FIELD OF THE INVENTION

[0001 ] The present invention generally relates to a drilling apparatus and more particularly to a vibration and/or shock absorbing floating subassembly for a drill string assembly. The invention is particularly applicable for absorbing vibrations that are transmitted through a drill string from the drilling actions of that drill string and it will be convenient to hereinafter disclose the invention in relation to that exemplary application.

BACKGROUND OF THE INVENTION

[0002] The following discussion of the background to the invention is intended to facilitate an understanding of the invention. However, it should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge as at the priority date of the application.

[0003] The drilling operation of a drill string can transmit a significant amount of vibration between the drill bit and the drill string. Shock and/or vibration absorber subassemblies can be used to reduce some of that vibration. Such shock subassemblies can greatly extend the life of the drill bit as well as the life of the entire drill string. Depending on the application, a shock subassembly can connected in a drill string directly above a drill bit, directly above a down hole hammer tool, adjacent to any stabilizers that may be included in the drill string, or adjacent the drive means of the drill string.

[0004] In some applications, a shock absorber can be incorporated into a floating sub arrangement. Floating subassemblies are used in a drill string between the top drive head and the drill string. The floating or axial slipping motion of the subassembly allows the driller to more effectively and efficiently manage the drill string by removing the feed cylinder and pipe weight forces from thread flanks during make-up or breakout of tool joints. Furthermore, the shock absorbing element within the subassembly allows the subassembly to reduce vibration forces transmitted to the hydraulic motor and gear box, commonly known as a rotary head, of the drilling rig. [0005] Existing floating subassemblies having vibration absorbing features generally have a complex arrangement of internal pistons or pins to transmit torsional forces and dampen axial shocks. One example of this type of piston vibration absorbing arrangement is described in international patent publication No. WO2009/135248A1 .

[0006] It would therefore be desirable to provide an alternative and/or simpler vibration absorbing floating subassembly for a drill string.

SUMMARY OF THE INVENTION

[0007] The present invention provides a drilling apparatus, and more preferably a floating subassembly for a drill string assembly. The drilling apparatus includes an outer housing having a longitudinal axis which extends longitudinally through the outer housing. The outer housing also has a chamber therein which has an axial cross-sectional shape (relative to the longitudinal axis) having an engagement configuration. The drilling apparatus also includes a first connector which has a first external connection section for connection to a section of a drill string, and a first insertion section which is axially received within the chamber. The first connector is securable to or forms a part of the outer housing when the apparatus is assembled. The drilling apparatus further includes a second connector which has a second external connection section for connection to a section of a drill string, and a second insertion section which is axially received within the chamber. The second insertion section has a complementary axial configuration to the chamber which engages with the chamber when received therein. The drilling apparatus also includes a vibration absorber seated within the chamber between the first connector and the second connector. In order to provide a float configuration, the second connector is axially moveable within the outer housing relative to the first connector. The second insertion section has a distal end which, in use, engages and compresses the absorber upon axial movement of the second connector towards the first connector within the outer housing.

[0008] The present invention therefore provides a floating subassembly which includes a vibration or shock absorbing dampening body which functions to reduce or substantially prevent drill string vibration in the axial plane from reaching the drive means/ rotary head of the drill string. The fit between the second connector section and outer housing enables the subassembly to transmit torsional force through the subassembly, and therefore be rotationally driven by and within the drill string assembly. Furthermore, the floating mounting of the second connector section provides the desired axial freedom and movement required by a floating subassembly which is useful for pipe connections.

[0009] The second connector is a floating body within the outer housing which is axially driven by means of the engagement between the outer housing and second connector. This configuration prevents axial rotation of that connector within the outer housing. In some embodiments, the engagement configuration provides an interference fit between the chamber and the second connector. The cross-sectional engagement configuration of the chamber can have any suitable shape or configuration. In some embodiments, the cross-sectional engagement configuration of the chamber includes at least one flat surface. Examples of suitable cross- sectional engagement configurations of the chamber include (but are not limited to) polygons such as a triangle, square, pentagon, heptagon, hexagon, octagon, nonagon, or decagon. In one exemplary embodiment, the cross-sectional engagement configuration of the chamber is a pentagon. Conversely, it is preferable for the outer housing have a cylindrical exterior shape.

