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DAIA:102
10
MECHANICAL-HYDRAULIC DOUBLE-ACTING DRILLING JAR
This invention relates generally to drilling jars and, in particular, to a
double-
acting mechanical-hydraulic drilling jar.
Drilling jars have long been known in the field of well drilling equipment. A
drilling jar is a tool employed when either drilling or production equipment
has
become stuck to such a degree that it cannot be readily dislodged from the
well bore.
The drilling jar is normally placed in the pipe string in the region of the:
stuck object
2 o and allows an operator at the surface to deliver a series of impact blovvs
to the drill
string via a manipulation of the drill string. These impact blows to the drill
string are
intended to dislodge the stuck object and permit continued operation.
Drilling jars contain a sliding joint which allows a relative axial movement
2 5 between an inner mandrel and an outer housing without allowing relative
rotational
movement therebetween. The mandrel typically has a hammer formed thereon,
while
the housing includes an anvil positioned adjacent to the mandrel hammer. Thus,
by
sliding the hammer and anvil together at high velocity, a substantial jarring
force may
be imparted to the stuck drill string, which is often sufficient to jar the
drill string free.
3 0 For most fishing applications it is desirable that the drilling jar be
capable of providing
both an upward and a downward jarring force.
There are four basic forms of drilling jars: purely hydraulic jars, purely
mechanical jars, bumper jars, and mechanical-hydraulic jars. The bumper jar is
used
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primarily to provide a downward jarring force. The bumper jar ordinarily
contains a
splined joint with sufticient axial leave( to allow the pipe to be lifted and
dropped,
causing the impact surfaces inside the bumper jar to come together to deliver
a
downward jarring force to the,string.
S
Mechanical, hydraulic, and mechanical-hydraulic jars differ from the bumper
jar in that they contain some type of tripping mechanism which retards the
motion of
the impact surfaces relative to each other until an axial strain, either
tensile or
compressive, has been applied to the drill string pipe. To provide an upward
jaxring
, force, the drill pipe is stretched by an axial tensile load applied at the
surface. This
tensile force is resisted by the tripping mechanism of the jar long enough to
allow the
pipe to stretch and store potential energy. When the jar trips, this stored
energy is
converted to kinetic energy causing the impact surfaces of the jar to move
together ai
a high velocity. To provide a do~ynward jarring force, the pipe weight is
slacked off
I5 at the surface and, if necessary, additional compressive force is applied,
to put the pipe
in compression. This compressive force is resisted by the tripping mechanism
of the
jar to allow the pipe to compress and store potential energy. 'Vhen the jar
trips, the
potential energy of the pipe compression and pipe weight is converted to
kinetic
energy causing the impact surfaces of the jar to come together at a high
velocity.
The tripping mechanism in most mechanical jars consists of some type of
friction sleeve coupled to the mandrel which resists movement of the mandrel
until
the load on the mandrel exceeds a preselected amount (i.e., the tripping load)
<as
can be seen from the PCT application WO 94109247>. The tripping mechanism in
most hydraulic jars consists of one or more pistons which pressurize fluid in
a
chamber in response to movement by the mandrel. ~'he compressed fluid resists
movement of the mandrel. The pressurized fluid is ordinarily allowed to bleed
off
at a preselected rate. As the fluid bleeds off, the piston translates,
eventually
reaching a point in the jar where the chamber seal is opened, and the
compressed
3 o fluid is allowed to rush out, freeing the mandrel to move rapidly.
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Mechanical jars and Jwdraulic jars each have certain advantas:es over the
other.
Mechanical drilling jars are generally less versatile and reliable than
hydraulic drilling
jars. Many mechanical drilling jars require the tripping load to be selected
and preset
at the surface tv trip at one specific load after the drilling jar is inserted
into the well
S bore. If it is necessary to re-adjust the tripping load, the drilling jar
must be pulled
from the welt bore. Other mechanical jars require a torque to be applied to
the drill
string from the surface in order to trigger the jar. The applied torque to the
drill string
not only represents a hazard to rig personnel, but torque cannot be applied to
coiled
tubing drill strings. Another signifcant disadvantage of mechanical jars is
apparent
in circumstances where the jar must be pIace~i in a cocked position prior to
insertion
into the well bore. Thus, in those circumstances, the 'tripping mechanism is
subjected
to stresses during the normal course of drilling if the jar is run as part of
the bottom
hole assembly. Finally, many mechanical jars have many surfaces that are
subject to
wear.
Hydraulic drilling jars offer several advantages over purely mechanical
drilling jars. Hydraulic drilling jars have the significant advantage of
offering a
wide variety of possible triggering loads. In the typical double acting
hydraulic
drilling jar, <as known for example from U,S. Patent 5,318,139>, the range of
2 0 possible triggering loads is a; function of the amount of axial strain
applied
by stretching or compressing the drill pipe, and is limited only by the
structural limits
of the jar and the seals therein. In addition, hydraulic drilling jars are
ordinarily less
susceptible to wear and, therefore, will ordinarily function longer than a
mechanical
jar under the same operating conditions. However, hydraulic drilling jars also
have
certain disadvantages. Far example, most purely hydraulic double acting
drilling jars
are relatively long, in some instances having a length exceeding 2~ feet. The
length
of a particular jar is ordinarily not a significant issue in drilling
situations where
regular threaded drill pipe is utilized. However, in coiled tubine
applications, it is
desirable that the length of all the tools in a particular drill string be no
loner than
the length of the lubricator of the particular coiled tubing injector. Thus,
it is
desirable that the drilling jar be as short as possible to enable the operator
to place as
many different types of tools in the drill string as possible mfiile still
keeping the
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overall length of the drill string less than the length of the lubricator. A
conventional
hydraulic drilling jar may take up one-half or more of the total length of a
given
lubricator, thus leaving perhaps less than half the length of the lubricator
to
accommodate other tools such as a mud motor, an orienting device, or a logging
tool.
