WO2015104347A1

WO2015104347A1 - Downhole assembly and method for reducing drag and friction on a tubular run in a wellbore

Info

Publication number: WO2015104347A1
Application number: PCT/EP2015/050277
Authority: WO
Inventors: John Hanton
Original assignee: Tercel Ip Limited; Tercel Oilfield Products Belgium Sa
Priority date: 2014-01-09
Filing date: 2015-01-08
Publication date: 2015-07-16
Also published as: GB201611371D0; GB2538407A; MX2016008797A; CA2934800A1; GB2538407B; AU2015205562A1

Abstract

An assembly (100) to be positioned on a tubular (200), said assembly comprising a first abutment (101), a second abutment (102), a body (103) to be positioned on said tubular such that said body is free to travel relative to said tubular and is limited by said abutments, characterized in that said body and at least an abutment have a shape (106, 106') such that upon rotation of said tubular, said body is periodically urged to move with an axial component relative to said tubular.

Description

Downhole assembly and method for reducing drag and friction on a tubular run in a wellbore

Technical field

[0001 ] According to a first aspect, the present invention relates to a downhole assembly to be positioned on a tubular, the assembly comprising a first abutment, a second abutment, and a body to be positioned on the tubular such that the body is free to travel relative to the tubular and is limited by the abutments. The assembly is characterized in that the body is arranged on the tubular such that upon rotation of the tubular, the body is periodically urged to move with an axial component relative to the tubular. According to a second aspect, the present invention relates to a method for reducing the friction and drag of a tubular run into a wellbore, by using the assembly. The present invention also relates to some parts of the assembly.

State of the art

[0002] Deploying a string, for example a drill string, a casing string or a liner into a deviated wellbore may be challenging because of the friction forces between the string and the wall of the wellbore.

[0003] Centralizers are commonly used in the oilfield industry for centralizing a string in a tubular section, for example, a wellbore or a casing placed in a wellbore. A centralizer is generally referred as a single body disposed around a pipe and secured on both sides by stop collars. The body of the centralizer is generally provided by blades for contacting the wall of the wellbore and separated by channels for allowing circulation of a fluid, for example a drilling fluid or cement.

[0004] Centralizing a casing string or a liner within a borehole is important to ensure efficient cementation of the casing string or liner. A string is often rotated while running into a wellbore for reducing the friction forces and allowing deployment of the string in deep or highly deviated areas of a wellbore. Some kinds of centralizers are fixed to the pipe of a string in a manner such that while the string is rotated, the centralizer is not rotating relative to the string. Therefore, when the string has to be put into movement within the wellbore, the weight on the string has to be increased for overcoming the static friction between the parts of the string in contact with the walls of the wellbore. Once the force applied on the string has overcome the static friction forces, the string starts to move resulting in a slack off weight on the string.

[0005] Other kinds of centralizers are fixed on the pipe in a manner such that the centralizers are rotating with the pipe of a string. In this case, the weight to apply on the string to move down the string is reduced because the friction forces to overcome are essentially dynamic rather than static.

[0006] However, there is still a need to reduce the friction forces between the centralizers and the wall of the wellbore. Some centralizers have been adapted for reducing these problems of friction. For example, document US6453999 present a centralizer comprising two annular bands spaced apart by six members having a U-shape cross section. Those members are provided with cylindrical rollers which are free to rotate about an axis which is perpendicular to the longitudinal axis of the centralizer. Such a centralizer cannot be rotated with the pipe and is destined for methods of running a string in a wellbore by sliding only.

[0007] Document US6585043 discloses a centralizer which can be used in a method of running a string within a wellbore by rotating the string. The centralizer body comprising blades provided with:

- a first group of rollers rotatably secured to the body and aligned with the axis of the bore for reducing the rotational friction between the centralizer and the pipe; and

- a second group of rollers rotatably secured to the body and aligned transversally to the bore for reducing the axial drag between the body and the wellbore or tubular disposed there around.

[0008] By the position of the first group of rollers and the second group of rollers, the string is allowed to rotate relative to the centralizer which is substantially not rotating. The rollers are disposed around an axle securing the roller in their position and fixed in place by welding or other suitable means. These axles may be prone to weakness and breakage. Additionally, granular material coming from the wall of the wellbore can accumulate around the rollers of the second group of rollers and reduce their effect of drag reducer. Therefore such kind of centralizers is more suitable for centralizing a pipe within a section of a wellbore already cased.

[0009] Another document US6688409 discloses a centralizer having a body provided by rotatable castors at the periphery of the body. Here again, rotating elements located at the external surface of a centralizer body in contact with the wall of a wellbore are subject to wear and breakage.

[0010] Document WO2012/092985 and document US2010/0252274 discloses an apparatus to reduce frictional resistance to rotation of a tubular string within a bore comprising:

- a centralizer body having a bore received onto a tubular segment coupled into the tubular string;

- a first stop collar having a bore received on the tubular segment and a bearing face disposed towards a second stop collar having a bore received on the tubular segment and a bearing face disposed towards the first stop collar; and

a first sleeve bearing having a bore received on the tubular segment axially intermediate the first and second stop collar and radially intermediate the bore of the centralizer body and the tubular segment.

[001 1 ] Document US7159668 discloses a centralizer for mounting on a casing and comprising a centralizer body arranged between two stop collars positioned on the casing such that to allow free rotation of the centralizer body relative to the casing. A first stop collar comprises a engagement surface facing an second engagement surface provided on a first end of the centralizer body, such that when those two engagement surfaces are bring together, the rotation of the casing engages the centralizer body. The second stop collar and the second end of the centralizer body both comprise non engaging surfaces such that when those two surfaces are bring together, the casing is allowed to rotate relative to the centralizer body.

