Jarring apparatus

Abstract

A jarring apparatus includes first and second jarring assemblies rotatable relative to each other. A first impact surface is provided on the first jarring assembly and a second impact surface is provided on the second jarring assembly, wherein, in use, the first and second impact surfaces are biased together. A first lifting structure is rotatably fixed relative to the first jarring assembly and a second lifting structure is rotatably fixed relative to the second jarring assembly, the first and second lifting structures being configured to cooperate during relative rotation therebetween to cause cyclical relative displacement in one axial direction to define a lifting phase and relative displacement in a reverse axial direction to define a dropping phase. The first and second lifting structures are axially fixed relative to their associated jarring assembly during the lifting phase to provide axial separation between the first and second impact surfaces, and the second lifting structure is axially released relative to the second jarring assembly prior to initiation of the dropping phase to permit the first and second impact surfaces to be axially impacted together.

Claims

1. A jarring apparatus, comprising: first and second jarring assemblies rotatable relative to each other; a first impact surface provided on the first jarring assembly and a second impact surface provided on the second jarring assembly, wherein, in use, the first and second impact surfaces are biased together; and a first lifting structure rotatably fixed relative to the first jarring assembly and a second lifting structure rotatably fixed relative to the second jarring assembly, the first and second lifting structures being configured to cooperate during relative rotation therebetween to cause cyclical relative displacement in one axial direction to define a lifting phase and relative displacement in a reverse axial direction to define a dropping phase, wherein the first and second lifting structures are axially fixed relative to their associated jarring assembly during the lifting phase to provide axial separation between the first and second impact surfaces, and the second lifting structure is axially released relative to the second jarring assembly prior to initiation of the dropping phase to permit the first and second impact surfaces to be axially impacted together.

2. The jarring apparatus according to claim 1, wherein loading between the first and second jarring assemblies is applied between the first and second lifting structures when the second lifting structure is axially fixed relative to the second jarring assembly, and axial release of the second lifting structure reduces loading applied between the first and second lifting structures prior to initiation of the dropping phase.

3. The jarring apparatus according to claim 1, wherein the second lifting structure is axially released relative to the second jarring assembly prior to completion of the lifting phase.

4. The jarring apparatus according to claim 1, wherein the first and second lifting structures comprise inter-engaging profiles which cooperate during relative rotation of the lifting structures to cause the cyclical lifting and dropping phases, the inter-engaging profiles being configured such that a surface area of contact therebetween reduces as the lifting phase progresses.

5. The jarring apparatus according to claim 4, wherein the inter-engaging profiles comprise rotary cam surfaces.

6. The jarring apparatus according to claim 4, wherein the inter-engaging profiles of the first and second lifting structures are prevented from axial engagement during or following the dropping phase.

7. The jarring apparatus according to claim 6, wherein the inter-engaging profiles remain separated during a portion of relative rotation between the first and second lifting structures following the dropping phase, and wherein the inter-engaging profiles are brought into contact to initiate a subsequent lifting phase.

8. The jarring apparatus according to claim 1, wherein the first lifting structure is permanently axially fixed relative to the first jarring assembly at least in a direction of loading applied between the first and second lifting structures.

9. The jarring apparatus according to claim 1, wherein one of the first and second jarring assemblies axially extends into the other of the first and second jarring assemblies.

10. The jarring apparatus according to claim 1, wherein the first and second lifting structures are radially interposed between the first and second jarring assemblies.

11. The jarring apparatus according to claim 1, comprising a locking system for selectively axially fixing and releasing the second lifting structure relative to the second jarring assembly.

12. The jarring apparatus according to claim 11, wherein the locking system is operated in response to relative rotational movement between the first and second jarring assemblies.

13. The jarring apparatus according to claim 11, wherein the locking system comprises a hydraulic locking system for hydraulically locking and releasing the second lifting structure relative to the second jarring assembly.

14. The jarring apparatus according to claim 13, wherein the hydraulic locking system, when locked, hydraulically locks a volume of hydraulic fluid axially between the second lifting structure and the second jarring assembly such that axial forces are transmitted between the second lifting structure and second jarring assembly via the hydraulically locked fluid.

15. The jarring apparatus according to claim 13, wherein the hydraulic locking system comprises a first hydraulic chamber, and is configured to: lock hydraulic fluid within the first hydraulic chamber to hydraulically lock the second lifting structure relative to the second jarring assembly; and: release the hydraulically locked fluid from the first hydraulic chamber to permit axial release of the second lifting structure relative to the second jarring assembly.

16. The jarring apparatus according to claim 15, wherein the hydraulic locking system comprises a valve assembly which is closed to hydraulically lock fluid within the first hydraulic chamber, and which is opened to release the hydraulically locked fluid from the first hydraulic chamber.

17. The jarring apparatus according to claim 16, wherein the valve assembly is selectively opened and closed by relative rotation between the first and second jarring assemblies.

18. The jarring apparatus according to claim 16, wherein the valve assembly comprises a first valve portion rotatably fixed relative to the first jarring assembly and a second valve portion rotatably fixed relative to the second jarring assembly such that relative rotation between the first and second jarring assemblies causes corresponding relative rotation between the first and second valve portions.

19. The jarring apparatus according to claim 18, wherein the first and second valve portions each comprise at least one port, wherein the ports are sequentially aligned and misaligned during relative rotation between the first and second valve portions.

20. The jarring apparatus according to claim 16, wherein the hydraulic locking system comprises a second hydraulic chamber and the valve assembly is interposed between the first and second hydraulic chambers, the valve assembly being configurable between open and closed configurations such that when the valve assembly is closed the first and second hydraulic chambers are isolated from each other, and when the valve assembly is open the first and second hydraulic chambers are presented in communication with each other.

21. The jarring apparatus according to claim 20, wherein the second hydraulic chamber is defined by a flow path through the jarring apparatus.

22. The jarring apparatus according to claim 20, wherein the second hydraulic chamber extends between the valve assembly and a moveable barrier, wherein the moveable barrier is biased in a direction to displace hydraulic fluid from the second hydraulic chamber into the first hydraulic chamber when the valve assembly is open to provide relative displacement between the first and second lifting structures during the dropping phase.

23. The jarring apparatus according to claim 1, wherein the first and second jarring assemblies are rotatable relative to each other when configured in a first mode of operation, and the first and second jarring assemblies are rotatably fixed relative to each other when configured in a second mode of operation.

24. The jarring apparatus according to claim 23, wherein the jarring assemblies are reconfigurable between the first and second modes of operation by relative axial movement therebetween.

