DESCRIPTION

The present invention relates to a device as defined in the preamble of claim 1, for ensuring continuous circulation in well drilling, particularly during insertion or removal of a drill string in wells for hydrocarbon exploration and production.

For simplicity, the present disclosure will be made without limitation with particular reference to the step of insertion of a new drill string, the same considerations being also applicable to the step of removal of drill strings, when the drilling bit must be removed from the well, e.g. for replacement.

When drilling a hydrocarbon well, the process of insertion of a drill string is required for increasing the well drilling depth.

During insertion of a new string, continuous circulation of drilling mud must be ensured throughout the process until a complete pipe is obtained and the whole hydraulic circuit is restored. Indeed, pressure drops or variations in mud circulation have been found to cause considerable structural stresses in the well being drilled, which involve collapse in uncased structures of the well being drilled.

In order to ensure such continuous circulation of drilling mud throughout the drilling process, and hence also during the steps of insertion of new drill strings or removal of existing strings, devices have been long provided, for ensuring steady circulation of drilling mud even during insertion or removal of a drill string. Devices of the above mentioned type are disposed in prior art documents US 3298385 and US 7845433.

The need to be met is to afford easy maintenance/servicing of the devices after various cycles of use. Contact with the drilling mud, which is acid and contains solid bodies, causes considerable wear of valve means, which are required to be easily removed from the tubular body for efficiency checks or for easy replacement of worn parts .

These valve means comprise a shut-off member carried by a cylindrical tubular support, which is coaxially and sealingly inserted in the tubular body of the device in an limit stop axial position. As a rule, to prevent such tubular cylindrical support from moving from the limit stop position in which it has been placed, the device comprises appropriate retainer means, ^' i.e. prismatic, generally L-shaped retainer blocks, which are partially inserted in an appropriate inner annular seat provided in the inner tubular wall of the tubular body.

These retainer blocks basically define an inner radial projection in the tubular body, which is abutted by the upper head end portion of the tubular support for the shut-off member.

The retainer blocks circumferentially extend to a preset angle, e.g. ranging from 90° to 120°, such that a plurality of said retainer blocks, i.e. three or four retainer blocks, are required, to cover the whole circumference of the tubular conduit.

In practice, removal of such retainer blocks from the inner annular seat provided in the inner tubular wall of the tubular body was found to be not easy at all. This is because drilling muds, which contact such retainer blocks, contain cement, barite, hematite and bentonite, and somewhat cause the portion of such retainer blocks inserted in said inner annular seat to be stuck therein.

Therefore, removal of the shut-off device and its tubular cylindrical support from the tubular body is a difficult and time-consuming operation, and often causes failure of the above mentioned retainer blocks .

The present invention is based on the problem of conceiving a device for ensuring continuous circulation in well drilling, particularly during insertion or removal of a drill string into and out of wells for hydrocarbon exploration and production, that has such structural and functional characteristics as to afford easy and quick replacement of the tubular cylindrical support and its shut-off member, while preventing cementation of the retainer means against the inner wall of the tubular body, thereby obviating the above mentioned prior art drawbacks .

This problem is solved by a device for ensuring continuous circulation in well drilling as defined in claim 1.

Further features and advantages of the device of the present invention for ensuring continuous circulation in well drilling will be apparent from the following description of a few preferred embodiments thereof, which are given by way of illustration and without limitation with reference to the accompanying figures, in which:

Figure 1 shows a simplified longitudinal sectional view of the device of the invention, with the lateral conduit closed by the shut-off member in a longitudinal position;

- Figure 2 shows a longitudinal sectional view of the device of Figure 1, with the axial conduit closed by the shut-off member in a transverse position;

- Figure 3 is an exploded view of the main parts of the device of Figure 1;

Figures 4a and 4b show the device of the invention in the configurations of Figure 1 and Figure 2 respectively, arrows being added to indicate the axis and direction followed by the drilling mud in two different configurations of use, according to the position assumed by the shut-off member;

Figure 5 shows a simplified diagrammatic perspective view of the device of Figure 1, in which means for positioning and centering the tubular support for the shut-off member may be seen;

