Note: Descriptions are shown in the official language in which they were submitted.
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INTRODUCTION
This application relates to jar tools and, more
particularly~ to two way jar tools that have both a bump and
jar stroke.
BACKGROUND OF THE INVENTION
Jar tools are used to free stuck drill pipe or well tools.
They provide a substantial shock to the drill string which is
transmitted to the stuck tool or "fish" and which is helpful in
dislodging it.
Hydraulic jars ~re jar tools using hydraulic fluid as the
working fluid. In these jars, an example of which is disclosed
in U.S. Patent 3,949,821, owned by the applicant, a piston is
provided which restricts the flow of hydraulic fluid from one
side of the piston to the other when the piston is in its home
or rest position~ It may, however, be moved from its home
position to an enlarged area where the fluid is able to rush by
the piston allowing the housing and mandrell to impact thùs
causing the jar. Following the jar, the driller may compress
the tool which causes a bump. While the impact or abutment
surfaces on the jar stroke are located inside the housing, the
bu~p surfaces are located on ~he outside of ~he housing~
It will be noted that the term "jar" refers to the impact
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caused when the jar tool is placed under a tension load and,
similarly, the term "bump" is the impact caused when the jar
tool is placed under a compression load.
This construction, however, suffers disadvantages. Since
the bump abutment surfa es are located externally of the
housing, they are exposed to mud and drill cuttings which
create wear. Further, since the mud and cuttings are pressed
between the abu~ment faces when the bump impact occurs, a small
amount may be forced through the seals with great pressure.
This "squeeze film effect" can cause seal deterioration and
bushing and drive spline wear and galling.
SUMMARY OF THE INVENTION
According to the present invention there is disclosed a jar
tool comprising a mandrell adapted for connection to a piece of
drill string at one end of said tool, a housing axially movable
relative to said mandrell and adapted for connection to said
drill string at the opposite end of said tool, a first ~nd
second pair of abutment faces between said mandrell and said
housing defining the jar and bump positions, respectively, and
piston means operable to regulate the passage of hydraulic
fluid from one side of said piston to ~he other, said first and
second pair of abutmen~ faces being enclosed within said
housing.
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BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
In drawings, which illustrate an embodiment of the
invention,
Figure 1 is a cross-sectional view of a known ~ar tool;
Figures lA, lB, lC and lD are enlarged partial
cross-sectional views of the jar tool taken from the top to the
bottom in Figure 1, respectively;
Figure 2 is a cross-sectional view of the jar tool
according to the present invention; and
Figures 2A, 2B, 2C and 2D are enlarged partial
cross-sectional views of the jar tool taken from the top to the
bottom in Figure 2, respectively.
DESCRIPTION OF SP~CIFIC EMBODIMENT
Referring to Figures 1 and lA through lD, a jar tool is
generally denoted 10. It comprises a mandrell generally
denoted 11 adapted to be connected to a length of drill s~ring
or collar (not shown) by threaded connection 12. A housing
generally denoted 13 surrounds the mandrell 11 and extends to
an oppos1te end which is adapted to be connected to a piece of
drill string or collar (not shown) through threaded connection
14.
The housing 13 comprises a sealing housing 15 connected to
~:ass~
spline housing 16. Spline housing 16 is connected to knocker
housing 17 which, in turn~ is connected to packing sub 18.
Packing sub 18 is connected to hydraulic cylinder l9 which is
connected ~o washpipe housing 20 having threaded connection 14.
Mandrell ll comprises a spline mandrell 21 connected ~o
knocker 22. Knocker 22 is connected to piston mandrell 23
which, in turn, is connected to washpipe 24~
Hydraulic fluid is enclosed within cavities 25, 26 between
the hydraulic cylinder 19 and the piston mandrell 23. A piston
27 is provided which is movable off shoulder 28 and which
restricts the flow of hydraulic fluid from cavity 25 to cavity
26. Valves or metering devices (not shown) are provided within
the piston 27 to allow adjustable release orce on the jar tool
lO and to provide for a more constant fluid flow through the
piston 27. A return mechanism in the form of spring 29 is
provided to keep the piston 27 against shoulder 28 and to
return the piston 27 to shoulder 28 ollowing the jar stroke.
A knocker gland 30 is positioned between knocker housing 17
and piston mandrell 23. It seals the oil filled chambers from
the drill mud and acts to equaliæe pressures inside and outside
the jar tool 10. The knocker gland 3C moves in response to
temperature and pressure variations.
There are two pairs of abutment surfaces on the jar tool
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10. The first pair generally denoted 31 are located one on the
spline mandrell 21 and the other on the sealing housing 15.
This first pair 31 define the i~pact position on the bump
stroke of the jar tool 10. The second pair of abutment faces
are denoted 32, 33 respectively. Abutment face 32 is located
on spline housing 16 and abutment face 33 is located on impact
ring 34 which is held in position by knocker 22 and travels
with the mandrell 11. Abutment faces 32, 33 impact on the jar
stroke.
