WO2007065986A1

WO2007065986A1 - Connection assembly for drill collars or heavy drill pipes

Info

Publication number: WO2007065986A1
Application number: PCT/FR2006/002629
Authority: WO
Inventors: Francois Kessler
Original assignee: Francois Kessler
Priority date: 2005-12-06
Filing date: 2006-12-01
Publication date: 2007-06-14
Also published as: DK1957850T3; ATE430280T1; US20080289879A1; EP1957850A1; FR2894279B1; EP1957850B1; DE602006006594D1; FR2894279A1

Abstract

The invention relates to a connection assembly (100) for drill collars or heavy drill pipes comprising: a male connection element which comprises, in its longitudinal direction, an at least partially threaded conical surface portion which tapers from the first portion towards its free end; a female connection element which comprises an at least partially threaded conical inner surface and a cylindrical inner surface (220), said two connection elements being complementary so that one can be assembled in the other by screwing, characterized in that the male connection element additionally comprises, between its free end and said conical surface portion, another surface portion whose conicity is less than that of said surface portion and which is dimensioned with respect to said cylindrical inner surface (220) such that there is a clearance by virtue of which these two surfaces bear one against the other when the assembly is subjected to a bending stress.

Description

Connection set for drill rods or heavy drill rods

The present invention relates to fittings for tubular or cylindrical elements and more particularly to fittings intended to form a column of elements for drilling wells, in particular oil wells. More specifically, it relates to a connector assembly for drill rods and / or heavy drill rods.

When drilling a well in the ground, it is necessary to connect portions of tubular conduits or other cylindrical elements so as to form a column or a train of elements making it possible to reach the desired depth. In the field of oil drilling, aimed at the extraction of liquid or gaseous hydrocarbons, it is fundamental that these connections guarantee, at the level of the assemblies of the elements, in particular structural resistance and resistance to pressure.

A drill string consists, generally, respectively from top to bottom, of four types of elements:

drill rods (in English: drill pipes)

- heavy rods (in English: heavy weight drill pipes)

drill rods (in English: drill collars)

drilling tool.

These three types of rods are drilled axially right through to provide a passage for the fluids to be extracted or injected during drilling.

These different types of rods are mainly distinguished by the fact that:

the drill rods are, by unit, the lightest of these three types of rods. They are generally an assembly by welding of a tube and two fittings (tool attached in English). The drill rods serve as a link between the tool and the surface, they are generally in tensile stress and serve to transmit the torque and the drilling fluid to the tool.

the heavy rods have a much larger section than the drill rods and can be in one piece; they are often stressed in flexion and have external bulges on the body (wear pads in English) in order to reduce contact and therefore wear on the walls of the well. They are useful as transition elements between drill rods and drill rods. They considerably reduce the vibrations generated by the cutting of the rock by the tool.

the drill sticks have very thick walls (of the order of several inches or several tens of millimeters); they are often machined in a spiral on their external part in order to leave a passage for the drilling fluid between the external surface of the rod mass and the wall of the well, this in order to reduce bonding by differential pressure. They can also receive external machining to facilitate their maneuver or their implementation ("slip and elevator recess" in English). They contribute by their weight to exert a cutting force on the drilling tool and to tension the drilling rods.

The set of heavy rods, drill rods and the drilling tool is sometimes called (in English) "Bottom HoIe Assembly".

The aim of the present invention is to connect the lower elements of such a drill string.

The gravity acting, in particular, on the heavy rods and mass rods makes it possible to use them in compression in order to apply a force of penetration to the cutting elements of the drilling tool at the lower end of the drilling column. The quantity of heavy rods and mass rods used in a given column depends on the load that one wishes to apply to the drilling end. In addition, the elements of the drill string are rotated to give a cutting movement to the drilling tool located at its lower end.

The elements of the drill string and in particular the drill rods and the heavy rods are therefore both stressed in compression and in torsion.

The rods constituting the drill string are provided with connections at each of their ends making it possible to assemble them to each other, in order to obtain a desired configuration.

