EP0517603A1 - Method for drilling a blind well, in particular of big diameter, and drilling tool for carrying it out - Google Patents

Abstract

In order to form a well 1 of large diameter without the presence of a subjacent gallery, there are presently available mining techniques which often require the ground to be frozen, or oil-drilling techniques using a supporting mud 16. In the latter case, the drilling is conventionally carried out from the top downwards. Within the scope of the present invention, a method for drilling from the bottom upwards as well as a tool 2 adapted for the implementation thereof are described. A main operation of this method consists in fact in widening a pre-existing well. The corresponding tool 2 is provided with arms 22 designed to be, firstly, folded up so that the tool 2 may be passed inside the pre-existing well in order to be lowered down to the bottom 15 of the latter and then, secondly, opened out while its teeth 23 cut into the ground 12, the tool 2 being rotated and pulled by a motor 31 supported by a mast 3 at the surface 11. It is then often advantageous thus to widen a guide well, and then to repeat the main operation on the resulting well and so on. Despite the number of passes required from then on in order to obtain the desired large-diameter well 1, the speed of progress of the tool 2 during each successive widening operation may in fact be so great that overall the well 1 is dug in a much shorter time and its cost is reduced compared to the usual methods. <IMAGE>

Description

The present invention relates to a method for drilling a blind well in particular of large diameter. It also relates to a tool for implementing this method.

Underground cavities are sometimes used to store large quantities of liquid or gaseous products, such as hydrocarbons. In order to realize them, then to exploit them as reserves, an access well is first dug. Its diameter is most often between one and a few meters so as to allow the passage of personnel and digging equipment as well as that of excavated material.

It is possible today to distinguish two kinds of methods for making such an access well, especially when it crosses relatively loose ground. The first uses civil engineering techniques, comparable to those used to drill a tunnel. Machines and workers to drive them then work at the bottom of the well being dug. In the case of particularly unstable layers (typically soils without cohesion), this often requires the ground to be frozen beforehand. Consequently, the cost of the well penalizes this type of storage.

The second method is similar to oil drilling techniques. A drilling tool is lowered into the well and is operated from the surface. It has the advantage of being able to work while it is immersed in a mud adapted to support the walls of the well. Given the large diameter of the wells considered, it is however necessary to considerably increase the drill string carrying the tool so that the latter exerts on the bottom of the well sufficient pressure to guarantee the attack on the ground. The "drill sticks" which are then used, are not very handy. Again, the cost of the work is burdened.

Thus a problem consists in finding a method for producing a well which will serve in particular as a well for access to a storage cavity, this method being able to be implemented, in the case of soft ground in particular, more quickly and at lower cost compared to conventional methods.

The solution to this problem in accordance with the present invention consists in combining two known drilling techniques. The first of them is most often designated by its name in English: "under-reaming". It is in particular described in US Patent 2,033,133 to WOODRUFF. It consists of widening the bottom of a borehole, for example to increase the productivity of an oil well or to create an anchor head for a foundation stake. To do this, it uses a tool comprising a rotating body on which one or more arms adapted to attack the ground are articulated.

OWENS US Patent 4,365,677 mentions a large list of previous publications disclosing this type of tool. Most use a system similar deployment of the arms as the bottom of the borehole is widened. This system is none other than that of automobile jacks so that deployment is obtained by exerting a compression force on the tool (using in particular a device known in the profession under the name of " kelly ").

European patent application EP 0 298 537 teaches a tool also intended for "under-reaming", but the arm of which is designed to deploy this time under the effect of centrifugal force when the body which carries it is put in rotation. Anyway, all these tools of the prior art work without it being applied traction. Above all, they are suitable for creating an enlarged cavity which remains at the bottom of the borehole. If this point is clear when the arms are deployed by compression, we understand that it could not be otherwise for the European tool when the ground is somewhat resistant.

The second technique called into question by the present invention carries in English the name of "raise-boring". It is primarily used in civil engineering and requires a pilot well communicating with a sufficiently spacious excavation at the end of the well. A drill string is then passed through the pilot well so that it extends into the excavation. A drilling head is also mounted within the excavation and subject to the drill string. The "raise-boring" then consists in exerting traction on the drill string so that the head widens the excavation by going up along the pilot well, for example by grinding its roof.