25. A method for providing jarring, comprising: providing a jarring apparatus which includes a first jarring assembly having a first impact surface and a first lifting structure rotatably and axially fixed relative to the first jarring assembly, and a second jarring apparatus having a second impact surface and a second lifting structure rotatably fixed relative to the second jarring assembly; axially fixing the second lifting structure relative to the second jarring assembly; establishing relative rotational movement between the first and second jarring assemblies to cause corresponding relative rotational movement between first and second lifting structures which cooperate to cause relative axial displacement in a lifting phase to cause axial separation between the first and second impact surfaces; and axially releasing the second lifting structure relative to the second jarring assembly to permit the first and second impact surfaces to be axially impacted together.

26. The method according to claim 25, wherein axially releasing the second lifting structure is performed by relative rotation between the first and second lifting structures.

27. The method according to claim 25, comprising, following axially releasing the second lifting structure, continuing relative rotational movement between the first and second jarring assemblies to cause reverse relative axial displacement in a dropping phase.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Aspects of the present disclosure will now be exemplified with reference to the accompanying drawings, in which:

(2) FIG. 1A is a longitudinal cross-sectional view of a jarring apparatus;

(3) FIG. 1B is an enlarged, split view of the jarring apparatus of FIG. 1A;

(4) FIG. 2 illustrates a fixed cam of a lifting mechanism of the jarring apparatus of FIG. 1A;

(5) FIG. 3 illustrates a shuttle cam of a lifting mechanism of the jarring apparatus of FIG. 1A;

(6) FIGS. 4A to 4D illustrates a rotary sequence of cooperation between the fixed and shuttle cams of the lifting mechanism;

(7) FIG. 5A is a perspective view of a rotary gate valve of the jarring apparatus of FIG. 1A;

(8) FIG. 5B is an exploded view of the rotary gate valve of FIG. 5A;

(9) FIGS. 6A to 6D diagrammatically illustrate stages of opening and closing of the rotary gate valve of FIG. 5A;

(10) FIGS. 7A to 12C illustrate the jarring apparatus of FIG. 1A in sequential stages of operation;

(11) FIG. 13 graphically illustrates the relative rotational progression and axial displacement between the shuttle and fixed cams of the lifting mechanism, and corresponding timing of the axial release of the shuttle cam;

(12) FIG. 14 is a part cut-way view of an alternative jarring apparatus, configured to generate a jarring force in a direction opposite to that provided by the jarring apparatus of FIG. 1A;

(13) FIGS. 15A and 15B diagrammatically illustrate, in part cut-away and sectional view, a jarring apparatus capable of being configured between non-jarring and jarring configurations;

(14) FIG. 16A is a longitudinal cross-sectional view of an alternative jarring apparatus;

(15) FIG. 16B is an enlarged, split view of the jarring apparatus of FIG. 16A;

(16) FIG. 17 is an elevational view of lifting structures and a valve assembly of the jarring apparatus of FIG. 16A;

(17) FIG. 18 is a cross sectional view taken along line 18-18 of FIG. 16B; and

(18) FIGS. 19A to 24C illustrate the jarring apparatus of FIG. 16A in sequential stages of operation.

DETAILED DESCRIPTION OF THE DRAWINGS

(19) Aspects of the present disclosure relate to a jarring apparatus. Such a jarring apparatus may be used in any application which requires the application of a jarring force. For the purposes of the present exemplary description a jarring apparatus for use within a wellbore is described. However, this is not limiting, and the principles of the present disclosure may be applied in any jarring application, which may or may not be utilised in a wellbore.

(20) A jarring apparatus, generally identified by reference numeral 10, is shown in cross-section in FIG. 1A. The jarring apparatus 10 is sized and arranged to be deployed into a wellbore. Although not shown, the jarring apparatus may be deployed into a wellbore on wireline, tubing, such as coiled tubing, jointed pipe or the like.

(21) The jarring apparatus 10 comprises a first jarring assembly in the form of a mandrel 12, and a second jarring assembly in the form of an outer housing assembly 14. The jarring apparatus 10 is configured such that relative rotation established between the mandrel 12 and outer housing assembly 14 causes repeated linear jarring forces to be generated. In use, the outer housing assembly 14 may be engaged with an object (not shown), such as a stuck object within a wellbore, with the mandrel 12 rotated via a suitable rotary drive, such as a motor, rotatable work string or the like, thus applying the generated jarring forces to the object.

(22) In the present example the jarring apparatus 10 is arranged to provide axial jarring forces in the direction of arrow 16, which may be defined as an uphole direction. An axial pulling force may be applied to the mandrel in the direction of arrow 16 during the jarring operation. As will be described below in more detail, axial jarring in an opposite (e.g., downhole) direction, illustrated by arrow 17, may also be possible, with an optional axial pushing force applied to the mandrel in the direction of arrow 17.

(23) To aid the current description an enlarged split view of the jarring apparatus 10 of FIG. 1A is illustrated in FIG. 1B, reference to which is now made.

(24) The mandrel 12 includes a tubular structure which extends into the outer housing assembly 14. A first or upper end of the mandrel 12 includes a suitable connector 18 for facilitating connection with a suitable deployment or drive structure, such as a work string.

(25) An impact mechanism 20 is positioned towards the upper end of the apparatus 10. The impact mechanism 20 includes a first axial impact surface 22 provided on a hammer 24 which is fixed to the mandrel 12 via a threaded connection 26, and a second axial impact surface 28 provided on an anvil 30 fixed to the housing 14. The impact mechanism 20 is open to a space externally of the housing 14 via a port 31. In use, the port 31 may permit the impact mechanism 20, particularly the first and second impact surfaces 22, 28, to be exposed to wellbore fluid which functions to cool and/or lubricate the impact mechanism 20. In other examples, the impact mechanism 20 may alternatively be open to fluid within the mandrel 12, which may provide a cleaner environment. In further examples, the impact mechanism may be provided within a flow path.

(26) A lifting mechanism 32 is positioned at a lower end of the apparatus 10, radially interposed between the mandrel 12 and the housing 14. The lifting mechanism 32 includes a first lifting structure in the form of a fixed cam 34, and a second lifting structure in the form of a shuttle cam 36. As will be described in more detail below, relative rotation between the fixed and shuttle cams 34, 36 permits relative axial movement, and corresponding potential energy, to be generated between the mandrel 12 and the housing 14, with corresponding axial separation provided between the first and second impact surfaces 22, 28 of the impact mechanism 20. Such axial separation may prepare the impact surfaces 22, 28 for subsequent axial impact together, as will be described in more detail below.

