Safety mechanism for an overshot, overshot including same, and method of using same

Abstract

An overshot (10') including a release sleeve (24') and a safety mechanism (52) for selectively covering part of the latch dogs (30) of the overshot (10'). The release sleeve (24') is movable along the overshot between distal and proximal positions, wherein the release sleeve (24') respectively covers the part of the latch dogs (30) and clears the latch (dogs). The safety mechanism (52) is configurable between locked and unlocked configurations in which the release sleeve (24') is respectively prevented from and allowed to reach the distal position.

Description

TITLE OF THE INVENTIONSafety mechanism for an overshot, overshot including same, and method of using same.FIELD OF THE INVENTION

[0001] This invention relates to core drilling, and more particularly, to a safety mechanism for an overshot, an overshot including the same, and a method of using the same.BACKGROUND OF THE INVENTION

[0002] A common method used in the mining and mineral exploration industry to investigate mineral geology is to extract rock core samples through wireline diamond core drilling. This method utilizes a diamond impregnated drill bit to cut rock core samples that are collected inside an inner tube. At regular intervals, the inner tube is retrieved from the bottom of the drill hole and brought to surface for emptying and collection. A device called an overshot, which connects to a head assembly threaded onto the inner tube, is used to collect the inner tube and the core section contained therein from the bottom of the drill hole.

[0003] The drill holes may be wet or dry holes. Wet holes are more common and can be thought of as always having a water table close to the collar, or beginning, of the hole, while dry holes have a very low or non-existent water table in the drill hole. This is important as the water table dictates how the inner tube is installed in the drill hole after emptying for collecting the next core section. In a wet hole, the inner tube is typically simply dropped into the drill hole and water acts as a buffer to limit its max velocity during drill hole descent. This cannot be performed in a dryhole as the inner tube descent speed would be too great and cause damage to equipment. Therefore, in a dry hole, the overshot and attached wireline cable are used to lower the inner tube the complete depth of the drill hole, with the overshot released at the bottom in-hole.

[0004] There are two styles of overshots on the market: spearhead overshots and spearhead-receiving overshots. Both styles of overshots use pivotable levers, named latch dogs, to selectively engage and disengaged from a head assembly, the latter being threaded onto the inner tube. Latch dogs have two positions: engaged and disengaged. Many overshots automatically transition between these positions depending on whether they are carrying a load or not, which is a passive safety feature. When the overshot is connected to an unsupported inner tube, the latch dogs move to the engaged position, wherein the head assembly is engaged. When the latch dogs are in the engaged position, they cannot be released. Once the inner tube is supported, for example on the ground or at the bottom of the drill hole, the latch dogs move to the disengaged position, which allows overshot release. Outside of the drill hole the overshot is disengaged by hand. Inside of the drill hole, a releasing mechanism is required.

[0005] When the latch dogs are in the disengaged position, a release sleeve can slide over the latch dogs, holding them in this position, which allows disconnection from head assembly / inner tube. When the latch dogs are in the engaged position, the release sleeve cannot slide over them, therefore, the overshot cannot release when carrying a load.

[0006] An issue that plagues this solution occurs when the inner tube bumps into or gets hung up on an obstacle during travel, which removes partially or completelythe load that is required to maintain the latch dogs in the engaged position, thus leading to the possibility that the latch dogs may move to the disengaged position. This can happen very rapidly and allow the release sleeve to slide over the latch dogs, releasing the overshot.

[0007] Against this background, there exists a need in the industry to provide safety mechanisms for overshots reducing or eliminating the risk that a release sleeve may inadvertently move to cover latch dogs and maintain them in their release position.

[0008] An object of the present invention is therefore to provide a safety mechanism.SUMMARY OF THE INVENTION

[0009] In a broad aspect, there is provided an overshot, comprising: latch dogs movable between latched and released configurations wherein the latch dogs are respectively positioned for engaging a head assembly and releasing from the head assembly; a release sleeve movable longitudinally along the overshot between proximal and distal positions, wherein in the proximal position, the release sleeve is withdrawn from the latch dogs; and in the distal position, the release sleeve is in register with at least part of the latch dogs so as to engage the latch dogs to lock the latch dogs in the released configuration; and a safety mechanism mechanically coupled to the release sleeve and configurable between a locked configuration and an unlocked configuration, wherein, in the locked configuration, the release sleeve is prevented from reaching the distal position, and in the unlocked configuration, the release sleeve is movable longitudinally to reach the distal position when the latch dogs are in the released configuration.

[0010] There may also be provided an overshot wherein the release sleeve and safety mechanism are engaged to each other so that cycling between application of a tension across the overshot and release of the tension multiple times with the overshot supported from below moves the safety mechanism from the locked configuration to the unlocked configuration.

[0011] There may also be provided an overshot wherein the release sleeve and safety mechanism are engaged to each other through a key and keyway assembly.

[0012] There may also be provided an overshot wherein the safety mechanism defines the keyway and the key extends from the release sleeve.

[0013] There may also be provided an overshot wherein the keyway defines circumferentially spaced apart keyway first and second ends, the key being at the keyway first end in the locked configuration and at the keyway second end in the unlocked configuration.

[0014] There may also be provided an overshot wherein the keyway defines a keyway first end segment at the keyway first end to receive the key in the locked configuration, a keyway second end segment at the keyway second end to receive the key in the unlocked configuration and a keyway intermediate segment extending therebetween, the keyway intermediate segment zigzagging circumferentially along the safety mechanism, the keyway second end segment extending distally to a greater extent than the keyway first end and intermediate segments.

[0015] There may also be provided an overshot wherein the overshot defines an overshot head to which the latch dogs are mounted and a longitudinally opposed jar terminated proximally by a wireline attachment, the jar including jar proximal and distal elements mounted to each other so as to be able to move in a reciprocating movement relative to each other; the keyway is longitudinally fixed relative to the jar distal element; the wireline attachment and overshot head are movable relative to each other in a reciprocating movement with the release sleeve remaining longitudinally fixed relative to the overshot head; and the keyway is configured so that in absence of other outside influence, the reciprocating movement moves the key relative to the keyway towards the keyway second end segment.

[0016] There may also be provided an overshot wherein the wireline attachment and overshot head are longitudinally biased away from each other.

