ASSEMBLY AND METHOD FOR CREATING AN EXPANDED TUBULAR ELEMENT IN A BOREHOLE

Abstract

In an assembly for lowering and expanding a tubular element in a borehole on an expansion string, at least part of the weight of the tubular element is transmitted to the expansion string via an internal upset and support means protruding from an outer surface of the expansion string below the internal upset.

Claims

1. An assembly for lowering and expanding a tubular element in a borehole, the assembly comprising: a starter section arranged at a downhole end of the tubular element and comprising an internal upset having an upset inner diameter smaller than an initial inner diameter of the unexpanded tubular element; an expander arranged at a downhole end of an expansion string for radially expanding the tubular element in the borehole by upward movement of the expansion string through the tubular element; and support means protruding from an outer surface of the expansion string below the internal upset, which support means support the internal upset of the starter section to transmit at least part of the weight of the unexpanded tubular element via the internal upset and the support means to the expansion string when the assembly is lowered into the borehole, the internal upset being adapted to be radially expanded by the support means upon upward movement of the expander through the tubular element.

2. The assembly of claim 1, wherein the support means have an outer diameter smaller than, or equal to, the initial inner diameter of the tubular element, the support means being arranged upwardly from the expander.

3. The assembly of claim 1, wherein the internal upset rests on a support surface of the support means, the support surface extending inclined relative to a longitudinal axis of the expansion string to promote radial expansion of the internal upset by the support means.

4. The assembly of claim 1, wherein the support means comprise a series of external splines, the external splines being arranged to cooperate with a series of internal splines provided on an inner surface of the starter section to form a splined connection that rotationally locks the expansion string to the starter section.

5. The assembly of claim 4, wherein the internal splines are supported by an upper portion of the expander.

6. The assembly of claim 1, wherein the internal upset comprises an annular internal upset extending along the inner circumference of the starter section.

7. The assembly of claim 6, wherein the annular internal upset extends into an annular recess formed in the expansion string to allow the tubular element to be pushed in downward direction by the expansion string.

8. The assembly of claim 7, the expansion string comprising a near-cone centralizer for centralising the expansion string in the tubular element, a lower portion of the near-cone centralizer defining a boundary of the annular recess.

9. The assembly of claim 8, the expansion string comprising a far-cone centralizer for centralising the expansion string in the tubular element, the far-cone centralizer being arranged upwardly with respect to the near-cone centralizer.

10. The assembly of claim 1, wherein the expansion string comprises a debris catcher arranged at an upper portion of the expansion string.

11. The assembly of claim 1, the starter section being connected to the tubular element in releasable manner

12. The assembly of claim 1, wherein an outer surface of the starter section is provided with a layer of friction material for increasing friction between the starter section and another tubular element enclosing the starter section.

13. The assembly of claim 1, the starter section comprising an outwardly flaring lower part supported by the expander to transmit another portion of the weight of the tubular element via the outwardly flaring lower part and the expander to the expansion string, wherein the outwardly flaring lower part of the starter section comprising a material of higher yield strength than a material of a remainder part of the starter section.

14. A method for lowering and expanding a tubular element in a borehole, the method comprising the steps of: arranging a starter section at a downhole end of the tubular element, the starter section comprising an internal upset having an upset inner diameter smaller than an initial inner diameter of the unexpanded tubular element; arranging within the tubular element an expansion string comprising an expander for radially expanding the tubular element in the borehole by upward movement of the expander through the tubular element and support means protruding from an outer surface of the expansion string below the internal upset for supporting the internal upset; lowering the assembly into the borehole while transmitting at least a portion of the weight of the unexpanded tubular element via the internal upset and the support means to the expansion string; and subsequently radially expanding the internal upset by the support means upon upward movement of the expander through the tubular element.

15. The method of claim 14, further comprising the step of rotationally locking the expansion string to the starter section by means of a splined connection including a series of external splines provided to the support means and a series of internal splines provided to the starter section.

16. The method of claim 14, wherein the internal upset comprises an annular internal upset extending along the inner circumference of the starter section.

