WO2012119186A1

WO2012119186A1 - Overshot

Info

Publication number: WO2012119186A1
Application number: PCT/AU2012/000181
Authority: WO
Inventors: Andrew Beach; Ben Blakeway; Gavin Mcleod; Ronald Edward THIESS
Original assignee: 2Ic Australia Pty Ltd
Priority date: 2011-03-04
Filing date: 2012-02-24
Publication date: 2012-09-13
Also published as: AU2012225191B2; CA2828254C; ZA201306280B; AU2012225191C1; CA2828254A1; AU2012225191A1

Abstract

An overshot (10) comprises a latching mechanism (12) for latching a member such as a spear point (14); and, an actuator (16) which actuates the latching mechanism (12). The latching mechanism (12) has a number of different operational states. One of these is a neutral state in which latching mechanism (12) is able to latch or capture a spear point (14). In the neutral state, latching mechanism (12) is able to open in order to receive spear point (14) and then self- close to latch or retain the spear point (14). Latching mechanism (12) also has a locked state in which it is locked in a closed position by actuator (16) to prevent the release of a latched spear point (14). The third state is the release state where the overshot is locked in an open position by actuator (16) to release a previously latched spear point (14). The actuator (16) operates as a linear to rotary motion converter which converts linear motion of one part of the actuator to a rotary motion of another part of the actuator between a plurality of rotationally spaced positions. The rotational positions determine the state of the latching mechanism.

Description

OVERSHOT

Field of the Invention The present invention relates to an overshot used for lowering and retrieving tools and other equipment to and from a well, borehole or drill string.

Background of the Invention In order to lower tools or equipment into a well or a drill string, it's common to use a wire line attached to an overshot. One end of the wire line is attached to a winch at ground level, while an opposite end is attached to the overshot. The overshot has a latching mechanism which is configured to engage a latching member such as a spear point coupled to an upper end of a tool or other piece of down hole equipment. It is critical for the overshot to operate reliably and in particular to not accidentally release an engaged spear point. An accidental release while a tool is being lowered through a well or drill string can cause substantial damage and downtime. Moreover, accidental disengagement of an overshot while lifting an engaged tool at ground level can cause serious injury or death to a drill rig operator.

Summary of the Invention

In one aspect the present invention provides an overshot comprising:

a latching mechanism having a: neutral state where the latching mechanism is able to latch a member; a locked state where the latching mechanism is locked in a closed position to prevent release of a latched member; and, a release state where the latching mechanism is locked in an open position to release a latched member or prevent latching of a member; and;

an actuator operable to switch the latching mechanism between the neutral, locked and release states.

In one embodiment the actuator mechanically engages the latching mechanism and is linearly movable up and down along an axis relative to the latching mechanism to switch the latching mechanism between the neutral, latched and released states. ln one embodiment the overshot comprises a first casing and wherein the latching mechanism is coupled to the first casing and fixed against linear motion relative to the first casing.

In one embodiment the actuator is linearly movable relative to the latching mechanism to switch the latching mechanism between the neutral, locked and released states. The latching mechanism may comprise two or more latch dogs each pivotally coupled to the first casing and wherein the actuator is mechanically coupled to each latch dog.

Each latch dog may comprise a slot elongated in a direction of the axis, and wherein the actuator is mechanically coupled to the slot of each latch dog.

The slots may be shaped such that when the actuator is in a first linear position relative to the latch member, the actuator holds the latching mechanism in the locked state, when the latching mechanism is in a second linear position relative to the latch mechanism, the actuator holds the latch member in the release state, and when the actuator is in an intermediate position the latching mechanism is in the neutral state.

The actuator may comprise a pin that passes through each slot.

The slots may be relatively configured so that the pin bears against each latch dog as the actuator moves up or down to cause a pivoting motion of the latch dogs. Each slot may comprise respective opposite ends that are laterally offset from each other and wherein each slot progressively widens from each end to an intermediate location of the slot.

In one embodiment when the actuator is in the first linear position, the pin resides in a first end of each slot, when the latching mechanism is in the second linear position, the pin resides in a second opposite end of each slot, and when the linear actuator is in an intermediate position, the pin is at the intermediate location of each slot.

In one embodiment the latching mechanism comprises a spring and is capable when in the neutral position to open against bias provided by the spring to receive a member and self close by action of the bias to retain a received member.

In one embodiment the actuator comprises a linear to rotary motion converter which is operable to convert linear motion of the actuator to a rotary motion of the actuator or a part thereof between a plurality of rotationally spaced positions and wherein the linear position of the actuator relative to the latching mechanism is controlled by the rotational position of the actuator or part thereof. In one embodiment the overshot comprises a rotator spring arranged to bias the rotator to move linearly toward the latching mechanism

In one embodiment the actuator comprises a rotator that is capable of combined simultaneous linear and rotational motion, the rotator comprising a cam track and at least one cam pin which resides in the cam track and is supported separately of the rotator.

The cam track may comprise a plurality of contiguous first and second undulations wherein successive first undulations are separated by at least one single second undulation, and wherein the second undulations and first undulations are of a different configuration.

In an alternate embodiment the actuator comprises a rotator capable of linear motion relative to the latching mechanism and a rotary mechanism supported on the rotator and arranged to rotate between successive rotationally displaced positions upon a linear reciprocal motion of the rotator.