[0010] The floating body of the second connector has free axial movement between two specified points within the chamber. The second connector preferably moves within the outer housing between a first position in which the distal end of the second insertion section is spaced apart by a float distance from an engagement end of the vibration absorber, and a second position in which the distal end of the second insertion section is in engagement with the engagement end of the absorber. The second connector typically moves to the second position from the first position when an axial load is applied to the second connector in the axial direction of the first connector, for example when the drill string is being forced downwardly into a drill hole during a drilling operation. The second connector typically moves from the second position to the first position when that axial load is relieved, for example if the drill string/ drill head is lifted away from the drilling face. [001 1 ] The vibration absorber is received and seated within the chamber between a first stop located on an inner wall of the chamber, and a second stop located on the first connector. The vibration absorbing means can be preloaded within the subassembly and form one stop of the floating drive connection. The absorber may be placed in a compressed state when located between a first stop located on an inner wall of the chamber and a second stop located on the first connector. The stops can be located in, on or within any suitable feature within the chamber. In some embodiments, the first stop comprises an annular shoulder formed by a step in the internal surface of the chamber. The step is preferably formed by a step change in the internal diameter of the chamber.

[0012] The vibration absorber can comprise any material or combination of materials which provide a shock and/or vibration absorbing function. It is therefore advantageous for the vibration absorber to include a resilient and/or elastic material, and more preferably an elastomeric material, for example at least one rubber material. The vibration absorber can be formed from a unitary material and/or be formed of a unitary body. However, it has been found that a combination of materials provides advantageous dampening properties. In one embodiment, the absorber comprises stacked arrangement of alternating sections of a resilient material and a substantially incompressible material. The alternating sections can comprise coaxial annular plates or pads, for example alternating plates of an elastomer and a metal such as rubber and steel. However, it should be appreciated that other configurations known in the art would also be suitable.

[0013] The first connector is preferably fixed to one end of the outer housing when the drilling apparatus is assembled. The first connector can be integrally formed with the outer housing. However, the first connector is more preferably configured to be releasably securable to one end of the outer housing. For example, the first connector may include an end plate which can be screwed onto or otherwise fastened to one end of the outer housing. In some embodiments, the first insertion section can have a portion having a complementary axial configuration to the chamber that engages with the chamber when received therein. This fit optimises the transfer of torsional forces through the first connector to the outer housing. [0014] The second connector is designed to float with axial freedom within the chamber of the outer housing. The drilling apparatus can preferably further include at least one retention cap which is releasably securable to one end of the outer housing to retain the second connector within the outer housing between the retaining cap and the first connector. The retention cap typically includes an opening through which the second connector section extends.

[0015] The subassembly can be designed to transfer fluid (for example, a liquid or a gas such as compressed air) between the first external connection section and the second external connection section. The first connector may therefore include an elongate connector shaft that axially extends from the first extension section and is received within an axial connection passage in the second insertion section of the second connector. The connector shaft preferably also extends through the vibration absorber. The distal connector shaft is preferably hollow and can therefore form, in connection with the axial connection passage, a substantially fluid tight passage between the first external connection section and the second external connection section. An annular fluid seal can be located between an outer surface of the connector shaft and inner surface of the axial connection passage of the second insertion section. The fluid seal forms a fluid tight seal between the connector shaft and the axial connection passage. The fluid seal can be seated within an annular recess within the inner surface of the axial connection passage of the second insertion section. Any suitable seal can be used.

[0016] The first connection section and the second connection sections are configured for engagement with sections of driven drill string and therefore preferably include threaded sections for connection to a complementary threaded section of a drill string. Each of the first connection section and the second connection sections may have an external thread or an internal box thread to match the threaded joint that connection section is to connect with. In a preferred embodiment, the first connection section includes an outer thread and the second connection section includes an internally threaded hole. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention will now be described with reference to the figures of the accompanying drawings, which illustrate particular preferred embodiments of the present invention, wherein:

[0018] Figure 1 is an exploded perspective view of a drilling apparatus according to one embodiment of the present invention.

[0019] Figure 2 is an assembled perspective view of the drilling apparatus shown in Figure 1 .

[0020] Figure 3 is an alternate exploded perspective view of the drilling apparatus shown in Figure 1 .

[0021 ] Figure 4 is a longitudinal cross-sectional view of the drilling apparatus shown in Figure 1 .

DETAILED DESCRIPTION

[0022] Figures 1 to 4 illustrate one embodiment of a vibration absorbing floating subassembly 10 according to the present invention. The subassembly 10 has an outer housing 14 through which runs a longitudinal axis X-X. The outer housing 14 has an outer cylindrical surface 16 and an inner surface 18, which together with an end cap 20 and an upper connector 22 secured over opposite ends of the outer housing 14, form an inner closed chamber 24. As best shown in Figures 1 and 3, the inner closed chamber 24 has a pentagon shaped axial cross-section (i.e. the cross- sectional shape which is perpendicular to the longitudinal axis X-X). Thus, the inner surface 18 of the outer housing 14 is shaped to provide the inner closed chamber with a pentagonal or any other suitably shaped cross section.