[0012] There is a need to reduce the drag and friction between a string and the walls of a wellbore.

[0013] There is also a need to improve the reduction of the drag and friction between a centralizer and the wall of a cased wellbore or of a non-cased wellbore. It is desirable to reduce the friction between the string including the centralizer and the wall of a wellbore for deploying the string in deep and highly deviated zones of the wellbore.

[0014] There is a further need for a means and a method for breaking high friction forces between a centralizer and the wall of a wellbore. Summary of the invention

[0015] According to a first aspect, the present invention relates to an assembly, e.g. a downhole assembly, to be positioned on a tubular, the assembly comprising:

- a first abutment;

- a second abutment;

- a body to be positioned on the tubular such that the body is free to travel relative to the tubular and is limited by the abutments;

characterized in that the body and at least one abutment have a shape such that upon rotation of the tubular, the (annular) body is periodically urged to move with an axial component relative to the tubular. The shapes of the body and at least one of the abutments are preferably configured depending on the dynamic friction coefficients between the body and the abutments, between the body and the wellbore wall, and between the body and the tubular such that the reciprocating axial motion is achieved. Preferably, the first and second abutments are fixedly attached on the tubular, whereas the body may rotate about the tubular and axially travel between the first and second abutments. The first and second abutments and the body are preferably configured such that when the body and whichever of the first and second abutments are in contact with each other a relative rotation between the body and the abutments translates into a reciprocating or vibrating axial displacement of the body relative to the abutments. Preferably, the body and the first and second abutments are configured such that the resulting frequency of the reciprocating or vibrating motion is at least twice as high as the frequency of the rotation of the body relative to the abutments.

[0016] The reciprocating or vibrating axial motion of the body reduces the friction between the string and the wellbore and prevents high torque on the string while rotating the string in the wellbore. Preferably, the body is a centralizer body.

[0017] The assembly is preferably provided on the external surface of the tubular.

[0018] The body comprises two sides facing the abutments. Furthermore:

- at least one of the abutment has a cam or a cam follower; and

- at least one side of the body faces the cam or cam follower and comprises a cam or a cam follower,

such that upon rotation of the tubular, the cam or cam follower forces the body to move with an axial component between the abutments. [0019] Preferably, at least one of the abutments comprises a cam having a surface extending between a first point on the circumference of the tubular (first extreme point) and a second point on the circumference of the tubular (second extreme point ). In the direction opposite to a predetermined direction of rotation of the tubular, the slope of the surface of the cam or the slope of any tangent to the surface of the cam (in case of a curved surface) points towards the body. The slope forms an angle with a plane orthogonal to the axis of the tubular such that the body slips on the at least one abutment when the tubular is rotated in the predetermined direction of rotation.

[0020] Preferably, at least one of the abutments comprises a cam or a plurality of cams on which the body slips when the tubular is rotated. Preferably, the slipping surface of each cam is helicoidially shaped over a circular sector about the axis of the tubular. The angle of inclination λ of the helicoidally shaped part of the cam with respect to a plane perpendicular to the axis of the tubular is preferably selected in accordance with the following formula:

0° < A < tan -1 — tan ¹ μ

(μι + μ₂)

Where:

μ is the dynamic friction coefficient between the cam and cam follower; μι is the dynamic friction coefficient between the inner surface of the body and the tubular;

μ2 is the dynamic friction coefficient between the outer surface of the body and the wellbore;

d is the inner diameter of the body; and

di is the outer diameter of the body.

[0021 ] The first abutments are arranged spaced from each other on the tubular such as to allow the body to move with a radial component relative to the tubular.

[0022] The body comprises an inner surface provided with rolling elements.

[0023] In an embodiment of the assembly according to the present invention, the first abutment is formed by a joint for holding a first tubular together with a second tubular.

[0024] Preferably, the second abutment is integral with the joint. [0025] Alternatively, the second abutment is integral with a second joint for holding the second tubular together with a third tubular.

[0026] Alternatively, the second abutment is formed by a stop collar.

[0027] In another embodiment of the assembly according to the present invention, the first abutment is formed by a first stop collar, and the second abutment is formed by a second stop collar.

[0028] Preferably, the assembly of the present invention further comprises a sleeve extending between the first abutment and the second abutment.

[0029] The sleeve provides a protecting surface to the tubular.

[0030] Preferably, the body is arranged on the sleeve.

[0031 ] Preferably, at least one of the cam comprises at least one surface inclined relative to a plane transversal to a longitudinal axis of the tubular.

[0032] Preferably, at least one of the cam follower includes a rolling element.

[0033] Preferably, at least one of the cam comprises a saw tooth profile having a plurality of teeth or a sinusoidal profile.

[0034] According to a second aspect, the present invention relates to a stop collar for an assembly as disclosed herein, characterized in that the stop collar comprises a cam profile or a cam follower.

[0035] Preferably, the stop collar comprises a compression olive, a compression nut and a compression pin.

[0036] Preferably, the compression olive has a first side comprising a plurality of fingers having an outer taper and the compression nut has an inner tapered section adapted to compress the fingers against the tubular when the compression nut is screwed to the compression pin.

[0037] Preferably, the compression olive comprises a second side opposite to the first side, and the compression pin comprises an inner surface adapted to compress the compression olive against the inner tapered section of the compression nut when the compression nut is screwed to the compression pin.