Usually, this type of connection is made using complementary threaded surfaces arranged at the ends of the elements to be assembled, on male and female portions respectively, usually using seals enclosed by two suitable surfaces of said two portions. In general, these are conical threads with a large pitch (several millimeters) in order to facilitate rapid assembly (a fraction of a turn necessary for tightening).

Such tapered thread fittings for oil drilling elements have been standardized in API Specification 7 considered here for reference (API: American Petroleum Institute).

A connector as defined by this standard is composed of a male element comprising a shoulder and an at least partially threaded conical portion extending from this shoulder to the free end of this element and of a complementary female element having a first internal conical surface threaded with the same conicity as the conical surface of the built-up element, but shorter than this, and extended by another smooth internal conical surface with a smaller conicity than said first conical surface.

A problem encountered in this technical field and in particular with this type of fittings results from the fact that the elements of the drill string, in particular the drill rods and the heavy rods, have radial dimensions several times less than their longitudinal dimensions (typically, for a heavy rod: 900cm in length for a diameter of 25cm). In addition, the diameter of the boreholes in which the heavy rods and the drill rods are used is much greater than their own diameter. In general, the diameter of such a borehole is 17 Vz inches (about 44.5 cm).

Consequently, being subjected to compressive stresses, these columns of drilling elements are naturally stressed to deform in buckling in the drilled hole. This buckling results locally in bending forces, in particular at the level of the connections between the elements constituting the column. In practice, these connections constitute geometric discontinuities, (in particular due to the reductions in section) relative to the rest of the column; they are therefore, in the event of buckling of the latter, the place of stress concentrations, that consequently significant risks of rupture at this level.

In particular, the torsional forces combined with repeated bending forces at the connections typically lead to fatigue failure problems caused mainly by stress concentrations on the female element, in particular on the circle forming the boundary between said two conical interior surfaces. It has been found, in practice, that ruptures caused by fatigue phenomena take place along this circle, portions of which are sometimes stressed in compression, sometimes in tension according to the random angular orientation of the buckling of the column.

The present invention aims to overcome these drawbacks and relates to a connection assembly for drilling elements, which best meets the API Specification 7 standard but which makes it possible to withstand high internal stresses, resulting from torsional, compression and buckling forces. of the drill string, and thus avoid the rupture of elements of the fitting, in particular by fatigue phenomenon. More particularly, it aims to reduce the maximum value of the local stresses observed at the connection.

To this end, it offers a connector assembly for heavy rods or drill rods comprising:

a male connector element having substantially a shape of revolution about a longitudinal axis and which comprises in its longitudinal direction respectively:

a first substantially cylindrical portion forming a shoulder at one of its ends,

- a second portion of conical surface at least partially threaded and tapering from the first portion towards the free end of the element

a substantially cylindrical female connector element, complementary to said male connector element, and which comprises:

a radial portion forming a bearing face for said shoulder of the first element and, longitudinally, coaxially and respectively, from this portion, an at least partially threaded conical inner surface complementary to the at least partially threaded conical surface of the male element,

a cylindrical inner surface

said two connecting elements being intended to be assembled into one another by screwing on several turns of the threads, characterized in that the male connecting element comprises, in addition, between said second portion and its free end, a third portion of conical surface less than that of the second conical surface portion, and dimensioned with respect to said cylindrical inner surface so that there is a clearance thanks to which, during a stress in bending of the assembly, these two surfaces respectively come into abutment.

Thus, the present invention makes it possible to reduce the stresses observed at the level of the connections, resulting in particular from the buckling of the elements, and thus to increase the resistance to rupture by fatigue at the level of the connections.

Preferably, the female element takes up the standard dimensions defined by the API Specification 7 standard and the male element is the only element of the connector assembly to be modified while being compatible with standard female elements according to this standard.

Thus, the invention further provides a male connector element for heavy rods or drill rod drills intended to cooperate with a female element and having substantially a shape of revolution around a longitudinal axis and which comprises in its longitudinal direction respectively:

a second portion of conical surface at least partially threaded and tapering from the first portion towards the free end of the element,

characterized in that the male connector element further comprises, between said second portion and its free end, a third portion of conical surface less than that of the second portion of conical surface.

