Note: Descriptions are shown in the official language in which they were submitted.
Ll~O~
BACRGROUND OF THE INV~NTION
After a wellbore has been formed into the ground and the
casing has been cemented into place, the hydrocarbon containing
zone usually is communicated with the casing interior by forming
a plurality of perforations through the casing which extend
radizlly away from the casing and out into the formation, thereby
communicating the hydrocarbon producing zone with the interior of
the casing.
It is common practice to run a jet perforating gun downhole
1~ and to fire the gun by the emp~ayment of a gun firing head which
is actuated by a bar dropped down through the interior of the
tubing string. Completion techniques in~olving this known com-
pletion process are se~ forth in U.S. Patents 3,706,344 and
4,009,757-
A bar actuated firing head cannot be used in certain situa-
tions and someti~es it is desirable to be able to detonate the
charges of a perforating gun without the use of a bar. Particu-
larly it would be ad~antageous to actuate the qun by effecting a
pressure within the pipe string or annulus or both, but a gun
firing head which could be detonated in response to pressure
effected within the borehole has been considered to be highly
dangerous by many logging and completion engineers for the reason
that leakage across some of the critical seals of the firing head
could inad~ertently detonate the firing head and prematurely
explode the shaped charges of the gun. Should this misfire occur
at an inappropriate time, untold damage could be done to the
wellbore if, for example, the explosion occurred while running
the gun into the hole, or if the explosion occurred before proper
flo~ passageways back to the surface had been provided for the
completed formation. If a pressure actuated gun is to be safe,
it is necessary that the firing head be unable to detonate the
shaped charges until the gun has been lowered downhole and prop-
erly located relative to the formation to be completed.
'~
U.S. Patent 3,189,094 to Hyde discloses a hydraulically
operAted firing apparatus on a gun perforator for purposes of
formation testing. The firing apparatus assembly includes a
tubing string having a conventional formation tester valve in a
housing and a conventional packer secured below the housing.
Firin~ apparatus housings, along with the gun perforator, are
series connected to the tubing string below the packer. In
conducting a formation test, the assembly is lowered into a fluid
filled wellbore so that, externally, all pzrts of the assembly
are subjected to the submergence pressure exerted by the fluid in
the well. The formation tester valve is initially closed so that
the pressure within the empty tubing string is essentially at
atmospheric pressure. When the packer is set, the zone opposite
the gun is isolated from the region above the packer. There-
after, when the formation tester valve is opened, the zone oppo-
site the gun is exposed essentially to atmospheric pressure~ or
at least to a pressure which is greatly lower than the submer-
gence pressure of the fluid in the well. Although various
em~odiments of the firing apparatus are disclosed, all of the
embodiments utilize the submergence pressure to arm the firing
apparatus during descent of the assembly and then utilize the low
pressure condition created when the packer has been set and the
formation tester valve opens to cause a pressure differential
which operates the firing apparatus and fires the gun. The gun
perforator penetrates the surrounding formation so that the
formation fluids flow into the tubing string to complete the
formation testing operation.
The present invention overcomes the deficiencies of the
prior art.
SUMMARY OF THE DISCLOSURE
According to the invention there is provided a pressure
actuated firing head for deto~ating the shaped charges of a
perforating gun to which the head is connected. The gun is
o'~
suspended downhole in a borehole on a tubing string, and the
firing head is in fluid communication with the surface so that
pressure can be e~fected at the s-~rface down to the fîring head
to detonate the gun. The firing head is set to detonate the
shaped charges of the gun at a predetermined pressure.
The pressure is elevated to a predetermined value, thereby
moving a plug located in the head in response to the pressure.
This action closes ports located in a piston of the head, wherehy
pressure can now be effected on the upper face of the piston,
thereby driving the piston into engagement with an explosive
initiator. The initiator, when detonated by the piston movement,
causes the shaped charges of the gun to be detonated.
Prior ~o movement of the plug, the flow path from ~he sur-
face to an upper chamber, located above the piston, is closed,
ana the ports through the piston into a lower chamber, located
between the piston and the initiator, are open. Should leakage
of well fluids into the upper chamber of the firing head inadver-
tently occur, the apparatus is rendered inoperative because the
leaking fluid flows through the ports of the piston to the lower
chamber so that equal fluid pressure is placed on opposed faces
of the piston, thereby rendering the piston immovable and non-'
responsive to pressure.
