GB2481203A

GB2481203A - Reamer having supportive struts

Info

Publication number: GB2481203A
Application number: GB1009888.7A
Authority: GB
Inventors: Steinar Wasa Tverlid
Original assignee: Statoil ASA
Current assignee: Equinor ASA
Priority date: 2010-06-14
Filing date: 2010-06-14
Publication date: 2011-12-21
Anticipated expiration: 2030-06-14
Also published as: GB2481203B; GB201009888D0; NO20110851A1; NO345043B1

Abstract

A reaming tool 20 for enlarging a borehole includes a cylindrical body 21, and a plurality of blades 22 carrying cutting elements 23, the blades 22 being circumferentially spaced around the cylindrical body 21. Each of the blades 22 is provided with at least one support 24 for maintaining the blade 22 in a reaming position. Each blade 22 and its corresponding at least one support 24 is coupled to the cylindrical body 21 such that, in use, when a force is applied to the cutting elements 23 due to rotation of the cylindrical body 21 within a borehole, the corresponding at least one support 24 is placed substantially under one of tensile or compressive stress and the blade 22 is placed substantially under the other of tensile or compressive stress.

Description

REAMING TOOL

Technical Field

The present invention relates to a reaming tool for use in drilled boreholes, as are typically utilised in oil and gas production.

BackQround of the Invention Following the initial drilling of a wellbore or borehole into a formation, it is sometimes necessary to ream or enlarge the borehole. For example, it may be required that the diameter of a borehole be larger than can be achieved with a drill bit that currently fits inside the borehole. Alternatively, if the drill bit has worn down during the drilling of the borehole, then a section of the borehole may not be as large as it should be, or a section of the wall of the borehole may have collapsed or moved into the borehole, at least partially obstructing the borehole.

Figures 1A to 1D illustrate a conventional borehole enlargement tool or reamer 10 that consists of a tubular body 11 attached to or within the drill string, and which has multiple radially-projecting blades or arms 12 spaced around its circumference. The blades are often retractable/extendable and are provided with cutting edges or elements 13 on their ends or tips. In use, the reamer 10 is rotated within the borehole such that the cutting elements 13 on the projecting blades make contact with the edges or walls of the borehole, dislodging formation material and enlarging the borehole.

The resistance of the formation material against the rotation of the radially-projecting blades 12 causes a shear force to be applied at the distal end of the blades, which in turn causes a force to act in the opposite direction at the proximal end of the blades where the blades are attached/coupled to the body 11 of the tool 10. The moment generated by these forces causes the blades to bend. These forces vary as the tool 10 is rotated and the blades 12 come into contact with the uneven surface of the borehole, such that the moment acting on the blades 12 also varies. This varying moment combined with the elasticity of the blades 12 causes the blades to vibrate (as illustrated in Figure 1D). This instability can damage the tool, the drill string and other tools on the drill string, and can affect the size and uniformity and general quality of the borehole.

Sum mary of the Invention It is an object of the present invention to provide a reaming tool that experiences minimal vibration when used to enlarge a borehole, thereby reducing the problems associated with such instability.

According to a first aspect of the invention, there is provided a reaming tool for enlarging a borehole. The reaming tool comprises a cylindrical body; and a plurality of blades carrying cutting elements, the blades being circumferentially spaced around the cylindrical body; wherein each of the blades is provided with at least one support for maintaining the blade in a reaming position, each blade and its corresponding at least one support being coupled to the cylindrical body such that, in use, when a force is applied to the cutting elements due to rotation of the cylindrical body within a borehole, the corresponding at least one support is placed substantially under one of tensile or compressive stress and the blade is placed substantially under the other of tensile or compressive stress.

Each blade may be coupled to its corresponding at least one support and to the cylindrical body so as to form a truss. The corresponding at least one support can be orientated such that it is substantially perpendicular to the blade when the blade is in the remaining position.

Each blade may be coupled to the cylindrical body at a proximal end, and the cutting elements on each blade disposed on or adjacent to a distal end of the blade. Each blade can coupled to its corresponding at least one support adjacent to the distal end of the blade. Each blade may be pivotally coupled to the cylindrical body and to its corresponding at least one support, and each corresponding at least one support may be pivotally and slidably coupled to the cylindrical body.

Each blade and corresponding at least one support may be retracted towards the cylindrical body. The cylindrical body may be formed with a recess adjacent to each blade and corresponding at least one support, each recess being suitable for accommodating a blade and corresponding at least one support when retracted.