[0038] Preferably, the compression nut or pin comprises a cam profile.

[0039] In an embodiment of the present invention, the stop collar comprises a fastening means included in one of the compression ring or compression pin or both such as to maintain the compression olive compressed between the compression ring, the compression pin and the pipe.

[0040] Preferably, the compression olive comprises a scraping inner surface. [0041 ] According to a third aspect, the present invention relates to a joint for joining two tubulars and for an assembly as disclosed herein, characterized in that the joint comprises at least one end provided with a cam or a cam follower.

[0042] According to a fourth aspect, the present invention relates to a body for an assembly as disclosed herein, wherein the body comprises an outer surface and an inner surface, the inner surface forming a bore thereon, characterized in that the inner surface is provided with roller elements.

[0043] Preferably, the roller elements are balls embedded in the inner surface.

[0044] Preferably, the body comprises at least a side comprising a cam profile or a cam follower.

[0045] According to a fifth aspect, the present invention relates to a method for reducing drag and friction on a tubular run in a wellbore characterized in that it comprises a step of providing on the tubular an assembly as disclosed herein, and a further step of rotating the tubular for providing a, preferably continuous, shunting motion of the body between the first abutment and the second abutment.

[0046] Preferably, the shunting motion made periodic.

[0047] Preferably, the method comprises a step of varying the rotation speed of the string for changing the frequency of pulsation of the body. Brief description of the figures

[0048] Fig. 1 a, 1 b, 1 c, 1d shows four side elevations of four embodiments of an assembly according to the present invention, wherein the assembly comprises a body arranged between two abutments, and wherein one of the abutments has a cam facing an extremity of the body having a cam follower.

[0049] Fig. 2a, 2b, 2c, 2d shows four side elevations of four embodiments of an assembly according to the present invention, wherein the assembly comprises a body arranged between two abutments, and wherein one of the abutments has a cam facing an extremity of the body having a first cam follower, and wherein the opposite extremity of the body further comprises a second cam follower.

[0050] Fig. 3a, 3b, 3c, 3d shows four side elevations of four embodiments of an assembly according to the present invention wherein the assembly comprises a body arranged between two abutments, and wherein one of the abutments has a cam facing an extremity of the body having a first cam follower, and wherein the assembly further comprises a tubular surface extending between the two abutments, the tubular surface on which is positioned the body.

[0051 ] Fig. 4a, 4b, 4c, 4d shows four side elevations of four embodiments of an assembly according to the present invention wherein the assembly comprises a body arranged between two abutments, and wherein each abutment is facing a cam follower provided on each extremity of the body.

[0052] Fig. 5 shows a side elevation of an embodiment of an assembly according to the present invention wherein the assembly comprises a body arranged between two abutments, wherein one of the abutments comprises a cam facing an first extremity of the body on which is provided a cam follower, and wherein the assembly further comprises a biasing member positioned between a second abutment and a second extremity of the body.

[0053] Fig. 6 shows a top elevation of an embodiment of a body for the assembly according to the present invention.

[0054] Fig. 7a shows a side view of a wellbore in which is run a string provided with an assembly according to an embodiment of the present invention, and wherein the cam of a first abutment of the assembly engages a first cam follower provided on a first extremity of the body, and wherein the second cam follower provided on the opposite extremity of the body is disengaged from the cam of the second abutment

[0055] Fig. 7b shows a side view of a wellbore in which is run a string provided with an assembly according to an embodiment of the present invention, and wherein the cam of the second abutment of the assembly is disengaged from the first cam follower of the first extremity of the body, and wherein the cam of the second abutment engages the second cam follower of the second extremity of the body.

[0056] Fig. 8 shows a longitudinal cross sectional view of a portion of an embodiment of the assembly according to the present invention, wherein the assembly comprises a body arranged between two stop collars providing the first and second abutments.

[0057] Fig. 9 shows a three dimensional elevated view of an embodiment of the assembly according to the present invention, arranged on a section of a tubular. [0058] Fig. 10 shows a longitudinal cross section of the assembly according to the embodiment of figure 9 showing a body arranged between two stop collars.

[0059] Fig. 1 1 shows an embodiment of a cam or cam follower comprising a roller.

[0060] Fig. 12a shows an embodiment of a stop collar comprising a pushing member adapted to move between two axial positions, wherein the pushing member is in a first axial position.

[0061 ] Fig. 12b shows an embodiment of a stop collar comprising a pushing member adapted to move between two axial positions, wherein the pushing member is in a second axial position.

[0062] Fig. 13 shows a portion of a casing string comprising an assembly according to a first embodiment of the invention wherein the assembly comprises a body arranged between two abutments formed by two stop collars.

[0063] Fig. 14 shows a portion of a casing string comprising an assembly according to a second embodiment of the invention wherein the assembly comprises a body arranged between two abutments formed on a casing joint.

[0064] Fig. 15 shows a portion of a casing string comprising an assembly according to a third embodiment of the invention wherein the assembly comprises a body arranged between a first abutment formed by a casing joint and a second abutment formed by a stop collar.

[0065] Fig. 16 shows a portion of a casing string comprising an assembly according to a fourth embodiment of the present invention wherein the assembly comprises a body arranged between two abutments formed by two casing joints.

[0066] Fig. 17 shows an embodiment of an assembly according to the present invention arranged on a tubular, the assembly comprising a body arranged between two abutments formed by two stop collars, and wherein the body and the two stop collars are each one made of at least two substantially longitudinal parts.

