, namely J3 of the J guide. During the descent of the mandrel 5, the drag block 43 remains in its position, fixed against the casing, not illustrated, and supporting in their place components formed by the sleeve J 39, which has inside the J guide 48, the clamp holder ring 38 and the clamps 34.
As a result of this drop of mandrel 5, seal 4 will sealingly abut against lip 6 and step 3A will push sleeve holders 7 causing the assembly consisting of balancing sleeve holders 7, balancing sleeves 9 and 13, piston holder body 16, with pistons 19, gasket holder sleeve 27, with gaskets or rubbers 28, sleeve 31 and cone 32 to move downwards.
As explained above, while clamps 34 are prevented from descending, by block 43, the same shall ascend the inclined plane 33 of cone 32 expanding in order to grip the inner walls of the casing pipe. This will secure the tool, packer plus service pipe, so as to prevent their drop. In other words, clamps 34 support the load or weight of the entire string of tubing and tools.
When clamps 34 are attached against the casing pipe, but continuing the drop of gasket holder sleeve 27, sleeve 31 and ring 30 shall form a limit for such drop so that rubber gaskets 28 shall begin to compress between rings 26 and 30 radially expanding due to deformation and sealing against the wall of the casing pipe. There, the whole service pipe and packer is in fixed and packed position, leaving the annular space between the service pipe and the casing pipe mechanically and hydraulically sealed by rubber gaskets, or packing rubbers 28. From here the treatment service operations under high pressure can be started.
High pressure service may involve for example, injecting fluid under high pressure for hard-casing, stimulation, etc. This injection is carried out inside the pipe, which in practice is called “by direct pathway”, that is inside the set of head 1, and upper 5 and lower 47 mandrels, with the fluid coming out of the open lower end of the lower mandrel 47. To understand the practice terms, when the fluid is injected into the annular space between the pipe and the casing pipe it is called “through annular space or gap”.
Upon entering the fluid by direct pathway, it fills and raises pressure in the section of the well below the packer, while pressure in the annular space above the packer remains the same as the pressure during the drop of the tool, i.e. as the pressure before high pressure injection by direct pathway. The pressurized fluid within said lower section of the well, goes up through the space existing between upper mandrel 5 and cone 32, the sleeve 27, the piston holder body 16, and the balancing sleeves 9 and 13. First, this pressure pushes pistons 19 outwards nailing them against the casing pipe to support the upward pressure than would tend to raise the tool. Moreover, as seal 4 closes against lip 6, the pressurized fluid actuates on upper balancing sleeve 9 which falls under the force of the fluid. On the other hand, chamber 7A, formed between seals 8 and 10, is in communication with the annular space, formed between the service pipe and the casing pipe, through the balancing hole 10A. Therefore, pressure inside chamber 7A is that one of the annular space out of the service pipe, i.e. it is less than the pressure within mandrel 5, the direct pathway, acting on the balancing sleeve 9.
Sleeve 9 has its lower end abutted on the upper end of the lower sleeve 13 therefore it moves downward to push this sleeve 13 which discharges the force on the star-shape ledge 15 of upper mandrel 5. Thus, the effect of high pressures that push the pipe and the tool upwards is compensated by the hydraulic load generating a downward force on balancing sleeve 9, which is transmitted to lower balancing sleeve 13, discharging this force on the star-shaped ledge 15 of upper mandrel 5, pushing all the assembly downwards so as to balance upward forces.
In addition to balancing sleeve 9, there is provided lower balancing sleeve 13 which, on its upper end, where the lower end of the sleeve 9 is supported, has such larger section shoulder 13A whose function is to generate an additional downward force. In effect, the pressurized fluid passing between mandrel 5 and sleeve 13 passes through holes 9A and 13A and acts on shoulder 13A pushing down sleeve 13. The fluid could pass between the lower end of sleeve 9 and the upper end of sleeve 13 but if pressure is too high the strong support between the ends form a metal-to-metal seal that would prevent the passage, so hole 9A offers communication as necessary. Like chamber 7A, the chamber 11A formed between seals 12 and 14, is in communication with the annular space formed between the service pipe and the casing pipe, through balancing hole 14A. Therefore, the pressure inside chamber 11A is that one of the annular space outside the service pipe, i.e. it is lower than the pressure inside the mandrel 5 (direct pathway) which acts on balancing sleeve 9.
Thus, sleeve 13 transmits to mandrel 5, through star-shaped end or ledge 15, the load coming from sleeve 9 plus the extra force which it receives from the hydraulic load on its upper end. Under these conditions, the service pipe and the tool, i.e. the packer, are installed and fixed in service position.
Tool Release
Once the service, hard-casing, fracking, stimulation, etc. are completed, the tool can be released for removing it from the well or performing an additional service in another section of the well.
In order to release the tool, the injection of pressurized fluid through direct pathway is interrupted and fluid is injected through the annular pathway thus permitting the injection fluid to fill the interior of the pipe and packer, i.e. by direct pathway, as well as the space between the service pipe and the casing pipe, i.e. the annular pathway.
It is intended that both columns reaches the same level so as to balance the pressures in the direct pathway and the annular pathway. Under these conditions, pistons 19 are retracted to their original position, pushed by springs 23, and balancing sleeves 9 and 13 no longer exert downward force on the set of mandrels. Thus, the pipe may be pulled upwards and head 1 are raised with mandrels 5 and 47 so as to detach seal 4 from lip 6 so that the fluid in the direct pathway is in communication with the fluid in the annular pathway through ail the holes and passages between mandrel 5 and sleeve 27, piston holder body 16 and balancing sleeves 9 and 13, with the fluid flowing upwards through the space between mandrel 5 and lip 6 of balancing sleeve holder 7. Also, rubber gaskets 28 are decompressed and retracted, cone 32 is lifted and clamps 34 are unfitted. In the latter case screw 36 keeps clamps 34 hanging from cone 32. Indeed, the run of each clamp 34 on cone holder 32 is delimited by such end screw 36 which is secured to such clamp holder ring 38 as mentioned above.
Once mandrel 5 and 47 have been lifted, with bolt or pin 40 at the upper end of section J3, the pipe, together with the whole head assembly 1 and mandrels 5 and 47, is turned clockwise, i.e. to the left as seen in the Figures, along section J2 of the J guide. When releasing the pipe, the bolt sits at the bottom of the section J1 where it was at the beginning so the tool is again able to be moved and positioned in another section of the well for another service.
It is clarified that J guide can be released from the left or from right which will depend on the thread of the service pipe sections. Also, J mechanism may be of the automatic type.
With this packer fluids can be circulated by direct route, i.e. inside the pipe, or by the pipe, i.e. below the mandrel, which allows efficient rinsing of all packer outside and inside. Thus, when it is deepened with a retrievable plug in tandem, it allows washing the tool and the well from below without contaminating the mechanisms.
In the case that it is required to perform additional operations, it shall be enough to perform again all changes of depth of the packer with the corresponding changes of cycles considered necessary to perform the required operations.
The packer of this invention has shown excellent effectiveness and simplicity of operation due to its particular design, particularly in very high pressure operations, close to, for example, 15,000 psi.
While preferred embodiments of the present invention have been illustrated and described, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined in the appended claims.