[0023] The subassembly 10 is designed to connect the rotary head or rotation head and the drill string (not illustrated) or can be between two sections of a drill string (not illustrated). The upper (or first) connector 22 of the subassembly 10 has an outer threaded connection section 28 configured to be connected to the rotary head or rotation head into an adjoining section of a drill string assembly (not illustrated). The subassembly 10 also has a lower (or second) connector 30 which is fitted in a slidable or floating manner within the chamber 24 of the outer housing 14. The lower connector 30 has an internally threaded cylindrical connection section 32 which provides a box connection through which the lower section of subassembly 10 can be connected into an adjoining section of a drill string assembly (not illustrated).

[0024] While the present description refers to the orientations of the upper connector 22 and lower connector 30, it is to be appreciated that these connectors 22, 30 need not be orientated in the position shown in the Figures. However in a conventional drill string assembly, the pin connection 28 of the upper connector 22 is connected directly to the output of the rotary drive of a drilling rig (not shown), hereinafter referred to as the drive portion of the drill string. Furthermore, the box connector 32 of the lower connector 30 is typically directly connected to the upper most section of the actual drill string, hereinafter referred to as the driven portion of the drill string.

[0025] The upper connector 22 and the lower connector 30 are operatively connected through the outer housing 14 of the subassembly 10.

[0026] The upper connector 22 comprises two main sections: the outer threaded connection section 28 for connection to a section of a drill string (not illustrated), and a first insertion section 36 which is axially received within the inner closed chamber 24 of the outer housing 14. The upper connector 22 has circular end plate 38 configured to be releasably securable to one end of the outer housing 14. The end plate 38 includes a plurality of annually spaced apart openings 40 which have complementary threaded bore holes 42 (Figure 3) in the respective end face 44 of the outer housing 14. As shown in Figures 2 and 4, the end plate 38 can therefore be screwed onto the respective end of the outer housing 14 using a plurality of fastening bolts 46. The first insertion section 36 also includes a pentagon shaped hub 50 which extends from the base of the end plate 38 and is inserted into the inner closed chamber 24 of the outer housing 14. This hub 50 has a complementary axial configuration to the chamber 24 and which engages with the chamber 24 when received therein. This fit optimises transfer of torsional forces through the upper connector 22 to the outer housing 14. However, it is to be appreciated that in an alternative embodiment, the hub 50 need could have an axial configuration that is not shaped complementarily to the chamber 24 as the first insertion section 36 is fixed to the outer housing 14 by the fastening bolts 46. The first insertion section 36 also includes a hollow elongate connector shaft 52 which axially extends from an inner face 51 of the hub 50 into the chamber 24. The upper connector 22 includes an axial fluid passageway 54 (Figure 4) through the outer threaded connection section 28 and insertion section 36 which is fluidly connected to the lower connector 30.

[0027] The lower connector 30 comprises two main sections: the internally threaded cylindrical connection section 32 for connection to a section of a drill string (not illustrated), and a second insertion section 60 which is axially received within the inner closed chamber 24 of the outer housing 14. The lower connector 30 is retained within the chamber 24 by the end cap 20. The end cap 20 is configured to be releasably securable to the opposite end of the outer housing 14 to the upper connector 22. The end cap 20 comprises a circular plate having a central opening 63 through which connection section 32 outwardly extends. The outer circumference of the end cap 20 includes a plurality of annually spaced apart openings 62 which have complementary threaded bore holes 64 (Figure 1 ) in the respective end face 66 (Figure 1 ) of the outer housing 14. As shown in Figures 2 and 4, the end plate 38 can therefore be screwed onto the respective end of the outer housing 14 using a plurality of fastening bolts 68. The second insertion section 60 of the lower connector 30 has a proximal end 65 comprised of a substantially flat surface which, in use, engages an inner surface 67 of the end cap 20 thereby capturing the second insertion section 60 within the inner chamber 24. Two O-ring seals 69, 70 are rebated into the central opening 63 of the end cap 20 to form a fluid seal between the central opening 63 and outer surface 33 of the connection section 32.

[0028] The second insertion section 60 has a complementary pentagonal axial configuration (i.e. pentagonal cross-section) to the inner closed chamber 24 of the outer housing 14 which engages with the chamber 24 when received therein. It should be appreciated that other complementary cross-sectional shapes for the second insertion section 60 would also be suitable without departing from the spirit or scope of the present invention. The invention should therefore not be limited to the pentagonal cross-sectional shape illustrated in the Figures. Examples of suitable cross-sectional configurations of the chamber include (but are not limited to) polygons such as a triangle, square, pentagon, heptagon, hexagon, octagon, nonagon, or decagon. In another possible embodiment, the second insertion section 60 may have axial splines that fit into axial recesses in the inner surface 18 of the outer housing 14, or vice versa. In another embodiment, the second insertion section 60 and the inner surface 18 of the outer housing 14 may be keyed together (e.g. with one or more keyways provided in one or the other of the second insertion section 60 and the inner surface 18 of the outer housing 14) so as to permit axial movement of the second insertion section 60 relative to the inner closed chamber 24 yet prevent relative rotation between the two parts and to enable forgue transmission.