In this embodiment the rotator comprises a plurality of keys and the rotary mechanism comprises a plurality of teeth on axially opposite sides and wherein the keys and teeth are arranged to engage on when the rotator is linearly reciprocated the engagement causing rotational motion of the rotary

mechanism. In one embodiment the actuator or part thereof has a first rotational position at which the actuator is in a first linear position where the actuator is able to operate the latching mechanism to release a latched member, and N

intermediate rotational positions which are sequentially adjacent the first rotational position where N is an integer greater than zero so that adjacent first rotational positions are spaced by N intermediate rotational positions wherein upon N successive linear reciprocations of the rotator the actuator or part thereof is rotated N times to place the actuator in the next first rotational positions.

In one embodiment when the actuator or part thereof is in any one of the N rotational positions the actuator maintains the latching mechanism in the neutral or locked states.

In a second aspect the invention provides an overshot comprising a latching mechanism capable of latching a member, the latching mechanism having: a locked state where the latching mechanism is locked in a closed position to prevent release of a latched member; and, a release state where the latching mechanism is locked in an open position to release a latched member or prevent latching of a member; and, a ratchet mechanism sequentially movable, one ratchet position at a time between respective adjacent ratchet positions upon each application of an externally applied force in a direction along a longitudinal axis of the latching mechanism, the ratchet mechanism operatively associated with the latching mechanism wherein when the ratchet mechanism is in a first ratchet position the ratchet mechanism holds the latching

mechanism in the locked position and when the ratchet mechanism is in a second ratchet position the ratchet mechanism holds the latching mechanism in the release position, and wherein there are N ratchet positions between the first and second ratchet positions where N is an integer≥ 1 .

In one embodiment the ratchet mechanism is a rotary ratchet mechanism and adjacent ratchet positions are circumferentially spaced about the longitudinal axis.

The overshot may comprise a rotator associated with the ratchet mechanism the rotator extending along the longitudinal axis and linearly movable along the longitudinal axis by action of the externally applied force wherein linear reciprocation of the rotator causes the ratchet mechanism to rotate from a current ratchet position to an adjacent ratchet position. The overshot may comprise a visual indicator associated with the rotator and capable of providing a visual indication to a user of a number of linear reciprocations of the rotator required to place the latching mechanism in the release state. The visual indicator may comprises markings on the rotary mechanism or ratchet mechanism and a window formed in the first casing at a location thought which the markings are visible.

In one embodiment the overshot comprises a locking mechanism manually movable between a lock position and a free position, the locking mechanism: when in the lock position operating the actuator to place and hold the latching mechanism in the locked state; and when in the free position allowing the actuator to operate to switch the latching mechanism between the neutral, locked and release states.

Brief Description of the Drawings

Specific embodiments of the overshot will now be described by way of example with reference to the accompanying drawings in which:

Figure 1 is a section view of the first embodiment of an overshot according to the present invention depicting internal components including a latching mechanism and actuator;

Figure 2 is an exploded view of the overshot shown in Fig 1 ;

Figure 3a is a section view of the overshot showing the latching mechanism in a neutral state;

Figure 3b is a partial section view of the overshot shown in Figure 3a but with a portion of the actuator not sectioned;

Figure 4a is a section of the overshot shown in Figures 1 and 2 with the latching mechanism in a locked state;

Figure 4b is a partial section view of the overshot shown in Figure 4a but with a portion of the of the actuator not sectioned; Figure 5a is a section view of the overshot shown in Figures 1 and 2 with the latching mechanism in a release state;

Figure 5b is a partial section view of the overshot in Figure 5a but with a portion of the of the actuator not sectioned;

Figure 6 is a schematic view of the overshot shown in Figures 1 and 2;

Figure 7a is a plan view of a lifting dog incorporated in the latching mechanism; Figure 7b is an isometric view of the lifting dog shown in Figure 7a;

Figure 7c is a side view of the lifting dog shown in Figure 7a;

Figure 7d is a view of section D-D of the lifting dog shown in Figure 7a;

Figure 8a is a side view of a torsion spring incorporated in the latching mechanism;

Figure 8b is a plan view of the torsion spring shown in Figure 8a;

Figure 9a is an isometric view of a rotator incorporated in the overshot;

Figure 9b is a first elevation of the rotator shown in Figure 9a;

Figure 9c is a second elevation view of the rotator turned through 90 degrees relative to that shown in Figure 9b;

Figure 9d is a view of section A-A of the rotation in figure 9b;

Figure 9e is a view of section B-B of the rotation in Figure 9b;

Figure 10a is a plan view of a lower casing incorporated in the overshot;

Figure 10b is a view of section A-A of the lower casing shown in Figure 9a; Figure 10c is an isometric view of the lower casing shown in Figure 9a;

Figure 1 1 a is a side view of a ratchet ring incorporated in the overshot;

Figure 1 1 b is an isometric view of the ratchet ring;

Figure 12a is a plan view of a ratchet segment incorporated in the overshot; Figure 12b is an isometric view of the ratchet segment shown in Figure 12a;

Figure 12c is an isometric view of a ratchet drum assembly comprising the ratchet ring of Figure 12a and two of the ratchet segments of Figure 12b;

Figure 13 is a section view of a second embodiment of the overshot;

Figure 14 is an exploded view of the overshot shown in Figure 13;

Figure 15a is a section view of the second embodiment of the overshot depicted in Figures 13 and 14 showing the latching mechanism in a neutral state;