- Figure 5a only shows the detail of the tubular support for the shut-off member and its seal;

- Figure 6 only shows the detail of the tubular body of the device of Figure 5; - Figure 7 shows a detail of the tubular support for the shut-off member of Figure 5a;

Figure 8 diagrammatically shows the circumferential arrangement of the positioning and centering means in the tubular body of the device of Figure 5;

Figure 9 shows a simplified perspective phantom view of a device of the invention, according to a second embodiment and with the lateral conduit closed by the shut-off member in a longitudinal position;

- Figure 10 shows an outer plane view of the device of Figure 9;

- Figure 11 shows a sectional view as seen along the longitudinal section line Ά-Α of Figure 10, with the lateral conduit closed by the shut-off member in a longitudinal position;

- Figure 12 shows a sectional view as seen along the longitudinal section line A-A of Figure 10, with the axial conduit closed by the shut-off member in a transverse position;

- Figure 13 shows a simplified exploded view of the main parts of the device of Figure 11;

- Figures 14a and 14b show the device of Figure 9 in the configurations of Figure 11 and Figure 12 respectively, arrows being added to indicate the axis and direction followed by the drilling mud in two different configurations of use, according to the position assumed by the shut-off member;

- Figure 15 shows a simplified partially phantom perspective view of the device of Figure 9, in which means for positioning and centering the tubular support for the shut-off member may be seen and

- Figure 15a shows an enlarged view of Figure

15.

Referring to the accompanying figures, numeral 1 generally designates an inventive device for ensuring continuous circulation in well drilling, namely a device for ensuring continuous circulation in well drilling particularly during insertion or removal of a drill string into or out of wells for hydrocarbon exploration and production.

It shall be noted that both the inventive device as shown in Figures 1 to 8 and the inventive device as shown in Figures 9 to 15 have been designated by numeral 1. Furthermore, it shall be noted that in both devices 1 the same numerals have been used to designate the same elements or structurally and/or functionally similar elements, although any notable difference between the two different embodiments will be highlighted throughout the disclosure.

The device 1 comprises:

- a substantially tubular body 2 extending in a preset axial direction X-X from an upstream end 2a to a downstream end 2b, the tubular body 2 being shown as having a circular cylindrical section;

- an axial conduit extending from the upstream end 2a to the downstream end 2b, for drilling mud to flow therethrough in the device 1;

first threaded connection means at the upstream end 2a for connection of the downstream end 2b of the device 1 to one end of a drill string;

second threaded connection means at the downstream end 2b for connection of the downstream end 2b of the device 1 to one end of a drill string;

- a lateral opening 3 located in the tubular body 2 between the upstream end 2a and the downstream end 2b to define a lateral conduit in the device 1, in fluid communication with the above mentioned axial conduit, the axial conduit having an axis Y-Y which is preferably perpendicular to the axis X-X of the axial conduit;

- a plug 5 removably fitted into the lateral opening 3 in a pressure-tight manner by a threaded nut-screw engagement, - valve means 6 located in the axial conduit to block the drilling mud and stop its flow from the upstream end 2a to the downstream end 2b;

wherein :

- these valve means comprise a shut-off member 6 that is movably supported in the axial conduit to move from a position transverse to the axial conduit (see Figures 2 and 4b for the first embodiment and Figures 12 and 14b for the second embodiment) , in which the shut-off member 6 extends transverse to the axis of the axial conduit to stop fluid continuity between the upstream end 2a and the downstream end 2b in the axial conduit, and a longitudinal position relative to the axial conduit (see Figures 1, 4a and

5 for the first embodiment and Figures 11 and 14a for the second embodiment), in which the shut-off member

6 substantially extends along the axis of the axial conduit and is located close to a side wall portion within the tubular body 2;

- in such transverse position (see Figures 2 and 4b for the first embodiment and Figures 12 and 14b for the second embodiment) the shut-off member 6 is located between the lateral conduit and the upstream end 2a of the tubular body 2 to be placed upstream from the above mentioned lateral opening 3, relative to the flow of the. drilling mud in the axial conduit from the upstream end 2a to the downstream end 2b and

- in such longitudinal position (see Figures 1, 4a and 5 for the first embodiment and Figures 11 and 14a for the second embodiment) the shut-off member 6 closes in a pressure-tight manner the lateral opening 3 to stop fluid continuity between the lateral conduit and the axial channel of the tubular body 2.