17. The method of claim 16, wherein the annular internal upset extends into an annular recess formed in the expansion string to allow the tubular element to be pushed in downward direction by the expansion string.

18. The method of claim 17, the expansion string comprising a near-cone centralizer for centralising the expansion string in the tubular element, a lower portion of the near-cone centralizer defining a boundary of the annular recess.

19. The method of claim 18, the expansion string comprising a far-cone centralizer for centralising the expansion string in the tubular element, the far-cone centralizer being arranged upwardly with respect to the near-cone centralizer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The invention will be described hereinafter in more detail and by way of example with reference to the accompanying schematic drawings in which:

[0032] FIG. 1 shows an exemplary embodiment of the assembly of the invention;

[0033] FIG. 2a shows a portion of an expansion string of the exemplary embodiment;

[0034] FIG. 2b shows a starter joint of the exemplary embodiment;

[0035] FIG. 3 shows the starter joint with some design parameters indicated; and

[0036] FIG. 4 shows a modified version of the starter joint.

[0037] In the detailed description and the figures, like reference numerals relate to like components.

DETAILED DESCRIPTION OF DEPICTED EMBODIMENTS

[0038] FIG. 1 shows an assembly including a tubular element 1 adapted to be radially expanded in a wellbore and an expansion string 2 for radially expanding the tubular element. The expansion string 2 may comprise a mandrel 4, a far-cone centralizer 6, a debris catcher 7 and an on-off sub 8 having lower and upper parts 8a, 8b. The on-off sub 8 connects the expansion string to the lower end of a drill pipe 10, and may be adapted to be disconnected by rotation of the drill pipe 10 relative to the mandrel 4. Expander 14 for expanding the tubular element 1 is arranged near a downhole end of the expansion string 2.

[0039] The mandrel 4 may be provided with a lock nut 12, the expander in the form of expansion cone 14, a torque retainer ring 16 and a near-cone centralizer 18. Each of the expansion cone 14, the torque retainer ring 16 and the near-cone centralizer 18 has a respective central passage 19, 20, 21 through which the mandrel 4 extends in slidable manner. The lock nut 12 is screwed to the mandrel 4 to lock the assembly of expansion cone 14, torque retainer ring 16 and near-cone centralizer 18 in place whereby the near-cone centralizer abuts against a shoulder 22 of the mandrel 4. The expansion cone 14 may be rotationally locked to the torque retainer ring 16 by a castellated connection 24. The torque retainer ring 16 may be rotationally locked to the near-cone centralizer 18 by a castellated connection 26. The near-cone centralizer 18 may be rotationally locked to the shoulder 22 of mandrel 4 by a castellated connection 28.

[0040] Alternatively the torque retainer ring 16 may be directly rotationally locked to the mandrel 4 by means of key slots in the torque retainer ring 16 and the mandrel 4, and keys fitting in such key slots. This way the castellated connections 26, 28 may be eliminated.

[0041] The expansion cone 14 has a nose portion 30 of diameter substantially equal to the inner diameter of the unexpanded tubular element 1. From the nose portion 30, the diameter of the expansion cone 14 gradually increases in downward direction to a diameter corresponding to a desired expansion ratio of the tubular element 1. The nose portion 30 is provided with an annular seal 32 of resilient material.

[0042] FIG. 2a shows the mandrel 4 with related components in more detail. An annular recess 34 may be formed between the torque retainer ring 16 and the near-cone centralizer 18, for instance at the level of the castellated connection 26. The torque retainer ring 16 may be provided with a series of external splines 36 regularly spaced along the outer circumference of the torque retainer ring. Each external spline 36 may have an upper surface 38 extending inclined relative to a longitudinal axis 39 of the mandrel 4. The respective upper surfaces 38 define the lower boundary of the annular recess 34. The upper boundary of the annular recess 34 is defined by a tapered lower surface 40 of the near-cone centralizer 18.