(27) Reference is additionally made to FIG. 2 which is a perspective view of the fixed cam 34, and FIG. 3 which is a perspective view of the shuttle cam 34. The fixed cam 34 includes a first rotary cam profile 38 which in the present example includes two circumferentially distributed cam lobes 40 each having a gradual ramp or rising portion 42, and a drop-off or falling portion 44, with a base portion 46 circumferentially positioned between each cam lobe 40. The shuttle cam 36 includes a complimentary second rotary cam profile 48, and thus includes two circumferentially distributed cam lobes 50 each having a gradual ramp or rising portion 52, and a drop-off or falling portion 54, with a base portion 56 circumferentially positioned between each cam lobe 50, 52.

(28) The complementary rotary cam profiles 38, 48 inter-engage and cooperate upon relative rotation therebetween to cyclically cause the cams 34, 36 to be displaced in one axial direction in a lifting phase, and to be displaced in a reverse axial direction in a dropping phase, as illustrated in FIGS. 4A to 4D. In this respect, FIG. 4A illustrates initial engagement of the respective ramp portions 42, 52 at the start of a lifting phase, with relative rotation therebetween permitting the cooperating ramp portions 42, 52 to circumferentially slide relative to each other and axially drive the cams 34, 36 apart towards a peak separation, as shown in FIG. 4B. As the cams 34, 36 progress towards the illustrated peak position in FIG. 4B the area of contact therebetween reduces, thus causing the stresses induced in the cams 34, 36 to increase. As will be described herein, the jarring apparatus 10 provides measures to minimise such stresses within the cams 34, 36, thus prolonging their operational life span.

(29) Following completion of this lifting phase the drop-off portions 44, 54 become aligned, allowing the cams 34, 36 to drop and cause reverse axial displacement in a dropping phase, as illustrated in FIG. 4C. The cams 34, 36 are arranged within the jarring apparatus 10 such that at this dropping phase the first and second cam profiles 38, 48 are prevented from axial engagement or impact therebetween. That is, immediately following the dropping phase an axial separation gap 57 is provided between the first and second cam profiles 38, 48. This is achieved, at least in part, in the present example by the provision of a no-go profile in the form of an annular lip 58 provided on the shuttle cam 36 which engages a corresponding axial shoulder 60 on the housing 14 (see FIG. 1B). Furthermore, engagement between the impact surfaces 22, 28 also prevents travel of the fixed cam 34, maintaining separation between the cams 34, 36.

(30) Following this dropping phase the cam lobes 40, 50 become aligned with the opposing base portions 46, 56, as illustrated in FIG. 4D, without contact therebetween, as noted above (i.e., the axial separation gap 57 is maintained). Further relative rotation may provide a transition from the completed dropping phase to initiation of a subsequent lifting phase, with the cycle of FIGS. 4A to 4D being repeated, causing cyclically lifting and dropping of the cams 34, 36. In the present examples, with each cam 34, 36 comprising two cam lobes 40, 50, the cams 34, 36 will undergo two cycles of lifting and dropping for each full 360 degrees of relative rotation therebetween. The provision of more or less cam lobes 40, 50 on each cam 34, 36 may facilitate more or less cycles for each full 360 degrees of relative rotation.

(31) The fixed cam 34 is positioned radially between the mandrel 12 and the housing 14 and is rotatably fixed relative to the mandrel 12 via corresponding non-round profiles, such as a hex-profile (see internal hex-profile 62 on the fixed cam 34 illustrated in FIG. 2). The fixed cam 34 is axially engaged against an end cap 64 which permits the fixed cam 34 to be axially fixed relative to the mandrel 12 in the direction of arrow 17.

(32) The shuttle cam 36 is also positioned radially between the mandrel 12 and the housing 14, and is sealed relative to the mandrel 12 via inner seals 66, and sealed relative to the housing 14 via outer seals 68. The shuttle cam 36 is rotatably fixed relative to the housing 14, specifically to a shuttle cam key coupling portion 70 of the housing 14. Referring again additionally to FIG. 3, the shuttle cam 36 includes a pair of diametrically opposed axially extending tabs or keys 72 which engage corresponding axial slots or keyways (not shown in FIG. 1B) formed in the shuttle cam key coupling portion 70 of the housing 14. Such a connection provides a rotary connection between the shuttle cam 36 and the housing, while still permitting relative axial movement therebetween.

(33) The shuttle cam 36 is configured to be selectively axially fixed and released relative to the housing 14 via a hydraulic locking system, which will be described below. In the present example the hydraulic locking system functions to fix the shuttle cam 36 relative to the housing 14 during the lifting phase between the fixed and shuttle cams 34, 36, which thus permits the cooperation of the cams 34, 36 to cause corresponding relative axial movement of the mandrel 12 and housing 14, to axially separate the first and second impact surface 22, 28 and develop potential energy between the mandrel and housing. The hydraulic locking system functions to release the shuttle cam 36 relative to the housing 14 prior to completion of the lifting phase between the cams 34, 36, with such axial release permitting the generated potential energy to rapidly drive the impact surfaces 22, 28 together, to generate a jarring force. Accordingly, the jarring event is not initiated or caused by the dropping phase between the cams 34, 36, thus avoiding or minimising potential problems in the art.

(34) The hydraulic locking system may be provided in numerous forms, to provide the function of cyclically hydraulically locking and releasing the shuttle cam 36 in accordance with operational requirements. Different examples will be described herein.

(35) In the present example, the hydraulic locking system includes a first hydraulic chamber 74 which is defined between the mandrel 12, housing 14 and the shuttle cam 36. In the present example the first annular chamber includes a space immediately behind the shuttle cam, an annular gap 76 defined between the shuttle cam key coupling portion 70 and the mandrel 12, and a valve chamber 78. In the present example the hydraulic locking system further includes a second hydraulic chamber 80 defined between the mandrel 12, housing 14 and a floating piston 82, wherein the floating piston 82 is sealed relative to the mandrel 12 and housing 14 via inner and outer seals 84, 86. The floating piston 82 is axially moveable in a radial space 88 and is spring biased by spring 90 in a direction to reduce the volume of the second hydraulic chamber 80. In the present example the second hydraulic chamber includes the space immediately behind the floating piston 82 and gun drilled holes 92 through a floating piston body portion 94 of the housing 14. A volume of an incompressible hydraulic fluid, such as hydraulic oil is contained within the first and second hydraulic chambers 74, 80. In some examples, the hydraulic fluid may be pre-pressurised. This may allow or accommodate for any fluid compression, and gas compression and small leakage.