Concerning drill strings, it shall be noted that, according to an applicable industry standard, these have a male threaded lower end and an opposed nut threaded upper end, which is designed for nut- screw engagement with the lower end of another drill string. According to this standard, in the device 1 the first screw connection means of the upstream end 2a consist of a nut screw, and the second screw connection means of the downstream end 2b consist of male screw threads, said nut screw and said male screw threads being equal to said nut threads and said male screw threads provided at the upper and lower ends respectively of each drill string.

At the lateral opening 3, the tubular body 2 of the device 1 has a seat for the shut-off member which is designed for pressure-tight engagement by the shut- off member 6, when such shut-off member is in the above mentioned longitudinal position (see Figures 1, 4a and 5 for the first embodiment and Figures 11 and 14a for the second embodiment), such seat for the shut-off member allowing the lateral opening 3 and the lateral channel defined thereby to be closed in a pressure-tight manner, as mentioned above.

Preferably, such seat for the shut-off member is an inserted seat 7, and is associated in integral and pressure-tight fashion with the tubular body 2. In accordance with the illustrated embodiments, the inserted seat 7 for the shut-off member is defined by a threaded ring nut, having:

- an outer portion with male screw threads, for pressure-tight nut-screw engagement with corresponding nut threads provided at the lateral opening 3, and

an inner portion with nut threads, for pressure-tight screw engagement with the male screw threads of the plug 5.

Alternatively, the above-mentioned inserted seat for the shut-off member may be formed as a one-piece with the tubular body 2, and an inserted seat for the shut-off member welded to the tubular body or secured thereto in a manner other than the above described screw connection, may be also used. Similarly, it shall be noted that the screw engagement between the plug 5 and the inserted seat 7 for the shut-off member is a preferred embodiment, although different removable pressure-tight connection arrangements may be provided.

In any case, the inserted seat -7 and the plug 5 should have small dimensions, and be at the most flush with the footprint of the outer wall of the tubular body 2, to prevent any radially projecting portion of the tubular body 2 of the device from creating interferences in the well being drilled.

Preferably, the shut-off member 6 comprises a convex, preferably a partially spherical portion/wall, whose convexity faces the lateral opening 3. This spherical portion/wall engages such inserted seat 7 for the shut-off member in a pressure-tight manner, when the shut-off member 6 is in the above mentioned longitudinal position (see Figures 1, 4a and 5 for the first embodiment and Figures 11 and 14a for the second embodiment) .

Preferably, the above-mentioned valve means consist of a flapper valve having a diaphragm shut- off member 6, which is connected by hinge connection means, at a peripheral portion thereof, to an axis of rotation 8, said diaphragm 6 moving from such longitudinal position (see Figures 1, 4a and 5 for the first embodiment and Figures 11 and 14a for the second embodiment) to such transverse position (see Figures 2 and 4b for the first embodiment and Figures 12 and 14b for the second embodiment) , and vice versa, by rotating about such axis of rotation 8. Such axis of rotation 8 :

- extends transverse, preferably perpendicular, to the longitudinal axis X-X of said axial conduit;

- is placed close to the inner wall of said tubular body 2;

is circumferentially placed to be substantially located at said lateral opening 3 and is located substantially proximate to said lateral opening 3 in the portion of the tubular body 2 located between said lateral opening 3 and the upstream end 2a of the tubular body 2.

As a result, when the tubular body 2 is placed with the longitudinal axis substantially in a vertical orientation, with the upstream end 2a located at a higher level than the downstream end 2b:

- the above mentioned hinge connection means and the axis of rotation 8 are placed above the through opening 3 and

- due to its weight force the shut-off member 6 to move to the above mentioned longitudinal position (see Figures 1, 4a and 5 for the first embodiment and Figures 11 and 14a for the second embodiment) , in which it seals the lateral opening 3.