[0017] There may also be provided an overshot wherein the wireline attachment and overshot head are longitudinally biased away from each other through a biasing element exerting a bias force insufficient for supporting at least one of a static weight and a dynamic weight of proximal components of the overshot jointly movable along with the wireline attachment.

[0018] There may also be provided an overshot further comprising a biasing element circumferentially biasing the key and keyway relative to each other so that the key is biased towards the keyway second end segment.

[0019] There may also be provided an overshot wherein the release sleeve defines a sleeve proximal portion and the safety mechanism defines a control sleeve configured to axially receive the sleeve proximal portion thereinto, the keyprotruding radially outwardly from the sleeve proximal portion, and the keyway extending through the control sleeve.

[0020] There may also be provided an overshot wherein, when the safety mechanism is moved between the locked and unlocked configurations, the release sleeve is axially rotated relative to the control sleeve.

[0021] There may also be provided an overshot wherein cycling between application of the tension across the overshot and release of the tension causes reciprocating movements of the control sleeve and release sleeve relative to each other, the reciprocating movements causing rotation of the release sleeve between the locked and unlocked configurations.

[0022] There may also be provided an overshot wherein the release sleeve is biased distally so as to be pushed distally towards the lifting dogs when the safety mechanism is in the unlocked configuration.

[0023] There may also be provided an overshot further comprising a lock for selectively locking the safety mechanism in the locked configuration.

[0024] There may also be provided an overshot wherein the safety mechanism is removably attached to the overshot so that the overshot is operable in a base configuration in which the safety mechanism is absent and in a sleeve actuating configuration in which the safety mechanism is present.

[0025] There may also be provided an overshot wherein the latch dogs each define a hook for engaging the head assembly, the latch dogs extending laterally relative to the overshot, the latch dogs protruding laterally to a greater extent in thelatched configuration than in the released configuration.

[0026] In another broad aspect, there is provided a safety mechanism for an overshot having latch dogs and a release sleeve, the latch dogs being movable between latched and released configurations wherein the latch dogs are respectively positioned for engaging a head assembly and releasing from the head assembly, the release sleeve being movable longitudinally along the overshot between proximal and distal positions, wherein in the proximal position, the release sleeve is withdrawn from the latch dogs, and in the distal position, the release sleeve is in register with at least part of the latch dogs so as to engage the latch dogs to lock the latch dogs in the released configuration, the safety mechanism comprising: a safety mechanism body defining a sleeve engaging portion for mechanically coupling to the release sleeve, the safety mechanism and release sleeve being movable relative to each other between locked and unlocked configurations, wherein, in the locked configuration, the release sleeve is prevented from reaching the distal position, and in the unlocked configuration, the release sleeve is movable longitudinally to reach the distal position when the latch dogs are in the released configuration.

[0027] In yet another broad aspect, there is provided a method of operating an overshot having latch dogs and a release sleeve for selectively maintaining the latch dogs in a released configuration, the overshot further including a safety mechanism for selectively locking the release sleeve proximally relative the latch dogs, the method comprising: engaging the release sleeve and the safety mechanism relative to each other so that the release sleeve is locked proximally relative the latch dogs; moving the latch dogs to a latched configuration wherein the latch dogs engage a head assembly; lowering the overshot attached to a head assembly in a drill hole to a bottom end thereof using a wire line; moving the latchdogs to the released configuration; and unlocking the release sleeve from the safety mechanism and moving the release sleeve so that the release sleeve is at least in part in register with the latch dogs to maintain the latch dogs in the released configuration.

[0028] There may also be provided a method wherein disengaging the release sleeve from the safety mechanism includes doing at least one cycle of pulling on the wireline and releasing tension in the wireline.

[0029] Advantageously, the proposed safety mechanism reduces the likelihood that shocks exerted on the head assembly and overshot during descent in a bore hole or handling outside of the bore hole result in accidental release of the overshot from the head assembly.

[0030] Other objects, advantages and features of the present invention will become more apparent upon reading of the following non-restrictive description of preferred embodiments thereof, given by way of example only with reference to the accompanying drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In the appended drawings:

[0032] Figure 1 , in a side elevation view, illustrates an overshot;

[0033] Figure 2, in a side cross-sectional line along section line ll-ll of FIG. 1 , illustrates the overshot of FIG. 1 ;

[0034] Figure 3, in a side elevation view, illustrates part of the overshot of FIG. 1 ;

[0035] Figure 4, in a side cross-sectional line along section line IV-IV of FIG. 3, illustrates the part of the overshot of FIG. 3;

[0036] Figure 5, in a side partially cut-away view, illustrates part of the overshot of FIGS. 1 to 4 with latch dogs thereof in a latched configuration and engaging a partially illustrated head assembly, the overshot having a release sleeve shown in a sleeve proximal position;

[0037] Figure 6, in a side partially cut-away view, illustrates the overshot of FIGS. 1 to 4 engaged in the head assembly of FIG. 5 with the latch dogs in a released configuration and the release sleeve in the sleeve proximal position;

[0038] Figure 7, in a side elevation view, illustrates the overshot of FIGS. 1 to 4 removed from the head assembly of FIG. 5 with the latch dogs in the released configuration and the release sleeve in a sleeve distal position;

[0039] Figure 8, in a side partially exploded elevation view, illustrates the overshot of FIGS. 1 to 4;

[0040] Figure 9, in a side partially exploded elevation view, illustrates an alternative overshot similar to the overshot of FIGS. 1 to 4 including an alternative release sleeve and a safety mechanism;

[0041] Figure 10, in a perspective exploded view, illustrates the release sleeve andsafety mechanism of FIG. 9

[0042] Figure 11 , in a perspective view, illustrates the release sleeve and safety mechanism of FIG. 9;

[0043] Figure 11 bis, in a perspective view with some hidden lines shown, illustrates the release sleeve of FIGS. 10 and 11 ;

[0044] Figure 12, in a partial side elevation view, illustrates the safety mechanism of the overshot of FIGS. 9 to 11 in a first, or locked, configuration;

[0045] Figure 13, in a partial side elevation and partially cut away view, illustrates the safety mechanism of the overshot of FIGS. 9 to 11 in a second configuration;

