An overshot adapted to engage and disengage a fishing neck in a well bore. The apparatus comprises an overshot body, a set of collet fingers which deflect radially and have a surface to grasp a fish in a well bore, a tapered surface abutting the collet fingers which deflect inwardly and outwardly to engage and disengage the fish, and a cam and cam follower mechanism. The cam preferably includes a set of inwardly projecting pins which engage grooves formed on a cam body. The grooves cause the cam body to move upwardly and downwardly with respect to the overshot body. The cam body reciprocates, moving the fingers relative to the tapered surface, thereby providing the engagement and disengagement movement. The cam body causes repetitive movement lengthwise of the cam body relative to the pins which serve as a cam. The groove enables movement toward one end of the body and then toward the other. A spring forces the cam body in one direction while it is forced in the other direction by contact with the fish. Movement in the two directions is typically achieved by jarring to set the tool and jarring to release the tool. A wash pipe through the tool is optionally included.

BACKGROUND OF THE INVENTION 
Overshots are available in the oilfield service industry. Overshots are 
described in the composite catalog at Pages 654 et seq. Some of the 
overshots shown are able to grasp a fish and lift it. However, they 
typically are limited in release operations. One common releasing and 
circulating overshot is released only by jarring down heavily and rotating 
simultaneously to the right. This limits the running of such a tool to a 
tubing string. It is inconvenient to assemble a tubing string and 
particularly snub it into a high pressure well to provide service to a 
down-hole tool. This is merely representative of overshots known in the 
past which are limited in that they can be run readily on a tubing string 
or wireline to engage a fish. However, they generally cannot be easily 
released without partly destroying the tool or requiring a tubing string 
for rotation to the right. Tools of the prior art are believed deficient 
in providing an overshot which can be run on a wireline and be releasable 
without destroying the tool. 
Some overshots are released by heavy jarring which shears a pin or the 
like. Such jarring is so forceful that it is likely to damage down-hole 
equipment. Survey instruments sometimes must be fished from the hole, and 
an overshot can be used to grasp the instrument for retrieval. If it is 
hung and a heavier overshot must be used, heavy jarring is required to 
free the overshot from the survey instrument. Survey instruments are 
formed of small, delicate instrumentation and can easily be damaged by 
jarring. It is inconvenient and difficult to use rotation to release 
overshots because they require a tubing string to transmit torque, while a 
wireline is much cheaper to run. 
The present invention is a releasable wireline overshot which releases on 
an up and down reciprocating motion and not on rotation or heavy jarring. 
This enables it to be run on a wireline which is far more convenient than 
a tubing string. 
SUMMARY OF THE INVENTION 
The present invention is directed to multiple embodiments of an overshot. 
The overshot is adapted to be run conveniently on a wireline, or if 
desired, can include a wash pipe enabling circulation through it on a 
wireline or connected at the lower end of a tubing string for circulation 
purposes. It incorporates an overshot body which supports a set of collet 
fingers. The collet fingers carry serrations which grasp a fish. The 
collet fingers are arranged with a tubular member concentric thereof. The 
tubular member has a facing tapered surface which deflects the collet 
fingers inwardly and outwardly on axial movement of the tubular member. 
The serrations or threads take a bite in the fish and engage it when 
forced radially toward the fish. They release by spring deflection when 
the tapered surface is moved. 
The overshot body supports a cam which has the form of inwardly directed 
pins, preferably two, arranged diametrically opposite of one another. The 
two pins engage a cam body which has a facing groove. The cam body is 
forced upwardly and downwardly and rotates controlled by the engagement of 
the grooves with the pin. Movement to one extreme is coupled to the collet 
fingers and tapered surface to provide a fish catching mechanism while 
movement of the cam body to the opposite extreme releases the collet 
fingers. The cam body is grooved preferably fully about its periphery. The 
groove has a pair of vertical extensions which extend to the upper end, 
enabling assembly. The groove is shaped to deflect the pin upon axial 
movement of the cam body, causing the pin moves from a first position to 
rebound off an opposing shoulder of the groove. The rebound directs the 
pin toward a facing shoulder which prevents return of the pin to its 
beginning position and holds it at a second position. The pin then travels 
in the groove by moving from the second position in a controlled direction 
along the groove against a facing shoulder, and rebounds toward the 
opposing shoulder which blocks the pin against return to its second 
position in the groove. This movement is repetitive. The fully encircling 
groove is in actuality a duplicate set of equipment and controls movement 
of the pins from a first position or location to a second and back to the 
first. This rotates the cam body preferably through 180.degree.. It 
represents a cycle of operation from released to engaged to released, 
referring to the operation of the collet fingers. Movement of the cam body 
is a result of urging by a spring compressed in the tool which bears on 
the cam body and an opposing force from a bumper sub which is contacted by 
the fish.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Attention is first directed to FIG. 1 where the releasable wireline 
overshot 10 is shown. The overshot 10 will be described proceeding from 
top to bottom of FIGS. 1A and 1B, considered jointly. The top end of the 
tool incorporates an upper sub 11 which has a fishing neck 12. The upper 
sub 11 has a narrow neck beneath the enlarged shoulder 12. It extends 
downwardly to an elongate cylindrical portion 13. It is threaded on the 
exterior at 14. The threads enable it to connect on the interior of an 
overshot body 15. The body 15 can be formed of one piece. However, it is 
more convenient to fabricate it of multiple pieces. The overshot body 15 
incorporates an upper threaded member 16 which threads to the upper sub 
11. The section 16 also threads at its lower end to an additional section 
17 which continues the overshot body 15. 