[0067] Fig. 18 shows an embodiment of an assembly according to the present invention arranged on a tubular comprising a body arranged on a protecting sleeve between two abutments formed by two stop collars, and wherein each of the body, protecting sleeve, and stop collars are made of at least two substantially longitudinal parts.

[0068] Fig. 19 shows an alternative embodiment of a stop collar for an assembly according to the present invention. [0069] Fig. 20 shows a schematic side elevation view of an embodiment of the assembly according to the present invention.

Detailed description of preferred embodiments of the invention

[0070] A preferred embodiment of the present invention relates to an assembly 100 positioned on the external surface of a tubular 200. The assembly 100 comprising:

- a first abutment 101 fixedly attached on the tubular;

- a second abutment 102 fixedly attached on the tubular at an axial distance from the first abutment; and

- a body 103 movably positioned on the tubular 200 such that the body is free to travel axially and rotatingly relative to the tubular and is limited in its movement by the abutments 101 and 102.

[0071 ] The body 103 and the abutments 101 , 102 are configured such that, upon rotation of the tubular 200 and the abutments 101 and 102, the body 103 is periodically urged to move with an axial component relative to the tubular 200.

[0072] The figure 1 a, 1 b, 1 c and 1 d shows four side elevations of four embodiments of an assembly 100 according to the present invention. The assembly 100 comprises a body 103 arranged between a first abutment 101 and a second abutment 102. A first abutment has a cam 106 facing a first extremity 104 of the body 103 having a cam follower 106'. The body 103 comprises a second extremity 105 opposed to the first extremity 104. In these four embodiments, the second abutment 102 is devoid of any cam and the second extremity 105 of the centralizer body 103 is devoid of any cam follower.

[0073] In these four first embodiments, the second abutment 102 may comprise a zone 102' made of low friction material extending from the surface destined to face the second extremity 105 of the body 103 such that the friction between the second abutment 102 while rotating relative to the body 103 is reduced. The second extremity 105 of the body 103 may be also provided by a zone made of low friction material. By low friction material, it is understood any material available allowing reduction of the friction between two contacting surfaces, such as, but non-limited to: polytetrafluoroethylene (PTFE), tetrafluorethylene-perfluoropropylene (FEP), Perfluoroalkoxy (PFA), polyethylene, medium density polyethylene or ultra-high molecular weight polyethylene. [0074] Alternative profiles of the cam 106 and of the cam follower 106' are presented on figures 1 a, 1 b, 1 c and 1 d. These profiles constitutes example of possible embodiments and are not limiting the present invention.

[0075] Fig. 1 a shows an assembly comprising a first abutment 101 provided with a cam 106 having a serpentine or sinusoidal profile and a body 103 having a first extremity 104 provided with a cam follower 106' having a serpentine or sinusoidal profile, that can be substantially identical to the serpentine or sinusoidal profile of the cam 106. Alternatively, the cam follower 106' may have a different profile than the cam 106, as long as the cam 106 and the cam follower 106' are profiled such that when the assembly is positioned on the tubular, and when the tubular is rotated in a predetermined direction, the cam follower 106' slips on the cam 106 that induces an axial motion to the body 103 along the tubular.

[0076] Figure 1 b shows an assembly comprising a first abutment 101 provided with a cam 106 having a saw-tooth profile and a body 103 having a first extremity 104 provided with a cam follower 106' having a saw tooth profile, that can be substantially equal to the saw tooth profile of the cam 106. The cam 106 and the cam follower 106' are oriented such that when the centralizer assembly is positioned on a tubular, and when the tubular is rotated in a predetermined direction, the cam follower 106' of the body slips on the cam 106 of the abutment that induces an axial motion to the body 103 along the tubular. Alternatively, the cam follower 106' may have a different profile than the cam 106, as long as the cam 106 and the cam follower are profiled such that when the assembly is positioned on the tubular, and when the tubular is rotated in a predetermined direction, the cam follower 106' of the body slips on the cam 106 of the first abutment 101 that induces an axial motion to the body 103 along the tubular.

[0077] Figure 1 c shows an assembly comprising a first abutment 101 provided with a cam 106 having a profile comprising a first flat section 106a, a second flat section 106b and a third flat section 106c, wherein the first flat section 106a and the second flat section 106b are substantially perpendicular to the axis of the assembly 100, separated by a height and joined together by the third flat section 106c. The assembly further comprises a body having a cam follower 106' having substantially the same profile than the cam 106 or a different profile than the cam 106, as long as the cam 106 and the cam follower 106' are profiled such that when the assembly is positioned on a tubular, and when the tubular is rotated in a predetermined direction, the cam follower 106' of the body slips on the cam 106 that induces an axial motion to the body 103 along the tubular. Alternatively, the cam 106 of the first abutment 101 and the cam follower 106' may comprise only a main surface inclined relative to the axis of the whole assembly.

[0078] Fig. 1d shows an assembly comprising a first abutment 101 provided with a cam 106 comprising a rolling element 120, for example a roller, a ball or a wheel, and a body 103 having an extremity 104 provided with a cam follower 106', for example a cam follower 106' comprising an inclined surface or any one of the profiles disclosed above. In this embodiment, when the centralizer assembly is positioned on the pipe, the cam 106 is able to roll against the cam follower 106' upon rotation of the pipe and to induce an axial motion of the body. Alternatively, the cam 106 comprises an inclined surface and the cam follower 106' comprises a rolling element 120. Also, both cam 106 and cam follower 106' may comprise roller elements.