[0046] Figure 14, in a partial side elevation view, illustrates the safety mechanism of the overshot of FIGS. 9 to 11 in a third configuration;

[0047] Figure 15, in a partial side elevation view, illustrates the safety mechanism of the overshot of FIGS. 9 to 11 in a fourth, or unlocked, configuration;

[0048] Figure 16, in a side partial cross-sectional view, illustrates the safety mechanism of the overshot of FIGS. 9 to 11 in a position similar to the third configuration;

[0049] Figure 17, in a side partial cross-sectional view, illustrates the safety mechanism of the overshot of FIGS. 9 to 11 in a configuration similar to thesecond configuration;

[0050] Figure 18, in a side cross-sectional view, illustrates the safety mechanism of the overshot of FIGS. 9 to 11 in the first configuration; and

[0051] Figure 19, in a side cross-sectional view, illustrates the safety mechanism of the overshot of FIGS. 9 to 11 in the fourth configuration.DETAILED DESCRIPTION

[0052] The terminology distal and proximal refers to the distance from an operator using the proposed safety mechanism in a drill hole. Proximal elements are closer to the operator in use than distal elements, which are deeper in the drill hole. The term “axial” refers to a direction parallel to the longitudinal axis of an overshot including the proposed safety mechanism. Also, the terminology “substantially” and “about” is used to denote variations in the thus qualified terms that have no significant effect on the principle of operation of the proposed overshot and safety mechanism. These variations may be minor variations in design or variations due to mechanical tolerances in manufacturing and use of the overshot and safety mechanism. These variations are to be seen with the eye of the reader skilled in the art.

[0053] In some embodiments, the proposed safety mechanism is retrofittable to an overshot 10 in which the safety mechanism is omitted, so that the overshot can also be used without the safety mechanism. An example of such an overshot 10 is illustrated and described referring collectively to FIGS. 1 and 2. The overshot 10 may a prior art overshot 10 of a specific type, but the proposed safety mechanism,described in details below, is in some embodiments usable with other types of overshots, including dedicated overshots, incorporating permanently the safety mechanism. Also, while the overshot 10 is of the spearhead type, the proposed safety mechanism and similar ones are in some embodiments usable with spearhead-receiving types overshots. It should be noted that FIGS. 1 and 2 illustrate the overshot 10 in two different orientations, rotated axially 90 degrees relative to each other.

[0054] The overshot 10 includes, from a proximal end 11 to a distal end 13, a cable swivel assembly 12, a sinking bar 14, a jar tube 16, a jar staff 18 and an overshot head 20. The jar tube 16 and jar staff 18 together form a jar, and can be considered respectively to be jar proximal and distal elements, as other components having the same functionality are usable in alternative embodiments of the invention. A release sleeve 24 is also mounted to the above-described assembly, overlapping at least part of the overshot head 20, and in some embodiments part of the jar staff 18. The cable swivel assembly 12, sinking bar 14 and jar tube 16 are secured to each other, for example by being threaded to each other. The jar tube 16 defines a jar tube cavity 22 receiving part of the jar staff 18 thereinto so that the jar staff 18 is longitudinally movable along the jar tube cavity 22 in a reciprocating movement, while being prevented from distally exiting the jar tube 16 through suitably shaped flanges creating mechanical interference at the distal end of the jar tube cavity 22. The jar staff 18 is secured distally to the overshot head 20. The release sleeve 24 is axially movable along the overshot head 20 as further described below. The cable swivel assembly 12 is usable for securing a wireline 15 thereto.

[0055] Referring collectively to FIGS. 3 and 4, the overshot head 20 includes anovershot head body 26 defining laterally opposed latch dog recesses 28 each receiving a respective latch dog 30. Each latch dog 30 defines latch dogs proximal and distal end portions 32 and 34 with a latch dog intermediate portion 36 extending therebetween. The latch dog intermediate portion 36 defines a pivot receiving recess 38, and the latch dogs 30 are pivotally mounted in the latch dog recesses 28 with the pivot receiving recess 38 receiving a pivot 40 about which the latch dog 30 is pivotable. The latch dogs 30 are configured so that when mounted to the overshot head body 26, the latch dog intermediate portion 36 crosses over the longitudinal axis of the overshot head body 26, such that the latch dog proximal and distal end portions 32 and 34 are provided on opposite sides of the overshot head body 26. The latch dog distal end portion 34 defines a hook 42 configured for engaging a head assembly 44 (shown in FIGS. 5 and 6) to be handled using the overshot 10. The hooks 42 define at least one hook cam 43 oriented so that the at least one hook cam 43 of both latch dogs 30 converge towards each other in a distally leading direction.

[0056] The latch dogs 30 are pivotable between latched and released configurations, as illustrated respectively in FIGS. 5 and 6. The latch dog proximal and distal end portions 32 and 34 protrude laterally to a greater extend in the latched configuration than in the released configuration. In the latched configuration, the hooks 42 engage a circumferential groove 46 defined in the head assembly 44, allowing the overshot to support against gravity the head assembly 44 and any component suspended therefrom, such as an inner tube. Also, the latch dog proximal end portion 32 protrudes enough laterally to block axial movements of the release sleeve 24 over the latch dogs 30 due to the diameter of the release sleeve 24 being smaller than a width of the extended latch dogs 30. In the released configuration, the hooks 42 are removed from the circumferential groove 46, allowing the overshot to be withdrawn from the headassembly 44. Also, the latch dog proximal end portion 32 are withdrawn laterally inwardly enough to extend less laterally than in internal diameter of the release sleeve 24, the latter then being allowed to move over the latch dog proximal end portions 32, locking the latch dogs 30 in the released configuration, as seen in FIG. 7.

[0057] The overshot 10 also includes other characteristics. For example, the overshot 10 is also typically provided with a latch dog biasing element 47 biasing the latch dogs 30 towards the latched configuration, for example in the form of a coil spring extending between the latch dog proximal end portions 32. Also, the latch dogs 30 may have pivot receiving recesses 38 configured to allow small axial movements of the latch dogs 30 relative to the overshot head body 26 as they move between the latched and released positions. In some embodiments, the latch dogs 30 are freely floating, so as to be free to move about the pivot 40. Finally, the overshot head body 26 may define a distal cam surface 48 against which the latch dog distal end portions 34 may abut , which guides the latch dog axial movements.