Figure 15b is a partial section view of the overshot shown in Figure 15a but with a portion of the actuator not sectioned;

Figure 16a is a section of the overshot shown in Figures 1 and 2 with the latching mechanism in a locked state;

Figure 16b is a partial section view of the overshot shown in Figure 16a but with a portion of the of the actuator not sectioned;

Figure 17a is a section view of the overshot shown in Figures 13 and 14 with the latching mechanism in a release state;

Figure 17b is a partial section view of the overshot in Figure 17a but with a portion of the of the actuator not sectioned;

Figure 18 is an isometric representation of the overshot shown in Figures 13 and 14;

Figure 19a is an isometric view of a portion of a rotator incorporated in the overshot;

Figure 19b is an elevation view of the rotator portion shown in Figure 19a; Figure 19c is a view of section A-A of the rotator portion shown in Figure 19b; Figure 19d is a development of a cam track provided on the rotator portion shown in Figures 19a and 19b;

Figure 20 is an isometric view of a second portion of the rotator;

Figure 21 a is a plan view of the lower casing of the overshot shown as Figures 13 and 14;

Figure 21 b is a view of section A-A of the lower casing shown in Figure 21 a; Figure 21 c is an isometric view of the lower casing shown in Figure 21 a; Figure 22a is an isometric view of a clevis collar incorporated in the overshot; Figure 22b is a side view of the clevis collar shown in Figure 22a;

Figure 23 is an isometric view of a cam pin that is incorporated in the overshot shown in Figures 13 and 14;

Figure 24a is side elevation of an overshot of the type shown in Figures 1 - 12c but modified by the incorporation of a locking mechanism;

Figure 24b is a side elevation of the overshot shown in figure 24b but rotated through 90°;

Figure 24c is a section view of the overshot shown in Figure 24 c;

Figure 25 is a side elevation of the locking mechanism shown in Figures 24a- 24, when in a lock position;

Figure 26 is a section view of the locking mechanism shown in Figure 25; Figure 27 is a side elevation of the locking mechanism shown in Figures 24a- 24, when in an unlock position; and

Figure 28 is a section view of the locking mechanism shown in Figure 27. Detailed Description of Preferred Embodiments

Figures 1-12 illustrate a first embodiment of an overshot 10 in accordance with the present invention. Overshot 10 comprises a latching mechanism 12 for latching a member such as a spear point 14 (shown in Figure 6); and, an actuator 16 which actuates the latching mechanism 12. The latching mechanism 12 has a number of different operational states. One of these is a neutral state which is shown in Figures 3a and 3b in which latching mechanism 12 is able to latch or capture a spear point 14. In the neutral state, latching mechanism 12 is able to open in order to receive spear point 14 and then self- close to latch or retain the spear point 14. Latching mechanism 12 also has a locked state shown in Figures 4a and 4b in which it is locked in a closed position by actuator 16 to prevent the release of a latched spear point 14. Figures 5a and 5b illustrate the latching mechanism 12 in its release state where it is locked in an open position by actuator 16 to release a previously latched spear point 14. The actuator 16 operates as a linear to rotary motion converter which converts linear motion of one part of the actuator to a rotary motion of another part of the actuator between a plurality of rotationally spaced positions. The rotational positions determine the state of the latching mechanism. By separating successive release states of the latching mechanism by, say, two or more rotational positions, the actuator or part thereof must be rotated through the two or more rotational positions to cause a latched spear point to be released. The linear motion on the actuator may be affected by applying a lifting or pulling force on the actuator. Each application of this force causes a rotation of the actuator to the next rotational position.

The structure and operation of overshot 10 in a particular latching mechanism 12 and actuator 16 will now be described in greater detail.

Latching mechanism 12 comprises two lifting dogs 18a and 18b (hereinafter referred to in general as "lifting dogs 18"). Lifting dogs 18 are arranged in a scissor-like manner and pivotally coupled to a tubular lower casing 20. Figures 7a-7d depict in detail a lifting dog 18. Lifting dog 18 comprises a shank 22 provided with a boss 24 intermediate its length. Boss 24 has a thickness less than the thickness of the shank 22 and is offset to one side of shank 22 leaving a void 26 for co-axially receiving a torsion spring 50 (shown in Figures 8a and 8b).

An up hole end 28 of lifting dog 18 is formed with a reduced thickness extension 30 in which is provided an elongated slot 32. Slot 32 has opposite concave ends 34 and 36 which are formed with the same radius but laterally offset from each other. The slot 32 progressively widens from each end 34 and 36 to an intermediate location 38 which represents the widest portion of slot 32 measured in the transverse direction. In this embodiment intermediate location 38 is closer to end 36 than to end 34. As seen most clearly in Figures 7b and 7c, portion 30 is one half the thickness of shank 22 and on the side of shank 22 opposite boss 24. This leaves a void 40 adjacent portion 30 to accommodate an identical portion 30 of the other lifting dog 18. Down hole end 42 of lifting dog 18 is provided with a hook-like structure 44. Hook-like structure 44 is configured to hook spear point 14 as shown most clearly in Figure 6 and is provided with a concave surface 46 of a radius substantially the same as the radius of a neck 48 of spear point 14. Each of lifting dogs 18a and 18b is of the same general configuration as shown in Figures 7a-7d.