[0043] FIG. 2b shows a starter section of the tubular element 1 in the form of starter joint 42. The starter joint 42 may form a lower portion of the tubular element 1. The starter joint 42 may for instance be adapted to be connected to an upper portion of the tubular element 1 (not shown) by pin member 43. The pin member may be a male part of a threaded connection, connectable to a corresponding box member of the upper portion of the tubular element.

[0044] The starter joint 42 may be provided with a series of internal splines 44 regularly spaced along the inner circumference of the starter joint 42. Slots 46 may be defined between the respective internal splines 44. The slots 46 are arranged to receive the external splines 36 of the torque retainer ring 16 so as to form a splined connection. Each slot 44 has an upper surface 47 extending at the same inclination as the upper surfaces 38 of the external splines 36.

[0045] The starter joint 42 may be provided with an annular internal upset 48 that fits into the annular recess 34. The lower boundary of the internal upset 48 is formed by the respective upper surfaces 47 of the slots 44. An annular indentation 50 is formed in the outer surface of the starter joint 42 at the level of the internal upset 48 so that the wall thickness of the starter joint 42 remains substantially constant along its length.

[0046] In an embodiment, the starter joint 42 has an outwardly flaring lower section 52 adapted to receive an upper part of the expansion cone 14, as shown in FIG. 1. The largest outer diameter of the lower section 52 is less than, or equal to, the largest outer diameter of the expansion cone 14. Also, the starter joint 42 may have an upper section 53 of inner diameter substantially equal to an initial inner diameter of the tubular element 1 prior to expansion thereof.

[0047] During operation, the starter joint 42 may be made-up with the expansion string 2 as follows. The near-cone centralizer 18 is fitted to the mandrel 4 so that the near-cone centralizer 18 abuts against shoulder 22 and is rotationally locked to the mandrel 4 by castellated connection 28. Then the upper portion 53 of the starter joint 42 is extended over the near-cone centralizer 18 until the annular internal upset 48 contacts the tapered lower surface 40 of the near-cone centralizer 18. Subsequently the torque retainer ring 16 is inserted into the starter joint 42 such that the external splines 36 slide into the slots 46 of the starter joint 42 until the upper surfaces 38 of the external splines 36 abut against the annular internal upset 48. In this position the torque retainer ring 16 is rotationally locked to the near-cone centralizer 18 by castellated connection 26.

[0048] Subsequently the expansion cone 14 is inserted into the starter joint 42 and fitted to the mandrel 4 until the nose portion 30 of the expansion cone 14 abuts against the torque retainer ring 16. In this position the expansion cone 14 is rotationally locked to the torque retainer ring 16 by castellated connection 24. Then the lock nut 12 is screwed to the mandrel 4 so as to axially lock the expansion cone 14, the torque retainer ring 16 and the near-cone centralizer 18 to the mandrel 4. The length of the internal splines 44 is such that these abut against the nose portion 30 of the expansion cone 14 after the lock nut 12 has been fastened. Subsequently the mandrel 4 is connected to the far-cone centralizer 6, the debris catcher 7 and the lower part 8a of the on-off sub 8 as shown in FIG. 1. Finally a joint of the tubular element 1 is connected to the pin member 43 of the starter section. The internal upset 48 prevents the expansion string 2 from dropping out of the tubular element and starter joint 42 during this phase.

[0049] In a next step the expansion string 2 is lowered into the wellbore whereby the remaining upper portion of the tubular element is formed by adding tubular sections to the tubular element 1 in correspondence with the total length of the tubular element required in the wellbore. Meanwhile the tubular element 1 is supported and locked against rotation by a support device (not shown) at a drilling rig above the wellbore.

[0050] Subsequently upper part 8b of the on-off sub 8 may be connected to the bottom of drill pipe 10. Sections of drill pipe are added to form drill pipe 10. The drill pipe 10 is lowered into the tubular. Then the on-off sub 8 is made-up, for instance through right-hand rotation of the drill pipe sections. Upon lifting up the assembly on the drill pipes, the top of the tubular element 1 is released from the support device.