In a more specific embodiment of the invention, the firing
head includes an elongated main housing having a passageway which
is in fluid communication with a flow path to the surface.
A relatively small inside diameter length of the passageway
is spaced from a relatively large inside diameter length thereof.
A relatively small outside diameter plug in the form of a piston
or plunger, is reciprocatingly received in sealed relationship
within the relatively small inside diameter length of the pas-
sageway. A relatively large outside diameter piston is recipro-
catingly received in sealed relationship within the relatively
large inside diameter length of the passage~ay.
1 2 ;3~0 L~ ~
A firing pin is connected at the lower end of the piston,
and the explosive initiator underlies the firing pin and is
adapted to explode when struck by the firing pin. The lower
chamber is formed below the piston.
An upwardly opening aperture is formed in the piston for
sealingly receiving a marginal end of the small outside diameter
plug therewithin. The upper chamber is formed above the piston
and a flow path extends from the upper chamber, through the
piston aperture and ports, and into the lower chamber. The upper
chamber is in communication with both the plug and piston. The
lower chamber is in communication with both the initiator and the
piston. A flow path extends from the surface, into the small
inside diameter length of the pass~geway to put pressure on the
plug. Spaced seals are placed about the plug to preclude flow
from the surface into the upper chamber.
In one embodiment of the invention, a bore extends from near
the upper end of the plug, through the plug, and into the upper
chamber above the piston to equalize pressure around the plug
should seals leak around a stem connected to and extending from
the upper end of the plug.
The stem extends upwardly to a location above the upper end
of the passageway where the stem i9 in fluid communication with
the surface and the upper end of the stem is exposed to pressure
from the surface. Upon application of a predetermined pressure
from the surface, the pressure forces the plug to move downhole
into sealed engagement with the aperture of the piston. Movement
of the plug opens fluid communication with the upper chamber and
therefore the piston so that pressure can be effected within the
upper end of the passageway and upper chamber, and the piston
forced to move dcwnwardly thereby causing the firing pin to
strike the initiator and fire the shaped charges of the jet
perforating gun.
r ~ .
1 ~3 ~C)~
Accordingly, pressure can be effected downhole frsm the
surface to initiate the first step required to actuate the gun
firing head. This moves the plug into the aperture of the
piston, thereby sealing the piston against flow therethrough.
This action also forms a flow path by which pressure effected
from the surface is also effected on the upper face of the
piston. The pressure differential across the plug and piston
drives the piston downhole, causing the firing pin to engage and
detonate the initiator.
~0 Also, should it be desirable and conditions permit, a bar
may be dropped down the pipe string to engage the upper end of
the stem to move the plug and piston downwardly to activate the
gun.
Should leakage occur into the area above the piston, it
becomes impossible to fire the gun because pressure across the
piston is equalized, and since there is no pressure differential,
the piston cannot be forced downwardly.
Accordingly~ a primary object of the present invention is
the provision of a fail safe, pressure actuated firing head for a
perforating gun which detonates the gun in response to a prede-
termined pressure being effected from the surface.
Another object of the present invention is the provision of
a pressure actuated firing head which can be actuated by using
only pressure from the surface, or by a combination of a bar and
the employment of hydraulic pressure.
A still further object o the present invention is the
provision of a pressure actuated firing head where a bar may be
dropped through a tubing string to impact the stem to partially
actuate the head, and thereafter pressure is utilized to detonate
the shaped charges.
A further object of the present invention is the provision
of a pressure actuated firing head for detonating the shaped
?
0i~
charges of a perforating -gun which will not explode should
leakage of well fluid into the apparatus inadvertently occur.
Another and still further object of the present invention is
the provision of a method of detonating the shaped charges of a
perforating gun which has a fail safe provision whereby leakage
of well fluid into the gun head renders the apparatus inopera-
tive.
An additional object of the present invention is the provi-
sion of a method of detonating the shaped charyes of a perforat-
ing gun by using pressure to move a plug into sealed engagementwith a piston and thereafter exposing the piston to the pressure
to move the piston into engagement with an explosive device so
that the explosive device detonates the shaped charges of the
perforating gun.