The torsion spring 50 (Figures 8a and 8b) is placed between lifting dogs 18 coaxial with their respective bosses 24 and acts in a manner to bias the hook-like structures 44 towards each other. Lifting dogs 18 and the torsion spring 50 are retained in lower casing 20 by a pivot pin 52 which passes through bosses 24 of each lifting dog 18 and the torsion spring 50.

Actuator 16 comprises a rotator 54 shown in Figures 9a-9e. Rotator 54 is in the general form of an elongated rod 56 having several distinct but contiguous portions. At an up hole end rod 56 is formed with a short threaded portion 58. This is followed by portion 60 having a constant but greater diameter than the portion 58. An increased diameter portion 62 extends from and forms a step 63 with portion 60. Rotator 54 terminates in a bifurcation 64 contiguous with portion 62 but having a greater outer diameter. The difference in outer diameter between portion 62 and 64 forms a circumferential shoulder 66.

In this particular embodiment portion 62 is formed with two upper keys 68 which extend axially from step 63 at diametrically opposed locations toward the bifurcation 64 as shown in Figure 9d. Two lower keys 70 also extend in an axial direction on portion 62 but from the shoulder 66 toward shoulder 63. The lower keys 70 are diagonally opposed to each other and circumferentially offset from the keys 68 as shown in Figure 9e. Bifurcation 64 comprises a pair of opposed arms 72 each of which is formed with a hole 74 at diametrically opposed locations. The rotator 54 and thus actuator 16 mechanically engage the latch mechanism 12 by a cam pin 76 which passes through slots 32 in each of the lifting dogs 18 and coupled to the arms 72 in their holes 74.

Referring to Figures 10a-10c, lower casing 20 is in the general form of a tube 80 provided with a pair of diametrically opposed axially extending cut-outs 82. A first hole 84 passes transversely through tube 80 midway between the slots 82. A further hole 86 is formed parallel to and up hole of hole 84. A pair of diametrically opposed windows 90 is also formed in tube 80 up hole of hole 86. Windows 90 open onto a drum seat 92 formed internally of tube 20. Lifting dogs 18 are assembled together with the torsion spring 50 and passed through one of the slots 82 so that the bosses 24 align with hole 84. The pivot pin 52 is then passed through hole 84 and bosses 24 retaining the lifting dogs 18 within outer casing 20. Referring to Figures 1 1 a - 12c a rotary mechanism in the form of ratchet drum assembly 94 is located about portion 62 of rotator 54 and seats in the drum seat 92. Ratchet drum assembly 94 comprises a ratchet ring 96 and two identical ratchet segments, one of which is depicted in Figures 12a and 12b. Ratchet ring 96 is formed with an outer diameter to provide a small clearance with seat 92 enabling rotation of ratchet drum 94 about its axis. A plurality of holes 100 is formed in a central band about ratchet ring 96.

Each ratchet segment 98 is radiused to fit inside ratchet ring 96 and extends in a circumferential direction for approximately 160°. In this specific embodiment five ratchet teeth 102a are formed along an upper end, and five ratchet teeth 102b are formed along a lower end of each segment 98. (The ratchet teeth 102a and 102b are referred to in general as "ratchet teeth 102"). Although in alternate embodiments a different number of teeth may be provided. Opposite axial sides 104 of the segments 98 are straight and mutually parallel. Ratchet drum assembly 94 is assembled by fixing two ratchet segments 98 inside ratchet ring 96 in a diametrically opposed relationship with longitudinal gaps 106 being formed between opposed adjacent sides 104 of the segments 98 as shown in Figures 3b, 4b, 5b and 12c. The fixing may be by way of spot welding through the holes 100.

With reference to Figures 1 and 2 a tubular upper casing 108 threadingly engages an up hole end of lower casing 20. Upper casing 108 accommodates a spring packer 1 10 which comprises a plurality of washers 1 12 that fit over portion 60 of rotator 54 and abut against shoulder 63. Upper casing 108 also accommodates a spring 1 14 that sits over portion 60 and abuts against the spring packer 1 10. Spring 1 14 is retained by an end cap 1 16 that screws into an up hole end of upper casing 108. End cap 1 16 is provided with an axial hole through which portion 60 and in particular thread portion 58 extend. Spring 1 14 biases the rotator 54 in a down hole direction relative to the latching mechanism 12. End 58 of rotator 54 is threadingly engaged with one end of a swivel housing 1 18. A swivel 120 is attached to an opposite end of swivel housing 118. A hole 122 is formed in swivel 120 for attachment to a wire line. This provides rotational decoupling from the wire line. Referring to Figures 3a and 3b when assembling the overshot 10, ratchet drum assembly 94 is placed on portion 62 of rotator 54. A thrust washer 124a is placed in a down hole end of drum seat 92 and the rotator 54 is inserted into lower casing 20 with the bifurcation 64 orientated so as to receive portions 30 of lifting dogs 18. Cam pin 76 is passed through hole 86 into the holes 74 and each of slots 32. A second of the thrust washers 124b is passed onto portion 60 of rotator 54 and rests on ratchet ring 96. Upper casing 108 screws into lower casing 20 and abuts against thrust washer 124b. The thrust washers 124a and 124b prevent freewheeling of the ratchet drum assembly 94, and hold it in place in the absence of contact with the keys 68 and 70. Spring packer 1 10 and spring 1 14 are seated over portion 60 of rotator 54 inside of upper casing 108. End cap 1 16 screws into upper casing 108 to retain spring 1 14 and rotator 54 within the upper and lower casings 20, 108. Finally, swivel housing 1 18 is threaded onto thread portion 58 of rotator 54 thereby rotationally decoupling the rotator 54 form a wire line to which overshot 10 is attached.

