Note: Descriptions are shown in the official language in which they were submitted.
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TIME DELAY PERFORATING APPA~ATUS
Background Of The Invention
1. Field Of The Invention
This invention relates to apparatus for perforating a
well bore, and more particularly, to an apparatus for firing
at least two guns with a predetermined time delay in between
and preventing fluid flow between the guns.
2. Description Of The Prior Art
In well bore perforating operations, it is i~portant for
the operator to know whether or not all of the guns have
been fired. Typically, a time delay device is positioned at
the bottom of the string below the lowermost guns. The
explosive output of one gun fires the next lower gun, and
this continues with the lowermost gun triggering the time
delay device. The time delay device has a relatively slow
burning material in it, and after this material burns, a
small explosive charge in the time delay device is deto-
nated.
At the surface, the operator can hear and feel the guns
firing, and after the guns cease firing, the operator
listens for the detonation of the time delay device. If he
hears it, he knows all of the guns have fired since the time
delay device cannot be actuated otherwise.
A problem with this prior apparatus is that depending
upon the depth and conditions of -the well, the ignition of
the small charge in the time delay device may not be heard.
If this is the case, then the operator does not know if the
last gun has fired.
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In U. S. Patent ~o. 4,478,294 to Sumner, assigned to the
assignee of the present invention, a time delay is posi-
tioned above the lower one or two guns in the string. The
firing of the last gun is thus delayed. The firing of the
last gun is significantly louder, and thus more easily
discerned, than the detonation of the small charge in the
prior art time delay device because the charge in the per-
forating guns is considerably larger. Electrical sensors
may also be provided to monitor the firing of the guns.
The apparatus of the present invention also uses a time
delay device between upper perforating guns and at least the
lowermost perforating gun. The time delay apparatus in-
cludes a housing positioned between the guns with a
separate, easily replaceable, time delay device positioned
in the housing.
Another problem with previous perforating tools is that
once some of the guns have fired, fluid is free to enter all
of the guns therebelow. If all of the guns do not fire, the
fluid in the lower guns makes retrieval more difficult.
Also, the entire tool must be broken down and drained in
order to reuse the lower guns.
In the present invention, the time delay device prevents
fluid communication between the upper guns and the gun or
guns below the time delay device. This allows the time
delay device and the guns therebelow to be rerun by simply
replacing the portions of the perforating string thereabove.
It is not necessary to break down the apparatus and drain
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it. In fact, the apparatus of the present invention could
be run in multiple positions in perforating string with each
location acting as a fluid isolation device to prevent fluid
entry into the lower guns in the event of a "stop-fire"
(misfire).
Prior art systems have included fluid isolation shims
which perform this function, but the shims are not com-
patible with all of the firing devices and therefore are not
usable in all situations. The present invention does not
have this problem.
Summary Of The Invention
The present invention includes a downhole tool for per-
forating a well bore comprising a first perforating gun, a
second perforating ~un longitudinally spaced from the first
perforating gun, and a time delay apparatus for delaying
firing of the second perforating gun for a predetermined
period of ti~e after firing of the first perforating gun.
The time delay device is positioned between the first and
second guns such that fluid communication between the guns
is prevented. One or more first guns may be used, and in
the event of incomplete firing, any fluid entering the first
gun or guns does not enter the second gun or guns. The
first perforating gun may be either above or below the
second perforating gun.
The time delay apparatus comprises housing means for
connecting to the first and second perforating guns and time
delay means in the housing means for the actual delaying of
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the firing of the second gun. The time delay means is
characterized in the preferred embodiment by a time delay
device disposed in the housing means. The housing means
defines a housing central opening therethrough, and the
apparatus further comprises sealing means for sealing be-
tween the time delay means and the housing central opening.
The time delay device comprises a primer assembly,
firing means, such as a firing pin, for impacting and
thereby detonating the primer assembly, a time delay mix
triggered by detonation of the primer assembly, and explo-
sive means for providing an explosive force which is
triggered by the time delay mix. Preferably, an ignition
mix is used between the primer assembly and time delay mix.
All of these components are positioned in a body central
opening defined in a time delay body. The explosive means
is preferably characterized by a primary explosive ignitable
by the delay mix and a secondary explosive ignitable by the
primary explosive.