According to both illustrated embodiments, the shut-off member 6 and the hinge connection means are supported by a tubular support 9 for the shut-off member, which is diagrammatically shown in Figure 5a, and is concentrically fitted in a pressure-tight manner into the tubular conduit defined in the tubular body 2 from the upstream end 2a to an axial end-of stroke position as defined by positioning and centering means, 11, 12 for the first embodiment and 31, 32, 33 for the second embodiment.

As shown in the figures, seal means 24 are provided between the tubular support 9 and the inner tubular wall of the tubular body, to afford pressure tightness. For this purpose, an annular seat is provided In the exterior of the tubular support 9, in which the seal means 24 are housed in outwardly projecting arrangement for interference with the inner tubular wall of the tubular body 2.

Preferably, in the first embodiment as shown in Figures 1 to 8, these positioning and centering means 11, 12 define a polarized insertion key, which is adapted to allow insertion of the tubular support 9 into the tubular conduit defined in the tubular body 2 to said limit stop axial position only when the tubular support 9 is properly angularly rotated relative to the axis X-X of the axial conduit such, in the above mentioned longitudinal position (see Figures 1, 4a and 5) the shut-off member 6 is located over said lateral opening 3 (namely in pressure-tight engagement relationship with the seat 7 for the shut- off member) for pressure-tight closure thereof.

According to the embodiment as shown in Figures 1 to 8, the above mentioned positioning and centering means comprise a plurality of supporting pawls 11, which radially project out of the inner tubular wall of the tubular body 2 into the axial conduit, as well as a corresponding plurality of recesses 12 provided in the outer wall of the tubular support 9.

More in detail, the tubular body 2 comprises three distinct supporting pawls 11, preferably located on the same diametral plane, which are in such position that a first pawl 11a is circumferentially spaced from the two remaining pawls lib by a first angle, other than a second angle that circumferentially separates the two remaining pawls lib. In the example of Figure 8, the first angle is 130° and the second angle is 100°.

Likewise, the tubular support 9 comprises three recesses 12, i.e. a first recess designed for engagement by the first pawl 11a and two remaining recesses designed for engagement by the remaining pawls lib.

It shall be noted that the above mentioned recesses 12 consist of grooves formed in the outer tubular wall of the tubular support 9 from the head end 9b of such support facing the downstream end 2b of the tubular body 2.

With the above described circumferential arrangement of the supporting pawls 11 and the recesses 12, it will be appreciated that, according to the first embodiment, the introduction of the tubular support 9 into the conduit of the tubular body 2 from the upstream end 2a thereof until the head ends 23 of the recesses 12 abut their respective pawls is only allowed at a single, particular circumferential position of the tubular support 9 about the axis X-X of the tubular body 2.

This arrangement is the above mentioned polarized insertion key, which is adapted to ensure that, in such longitudinal position (see Figures 1, 4a and 5), the shut-off member 6 will be located exactly at the lateral opening 3, thereby providing the above mentioned pressure-tight engagement with the seat 7 for the shut-off member.

Preferably, the two remaining recesses have such a circumferential width as to allow insertion of their respective supporting pawls lib with a circumferential clearance, whereas the circumferential width of the recess 12a allows its respective supporting pawl 11a to fit therein with a reduced clearance. Preferably, the above mentioned recess 12a is shaped with a lead-in flare (see Figure 7) at the head end 9b of the tubular support 9, for facilitated insertion of the supporting pawl 11a into the recess 12a.

As an alternative to the above, the positioning and centering means may have different shapes and/or the polarized insertion key between the tubular body 2 and the tubular support 9 may be obtained in a structurally or functionally different manner, the above arrangement having the advantage of being simple, reliable, easily connectable and inexpensive.

Thus, for example, according to the second embodiment as shown in Figures 9 to 15, the above positioning and centering means comprise:

- a through hole 31 provided in the wall of the tubular body 2 perpendicular to the axis X-X,

- a blind hole 32 provided in the outer wall of the tubular support 9 perpendicular to the axis X-X and

- a pin 33 adapted to fit into the through hole 31 of the tubular body 2 to engagement of the blind hole 32 of the tubular support.