[0079] The figure 1 1 shows an example of a cam 106 or cam follower 106' comprising a roller element 120 that is a wheel fixed by a pin 121 on a portion of an abutment or on a portion of the body. The pin is preferably inserted through an inner surface of an abutment or of the body, to prevent accidental loss of the pin and wheel.

[0080] The figures 2a, 2b, 2c and 2d shows four side elevations of four other embodiments of an assembly according to the present invention, wherein the assembly comprises a body arranged between two abutments, and wherein one of the abutments has a cam facing an extremity of the body having a first cam follower, and wherein the opposite extremity of the body further comprises a second cam follower. These embodiments differs from the assemblies shown in figures 1 a, 1 b 1 c and 1 d in that the first extremity 104 and the second extremity 105 of the body 103 both comprise a cam follower 106'. The first abutment 101 comprises a cam 106 and the second abutment 102 is devoid of any cam. The second abutment 102 may also comprise a zone 102' made of low friction material extending from the surface destined to face the second extremity 105 of the body 103 such that the friction between the second abutment 102 and the body 103 is reduced. The first extremity 104 and the second extremity 105 of the body 103 may be also provided by a low friction material. These embodiments of figures 2a, 2b, 2c and 2d prevents wrong positioning of the body 103 respect to the first and second abutments 101 , 102.

[0081 ] The figures 3a, 3b, 3c, 3d shows four side elevations of four embodiments of an assembly according to the present invention wherein the assembly comprises a body arranged between two abutments, and wherein one of the abutments has a cam facing an extremity of the body having a first cam follower, and wherein the assembly further comprises a tubular surface extending between the two abutments, the tubular surface on which is positioned the body. These embodiments differs from the assemblies shown in figures 1 a, 1 b, 1 c and 1 d in that the assemblies further comprise a tubular surface 1 10 extending from a first abutment 101 to a second abutment 102 and on which is positioned a body 103. The tubular surface 1 10 prevents wear of the tubular, which is preferably a pipe, under repeated movement of the body 103 along the tubular. Preferably, the tubular surface 1 10 is made of a low friction material for reducing the friction between the inner surface of the body 103 and the tubular 200 upon rotational or axial movement of the body around the tubular. The tubular surface 1 10 can be a sleeve, an external layer on a sleeve, an external layer of a casing joint or a coating. By low friction material, it is understood any material available allowing reduction of the friction between two contacting surfaces, such as, but non-limited to: polytetrafluoroethylene (PTFE), tetrafluorethylene-perfluoropropylene (FEP), Perfluoroalkoxy (PFA), polyethylene, medium density polyethylene or ultra-high molecular weight polyethylene. In an embodiment of the invention, the tubular surface 1 10 is the external surface of a tubular sleeve made of a low friction material. In an alternative embodiment of the invention, the tubular surface 1 10 is a coating of a low friction material on a metallic tubular sleeve to be disposed on the pipe. In another alternative embodiment of the invention, the tubular surface 1 10 is a coating of low friction material provided directly on the pipe or on a casing joint.

[0082] The figures 4a, 4b, 4c, 4d shows four side elevations of four embodiments of an assembly according to the present invention wherein the assembly comprises a body arranged between two abutments, and wherein each abutment is facing a cam follower provided on each extremity of the body. These embodiments differs from the assemblies shown in figures 1 a, 1 b, 1 c and 1 d, in that both first abutment 101 and second abutment 102 comprise a cam 106 and both first extremity 104 and second extremity 105 of the body 103 comprise a cam follower 106' so that the assembly allows movement of the body 103 upon rotation of the tubular combined with a movement of the tubular in both axial directions.

[0083] Fig. 5 shows a side elevation of an embodiment of an assembly according to the present invention wherein the assembly comprises a body arranged between two abutments, wherein one of the abutments comprises a cam facing an first extremity of the body on which is provided a cam follower, and wherein the assembly further comprises a biasing member positioned between a second abutment and a second extremity of the body. The biasing member can be for example a spring 1 13 arranged between one of the abutments 102 and the body 103. The spring 1 13 may be fixed or not to the abutment 102 or to the body 103. When the assembly is arranged on a tubular and the tubular is rotated, the cam follower 106' located on a first extremity 104 of the body 103 slips on the cam 106 of the first abutment 101 that induces an axial movement of the body 103. The biasing member 1 13 further ensures the oscillation of the body 103 between the first abutment 101 and the second abutment 102.

[0084] Figure 6 shows a cross sectional view of an embodiment of a body 103 for an assembly 100 according to the present invention. The inner surface 108 of the body is provided with roller elements 109 allowing at least a longitudinal movement of the body along the pipe. Roller elements 109 are preferably balls 109, so that they easily provide axial and rotational motion of the body, each of the balls being maintained within a cavity made in the inner surface of the body such that the balls 109 are able to roll without falling out of the cavities. For example, the balls 109 are maintained in their cavities by a collar provided with openings sized with a diameter smaller than the diameter of the balls.

[0085] Another embodiment is presented in figure 8 wherein the balls are partially embedded into a bloc. Preferably, the body 103 comprises at least a blade 1 12 rising from the outer surface of the body, and the bloc including the balls is arranged into the blade 1 12 such that the balls are able to roll against the surface of the tubular 200 or on a tubular surface 1 10.