A still further object of this invention is the provision of
a method of perforating of hydrocar~on containing formation
located downhole in a cased borehole by the provision of a pres-
sure actuated gun firing head attached between a gun and the end
of the tubing string, and wherein the gun firing head is set to
detonate the shaped charges of the gun at a predetermined pres-
sure, and wherein the pressure is selected in accordance with the
anticipated downhole formation pressure~
Another and still further object of the present invention is
the provision of a method of perforating a pay zone located
downhole in a borehole by elevating the downhole pressure to a
predetermined value, dropping a bar down the tubing string,
whereupon the act of arresting the bar is used to move a plug in
order to seal an aperture located in a piston, and thereafter the
pressure forces the plug and piston to move into engagement with
an initiator which detonates the shaped charges of the perforat-
ing gun.
These and various other objects and advantages of the inven-
tion will become readily apparent to those skilled in the art
~ ~3 ~
upon reading the following detailed description and claims and by
referring to the accompanying drawings~
The above objects are attained in accordance with the pre-
sent invention by the provision of a method for use with appara-
tus fabricated in a manner substantially as described in the
above abstract and summary.
BRIEF DESCRIPTION OF THE DRhWINGS
For a detailed descr~ption of a preferred embodiment of the
in~ention, rPference will now be made to the accompanying draw-
ings wh~rein:
Figure 1 is a fragmentary, partly schematic, partly diagram-
matic, partly cross-sectional view of a well with a substantially
vertical boxehole and an apparatus made in accordance with the
present invention associated therewith;
Figure 2 is an enlarged cross-sectional view of part of the
apparatus disclosed in Figure 1 prior to actuation;
Figure 3 is a cross-sectional view of the apparatus dis-
closed in Figure 2 after partial actuation;
Figure 4 i5 a cross-sectional view of the apparatus dis-
closed in Figure 3 after full actuation and detonation of the'perforating gun;
Figure 5 is an enlarged cross-sectional view of another
embodiment of the apparatus disclosed in Figures 2 through 4;
Figure 6 is a cross-sectional view taken along line 6-6 of
Figure 5;
Figure 7 is an enlarged cross-sectional view of the embodi-
ment of Figure 5 after partial actuation;
Figure 8 is an enlarged cross-sectional view of the em~odi-
ment of Figure 5 after full actuation and detonation of the
perforating gunF
Figure 9 is a fragmentary, partly schematic, partly diagram-
matic, partly c.ross-sectional view of a highly deviated well and
~L~3L1~)4~
an apparatus made in accord nce with the present inventlon asso-
ciated therewith;
Figure 10 is a partly schematic, partly diagrammatic view of
a well for perforation of multiple portions of the cased borehole
using a plurality of apparatus made in accordance with the
present invention associ~ted therewith; and
Figure 11 is a fragmentary, partly schematic, paxtly dia-
grammatic, party cross-sectional view of a well and a perforating
gun having both a bar-actuated firing head and the apparatus of
the present invention.
DETAILED DESCRIPTION O~ THE PREFERRED EMBODIMENTS
Referring initially to Figure 1, there is disclosed a typi-
cal well having borehole 10 extending downhole from the surface
12 of the ground through a hydrocarbon-containing formation 14.
The borehole 10 is cased by a string of casing 16 hung from
wellhead 18 and within surface casing 20. Casing string 16 is
cemented into boxehole 10 and casing 20 as shown at 22. Casing
16 isolates the wellbore 24 from formation 14. A string of
production tubing 26 is suspended within casing 16 and extends
from the surface 12 axially through casing 16. Tubing 26 within
casing 16 forms borehole annulus 28, and pac~er 30, disposed on
tubing 26, divides the borehole annulus 28 into an upper annulus
32 and a lower annulus 34. Suitable outlets are provided at the
surface 12 for the tubing flow bore and each annulus formed by
adjacent casing strings with each of the outlets being provided
with suitable valves and the like, including ~alve 36 for the
outlet communicating with the borehole annulus 28 and valves 38,
39 for the outlet communicating with the flow bore 40 of tubing
string 26. A lubricator 42 is provided for access to tubing flow
bore 40 for the use of slick line tools.