Say in an initial state, the upper keys 68 reside within the gaps 106 between ratchet segments 98 as shown in Figures 5a and 5b. In the absence of application of any force to the actuator, overshot 10 will remain in this state by virtue of the bias applied by spring 1 14 on rotator 54. This bias forces rotator 54 in a down hole direction relative to lifting dogs 18 pushing the cam pin 76 to the lower ends 36 of each slot 32. This has the effect of spreading the down hole end 42 of latching mechanism 12 apart as shown in Figures 1 , 5a and 5b. This corresponds to the release position and either: prevents engagement with a spear point 14; or, if a spear point 14 was previously engaged, now releases the spear point. Prior to lowering the overshot 10 through a drill string or well to engage a spear point of a down hole tool, actuator 16 is operated to place the latching mechanism 12 in the neutral state as shown in Figures 3a and 3b. To do this, a force is applied to actuator 16 pulling it in an upward direction relative to latching mechanism 12 against the bias of spring 1 14. This motion results in the upper keys 68 being retracted from the gap 106 and eventually, the lower keys 70 engaging ratchet teeth 102b. Due to their relative configuration, when keys 70 engage the teeth 102b, and the upward force is still applied, the ratchet drum 94 is rotated in a clockwise direction about its axis viewed from the end of the latching mechanism 12. Simultaneously, the pin 76 is being moved upwardly through slots 32. The upward motion is stopped when keys 70 are located in the root of teeth 102b and pin 76 is seated in the end 34. This motion of the pin 76 through the slots 32 pulls hook portions 44 of latching dogs 18 together. While pin 76 seats in ends 34, it effectively locks the latching mechanism 12 in the closed state. This will prevent the release of a previously engaged spear point 18; and, in the event that a spear point was not previously engaged, will also prevent the spear point from being captured by the latching mechanism 12.

When the pulling force on rotator 54 is released, spring 1 14 biases rotator 54 in the downward direction sliding the upper keys 68 into contact with ratchet teeth 102. This again has the effect of rotating the ratchet drum 94 in the same direction as previously rotated. The successive clockwise direction rotations caused by contact with the lower keys 70 then the upper keys 68 arising from a single application and release of a pulling force on actuator 16 represent a rotation of the actuator through one ratchet position.

The downward stroke or motion of rotator 54 arising from the bias of spring 1 14 is limited by engagement of the keys 68 with the root of teeth 102a as shown in Figures 3a and 3b. This corresponds with the neutral state of actuator 16. In this state, pin 76 resides at the intermediate location 38 within slots 32. When in this state, latch mechanism 12 is able to latch onto a spear point 14. For example, if overshot 10 is lowered through a drill string on a wire line and impacts on a spear point 14 of a down hole tool, the lifting dogs 18 will spread against the bias of torsion spring 50 to enable the head 48 of the spear point 14 to become engaged by the hook-like portions 44. Lifting dogs 18 are able to spread to allow engagement of spear point 14 by virtue of the shape of slots 32 and location of pin 76. This spreading is facilitated by the up-hole ends of lifting dogs 18a and 18b pivoting away from each other, and is enabled by virtue of the widening of slots 32 at the intermediate location 38 at which pin 76 resides.

Once a spear point 14 is engaged with latching mechanism 12 when in the neutral state, torsion spring 50 acts to maintain the latching mechanism 12 in engagement with the spear point 14.

If it is now desired to retrieve the down hole tool, the wire line to which overshot 10 is attached is reeled in. This places a load on the overshot 10 generating an equal and opposite force on rotator 54 causing rotator 54 to move linearly away from latching mechanism 12 so that pin 76 seats in ends 34 of the slots. This places latching mechanism 12 in the locked state as shown in Figures 4a and 4b with lower keys 70 seating in the root of ratchet teeth 102b. In order to release the tool from the overshot 10, the actuator 16 must be pulled or toggled a number of times to cause the ratchet drum to rotate a plurality of times between spaced apart rotational positions until upper keys 68 again align with and extend into the gaps 106. The number of rotations of ratchet drum 94 (which equates to the number of times rotator 54 is required to be pulled) in order to place the latching mechanism 12 in a release state, is visible through windows 90. To this end, numbers may be engraved or otherwise marked on the ratchet teeth 102 to provide visual indicating of the number of rotations or pulls required in order to place the latching mechanism 12 in the released state.

A second embodiment of the overshot 10' will now be described with reference to Figures 13-23. In describing overshot 10' components or features of the same or similar structure and/or operation as for overshot 10 will be denoted with the same reference numbers but with the addition of the prime symbol. Overshot 10' functions in an identical manner to overshot 10 in that its latching mechanism 12' has three operational states namely neutral, locked and released; and, its actuator 16' converts sequential linear motion into sequential rotary motion to switch the latching mechanism 12' between different operational states. The substantive difference between the overshot 10 and overshot 10' resides in the construction of the actuator 16'.

Latching mechanism 12' including latch dogs 18' and torsion string 50'; upper casing 108'; spring packer 1 10'; spring 1 14'; end cap 1 16'; swivel housing 1 18'; and, swivel 1 12' of overshot 10'are identical in construction to the

corresponding components of overshot 10.