Referring now to Figures 2 and 2A through 2D, the jar tool
of the present invention is generally denoted 35~ It comprises
a mandrell generally shown at 36 and a housing generally shown
at 37. The mandrell 36 is connected to drill pipe at one end
through threaded connection 38 and the housing 37 i~ connected
to drill pipe at the other end by threaded connection 39.
The housing 37 comprises, from let to ri~ht, end cap 40;
sealing housing 41, spline housing 42, knocker housing 43,
packing sub 44, hydraulic cylinder 45 and washpipe h~using 46,
all connected~
The mandrell 36 comprises~ rom left to right, spline
mandrell 47, knocker 48, piston mandrell 49 and washpipe 50,
all connected.
A piston 51 is provided which acts to restrict fluid flow
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between chambers 52, 53 respectively. A spring 54 acting
between the packing sub 44 and piston 51 seats the piston 51 on
a shoulder 55 on hydraulic cylinder 45 following the jar stroke.
Four removable oil fill plugs 56 are inserted into the
housing 37. The fill plugs 56 are mounted, one in each of the
sealing housing 41 and the knocker housing 43, respectively,
and two in the hydraulic cylinder 45.
A knocker gland 57 is fitted around piston mandrell 49 and
i5 movable relative thereto between knocker 48 and packing sub
44 to equalize pressure and to seal the oil filled chambers
from the drill mud which can enter the jar tool 10 through the
aperture 58. An upper gland nut 59 i5 inserted around the
packing sub 44.
A first set of abutment surfaces is shown generally at 60.
These surfaces abut and define the impact position during the
bump stroke. A first impact ring 61 is providedO The impact
ring 61 is held in position against a shoulder 62 by spline
housing 42. The impact rin~ 61 impacts against a shoulder 63
on spline mandrell 47.
The second set of abutment surfaces are defined by 64, 65
respectively. Abutm~nt face 64 is on spline housing 42 and
abutment face 65 is on second impact ring 66~ Second impact
ring 66 i5 held in position against a shoulder 67 on spline
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mandrell 47 by knocker 48.
Both the first and second set of abutment faces 60 and 64,
65 respectively are enclosed within the jar tool 35.
End cap 40 is connected to sealing housing 41 and
terminates the housing 37. A wiper 68 and three seals 69, 70,
71 seal the inside of the housing 37 from the outside mud and
other foreign substances which can cause contamination and
undesirable wear if they are allowed to enter the jar tool.
OPERATIO_
Both embodiments operate substantially along similar lines
and, therefore, only the operation of the embodiment depicted
in Figures 2 and 2A through 2D will be described.
The jar to~l 3S is shown in its collapsed or bump position
and, it will be assumed, is connected to respective pieces of
the drill string (not shown~ at both ends. The driller, to
perform the jar operation, will create a tension force on the
jar tool 35 by raising the drill string. This will cause the
mandrell 36 to move upwardly or leftwardly relatiYe to the
housing 37. The housing 37 will remain stationary since it is
~onnected to the stuck tool or fish. As the mandrell 36 moves,
the abutment surfaces 60 separate and pis~on 51 is held in
s~
position against shoulder 55 on hydraulic cylinder 45 by piston
return spring 54 until the piston actuator 72 ~ontacts the
piston 51. Un~il this time, ~luid has freely flowed between
chambers 52, 53 past the inside diameter of piston 51. ~7hen
the piston actuator 72 con~acts piston 51, seal 73 seals
against piston actuator 72 and the fluid may then only pass
through the metering passageway 74 in piston 51. The piston 51
will move leftwardly under the influence of piston actuator 72
with the restriction to fluid passage past piston 51 causing
very high fluid pressure in chamber 52. When the seal on
piston 51 enters the enlarged area 75 of chamber 52, the
hydraulic fluid rushes by the piston 51 and into chamber 53.
The rele~se of this fluid allows a large acceleration to occur
between the housing 37 and mandrell 36 until the collision
between impact ring 66 and abutment face 64 on spline housing
42 occurs which completes the jar stroke on the drill string.
Thereafter, the driller may desire a bump stroke. If so,
he ~ill quickly lower the drill string so that the mandrell 36
moves downwardly relative to the housing 37. The piston 51
will be returned to its home position against shoulder 55 of
hydraulic cylinder 45 by the action of spring 54. During the
bump or return stroke, fluid may bypass the piston 51 from
chamber 53 to chamber 52 either by going around the outside
diameter of piston Sl or by going through the inside diameter
of piston 51 and the gap betwe~n piston 51 and piston actuator
72 which is caused by the pressure difference between hambers
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52, 53 compressing the spring 54. Because of the stretch and
weight of the drill string, the mandrell 36 may travel very
quickly relative to the housing 37 until the abutment surfaces
60 impact thus causing the bump in the drill string.
There has been described a specific embodiment of a jar
tool according to the present invention in which many
modifications may be made without departing from the invention
which should, therefore, be defined in accordance with the
accompanying claims.