An upper retainer is engaged with the body for at least
partially closing an upper end of the body central opening,
and a lower retainer is provided for at least partially clo-
sing a lower end of the body centr-al opening. A screen may
be disposed between the primer assembly and the delay mix.
The firing pin is shearably positioned in the body and has a
shearable flange which engages a shoulder in the body.
Preferably, a sealing means is provided for sealing between
the firing pin and the body central opening.
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An important object of the invention is to provide a
well perforating apparatus by which a well operator has a
positive indication that all perforating guns in the tool
string have fired.
Another object of the invention is to provide a downhole
tool for perforating a well bore having first and second
guns with a time delay for delaying firing of the second gun
for a predetermined period of time after firing of the first
gun, the time delay being positioned between the first and
second guns such that fluid communication therebetween is
prevented.
An additional object of the invention is to provide an
apparatus for perforating a well bore in which a housing is
disposed between upper and lower guns with a time delay
device positioned in the housing for delaying firing of one
of said upper and lower guns for a predetermined period of
time after firing of the other of said upper and lower guns.
A further object of the invention is to provide a time
delay apparatus having a body defining a body central
opening therethrough and firing means disposed across the
body central opening for preventing fluid flow therethrough.
Still another object oE the invention is to provide a
time delay apparatus having a primary explosive ignitable by
a time delay mix and a secondary explosive ignitable by the
primary explosive.
Additional objects and advantages of the invention will
become apparent as the following detailed description of the
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invention i9 read in conjunction with the drawings which
illustrate such preferred embodiment.
Brief Description Of The Drawings
:
FIG. 1 illustrates the time delay perforating apparatus
of the present invention in position in a well bore at the
end of a tool string.
FIG. 2 is an enlarged cross-sectional detail of the por-
tion of the tool string which holds the time delay device.
FIG. 3 is a longitudinal cross section of the time delay
device.
Description Of The Preferred Embodiment
Referring now to the drawings, and more particularly to
FIG. 1, the time delay perforating apparatus of the present
invention is shown and generally designated by the numeral
10. Apparatus 10 is connected to the lower end of a tool
string 12 and is positioned in a well bore 14 which may or
may not have a casing 16. Apparatus 10 is positioned adja-
cent to a formation 18 to be perforated.
Apparatus 10 includes at least one first or upper gun 20
and at least one second or lower gun 22. In the preferred
embodiment, there will be a plurality of upper guns 20 and a
relatively fewer number of lower guns 22. The invention
requires at least one lower gun, but more may be used.
While guns 20 have been referred to as upper guns, and guns
22 have been referred to as lower guns, it will be
understood by those skilled in the art that the guns could
be reversed. That is, the firing se~uence could be from
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bottom to top with the uppermost gun being fired after the
time delay, rather than fired from top to bottom with the
lowermost gun being fired after the time delay. A more
detailed description of the firing sequence is provided
herein.
Referring now also to FIG. 2, a time delay housing means
24 is disposed between upper and lower guns 20 and 22. In
the preferred embodiment, housing means 24 is characterized
by an elongated housing 24 defining a longitudinal housing
central opening 26 therein.
The upper end of housing 24 is connected to an upper gun
20 at threaded connection 28. Sealing means, such as 0-
rings 30, provide sealing engagement between the housing and
lower gun.
The lower end of housing 24 is attached to lower gun 22
at threaded connection 32 with a sealing means, such as 0-
rings 34, therebetween.
Housing central opening 26 includes a first bore 36, a
slightly larger second bore 38, and an even larger third
bore 40 in housing 24. A generally annular, downwardly
facing shoulder 42 extends between first and second bores 36
and 38, and another generally annular downwardly facing
shoulder 44 extends between second bore 38 and third bore
40. A tapered bore 46 extends outwardly away from the lower
end of third bore 40.
A time delay device 50 is positioned in central opening
26 of housing 24 and closes off the housing central opening
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as best shown in FIG. 2. Sealing means, such as a pair of
0-rings 52~ provide sealing engagement between ti~le delay
device 50 and third bore 40 of housing 24. A detonation or
primer cord 54 extends downwardly from the explosive portion
(not shown3 of upper gun 20 and into contact with time delay
device 50, as will be further discussed herein.