In order to complete the well or test the formation, it is
necessary to access the hydrocarbons in fonmation 14 with the
, .r~,
~ 2 3'~ Z
wellbore 24. This is accomplished by supporting a perforating
gun 50 at the lower end of the tubing string 26. Gun 50 is
preferably a jet casing gun j but it should be understood that the
term is intended to include any means for communicating the
hydrocarbon producing formation 14 with lower annulus 34. The
jet perforating gun of the casing type shoots metallic particles
into the formation 14 to form perforations 44 and corresponding
channels or tunnels 46. Numerals 44 and 46 broadly indicate a
few of a plurality of perforations. and tunnels which are formed
when the charges 52 of gun 50 are detonated. Perforating objec-
t~ves include perforations of a desired size and configuration,
prevention of further formation invasion and contamination during
the perforating process, and maximum capacity to mo~e the hydro-
carbons from formation 14 to lower annulus 34.
During the drilling of the borehole 10, the formation pres-
sures are controlled by weighted drilling fluid, filtrate and
perhaps fines which invade the formation, interacting with in
situ solids and fluids to create a contaminated zone 48, reducing
permeability, and leaving on the face of formation 14 a low-
permeability filter cake. The cementing operation also includes
fluids and fines which invade and damage the formation 14 at the
contaminated zone 48. Thus, the jet perforatlng gun 5~ of the
casing type using shaped charges 52 must penetrate deeply into
the formation 14 to form tunnels 46 that pass through casing 16,
cement 22, and contaminated zone 48 and into the uncontaminated
or sterile zone 54 of formation 14. ~erforations 44 and tunnels
46 form the final passageways which enble the hydrocarbons to
flow from the formation 14, through tunnels 46 and perforations
44 and into lower annulus 34 for movement to the surface 12.
Various tool strings may be included with tubing string 26,
packer 30, and gun 50 to complete the well and/or test the forma
tion. Figure 1 illustrates one variation of a tool string to
complete the well and transport the hydrocarbons contained in
~ ~ 3'~Q~
formation 14 to the surface. As shown, the tool string includestubing string 26, a perforated nipple or vent assembly 56, a
releasable coupling device 58, packer 30, a pressure actuated
firing head 60 in accordance with the present invention, and
casing perforating gun 50.
Vent assembly 56 is located in underlying relationship
relative to packer 30 and made of the designs described in U.S.
Patents 4,151,830; 4,040,485 and 3,871,448. Although not essen-
tial, it is sometimes desirable to include a releasable coupling
~o 58, such as described in U.S. Patent 3,966,236, to release gun ~0
after detonation.
Perforating gun 50, such as disclosed in U.S. Patents
3,706,344 or 4,140,180, is connected to the lower end of tubin~
string 26 and includes shaped charges 52 of known design, which,
when detonated, form perforations 44 through the sidewall of
casing 16 and form tunnels 46 which extend radially from borehole
10 and back up into the sterile zone 54 of formation 14.
In the tool string shown in Figure 1, pressure firing head
60 forms the upper end of perforating gun 50. Pressure actuated
firing head 60 connects the housing or charge carrier of gun 50
to the lower end of tubing string 26; and, tubing string 26,
casing 16, packer 30, vent assembly 56, releasable coupling 58,
gun firing head 60, and jet firing gun 50 are all more or less
arranged along a common axial centerline. In some instances,
borehole 10 may be deviated, or slanted almost bac~ to the hori-
zontal as shown in Figure 9, and in that instance, the apparatus
o~ the tool string may instead be eccentrically arranged relative
to one another. This invention can therefore be used in vertical
as well as slanted boreholes and is especi~lly adapted for use
where difficulty is experienced in actuating the gun firing head,
as for example in instances where a bar cannot be gravitated
downhole, or where a slick line cannot be used in conjunction
~'~3 ~
with a bar or fishing tool in order to detonate the gun firing
head by impact.
Although various methods of operation will be hereinafter
set forth r ~riefly, the well is typically completed by setting
packer 30 and opening vent assembly 56, pressurizing the fluid in
flow bore 40 of tubing string 26 to actuate firing head 60 r
detonating gun 50 r perforating formation 14, and flowin~ hydro-
-carbons into the lower annulus 34 r through open vent assembly 56 r
and up tu~ing flow bore 40 to the outlet valve 38.