A spring washer 20 abuts the lower end of the top sub 11. It is captured on 
the interior of the overshot body 15. It supports a coiled spring 21 on a 
shoulder. It extends axially of an internal cavity within the overshot 
body 15. It bears against a lower washer 23 and has an upwardly facing 
shoulder and a centering pin to capture the spring on the shoulder. The 
spring forces the washer 23 downwardly. 
The tubular member 17 includes an internal shoulder 24 which limits 
downward travel of the washer 23 at the urging of the spring 21. The 
washer 23 transmits a force against a cylindrical tubular member 26. The 
cylindrical member 26 abuts a cam body 27 which is cylindrical and hollow, 
preferably fitting about a hollow tubular member 28. The cam body 27 
rotates around the tubular member 28 and is captured at its upper end by a 
thrust washer 29 and a similar thrust washer 30 at the lower end. The cam 
body 27 is slightly smaller than the surrounding tubular member 17 and is 
free to rotate. Rotation is controlled or guided by a protruding lug or 
pin 32. Only one pin is required, but preferably two are included for 
symmetry. The pins are identical, and are preferably located diametrically 
opposite one another and protrude inwardly. They fit into grooves or slots 
cut on the exterior of the cam body 27. The shape of the cam (the groove) 
will be discussed hereinafter. 
The cam body 27 rotates and moves vertically. As it moves vertically, it 
moves between upper and lower limits of travel. Its travel is communicated 
to the tubular member 28 which is hollow and receives a concentric 
elongate member 32 which threads into a cylindrical member 34. The 
cylindrical member 34 has an enlarged shoulder 35 which faces upwardly and 
abuts against a shoulder 36 formed on the interior of the overshot body 
15. The two shoulders cooperate to limit upward travel of the apparatus on 
the interior of the overshot body 15. This limit on upward travel is 
similar to the limit on downward travel engendered by the internal 
shoulder 24 shown at the upper portions of FIG. 1B. 
The body 34 is axially drilled at 38. It is tapped with threads to enable 
the member 32 to thread into it at the upper end of the axial passage. A 
bumper sub 39 is threaded into the lower portions of the passage 38. The 
bumper sub 39 extends beyond and below the body 34. The bumper sub 39 is 
threaded to and extends below the body 34 and serves to communicate an 
axial push from a fish. The bumper sub 39 is smaller in diameter and 
extends below the body 34. The body 34 has threads 40 on its exterior 
which support an encircling collar 41 which threads on the threads and 
supports a number of fingers 42. The fingers 42 are cut in the stock of 
which the collar 41 is an integral part, and they define a number of 
flexible collet fingers. The fingers 42 are elongate, ending at a slightly 
inwardly tapered surface 43. The fingers 42 are separated by elongate 
slots 44 cut in the stock. The slots end at a stress-relieving circular 
hole. 
On the interior of the fingers, a set of serrations 45 is defined. The 
serrations face inwardly and upwardly and collectively grip a fish and 
take a bite into the fish when the collet fingers are forced against it. 
The serrations 45 are able to grip and hold a fish. They move radially 
inwardly and outwardly with the fingers 42 which act as springs deflecting 
in a controlled manner. 
The collet fingers 42 are fixed relative to the bumper sub 39 which defines 
the depth to which a fish penetrates the set of collet fingers. It is 
possible for the tool to swallow more of the fish, but it is not 
necessary. Only shallow penetration is required. 