The through hole 31 and the blind hole 32 are placed in such positions relative to the tubular body 2 and the tubular support 9, as to be exactly aligned when the tubular support 9 is properly angularly rotated about the axis X-X of the axial conduit such that, in the above mentioned longitudinal position (Figures 11 and 14a) , the shut-off member 6 is located over said lateral opening 3 (namely in pressure-tight engagement relationship with the seat 7 for the shut-off member) for pressure-tight closure thereof .

Therefore, the engagement of the pin 33 in the through hole 31 and the blind hole 32 confirms proper positioning of the tubular support 9 in the tubular conduit 2. It shall be noted that, in the case of the second embodiment (Figures 9 to 15), the proper depth of insertion of the tubular support 9 in the axial channel of the tubular body 2 is ensured by abutment of the head end 9b of the tubular support 9 against an inner annular shoulder 34 of the annular body 2.

The above mentioned pin 33 is carried by a support plate 35, which is mounted to the tubular body 2 from the outside by means of fastening screws 36. For this purpose, a seat 37 is provided in the outer wall of the tubular body 2 for receiving the support plate 35, the insertion of the support plate 35 in the receiving seat 37 confirming that the pin 33 is also inserted in the blind hole 32 of the tubular support 9 and hence that the tubular support 9 is properly positioned (both axially and angularly) within the tubular body 2.

Preferably, the above mentioned support plate 35 axially extends to engagement of an outer seat for the removable plug 5, thereby also acting as a safety feature to prevent rotation and hence loosening of the removable plug 5.

The device 1 further comprises retainer means 13 for maintaining the tubular support 9 inserted in the axial conduit, in the above mentioned limit stop axial position.

These retainer means 13 comprise:

- a plurality of retainer elements 14, placed in said tubular conduit in a circumferentially offset position and close to the head end 9a of the tubular support 9 facing the upstream end 2a of the tubular body 2, said retainer elements 14 acting as retainer means to prevent the tubular support 9 from axially moving toward the upstream end 2a of the tubular body 2;

- an inner seat 15 provided in the inner tubular wall of said tubular body 2, which only houses a first portion of the retainer elements 14, a second portion of the retainer elements 14 projecting out of the inner tubular wall of the tubular body 2 into the axial channel and

- a locking guide 16 for maintaining said first portion of the retainer elements within the inner seat 15.

The above mentioned plurality of retainer elements 14 comprise a great number of retainer elements 14, more than ten, preferably at least fifteen, for covering substantially the entire circumferential extent of the inner annular seat 15.

In practice, the above mentioned retainer elements 14 are circumferentially offset along the inner annular seat 15 in substantially juxtaposed relationship, to define as a whole an annular retainer element whose inside diameter is smaller than the inside diameter of the lateral opening 3.

With the respective second portions projecting out of the inner tubular wall of the tubular body 2 into the axial channel, the above mentioned plurality of retainer elements 14 can accomplish as a whole an effective and uniform retaining action on the upper head of the tubular support 9 for the shut-off member, while avoiding cementation problems that might occur during disassembly and servicing of the device 1.

Indeed, each retainer element 14 circumferentially covers a limited circumferential arc of the inner annular seat 15 (e.g. less than 30°, more preferably less than 25°), therefore each retainer element 14 can be easily removed from the inner annular seat 15 even though it is cemented therein, without damaging the inner annular seat 15. This is allowed by the small size of the retainer elements 14, requiring not particularly large forces to remove each retainer element 14 from the inner annular seat 15, even when it is cemented in the inner annular seat 15. Furthermore, once the first retainer element has been removed, the remaining retainer elements 14 may be easily acted upon, e.g. by a high-pressure water jet or a bit, for easy removal thereof from the inner annular seat 15 without causing any damage.

According to the first embodiment shown in Figures 1 to 8, the retainer elements 14 have a spherical shape or comprise spherical surface portions .

Preferably, the above mentioned first portion of the spherical retainer elements 14 inserted in the inner seat 15 is about 40-55% the volume of the spherical retainer elements 14. More preferably, the above mentioned first portion of the spherical retainer elements 14 is substantially the half part of the spherical retainer elements 14.

Preferably, the above mentioned inner seat 15 comprises a hemispherical profile matching the profile of said first portion of said spherical retainer elements 14.