The reaming tool may be configured to be rotated in a direction such that, in use, when a force is applied to the cutting elements due to rotation of the cylindrical body within a borehole, the corresponding at least one support is placed substantially under tensile stress and the blade is placed substantially under compressive stress. Alternatively, the reaming tool may configured to be rotated in a direction such that, in use, when a force is applied to the cutting elements due to rotation of the cylindrical body within a borehole, the corresponding at least one support is placed substantially under compressive stress and the blade is placed substantially under tensile stress. The exposed cutting surface of each cutting element will face in substantially the same direction to that in which the reaming tool is configured to rotate.

When in the reaming position, each blade can be configured to project away from the cylindrical body in a substantially tangential direction. As such, each blade may be coupled to the cylindrical body and to its corresponding at least one support such that each blade projects substantially tangentially away from the cylindrical body when in the remaining position.

Brief Descrirtion of the Drawings Figure 1A is a perspective view of a reamer; Figure 1 B is a cross-section through the reamer of Figure 1A with the blades retracted; Figure 1 C is a cross-section through the reamer of Figure 1A with the blades extended; Figure 1 D is a cross-section though a blade of the reamer of Figure 1A; Figure 2A is a perspective view of a reamer according to a first embodiment; Figure 2B is a cross-section through the reamer of Figure 2A with the blades extended; Figure 2C is a cross-section though a blade of the reamer of Figure 2A; Figure 2D is a perspective view of the reamer of Figure 2A with the blades partially retracted; Figure 3 is a side view of the reamer of Figure 2A within a borehole; Figure 4A is a cross-section through a reamer according to a second embodiment; Figure 4B is a cross-section though a blade of the reamer of Figure 4A, and Figure 5A is a perspective view of a reamer according to an alternate embodiment; Figure 5B is an underneath view of the reamer of Figure 5A.

Detailed Descriition of the Invention In order to reduce the vibration that occurs when using conventional reaming tools, and therefore overcome the problems associated with such vibration, it is proposed here to make use of a reaming tool in which the shear force and therefore the moment experienced by the blades is minimised. This is achieved by providing that each blade of the reaming tool has at least one support arm that is coupled to the blade and to the body of the tool so as to form a truss-type structure. A truss is a structure for supporting a load and is comprised of straight members whose ends are connected so as to form one or more triangular units in the load direction, such that the forces in the members when supporting the load are either tensile or compressive forces. Each blade, its corresponding support arms and the section of the body of the tool between each blade and the corresponding support arms form the chords or members of the truss.

Figures 2A to 2D illustrate schematically an embodiment of a reamer or reaming tool suitable for enlarging a borehole whilst minimising vibration. The reaming tool 20 comprises a cylindrical body 21 that can be attached to or within a drill string, and which has multiple retractable/extendable blades or arms 22 spaced around its circumference. The profile of each blade 22 narrows to a point at the lower end of the blade in order to enable the blade 22 to gradually widen the borehole as it is rotated and driven down into the borehole. Each blade 22 has a cutting element 23 located around or adjacent to its exposed edge. Each blade is also provided with a number of corresponding support arms 24 that are attached to both the blade 22 and the body 21 of the tool. These support arms 24 enable the extension and retraction of the blades, and act as braces or struts in order to prevent the blades 22 from bending when in the extended reaming position (as illustrated in Figure 2A and Figure 2B).

Adjacent to each blade-support pair, the outer surface of the cylindrical body 21 is formed with a recess 25, and each of these recesses 25 is shaped so as to receive/accommodate both the blade 22 and support 24 when the blades 22 are retracted, as illustrated in Figure 2D.

The proximal end of each blade 22 is rotatably/pivotally coupled to the cylindrical body 21 by means of a blade hinge 26. Adjacent to its distal end or tip each blade 22 is also rotatably/pivotally coupled to the distal end of each corresponding support arm 24 by a means of a support hinge 27. The opposing or proximal end of each support arm 24 is then pivotally and slidably coupled to the cylindrical body 21 by means of a slidable hinge 28 located within a slot or channel 29 formed in the recess 25 (see Figure 2A).

This multi-hinged configuration provides that each blade 22 and its corresponding support arm 24 form a collapsible truss-type structure.