Referring in particular to Figures 14 and 21 a to 21 c lower casing 20' of overshot 10' differs marginally from lower casing 20 by the provision of diametrically opposed holes 130 that lie on a plane containing cutouts 82' and at a location between holes 86' and windows 90'. In a further variation, drum seat 92' is of a slightly shorter length than drum seat 92, and there is a reconfiguration of an interior surface profile of casing 20' in a region 132 between cutout 82' and window 90'.

Holes 130 threadingly receive respective cam pins 134 shown in Figures 13, 14 and 23. Each cam pin 134 is provided with a cylindrical cam surface 136 that protrudes into lower casing 20' and engages actuator 16'.

Rod 56' of rotator 54' is formed of two connected components 56'a and 56'b. The first component 56'a is shown in Figures 19a-19c and comprises threaded end 58', and contiguous portions 60' and 62'. The second portion 56'b shown in Figures 13, 14 and 20 comprises the bifurcation 64' which is attached to portion 62' via a clevis collar 137 shown also in Figures 22a and 22b.

Bifurcation 64' is formed with spaced apart parallel arms 72' each provided with a hole 74'. Extending co-axially from one end of bifurcation 64' is a threaded stud 138. Stud 138 passes through an axial hole 140 formed in clevis collar 137. As shown in Figure 13, bifurcation 64' is coupled to the clevis collar 137 by passing stud 138 through hole 140 and subsequently placing a thrust washer 142 over stud 138 and screwing down a nut 144 on the stud 138. This method of attachment provides rotational decoupling between bifurcation 64' and the clevis collar 137. An outer circumferential portion 146 of clevis collar 137 is provided with a screw thread which is configured to engage an internal thread formed on an axial blind internal hole 148 formed in portion 62' (see Figures 13 and 19c).

Portion 62' is formed with a stepped transition 63' adjacent the portion 60'; and, a radially protruding circumferential band 150 intermediate the step 63' and an end 152 of portion 62'. In addition, an endless cam track 154 is formed in the outer circumferential surface of portion 62' between band 150 and end 152.

With particular reference to Figure 19d, it can be seen that the cam track 154 comprises first undulations 156 spaced by second undulations 158. The first undulations 156 are each of the same configuration and have respective peaks 160 at the same level and respective troughs 162 at the same level. The second undulations 158 are the same configuration as each other with troughs 164 of the same level as troughs 162, but a peak 166 which is higher than the peaks 160. In this particular embodiment, three successive first undulations 156 are separated by respective second single undulations 158. The first undulations 156 may be equated with the rotator teeth 102 of the first embodiment, which second undulations 158 may be equated with the gaps 106.

In the assembled overshot 10', the cam pins 134 when screwed into lower casing 20' seat in the cam track 154. As a consequence, when a linear force is applied in an upward direction on actuator 16' and rotator 54', this upward motion causes a simultaneous rotation of the rotator 54' due to the engagement of cam pins 134 with the cam track 154. The extent of linear rotation is limited by the configuration of the cam track and in particular the undulations in which the pins 134 reside at any one time. Due to the coupling of the bifurcation 64' with the remainder of the rotator 54' via the clevis collar 137, the bifurcation 64' does not rotate with the remainder of the rotator 54'. The sequential application and release of a pulling force on the rotator 54' causes a rotation of the rotator 54' commensurate with the rotational spacing between adjacent undulations 156,158. When the cam pin resides in the peak 160 of undulations 156, the actuator 16' holds the latching mechanism 12' in the neutral state (Figures 15a and 15b). When the cam pin resides in the troughs 162 or 164 of undulations 156 or 158, the actuator 16' holds the latching mechanism 12' in the locked state (Figures 16a and 16b). In order for the latching mechanism 12' to be switched to the release state, the rotator 54' must be pulled a sufficient number of times to rotate the cam track 154 to a position where the cam pins 134 are located within the peaks 166 of second undulations 158. This configuration is shown in Figures 17a and 17b. At this time, spring 1 14' is able to bias the rotator 54' in a down hole direction relative to latching mechanism 12' to the extent that the pin 76' is pushed into and resides in ends 36' of the lifting dogs 18'. This forces the down hole or lower end 44' of latching mechanism 16' apart to release a previously engaged spear point. The number of times lifting force is required to be applied in order to switch the latching mechanism 12' to be switched to the released state is visible through window 90'.

Figures 24a - 29 illustrate a locking mechanism 200 that can be incorporated into either embodiment of the overshot 10 or 10'. However the construction and operation of the locking mechanism will be described in relation to the overshot 10.

In broad terms the function of the locking mechanism is to lock the overshot in the locked state and prevent an operator from changing the operational state of the latching mechanism. This in turn prevents an operator from accidentally releasing an engaged spear point 14.

The locking mechanism 200 comprises a swivel housing 1 18a which in essence is the same as the swivel housing 1 18 but with an axially extending rod 202. A swivel 120a (see Figures 24a-24c) extends from an opposite end of and is rotatably coupled to the swivel housing 1 18a. As shown in Figure 26 the rod 202 is formed with an axial blind threaded hole 204 at its distal end 206. In addition two transverse holes 208 and 210 are formed through the rod 204. Hole 208 is closest to the housing 1 18a and retains a roller pin 212. The pin 212 protrudes from one end of hole 208. Hole 210 is closest to the end 206 and holds balls 214 which are biases away from each other by an intervening spring 216. The locking mechanism 200 also comprises a twist lock handle 218 which is retained on the rod 202. The handle 218 is in the form of a tube or sleeve 220 having an axial passage 222 of an inner diameter slightly larger than an outer diameter of the rod 202. A helical slot 224 is formed in the sleeve 220 and extends circumferentially for about 140° and axially for a distance D (see Figure 25) An end of the slot 224 nearest the swivel housing 1 18a is formed with a rebated pin seat 226. The roller pin extends into the slot 224 thereby retaining the twist lock handle 220 on the rod 202.