(36) Although not illustrated, a pressure relief arrangement (e.g., a pressure relief valve) may be provided within the hydraulic locking system to prevent or minimise risk of overpressure causing damage.

(37) A valve assembly 96 is interposed between the mandrel 12 and housing 14, and also between the first and second hydraulic chambers 74, 80, and is configurable between open and closed positions by relative rotation between the mandrel 12 and housing 14. When the valve assembly 96 is in its closed position fluid communication between the first and second hydraulic chambers 74, 80 is prevented, thus hydraulically locking the hydraulic fluid in the first hydraulic chamber 74, effectively axially fixing the shuttle cam 36 relative to the housing 14.

(38) When the valve assembly 96 is in its open position fluid communication between the first and second hydraulic chambers 74, 80 is permitted, allowing fluid to be displaced from the first hydraulic chamber 74 to the second hydraulic chamber 80, with such fluid displacement accommodated by an increase in the volume of the second hydraulic chamber 80 by virtue of movement of the floating piston 82. Such displacement of fluid from the first hydraulic chamber 74 may effectively axially release the shuttle cam 36 from the housing 14.

(39) The floating piston 82 may also function to accommodate thermal expansion/contraction of the fluid within the hydraulic locking system.

(40) In the present example the shuttle cam 36 and the floating piston 82 are pressure balanced by virtue of equivalent sealed areas and by exposure to a common pressure (e.g., pressure within the mandrel 12 or externally of the housing 14.

(41) Reference is additionally made to FIG. 5A which illustrates the valve assembly 96 and the floating piston body portion 94 of the housing 14, removed from the apparatus 10, and also to FIG. 5B which is an exploded view of the valve assembly 96 and the floating piston body portion 94.

(42) The valve assembly 96 in the present example is provided in the form of a rotary gate valve assembly and comprises a gate valve nose 98 which is rotatably fixed to the floating piston body portion 94, and thus to the housing 14, via a pair of diametrically opposed key tabs 100 received in complimentary slots 102 in the floating piston body portion 94. In an alternative example the valve nose 98 may be integrally formed with the floating piston body 94/housing 14. The valve nose 98 includes two circumferentially arranged (in this case diametrically opposed) ports 104 extending axially therethrough and aligned with the gun drilled bores 92 in the floating piston body portion 94.

(43) The valve assembly further comprises a gate valve selector 106 which is rotatably fixed relative to the mandrel via keys (not shown) which extend through key slots 108 in the valve selector 106. The valve selector 106 includes two circumferentially arranged ports 110 which are arranged at the same circumferential spacing as the corresponding ports 104 in the valve nose 98 (i.e., also diametrically opposed).

(44) The valve selector 106 is axially engaged against the valve nose 98, with a gate spring 112 (see FIG. 1B) applying a biasing force therebetween. Relative rotation between the mandrel 12 and housing 14 causes corresponding relative rotation and sliding engagement between the valve nose 98 and the valve selector 106, thus cyclically aligning and misaligning the ports 104, 110, thus providing corresponding opening and closing of the valve assembly 96.

(45) Such relative rotation between the valve selector 106 and valve nose 98 is diagrammatically illustrated in the sequence of FIGS. 6A to 6D. FIG. 6A illustrates the valve selector 106 and valve nose 98 being rotatably positioned such that the respective ports 110, 104 are misaligned and the valve assembly 96 thus being closed. FIG. 6B illustrates the valve selector 106 and valve nose 96 being rotatably advanced until the respective ports 110, 104 start to become aligned, and thus initiating reconfiguration of the valve assembly 96 to its open position. In this respect it will be noted that the leading (i.e., rotatably leading) portions of the ports 110, 104 define a tapering profile. This may provide a gradual increase in flow area as the ports begin to align, which may provide advantages such as minimising hydraulic shock as the valve assembly 96 begins to open. It should be understood that any port profile may be incorporated, in accordance with operational requirements. For examples, the ports may be formed to ensure a large flow area is rapidly developed during initial valve opening.

(46) Further relative rotation between the valve selector and nose 106, 98 allows the ports 110, 104 to become fully aligned, as shown in FIG. 6C, and subsequently to begin to become misaligned again, as shown in FIG. 6D.

(47) Accordingly, by appropriate timing between the lifting and dropping phases of the fixed and shuttle cams 34, 36 within the lifting mechanism 32, and of the opening and closing of the valve assembly 96, suitable operation of the jarring apparatus 10 may be achieved. In this respect, such timing may be readily facilitated by virtue of both the lifting mechanism 32 and valve assembly 96 being commonly operated by relative rotation between the mandrel 12 and housing 14.

(48) A full cycle of operation of the apparatus 10 will now be described with reference to FIGS. 7A to 12C.

(49) Reference is initially made to FIGS. 7A to 7C, wherein the apparatus 10 is illustrated in an initial configuration in FIG. 7A, the corresponding configuration of the valve assembly 96 is illustrated in FIG. 7B, which is a cross-section taken through line 7B-7B of FIG. 7A, and the corresponding configuration of the lifting mechanism 32 is illustrated in FIG. 7C. When in this initial position the housing 14 may be engaged with an object (not shown), such as an object stuck in a wellbore, which effectively causes the housing 14 to become fixed. The mandrel 12 is coupled to a drive structure, such as a work string (not shown), and is thus operated to rotate relative to the housing 14. An axial pulling force may be applied to the mandrel 12, for example via a work string, to apply axial preloading between the mandrel and housing 14.

(50) When in this initial configuration the impact surfaces 22, 28 of the impact mechanism 20 are engaged such that any initial pulling force applied to the mandrel 12 generates loading between said impact surfaces 22, 28, and thus between the mandrel 12 and the housing 14. The ports 104, 110 of the valve assembly 96 are aligned such that the valve 96 is in an open configuration and the shuttle cam 36 is thus axially released from the housing 14. Although the shuttle cam 36 may be considered to be axially released from the housing 14 when the valve assembly 96 is open, the shuttle cam 36 is nevertheless biased axially towards the fixed cam 34 by virtue of the spring 90 acting on floating piston 82, which in turn acts on the hydraulic fluid contained within the first and second hydraulic chamber 74, 80. When in this initial configuration the annular lip 58 of the shuttle cam 36 is engaged with the axial shoulder 60 of the housing 14.

(51) As illustrated in FIG. 7C, the first and second cam profiles 38, 48 of the fixed and shuttle cams 34, 36 respectively are not engaged (separation gap 57).