Preferably, the above mentioned inner seat 15 is an annular . seat .

Preferably, a circumferential groove 26 is provided in the inner annular seat 15, for receiving magnets, preferably in the form of annular sectors or an open ring 18, whereby the spherical retainer elements 14 can be held in position in the inner annular seat 15 during assembly of the device 1, namely prior to positioning of the locking guide 16.

Instead of or in addition to the provision of the above mentioned magnets in the inner annular seat 15, the retainer elements 14 may be provided in the form of magnetic element. This may be achieved by magnetizing the spherical retainer elements 14 or associating magnets therewith.

Concerning the above mentioned locking guide 16 for locking the spherical retainer elements 14, it will be appreciated that it may be conveniently held in position within the tubular conduit 2, against the inner wall of the tubular conduit 2, using a Seeger ring 19, which engages in part an inner circumferential groove 20 provided in the inner tubular wall of the tubular body 2 and in part a circumferential groove 21 provided in the outer wall of the locking guide 16.

According to the second embodiment shown in Figures 9 to 15, the above mentioned retainer elements 14 comprise a plurality of rollers located with their respective axes parallel to the longitudinal axis X-X of the tubular body 2.

By way of example and without limitation, the diameter of these roller retainer elements 14 preferably ranges from 10 to 30 mm, and is more preferably about 15 millimeters, whereas the height of the inner annular seat 15 is of the order of 10-20 mm, as measured in the axial direction X-X.

Preferably, the above mentioned first portion of the roller retainer elements 14 inserted in the inner seat 15 is about 40-55% the volume of the roller retainer elements 14. More preferably, the above mentioned first portion of the roller retainer elements 14 is substantially the half part of the roller retainer elements 14.

Preferably, the inner seat 15 comprises a profile matching the profile of said first portion of said roller retainer elements 14, thereby affording optimal support/accommodation of the roller retainer elements 14 in the annular inner seat 15, particularly in the axial direction X-X.

Like in the first embodiment of the device 1 of the invention, a circumferential groove (not shown) may be provided in the inner annular seat 15, for receiving magnets, preferably in the form of annular sectors or an open ring, whereby the roller retainer elements 14 can be held in position in the inner annular seat 15 during assembly of the device 1, namely prior to positioning of the locking guide 16.

Instead of or in addition to the provision of the above mentioned magnets in the inner annular seat 15, the roller retainer elements 14 may be provided in the form of magnetic rollers.

Concerning the above mentioned locking guide 16 for locking the roller retainer elements 14, it will be appreciated that it may be conveniently held in position within the tubular conduit 2, against the inner wall of the tubular conduit 2, using a Seeger ring 19, which is housed in an inner circumferential groove 20 provided in the inner tubular wall of the tubular body 2 directly above the locking guide 16.

The outer tubular wall of the locking guide 16 comprises a circumferential groove, in which an CD- ring is housed with a portion projecting outwards. This CD-ring provides pressure-tightness between the outer annular wall of the locking guide 16 and the inner wall of the tubular conduit 2.

Preferably, the devices 1 of both embodiments comprise magnetic means 22 for exerting an attractive force on the shut-off member 6 in the longitudinal position (see Figures 1, 4a and 5 for the first embodiment, and Figures 11 and 14a for the second embodiment) , or in a position proximate thereto, and/or for holding it in said longitudinal position with a preset load, such that only when a force that can exceed such magnetic attractive force is exerted on the shut-off member 6, such shut-off member 6 may be moved toward the above mentioned transverse position (see Figures 2 and 4b for the first embodiment and Figures 12 and 14b for the second embodiment) .

Preferably, these magnetic means 22 have a ring shape, although magnets having the shape of annular sectors, disks or others may be used and placed on/in the plug 5.

According to the illustrated embodiments, these magnetic means are carried by the plug 5, preferably by the inner side of the plug 5, i.e. the side of the plug 5 that faces the above mentioned axial channel when the plug 5 is applied to close the lateral opening 3 in a pressure-tight manner.