The blade hinges 26, support hinges 27 and slidable hinges 28 enable the blades 22 to be extended out from within the recess 25 and retracted back into the recess 25. In order to extend each blade 22 out from within its corresponding recess 25, an actuator (not shown) is activated to push/drive the slidable hinge 28 along channel 29 towards the blade 22. For example, the actuator could take the form of a hydraulic ram. This movement of the slidable hinge 28 shortens the distance between the slidable hinge 28 and the blade hinge 26, pushing both the support 24 and the blade 22 away from the body 21 of the reaming tool 20. In doing so, the support 24 pivots around the slidable hinge 28 and the support hinge 27, whilst the blade 22 rotates around the support hinge 27 and the blade hinge 26. The slidable hinge 28 can be held in this position using a locking mechanism (not shown) such that the blade 22 will be secured in an extended position (as illustrated in Figures 2A to 2C). This locking mechanism can also be provided with a suspension or shock absorption system that would allow the blades some freedom to partially retract before returning to the extended position. This would be particularly useful in reducing vibration when reaming a borehole whose surface is especially rough.

When in the extended configuration, each blade 22 projects substantially tangentially from the point on the body 21 at which the blade 22 is coupled to the body by the blade hinge 26, as illustrated by the tangential projection arrow in Figure 2B. In this embodiment, when the blades 22 are extended, the exposed cutting surface of the cutting element 23 faces in substantially the same direction as that in which the blade 22 projects. In other words, the exposed cutting surface of the cutting element 23 faces away from the point at which the blade 22 is attached to the tubular body 21.

When it is required to retract a blade 22, the locking mechanism is released and the actuator is activated in order to draw/pull the slidable hinge 28 back along channel 29 away from the blade 22. This movement of the slidable hinge 28 lengthens the distance between the slidable hinge 28 and the blade hinge 26, therefore pulling both the support 24 and the blade 22 back into the recess 25. In doing so, the support 24 pivots around the slidable hinge 28 and the support hinge 27, whilst the blade 22 pivots around the support hinge 27 and the blade hinge 26. The locking mechanism can also be used to hold the slidable hinge 28 in this position, securing the blade 22 in the retracted configuration.

When required, the reaming tool 20 with the blades 22 retracted will be attached to or within a drill string and lowered into a borehole that is to be enlarged. Once the reaming tool 20 has been located in the section of the borehole that requires enlargement, the blades 22 are extended into a reaming position. The reaming tool 20 is then rotated within the borehole in the direction that enables reaming of the borehole (i.e. the direction in which the exposed cutting surfaces of the cutting elements 23 are facing). The cutting elements 23 on the projecting blades 22 then make contact with the edges or walls of the borehole, dislodging formation material and enlarging the borehole, as illustrated in Figure 3.

The resistance of the formation material against the rotation of the projecting blades 22 acts predominantly as a compressive force directed through the blades 22, from the ends of the blades 22 towards the point at which the blades 22 are coupled to the body 21 by the blade hinges 26. In addition, any minor component of the resistive force that is directed perpendicularly to the blades 22, and not directed along the blades, will cause a tensile force to act through the support 24 (as illustrated in Figure 2C). As such, this arrangement of the blades 22 and their corresponding supports 24 enables them to act as a truss-type structure, in which the force in each of the blade and the support is either tensile or compressive, therefore largely avoiding the shear forces and bending moments that can cause the blades to bend and induce vibrations in the reamer. When the reaming operation is completed the blades 22 can be retracted back into their associated recesses 25 to enable the reaming tool 20 to be removed from the borehole. In order to assist in the retraction of the blades 22, the reaming tool can be rotated in the opposite direction to the reaming direction (i.e. in the direction opposite to that of the arrows in Figure 2C and Figure 3).

Figures 4A and 4B illustrate schematically an alternative embodiment of a reaming tool 20' suitable for enlarging a borehole whilst minimising vibration. This alternative embodiment is similar to that of Figures 2A to 2D and like parts have been given like reference numbers. According to this alternative embodiment, the exposed cutting surface of each cutting element 23' faces in substantially the opposite direction to that in which the blade 22' projects. In other words, the exposed cutting surface of the cutting element 23' faces in the opposite direction to that of the cutting elements 23 illustrated in Figures 2A to 2D.

In use, the reaming tool 20' is rotated in the direction that the exposed cutting surfaces of the cutting elements 23' are facing. The cutting elements 23' on the projecting blades 22' then make contact with the edges or walls of the borehole, dislodging formation material and enlarging the borehole. However, the resistance of the formation material against the rotation of the projecting blades 22' acts predominantly as a tensile force directed through the blades 22', from the point at which the blades 22' are coupled to the body 21' by the blade hinges 26' towards the ends of the blades 22'. Any minor component of the resistive force that is directed perpendicularly to the blades 22', and not directed along the blades, will cause a compressive force to act through the support 24' (as illustrated in Figure 4B).