[0058] In operation, the overshot 10 can be secured to a head assembly 44, which may support an inner tube (not shown in the drawings). In this configuration, the latch dogs 30 are in the latched configuration, and the head assembly 44 is suspended from the overshot 10. Therefore, the weight of the elements secured to the overshot will move the jar staff 18 to its distalmost position in the jar tube 16. The overshot 10, along with the components secured thereto, can then be lowered in a drill hole. Once the bottom of the drill hole is reached, the jar staff 18, and all the structures secured thereto distally, are supported from the bottom, and further lowering of the wireline 15 will allow the jar tube 16 to move distally until the jarstaff 18 abuts proximally against the end of the jar tube cavity 22. This will transfer the whole weight of the sinking bar 14 to the jar staff 18, which will push the whole overshot 10 slightly into the head assembly 44, leading to withdrawal of the latch dogs 30 to the released configuration due to the hook cams 43 sliding along suitable structures in the head assembly 44. Such structures include for example the rim of the circumferential groove 46 and the proximal rim of the head assembly 44, which may be bevelled to match the hook cams 43. Once the latch dogs 30 have withdrawn to the released configuration, the release sleeve 24 will be free to fall under gravity over the latch dog proximal end portion 32 to cover the latter, which allows withdrawal of the overshot 10 from the head assembly 44 as the latch dogs 30 are then locked in the released configuration.

[0059] Overshots similar to the above-described overshot 10 are known in the art, and no further details on their structure and operation is provided, as they are well- known, and can also vary slightly between specific embodiments of the overshot.

[0060] FIGS. 8 and 9 illustrate respectively the overshot 10 and an alternative overshot 10’ side by side to better illustrate the similarities and differences existing therebetween. The overshot 10’ is similar to the overshot 10, except that the overshot 10’ incorporates the proposed safety mechanism 52 and an alternative release sleeve 24’. Otherwise, the cable swivel assembly 12, sinking bar 14, jar tube 16, jar staff 18 and overshot head 20 are present in both overshots 10 and 10’. In the overshot 10’, the safety mechanism 52 extends between the overshot head 20 and the jar staff 18, as opposed to the jar staff 18 being directly secured to the overshot head 20 in the overshot 10. Also, the release sleeve 24’ is provided in register with the safety mechanism 52 when the release sleeve 24’ is in a sleeve proximal position, and the release sleeve 24’ has at least part thereofthat is in register with the overshot head 20, and more particularly with the latch dog proximal end portions 32, when the release sleeve 24’ is in a sleeve distal position. Therefore, there is no overlap between the jar staff 18 and the release sleeve 24’ in the overshot 10’.

[0061] Generally speaking, the safety mechanism 52 is mechanically coupled to the release sleeve 24’ and configurable between a locked configuration, seen for example in FIG. 12 and 18, and an unlocked configuration, seen for example in FIGS. 15 and 19. In the locked configuration, the release sleeve 24’ is prevented from reaching the sleeve distal position, and in the unlocked configuration, the release sleeve 24’ is movable longitudinally to reach the sleeve distal position when the latch dogs 30 are in the released configuration. Therefore, the safety mechanism 52 is provided to prevent the release sleeve 24’ from reaching the latch dogs 30 should the latter momentarily achieve the released configuration by accident, or to at least greatly reduce the chances that this happens. By examining the manner in which the latch dogs 30 operate, one can see that if the latch dogs are moved to the released configuration in the absence of the release sleeve 24’ due to the overshot 10 or 10’ entering deeper into the head assembly 44, any attempt at withdrawal of the overshot from the head assembly 44 will allow the latch dogs 30 to resume the latched configuration as the overshot 10 or 10’ moved proximally relative to head assembly 44, in register with the circumferential groove 46, which will result in the overshot 10 or 10’ reengaging the head assembly 44 before the overshot 10 or 10’ is completely withdrawn. This is because the latch dogs are biased towards the extended configuration.

[0062] The modular structure described above allows one to switch between the configurations of the overshots 10 and 10’ relatively easy, depending on need, orto retrofit an existing overshot 10 with the safety mechanism 52.

[0063] Advantageously, in some embodiments, and as further described below, the safety mechanism 52 can be operated from the surface without any additional wire or component running from the surface added to the conventional overshot 10. For example, the release sleeve 24’ and safety mechanism 52 are engaged to each other so that cycling between the application of a tension across the overshot 10’ and release of the tension multiple times moves the safety mechanism 52 from the locked configuration to the unlocked configuration. Thus, once the overshot 10’ has reached the bottom of the drill hole and the inner tube and head assembly 44 are supported, the overshot 10’ can be released by repeatedly pulling for a small amount of time on the wireline 15, followed by releasing, which can be easily performed by drilling personnel, either manually, or using the wireline 15 handling equipment. The above-described forces cause a reciprocating movement between the proximal and distal ends 11 and 13 of the overshot 10’ as the latter includes components that can move relative to each other, as described below. This reciprocating movement is used to operate the safety mechanism 52.

[0064] Referring collectively to FIGS. 10 and 11 , the release sleeve 24’ is hollow and generally elongated. The release sleeve 24’ defines sleeve proximal and distal sections 54 and 56 extending from each other. The sleeve proximal section 54 is configured to be engaged with the safety mechanism 52, and the sleeve distal section 56 is configured to engage the latch dogs 30 in the sleeve distal position. For example, the safety mechanism 52 is configured to receive axially thereinto the sleeve proximal section 54. Typically, if the safety mechanism 52 has an outer diameter similar to that of the sleeve distal section 56, the sleeve proximal section 54 therefore has a smaller diameter than the sleeve distal section 56, so that thesafety mechanism and sleeve 24’ assembly has a substantially uniform outer diameter therealong in the locked configuration.