The sleeve 220 is also formed with first and second pairs of ball seats 228 and 230. The ball seats 228, 230 are dimensioned to enable the balls 214, under the bias of spring 216 to protrude partially into them but not pass all the way through. The first pair of ball seats are in the form of diametrically opposed elongated holes formed in sleeve 220. The second pair of ball seats are also in the form of diametrically opposed elongated holes formed in sleeve 220 but are radially offset form the first holes and closer to the distal end 232 of sleeve 220. The first ball seats 228 are located to receive the balls 214 when the pin is in the rebated hole pin seat 226. In this configuration the locking mechanism 200 is in a lock position and locks the overshot 10 and latching mechanism 12 in the locked state. The second ball seats 230 are located to receive the balls 214 when the roller pin is at an opposite end 234 of the slot 224. In this

configuration the locking mechanism 200 is in a free position allowing the overshot 10 to operate as hereinbefore described.

The rotator 54 is connected to the rod 202 by passing though the end 232 of sleeve 220 and screwing into the hole 204.

It will be noted that when the locking mechanism 200 is in the lock position with the balls 214 in the ball seats 228, the end 232 of sleeve 220 abuts the end cap 1 16 and the rod 202 is retracted into the sleeve 220. Because the rod 202 is connected to the rotator 54, the rotator 54 is also in effect pulled back against the bias of spring 1 14. This moves the pin 76 to the end 34 of slots 32 and thus places the overshot 10 in the locked state as shown in Figures 4a and 4b. The overshot stays in this state until the twist lock handle 218 is rotated to locate the roller pin to the end 234 of slot 212. To do this a user must grip the handle 218 and the swivel housing 1 18 and apply sufficient torque to cause the sleeve 220 to force the balls 214 from holes 228 in the sleeve 220 into the hole 210 against the bias of spring 216; and rotate the sleeve until the roller pin 212 seats in end 234. At this time the holes 230 will register with the balls 214. The balls 214 are now forced into the holes 230 to hold the twist lock handle and locking mechanism 200 in the free position. The rotator 54 is now able to be pulled in an upward direction to toggle the overshot 10 between its normal operation states.

To place the locking mechanism 200 back to the lock position the twist lock handle 218 is rotated in an opposite direction. As the roller pin 212 is retained in the slot this rotation causes the rod 202 to retract into the sleeve 220 and the rotator 54 to be pulled back against the bias of spring 1 14. The pin 76 in coupled to the rotator 54 slides in the slots 32 and closes the lifting dogs 18. At this time the holes 228 will register with the balls 214 and the roller pin 212 will register with pin seat 226. This combination forms a double lock mechanism to hold the twist lock handle 218 in the locked position. The overshot is now back in the locked state in which it remains until the locking mechanism is subsequently moved to the free position.

Now that the embodiments of the invention have been described in detail, it would be apparent to those skilled in the relevant arts that numerous modifications and variations may be made without departing from the basic inventive concepts. For example with reference to the embodiment shown in Figures 1-12c the rotator 54 is described and depicted as comprising two upper key 68. However in one variation of this embodiment the rotator 54 can be formed with a single upper key and the ratchet drum assembly 94 formed with a single gap 106 between the ratchet segments 98. If the number of teeth 102 on the ratchet segments 98 remains the same then this variation will double the number of linear reciprocations (i.e. the number of ratchets) of rotator 54 between successive release states of the latching mechanism 12. It is envisaged that this variation may have application with smaller size overshots (used in smaller diameter drill pipe) where fewer, for example two to four teeth 102 in total, are provided in the ratchet drum assembly 94. Similarly with respect to the second embodiment shown in Figures 13-23, the number of undulations 156 and/or 158 may be varied to vary the number of linear reciprocations (i.e. the number of ratchets) of rotator 54' between successive release states of the latching mechanism 12.

All such modifications and variations together with other that would be obvious to those skilled in the art are deemed to be within the scope of the present invention the nature of which is to be determined from the above description and the appended claims.

Claims

1 . An overshot comprising:

2. The overshot according to claim 1 wherein the actuator mechanically engages the latching mechanism and is movable relative to the latching mechanism to switch the latching mechanism between the neutral, latched and released states.

3. The overshot according to claim 1 or 2 comprising a first casing and wherein the latching mechanism is coupled to the first casing and fixed against linear motion relative to the first casing.

4. The overshot according to claim 3 wherein the actuator is linearly movable relative to the latching mechanism to switch the latching mechanism between the neutral, locked and released states.

5. The overshot according to claim 3 or 4 wherein the latching mechanism comprises two or more latch dogs each pivotally coupled to the first casing and wherein the actuator is mechanically coupled to each latch dog.

6. The overshot according to claim 5 wherein each latch dog comprises a slot elongated in a direction of the axis, and wherein the actuator is

mechanically coupled to the slot of each latch dog.