[0051] Subsequently the tubular assembly is run into the wellbore by adding drill pipes in correspondence with the depth of the wellbore. During running-in the assembly into the wellbore the weight of the tubular element 1 is transferred to the expansion string 2 via the contact between the internal upset 48 and the external splines 36, via the contact between the internal splines 44 and the nose portion 30 of the expansion cone 14, and via the contact between outwardly flaring lower portion 52 of the starter joint 42 and the expansion cone 14.

[0052] Rotary torque required for making-up the on-off sub 8, or for reaming the wellbore while running the assembly into the wellbore, is transferred from the mandrel 4 via the castellated connection 28 to the near-cone centralizer 18, then via the castellated connection 26 to the torque retainer ring 16, then via the splined connection to the starter joint 42, and then via the pin member 43 and the corresponding box member to the remaining upper portion of the tubular element 1.

[0053] If the expansion cone 14 may get stuck in the tubular element 1 during the expansion process, for example while the expansion cone is located in an overlap section wherein the tubular element 1 overlaps a previous liner or casing, the drill pipe may be disconnected from the expansion string 2 by breaking out the on-off sub. At this stage the external splines 36 of the torque retainer ring 16 may no longer be in contact with the internal splines 44 of the starter joint 42. In such instance the break-out torque for breaking out the on-off sub is transmitted from the drill pipe via the on-off sub to the mandrel 4, then via the castellated connections 28, 26, 24 to the expansion cone 14, and finally via the face of the expansion cone 14 to the tubular element 1.

[0054] If the tubular element needs to be pushed in downward direction to overcome friction between the tubular element 1 and the wellbore wall, for example during running-in the expansion assembly into a high inclination borehole, the required downward force is transmitted from the drill pipe and mandrel 4 via the near-cone centralizer 18 to the annular internal upset 48 of the starter joint 42 and hence to the stuck point of the tubular element 1.

[0055] Once the expansion assembly has reached the target depth in the wellbore, the expansion process is started by applying a selected upward force to the drill pipe to move the expansion string 2 upwardly while the tubular element 1 is held stationary, for example by anchoring the tubular element 1 to another tubular element arranged in the wellbore. In this manner the external splines 36 of the torque retainer ring 16 expand the internal upset 48 of the starter joint 42 until the internal upset becomes flush with the outer diameter of the nose portion 30 of the expansion cone 14. The inclined upper surfaces 38 of the external splines 36 and the correspondingly inclined upper surfaces 47 of the slots 46 induce the onset of expanding the internal upset. Simultaneously, the expansion cone 14 expands the lower section 52 of the starter joint 42 followed by the splined portion of the starter joint, and subsequently the remainder of the tubular element 1.

[0056] In view of the relatively high local contact stresses that may occur between the expansion cone 14 and the edges of the internal splines 44 during expansion, the inner surface of the starter joint 42 may be provided with a dedicated coating, for instance a solid lubricant. A suitable example of such coating is Manganese Phosphate overlayed by a layer of a teflon based material, for example Xylan™ coating. A solids free coating, e.g. Rust Preventing Solid Lubricant film, may be used in combination with such coating.

[0057] The load carrying capacity of the starter joint 42 is selected such that the force required to release the expansion string 2 from the starter joint 42 exceeds the buoyant weight of the tubular element 1 in a vertical borehole. In this manner premature plastic deformation of the starter joint 42 is prevented. Such premature plastic deformation could otherwise result in an increase of the maximum diameter of the lower section 52 of the starter joint 42 to the extent that the starter joint 42 cannot pass through another tubular element already installed in the wellbore.

[0058] FIG. 3 indicates some design parameters that may be used to achieve the required minimum force to release the expansion string 2 from the starter joint 42. The starter joint 42 has a reference wall thickness t.sub.o substantially equal to that of the remainder of the tubular element 1. The started joint may be manufactured from the same expandable material as the remainder of the tubular element 1.

[0059] A suitale material may be for example VM-50 expandable tubular, marketed by Vallourec (France). VM 50 P110 is nickel based, and made of an austenitic Corrosion Resistant Alloy. The main alloying elements may be 54% Ni, 20% Cr and 9% Mo.