Referring now to Figure 2 for a description of one embodi-
ment of the present invention, the pressure actuated firing head
60 includes a tubular housing 62 composed of an upper cylinder 64
and a lower mandrel 66. Cylinder 64 has an outer cylindrical
surface 68 which is of the same diameter as the outer cylindrical
surface 72 of mandrel 66. An axial fluid passageway 70 extends
the length of cylinder 64 and includes a counter~ore forming box
74 at the lower end thereof. Reference to "lower" and "upper"
parts of the present invention refers to their position shown on
the drawings attached hereto for convenience and does not neces-
sarily indicate their position during actual operation. Although
firing head 60 is shown positioned in one direction in the well'
as shown in Figure 1, head 60 is positioned in the opposite
direction as shown in Figure 11. Thus references to "lower" or
"upper" are not to be limiting.
Mandrel 66 includes a reduced diameter portion or pin 76
which is telescopingly received within box 74 of cylinder 64.
Pin 76 is threadingly engaged to box 74 at 78 by external threads
on pin 76 and internal threads on box 74. Pin 76 forms an
annular shoulder 82 for seating the lower end of cylinder 64 upon
complete attachment. Set screws 84 are provided in threaded
bores in the lower end of cylinder 64 to er.gzge the out~r surface
of pin 76 and prevent any inadvertent disengagement of cylinder
64 and mandrel 66. Pin 76 has annula. seal grooves in whicn are
-`` ?
~ ~ 3~0 ~
disposed sealing members 112, 114 for sealing engagement with the
internal surface of box 74 to prevent lea~age at connection 78.
At the upper end of cylinder 64 is a tapered threaded pin 86
and tapered shoulder 88 for making connection with one of the
pipe membçrs making up tubing string 26. The pipe member of
string 26 adjacent pin 86 has a threaded box which threadingly
receives pin 86 for mounting firing head 60 onto tubing string
26. Pipe readily available at the well site is often used for
tubing string 26. Since that pipe may often be drill pipe or
lo drill collars, the connection on the upper end of housing 62 may
be a rotaxy shouldered connection compatible with such pipe.
Mandrel 66 includes a lower threaded box end 92 for thread-
ingly rece~ving a sub 51 on the upper end of perforating gun 50.
Pin 76, extending above box end 92, has a central bore 80 gener-
ally having the same internal diameter as axial passageway 70 in
cylinder 64. Central bore 80 has a lower counterbore 94 adja-cent
box end 92 for receiving initiator 90 as hereinafter described,
and is restricted by an inwardly directed annular shoulder g6
located near the upper end of pin 76. Annular shoulder 96
includes an upwardly facing seat 98 forming an insert counterbore
102 with the upper portion of bore 80 and a downwardly facing
seat 104 forming a chamber 100 with the lower portion of boxe 80.
Insert counterbore 102 receives closure assemhly 110, hereinafter
described, and chamber 100 houses piston 120, hereinafter
described. The upper end of bore 80 is bevelled at 106 for
receiving closure assembly 110, and pin 76 is reduced in outer
diameter at 108 along its upper end.
Piston 120 is slidingly received by chamber lO0 for recipro-
cation therein and has annular grooves housing upper and lower
O-ring seals 116, 118, respectively, for sealing engagement with
the inte,nal cylindrical surface of chamber lO0.
Initiator 90 is mounted within a bore 122 in an initiator
support 124 which is telescopingly received within lower ccunter-
bore 94 of central bore 80. Support 124 has O-rings 126 disposed
in annular grooves therearound for sealing with the internal
surface forming counterbore 94. Counterbore 94 and bore 80 form
a downwardly faciny annular shoulder 128 for abutting the upper
face 130 of support 124. As the sub Sl of perforating gun 50 is
threaded into box end 92, the upper end of the sub 51 engages the
lower face 132 of support 124 and the lower end of initiator 90
to secure suppsrt 124 and initiator 90 within lower counterbore
94. Initiator 90 supports a plurality of seal rings 134 on its
exterior for sealing engagement with the inner surface of bore
122 and has an elastomeric ring 135 on its upper end to take up
any end play as sub Sl is threaded into end 92. A prima cord 53
extends from initiator 90 to the shaped charges 52 of gun 50
whereby upon the initiation of initiator 90, charges 52 are
detonated. ~he upper end of bore 122 is reduced in diameter
forming an entry bore 136 for a firing pin to be described.