7. The overshot according to claim 6 wherein the slots are shaped such that when the actuator is in a first linear position relative to the latch member, the actuator holds the latching mechanism in the locked state, when the latching mechanism is in a second linear position relative to the latch mechanism, the actuator holds the latch member in the release state, and when the actuator is in an intermediate position the latching mechanism is in the neutral state.

8. The overshot according to claim 6 or 7 wherein the actuator comprises a pin that passes through each slot to mechanically engage the actuator with the latching mechanism.

9. The overshot according to claim 8 wherein the slots are relatively configured so that the pin bears against each latch dog as the actuator moves up or down to cause a pivoting motion of the latch dogs.

10. The overshot according to claim 8 or 9 wherein each slot comprises respective opposite ends that are laterally offset from each other and wherein each slot progressively widens from each end to an intermediate location of the slot.

1 1. The overshot according to any one of claims 8 to 10 wherein when the actuator is in the first linear position the pin resides in a first end of each slot, when the latching mechanism is in the second linear position, the pin resides in a second opposite end of each slot, and when the linear actuator is in an intermediate position, the pin is at the intermediate location of each slot.

12. The overshot according to any one of claims 1 to 1 1 wherein the latching mechanism comprises a spring and is capable when in the neutral position to open against bias provided by the spring to receive a member and self close by action of the bias to retain a received member.

13. The overshot according to any one of claims 2 to 12 wherein the actuator comprises a linear to rotary motion converter which is operable to convert linear motion of the actuator to a rotary motion of the actuator or a part thereof between a plurality of rotationally spaced positions and wherein the linear position of the actuator relative to the latching mechanism is controlled by the rotational position of the actuator or part thereof.

14. The overshot according to claim 13 comprising an actuator spring arranged to bias the actuator to move linearly toward the latching mechanism.

15. The overshot according to claim 13 or 14 wherein the actuator comprises a rotator that is capable of combined simultaneous linear and rotational motion, and a rotary mechanism comprising a cam track and at least one cam pin which resides in the cam track one of the cam track and the at least one cam pins being formed on or otherwise fixed to the rotator.

16. The overshot according to claim 15 wherein the cam track comprises a plurality of contiguous first and second undulations wherein successive first undulations are separated by at least one single second undulation, and wherein the second undulations and first undulations are of a different configuration.

17. The overshot according to claim 13 or 14 wherein the actuator comprises a rotator capable of linear motion relative to the latching mechanism and a rotary mechanism supported on the rotator and arrange to rotate between successive rotationally displaced positions upon a linear reciprocal motion of the rotator.

18. The overshot according to claim 17 wherein the rotator comprises a plurality of keys and the rotary mechanism comprises a plurality of teeth on axially opposite sides and wherein the keys and teeth are arranged to engage on when the rotator is linearly reciprocated the engagement causing rotational motion of the rotary mechanism.

19. The overshot according to any one of claims 15 to 18 wherein the actuator or part thereof has a first rotational position at which the actuator is in a first linear position where the actuator is able to operate the latching

mechanism to release a latched member, and N intermediate rotational positions which are sequentially adjacent the first rotational position where N is an integer greater than zero so that adjacent first rotational positions are spaced by N intermediate rotational positions wherein upon N successive linear reciprocations of the rotator the actuator or part thereof is rotated N times to place the actuator in the next first rotational positions.

20. The overshot according to claim 19 wherein when the actuator or part thereof is in the N rotational positions the actuator maintains the latching mechanism in the neutral or locked states.

21. An overshot comprising a latching mechanism capable of latching a member, the latching mechanism having: a locked state where the latching mechanism is locked in a closed position to prevent release of a latched member; and, a release state where the latching mechanism is locked in an open position to release a latched member or prevent latching of a member; and, a ratchet mechanism sequentially movable, one ratchet position at a time between respective adjacent ratchet positions upon each application of an externally applied force in a direction along a longitudinal axis of the latching mechanism, the ratchet mechanism operatively associated with the latching mechanism wherein when the ratchet mechanism is in a first ratchet position the ratchet mechanism holds the latching mechanism in the locked position and when the ratchet mechanism is in a second ratchet position the ratchet mechanism holds the latching mechanism in the release position, and wherein there are N ratchet positions between the first and second ratchet positions where N is an integer≥ 1.

22. The overshot according to claim 21 wherein the ratchet mechanism is a rotary ratchet mechanism and adjacent ratchet positions are circumferentially spaced about the longitudinal axis.

23. The overshot according to claim 21 or 22 comprising a rotator associated with the ratchet mechanism the rotator extending along the longitudinal axis and linearly movable along the longitudinal axis by action of the externally applied force wherein linear motion of the rotator causes the ratchet mechanism to rotate from a current ratchet position to an adjacent ratchet position.

24. The overshot according to any one of claims 19 to 23 comprising a visual indicator associated with the rotator and capable of providing a visual indication to a user of a number of linear reciprocations of the rotator required to place the latching mechanism in the release state.

25. The overshot according to claim 24 wherein the visual indicator comprises markings on the rotary mechanism or ratchet mechanism and a window formed in the first casing at a location thought which the markings are visible.

26. An overshot according to any one of claims 1 to 25 comprising a locking mechanism manually movable between a lock position and a free position, the locking mechanism: when in the lock position operating the actuator to place and hold the latching mechanism in the locked state; and when in the free position allowing the actuator to operate to switch the latching mechanism between the neutral, locked and release states.