According to an embodiment that is not shown in the figures, the above mentioned magnetic means may comprise one or more magnets carried by the shut-off member at the side of the shut-off member 6 that faces the lateral opening 3 when the shut-off member 6 is in the above mentioned longitudinal position, whereby such magnets may interact with the inner wall of the tubular body 2, with the seat 7 for the shut- off member and/or preferably with a portion of the plug 5. These magnetic means may also have a ring shape and are applied to the side of the shut-off member 6 that faces the lateral opening 3 when the shut-off member 6 is in the longitudinal position. This is particularly advantageous when the shut-off member 6 has a substantially circular shape, because the magnetic ring may be applied to the shut-off member 6 in concentric arrangement.

Possibly, the above mentioned magnetic means 22 may be arranged to be carried both by the plug 5 and by the shut-off member 6, in which case the magnets of the plug and the shut-off member should be arranged in substantially facing positions, for mutual magnetic attraction when the shut-off member 6 is in the above mentioned longitudinal position (see Figures 1, 4a and 5 for the first embodiment and Figures 11 and 14a for the second embodiment) .

Concerning the attractive force that attracts the shut-off member 6 toward the plug, it will be appreciated that such attractive force is useful during the transient steps in which the shut-off member 6 is carried from the above mentioned transverse position to the longitudinal position. Indeed, when the drilling mud flows along the axial channel from the end 2a to the end 2b, the mud flow itself pushes the shut-off member and holds it in the above mentioned longitudinal position. Therefore, the magnets 22 help the shut-off member 6 to adhere against the inserted seat 7 prior to the action of the inner pressure of the drilling mud.

Once the adapter has been mounted and the mud flow has been deflected from the axial to the radial direction, the flow will open the shut-off member without having to overcome any magnetic attraction, as magnets have already been removed with the plug (as they were joined to the plug) .

Preferably, there is no direct contact between the plug 5 and the shut-off member 6, a minimum distance being always provided therebetween, to avoid that residual mud prevents the shut-off member to reach the above identified longitudinal position (see Figures 1, 4a and 5 for the first embodiment and Figures 11 and 14a for the second embodiment) in which it seals the lateral opening.

As a result, when the shut-off member 6 is in the above mentioned longitudinal position (see Figures 1, 4a and 5 for the first embodiment and Figures 11 and 14a for the second embodiment) , a closed chamber is defined between the shut-off member 6 and the plug 5. In order to provide depressurization of such chamber, according to a preferred embodiment the plug 5 comprises an axial through opening (not shown) at which a discharge valve (not shown) is located, which is adapted to be actuated in a pressure-tight closed state and an open state, for respectively obstructing and allowing the passage of fluid through the through opening, in the latter case allowing the passage of the drilling mud.

Therefore, by opening the above mentioned discharge valve, any drilling mud retained thereby may be evacuated, which will improve the stability of the shut-off member in the longitudinal position (see Figures 1, 4a and 5 for the first embodiment and Figures 11 and 14a for the second embodiment) , and will ensure pressure-tight closure of the lateral passage.

Preferably, the above identified magnetic means 22 are applied to the plug 5 in such a way to be disposed around said through opening where the discharge valve is housed.

As clearly shown in the above description, the device 1 of the present invention fulfills the above mentioned need and also obviates prior art drawbacks as set out in the introduction of this disclosure. The provision of a great number of the above mentioned retainer elements affords an effective retaining action on the upper head of the tubular support and avoids, for the above described reasons, the problems occurring during disassembly and/or servicing of the device of the invention, due to cementation of the retainer elements in the inner annular seat of the tubular conduit.

Particularly, the use of rollers or spherical retainer elements obviates the problems that occur upon sticking and cementation thereof in the corresponding spherical inner annular seat of the tubular body when the tubular support must be removed for maintenance. In this case, the first portion of the spherical retainer elements allows the axial force exerted thereon by the tubular support to be directly discharged to the walls of the inner annular seat of the tubular body.

Advantageously, the provision of magnetic means housed in the inner annular seat of the tubular body allows the spherical retainer elements to be held in position in the inner annular seat during assembly of the device, namely prior to positioning of the locking guide.

Those skilled in the art will obviously appreciate that a number of changes and variants may be made to the above device, still within the scope of the invention, as defined in the following claims.

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