The present invention therefore relates to a method, the main operation of which consists in widening a pre-existing well filled with a retaining mud, starting at the bottom to go up towards the mouth surface of the blind well to be produced, characterized in that this is achieved by exerting traction on a drilling tool having a body adapted to rotate around the axis of the well as well as arms provided with elements for attacking the ground by clearing cuttings and adapted to be deployed to protrude from the body while transmitting traction.

• faire descendre dans un puits préexistant l'outil alors que ses bras sont repliés,
• mettre en rotation le corps de l'outil de forage tout en déployant ses bras de sorte que les éléments pour attaquer le terrain créent un épaulement à la paroi du puits qui définit la transition entre le puits en cours d'élargissement et le puits préexistant,
• tirer le corps de sorte que les éléments pour attaquer le terrain attaquent l'épaulement et le font progresser vers la surface d'embouchure, la boue étant mise en circulation autour de l'outil de façon à entraîner la majorité des déblais jusqu'à la surface d'embouchure, la traction et la rotation de l'outil ainsi que la circulation de la boue étant maintenues jusqu'à ce que le puits ait été élargi sur toute sa hauteur.

More specifically, the main operation includes the steps of:

• bring the tool down into a pre-existing well while its arms are folded,
• rotate the body of the drilling tool while deploying its arms so that the elements for attacking the ground create a shoulder at the wall of the well which defines the transition between the well being enlarged and the pre-existing well,
• pull the body so that the elements for attacking the ground attack the shoulder and advance it towards the mouth surface, the mud being circulated around the tool so as to entrain the majority of the cuttings up to the mouth area, traction and rotation of the tool as well as the circulation of the mud being maintained until the well has been widened over its entire height.

Advantageously, the bottom of the pre-existing well is located below the bottom of the blind well to be drilled so as to allow the tool to descend so that its arms are at this bottom.

Advantageously, the step of lowering the tool is carried out by adding rods to a string of rods at the lower end from which the tool is suspended. In this case, the steps of rotating and pulling the tool are preferably carried out by passing the upper end of the drill string through an apparatus of the "power-swivel" type, the rods being removed from the drill string at as the tool is pulled toward the mouth of the well. For example, the device of the "power-swivel" type is mounted in a superstructure disposed above the mouth of the well.

Advantageously, the mud is circulated by continuously introducing mud into the well from its mouth surface and by sucking it under the tool in a tube to bring it through the well to its mouth area.

Advantageously, a widening factor defined by the ratio of the diameter of the well resulting from the main operation to the diameter of the pre-existing well is chosen in particular according to the mechanical strength of the drilling tool and, the drilling tool being pulled out and set in rotation by a motor, according to the torque that the motor can deliver. The widening factor is preferably between 1.15 and 1.30.

Advantageously, a preliminary operation of the method consists in drilling a pilot well, the main operation being carried out a first time while the pre-existing well is the pilot well, then the main operation being reiterated while the pre-existing well is the well resulting from the previous iteration, and this until the diameter of the blind well to be drilled is reached, a final operation consisting finally in coating the well and removing the mud. For example, the widening factor is the same at least for a series of consecutive iterations. But also, the enlargement factor can be reduced at least for a series of consecutive iterations.

The present invention also relates to a drilling tool for implementing this method. For this, it comprises a body adapted to rotate around the axis of the well as well as arms provided with elements for attacking the ground, adapted to pass from a folded position on the body to a deployed position to protrude from the body and capable of transmitting the traction exerted on the tool.

Advantageously, the arms are secured to the body by means of a cam, rack or hydraulic system adapted to pass the arms from their folded position to their deployed position and vice versa. However, they can also be secured to the body by a pivoting link adapted to pass the arms from their folded position to their deployed position.

Advantageously, the arms are adapted to be mounted on a series of bodies each having a different diameter.

Advantageously, the body has a lower extension adapted to let the mud pass as well as cuttings. In this case, the extension is preferably provided below with an umbrella-shaped deflector so that most of the cuttings are guided towards the extension.

In truth, we had never before considered combining the techniques of "under-reaming" and "raise-boring". The process which thus consists in widening a pilot well while going up thanks to a tool with deployable arms is consequently new as well as the corresponding tool. The latter is then characterized by a system adapted to the deployment of the arms while guaranteeing the possibility of pulling on the body of the tool. In other words, it is necessary to provide articulations capable of supporting and transmitting tensile forces.