In fact, it has already been proposed by document FR-2 508 970 to use cylindrical guide bearing surfaces on each of the elements to be assembled, on either side of the threaded conical portions, said bearing surfaces being dimensioned so that that they are nested one inside the other before the threads come into engagement, with the objective of ensuring a correct alignment of these prior to screwing, to avoid any damage to the threads. However, this document is in a field very different from that of oil drilling since it is located in the field of surface casing, especially at sea.

The tubular elements described by this document are not actual drilling equipment. They are used almost statically during the exploitation of a drilled hole, and are not subjected to torsional and compression forces that are encountered in drilling equipment. These elements are only subjected to tensile forces exerted by their own weight. The role of the connections between these elements is limited to ensuring the seal between said elements and the external environment. The mechanical stresses which apply to these casing elements are therefore completely different from those of the present invention. In addition, on the type of casing described in document FR 2 508 970, the main problem is to guide the thread when assembling two elements so as not to damage it during screwing.

Conversely, the connections between drill pipes, object of the present invention, generally do not pose a screwing problem, and do not require guide elements.

However, the present invention aims to reduce, at the connections between drilling elements, the concentration of stresses generated by the buckling resulting from the compression / twisting forces acting on the column.

It follows from the above, that a person skilled in the art seeking to improve the fittings for drilling elements has a priori no reason to call on the knowledge of the diametrically opposite technical field of fittings for casings for extraction, especially as the standards applicable to drilling are very strict and dissuade in practice the person skilled in the art from seeking to retouch them.

Document US Pat. No. 5,908,212 has a tool connection with high torque resistance, with two shoulders, implying the abutment of shoulders situated on either side of the threaded zone respectively on the male and female portion. , which excludes any possibility of consumption of the clearance between the nose of the male element and the internal surface of the corresponding female element. Thus, such a tool fitting is unable to solve the problem of reducing the maximum value of the local stresses observed at the fitting.

The same goes for document WO 2005/095840 A1, which describes a tool seal with high torque resistance, with double shoulder, which also excludes any possibility of consumption of the clearance, for the same reasons.

According to advantageous characteristics of the invention, possibly combined: the male element has a groove disposed between said second portion and said third portion, such that, when said two elements are assembled, and when said shoulder is in abutment against the radial bearing face, the geometric limit between said conical inner surface and said cylindrical inner surface is included in the space formed by said groove;

- The third surface portion of the male element forming a bearing is substantially cylindrical;

- Said portion is partially conical at its free end;

- Said taper is less than that of the second conical portion at least partially threaded;

the third portion has a longitudinal dimension at most equal to 2/3 of the longitudinal dimension of the second portion;

- The third portion has a longitudinal dimension between 10% and 50% of its diameter;

- the groove has a radius of curvature between ^Λ A and 3 inches, or approximately between 12 millimeters and 76 millimeters depending on the diameter of the fittings.

- the two elements are axially drilled and through. Thus, the present invention proposes to distribute the stresses on either side of the limit between the two surfaces, without stressing this critical area directly by mechanical contact.

In other words, for the same bending of the connector, the invention proposes to distribute the forces resulting from this bending over a higher contact surface between the two elements constituting the connector, and therefore to reduce the value of the maximum stresses observed. (the constraint being by definition a force per unit of surface).

In addition, the fact of adding a slightly conical, or even cylindrical, range beyond this critical zone, makes it possible to move part of the forces on a surface more distant from the free end of the female element towards a portion of this female element where the walls have a larger section allowing them to better resist mechanical stresses. The characteristics and advantages of the invention will emerge from the description which follows, given by way of illustration and in no way limiting, with reference to the appended drawings in which:

Figure 1 is a longitudinal sectional view of a conventional female element in itself, in accordance with the API standard.

FIG. 2 is a view in longitudinal section of a built-up element according to the invention,

Figure 3 is a longitudinal sectional view of the two aforementioned elements in the assembled state according to the invention.