Many hydraulic drilling jar designs also have a disadvantageously long
metering stroke. The metering stroke is the amount of relative movement
between the
mandrel and the housing that must occur for the jar to trigger after it is
cocked by
application of an axial load. When an ordinary hydraulic drilling jar is
cocked by
1 o application of an axial load, fluid is press'>zrized in a chamber to
resist relative
movement of the mandrel and the housing. One or more metering orifices in the
jar
allow the compressed fluid to bleed off at a relatively slow rate. As the
fluid is
bleeding off, there is some relative axial movement between the mandrel and
the
housing. The amount of relative axial movement between the mandrel and the
housing that occurs after the jar is cocked, but before the jar triggers, is
known as
bleed off. The bleed off represents lost potential energy that would
ordinarily be
converted into additional jarring force. Many current hydraulic drilling jar
designs
have a relatively long metering stroke of 12 inches or more and, therefore, a
significant amount of bleed off. A long metering stroke also leads to heat
buildup in
2 0 the hydraulic fluid, which may require costly intervals between firings
and lead to
degradation of fluid.
Mechanical-hydraulic drilling jars ordinarily combine some features of both
purely mechanical and purely hydraulic drilling jars. For example, one design
utilizes
2 5 both a slowly metered fluid and a mechanical spring element to resist
relative axial
movement of the mandrel and the housing. This design has the same
disadvantages
associated with ordinary hydraulic drilling jars, namely length, long metering
stroke,
and fluid heating. Another design utilizes a combination of a slowly metered
fluid and
a mechanical brake to retard the relative movement between the mandrel and the
3 0 housing. In this design, drilling mud is used as the hydraulic medium.
Therefore, the
string must be pressurized before the drilling jar will operate. This
pressurization step
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will ordinarily require a work stoppage and the insertion of a ball into the
work string
to act as a sealing device. After the drilling jar is triggered, the ball must
be retrieved
before normal operations can continue.
The present invention is intended to overcome or minimize one or more of the
foregoing disadvantages.
In one aspect of the present invention, a mechanical-hydraulic double-acting
drilling jar is provided. The jar includes a mandrel, a housing telescopingly
positioned
1 o about the mandrel, and first and second pistons positioned between the
mandrel and
the housing and spaced longitudinally apart. The pistons respectively close
first and
second substantially sealed chambers in,the housing. Each of the first and
second
pistons has first and second flow passages formed therein and extending
therethrough.
A collet is positioned between the mandrel and the housing and between the
first and
second pistons.
In another aspect of the present invention, a mechanical-hydraulic double-
acting
drilling jar is provided. The jar includes a mandrel, a housing telescopingly
positioned
about the mandrel, and first and second pistons positioned between the mandrel
and
2 0 the housing and spaced longitudinally apart. The pistons respectively
close first and
second substantially sealed chambers in the housing. Each of the first and
second
pistons has first and second flow passages formed therein and extending
therethrough.
There are first and second biasing members positioned between the mandrel and
the
housing. The first biasing member is operable to resist longitudinal movement
of the
2 5 first piston in a first direction and the second biasing member is
operable to resist
longitudinal movement of the second piston in a second direction. The second
direction is opposite to the first direction. There is also a tubular col.let
positioned
between the mandrel and the housing and between the first and second pistons.
3 o In another aspect of the present invention, a mechanical-hydraulic double-
acting
drilling jar is provided. The jar includes a mandrel that has a first exterior
surface and
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groove circumferentially disposed in the first exterior surface. A housing is
telescopingly positioned about the mandrel. The housing has an interior
surface that
has a radially inwardly projecting third flange. The third flange has a first
end
forming a first shoulder and a second end forming a second shoulder. 'There
are first
and second pistons positioned between the mandrel and the housing and spaced
longitudinally apart. The pistons respectively close first and second.
substantially
sealed .chambers in the housing. Each of the first and second pistons has
first and
second flow passages formed therein and extending therethrough. First and
second
biasing members are positioned between the mandrel and the housing. The first
biasing member is operable to resist longitudinal movement of the first piston
in a first
direction and the second biasing member is operable to resist longitudinal
movement
of the second piston in a second direction. The second direction is opposite
to the first
direction. A tubular collet is positioned between the first and second
pistons. The
collet has an interior surface that has at least one circumferential flange
projecting
radially outward therefrom. The collet also has a second exterior surface that
has at
least one circumferential flange inwardly projecting therefrom. The collet is
adapted
such that the at least one inwardly projecting flange is disposed in the
circumferentially disposed groove when the at least one outwardly projecting
flange
is in contact with the third flange, and such that the collet expands radially
when the
at least one outwardly projecting flange is moved past the first or second
shoulders.