[0065] In some embodiments, the sleeve distal section 56 defines external ribs 58 to facilitate handling of the release sleeve 24’ by improving grip for intended users handling the release sleeve 24’ with their hands, for example when initially arming the safety mechanism 52 to the locked configuration outside of the bore hole. Also, the sleeve proximal section 54 defines an axially oriented elongated guiding groove 59 (seen for example in FIG. 19) extending axially along at least part of the length of the sleeve proximal section 54, allowing a plunger protrusion 103, to be described below, to extend between the inside and outside of the sleeve proximal section 54. The guiding groove 59 is terminated distally by a circumferentially extending end groove 61 formed in the interior surface of the release sleeve 24’. When the plunger protrusion 103 reaches the end groove 61 , the release sleeve 24’ can rotate axially relative a plunger 18 as the plunger protrusion 103 is received in the end groove 61. Furthermore, in some embodiments, an access aperture 57 also extends through the sleeve distal section 56 to allow access to the inside of the release sleeve 24’ to facilitate assembly and disassembly of the overshot 10’.

[0066] The safety mechanism 52 includes a control sleeve 60, a plunger 64, a key 66, a primary biasing element 69, a secondary biasing element 70 and a control pin 72. In some embodiments, the safety mechanism 52 also include a lock, for example in the form of a lock pin 74, to prevent accidental movement of the safety mechanism 52 to the released configuration from the locked configuration, for example during handling of the overshot 10’ outside of the bore hole. The lock pin 74 is removed from the overshot 10’ before the latter is lowered in the bore hole.Other types of locks are within the scope of the invention, for example not including a removable component, but simply a component movable across any suitable component of the safety mechanism 52 to prevent accidental release of the release sleeve 24’.

[0067] Generally speaking, the safety mechanism 52 operates using a key 66 and keyway 68 arrangement moving the safety mechanism 52 from the locked configuration to the unlocked configuration by converting axial movements between distal and proximal components of the overshot 10’ to a relative rotational movement of the release sleeve 24’ relative to the control sleeve 60. Once the rotation has been completed, the release sleeve 24’ is released by the safety mechanism 52, so that the release sleeve 24’ can reach the sleeve distal position.

[0068] The key 66 is mounted to the sleeve proximal section 54 and protrudes radially outwardly therefrom. For example, the key 66 takes the form of a generally elongated member oriented axially and protruding radially outside of the sleeve proximal section 54. However, other shapes for the key 66 are possible in alternative embodiments, such as for example pin shaped keys.

[0069] The control sleeve 60 defines a control sleeve cavity 65 opening distally, and is terminated proximally by an attachment 62 attachable to the jar staff 18 (not shown in FIGS. 10 and 11), either directly or using a suitable coupler, such as a pivot body. This attachment 62 is similar to the attachment of the overshot head 20, as they are both configured to attach to the jar staff 18. For example, the attachment 62 includes a pair of legs for receiving an elongated member therebetween so that apertures extending through the legs and the elongated member can receive a suitable fastener therebetween locking the legs andelongated member to each other. However, any other attachment used in the field of core drilling equipment can be used in alternative embodiments.

[0070] The control sleeve 60 defines a keyway 68 extending between outside of the control sleeve 60, from a circumferential outer surface thereof, and the control sleeve cavity 65. The keyway 68 is configured for receiving the key 66 and allowing movements of the key 66 therealong when at least part of the sleeve proximal section 54 is received in the control sleeve cavity 65. For example, the keyway 68 is defined in a distal half of the control sleeve 60. The control sleeve 60 also defines a pair of diametrically opposed elongated control grooves 80 (only one of which is shown in FIGS. 10 and 11) extending longitudinally therealong between outside of the control sleeve 60 and the control sleeve cavity 65 and configured for receiving the control pin 72 therethrough. The control grooves 80 are for example located in a proximal half of the control sleeve 60. The control pin 72 is therefore movable in a reciprocating movement along the control grooves 80. In embodiments including the lock pin 74, a pair of laterally opposed lock pin apertures 82 (only one of which is shown in FIGS. 10 and 11) are provided for receiving the lock pin 74 therethrough so that the latter extends laterally across the control sleeve cavity 65. In some embodiments, the lock pin 74 thus inserted in the lock pin apertures 82 extends offset from the longitudinal axis of the overshot 10’.

[0071] Referring collectively to FIGS. 12 to 15, the keyway 68 defines circumferentially spaced apart keyway first and second ends 84 and 86, the key 66 being at the keyway first end 84 in the locked configuration and at the keyway second end 86 in the unlocked configuration. The keyway second end 86 opens distally to allow the key 66 to enter and leave the keyway 68 during assembly and disassembly of the overshot 10’. However, typically, the key 66 remains in thekeyway 68 even in the unlocked configuration during operation of the safety mechanism 52. In some embodiments, the keyway first and second ends 84 and 86 are circumferentially spaced apart by about 180 degrees, but other values of this angular separation are possible, for example between about 90 degrees and about 270 degrees.

[0072] The keyway 68 defines a keyway first end segment 88 at the keyway first end 84 to receive the key 66 in the locked configuration, a keyway second end segment 90 at the keyway second end 86 to receive the key 66 in the unlocked configuration and a keyway intermediate segment 92 extending therebetween. The keyway intermediate segment 92 zigzags circumferentially along the control sleeve 60 and defines circumferentially spaced apart proximal teeth 94 and circumferentially spaced apart distal teeth 96. The proximal and distal teeth 94 and 96 alternate circumferentially and are shaped to allow movements of the key 66 along the keyway intermediate segment 92. Typically, the proximal and distal teeth 94 and 96 terminate axially at about the same level, so that the key 66 is always engaged to one of the proximal and distal teeth 94 as the key 66 is moved along the keyway intermediate segment 92. Due to its axially elongated configuration, the key 66 may briefly engage both one of the proximal teeth 94 and one of the distal teeth 96 when moved along the keyway intermediate segment 92. The proximal and distal teeth 94 and 96 may each define a bevelled second surface 98, circumferentially facing in the keyway 68 and angled relative to the longitudinal direction to guide the key 66 during its movements along the keyway 68. For example, the bevelled second surfaces 98 face generally towards the keyway second end 86. The opposed first surfaces 100 of each of the proximal and distal teeth 94 and 96, facing circumferentially generally towards the keyway first end 84, extend generally axially. In some embodiments, the proximal potion of the keyway first end segment 88 is similar to the second surfaces 98 in shape and orientation.