[0029] The fit between the second insertion section 60 and the cross-sectional shape of the inner closed chamber 24 prevents axial rotation of the lower connector 30 within the outer housing 14. Accordingly, this fit enables torsional forces to be transferred between the outer body 14 and lower connector 30, thereby enabling the lower connector to be axially driven by the upper connector 22 through the outer body 14. Thus, when the subassembly 10 is connected between a drive portion of the drill rig (not illustrated) and the driven portion of the drill string (not illustrated), rotational forces from the drive portion can be effectively transferred through the subassembly 10 to the connected driven portion of the drill string.

[0030] The lower connector 30 has free axial movement within the chamber 24 between a first position in which the distal end 70 of the second insertion section 60 is spaced apart by a float distance F from an engagement end 72 of a vibration absorber 75 (described below) of the subassembly 10 (as shown in Figure 4), and a second position in which the distal end 70 of the second insertion section 60 is in engagement with the engagement end 72 of the vibration absorber 75. During drilling operation, where the subassembly 10 is connected between a drive means (not illustrated) and a drill string assembly (not illustrated), the lower connector 30 typically moves to the second position from the first position when an upwardly directed axial load is applied to the lower connector 30 from the drill string, for example when the drill string is being forced downwardly into a drill hole during a drilling operation. The lower connector 30 typically moves from the second position to the first position when that axial load is relieved, for example if the drill string/ drill head is lifted away from the drilling face. [0031 ] The lower connector 30 also includes an axial fluid passageway 76 (Figure 4) through the internally threaded cylindrical box connection section 32 and insertion section 60 which is fluidly connected to the upper connector 22. In this respect, the hollow elongate connector shaft 52 of the upper connector 22 axially extends and is received within the axial fluid passageway 76 of the lower connector 30. An O-ring fluid seal 78 (Figure 4) is seated within an annular recess 79 within the inner surface of the axial fluid passageway 76 of the lower connector 30 to form a substantially fluid tight seal between the connector shaft 52 and axial fluid passageway 76. The subassembly 10 can therefore transfer fluid between the outer threaded connection section 28 of the upper connector 22 and the internally threaded cylindrical box connection section 32 of the lower connector 30.

[0032] The vibration and/or shock absorbing capability of the subassembly 10 is provided by a vibration absorber 75 seated within the internal closed chamber 24 of the outer housing 15 between the upper connector 22 and the lower connector 30 and seated around the hollow elongate connector shaft 52 of the upper connector 22. The second insertion section 60 of the lower connector 30 has a distal end 70 comprised of a substantially flat surface 71 which, in use, engages and compresses the absorber 75 upon axial movement of the lower connector 30 towards the upper connector 22 within the outer housing 14.

[0033] The illustrated vibration absorber 75 comprises a stacked arrangement of alternating coaxial annular plates or pads 80 of rubber 81 and metal, preferably steel 82 (Figure 4). A metal, preferably steel, end plate 84 is also provided. However, it should be appreciated that other configurations known in the art would also be suitable for example a unitary elastomeric body or other suitable composite material, structure or body. The vibration absorber 75 functions to reduce or substantially prevents drill string vibration in the axial plane from reaching the drive means/ rotary head of a drill string (not illustrated).

[0034] The vibration absorber 75 is received and seated within the inner chamber 24 of the outer housing 14 between a first stop comprising an annular shoulder 86 (Figure 4) formed by a step in the internal diameter of the chamber 24, and a second stop comprising the inner face 51 of the hub 50 of upper connector 22. In some embodiments, the vibration absorbing means can be preloaded into the chamber 24 and are therefore ready for use during drilling operation as soon as that subassembly is installed within a drill string assembly.

[0035] In use, the illustrated subassembly 10 is connected between the drive portion of the drill string (not illustrated) and the driven portion of the drill string (not illustrated). The subassembly 10 functions both as a floating subassembly and a vibration or shock absorbing dampening body which reduces or substantially prevents drill string vibration in the axial plane from reaching the drive means or rotary head of the drill string.

[0036] Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is understood that the invention includes all such variations and modifications which fall within the spirit and scope of the present invention.

[0037] Where the terms "comprise", "comprises", "comprised" or "comprising" are used in this specification (including the claims) they are to be interpreted as specifying the presence of the stated features, integers, steps or components, but not precluding the presence of one or more other feature, integer, step, component or group thereof.