Referring now to FIG. 3, the details of time delay
device 50 are shown. Time delay device 50 includes an
elongated body 56 having an outer surface 58 adapted to fit
closely within third bore 40 of housing 24. An upper end 60
of body 56 is positioned adjacent to shoulder 44 in housing
24. A pair of annular grooves 62 in outer surface 58
receive 0-rings 52 therein.
Body 56 defines a body central opening 64 therethrough.
Body central opening 64 includes a first threaded opening 66
adjacent to upper end 60, a first bore 68, a somewhat
smaller second bore 70, and a second threaded opening 72 at
the lower end of second bore 70. A generally annular
upwardly facing shoulder 74 extends between first and second
bores 68 and 70 in body 56.
A firing pin housing 76 is disposed in the upper portion
of body central opening 64 in body 56 and has a threaded
portion 78 engaged with threaded opening 66 and a lower por-
tion 80 which extends into first bore 68 in close rela-
tionship therewith. Sealing means, such as 0-rings 82,
provide sealing engagement between firing pin housing and
first bore 68.
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Firing pin housing 76 has a bore 84 therein with a coun-
terbore 86 at an upper end thereof such that an annular,
upwardly facing shoulder 88 is formed. The bottom of firing
pin housing 76 has a hole 90 therethrough which is somewhat
smaller than bore 84.
A Eiring means, such as a firing pin 92, is disposed in
firing pin housing 76. A central portion 94 of firing pin
92 fits closely within bore 84. Sealing means, such as 0-
rings 96, provide sealing engagement between firing pin 92
and bore 84. It will thus be seen that firing pin housing
76 and firing pin 92 close off body central opening 64, and
it may be generally said that the firing means closes off
the body central opening.
At the upper end of firing pin 92 is a shearable flange
98 which fits in counterbore 86 and rests on shoulder 88
initially. As will be discussed in more detail herein,
flange 98 will be sheared when exposed to the explosive out-
put of gun 20 thereabove.
At the lower end of firing pin 92 is pin portion 100
which is sized to fit within hole 90 in firing pin housing
76.
Disposed below firing pin housing 76 in first bore 68 of
body 56 is a primer assembly 102. Primer assembly 102 is of
a kind known in the art and is adapted ~or detonation upon
impact by pin portion 100 of firing pin 92. One such primer
assembly comprises titanium potassium perchlorate (TiKC104).
A primer retainer 104 is disposed in first bore 68 of
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body 56 below primer assembly 102. Primer retainer 104
deEines a central opening 106 therethrough.
A disc-like screen 108 having a plurality of holes 110
therein is positioned between primer retainer 104 and
shoulder 74 in body 56~
Firing pin housing 76, firing pin 92, primer assembly
102, primer retainer 104 and screen 108 are clamped in the
position shown in FIG. 3 by an upper retainer 112 which has
a threaded portion 114 engaged with threaded opening 66 in
body 56. Upper retainer 112 defines a central opening 116
therein which is adapted for receiving a lower end of deto-
nation cord 54.
The present invention includes explosive means disposed
in second bore 70 of body 56 below screen 108. The explo-
sive means comprises several components in the preferred
embodiment.
Immediately below screen 108 is an ignition mix 116,
such as an AlA element.
Below ignition mix 116 is a time delay means 118, such
as a time delay mix 118. A tungsten material is used in
time delay mix 118 in the preferred embodiment, although the
invention is not intended to be limited to tungsten. As is
known in the art, the tungsten material is in powdered form,
and a small portion is poured into second bore 70 of body 56
and compressed to form a tungsten increment 120. Additional
tungsten increments 1~0 are formed in the same way so that a
series of such increments are adjacent to one another in
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second bore 70 as seen in FIG. 3. By varying the quantity
of tungsten material and the amount of compression of the
powder which affects the density thereof different burn
rates of time delay mix 118 are obtained.
Below time delay mix 118 is a primary explosive 122. In
the preferred embodiment primary explosive 122 comprises a
titanium potassium perchlorate (TiKClO~) element 124 and a
lead azide element 126. Lead azide element 126 is encap-
sulated in a small cup 128.
Below primary explosive 122 is a secondary explosive 130
which preferably comprises a PYX charge 132 in an output
cup 134. Lead azide element 126 and small cup 128 are also
disposed in output cup 128 but are still generally con-
sidered part of primary explosive 122 rather than secondary
explosive 130.