From a mechanical point of view, the development of such joints poses no problem to those skilled in the art. The present application provides several solutions in this regard. And this is not where the inventive aspect of the approach resides. It is rather in the very idea of combining two techniques known for several decades and yet never brought together. However, as long as the nature of the terrain lends itself to this, there are many advantages.

For example, the drilling method which consists in widening a pre-existing well starting from the bottom, involves a traction of the drilling tool. As a result, the linearity of the well is much more surely guaranteed. This advantage is indeed known in relation to mining techniques such as "raise-boring". However, the latter provide for the application of the method only when the bottom of the well communicates with a gallery. This configuration indeed allows the removal of cuttings (also called in the profession "cuttings") by the gallery where they accumulate by simple gravity. There is therefore no question of practicing "raise-boring" in terrains that need temporary support such as mud. In other words, the present process extends the application of "raise-boring" to the case of soft ground. It therefore enjoys all the qualities of "raise-boring".

The complementary aspect of the present process highlighted above in conjunction with a limited widening factor also guarantees it in certain cases increased performance compared to the usual drilling methods. Suppose indeed that the tool used in this case develops an effort identical to the tool used work to traditionally drill the well from top to bottom and all at once. As the surface to be attacked at each "pass" represents only a fraction of the total section of the final well, the pressure exerted on the elements which attack the ground, is in fact multiplied. It follows a very important speed of advance. And as long as the nature of the terrain is suitable, it exceeds the speed of advance in traditional drilling in such proportions that the entire well is drilled more quickly despite the completion of several passes.

Other factors can also save time. On the one hand, the speed with which the tool turns on itself is likely to be increased since we no longer need masses which create in rotation a large reactive inertia. The same applies to the force exerted on the tool. These parameters are in fact linked to the engine used and in particular to the torque that it is capable of developing. The resistance offered by a small area of ground to be attacked being significantly reduced, this torque remains limited on each pass. The superstructure which supports it (and therefore takes back its torque) can consequently be much lighter than similar devices used in traditional drilling. From then on the handling of the material becomes easier and is therefore carried out more quickly. All these factors adding more or less to each other, they often guarantee a saving of time and therefore money justifying the multiplication of drilling passes. To do this, it suffices to optimize, when possible, their number in relation to the properties of the ground as well as with the digging equipment.

As for the present tool, its deployable arms allow its use in blind wells. Certainly, in mining technique, different machines have been developed for the implementation of "raise-boring". However, teeth, wheels, etc. which allow them to attack the ground, are not carried by movable arms. In practice, they are assembled in the gallery at the bottom of the well where there is enough room to receive them. The present tool, on the contrary, passes into the pre-existing well, which authorizes surface assembly.

In parallel, in "under-reaming", drilling tools have been developed provided with deployable arms. However, these necessarily have a small diameter body, which consequently limits the overall section of the well to be dug. As in addition, the tool works in a conventional manner when descending, the arms and the articulations of the arms are particularly stressed and thus experience frequent breaks. These expanders with movable arms cannot therefore be used for drilling large-diameter wells.

Although the present tool can borrow their technology from the "under-reamers" (for the arm joints in particular), the ruptures are much less to fear. In connection with the complementary aspect of the present process, the elements for attacking the ground which the arms carry, have in fact to be applied on a very reduced surface compared to the complete section of the well. Also for a given pressure of these elements on the ground, the tensile force to be transmitted to the body of the tool does not need to be very high. This contributes to sparing the connections of the arms made fragile by their mobility.

To this end also, it is conceivable to develop arms adaptable to several bodies. So as the well is widened, we change the body and, each time with a body with a diameter greater than the previous one, we manage to maintain a low rate of stress on the joints of the arms.

• la figure unique est un schéma de principe de l'étape principale du présent procédé. Elle montre notamment une coupe d'un puits en cours de forage selon ce procédé tandis qu'un outil de forage adapté à sa mise en oeuvre est quant à lui représenté en vue de côté au sein du puits.

The invention will be better understood on reading the detailed description which follows and on examining the appended drawing which represents, by way of nonlimiting example, an embodiment of the invention. On this drawing :

• the single figure is a block diagram of the main step of the present method. It shows in particular a section of a well being drilled according to this method while a drilling tool adapted to its implementation is shown in side view within the well.

In accordance with the single figure, the present method consists first of all in drilling a pilot well 1 of small diameter. Its diameter can vary between 50 cm and 1 m. In accordance with the practice in the profession, it is usually measured in inches so that diameters of 26 or 36 inches for example are envisaged. These values are in fact associated with traditional drilling methods such as those using a process called "rotary" very well known in the profession.