[0086] Additionally, the external surfaces of the blades 1 12 of the body may be provided with rolling elements (not shown) such as balls, rollers or wheels so as to decrease the friction between the walls of the wellbore and the blades 1 12. [0087] The figure 7a shows a side view of a wellbore in which is run a string 200 provided with an assembly 100 according to an embodiment of the present invention, and wherein the cam 106 of a first abutment 101 of the assembly 100 engages a first cam follower 106' provided on a first extremity 104 of the body 103, and wherein the second cam follower 106' provided on the opposite extremity 105 of the body 103 is disengaged from the cam 106 of the second abutment 102. The figure 7b shows a side view of the same string 200 provided with the same assembly 100 than figure 7a, wherein the body 103 has moved towards the cam 106 of the second abutment 102, upon rotation of the string 200, and wherein the cam 106 of the first abutment 101 is disengaged from the first cam follower 106' of the first extremity 104 of the body 103. While the string 200 is kept rotating, the cam follower 106' of the second extremity 105 of the body 103 slips on the cam 106 of the second abutment 102 that causes the body 103 to move back towards the first abutment 101 . Continuous rotation of the string 200 causes each of the cam 106 of the first and second abutments 101 , 102 to give a pulse on the body 103 that goes and go back between the first abutment and the second abutment.

[0088] The string is preferably rotated according to a predetermined direction which is preferably in a clockwise direction so as to prevent disconnection of threaded connections between each of the pipes of the string.

[0089] The figure 9 shows a three dimensional elevated view of an embodiment of the assembly 100 according to the present invention, arranged on a section of a tubular 200. In that embodiment, the first abutment is formed by a first stop collar 101 and the second abutment is formed by a second stop collar 102. The body of the assembly comprises a plurality of blades 1 12 separated by flutes 126. Preferably, the embodiment of the assembly represented at the figure 9 is destined to be arranged on a casing pipe. A casing pipe is a tubular of constant external diameter provided with threaded connections at the extremities. All the parts of the first stop collar 101 are slid on the casing pipe 200, fastened to the casing pipe, then the body 103 is slid on the casing pipe, and then all the parts of the second stop collar 102 are fastened to the casing pipe at a distance from the first stop collar allowing free rotation and axial motion of the body 103.

[0090] The figure 10 shows a longitudinal cross section of the assembly according to the embodiment of figure 9. In that embodiment, the first stop collar 101 and the second stop collar 102 are made of three parts. A first part is a compression olive 1 14 having a plurality of fingers 1 18 arranged circumferentially at one side and comprising an outer taper. A second part is a compression nut 1 15 having an inner taper destined to contact the taper of the plurality of fingers 1 18 and to compress the fingers against the casing pipe. The compression nut further comprises an inner thread. The third part comprises a compression pin 1 16 including an outer thread for screwing to the compression nut. The compression pin further comprises an edge for compressing the side of the compression olive opposed to the side compressed by the compression nut. In an embodiment, the compression olive may have two sided comprising a plurality of fingers arranged circumferentially.

[0091 ] The external surfaces of the compression nut 1 15 and of the compression pin 1 16 comprise a keyway 126, for example a set of holes, for insertion of a key for screwing the compression pin 1 16 against the compression nut.

[0092] Preferably, the compression olive comprises a scraping inner surface.

[0093] In an embodiment of the present invention such as presented in figure 19, the stop collar comprises a fastening means, for example a screw 131 included in one of the compression nut 1 15 or compression pin 1 16 or both such as to maintain the compression olive 1 14 compressed between the compression nut 1 15, the compression pin 1 16 and the tubular.

[0094] The figure 12a shows an embodiment of a stop collar comprising a member 103a adapted to move between two axial positions, wherein the member 103a is in a first axial position. The figure 12b shows the same stop collar, wherein the member 103a is in a second axial position. The member 103a comprises an inner shoulder 129 comprising a cam follower 106' on both sides and arranged in a cavity 122 of the stop collar. The cavity 122 is larger than the shoulder 129 and forms a first abutment 101 and a second abutment 102. The first abutment 101 and the second abutment both comprise a cam 106 for giving a pulse to the member 103a upon rotation of the tubular on which is fastened the stop collar, and providing back and forth movements of the member 103a between the first abutment 101 and the second abutment 102.

[0095] In an embodiment, the member is used as a body 103 such as disclosed in any one of the precedent embodiments wherein the back and forth movements of the member 103a provides reduction of friction and drag between the tubular and the wall of a wellbore.

[0096] In a preferred embodiment, the stop collar of figure 12a and 12b is a part of an assembly comprising an identical second stop collar, and a body 103 arranged between the two stop collars, more particularly between two abutments 123 formed by the two members 103a. The back and forth movements of the two members 103a are used to push the body 103 and provide a back and forth movement of the body between the two members 103a, upon rotation of the tubular. In that embodiment, the body doesn't need to comprise any cam, so that most of the bodies of prior art can be used in combination with the stop collar according to that embodiment to form an assembly according to the present invention.

[0097] The figure 13 shows a portion of a casing string comprising an assembly 100 according to an embodiment of the invention wherein the assembly 100 comprises a body 103 arranged between two abutments 101 , 102 formed by two stop collars fastened to the casing pipes.

[0098] The figure 14 shows a portion of a casing string comprising an assembly 100 according to an alternative embodiment of the invention wherein the assembly 100 comprises a body 103 arranged between two abutments 101 , 102 formed on a casing joint 130.

[0099] The figure 15 shows a portion of a casing string comprising an assembly 100 according to another alternative embodiment of the invention wherein the assembly 100 comprises a body 103 arranged between a first abutment 101 formed by a casing joint 130 and a second abutment 102 formed by a stop collar.

