OVERSHOT FOR DOWN HOLE DRILLING OPERATIONS

CLOCHE DE REPECHAGE POUR OPERATIONS DE FORAGE DE FOND

English Abstract

An overshot tool (10) for bore hole operations comprising a lower end portion
(11) including lifting dogs (12) for engaging an article such as a tube in a
bore hole, a first jar staff (15) engaged with the upper end of the lower end
portion, a second jar staff (17) slidably mounted on the first jar staff (15)
and adapted to be connected by its upper end to a wireline rope, a lower drive
key (14) on the lower end portion (11), an upper drive key (31) on the second
jar staff (17) and a drive sleeve (16, 18) rotatable and slidable along the
second jar staff (17), the drive sleeve (16, 18) having a first array of teeth
(27) adapted to engage and be rotated by the lower drive key (14) upon
downward movement of the drive sleeve (16, 18), and a second array of teeth
(30) spaced from the first array of teeth (27) adapted to engage and be
rotated by the upper drive key (31) upon upward movement of the drive sleeve
(16, 18) and wherein the lower end of the drive sleeve (16, 18) has a slot
(28) which when aligned with the lower drive key (14) by the rotation of the
drive sleeve (16, 18) allows the lower end of the drive sleeve (16, 18) to
engage the upper end of the lifting dogs (12) so as to open the lower end of
the lifting dogs (12).

French Abstract

L~invention concerne une cloche de repêchage (10) pour opérations de forage de fond, comprenant une partie d~extrémité inférieure (11) comportant des crampons de levage (12) servant à accrocher un article tel qu~un tube dans un trou de forage, une première coulisse (15) en prise avec l~extrémité supérieure de la partie d~extrémité inférieure, une deuxième coulisse (17) montée coulissante sur la première coulisse (15) et conçue pour être raccordée par son extrémité supérieure à un câble métallique, une clavette d~entraînement infrérieure (14) sur la partie d~extrémité inférieure (11), une clavette d~entraînement supérieure (31) sur la deuxième coulisse (17) et un manchon d~entraînement (16, 18) rotatif et coulissant le long de la deuxième coulisse (17), le manchon d~entraînement (16, 18) présentant un premier groupe de dents (27) conçues pour s~engrener de façon rotative sur la clavette d~entraînement inférieure (14) lors de la descente du manchon d~entraînement (16, 18), et un deuxième groupe de dents (30) espacées du premier groupe de dents (27) conçues pour s~engrener de façon rotative sur la clavette d~entraînement supérieure (31) lors de l~ascension du manchon d~entraînement (16, 18). La coche de repêchage est caractérisée en ce que l~extrémité inférieure du manchon d~entraînement (16, 18) comporte une fente (28) qui, une fois alignée sur la clavette d~entraînement inférieure (14) par rotation du manchon d~entraînement (16, 18) permet à l~extrémité inférieure du manchon d~entraînement (16, 18) de venir en prise avec les crampons de levage (12) pour en ouvrir l~extrémité inférieure.

Claims

6
CLAIMS:
1. An overshot tool for bore hole operations comprising a lower end portion
including lifting dogs for engaging an article such as a tube in a bore hole,
a
first jar staff engaged with the upper end of the lower end portion, a second
jar
staff slidably mounted on the first jar staff and adapted to be connected by
its
upper end to a wireline rope, a lower drive key on the lower end portion, an
upper drive key on the second jar staff and a drive sleeve rotatable and
slidable
along the second jar staff, the drive sleeve having a first array of teeth
adapted
to engage and be rotated by the lower drive key upon downward movement of
the drive sleeve, and a second array of teeth spaced from the first array of
teeth adapted to engage and be rotated by the upper drive key upon upward
movement of the drive sleeve and wherein the lower end of the drive sleeve
has a slot which when aligned with the lower drive key by the rotation of the
drive sleeve allows the lower end of the drive sleeve to engage the upper end
of the lifting dogs so as to open the lower end of the lifting dogs.
2. An overshot tool according to claim 1 wherein the drive sleeve
comprises a lower drive sleeve having the first array of teeth and an upper
drive sleeve having the second array of teeth.
3. An overshot according to claim 1 and further including a locking
mechanism for the lifting dogs, the locking mechanism including a locking pin
moveable between a locked position and an unlocked position, and a locking
arm on the locking pin located between the upper ends of the lifting dogs.
4. An overshot according to claim 3 wherein the locking pin is biased by a
spring and wherein the locking arm is moved between a locked position and an