This pilot well 1 is also filled with mud 16 to provide temporary support for its wall 13. In the context of the present method, it is also preferable for its bottom to be a little below the final bottom 15 of the well to be dug . As will be better understood on reading the following paragraphs, the difference in depth of the bottom of the wells is in fact a function of the drilling tool 2 which is then lowered into the pilot well 1 in accordance with the invention.

This tool 2 is in fact made up of a body 21 adapted to pass into the pilot well 1. It comprises elements intended to attack the ground, teeth 23 in particular, which are in turn carried by movable arms 22. These are subject to the body 21 so that they can be folded back when, in particular, the tool 2 is lowered along the pilot well 1. And it is only after the tool 2 has reached the bottom of the well 1 that the arms 22 are deployed.

Different mechanical systems can be imagined to subject the arms 22 to the body 21. Let us quote for example a connection involving a cam so that a relative angular position of the arm 22 relative to the body 21 corresponds to the folding of the arm and another position corresponds to the deployment of the arm. Another example is a rack system or a hydraulic system.

This is because, in the main step of the present method, it is planned to rotate the tool 2 about a vertical axis. The latter, in truth, coincides with that of the well. The rotational movement is transmitted by a train of rods 34 at the lower end of which the tool 2 is rigidly linked. In order to lower or raise the tool 2, rods 34 are added to or removed from the rod train, as the case may be. Such maneuvers involve routine operations in the profession. The rods 34 each have for example a length of 9 m. They are held one after the other, for example by means of coupling sleeves.

The upper end of the drill string 34 advantageously passes into an apparatus known in the profession under the name of "power-swivel" 31 which can be translated by motorized injection head. The latter is provided in particular with a motor to impart a relatively rapid rotational movement to the drill string 34. At the same time, it exerts traction. The traction thus developed can in particular reach 200 tonnes.

The "power-swivel" 31 is supported, meanwhile, by a metal superstructure disposed on the surface above the well 1. In the context of this perfectly conventional configuration, this superstructure is rather called "mast" 3. It s indeed extends well above the "power-swivel" 31 in order to authorize the maneuvers of the rods 34 mentioned above. From this point of view, hook heights of 40 m are perfectly conceivable so that a "work in triplicate" (adding or removing the rods three by three) is made possible. The mast 3 has for this purpose an elevation system illustrated in the figure by a pulley 32 and a cable 33.

This is how the main stage of the present process begins while the tool 2 is lowered to the bottom of the pilot well 1. The "power-swivel" 31 then turns the tool 2 around the axis of Wells. Initially, the arms 22 of the tool 2 are always folded. Provided that their teeth 23 are properly oriented, they then dig a housing in the wall 13 of the well 1 which authorizes a start of deployment for the arms 22. The process continues in this way until the complete deployment of the arms 22. Therefore the wall 13 of the well 1 has a shoulder 14 at the passage of the housing to the rest of the well 1 located above. Its dimension corresponds to the depth of the bottom 15 of the final well, this bottom 15 therefore being separated from the bottom of the well 1 pilot by the distance between the base of the tool 2 and the upper end of its arms 22.

Then, the "power-swivel" 31 begins to exert in addition on the tool 2 a traction. This ensures the application of the teeth 23 of the arms 22 deployed against the shoulder 14. As soon as the corresponding pressure becomes sufficient (in particular by exceeding a threshold depending on the nature of the terrain), it follows the continuation of the digging housing. And a widening of the well is obtained which, from the bottom, progresses towards the surface as the tool 2 is pulled towards the surface 11.

This progression results in fact from the attack of the ground by the teeth 23 of the tool 2 at the level of the shoulder 14, the latter being somehow "machined". This is accompanied by the detachment of material, grains and larger blocks from the ground traditionally called "cuttings" 17. And if we were not careful, these cuttings would fall to the bottom of the well and accumulate there.

To limit this inconvenience, the present invention provides for circulating the mud in which the tool 2 is immersed. Arrows in the figure show a first way of making it flow from the surface 11 of the ground where mud 16 is introduced continuously into the well 1. It is then caused to pass along the shoulder 14 in progress drilling. The sludge can be activated by a system (not shown) of pumps or "air-lift" (delivery using pressurized air). Thus it is sucked in at an extension 25 of the tool 2. If it is clear that the extension 25 must imperatively be fixed under the body 21 in order to collect the "cuttings" 17, its structure remains a matter choice of designer. The figure fixes the ideas by giving it the simple form of a tube provided with openings for the passage of the "cuttings" 17. They are indeed evacuated with the mud sucked towards the surface 11 while going up inside the train of rods 34 or a sheath provided for this purpose (not shown).