[0100] The figure 16 shows a portion of a casing string comprising an assembly 100 according to another alternative embodiment of the present invention wherein the assembly 100 comprises a body 103 arranged between two abutments 101 , 102 formed by two casing joints 130.

[0101 ] The figure 17 shows an alternative embodiment of an assembly 100 according to the present invention arranged on a tubular 200, the assembly comprising a body 103 arranged between two abutments 101 , 102 formed by two stop collars, and wherein the body and the two stop collars are each one made of at least two substantially longitudinal parts. Preferably, the body 103 and the stop collars all comprise two hemi annular sections secured together in position around the tubular 200 by means of pin and hinges. Such embodiment allows the assembly 100 to be fixed on a first portion of a tubular having a first external diameter and comprised between two other portions having an external diameter superior than the one of the first portion of the tubular. Such a tubular can be for example a drilling pipe.

[0102] The figure 18 shows an alternative embodiment of an assembly 100 according to the present invention arranged on a tubular 200, wherein the assembly comprises a body 103 arranged on a protecting sleeve 1 10 between two abutments 101 , 102 formed by two stop collars, and wherein each of the body 103, protecting sleeve 1 10, and stop collars are made of at least two substantially longitudinal parts. The protecting sleeve is generally formed from two parts hold together under compression against the pipe by the stop collars. Preferably, the body 103 and the stop collars all comprise two hemi annular sections secured together in position around the tubular 200 by means of pin and hinges. Such embodiment allows the assembly 100 to be fixed on a first portion of a tubular having a first external diameter and comprised between two other portions having an external diameter superior than the one of the first portion of the tubular. Such a tubular can be for example a drilling pipe.

[0103] In an embodiment of the present invention, the assembly 100 is a centralizing assembly for centralizing a pipe 200 within a wellbore or within a tubular 300, such as a section of casing already installed in a wellbore.

[0104] The present invention also relates to a method by providing an assembly 100 on a tubular 200, for example a casing, the assembly being an assembly as any one of the embodiments presented herein above or any one of the embodiments falling into the scope of protection of the claims. The method comprises the steps of:

- positioning the body 103 around the tubular 200; and

- providing a first abutment 101 and a second abutment on the tubular 200 such that the body 103 is allowed to move according to a substantially axial motion between the first abutment 101 and the second abutment 102.

[0105] When the abutments are formed by stop collars, the stop collars are preferably fixed on the pipe by compression fittings, slip on nut, welding or any other suitable fastening means known by the man skilled in the art. The body 103 is slid on the pipe before the fixation of the two stop collars 101 , 102. The first stop collar 101 and the second stop collar 102 are fixed at a distance from each other such that the body 103 is allowed to move axially along the pipe 200 between the two stop collars 101 , 102.

[0106] The string deployed in a wellbore can be a drill string, a casing string, a liner or a production string. Figures 7a and 7b shows a string into rotation within a wellbore, wherein an assembly 100 according to the invention is arranged around a pipe of the string.

[0107] In figure 7a, the string is lowered down in the wellbore while rotating the string to reduce the friction. The cam 106 of the upper stop collar engages the first extremity 104 of the centralizer body 103 which is therefore rotated with the pipe. The rotation of the cam 106 provides a conversion of rotational energy into axial force on the body 103, resulting in a shunting motion of the body 103 between the first stop collar 101 and the second stop collar 102 as shown in figure 7b, thereby reducing the axial drag while running the string within the wellbore without significant increase of torque.

[0108] The conversion of radial to axial force can be adjusted by changing the profile of the cam, for example by reducing the slope and/or the height of the cam 106 for inducing less axial force on the centralizer body 103 with lower drag reduction and less torque, or by increasing the slope/and or the height of the cam 106 for inducing more axial force on the centralizer body 103 with higher drag reduction and more torque.

[0109] The rotation speed of the string 200 can be varied for changing the frequency of pulsation of the body.

[01 10] As presented on figure 20, at least one of the abutments 101 , 102 comprises a cam 106 having a surface S extending between a first extreme point A and a second extreme point B, the surface S having a slope or the slope of any tangent to the surface S pointing towards the body 103 and oriented opposite to the direction of rotation of the tubular 200, the slope forming an optimal angle λ with a plane orthogonal to the axis of the tubular 200 such that it allows the body 103to slip on the at least one abutment 101 , 102 while the tubular is rotated in the predetermined direction of rotation. The predetermined direction of rotation of the tubular is preferably right hand rotation. [01 1 1 ] It has been found that an optimal inclination angle λ is given according to the equation:

0° < A < tan^-1 — tan ¹ μ

(μι + μ₂) where

μ2 is the dynamic friction coefficient between the outer surface of the body and the wellbore

d is the inner diameter of the body; and

di is the outer diameter of the body.

[01 12] In a first example for an embodiment of an assembly as presented in figure 20, wherein possible values of friction coefficients and body dimensions are: μ = 0.18

μι = 0.15

μ₂ = 0.3

d = 24.45 cm (9.625")

di = 30.48 cm (12.00"),

the angle λ must be less than 16.26° to prevent the body 103 from rotating with the abutment.

[01 13] If cam rollers are used, a possible value of the friction coefficient μ is 0.0015 and the angle λ must thus be less than 26.375°.

[01 14] While specific embodiments have been described herein in detail, those skilled in the art will appreciate that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements and numerical examples disclosed are meant to be illustrative only and not limiting as to the scope of the invention, which is to be given the full breadth of the appended claims and any and all equivalents thereof.