(52) Rotation of the mandrel 12 relative to the housing 14 eventually causes the valve assembly 96 to close by misalignment of the ports 104, 110, as illustrated in FIGS. 8A and 8B, wherein FIG. 8B is a sectional view taken through line 8B-8B of FIG. 8A. The shuttle cam 36 thus becomes hydraulically locked relative to the housing 14. When in this configuration the fixed cam 34 has rotatably progressed, but the first and second cam profiles 38, 48 remain separated and non-engaged (separation gap 57). As an example, the mandrel may have been rotated by around 40 degrees relative to the initial position of FIG. 7A to reach this stage in which the valve assembly 96 becomes closed.

(53) Continued rotation of the mandrel 12, illustrated in FIG. 9A, maintains the valve assembly 96 in its closed configuration, as illustrated in FIG. 9B, which is a sectional view taken through line 9B-9B of FIG. 9A, and eventually brings the cam profiles 38, 48 into engagement, as illustrated in FIG. 9C. Specifically, opposing ramp portions 42, 52 become engaged in preparation to initiate the lifting phase. When in the configuration illustrated in FIG. 9A, the impact surfaces 22, 28 of the impact mechanism remain engaged. As an example, the mandrel may have been rotated by around 77 degrees relative to the initial position of FIG. 7A to reach this stage.

(54) Further rotation of the mandrel 12, illustrated in FIG. 10A, maintains the valve assembly 96 in its closed configuration, as illustrated in FIG. 10B, which is a sectional view taken through line 10B-10B, and causes the ramp portions 42, 52 of the fixed and shuttle cams 34, 36 to slide over each other and cause relative axial displacement of the cams 34, 36 to provide the lifting phase, as illustrated in FIG. 10C. By virtue of the shuttle cam 36 being hydraulically locked and axially fixed to the housing 14 the axial separation between the cams 34, 36 causes the mandrel 12 to be moved axially in the direction of arrow 17, causing the first and second impact surfaces 22, 28 to become axially separated by distance 112. Such axial movement of the mandrel 12 generates potential energy between the mandrel 12 and housing 14. As an example, the mandrel may have been rotated by 128 degrees relative to the initial position of FIG. 7A to reach this stage.

(55) Further rotation of the mandrel 12, illustrated in FIG. 11A, causes the ports 104, 110 of the valve assembly 96 to start to become aligned, as illustrated in FIG. 10B, which is a sectional view taken through line 11B-11B, thus reconfiguring the valve assembly 96 into its open configuration. This establishes communication between the first and second hydraulic chambers 74, 80 and axially releases the shuttle cam 36 from the housing 14. This axial release of the shuttle cam 36 permits the loading and potential energy generated between the mandrel 12 and housing 14 to be rapidly relieved, causing mandrel 12 to axially move in the direction of arrow 16 and the first and second impact surfaces 22, 28 to be rapidly impacted together, generating a jarring force. As illustrated in FIG. 11A, as the shuttle cam 36 is axially released from the housing 14 the movement of the mandrel 12 in the direction of arrow 16 causes the shuttle cam 36 to also move axially in the direction of arrow 16, axially separating the annular lip 58 of the shuttle cam 36 from the axial shoulder 60 of the housing 14. As an example, the mandrel may have been rotated by 129 degrees relative to the initial position of FIG. 7A to reach this stage of generating a jarring force within the apparatus 10.

(56) As illustrated in FIG. 11C, the ramp profiles 38, 48 of the fixed and shuttle cams 34, 36 remain engaged. However, the axial release of the shuttle cam 36 from the housing 14 relieves or reduces, for example significantly reduces, loading applied between the fixed and shuttle cams 34, 36, thus minimising stress therein. The timing of axial release of the shuttle cam 36 may be selected to be such that a relatively large surface area of contact between the ramp profiles 38, 48 exists during the initial lifting and loading phase, again assisting to control levels of stresses applied in the cams 34, 36.

(57) The configuration of the apparatus 10 upon further rotation of the mandrel 12 is illustrated in FIG. 12A. As shown in FIG. 12B, which is a sectional view taken through lines 12B-12B in FIG. 12A, the valve assembly 96 remains opened, with the ports 104, 110 still aligned during this further rotation. The further rotation also causes the fixed cam 34 to further rotate relative to the shuttle cam 36, causing the ramp profiles 38, 48 to reach the peak position, as illustrated in FIG. 12C, reflecting the maximum axial separation between the cams 34, 36. As the valve assembly 96 remains open during this phase of rotation loading applied between the reducing contact area between the ramp profiles 38, 48 is minimised, thus minimising stresses within the cams 34, 36. As an example, the mandrel may have been rotated by 168 degrees relative to the initial position of FIG. 7A to reach this stage of the cams 34, 36 peaking.

(58) Further rotation of the mandrel 12, for example now 180 degrees relative to the initial position of FIG. 7A, will cause the cams 34, 36 to effectively drop (i.e., the shuttle cam 36 drops relative to the fixed cam 34), returning the apparatus 10 to the initial configuration of FIG. 7A. Continuous rotation of the mandrel 12 will cause continuous cycles of jarring, as described above. In this respect the jarring frequency will be a function of the number of cam profiles 40, 50 provides on the cams 34, 36, and the rotational speed of the mandrel 12. The jarring frequency may also be influenced by the number of ports provided in the valve assembly 96. In use, the jarring frequency may be readily adjusted by adjusting the rotational speed of the mandrel 12.

(59) Furthermore, the force applied for each impact event may be dictated by the level of initial preloading applied (e.g., magnitude of pulling force on the mandrel 12) and the axial displacement of the mandrel 12 relative to housing 14 prior to impact. Accordingly, a user may readily adjust the desired jarring force generated within the apparatus 10.

(60) The operational cycle of the apparatus 10 may be represented graphically in FIG. 13. This graph illustrates the axial displacement of the cams 34, 36 during rotation of the mandrel 12, and is overlaid with the associated cyclical reconfiguration of the valve assembly 96 between its open and closed configurations. While example rotational and axial displacements are presented in FIG. 13 and the description below, these are provided only for exemplary purposes and are in no way limiting.