As can be seen in FIG. 3, a connector assembly 100 according to the invention is composed of a maie element 300 and a female element 200 assembled. These two elements are respectively visible in isolation in FIGS. 2 and 1.

The male connector element 300 has a shape of revolution and comprises in its longitudinal direction a first substantially cylindrical portion 302 shaped at one of its shoulder ends 301, and intended, at its opposite end, to cooperate with a column element of drilling (not shown), a conical portion 310 provided with a thread 311, a groove 320 being provided between said substantially cylindrical portion 302 shaped as a shoulder 301 and the conical portion 310, and a substantially cylindrical portion 330 forming the end of the element 300, and connected to the conical portion 310 by a groove 340.

This groove advantageously has a radius of curvature between ^Λ A and 3 inches depending on the diameters of the fittings, that is to say between approximately 12 millimeters and 76 millimeters.

The connection element 300 is pierced at the end intended to cooperate with a column element of a substantially cylindrical bore 350 terminated by a conical portion 360 widening to open at the opposite end of the connection element 300 .

The female connector element 200 also opens out and has a substantially cylindrical external shape, and, at its end opposite the end intended to cooperate with a drill string element (not shown), a radial face 201 forming face d support for cooperating with said shoulder 301, and, in the longitudinal direction, coaxially respectively, a portion of conical inner surface 210 partially provided with a thread 211 complementary to the conical surface 310 provided with the thread 311, a substantially cylindrical interior surface portion 220 intended to cooperate with the cylindrical portion 330 in free adjustment and preferably just sliding, a conical interior surface portion 230 of the same conicity as the portion 210 , an inner surface portion 240 of substantially higher taper than the portion 210, and a cylindrical surface portion 250 opening at the end intended to cooperate with a drill string element (not shown).

As shown in Figure 3, when the two elements 200 and 300 are assembled, the shoulder 301 is in abutment against the radial surface 201, and the range 330 substantially opposite the range 220, a slight play, exaggerated for clarity in the figure, being visible between these two staves. This clearance is advantageously of the order of an H7g6 adjustment, for example (according to NF R91-011).

The contact between the shoulder 301 and the radial surface 201 seals the assembly.

The groove 340 is located between the conical surface 210 and the cylindrical surface 220, substantially opposite the circle 260 forming the boundary between these two surfaces.

Thus, during a bending stress on the assembly 100, the two surfaces forming bearing 330 and 220 come into contact then in support, which makes it possible to distribute the forces, reduce the stresses observed at the level of the female element, without the critical circle and its immediate vicinity being contacted.

It should be noted that the grooves 320 and 340 can be used for engaging and disengaging a cutting tool used for machining the thread 311 of the part 310 that they frame. The thread 311 can, however, be produced by any other method.

Furthermore, the two grooves can also serve as relaxation grooves for pressurized fluids in order to contribute to the tightness of the assembly.

Advantageously, these two grooves can receive seals (not shown), for example O-rings, in order to improve the tightness of the connector.

Alternatively or in addition to the above, a groove (not shown) can be machined in the bearing 330 in order to accommodate a seal sealing, for example an O-ring, always with a view to improving the sealing of the assembly, in particular during an erupting drilling, for example.

Advantageously, the bearing 330 can be not cylindrical but slightly conical (with a taper less than that of the threaded portions), at least partially, at its free end, to facilitate linear contact with bearing 220 in the event of bending of the assembly , and ensure better distribution

(distribution) of the constraints.

These elements advantageously comply with the API Specification 7 standard.

More precisely, the elements advantageously have the following dimensions, given by way of example (for an NC50 type connection according to the API standard):

maximum internal diameter of the portion 210: approximately 153 millimeters;