The arrangement of the blades 22' and their corresponding supports 24' enables them to act as a truss-type structure in which the force in each of the blade and the support is either tensile or compressive, therefore largely avoiding the shear forces and the bending moments that can cause the blades to bend and induce vibrations in the reamer. However, the alternative orientation of the cutting elements 23' on the blades 22' provides that it is the blades 22' that are placed under tension whilst it is the supports 24' that are compressed.

Figures 5A and SB illustrate schematically an alternative embodiment of a reaming tool 20" suitable for enlarging a borehole whilst minimising vibration. This alternative embodiment is similar to that of Figures 2A to 2D and Figures 4A and 4B and like parts have been given like reference numbers. Whilst the blades of the above-described embodiments have been illustrated as being substantially planar or flat, the vibration of the reamer can be further reduced by distributing the load on the blades around the circumference of the tubular body. This can be achieved through the use of blades 22" that are at least partially curved such that they extend around at least part of the cylindrical body 21" of the tool 20". Preferably the exposed edges of the blades at which the cutting elements 23" are located, form a partial helix, curving around the periphery of and extending longitudinally in relation to the cylindrical body 21", as illustrated by the bottom-up view of Figure 5B.

It will be appreciated by the person of skill in the art that various modifications may be made to the above described embodiments without departing from the scope of the present invention. For example, whilst the reaming tool of the above described embodiments has a cylindrical body, the body of the reaming tool could be tubular or take any other appropriate shape. In addition, whilst in the above-described embodiments each blade and its corresponding supports have been illustrated as being of substantially the same length, the length of each blade may well be greater than that of its corresponding support arms. In particular, this could be the case if the blades were required to extend a significant distance away from the body of the reamer when in a reaming position. Furthermore, in the above-described embodiments each blade has been illustrated as projecting substantially tangentially from the body of the reamer when in the reaming position. However, this need not be the case provided that, when in use and a force is applied to the cutting elements due to rotation of the reamer within a borehole, each blade is placed under one of tensile or compressive stress whilst its corresponding supports are placed substantially under the other of tensile or compressive stress.

Claims

CLAIMS: 1. A reaming tool for enlarging a borehole, the reaming tool comprising: a cylindrical body; and a plurality of blades carrying cutting elements, the blades being circumferentially spaced around the cylindrical body; wherein each of the blades is provided with at least one support for maintaining the blade in a reaming position, each blade and its corresponding at least one support being coupled to the cylindrical body such that, in use, when a force is applied to the cutting elements due to rotation of the cylindrical body within a borehole, the corresponding at least one support is placed substantially under one of tensile or compressive stress and the blade is placed substantially under the other of tensile or compressive stress.
2. A reaming tool as claimed in claim 1, wherein each blade is coupled to its corresponding at least one support and to the cylindrical body so as to form a truss.
3. A reaming tool as claimed in any preceding claim, wherein, for each blade, the corresponding at least one support is orientated such that it is substantially perpendicular to the blade when the blade is in the reaming position.
4. A reamer as claimed in any preceding claim, wherein each blade is coupled to the cylindrical body at a proximal end and the cutting elements on each blade are disposed on or adjacent to a distal end of the blade.
5. A reamer as claimed in claim 4, wherein each blade is coupled to its corresponding at least one support adjacent to the distal end of the blade.
6. A reaming tool as claimed in any preceding claim, wherein the reaming tool is configured to be rotated in a direction such that, in use, when a force is applied to the cutting elements due to rotation of the cylindrical body within a borehole, the corresponding at least one support is placed substantially under tensile stress and the blade is placed substantially under compressive stress.
7. A reaming tool as claimed in any of claims 1 to 5, wherein the reaming tool is configured to be rotated in a direction such that, in use, when a force is applied to the cutting elements due to rotation of the cylindrical body within a borehole, the corresponding at least one support is placed substantially under compressive stress and the blade is placed substantially under tensile stress.
8. A reaming tool as claimed in any of claims 6 or 7, wherein an exposed cutting surface of each cutting element faces in substantially the same direction to that in which the reaming tool is configured to rotate.
9. A reaming tool as claimed in any preceding claim, wherein each blade and its corresponding at least one support can be retracted towards the cylindrical body.
10. A reaming tool as claimed in claim 9, wherein the cylindrical body is formed with a recess adjacent to each blade and corresponding at least one support, each recess being suitable for accommodating a blade and corresponding at least one support when retracted.
11. A reaming tool as claimed in claim 9, wherein each blade is pivotally coupled to the cylindrical body and to its corresponding at least one support, and each corresponding at least one support is also pivotally and slidably coupled to cylindrical body.