Other objects and advantages of the invention will become apparent upon
reading the following detailed description and upon reference to the drawings
in
which:
2 5 FIGS. 1 A-1 E illustrate successive portions, in combined quarter section
and
partial section, of a mechanical-hydraulic double-acting drilling jar in its
neutral
operating position;
FIG. 2 illustrates an exploded pictorial view of the collet, upper and lower
3 0 annular pressure pistons, and biasing members from the mechanical-
hydraulic double
acting drilling jar of FIGS. lA-lE;
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FIGS. 3A-3C illustrate successive portions, in quarter section, of the
mechanical-hydraulic double-acting drilling jar of FIGS. 1 A-1 E in its post-
triggered
upward jarring position; and
FIGS. 4A-4C illustrate successive portions, in quarter section, of the
mechanical-hydraulic double-acting drilling jar of FIGS. lA-lE in its post-
triggered
downward jarring position.
FIG. 5 illustrates a partial cutaway view of an alternative structure to the
collet
of FIG. 2.
FIG. 6 illustrates a pictorial view of another alternative structure to the
collet
of FIG. 2.
Referring now to the drawings, and, in particular to FIGS. 1 A-1 E, inclusive,
there is shown a mechanical-hydraulic double-acting drilling jar 10 which is
of
substantial length necessitating that it be shown in five longitudinally
'broken partial
sectional views, vis-a-vis FIGS. 1 A, 1 B, 1 C, 1 D, and 1 E. Each of these
views depicts
the right half of the drilling jar 10 in a quarter sectional view, and the
left half of the
drilling jar 10 in a cutaway view. The drilling jar 10 generally comprises an
inner
2 o tubular mandrel 12 telescopingly supported inside an outer tubular housing
14. The
mandrel 12 and the housing 14 each consist of a plurality of tubular segments
joined
together, preferably by threaded inner connections.
The mandrel 12 consists of an upper tubular portion 16 having an inner
2 5 longitudinal passage 18 extending therethrough. The upper end of the
tubular portion
16 is enlarged as indicated at 20 so as to form a substantially flat shoulder
or
downward hammer surface 21, and is internally threaded at 22 for cannection to
a
conventional drill string or the like (not shown). The lower end of the upper
tubular
portion 16 is provided with a counter bore ending in an internal shoulder 24
and is
3 0 internally threaded as indicated at 26 and externally threaded as
indical:ed at 28. An
annular hammer 29 is disposed about the upper tubular portion 16 and is
internally
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threaded, as indicated at 30, for engagement with the upper tubular portion 16
at 28.
Two or more circumferentially spaced lock screws 31~ also bind the annular
hammer
29 to the upper tubular portion 16 to prevent relative rotational movement
therebetween. The lock screws 31 are sunk to present a flush surface with the
exterior
of the annular hammer 29. The annular hammer 29 has a substantially flat upper
hammer surface 32 at its upper end.
An intermediate portion of the mandrel 12 consists of a tubular portion 33
which has its upper end threaded as indicated at 34 for connection inside the
threaded
portion 26 of the upper tubular portion 16 CVith the upper end portion
abutting the
shoulder 24.
The lower end 35 of the tubular portion 16 terminates in a cylindrical chamber
36 in the housing 14 and is provided with an internal bore or passage 37,
which is a
continuation of the passage 18 in the upper tubular portion 16. An O-ring 38
disposed
in an annular recess 39 in the lower end of the upper tubular portion 16
provides a
fluid seal between the upper tubular portion 16 and the tubular portion 33.
The tubular housing 14 is formed in several sections for purposes of assembly,
2 0 somewhat similar to the mandrel 12. The upper end of the tubular housing
14 consists
of an upper tubular portion 40. The upper end of the upper tubular portion 40
has a
substantially flat downward anvil surface 41 for engagement with t:he downward
hammer surface 21, as discussed more below. The lower portion of the upper
tubular
portion 40 is provided with an external counter bore 42 that has a shoulder
43. The
lower end of the external counter bore 42 terminates in an upward anvil
surface 44 for
engagement with the upward hammer surface 32, as discussed more: below. The
counter bore 42 is externally threaded at 46. The interior surface of the
tubular
portion 40 has a plurality of inwardly facing circumferentially spaced splines
48. The
splines 48 are configured to mate with a matching set of outwardly projecting
3 0 circumferentially spaced splines 50 on the exterior surface of the upper
tubular portion
16 of the mandrel 12. The sliding interaction of the splines 48 and the
splines 50
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provide for relative sliding movement of the mandrel 12 and the housing 14
without
relative rotational movement therebetween.
The tubular housing 14 is provided with an intermediate tubular member 52
which is internally threaded, as indicated at 54, at its upper end for
connection to the
threaded portion of the tubular member 40. The upper end of the intermediate
tubular
portion 52 abuts the shoulder 43 when the threaded connection at 46 and 54 is
securely tightened. The lower end of the intermediate portion 52 is internally
threaded
as indicated at 56.