- minimum internal diameter of the portion 210: approximately 134 millimeters;

total length of the conical portion 210: approximately 114 millimeters; threaded length of the conical portion 210: about 98 millimeters; length of the cylindrical portion 220: approximately 51 millimeters; - internal diameter of the cylindrical portion 220: approximately 134 millimeters;

length of the conical portion 230: approximately 51 millimeters;

taper of the portion 240: approximately 30 °;

internal diameter of the cylindrical portion 250: approximately 76 millimeters;

internal diameter of the throat 320: approximately 138 millimeters;

maximum outside diameter of the conical portion 310: approximately 154 millimeters;

length between the shoulder 301 and the end furthest from the groove 340: approximately 114 millimeters;

minimum throat diameter 340: approximately 128 millimeters;

maximum width of the groove 340: approximately 20 millimeters;

minimum radius of curvature of the groove 340:

inside diameter of the portion 350: approximately 76 millimeters; maximum internal diameter of the conical portion 360: approximately 83 millimeters;

clearance on the diameter between the portions 330 and 220: adjustment H7g6)

A test made it possible to evaluate the reduction of stresses thus obtained at approximately 60% at 10 cm from the sealing surface, constituted by the contact between the shoulder 301 and the radial surface 201 (this test was carried out with gauges stresses placed on the external surface of the female element, at 2, 4, 6, 8 inches, namely 50.8; 101, 6; 152.4; 203.2 millimeters, of the sealing surface

201).

It should be noted that many modifications or variants of the connector assembly described and shown can be easily carried out by a person skilled in the art without departing from the scope of the invention.

Claims

1. Connection assembly (100) for heavy rods or drill rods comprising:

- a male connector element (300) having substantially a shape of revolution around a longitudinal axis and which comprises in its longitudinal direction respectively:

a first substantially cylindrical portion (302) forming a shoulder (301) at one of its ends,

a second portion of conical surface (310) at least partially threaded and tapering from the first portion towards the free end of the element

a substantially cylindrical female connector element (200), complementary to said male connector element, and which comprises:

a radial portion (201) forming a bearing face for said shoulder (301) of the first element and, longitudinally, coaxially and respectively, from this portion, a conical inner surface (210) at least partially threaded complementary to the surface conical (310) at least partially threaded of the male element,

- a cylindrical interior surface (220)

said two connecting elements (200, 300) being intended to be assembled into one another by screwing on several turns of the threads, characterized in that the male connecting element comprises, in addition, between said second portion ( 310) and its free end, a third surface portion (330) of taper less than that of the second conical surface portion (310), and dimensioned relative to said cylindrical inner surface (220) so that it there is a clearance whereby, when the assembly undergoes bending, these two surfaces come into contact respectively.

2. connector assembly (100) according to claim 1 characterized in that the male element (300) comprises a groove (340) disposed between said second portion (310) and said third portion (330), so that, when said two elements are assembled, and when said shoulder (301) is in abutment against the radial bearing face, the geometric limit between said conical inner surface and said cylindrical inner surface is included in the space formed by said groove.

3. Fitting assembly (100) according to one of the preceding claims characterized in that the third surface portion (330) of the male element forming a bearing is substantially cylindrical.

4. A connector assembly (100) according to claim 3, characterized in that said portion (330) is partially conical at its free end.

5. A connector assembly (100) according to claim 4, characterized in that said taper is less than that of the second conical portion (310) at least partially threaded.

6. fitting assembly (100) according to any one of claims 1 to 5, characterized in that the third portion (330) has a longitudinal dimension at most equal to 2/3 of the longitudinal dimension of the second portion (310 ).

7. connector assembly (100) according to any one of claims 1 to 6, characterized in that the third portion (330) has a longitudinal dimension between 10% and 50% of its diameter.

8. A connector assembly (100) according to any one of claims 1 to 7, characterized in that the groove (340) has a radius of curvature between! 4 and 3 inches is approximately between 12 millimeters and 76 millimeters.

9. connector assembly (100) according to one of the preceding claims characterized in that the two elements (200, 300) are axially drilled and through.

10. Male connector element (300) for heavy rods or drill rod masses intended to cooperate with a female element (200) and having substantially a shape of revolution around a longitudinal axis and which comprises in its longitudinal direction respectively:

a second portion of conical surface (310) at least partially threaded and tapering from the first portion towards the free end of the element, characterized in that the male connector element further comprises, between said second portion and its free end, a third surface portion (330) of conicity less than that of the second conical surface portion.