(61) The following sequence is illustrated:

(62) 1. The origin O of the graph reflects the configuration of the apparatus as shown in FIGS. 7A to 7C, wherein the valve assembly 96 is open and there is zero displacement between the cams 34, 36;

(63) 2. The mandrel reaches 40 degrees of rotation, illustrated by point 120, causing the valve assembly 96 to close, with still zero displacement between the cams 34, 36, reflecting the configuration of the apparatus 10 in FIGS. 8A to 8C;

(64) 3. The mandrel reaches 77 degrees of rotation, illustrated by point 122, at which the cams 34, 36 initiate their lifting phase, reflecting the configuration of the apparatus 10 in FIGS. 9A to 9C;

(65) 4. The mandrel reaches 129 degrees of rotation, illustrated by point 124, at which the valve assembly 96 is opened allowing jarring impact to be achieved, reflecting the configuration of the apparatus in FIGS. 11A to 11C. In the present example the axial displacement of the cams 34, 36, and of the first and second impact surfaces 22, 28 of the impact mechanism (see, for example, FIG. 1B) may be in the region of 15 mm;

(66) 5. The mandrel reaches approximately 168 to 180 degrees of rotation, illustrated by point 126, at which the cams 34, 36 peak and then drop or reset in their dropping phase. In the present example the peak axial displacement between the cams 34, 36 may be in the region of 25 mm.

(67) The cycle above is repeated during continuous rotation of the mandrel 13, as illustrated in FIG. 13.

(68) The timing of the lifting and dropping phases of the cams 34, 36 and the opening and closing of the valve apparatus 96 may be readily adjusted to achieve the desired operation of the apparatus 10. For example, delaying the opening of the valve assembly 96 may permit a greater separation between impact surfaces 22, 28 to be achieved, and thus more energy to be generated between the mandrel 12 and housing.

(69) The common operation of the valve assembly 96 and the lifting mechanism 32 by the relative rotation between the mandrel 12 and the housing 14 may facilitate the appropriate timing of operation to be readily achieved and adjusted, for example by simple relative alignment of the different components on the mandrel 12 and/or housing 14.

(70) In FIG. 13 the axial displacement of the cams 34, 36 is illustrated as being linear during rotation of the mandrel. However, this need not be the case, and a non-linear profile may be achieved in accordance with the profile selected for the ramp portions 38, 48 of the respective cams 34, 36 (see, for example, FIGS. 2 and 3).

(71) In the example provided above the apparatus 10 is configured to generate a jarring force in an uphole direction. In other examples, however, a jarring apparatus may be provided which permits jarring in a downhole direction. An example of such a jarring apparatus, which is generally identified by reference numeral 210, is illustrated in FIG. 14. For ease of reference, only selected sections of the apparatus 210 is shown in part cut-away.

(72) The apparatus 210 is effectively configured in a similar manner to apparatus 10 and as such like features share like reference numerals, incremented by 200. In the present case the apparatus 210 also includes a mandrel 212, housing 214, an impact mechanism 220, lifting mechanism 232 and valve assembly 296, each configured similarly to their counterpart in the apparatus 10 described above. However, in the present case these features are, as illustrated, arranged in inverted order. All other operational principles as described above in relation to apparatus 10 also apply to the present illustrated apparatus 210. However, in the present case an axial pushing force in the direction of arrow 17 may optionally be applied on the mandrel 212 to provide preloading.

(73) In some examples a simple inversion of the lifting mechanism may require an opposite rotation of the mandrel. In some cases this may be acceptable. However, in other cases such opposite rotation may not be desired, for example where there might be a risk of causing threaded connections in the apparatus or connected infrastructure from being backed-off. In such cases it may be desirable to reverse the cam structures to maintain a desired relative rotation direction.

(74) In some examples a jarring apparatus may be provided which includes two separate and inverted jarring assemblies, such that the same jarring apparatus may be capable of providing jarring in opposite directions.

(75) In the examples provided above the jarring apparatus may be provided in a single jarring mode of operation, in which the mandrel and housing are rotatable relative to each other to cause cyclical jarring events, as described above. However, in other examples a jarring apparatus may be provided which is reconfigurable between a jarring mode of operation and a non-jarring mode of operation. Such a jarring apparatus, generally identified by reference numeral 310, will now be described with reference to FIGS. 15A and 15B, wherein FIG. 15A illustrates the apparatus 310 when configured in a non-jarring configuration, and FIG. 15B illustrates the apparatus 310 when configured in a jarring configuration. Both FIGS. 15A and 15B include part cutaway sections to illustrate internal detail. The jarring apparatus 310 is similar in many respects to apparatus 10 described above, and as such like features share like reference numerals, incremented by 300. In particular, the jarring apparatus 310 is structured in the same way as in apparatus 10 to provide axial jarring forces in response to a rotary drive.

(76) The apparatus 310 includes a mandrel 312 and a housing 314, and a rotatable locking mechanism 150 interposed between the mandrel 312 and housing 314. The rotatable locking mechanism includes a number of keys 152 mounted on the mandrel 312 and a number of corresponding keyways 154 provided in the housing 314. When the apparatus 310 is configured in its non-jarring configuration as shown in FIG. 15A, the mandrel 312 and housing 314 are axially positioned relative to each other such that the keys 152 are received in the keyways 154, thus rotatably locking the mandrel 312 and housing 314 together. Accordingly, relative rotation between the mandrel 312 and housing 314 may not be permitted, and as such any jarring which would otherwise be generated by such relative rotational movement may be prevented.

(77) By rotatably locking the mandrel 312 and housing 314 together it will be possible to transmit torque therethrough. Such transmission of torque may permit the apparatus 310 to have application in, for example, drilling operations. In one example, the mandrel 312 may be coupled to a rotary drill string (not shown), and the housing 314 may be coupled to a drilling BHA (also not shown), wherein rotation of the drill string causes corresponding rotation of the BHA.

(78) The apparatus 310 further comprises an axial locking (or release) system 160 interposed between the mandrel 312 and housing 314. The axial locking system 160 includes a circumferential array of keys or dogs 162 which are positioned within a radial gap 164 between the mandrel 312 and housing 314. The dogs 162 are axially biased, with reference to the housing 314, by a spring 166 in the direction of arrow 17. In the configuration of FIG. 15A the dogs 162 are axially engaged with an annular no-go profile 168 provided on the mandrel 312. Accordingly, applying a pulling force on the mandrel 312 in the direction of arrow 16 (and/or applying a pushing force on the housing 314 in the direction of arrow 17) will cause the mandrel 312 and housing 314 to move axially relative to each other, against the force applied by the spring 166. Release of any axial force will permit the spring 166 to return the mandrel 312 and housing 314 to their initial position.