[0073] Due to their orientation and shape, the second surfaces 98 couple longitudinal movements of the key 66 along the keyway 68 with circumferential movements of key 66, such that movements of the key proximally or distally away from the midplane of the keyway 68 rotates the release sleeve 24’ towards the released configuration, which contributes to the reliability of the safety mechanism 52. Indeed, it would be a major inconvenience to have to raise the overshot 10’ still attached to the head assembly 44 if the release sleeve 24’ would not release due to a stuck safety mechanism 52. By actively guiding the release sleeve 24’ so that the key 66 rotates towards the keyway second end 86 when active release of the safety mechanism 52 is sought, as described below, the likelihood of such a failure to unlock is reduced. This movement is helped by a bias of the release sleeve 24’ towards the released configuration, as detailed below.

[0074] Returning to FIG. 10, the plunger 64 includes a plunger staff 102 and a plunger head 104. The plunger head 104 is proximally secured to the plunger staff 102. This attachment can be permanent, or the plunger staff and head 102 and 104 may be detachable from each other. The plunger head 104 is substantially cylindrical and sized to be received in the control sleeve cavity 65 so as to be longitudinally movable therealong. The plunger staff 102 is narrower than the plunger head 104 and terminated distally by a plunger attachment 106 for attaching the plunger staff 102 to the overshot head 20, similarly to the manner in which the jar staff 18 attached to the overshot head 20 in the overshot 10. This attachment may be direct, using a fastener, or performed using an intermediary coupler, such as a pivot body. The plunger staff 102 also defines a plunger protrusion 103 protruding radially therefrom and configured and sized to be received in the guiding groove 59 and end groove 61. The plunger head 104 defines a pair of diametrically opposed control pin receiving apertures 108 for receiving the control pin 72 therethrough. In some embodiments, the control pin 72also secures the plunger staff 102 to the plunger head 104 by being also inserted through a plunger staff aperture 109 extending through the plunger head 104 in the portion thereof received by the plunger head 104. In some embodiments, the plunger attachment 106 is located such that the access aperture 57 is in register therewith when the overshot 10’ is assembled and the release sleeve 24’ is in a predetermined position, for example the released position, to facilitate assembly and disassembly of the overshot 10’.

[0075] The primary and secondary biasing elements 69 and 70 are for example both coil springs. The primary biasing element 69 operates both in torsion and in compression, while the secondary biasing element 70 operates in compression. In alternative embodiments, the torsion and compression functionalities of the primary biasing element 69 may be provided by two distinct biasing elements. To be able to provide a torque, the primary biasing element 69 is configured to engage the components between which it extends at a fixed location, for example through axially extending legs provided at each end thereof. In some embodiments, the primary biasing element 69 is biased in rotation so that the release sleeve 24’ is biased in a direction leading towards the released configuration. This bias may be present along the whole range of rotation of the release sleeve 24’. This bias cooperates with the shape of the first and second surfaces 100 and 98 to contribute to the reliability of the safety mechanism 52.

[0076] The assembled structure of the safety mechanism 52 with the release sleeve 24’ is described with reference to FIGS. 11 and 16 to 19 collectively, some details of this assembly being visible on only some of these figures. Generally speaking, the plunger 64 is mounted inside the control sleeve 60 so as to be movable between plunger proximalmost and distalmost positions, seen forexample in FIGS. 17 and 16 respectively. To that effect, the control pin 72 extends through and between the control grooves 80, intersecting the plunger head 104 and plunger staff 102. This limits the course of the plunger 64 inside the control sleeve 60. The secondary biasing element 70 is provided between the plunger head 104 and the attachment 62, inside the control sleeve cavity 65, biasing the plunger 64 towards the plunger distalmost position. The control grooves 80 also prevent relative rotational movements between the plunger 64 and the control sleeve 60.

[0077] In the plunger distalmost position, the plunger head 104 is shy of the lock pin apertures 82, as seen for example in FIG. 19. In the plunger proximalmost position, the plunger head 104 will move in register with the lock pin apertures 82. Thus, movements of the plunger 64 towards the plunger proximalmost position can be obstructed by the lock pin 74 when the latter is inserted through the lock pin apertures 82, as shown in FIG. 11 .

[0078] The release sleeve 24’ is mounted to the safety mechanism 52 such that the plunger 64 extends through the release sleeve 24’. The release sleeve 24’ is axially rotatable relative to the control sleeve 60. However, this rotation can only occur when the safety mechanism is not in the unlocked configuration due to the plunger protrusion 103. Indeed, in the unlocked configuration, the plunger protrusion 103 is engaged in the guiding groove 59, which extends axially. Once the key 66 is engaged in the keyway intermediate segment 92, the plunger protrusion 103 engages the end groove 61 , which allows rotation of the release sleeve 24’ relative to the plunger 64, while maintaining the plunger 64 and control sleeve 60 axially fixed relative to each other. In some embodiments, the plunger attachment 106 is sized to be able to enter through the sleeve distal portion 56,but is too large to enter the sleeve proximal portion 54, which limits the relative axial movement between the release sleeve 24’ and the control sleeve 60, as the plunger 64 is itself limited in its movements relative to the control sleeve 60. The primary biasing element 69 extends between the plunger head 104 and the rotatable portion. The release sleeve 24’ is positioned and configured so that the key 66 is engaged in the keyway 68.

[0079] The proximal and distal teeth 94 and 96 are configured such that when the release sleeve 24’ is engaged in the keyway intermediate segment 92, the plunger 64 is in the plunger distalmost position when the key 66 is provided between adjacent distal teeth 96, and the plunger 64 is in the plunger proximalmost position when the key 66 is provided between adjacent proximal teeth 94. Therefore, relative movements between the key 66 and the keyway 68 require reciprocating movements of the plunger 64 relative to the control sleeve 60. While the key 66 is in the keyway intermediate segment 92, the primary biasing element 69 typically remains substantially completely compressed, such that longitudinal movements of the control sleeve 24’ correspond to similar longitudinal movements of the plunger 64. The primary biasing element 69 biases the release sleeve 24’ distally, such that when the key 66 reaches the keyway second end segment 90, the release sleeve 24’ is pushed distally as the key 66 slides along the keyway second end segment 90.