A lower retainer 136, having a threaded portion 138
engaged with second threaded opening 76 in body 56, holds
ignition mix 116, time delay mix 118, primary explosive
122 and secondary explosive 130 in pla~e. ~ower retainer
136 defines a hole 140 therein which is in communication
with lower gun 22.
Operation Of The Invention
After apparatus 10 is positioned as desired in well bore
14, upper guns 20 are triggered in any manner known in the
art, and as also known in the art, sequentially fire one
another. The speed of this downward sequence is typically
on the order of about 8000 feet per second. This is much
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too fast for the operator to tell how many guns have fired.
When the lowermost one of guns 20 is fired, it ignites
detonation cord 54 which provides an explosive force against
the upper end of firing pin 92. This force is sufficient to
shear flange 98 so that firing pin 92 is moved downwardly
until pin portion 100 thereof impacts primer assembly 102.
Primer assembly 102 is thus detonated and the explosive for-
ces directed downwardly through central opening 106 in
primer retainer 104 and through holes 110 in screen 108 to
ignite ignition mix 116.
The heat from ignition mix 116 starts the burning of
time delay mix 118. The number and density of time delay
increments 120 is preselected so that a predetermined period
of time is required for time delay mix 118 to completely
burn, usually about 10 seconds, although any time may be
selected. Once this time has passed, titanium potassium
perchlorate element 124 is detonated by the burning of time
delay increments 120. The output of element 124 in turn
ignites lead azide element 126. Thus, in the preferred
:~ embodiment, two components of primary explosive 122 are
used.
The explosion from element 126 detonates PYX charge 132
of secondary explosive 130. The explosive output of secon-
dary explosive 130 is directed downwardly through hole 140
in lower retainer 136 and into lower gun 22. This explosive
force from secondary explosive 130 then triggers lower guns
22. The actual ignition of lower guns 22 is known in the
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art.
Thus, the operator at the surface fires the upper guns
which quickly and sequentially fire until time delay device
50 is actuated. Because of the time delay and burning of
time delay elements 120 in time delay means 118, the explo-
sive force necessary to trigger lower guns 22 is thus
delayed by the predetermined amount. When lower guns 22 do
fire, the significant noise and vibration resulting
therefrom is observed by the operator to occur this prede-
termined time after the firing of upper guns 20. In this
way, the operator knows that all of the guns have fired
because lower guns 22 fired. If all of upper guns 20 do not
fire, then time delay device 50 is never actuated, and the
operator will know that the perforation operation is
incomplete because the time delayed firing of lower guns 22
does not occur. As already noted, the tool can be inverted
so that the firing sequence is from bottom to top rather
than top to bottom. The components described herein would
be the same for such an orientation except that each of
those components normally would be inverted as well.
Once any of upper guns 20 are fired, fluid is free to
enter the tool string through those guns. All of upper guns
20 are in fluid communication with one another, and they
thus become filled with fluid. However, the time delay
device 50 positioned in housing 24 blocks any fluid com-
munication between upper guns 20 and lower guns 22. In the
event of misfire of upper guns 20, lower guns 22 will not be
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flooded with fluid. Thus, if the tool string is retrieved,
it is only necessary to replace the components above time
delay device 50. The time delay device and all of the com-
ponents therebelow may be reused without the necessity of
disassembly with cleaning or replacement of parts. This
feature of the present invention therefore provides a means
of fluid isolation on long gun intervals.
Several of housings 24 with time delay devices 50
therein could be positioned along the perforating string to
isolate the guns below each time delay device from the guns
thereabove. Thus, in addition to the time delay benefits,
this fluid isolation benefit saves considerable time in
retrieving and refitting a perforating string in which there
has been a misfire, and also insures the reuse of components
which would otherwise have to be disassembled with some
items replaced.
It will be seen, therefore, that the time delay per-
forating apparatus of the present invention is well adapted
to carry out the ends and advantages mentioned as well as
those inherent therein. While a presently preferred embodi-
ment of the invention has been described for the purposes of
this disclosure, numerous changes in the arrangement and
construction of parts may be made by those skilled in the
art. In particular, but not by way of limitation, different
explosive compositions may be used for the various com-
: ponents in addition to the specific compounds cited. All
such changes are encompassed within the scope and spirit of
appended claims.
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