(79) In the event of jarring being required, for example due to sticking of a drill string, BHA or the like, the apparatus 310 may be reconfigured to a jarring configuration by applying a sufficiently large pulling force on the mandrel 312 (and/or pushing force on the housing 314) such that the dogs 162 become aligned with an annular recess 170 formed on an inner surface of the housing 314, allowing the dogs 162 to become released from the no-go profile 168 on the mandrel, as illustrated in FIG. 15B. This may disengage the locking or resistance effect of the dogs 162 and spring 166, such that sufficient axial movement between the mandrel 312 and housing 314 may be achieved to disengage the keys 152 from the keyways 154 of the rotatable locking mechanism 150, as shown in FIG. 15B. Such sufficient relative axial movement may permit appropriate operational alignment or reconfiguration of an impact mechanism 320, lifting mechanism 332 and valve assembly 96, which may function in a similar manner to that described above with reference to apparatus 10 to generate axial jarring in response to relative rotation between the mandrel 312 and housing 314.

(80) Should it be desirable to reconfigure the apparatus 310 back to the non-jarring configuration then reverse relative axial movement between the mandrel 312 and housing 314 may be performed, to reset the axial locking system 160, and reengage the keys 152 with the keyways 154 of the rotatable locking mechanism 150.

(81) In examples described above a hydraulic locking system is included for cyclically hydraulically locking and releasing the shuttle cam. Specifically, an example described above (apparatus 10) includes a valve assembly 96 incorporating axially arranged ports 104, 110, and operable to selectively isolate and communicate first and second hydraulic chambers. However, other examples may use a different form of valve assembly, for example one which includes radial ports. Further, the second hydraulic chamber may instead be provided by a flow path which extends through the jarring apparatus. Such alternative examples will now be described with reference to FIGS. 16A to 24C.

(82) A jarring apparatus, generally identified by reference numeral 410, is shown in cross-section in FIG. 16A. To aid the current description an enlarged split view of the jarring apparatus 410 of FIG. 16A is illustrated in FIG. 16B. The apparatus 410 is similar in many respects to the apparatus 10 first shown in FIG. 1A, and as such like features share like reference numerals, incremented by 400.

(83) The jarring apparatus 410 comprises a first jarring assembly in the form of a mandrel 412 and a second jarring assembly in the form of an outer housing assembly 414. The apparatus 410 is configured such that relative rotation established between the mandrel 412 and outer housing assembly 414 causes repeated linear jarring forces to be generated in the direction of arrow 16.

(84) An impact mechanism 420 is positioned towards the upper end of the apparatus 410 and includes a first axial impact surface 422 provided on a hammer 424 which is fixed to the mandrel 412, and a second axial impact surface 428 provided on an anvil 430 fixed to the housing 414.

(85) A lifting mechanism 432 is positioned at a lower end of the apparatus 410, radially interposed between the mandrel 412 and the housing 414. The lifting mechanism 432 includes a first lifting structure in the form of a fixed cam 434, and a second lifting structure in the form of a shuttle cam 436. The fixed and shuttle cams 434, 436 are provided largely in the same form and function in the same manner as the corresponding cams 34, 36 in the apparatus 10 described above. As such, no further detailed description will be given, other than to note that each cam 434, 436 includes respective and complimentary rotary cam profiles 438, 448 which inter-engage and cooperate upon relative rotation therebetween to cyclically cause the cams 434, 436 to be displaced in one axial direction in a lifting phase, and to be displaced in a reverse axial direction in a dropping phase.

(86) The fixed cam 434 is positioned radially between the mandrel 412 and the housing 414 and is rotatably fixed relative to the mandrel 412. The shuttle cam 436 is also positioned radially between the mandrel 412 and the housing 414, and is sealed relative to the mandrel 412 via inner seals 466, and sealed relative to the housing 414 via outer seals 468. The shuttle cam 436 is rotatably fixed relative to the housing 414, specifically to a shuttle cam key coupling portion 470 of the housing 414, which will be described in more detail below. A spring 490 biases the shuttle cam 436 towards the fixed cam 434.

(87) The shuttle cam 436 is configured to be selectively axially fixed and released relative to the housing 414 via a hydraulic locking system. The hydraulic locking system functions to fix the shuttle cam 436 relative to the housing 414 during the lifting phase between the fixed and shuttle cams 434, 436, which thus permits the cooperation of the cams 434, 436 to cause corresponding relative axial movement of the mandrel 412 and housing 414, to axially separate the first and second impact surface 422, 428 and develop potential energy between the mandrel and housing. The hydraulic locking system functions to release the shuttle cam 436 relative to the housing 414 prior to completion of the lifting phase between the cams 434, 436, with such axial release permitting the generated potential energy to rapidly drive the impact surfaces 422, 428 together, to generate a jarring force.

(88) In the present example, the hydraulic locking system includes a first hydraulic chamber 474 which is defined radially between the mandrel 412 and housing 414, and axially between the shuttle cam 436 and the shuttle cam key coupling portion 470. The hydraulic locking system further includes a second hydraulic chamber 480 defined by a flow path extending through the mandrel 412.

(89) A valve assembly 496 is provided between the first and second hydraulic chambers 474, 480, and is configurable between open and closed positions by relative rotation between the mandrel 412 and housing 414. When the valve assembly 496 is in its closed position fluid communication between the first and second hydraulic chambers 474, 480 is prevented, thus hydraulically locking the hydraulic fluid in the first hydraulic chamber 474, effectively axially fixing the shuttle cam 436 relative to the housing 414. When the valve assembly 496 is in its open position fluid communication between the first and second hydraulic chambers 474, 480 is permitted, allowing fluid to be displaced from the first hydraulic chamber 474 to the second hydraulic chamber 480, and effectively axially release the shuttle cam 436 from the housing 414.

(90) Reference is additionally made to FIG. 17 which illustrates the valve assembly 496 and cams 434, 436, and also to FIG. 18 which is sectional view along line 18-18 of FIG. 16B, with the spring 490 removed for clarity.

(91) The valve assembly 496 in the present example is provided in the form of a rotary plug valve and comprises a valve sleeve 498 which is rotatably fixed to the shuttle cam key coupling portion 470, and thus to the housing 414, via a pair of diametrically opposed key tabs 500 (only one visible in FIG. 17) received in complimentary slots 502 in the shuttle cam key coupling portion 470. In this example the valve sleeve 498 is integrally formed with the shuttle cam 436, and thus provides a rotary connection between the housing 414 and the shuttle cam 436.

(92) The valve sleeve 498 includes two circumferentially arranged (in this case diametrically opposed) ports 504 extending radially therethrough.

(93) The valve assembly 496 further comprises a valve selector portion 506, which is formed by the mandrel 412, and includes a single port 510 extending radially through the valve selector portion 506 (two diametrically opposed ports could be provided in the selector portion 506).