[0080] In use, the safety mechanism 52 must first be armed. To that effect, an operator has to manually move the control sleeve 60 from the unlocked configuration to the locked configuration. More specifically, the operator starts for example from the unlocked position, with the key in the keyway second end segment 90, and compresses the release sleeve 24’ and the control sleeve 60towards each other, for example by grabbing the ribs 58 and pushing towards a sturdily immobilized attachment 62. Once a proximal end of the keyway second end segment 90 is reached, the operator can twist the rotatable portion against the resistance provided by the primary biasing element 69 towards the nearest proximal tooth 94 and gradually axially release the compression of the release sleeve 24’ while leading the key 66 along the second surface 98 of this first proximal tooth 94, until the key 66 reaches the first surface 100 of the first distal tooth 96. Then, the same operation is repeated for each successive proximal and distal teeth 94 and 96 pairs until the key reaches the key first end segment 88. If desired, the lock pin 74 can then be inserted through the lock pin apertures 82 to lock the safety mechanism 52.

[0081] Then, the overshot 10’ can be attached to the head assembly 44 and any component attached thereto in a conventional manner. Due to the lock pin 74, the release sleeve 24’ cannot move significantly relative to the control sleeve 60 during this operation, which avoid accidental release of the control sleeve 24’ should repeated shocks be exerted on the overshot 10’. When the overshot 10’ is ready to be lowered in the drill hole, the lock pin 74 can be removed.

[0082] Once the overshot 10’ reaches the bottom of the drill hole, the wireline 15 will go slack and the weight of the overshot 10’ will no longer be supported. This will result in compression of the secondary biasing element 70, as all overhanging structures are selected to have a weight sufficient for overcoming the biasing force provided by the latter. In some embodiments, this weight is a static weight, that is the weight when no movement is present. In other embodiments, the weight is a dynamic weight, that is a force exerted due both to the static weight and the momentum of the relevant parts of the overshot 10’. In turn, this will allow thecontrol sleeve 60 to move distally relative to the plunger 64, as the latter is supported by the overshot head 20, which is itself then supported in compression by the head assembly 44. Of note, during this operation, the latch dogs 30 will achieve the released configuration, but have their hooks 42 positioned distally relative to the circumferential groove 46. In other words, the latch dogs are laterally withdrawn, but located deeper in the head assembly 44 than when latched.

[0083] The movement of the control sleeve 60 along the plunger 64, along with the axial rotation biasing force provided by the primary biasing element 69 will then cause the key 66 to guide a rotational movement of the release sleeve 24’ as the key 66 advances along the keyway first end segment 88 . Once the key 66 clears the proximal tip of this first distal tooth 96, the key 66 will engage the first surface 100 of the first proximal tooth 94 until reaching an apex of the keyway 68 between the keyway first end segoment 88 and the proximal tooth 94 closest to the keyway first end segment 88. At this point, a tension is exerted on the overshot 10’ using the wireline 15, which causes retraction of the control sleeve 60 proximally relative to the plunger 64. The key 66 will then guide the release sleeve 24’ to continue its rotation through contact with the first surface 100 of the first proximal tooth 94 until the key 66 reaches the second surface 98 of the first distal tooth 96, at which point the key 66 will engage the first distal tooth 96 until it reaches a nadir between the first two distal teeth 96. Repeating this cycle allows the key 66 to index along the keyway 68 towards the released configuration, until the key 66 is received in the keyway second end segment 90. Due to the fact that this keyway second end segment 90 reaches distally past the keyway intermediate segment 92, the primary biasing element 69 will be allowed to decompress, which will propel the release sleeve 24’ over the latch dog proximal end portions 32 and allow removal of the overshot 10’ from the drill hole.

[0084] Due to the weight of the components supported by the overshot 10’, and to the force exerted by the secondary biasing element 70 during normal operation, the key 66 does not move relative to the keyway 68 while the overshot 10’ is lowered in the drill hole. This is the case even if minor shocks leading to partial or very momentary loss of tension in the wireline 15 occur. It may happen that the overshot experiences a larger shock while descending downhole. These larger shocks are typically very infrequent. If these larger shock occur, the key 66 may be allowed to move along the keyway 68 down one tooth pair, similar to the first release and tension operation that will be effected once the bottom of the borehole has been reached. However, the safety mechanism 52 is still operational, as multiple tension and release cycles are required to free the release sleeve 24. If an unusually larger number of such larger shocks occur, they may be detected by the operator lowering the overshot 10’ so that the overshot 10’ can be raised back to the surface to re-arm the safety mechanism or to further investigate the structure of the borehole.

[0085] The above-described safety mechanism 52 has been described in the context of surface drilling, with boreholes positioned below horizontal. In alternative embodiments, the safety mechanism 52, or variants thereof, are usable in underground drilling, to be understood as drilling wherein the boreholes are positioned above horizontal, so that gravity is working against the drilling equipment. Underground tooling uses a series of pump-in seals that allow the user to pump high flow water behind the overshot so it can travel up boreholes, opposing gravity. Then, an overshot including the safety mechanism 52, or close variants thereof may be used. Typically, these alternative overshots would be used when the inner tube becomes stuck in the hole. As the overshot is then no longer supported from below thanks to gravity, the manner in which the overshot is used needs to be changed as it is then used to pull against a stuck inner tube / overshot.However, the principle of operation of the safety mechanism remains similar.

[0086] For example, in such underground operation, the secondary biasing element 70 is much stiffer than in the above described overshot 10’. Therefore, compression of the overshot is not performed by gravity, but requires an operator to greatly increase the pressure of the water pumped up the borehole. However, the general mechanism of operation remains the same, in that unless the operator performs a predetermined operation, here an increase in pressure, the safety mechanism 52 remains locked.

[0087] Although the present invention has been described hereinabove by way of exemplary embodiments thereof, it will be readily appreciated that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, the scope of the claims should not be limited by the exemplary embodiments, but should be given the broadest interpretation consistent with the description as a whole. The present invention can thus be modified without departing from the spirit and nature of the subject invention as defined in the appended claims.