The tubular housing 14 is provided with an intermediate tubular member 58
that is externally threaded, as indicated at 60, at its upper end for
connection to the
threaded portion 56 of the intermediate tubular member 52, and is externally
threaded,
as indicated at 62, at its lower end for connection to another tubular portion
of the
25 tubular housing to be discussed below. The upper end portion of the
intermediate
tubular member 58 has a portion of reduced diameter forming a shoulder 64
which
abuts the lower end of the intermediate tubular portion 52 when the threaded
connection at 56 and 60 is securely tightened. The lower end portion of the
intermediate tubular member 58 also has a portion of reduced diameter forming
a
2 0 shoulder 65 which abuts another intermediate tubular member discussed
below.
There is an annular chamber 66 that is formed within the intermediate tubular
portion 52 between the upper end of the intermediate tubular portion 58 and
the lower
ends of the annular hammer 29 and the lower portion of the upper tubular
portion 16
2 5 of the mandrel 12. The annular chamber 66 is vented to the well annulus
(not shown)
by way of a port 68 in the intermediate tubular portion 52.
The intermediate tubular portion 58 is provided with a fill port: 70 to permit
introduction of a suitable operating fluid, e.g., hydraulic fluid into the
drilling jar 10.
3 0 The filling port 70 is counter sunk with a fill passage 72 leading into
the drilling jar
10, and has a threaded opening that is capped with a fill plug 74 that is
threadedly
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connected to the intermediate tubular member 58_ The plug 74 has an O-ring 76
to
act as a seal.
It is desirable to both prevent mud or other material from the well annulus
from contaminating the jar operating fluid, and to prevent loss of jar
operating fluid
into the well annulus. Accordingly, the upper end of the intermediate tubular
portion
58 includes a seal arrangement that consists of an O-.ring 78 and a wiper 80
that is
disposed just above the O-ring 78, that are disposed respectively in armular
recesses
81 and 82 in the intermediate tubular portion 58, and are both in contact with
the
intermediate tubular member 33. Similarly, to prevent flow of jar operating
fluid past
the threaded portion 62, an O-ring 83 is disposed at the lower end of th.e
intermediate
tubular portion 58.
The tubular housing 14 is provided with an intermediate tubular member 84
I5 which is internally threaded as indicated at 86 at its upper end for a
threaded
connection to the threaded portion 62 of the intermediate tubular member 58.
The
intermediate tubular member 84 is internally threaded at its lower end as
indicated at
88 to threadedly connect to another tubular member as discussed more fully
below.
The upper end of the intermediate tubular member 84 abuts the shoulder 65 on
the
2 o intermediate tubular member 58 when the threaded interconnection at 62 and
86 is
securely tightened.
The tubular housing 14 is provided with an intermediate tubular member 90
that is externally threaded at its upper end, as indicated at 92, for
connection to the
25 threaded portion 88 of the intermediate tubular member 84. The upper end of
the
intermediate tubular member 90 has a portion of reduced diameter forming a
shoulder
94 that abuts the lower end of the intermediate tubular member 84 when the
threaded
connection at 88 and 92 is securely tightened. An O-ring 96 is disposed in a
recess
97 in the upper end of the intermediate tubular member 90 to prevent leakage
of
3 0 hydraulic fluid past the threaded connection at 88 and 92. The lower end
of the
intermediate tubular member 90 has a portion of reduced diameter that is
externally
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threaded, as indicated at 98, and forms a shoulder 100. The intermediate
tubular
member 90 has a fill port 102 to enable the operator to fill the drilling jar
10 with
hydraulic fluid. The filling port 102 is counter sunk to provide a flow
passage 104
leading to the interior of the drill jar 10, and a larger diameter opening
that is capped
by a threadedly connected plug 106. The plug 106 has an O-ring seal that
engages
the intermediate tubular member 90 proximate the fill passage 104.
It is desirable to both prevent the contamination of the hydraulic fluid in
the
drilling jar 10 by material, such as drilling mud, emanating from the bore 36
and to
prevent the loss of hydraulic fluid from the drilling jar 10 at the interface
between the
intermediate tubular member 90 and the lower end of the mandrel 12.
Accordingly,
the intermediate tubular member 90 includes at its lower end a seal
arrangement that
is substantially similar to the seal arrangement for the intermediate tubular
member 58,
and which consists of an O-ring 110 and a wiper 1 I2 disposed in annular
recesses 114
and 116 in the intermediate tubular member 90. The wiper 112 is disposed just
below
the O-ring 110.
The lower end of the tubular housing 14 consists of a lower tubular member
118 that is internally threaded at its upper end as indicated at 120 for
connection to
2 o the threaded portion 98 of the intermediate tubular member 90. The upper
end of the
lower tubular member 118 abuts the shoulder 100 of the intermediate tubular
member
90 when the threaded connection at 98 and 120 is securely tightened. To
prevent the
escape of mud or other material emanating from the bore 36, an O-ring 122 is
disposed in an annular recess 123 in the lower end of the intermediate tubular
member
2 5 90 proximate the upper end of the lower tubular member 118. The clearance
between
the upper end of the lower tubular member 118 and the lower end 35 of the
mandrel
12 is such that the cylindrical chamber 36 is large enough to accommodate the
movement of the lower end 35 of the mandrel 12 therein while at the same time
accommodating a quantity of pressurized fluid, such as drilling mud. The lower
end
3 0 of the annular chamber 36 is continuous with a reduced diameter flow
passage 126
that extends and opens to the bottom of the drilling jar (not shown). The
bottom (not
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shown) of the drilling jar 10 may be internally or externally threaded as the
case may
be to connect to another portion of the drill string (not shown).