7
unlocked position by pushing the locking pin against the spring and rotating
the
locking pin and hence the locking arm.

Description

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1
OVERSHOT FOR DOWN HOLE DRILLING OPERATIONS
FIELD OF THE INVENTION
This invention relates to an overshot for bore hole drilling operations.
An overshot is a down hole tool used for retrieving, inter alia, an inner tube
of a
drill string from a bore hole.
BACKGROUND ART
A typical prior art overshot consists of a body portion having a swivel at
its upper end which is connected to a wireline rope. A jar staff connects the
body portion to a head portion which has pivotally mounted lifting dogs that
are
spring biased to a latching position in which they are adapted to engage the
lower end of the inner tube.
The overshot is lowered down the bore hole, inside the drill rods, on a
wireline rope until the lifting dogs couple to a spear point on the latch body
of
the inner tube. The wireline is then retrieved by a winch drum to bring the
inner
tube to the surface.
In the event of loss of circulation fluid in the hole, a dry lowering sleeve
is placed on the head of the overshot above the lifting dogs. The dry lowering
sleeve has an elongated slice along and around its periphery to allow access
over the wireline rope.
When the tube reaches support for its weight, which may be its position
in the core barrel or a water level, the shape below the spear point causes
the
lifting dogs to open on the spear point and thus close on the upper side of
the
pivot pin. The dry lowering sleeve descends, holding the upper side closed
and conversely the bottom side of the dogs open thus releasing the tube.
In the event of a tube becoming stuck in the core barrel for whatever
reason (and there are a lot of possible ways for that to happen), the dry
lowering sleeve is lowered over the wireline, taped up and dropped down the

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hole. Sometimes the dry lowering sleeve arrives in place to release the tube
and sometimes it doesn't. Even if the dry lowering sleeve arrives in place, it
can take a lot of time depending on the hole depth. In the event that the dry
lowering sleeve does not arrive in place it presents a difficult retrieval
problem.
SUMMARY OF THE INVENTION
According to one aspect of the invention there is provided an overshot
tool for bore hole operations comprising a lower end portion including lifting
dogs for engaging an article such as a tube in a bore hole, a first jar staff
engaged with the upper end of the lower end portion, a second jar staff
slidably
mounted on the first jar staff and adapted to be connected by its upper end to
a
wireline rope, a lower drive key on the lower end portion, an upper drive key
on
the second jar staff and a drive sleeve rotatable and slidable along the
second
jar staff, the drive sleeve having a first array of teeth adapted to engage
and be
rotated by the lower drive key upon downward movement of the drive sleeve,
and a second array of teeth spaced from the first array of teeth adapted to
engage and be rotated by the upper drive key upon upward movement of the
drive sleeve and wherein the lower end of the drive sleeve has a slot which
when aligned with the lower drive key by the rotation of the drive sleeve
allows
the lower end of the drive sleeve to engage the upper end of the lifting dogs
so
as to open the lower end of the lifting dogs.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a cross-sectional view of an overshot according
to one embodiment of the invention,
Fig. 2 is an exploded cross-sectional view of the overshot
shown in Fig. 1,
Fig. 3 is a cross sectional view of the locking mechanism in the
lower part of the overshot, and