Piston 120 includes a reduced diameter lower end 138 which
supports a firing pin 140 positioned on piston 120 to be received
by entry bore 136 when piston 120 is moved to its lowermost'
position. Firing pin 140 has threads on one end which is
threaded into a hole at 142 in the lower face of end 138 and
secured by a set screw (not shown), and a point 146 for impacting
and setting off initiator 90. As best shown in Figure 2,
initially piston 120 is secured by shear pins 150 in an uppermost
position against lower seat 104 in chamber 100. Shear pins 150
are sized to shear ~pon the application of a predetermined pres-
sure force on the upper face of piston 120.
Closure assembly 110 is mounted on pin 76 to open and close
fluid communication with chamber 100. Assembly 110 includes a
generally cylindrical bonnet 152 having a lower threaded end 154
and an outwar~ly extending radial annular flange 156. The
aperture through annular shoulder 96 of pin 76 is threaded to
3~1)'1~
threadingly engage at 155 end 154 and secured closure assembly
110 to the upper end of pin 76. Annular flange 155 is slidingly
received by insert counterbore 102 and ~ncludes an O-ring seal
158 received in an annular groove in the radial circumference of
shoulder 156 to seal with the internal wall forming insart coun-
terbore 1~2.
Closure assembly 110 further includes a piston member or a
plunger or a plug 160 reciprocably reoeived in a cylinder 162
formed by cooperating blind bores 164, 166 in bonnet 152 and
piston 120, respectively, having a common inner diameter. Each
mouth of blind bores 164, 166 is conically tapered for ease of
passage of plug 160 between bores 164, 166. Bonnet bore 164, as
shown, opens downwardly opposite the upwardly facing open end of
piston bore 166. The bottom 172 of bonnet blind bore 164 has a
hole 168 for slidably recei~i~g a shaft or stem 174 on plug 160
extending upwardly therethrough. Stem 174 has a stop shoulder
176 which engages bottom 172 to limit the upward movement of plug
160 within bonnet bore 164. A stem head 178 may be threaded at
179 onto the uppermos~ end of stem 174 where auxiliary bar actua-
tion of head 60 may be desirable. The piston portion of plug 160
has annular grooves therearound in which are housed O-ring seal
members 182, 184 for sealingly engaging the cylindrical walls of
cylinder 162 as plug 160 reciprscates therein.
~onn~t bore 164 is part of a fluid flow path which ulti-
mately extends to the surface 12. A plurality of radial fluid
ports 180, located adjacent bottom 172 of bonnet bore 164, extend
from blind hore 164 to the exterior of bonnet 152 and axial fluid
flow passageway 70 of cylinder 64. Shoulder 176 of stem 174
pre~ents plug 160 from moving over bonnet ports 180 so as to
damage O-ring seal members 182, 184. Initially, as shown in
Figure 2, plug 160 is in the upper and bonnet port sealing posi-
tion preventing any fluid flow from passageway 70 to chamber 100.
Plug 160 is held in the upper position by shear pin 188 sized to
shear upon tne application of a predetermined fluid pressure in
~ ~ 340~
passageway 70 through bonnet ports 180 and that portion of bonnet
bore 164 above plug 160. Roll pins 189 pass through closure
assembly 110 to hold shear pin 188 in position.
Shear pins 188 determine the amount of fluid pressure
required in passageway 70 to actuate firing head 60. Where head
60 is to be actuated solely by fluid pressure, i.e. without the
use of a bar, shear pins 188 are sized to shear at a predeter-
mined pressure approximately 2000 to 3Q00 psi above hydrostatic
pressure. The hydrostatic pressure is th~ heavier of the hydro-
static head in the casing annulus 28 or the tubing flow bore 40.
If the predetermined pressure were calculated based on the tubing
flow bore hydrostatic and the casing annulus hydrostatic was
greater than the predetermined pressure set to shear pins 188, a
leak from the casing annulus into the tubing flow bore might
raise the fluid pressure in passageway 70 to the predetermined
pressure and prematurely detonate gun 50. Thus, shear pins 188
must be heavy enough to insure that pins 188 will not be sheared
by the largest hydrostatic head in the well.