Complementary installations can make it possible to separate the "cuttings" 17 recovered from the surface of the mud 16 with a view to reintroducing the latter into the well 1, thus creating a flow in a closed circuit. It is noted that, compared to comparable drilling methods, the flow of the liquid for evacuating the "cuttings" 17 occurs here in the opposite direction. This has in particular the advantage of guaranteeing a particularly high rate of ascent of the mud, the passage section in the drill string 34 or the sheath being notably smaller than that of the well. This ensures that the sedimentation speed of the "cuttings" 17 is exceeded and therefore that they are properly trained.

However, a circulation of the mud in the other direction (normal direction compared to the traditional methods) is possible even with relatively low flow velocities. In this case therefore the mud descends through the drill string 34 by example and goes back up by the well 1. However, it approaches this last circulation zone at the exit of the enlarged section of the well so that it also sees its speed increasing after being loaded with excavated material. It then suffices to adapt its rheological characteristics, in particular its viscosity (in particular by increasing it) so that the ascent rate in the part of the well not yet enlarged is greater than the sedimentation speed of the "cuttings".

In order to ensure better recovery of the “cuttings” 17 in reverse circulation in particular, the present invention envisages the advantageous use of a deflector 24 disposed at the lower end of the extension 25. It is for example a metal part shaped like an umbrella. This deflector 24 then plays a role of guide with respect to the flow of the mud which thus more effectively drives the "cuttings" 17 towards the extension 25. The loss of certain debris at the bottom 15 of the well seems inevitable . This is not otherwise troublesome insofar as they can be removed by circulation of mud, or even mechanically.

In accordance with a complementary aspect of the present invention, the pilot well 1 is thus only partially enlarged. Its new diameter does not exceed its previous diameter by more than a ratio of 1.5 or 2. Preferably, this enlargement factor is between 1.15 and 1.30 times its initial diameter. It is that from a technological point of view, it is better to limit the application surface of the tool 2 to the ground, that is to say the shoulder 14 which is "machined" as described below. -above. It follows in fact a significant increase in the pressure of the teeth 23 on the ground 12 and the speed of progression of the tool 2 is therefore generally increased in considerable proportions.

Thus, in order to pass from the pilot well 1 to the final well, the present method provides for repeating the main operation which has just been described with the aid of the figure. And it is in the well which has just been widened that the tool 2 is lowered, arms 22 folded, that the drill string 34 gives the tool 2 the rotary movement in order to dig the first housing allowing the progressive deployment arms 22, and then transmits traction to it so as to widen the well a little more.

If this new pass involves a series of maneuvers identical to those carried out during the first, it is however necessary to modify the geometry of tool 2 once on the other. The teeth 23 must indeed follow the shoulder 14 which has an increasingly large average diameter. This can be achieved by changing tools with each pass. More advantageously, a body 21 is used whose diameter is adapted to that of the pre-existing well. The larger the cross section of the latter, the more massive the body 21 chosen. Thus the same arms 22 can be used for each pass (subject of course to be removable).

Depending on the equipment at its disposal, the operator will have an interest in playing on two parameters in particular to establish its enlargement plan. He can for example choose to widen the well in the same ratio with each pass (constant widening factor). Consequently, the traction to be developed on the drill string and therefore the torque received by the mast 3 increases pass by pass with the surface of the shoulder 14. Also, to use from one end to the other the same mast 3, the operator is likely to prefer to maintain a constant torque. The enlargement then takes place in an increasingly weaker ratio.

When the well has reached the desired final diameter, the present method provides for coating it according to the usual methods, the retaining mud being removed from the well. It can in particular be fitted with a cemented casing.

The process which has just been described is applicable not only to the digging of access wells to storage cavities in accordance with the aim stipulated at the start, but also to the drilling of oil wells. It could replace the methods currently used and which have been previously mentioned in relation to "under-reamers".