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Fig. 4 is a front elevational view of the locking mechanism shown
in Fig. 3.
BEST MODE FOR CARRYING OUT THE INVENTION
The overshot 10 shown in the drawings has a lifting dog body 11 at its
lower end which carries a pair of lifting dogs 12 which will be described in
detail
below. On the outside of the upper end 13 of the lifting dog body 11 there is
a
lower drive key 14.
The overshot 10 also includes an internal jar staff 15, a lower sleeve 16,
an external jar staff 17 and an upper sleeve 18. The lower sleeve 16 and
upper sleeve 18 constitute a drive sleeve which is rotatable and slidable
along
the external jar staff 17. The lower end 19 of the internal jar staff 15 has a
threaded portion 20 which engages into a correspondingly threaded portion 21
in recess 22 at the upper end 13 of the dog body 11. A lock screw 23 engages
the threaded portion 20 to prevent rotation of the internal jar staff 15 with
respect to the lifting dog body 11.
At the upper end of the internal jar staff 15 there is an enlarged head 24
which abuts against the internal shoulder 25 of the external jar staff 17
whereby the internal jar staff 15 is held captive by the extemal jar staff 17.
Along the external face of the internal jar staff 15 there is a guide 26 which
slides in a guide way 26a in the lower end of the external jar staff 17.
The lower sleeve 16 has an array of teeth 27 around its lower periphery
and a slot 28 in between adjacent teeth 27. The teeth 27 sequentially engage
the lower drive key 14 and in so doing rotate the lower sleeve 16 one half of
the pitch between adjacent teeth 27. The upper end 38 of the lower sleeve 16
has a threaded recess 39 which receives the correspondingly threaded lower

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end portion 37 of the upper sleeve 18. The lower and upper sleeves 16 and 18
are secured together by lock nut 29.
Around the lower periphery of the upper sleeve 18 there is an array of
teeth 30 which are sequentially engaged by an upper drive key 31 on the
external jar staff 17 and in so doing rotate the lower sleeve 16 one half of
the
pitch between adjacent teeth 30. The pitch of the teeth 27 is the same as the
pitch of the teeth 30 so that when the external jar staff 17 is raised and
lowered
the lower sleeve 16 is rotated by the pitch of the teeth.
When the lower sleeve 16 has been sufficiently rotated, the slot 28
aligns with the lower drive key 14 on the lifting dog body 11 so that the
lower
sleeve 16 can pass over the upper ends of the dogs 12 to latch open the lower
ends of the dogs 12. The number of lifts of the external jar staff 17 leading
to
the latching of the dogs 12 can be initially set by rotating the lower sleeve
16
so that the drive key 16 is spaced from the slot 28 by the required number of
teeth (see the markings on the teeth 27 in Fig. 1) which represents the
required
number of up and down movements of the external jar staff 17.
Within the lifting dog body 11 there is a locking mechanism 40 which
includes a lock pin 41. The locking mechanism 40 is shown in detail in Figs. 3
and 4. The locking pin 41 has a slot 43 for receiving the blade of a
screwdriver
so that it may be rotated between the horizontal locked position shown in Fig.
4
or the vertical unlocked position shown in dotted outline in Fig. 4. The
locking
pin 41 has a locking arm 42 located between the upper ends 44 of the dogs 45.
The overshot is lowered into a bore hole in the same way as when
lowering a dry lowering sleeve. By working the external jar staff 17 up and
down, the required number of times, the overshot uniatches with the tube in
place or supported by fluid. When the slot 43 in the push-in pin 41 is in the
vertical position the dogs 45 are unlatched. By puiting a screwdriver blade
into

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the slot 43, pushing in against spring 46 and turning 900 and releasing, the
locking arm 42 is turned into position to lock the dogs 45 in the hold
position
thereby ensuring that the tube is not accidentally released.
By turning the arm 42 90 back to the vertical position, the dogs 45 are
5 unlocked and the tube can be released from the dogs.
Various modifications may be made in details of design and construction
without departing from the scope and ambit of the invention.

Representative Drawing