(94) The valve sleeve 498 and valve selector portion 506 are thus arranged for relative rotation therebetween in accordance with relative rotation between the mandrel 412 and the housing 414 to cause cyclical alignment and misalignment of the ports 504, 510 to effectively open and close the valve assembly 496.

(95) By appropriate timing between the lifting and dropping phases of the fixed and shuttle cams 434, 436 within the lifting mechanism 432, and of the opening and closing of the valve assembly 496, suitable operation of the jarring apparatus 410 may be achieved. In this respect, such timing may be readily facilitated by virtue of both the lifting mechanism 432 and valve assembly 496 being commonly operated by relative rotation between the mandrel 412 and housing 414.

(96) A full cycle of operation of the apparatus 410 will now be described with reference to FIGS. 19A to 24C.

(97) Reference is initially made to FIGS. 19A to 19C, wherein the apparatus 410 is illustrated in an initial configuration in FIG. 19A, the corresponding configuration of the valve assembly 496 is illustrated in FIG. 19B, which is a cross-section taken through line 19B-19B of FIG. 19A, and the corresponding configuration of the lifting mechanism 432 is illustrated in FIG. 19C. When in this initial position the housing 414 may be engaged with an object (not shown), such as an object stuck in a wellbore, which effectively causes the housing 414 to become fixed. The mandrel 412 is coupled to a drive structure, such as a work string (not shown), and is thus operated to rotate relative to the housing 414. An axial pulling force may be applied to the mandrel 412, for example via a work string, to apply axial preloading between the mandrel 412 and housing 414.

(98) When in this initial configuration the impact surfaces 422, 428 of the impact mechanism 420 are engaged such that any initial pulling force applied to the mandrel 412 generates loading between said impact surfaces 422, 428, and thus between the mandrel 412 and the housing 414. The ports 504, 510 of the valve assembly 496 are aligned such that the valve 496 is in an open configuration and the shuttle cam 436 is thus axially released from the housing 414. Although the shuttle cam 436 may be considered to be axially released from the housing 414 when the valve assembly 496 is open, the shuttle cam 436 is nevertheless biased axially towards the fixed cam 434 by virtue of the spring 490.

(99) As illustrated in FIG. 19C, the first and second cam profiles 438, 448 of the fixed and shuttle cams 34, 36 respectively are not engaged (separation gap 457).

(100) Rotation of the mandrel 412 relative to the housing 414 eventually causes the valve assembly 496 to close by misalignment of the ports 504, 510, as illustrated in FIGS. 20A and 20B, wherein FIG. 20B is a sectional view taken through line 20B-20B of FIG. 20A. The shuttle cam 436 thus becomes hydraulically locked relative to the housing 414. When in this configuration the fixed cam 434 has rotatably progressed, but the first and second cam profiles 438, 448 remain separated and non-engaged (separation gap 457).

(101) Continued rotation of the mandrel 412, illustrated in FIG. 21A, maintains the valve assembly 496 in its closed configuration, as illustrated in FIG. 21B, which is a sectional view taken through line 21B-21B of FIG. 21A, and eventually brings the cam profiles 438, 448 into engagement, as illustrated in FIG. 21C, in preparation to initiate the lifting phase. When in the configuration illustrated in FIG. 21A, the impact surfaces 422, 428 of the impact mechanism 420 remain engaged.

(102) Further rotation of the mandrel 12, illustrated in FIG. 22A, maintains the valve assembly 496 in its closed configuration, as illustrated in FIG. 22C, which is a sectional view taken through line 22C-22C, and causes the first and second cam profiles 438, 448 of the fixed and shuttle cams 434, 436 to slide over each other and cause relative axial displacement of the cams 434, 436 to provide the lifting phase, as illustrated in FIG. 22D. By virtue of the shuttle cam 436 being hydraulically locked and axially fixed to the housing 414 the axial separation between the cams 434, 436 causes the mandrel 412 to be moved axially in the direction of arrow 17, causing the first and second impact surfaces 422, 428 to become axially separated, as also illustrated in the enlarged view of FIG. 22B. Such axial movement of the mandrel 412 generates potential energy between the mandrel 412 and housing 414.

(103) Further rotation of the mandrel 412, illustrated in FIG. 23A, causes the ports 504, 510 of the valve assembly 496 to start to become aligned, as illustrated in FIG. 23B, which is a sectional view taken through line 23B-23B, thus reconfiguring the valve assembly 496 into its open configuration. This establishes communication between the first and second hydraulic chambers 474, 480 and axially releases the shuttle cam 436 from the housing 414. This axial release of the shuttle cam 436 permits the loading and potential energy generated between the mandrel 412 and housing 414 to be rapidly relieved, causing mandrel 412 to axially move in the direction of arrow 16 and the first and second impact surfaces 422, 428 to be rapidly impacted together, generating a jarring force.

(104) As illustrated in FIG. 23C, the ramp profiles 438, 448 of the fixed and shuttle cams 434, 436 remain engaged. However, the axial release of the shuttle cam 436 from the housing 414 relieves or reduces, for example significantly reduces, loading applied between the fixed and shuttle cams 434, 436, thus minimising stress therein.

(105) The configuration of the apparatus 410 upon further rotation of the mandrel 412 is illustrated in FIG. 24A. As shown in FIG. 24B, which is a sectional view taken through lines 24B-24B in FIG. 24A, the valve assembly 496 remains opened, with the ports 504, 510 still aligned during this further rotation. The further rotation also causes the fixed cam 534 to further rotate relative to the shuttle cam 536, causing the ramp profiles 538, 548 to reach the peak position, as illustrated in FIG. 24C, reflecting the maximum axial separation between the cams 434, 436. As the valve assembly 496 remains open during this phase of rotation loading applied between the reducing contact area between the ramp profiles 438, 448 is minimised, thus minimising stresses within the cams 434, 436.

(106) Further rotation of the mandrel 412 will cause the cams 434, 436 to effectively drop (i.e., the shuttle cam 436 drops relative to the fixed cam 434), returning the apparatus 410 to the initial configuration of FIG. 19A. Continuous rotation of the mandrel 412 will cause continuous cycles of jarring, as described above.

(107) It should be recognised that the examples provided herein are indeed only exemplary, and that various modifications may be made thereto. For example, in the various apparatus described above a fixed cam of a lifting mechanism is associated with the mandrel and a shuttle cam is associated with the housing. However, this arrangement may be reversed. Such reversal of components may also be the case in relation to the valve assembly and/or the impact mechanism.

(108) Furthermore, while the axial locking system 160 of apparatus 310 (Figured 15A and 15B) is provided by a mechanical arrangement, a fluid or hydraulic arrangement may alternatively or additionally be provided.