An inner surface 128 of the intermediate tubular member 8~a. and an outer
surface 130 of the tubular portion 33 of mandrel 12 are spaced apart to define
an
upper hydraulic chamber 132. Generally, the upper hydraulic chamber 132
resists
upward movement of the mandrel 12 relative to the housing 14. That is, upward
relative movement of the mandrel 12 relative to the housing 14 reduces the
volume
of the upper hydraulic chamber I32, causing a significant increase in the
internal
pressure of the upper hydraulic chamber 132; thereby producing a force to
resist this
relative movement. This resistance to relative movement allows a large buildup
of
potential energy.
Accordingly, a mechanism is provided for substantially sealing the upper
hydraulic chamber 132 to permit the~buildup of pressure therein. The surfaces
128
and 130 of the upper hydraulic chamber 132 are smooth cylindrical surfaces
permitting
free movement of an upper annular pressure piston 134. The upper annular
pressure
piston 134 has a smooth cylindrical bore 136 through which the mandrel 12 is
slidably
journalled. The upper annular piston 134 is sealed against leakage past the
bore 136
2 0 by an O-ring 138 disposed in an annular recess 139 in the lower end of the
upper
annular pressure piston 134, and against leakage between the exterior surface
140 of
the upper annular piston 134 and the interior surface 128 by an O-ring 142
that is
disposed in an annular recess 143 in the upper annular pressure piston 134.
The interior surface 128 of the intermediate tubular member 84 has a reduced
diameter section that has at its upper end an upward facing annular shoulder
144 and
at its lower end a downward facing annular shoulder 145. The upward facing
annular
shoulder 144 is engagable with the lower end of the upper annular pressure
piston 134
to define the limit of downward movement of the upper annular pressure piston
134.
3 o Similarly, the downward facing shoulder 145 is engagable with another
annular
pressure piston to define the limit of upward movement thereof, as discussed
below.
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Referring now also to FIG. 2, which is an exploded pictorial view showing the
upper and lower annular pressure pistons 134 and 166 and other components to
be
described below, the upper annular pressure piston 134 has two substantially
parallel
flow passages 146 and 148 extending therethrough. The first flow passage 146
is in
fluid communication at its upper end with the upper hydraulic chamber 132 and
in
fluid communication at its lower end with a slot 149 formed in the exterior of
the
lower end of the upper annular pressure piston 134. The first flow passage 146
is
designed to permit restricted flow of fluid from the upper hydraulic chamber
132 to
permit buildup of pressure in the upper hydraulic chamber 132 while permitting
the
upper annular pressure piston 134 to translate upwards until the jar 10
triggers, as
described more below. To that end, the upper portion of the first flow passage
146
includes a conventional flow restriction orifice I50 to restrict the flow of
fluid from
the upper hydraulic chamber 132. The flow restriction orifice 1 ~0 is
preferably a Lee
.IEVA, manufactured by Lee Company, Westbrook, Connecticut, or other suitable
orifice.
Like the first flow passage 146, the second flow passage 148 is in fluid
communication at its upper end with the upper hydraulic chamber 132 and in
fluid
communication at its lower end with a slot 152 formed in the exterior of the
lower end
2 0 of the upper annular pressure piston I 34. The second flow passage 148 is
designed
to prevent flow Qf fluid from the upper hydraulic chamber 132 through the
upper
annular pressure piston 134 during upward movement of the upper annular
pressure
piston 134 while permitting a free flow of fluid in the reverse direction
during
downward movement of the upper annular pressure piston I34. To that end, the
flow
2 5 passage 148 includes a conventional one way flow 'valve I 54, shown
schematically as
a ball valve, to permit flow of fluid in the directions indicated by the arrow
156. The
TM
one way flow valve 1 ~4 is preferably a Lee Chek model I 87, manufactured by
the Lee
Company, Westbrook, Connecticut, or other suitable one way flaw valve.
3 o Note that both the flow passages I46 and 148 terminate at their Lower ends
in
a 90° elbow. This configuration is necessary only to avoid the O-ring
142. It should
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be understood that the flow passages 146 and 148 may alternately extend
through the
entire length of the piston 134, thus obviating the need for the 90°
elbow and the slots
147 and 152.
There is a biasing member 162 disposed in the upper hydraulic chamber 132,
through which the mandrel 12 is journalled. The upper end of the biasing
member
162 bears against the lower end of the intermediate tubular member 58, and the
lower
end of the biasing member 162 bears against the upper end of the upper annular
pressure piston 134. As discussed more fully below, the biasing member 162
1 o functions to resist upward movement of the upper annular pressure piston
134 and to
return the upper annular pressure piston 134 to the position shown in FI(s. 1
C after
an upward jarring movement of the drilling jar 10. The biasing member 162 is
preferably a stack of bellville springs, though other types of spring
arrangements may
be possible, such as one or more coil springs. Regardless of the pat~ticular
design
chosen, it is desirable in one preferred embodiment that the biasing member
162
provide a minimum of approximately 250 pounds of force when fully compressed.