Claims

WHAT IS CLAIMED IS:

1. An overshot, comprising:- latch dogs movable between latched and released configurations wherein the latch dogs are respectively positioned for engaging a head assembly and releasing from the head assembly;- a release sleeve movable longitudinally along the overshot between proximal and distal positions, wherein- in the proximal position, the release sleeve is withdrawn from the latch dogs; and- in the distal position, the release sleeve is in register with at least part of the latch dogs so as to engage the latch dogs to lock the latch dogs in the released configuration; and- a safety mechanism mechanically coupled to the release sleeve and configurable between a locked configuration and an unlocked configuration, wherein, in the locked configuration, the release sleeve is prevented from reaching the distal position, and in the unlocked configuration, the release sleeve is movable longitudinally to reach the distal position when the latch dogs are in the released configuration.

2. The overshot as defined in claim 1 , wherein the release sleeve and safety mechanism are engaged to each other so that cycling between application of a tension across the overshot and release of the tension multiple times with the overshot supported from below moves the safety mechanism from the locked configuration to the unlocked configuration.

3. The overshot as defined in claim 1 or 2, wherein the release sleeve and safety mechanism are engaged to each other through a key and keyway assembly.

4. The overshot as defined in claim 3, wherein the safety mechanism defines the keyway and the key extends from the release sleeve.

5. The overshot as defined in claim 3 or 4, wherein the keyway defines circumferentially spaced apart keyway first and second ends, the key being at the keyway first end in the locked configuration and at the keyway second end in the unlocked configuration.

6. The overshot as defined in claim 5, wherein the keyway defines a keyway first end segment at the keyway first end to receive the key in the locked configuration, a keyway second end segment at the keyway second end to receive the key in the unlocked configuration and a keyway intermediate segment extending therebetween, the keyway intermediate segment zigzagging circumferentially along the safety mechanism, the keyway second end segment extending distally to a greater extent than the keyway first end and intermediate segments.

7. The overshot as defined in claim 6, wherein- the overshot defines an overshot head to which the latch dogs are mounted and a longitudinally opposed jar terminated proximally by a wireline attachment, the jar including jar proximal and distal elements mounted to each other so as to be able to move in a reciprocating movement relative to each other;- the keyway is longitudinally fixed relative to the jar distal element;- the wireline attachment and overshot head are movable relative to each other in a reciprocating movement with the release sleeve remaining longitudinally fixed relative to the overshot head; and- the keyway is configured so that in absence of other outside influence, the reciprocating movement moves the key relative to the keyway towards the keyway second end segment.

8. The overshot as defined in claim 7, wherein the wireline attachment and overshot head are longitudinally biased away from each other.

9. The overshot as defined in claim 7, wherein the wireline attachment and overshot head are longitudinally biased away from each other through a biasing element exerting a bias force insufficient for supporting at least one of a static weight and a dynamic weight of proximal components of the overshot jointly movable along with the wireline attachment.

10. The overshot as defined in any one of claims 5 to 9, further comprising a biasing element circumferentially biasing the key and keyway relative to each other so that the key is biased towards the keyway second end segment.11 . The overshot as defined in any one of claims 3 to 10, wherein the release sleeve defines a sleeve proximal portion and the safety mechanism defines a control sleeve configured to axially receive the sleeve proximal portion thereinto, the key protruding radially outwardly from the sleeve proximal portion, and the keyway extending through the control sleeve.

12. The overshot as defined in claim 11 , wherein, when the safety mechanism is moved between the locked and unlocked configurations, the release sleeve is axially rotated relative to the control sleeve.

13. The overshot as defined in claim 12, wherein cycling between application of the tension across the overshot and release of the tension causes reciprocating movements of the control sleeve and release sleeve relative to each other, the reciprocating movements causingrotation of the release sleeve between the locked and unlocked configurations.

14. The overshot as defined in any one of claims 1 to 13, wherein the release sleeve is biased distally so as to be pushed distally towards the lifting dogs when the safety mechanism is in the unlocked configuration.

15. The overshot as defined in any one of claims 1 to 14, further comprising a lock for selectively locking the safety mechanism in the locked configuration.

16. The overshot as defined in any one of claims 1 to 15, wherein the safety mechanism is removably attached to the overshot so that the overshot is operable in a base configuration in which the safety mechanism is absent and in a sleeve actuating configuration in which the safety mechanism is present.

17. The overshot as defined in any one of claims 1 to 16, wherein the latch dogs each define a hook for engaging the head assembly, the latch dogs extending laterally relative to the overshot, the latch dogs protruding laterally to a greater extent in the latched configuration than in the released configuration.

18. A safety mechanism for an overshot having latch dogs and a release sleeve, the latch dogs being movable between latched and released configurations wherein the latch dogs are respectively positioned for engaging a head assembly and releasing from the head assembly, the release sleeve being movable longitudinally along the overshot between proximal and distal positions, wherein in the proximal position, the release sleeve is withdrawn from the latch dogs, and in thedistal position, the release sleeve is in register with at least part of the latch dogs so as to engage the latch dogs to lock the latch dogs in the released configuration, the safety mechanism comprising:- a safety mechanism body defining a sleeve engaging portion for mechanically coupling to the release sleeve, the safety mechanism and release sleeve being movable relative to each other between locked and unlocked configurations, wherein, in the locked configuration, the release sleeve is prevented from reaching the distal position, and in the unlocked configuration, the release sleeve is movable longitudinally to reach the distal position when the latch dogs are in the released configuration.

19. A method of operating an overshot having latch dogs and a release sleeve for selectively maintaining the latch dogs in a released configuration, the overshot further including a safety mechanism for selectively maintaining the release sleeve proximally relative the latch dogs, the method comprising:- engaging the release sleeve and the safety mechanism relative to each other so that the release sleeve is locked proximally relative the latch dogs;- moving the latch dogs to a latched configuration wherein the latch dogs engage a head assembly;- lowering the overshot attached to a head assembly in a drill hole to a bottom end thereof using a wire line;- moving the latch dogs to the released configuration; and- unlocking the release sleeve from the safety mechanism and moving the release sleeve so that the release sleeve is at least in part in register with the latch dogs to maintain the latch dogs in the released configuration.

20. The method as defined in claim 19, wherein unlocking the release sleeve from the safety mechanism includes doing at least one cycle of pulling on the wireline and releasing tension in the wireline.

Images