The body 34, collar 41, collet fingers 42, and bumper sub 39 all move 
upwardly and downwardly as a unit on the interior of the tubular member 
17. The lower portions of the tubular member 17 are identified at 47. This 
defines a surrounding surface about the collet fingers 42. The tubular 
member 17 incorporates an inwardly directed tapered surface 48 which is 
adjacent to the lower end 43 of the collet fingers. The surface 48 
cooperates with the collet fingers to deflect the tips inwardly and 
outwardly. The lower end of the tubular member 17 provides a tapered 
surface which deflects the fingers inwardly and outwardly. When they 
deflect outwardly, they release or disengage a fish. When they deflect 
inwardly, the serrations collectively define a gripping surface which 
grabs and holds the fish. The deflection inwardly and outwardly is 
determined by axial movement of the equipment on the interior of the 
tubular member 17. This is controlled by the cam to be described 
hereinafter. 
FIG. 3 shows the pins 32 extending into grooves formed in the cam body 47. 
The tubular member 17 supports the pins so that the cam body 27 is guided 
dependent on axial and rotational movement for its operation under control 
of the pins. The pins serve as a cam follower mechanism. 
In FIG. 2, all of the apparatus remains the same as shown in FIGS. 1A and 
1B. However, the movable components on the interior of the tubular body 17 
are moved relatively downward in grasping a fish 50. The exemplary fish 
has a standard API fishing neck on it and is stabbed into the interior 
space toward abutment against the bumper sub 39. The bumper sub 39 is 
pushed axially relative to the hollow body 17. In the sequence of 
operation, the overshot 10 is forced over the fish 50 by its own weight 
which is optionally enhanced by weight bars. The fish 50 stabs internally 
of the collet fingers and contacts the bumper sub 39. The bumper sub 39 is 
forced upwardly against the force of the spring. When it moves upwardly, 
the cam body 27 moves in a manner to be described, permitting its upward 
movement toward a top-most position. The top-most position compresses the 
spring and the spring subsequently forces the movable parts downwardly. 
When they move downwardly, the cam body 27 rotates and assumes a new 
relationship to the pin 32. This downward and rotative movement causes 
relative axial movement of the external hollow body 17. FIG. 2 should be 
contrasted with FIG. 1B. It shows the collet fingers forced downwardly and 
inwardly. The tubular member 17 moves relatively upwardly to engage the 
collet fingers to force them inwardly toward a gripping position. Gripping 
of the fish is achieved in FIG. 2. The collet fingers are jammed inwardly 
against the fish 50 to grip and hold it firmly. When they hold it, they 
prevent the fish from escaping the grip of the overshot 10. This is 
achieved on relative downward movement of the collet fingers under control 
of the cam and cam follower mechanism. 
FIG. 4 shows the way the cam and cam body are constructed. The groove means 
formed on the exterior surface of the cam body 27 is shown planar 
representing the circular surface as a rectangle. The degree markings of 
FIG. 4 locate the groove which is cut in the cam body. The groove is 
repeated in two segments of 180.degree. each. The two pins cooperate with 
the two identical segments of the groove. This is the preferred 
construction. A description of operation will focus on the path of only 
one pin, the second pin moving in a similar fashion in the duplicate 
segment of the groove. 
The lengthwise groove 55 receives the pin 32 during assembly. Thereafter, 
the pin does not travel to the extremity or upper end of the groove 55. 
The groove 55 provides a resting place or first position for the pin at 
56. This is approximately where the pin rests when the cam body 27 is 
moved as low as possible in the overshot body 15, and this is the position 
of FIG. 2. Movement of the pin from the position 56 is relatively 
downwardly and against the facing angled shoulder or wall 57. When this 
occurs, the cam body is rotated by the fixed pin and the spring 21 causes 
the pin to rebound, relatively speaking, off the facing wall 57 and 
directs it toward a facing angled wall 58. The opposing wall 58 prevents 
the pin from returning toward the groove portion 55. The pin is then 
captured in the V-shaped portion of the groove defined by the walls or 
shoulders 58 and 62. The pin then comes to rest at a second position 
indicated in dotted line at 60. This is the other extremity of movement of 
the cam body. This is achieved when the equipment within the overshot body 
15 slides upwardly until it is limited by the shoulder 36. The limit on 
travel of the shoulder 36 causes the rebound of the pin from the facing 
wall 57 whereupon the pin relatively travels upwardly in the grooves but 
encounters the angled wall 58 which deflects it to the second position. 