The inner surface 128 of the intermediate tubular member 84 and the outer
surface of the mandrel 12 are spaced apart to define a lower hydraulic chamber
164,
2 0 which is substantially similar to the upper hydraulic chamber 132. Like
the upper
hydraulic chamber 132, the lower hydraulic chamber 164 resists longitudinal
movement of the mandrel 12. However, in this case the lower hydraulic chamber
164
resists downward longitudinal movement of the mandrel 12. A lower annular
pressure
piston 166 is disposed within the housing 14 to substantially seal the lower
hydraulic
2 5 chamber 164 to permit the buildup of pressure therein.
The lower annular pressure piston 166 is substantially similar i.n structure
to
the upper annular pressure piston 134. However, the lower annular pressure
piston
166 is inverted in comparison to the upper annular pressure piston 134. The
lower
3 0 annular pressure piston 166 includes two flow passages 168 and 169 that
extend
therethrough. The first flow passage 168 is in fluid communication with both
the
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lower hydraulic chamber 164 and a slot 170 in the piston 166, <~nd contains a
conventional flow restriction orifice 172. The second flow passage 169 is in
fluid
communication with both the lower hydraulic chamber 164 and a slot 174 in the
piston
166, and contains a conventional one way flow valve 175 that permits flow in
the
direction indicated, by the arrow 176. The lower annular pressure piston 166
has O-
rings 177 and 178 that are identical in structure and operation to O-rings 142
and 138.
As noted above, the upper end of the lower annular pressure piston 166 is
engagable
with the downward facing shoulder 145, which defines the limit of upward
movement
thereof.
The downward movement of the lower annular pressure piston 166 is retarded
not only by the pressure of hydraulic fluid compressed within the lower
hydraulic
chamber 164, but also by a biasing member 180 that is disposed in the lower
hydraulic
chamber 164 and through which the mandrel 12 is journalled. The upper end of
the
biasing member 164 abuts the lower end of the lower annular pressure piston
166.
The lower end of the biasing member 180 abuts the upper end of th.e
intermediate
tubular member 90. The biasing member 180 is substantially identical to the
biasing
member 162 in structure and function.
2 0 It should be appreciated that the upper annular pressure piston 134, in
conjunction with the fluid pressure in the upper hydraulic chamber 132 and the
biasing
member 162, function to retard the upward movement of the mandrel 12 to allow
a
buildup of potential energy in the drill string when a tensile load is placed
on the
mandrel 12 from the surface. Similarly, it should be appreciated that the
downward
2 5 movement of the mandrel 12 is restricted by the lower annular pressure
piston 166
acting in concert with the fluid pressure within the lower hydraulic chamber
164 and
the biasing member 180 to allow a buildup of potential energy in the drill
string when
a compressive load from the surface is applied to the mandrel.12. Th.e
transmission
of an upward acting force from the mandrel 12 to the upper annular pressure
piston
3 0 134 and the transmission of a downward acting force from the mandrel 12 to
the
lower annular pressure piston 166 requires a mechanical linkage between the
mandrel
' ' CA 02223144 1997-12-03
y
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12 and the upper and lower annular pressure pistons 134 and 166. The
mechanical
linkage is provided by a generally tubular collet 184 which is disposed in the
intermediate tubular section 84 between the upper annular pressure piston 134
and the
lower annular pressure piston 166. The mandrel 12 is journalIed through the
collet
184.
The collet 184 has a plurality of longitudinally extending and
circumferentially
spaced slots 186 that divide the central portion of the collet 184 into a
plurality of
longitudinally extending and circumferentially spaced segments 188. During
operation
of the drilling jar 10, the segments 188 will be subjected to bending
stresses.
Accordingly, it is desirable to round the ends 190 of the slots 186 to avoid
creating
stress risers. Each longitudinal segment 188 has an outwardly projecting
flange 192
formed on the exterior surface 194 thereof and an inwardly projecting flange
196
formed on the interior surface 198 thereof and proximate the outwardly
projecting
flange 192. It should be understood that the collet 184 need not have a fully
annular
horizonal cross section as shown in FIGS. 1 C-1 D, inclusive, and FIG. 2. The
collet
may be less than fully annular, e.g., formed to have a semicircular horizontal
cross
section. Accordingly, the number and spacing of segments 188 may be varied.
A portion of the mandrel 12 that is journalled through the collet 184 has an
annular recess 200 formed therein that extends around the circumference
thereof. The
annular recess 200 has an upper tapered shoulder 202 and a lower tapered
shoulder
204. Each of the inwardly projecting flanges 196 has an upper bevelled surface
206
and a lower bevelled surface 208. An upward acting force on the mandrel 12 is
transmitted to the collet 184, and thus, in turn, to the upper annular
pressure piston
134, by the interaction between the shoulder 204 and the lower bevelled
surfaces 208.
Conversely, a downward acting force on the mandrel 12 is transmitted to the
collet
184, and thus, in turn, the lower annular pressure piston 166, by tlhe
interaction
between the shoulder 202 and the upper bevelled surfaces 206.
' ' CA 02223144 1997-12-03
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The outwardly projecting flanges 192, which have an upper bevelled surface
210 and a lowzr bevelled surface 212, engage the relatively smooth inner
surface 214
of an inwardly projecting annular flange 216 that projects inwardly .from the
inner
surface 128 of the intermediate tubular member 84. The inwardly projecting
flange
216 has at its upper end a bevelled shoulder 218 and at its lower end a
bevelled
shoulder 220.