Claims (18)

1. - Method for drilling a blind well (1) in particular of large diameter and having an axis of revolution, a wall (13), a bottom (15) as well as a mouth surface (11), a main operation of the process consisting in widening a pre-existing well filled with a supporting mud (16) starting with the bottom (15) to go up towards the surface (11) of mouth of the blind well (1) to be drilled, characterized in that is achieved by exerting traction on a drilling tool (2) having a body (21) adapted to rotate around the axis of the well (1) as well as arms (22) provided with elements (23) to attack the terrain by clearing cuttings (17) and adapted to be deployed to protrude from the body (21) while transmitting traction. 2. - Method according to claim 1, characterized in that the main operation comprises the steps of: - lower the tool (2) into the pre-existing well while its arms are folded back, - Rotating the body (21) of the drilling tool (2) while deploying its arms (22) so that the elements (23) to attack the ground create a shoulder (14) on the wall (13) the well (1) which defines the transition between the well being enlarged and the pre-existing well, - pull the body (21) so that the elements (23) to attack the ground attack the shoulder (14) and make it progress towards the surface (11) of mouth, the mud (16) being circulated around from the tool (2) so as to drive the majority of the cuttings (17) up to the mouth surface (11), the traction and rotation of the tool (2) as well as the circulation of the mud ( 16) being maintained until the well (1) has been widened over its entire height. 3. - Method according to claim 2, characterized in that the bottom of the pre-existing well is located below the bottom (15) of the well (1) blind to drill so as to allow the descent of the tool (2) so that its arms (22) are at this bottom (15). 4. - Method according to claim 2 or claim 3, characterized in that the step of lowering the tool (2) is performed by adding rods (34) to a train of rods (34) at the end bottom of which and suspended the tool (2). 5. - Method according to claim 4, characterized in that the steps of rotating and pulling the tool (2) are carried out by passing the upper end of the drill string in an apparatus (31) of the type "power -swivel ", rods being removed from the train rods (34) as the tool (2) is pulled towards the surface (11) of the mouth of the well (1). 6. - Method according to claim 5, characterized in that the device (31) of the "power-swivel" type is mounted in a superstructure (3) disposed above the surface (11) of the mouth of the well ( 1). 7. - Method according to any one of claims 2 to 6, characterized in that the mud (16) is circulated by continuously introducing mud into the well (1) from its surface (11) mouth and by sucking it under the tool (2) in a tube (25, 34) to bring it through the well (1) to its surface (11) mouth. 8. - Method according to any one of claims 1 to 7, characterized in that a widening factor defined by the ratio of the diameter of the well resulting from the main operation on the diameter of the pre-existing well is chosen in particular according to the mechanical resistance of the drilling tool (2) and, the drilling tool (2) being pulled and rotated by a motor, according to the torque that the motor can deliver. 9. - Method according to claim 8, characterized in that the widening factor is between 1.15 and 1.30. 10. - Method according to claim 8 or claim 9, characterized in that a preliminary operation of the process consists in drilling a pilot well, the main operation being carried out a first time while the pre-existing well is the pilot well, then the main operation being repeated while the pre-existing well is the well resulting from the previous iteration, and this until the diameter of the blind well (1) to be drilled is reached, a final operation consisting finally in coating the well (1) and to remove the mud (16). 11. - Method according to claim 10, characterized in that the widening factor is the same at least for a series of consecutive iterations. 12. - Method according to claim 10, characterized in that the widening factor is reduced at least for a series of consecutive iterations. 13. - drilling tool for implementing a method according to any one of the preceding claims, characterized in that it comprises a body (21) adapted to rotate around the axis of the well (1) as well as arms (22) provided with elements (23) for attacking the ground, adapted to pass from an urn in the folded position on the body (21) to a deployed position to protrude from the body (21) and capable of transmitting the traction exerted on the tool (2). 14. - Tool according to claim 16, characterized in that the arms (22) are subject to the body (21) via a rack cam or hydraulic system. 15. - Tool according to claim 13, characterized in that the arms (22) are subject to the body (21) by a pivoting connection adapted to pass the arms (22) from their folded position to their deployed position. 16. - Tool according to any one of claims 13 to 15, characterized in that the arms (22) are adapted to be mounted on a series of bodies (21) each having a different diameter. 17. - Tool according to any one of claims 13 to 16, characterized in that the body (21) has a lower extension (25) adapted to let the mud pass (16) as well as cuttings (17). 18. - Tool according to claim 17, characterized in that the extension (25) is provided below with a deflector (24) in the form of an umbrella so that most of the cuttings (17) are guided towards the extension (25).

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