Claims

Assembly (100) to be positioned on a tubular (200), said assembly (100) comprising:

- a first abutment (101 );

- a second abutment (102);

- a body (103) to be positioned on said tubular (200) such that said body is free to travel relative to said tubular and is limited by said abutments;

characterized in that said body (103) and at least an abutment have a shape such that upon rotation of said tubular, said body is periodically urged to move with an axial component relative to said tubular.

Assembly according to claim 1 characterized in that the assembly is provided on the external surface of the tubular.

Assembly according to claim 1 or 2 wherein said body comprises two sides (104, 105) facing said abutments (101 , 102) and wherein:

- at least one of said abutment (101 , 102) has a cam (106) or a cam follower, and;

- at least one side (104, 105) of said body (103) faces said cam (106) or cam follower and comprises a cam or a cam follower (106'),

such that upon rotation of the tubular (200), said cam (106) or cam follower forces the body (103) to move with an axial component between said abutments (101 , 102).

Assembly according to any one of the preceding claims characterized in that at least one of said abutments (101 , 102) comprises a cam (106) having a surface (S) extending between a first extreme point (A) and a second extreme point (B), said surface (S) having a slope or the slope of any tangent to said surface (S) pointing towards the said body (103) and oriented opposite to a predetermined direction of rotation of the said tubular (200), said surface forming an inclination angle with a plane (P) orthogonal to the axis (X) of said tubular (200) such that said body (103) slips on said at least one abutment (101 , 102) when said tubular is rotated in said predetermined direction of rotation.

5. Assembly according to any one of the preceding claims wherein said first abutments are arranged on the tubular such as to allow said body to move with a radial component relative to said tubular.

6. Assembly (100) according to any one of the preceding claims wherein said body (103) comprises an inner surface (108) provided with rolling elements (109).

7. Assembly according to any one of the preceding claims wherein said first abutment is formed by a joint for holding a first tubular together with a second tubular.

8. Assembly according to claim 6 wherein said second abutment is integral with said joint.

9. Assembly according to any one of the claims 1 to 6 wherein said second abutment is formed by a second joint for holding said second tubular together with a third tubular.

10. Assembly according to any one of the claims 1 to 6 wherein said second abutment is formed by a stop collar.

1 1 . Assembly according to any one of the claims 1 to 5 wherein said first abutment is formed by a first stop collar, and said second abutment is formed by a second stop collar.

12. Assembly (100) according to any one of the preceding claims characterized in that it further comprises a tubular surface (1 10) extending between said first abutment (101 ) and said second abutment (102).

13. Assembly according to any one of the preceding claims wherein said tubular surface provides a protecting surface to said tubular.

14. Assembly according to any one of the claims 1 1 or 12 wherein said body is arranged on said sleeve.

15. Assembly according to any one of the preceding claims wherein at least one of the cam (106) comprises at least one surface inclined relative to a plane transversal to a longitudinal axis of said tubular.

16. Assembly according to any one of the claims 3 to 14 wherein at least one of said cam follower (106') includes a rolling element.

17. Assembly according to any one of the claims 3 to 15 wherein at least one of said cam (106) comprises a saw tooth profile having a plurality of teeth or a sinusoidal profile.

18. Stop collar for an assembly according to any of the preceding claims characterized in that it comprises a cam profile or a cam follower.

19. Stop collar according to claim 17 characterized in that it comprises a compression olive, a compression nut and a compression pin.

20. Stop collar according to claim 17 or 18 characterized in that said compression olive has a trapezoidal cross section having at least an outer tapered periphery comprising a plurality of fingers and said compression ring/pin has an inner tapered periphery adapted to compress the compression olive against the pipe when the compression ring is screwed to the compression pin.

21 . Stop collar according to any one of the claims 17 to 19 characterized in that said compression olive comprises a straight periphery opposite to said outer tapered periphery, and said compression pin/ring comprises a straight inner shoulder adapted to compress the compression olive against the inner tapered periphery of the compression ring/pin when the compression ring is screwed to the compression pin.

22. Stop collar according to any one of the claims 17 to 20 characterized in that said compression ring/pin comprises a cam profile.

23. Stop collar according to any one of the claims 17 to 21 comprising a fastening means included in one of said compression ring or compression pin or both such as to maintain said compression olive compressed between the compression ring, the compression pin and the pipe.

24. Stop collar according to any one of the claims 17 to 22 wherein the compression olive comprises a scraping inner surface.

25. Body for an assembly according to any one of the claims 1 to 16 comprising an outer surface and an inner surface wherein said inner surface forms a bore thereon, characterized in that said inner surface is provided with roller elements.

26. Body according to claim 23 wherein said roller elements are balls embedded in said inner surface.

27. Body according to any one of the claims 24 or 25 characterized in that it comprises at least a side comprising a cam profile or a cam follower.

28. Method of reducing drag and friction on a tubular run in a wellbore (300) characterized in that it comprises a step of providing on said tubular an assembly (100) according to any one of the claims 1 to 16, and a further step of rotating said tubular for providing a shunting motion of said body (103) between said first abutment (101 ) and the second abutment (102).

29. Method according to claim 26 wherein said shunting motion is periodic.

30. Method according to claim 25 or 26 comprising a step of varying the rotation speed of said string (200) for changing the frequency of pulsation of said body.

31 .Joint for joining two tubulars and for an assembly according to any one of the claims 1 to 16, characterized in that said joint comprises at least one end provided with a cam or a cam follower.