In the unloaded or neutral condition depicted in FIGS. lA-lE, inclusive, the
collet 184 is positioned so that the outwardly projecting flanges 192 are
positioned at
approximately the center point of the inwardly projecting annular flange 216.
The
collet 184 is urged to remain in this central position by the biasing action
of the
biasing members 162 and 180, which transmit their respective compressive
forces
against the collet 184 via the upper and lower annular pressure pistons. 134
and 166.
The collet 184 functions not only as a linkage for the transmission of upward
and downward forces from the mandrel 12 to the upper and lower annular
pressure
pistons 134 and 166, but also serves as the triggering mechanism to free the
mandrel
12 to move rapidly relative to the housing 14.
As discussed more fully below, the drilling jar 10 will trigger in an upward
jarring mode when the lower bevelled surface 212 is moved past the bevelled
shoulder
218. Conversely, the drilling jar 10 will trigger in a downward jarring mode
when the
upper bevelled surface 210 passes the lower bevelled shoulder 220.
UPWARD JARRING MOVEMENT
The upward jarring movement capability of the drilling jar 10 can be
understood by reference to FIGS. lA-lE, inclusive, and FIGS. 3A-3C, inclusive.
FIGS. 3A-3C, inclusive, show the drilling jar 10 just after it has fired in an
upward
jarring movement. Each of FIGS. 3A-3C is shown in a longitudinal quarter
section
extending from the center line 222 of the jar 10 to the outer periphery
thereof. In an
' CA 02223144 1997-12-03
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unloaded condition, the drilling jar 10 is in a neutral position as depicted
in FIGS. lA-
1 E, inclusive. To initiate an upward jarring movement of the drilling jar 10,
an
upwardly directed tensile load is applied to the mandrel 12. The range of
permissible
magnitudes of tensile loads, and thus imparted upward jarring force, is
limited only
by the structural limits of the jar 10 and the seals therein. As force is
applied to the
mandrel 12, the lower shoulder 204 of the recess 200 engages the lower
bevelled .
surfaces 208 of the inwardly projecting flanges 196 of the collet 184. The
upward
acting force from the mandrel 12 is transmitted to the collet 184, and in turn
to the
upper annular pressure piston 134, urging both the collet 184 and the upper
annular
pressure piston 134 upwards. As the upper annular pressure piston 134 is
translated
upwards, the fluid within the upper hydraulic chamber 132 is compressed. The
upward movement of the upper annular pressure piston 134, and in turn the
collet 184
and the mandrel 12 are retarded by the pressure of the fluid compressed within
the
upper hydraulic chamber 132 and by the downward acting force of the biasing
member
162 acting on the upper end of the upper annular pressure piston 134, allowing
potential energy in the drill string to build. As noted above, upward movement
of the
upper annular pressure piston 134 is accommodated by a restricted flow of
hydraulic
fluid from the upper hydraulic chamber 132 through the first flow passage 146.
The
upper annular pressure piston 134, the collet 184, and the mandrel 12 continue
a
2 o steady but slow upward creep as fluid continues to flow from the ulaper
hydraulic
chamber 132 through the upper annular pressure piston 134, and into the space
between the upper and lower annular pressure pistons 134 and 166. When the
lower
bevelled surface 212 on the outwardly projecting flanges 192 reach the upper
shoulder
218 on the inwardly projecting annular flange 216, there will be a wedging
action
between the lower shoulder 204 of the annular recess 200 and the lower
bevelled
surface 208 of the inwardly projecting flange 196 that will cause the segments
188 to
bend radially outward. The spacing between the inner surface 128 of the
intermediate
tubular member 84 and the exterior of the intermediate portion 33 of the
mandrel 12
is such that the segments 188 may expand radially outward enough to clear the
3 0 inwardly projecting flanges 196 from the annular recess 200, thereby
allowing the
mandrel 12 to translate upwards freely and rapidly relative to the housing 14.
Without
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the strictures of the collet 184 and the upper annular pressure piston 134,
the mandrel
12 accelerates upward rapidly bringing the hammer surface 32 of the aapper
hammer
29 rapidly in contact with the anvil surface 44 of the upper anvil 40. Note
that the
lower annular pressure piston 166 is held substantially in its neutral
position during
upward jarring by the shoulder 145.
The collet 184 provides for a relatively short firing, or metering stroke. For
an upward jarring movement, the metering stroke is defined approxiimately by
the
distance between the lower bevelled surfaces 212 on the outwardly projecting
flanges
192 and the upper shoulder 218 on the inwardly projecting annular flange 216.
Similarly, the metering stroke for a downward jarring movement is
approximately
defined by the distance between the upper bevelled surface 210 on the
outwardly
projecting flanges 192 and the lower shoulder 220 on the inwardly projecting
annular
flange 216. This relatively short metering stroke serves two useful functions.
First,
the short metering stroke minimizes the amount of bleed off, or lost potential
energy,
that is associated with long metering strokes. Secondly, the short metering
stroke
minimizes the amount of hydraulic fluid that must be rapidly past through flow
passages, thereby reducing heat buildup in the fluid.