This is where it comes to rest to achieve the position of FIG. 1B. The 
first and second positions are stable and hold the parts indefinitely. The 
transition from the first to the second position represents a shift from 
the fish engaging position of FIG. 2 to the fish releasing position of 
FIG. 1B. 
Transition from the second position back to the first is achieved in 
similar manner. The pin travels vertically from the second position 60 and 
is deflected at an angle by the opposing surface or shoulder 64. This 
deflects the pin to the right as viewed in FIG. 4, and the limit on 
vertical movement is reached whereupon the spring force carries the pin 
relatively toward the surface 65. The surface or shoulders 62 and 65 
define a protruding point which prevents the pin from returning to the 
position 60. It travels from the second position to contact the shoulder 
64 and deflects toward the shoulder 65, and is guided by that shoulder to 
the first position 56 again. It will be noted that the straight portion 55 
is duplicated at two locations. They are diametrically opposite. The 
grooves which extend around the cam body 47 are duplicated. Rotation of 
the cam body 180.degree. completes one cycle of operation in operating the 
overshot from a fish disengaged position to an engaged position and back 
to the disengaged position, or in the opposite sequence. The arrangement 
of the groove means on the exterior of the cam body 27 transmits the 
described motion to body pins which are diametrically opposite one 
another. 
The facing shoulders which define the groove mechanism are equipped with 
strategically located corners 66 and 67 which force the pin to "turn the 
corner" in the guided path and prevent return of the pin toward the 
beginning position. 
In operation, the tool is run into a tubing string on a wireline equipped 
with a set of jars. When it engages a fish, the fish is pushed into the 
collet fingers which are retracted as shown in FIG. 1B. The fish pushes 
upwardly and contacts the bumper sub 39. This forces the bumper sub 
upwardly and the camming action occurs. The camming action begins with the 
pin originally in the release position 60. The bumper sub 39 and the 
movable equipment on the interior of the tool slide axially. The cam body 
27 rotates simultaneously. In FIG. 2, the movable internal parts slide 
upwardly while the camming action enables movement of the pin from the 
position 60 and its transition to the bottom line position 56. The spring 
21 forces the cam and the slidable parts downwardly through the limits of 
travel defined by the shoulder 24. When this occurs, the collet fingers 
are jammed against the surrounding internal tapered surface 48 and are 
deflected inwardly to take a bite on the fish. This grasps or engages the 
fish. Release is achieved in the same manner, by jarring downwardly on the 
tool which causes the camming action and results in positioning the collet 
fingers as shown in FIG. 1B where they are spaced from the surrounding 
tapered surface which are free to deflect outwardly, permitting 
disengagement of the fish. 
The apparatus engages and disengages a fish by simple jarring action. 
FIGS. 5A and 5B show an alternative embodiment 100. It differs in that it 
provides a wash pipe through the apparatus. Ordinarily the embodiment 10 
is run on a wireline. The embodiment 100 can be run on a tubing string. A 
connector 101 which provides fluid flow from a tubing string is shown. The 
apparatus is similar in construction to the embodiment 10, and this 
description will be directed to the path through the equipment which 
incorporates the wash pipe. The upper end of the tubing includes the 
passage 102. It extends downwardly to an enlarged passage 103. The 
passages 102 and 103 are formed in the upper sub described in the 
embodiment 10. The washer 20 is duplicated, but is drilled axially with a 
passage. The washer 120 is adapted to receive a hollow tubular member 105 
in it. The wash pipe 105 is sealed by a surrounding seal 106. The wash 
pipe 105 is free to slide vertically with operation of the cam mechanism. 
The wash pipe 105 extends through the spring down to the lower thrust 
washer 23 which is modified into a center-drilled washer 123. The solid 
cylindrical spacer member 126 is drilled and is internally threaded to 
engage the wash pipe 105. It is drilled axially all the way to the bottom 
and threads to the tubular member 34. The bumper sub 39 is drilled axially 
and is the element 139. This completes the passage through the tool and 
enables the tool to be used to grasp a fish, for instance, which is 
surrounded by sand and enable fluid to be pumped through a tubing string 
and through the overshot 100 to wash away the sand. It is also useful in 
washing away cuttings from a milling operation or the like. If circulation 
can be maintained through the tool, and the apparatus 100 enables this, 
certain down-hole remedial steps can be more easily accomplished. 
In operation, the embodiment 100 functions identically to the embodiment 
10. It sets and releases in the same manner. The only difference is the 
provision of the axial passage through the tool to enable circulation to 
be maintained through it.