[0060] The push-down force capability, i.e. the capability of pushing the tubular element 1 downwardly via the expansion string 2, is dependent on the dimensions of the internal upset 48: h, t.sub.u and α. The rotational torque transmission capability via the splined connection is dependent on the dimensions of the splines: l, w and h. The weight carrying capacity of the starter joint 42 is dependent on the dimensions of the internal upset 48: h, β, the cross-sectional area and number of external and internal splines 36, 44, and the maximum diameter of the lower section 52 of the starter joint.

[0061] Furthermore, the friction factor at the interface between the expansion cone 14 and the lower section 52 can be increased to increase the weight carrying capacity, for example by application of a high-friction copper coating at the interface.

[0062] The weight carrying capacity obtained by the internal upset 48, the splines 36, 44 and the lower section 52 enables a maximum length of the tubular element 1 to be carried into the wellbore whereby the buoyant weight of the tubular element in a vertical hole is less than the expansion force required to expand the tubular element 1.

[0063] A safety margin may be applied to compensate for variations in friction factor at the interface between the expansion cone 14 and the lower section 52 of the starter joint 42, and to compensate for reduction of the material yield strength with increasing temperature. The length of tubular element that may be run into the wellbore with the starter joint 42 may be up to 3500 ft (1067 m).

[0064] The load carrying capacity of the starter joint 42 may be increased in the following ways: [0065] increase the wall thickness t.sub.u at the internal upset 48; [0066] increase the wall thickness of the outwardly flaring lower section 52 from t.sub.0 to t.sub.1; [0067] increase the yield grade of the material of the outwardly flaring lower section 52 from e.g. steel grade 50 to an expandable steel grade 80, which may be combined with an increased wall thickness of lower section 52. The latter may be butt welded to the remaining portion of the starter joint 42.

[0068] A combination of the above measures may result in an increase of the load carrying capacity of the starter joint 42 of about 100% or more. The invention thus enables for instance about 7000 ft (2134 m) of expandable tubular element to be run into the borehole in a controlled way in a single trip.

[0069] The above design modifications may result in a significantly increased peak expansion force of the starter joint relative to the load carrying capacity, which may put a high demand on the pulling capacity of the drilling rig. To mitigate this effect the wall thickness of a section of the starter joint just above the outwardly flaring lower section 52 may be reduced.

[0070] Referring to FIG. 4, the starter joint 42 also may be used for cladding of a host casing in a wellbore. The host casing may for example be a conventional casing or an already expanded casing. Cladding the existing casing may increase the collapse rating of the host casing. In such application, a constant wall thickness of the starter joint may be required in order to provide a constant support to the host casing and to control the peak expansion force.

[0071] The starter joint 42 may also function to anchor the expanded tubular element to the host casing. Thus, the expanded starter joint will form a cased hole anchor, i.e. an anchor for anchoring the expanded tubular element to the casing of the cased borehole. This can be achieved by providing cylindrical section 56 of the starter joint 42 with a high friction layer 58. For this purpose carbide particles may be used that may be brazed or laser-coated to the outer surface of cylindrical section 56. Alternatively small ceramic ball may be partly pressed into the wall of cylindrical section 56. Such cased hole anchor provides a very effective means of anchoring the expanded tubular element to the host casing and allows the remainder of the tubular element to be expanded by rig overpull.

[0072] With the assembly of the invention it may be achieved that the expansion string is locked to the starter joint during transport to the rig and during make-up of the tubular element on the rig floor. Further, the starter joint transfers the weight of the tubular element to the expansion string without the tubular element being prematurely expanded, and transfers rotary torque from the expansion string to the tubular element required for making-up and breaking-out of the on-off sub connection and for reaming with the expansion assembly while running into the borehole. Also, the starter joint transfers a downward force from the expansion string to the tubular element to enable the tubular element to be pushed into the borehole in case obstructions are encountered on the way down.

[0073] The present invention is not limited to the embodiments thereof described above, wherein many modifications are conceivable within the scope of the appended claims. Features of respective embodiments may for instance be combined.