To reset the drilling jar 10 to its neutral position, the mandrel 12 is moved
downward relative to the housing 14. As the mandrel 12 is moved downward, the
upper shoulder 202 of the annular recess 200 engages the upper bevelled
surface 206
of the inwardly projecting flanges 196. Via a wedging interaction between the
lower
bevelled surface 212 and the upper shoulder 218, the segments 188 contract
radially
inward until the outwardly projecting flanges 192 slidably engage the inner
surface
214 of the inwardly projecting annular flange 216. As the mandrel 12 is
translated
downwards, the upper annular pressure piston 134 is urged downward with
relative
ease by the biasing member 162. This freedom of movement is made possible by
the
one way flow valve 154 in the upper annular pressure piston 134, which allows
a
3 0 relatively free flow of fluid from the space between the upper and lower
annular
' ' CA 02223144 1997-12-03
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pressure pistons 134 and 166 through the upper annular pressure piston 134 and
into
the upper hydraulic chamber 132.
DOWNWARD JARRING MOVEMENT
The downward jarring movement capability of the drilling jar 10 can be
understood by reference to FIGS. lA-lE, inclusive, and FIGS. 4A-4C, inclusive.
FIGS. 4A-4C, inclusive, show the drilling jar 10 just after it has fired i;n a
downward
jarring movement. Each of FIGS. 4A-4C is shown in a longitudinal duarter
section
extending from the center line 222 of the jar'10 to the outer periphery
thereof. In an
unloaded condition, the drilling jar 10 is in a neutral position as depicted
in FIGS. lA-
lE, inclusive. To initiate a downward jarring movement of the drilling jar 10,
a
compressive load is applied to the mandrel 12. The range of permissible
magnitudes
of compressive loads, and thus downward jarring force, is limited only by the
structural limits of the jar 10 and the seals therein. When the mandrel 12 is
urged
downward, the upper shoulder 202 in the annular recess 200 engage the upper
bevelled
surfaces 206 on the inwardly projecting flanges 196, thereby urging the collet
184, and
therefore the lower annular pressure piston 166 downward. As the lower annular
pressure piston 166 is urged downward, the fluid in the lower hydraulic
chamber 164
2 o is compressed. The combination of the compression of the fluid in the
lower
hydraulic chamber 164 and the opposing force from the compressed biasing
member
180 act in concert to retard the movement of the lower annular pressure piston
166,
and therefore the collet 184 and the mandrel 12, allowing potential enerl;y in
the drill
string to build. When the upper bevelled surfaces 210 of the outwardly
projecting
flanges 192 clear the lower shoulder 220 of the inwardly projecting annular
flange
216, a wedging interaction between the upper shoulder 202 and the upper
bevelled
surfaces 206 of the inwardly projecting flanges 196 urges the segments 188 to
bend
radially outward. As with the upper jarring movement, the spacing between the
inner
surface 128 and the exterior of the intermediate portion 33 of the mandrel 12
is such
3 o that the segments 188 may expand outward a sufficient amount to clear the
inwardly
projecting flanges 196 from the annular recess 200, thereby enabling the
mandrel 12
CA 02223144 2005-04-15
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to rapidly and freely accelerate downward. The rapid and free downward
acceleration
of the mandrel 12 rapidly brims the downward hanuner surface ? I of the
mandrel 1 ?
in contact with the downward anvil surface 41. thereby imparting a downward
jarring
.. <<
blow to the drilling jar 10.
To return the drilling jar to a neutral position from a downward firing
position.
the mandrel 12 is moved upwards until the inwardly projecting flanges 196 snap
back
into position within the annular recess 200. The nnandrel 1? is moved upward
until
the collet 184 assumes the neutral position. As the anandrel 12 is moved
upwards, the
IO lower annular pressure piston 166 is urged tTpward by the biasing member
180. A
relatively free flow of fluid from the space between the upper and Lower
annular
pressure pistons 134 and 166 through the one way flow valve I75 permits the
lower
annular pressure -piston I66 to translate upward to its original neutral
position with
relative freedom. The advantages associated with a short metering stroke
discussed
above with regard to the upv,~ard jarring movement are identical in the
downward
jarring movement mode.
Alternatively, the collet may be replaced by an annular retaining ring 224,
which is circumferentially disposed in the annular recess 200 in the mandrel
as shown
2 o in FIG. 5. The annular ring 224 is split as indicated at 226 to enable the
ring 224 to
expand radially outward as would the segments 188 in the above preferred
embodiment. Upward or downward force from the mandrel 12 is transmitted from
the
annular ring 224 to the upper and lower annular pressure pistons 134 and 166
by
upper and lower spacer rings 228 and 230 that are respectively disposed
between the
2 5 annular ring 224 and the upper annular pressure piston 134 and between the
annular
ring 134 and the lower annular pressure piston 166. The spacer rings 228 and
230 are
shown partially cutaway to reveal the detail of the annular ring 224.
CA 02223144 1997-12-03
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Similarly, as shown in FIG. 6, the collet 184 may be replaced. by a plurality
of circumferentially spaced, but separated, annular segments 232 that are
disposed
about the mandrel 12, shown in phantom. The annular segments '~32 each have
inwardly and outwardly projecting flanges 234 and inwardly projecting flanges
236
that are substantially similar in structure and function to the flanges 192
and 196. The
annular segments 232 are free to move inward and outward radially as would the
segments 188, though without bending. .