Claims

1. Retrievable packer for operations in wells cased by means of a casing pipe, where the packer is one of the type employed to temporarily or permanently seal the annular space between the casing pipe of the well and a service pipe which is inserted into the casing for operations of treatment of one or more sections of the cased well, the packer comprising:

a head for connection to the service pipe,

an upper mandrel,

a lower mandrel threaded to the upper mandrel,

pistons and clamps for fixing the packer against the casing pipe, arranged to resist the upward and downward forces, respectively,

a set of rubber gaskets to seal said annular space,

a balancing sleeve holder concentrically arranged one such upper mandrel whereby a hydraulic pressure space is defined between the balancing sleeve holder and the upper mandrel,

at least, one balancing sleeve arranged in said hydraulic pressure space,

an annular ledge of the upper mandrel, aligned with and arranged below said at least one balancing sleeve, and wherein said pistons and clamps respectively comprise a piston holder body, and a set of clamps.

2. Retrievable packer according to claim 1, wherein said at least one balancing sleeve comprises an upper balancing sleeve and a lower balancing sleeve.

3. Retrievable packer according to claim 2, wherein said upper balancing sleeve has an upper end including seals, wherein the seals of the upper end of the upper balancing sleeve seal against said sleeve holder, and a lower end abutting against an upper end of said lower balancing sleeve.

4. Retrievable packer according to claim 3, wherein said lower balancing sleeve is slidably mounted between said upper mandrel and a connecting sleeve fixed to said sleeve holder, with the upper end of said lower balancing sleeve having seals sealing against said connecting sleeve, with the connecting sleeve also having seals sealing against a middle portion of said upper balancing sleeve.

5. Retrievable packer according to claim 4, wherein said sleeve holder has at least one balancing hole below said seals of the upper end of the upper balancing sleeve.

6. Retrievable packer according to claim 5, wherein said connecting sleeve has at least one balancing hole below said seals of the upper end of the lower balancing sleeve.

7. Retrievable packer according to claim 6, wherein said sleeve holder has an upper lip, separated from said upper mandrel, for sealing against a seal arranged in said connecting head to seal the space between said lip and the upper mandrel.

8. Retrievable packer according to claim 1, wherein said annular ledge is a star-shape ledge.

9. Retrievable packer according to claim 1, wherein said piston holder body accommodates four sets of securing pistons.

10. Retrievable packer according to claim 9, wherein each securing piston comprises a piston mounted in a radially extensible way within a corresponding housing of the piston holder body, the housing being open towards the interior of the piston holder body and in communication with circulating pressurized fluid inside the piston holder body.

11. Retrievable packer according to claim 1, wherein said set of rubber gaskets comprises four annular rubber gaskets axially arranged one below the other, having two end gaskets and two internal gaskets of different hardness.

12. Retrievable packer according to claim 1, wherein a drag block is arranged concentrically on said lower mandrel, with the drag block being mounted in a radially and elastically compressible way.

13. Retrievable packer according to claim 12, wherein a clamp holder ring is concentrically arranged on a lower section of said upper mandrel, with said set of clamps being mounted in said clamp holder ring, and said clamp holder ring carries attached thereto a screw for limiting each of the clamps, each ring forming a limitation to the movement of each clamp.

14. Retrievable packer according to claim 13, wherein said clamp holder ring holds a J-guide sleeve that has, carved in an inner wall thereof, a J-shaped guide, with a J-guide pin guidably sliding in the J-shaped guide and the pin being part of said lower mandrel.