Piston bore 166 also has a plurality of radial fluid ports
190 located adjacent the bottom 192 of piston bore 166 permitting
fluid flow between that portion of chamber 100 abo~e piston 120,'
i.e. upper chamber lOOA, and that portion of chamber 100 below
piston 120, i.e. lower chamber lOOB. So long as piston ports 190
are open, the fluid pressures will be equal in upper and lower
chambers lOOA, lOOB since ports 190 will permit equalizing flow
therebetween. This flow pathway between chambers lOOA, lOOB
provides a pressure balancing means across piston 120 to prevent
the inadvertent and premature detonation of gun 50 due to a
pressure buildup in upper chamber lOOA. For example, if plug
seals 182, 184 or bonnet seal 158 were to leak fluid from axial
fluid passageway iO i~to upper chamber lOOA, such a pressure
increase would merely equalize across piston 120 due to flow
through piston ports 130 into lower chamber lOOB.
1;23'~04~
Referring now also to Figure 3 showing partial actuation,
shear pin 188 is sheared by increasing the fluid pressure in
axial passageway 70 which, when applied to the cross-sectional
area of stem 174 projecting into passageway 70 and to the remain-
ing cross-sectional area of plug 60 in that portion of bonnet
bore 164 above plug 160 via bonnet ports 180, the force will
reach the predetermined amount which will shear pin 188. The
pressure on plug 160 and stem 174 causes plug 160 to move down-
wardly in cylinder 162, passing from bonnet bore 164 where bonnet
lG ports 180 are sealed to piston bore 166 where seal memhers 182,
184 of plug 160 sealingly engage the cylindrical wall of piston
bore ~66 and seal off piston ports 190.
Referring now also to Figure 4, pressure actuated firing
head 60 is shown fully actuated. By unsealing bonnet ports 180 !
the fluid from axial passageway 70 now flows into upper chamber
lOOA. Further, because plug 160 has now sealed piston ports -l90,
a pressure differential is effected across piston 120. Upon the
application of this increased fluid pressure onto the upper face
of piston 120 and the impact of plug 160 engaging bottom 192 of
piston bore 166, pins 150 are sheared. Sh~ar pins 150 for piston
120 may be larger than shear pins 188 for plug 160 because the
cross-section of piston 120, i.e. pressure area, is greater than
the cross-section of plug 160. Since piston 120 is substantially
heavier than plug lZ0, pins 150 need to be larger to pass the
drop test. Pins 150 are not strong enough to withstand the
hydrostatic head and would shear.
Upon shearing pins 150, piston 120 moves downwardly in
chamber 100 with the point 146 of firing pin 140 impacting ini-
tiator 90 to detonate charges 52 of perforating gun 50. Piston
120 snaps downwardly to provide a substantial lmpact of pin 140
with initiator 90. The lower fzce of piston 120 engages the
upper face 130 of support 124 to arrest the downward movement of
piston 120.
~ ~3~ L~
In operation, fluid pressure is effected into passageway 70
t~ actuate head 60. Although normally the fluid pressure will be
hydraulic pressure from a liquid, it is possibie that a gas may
be used to actuate head 60. Further, fluid pressure may be
effected in passageway 70 by pressuring down the flow bore 40 of
tubing string 26, or pressuring down the casing annulus 28, or
pressuring down both the tubing flow bore 40 and casing annulus
28, or pressuring down a flow path made up of portions of tubing
flow bore 40 and casing annulus 28 to communicate with passageway
l~ 70.
The pressure effected into passageway 70 is hydrostatic
pressure plus a safety margin pressure such as 20~ of hydrostatic
pressure or about 2000 to 3000 psi. Again the heaviest hydro-
static pressure in the well is used to calculate the predeter-
mined pressure required to actuate firing head 60. Once the
fluid pressure in passageway 70 exceeds the predetermined pres-
sure limit for shear pins 188, pins 188 shear and free plug 160
to move dow~wardlyO
A su~stantial pressure differential is created across plug
160. On the upper face of plug 160 and stem 174 is hydrostatic
pressure plus 2000 to 3000 psi and on the lower face of plug 160
is atmospheric pressure since cylindex 162 and chamber 100 are at
atmospheric. As plug 160 moves downward under the pressure
differential, seal 182 continues to seal with bonnet 152 until
after lower seal 184 has sealingly engaged the walls of cylinder
162 of piston 120. As plug 160 moves into cylinder 162, any
trapped pressure is exhausted through piston ports 190v Once
plug 160 is received within cylinder 162 and seal 184 has sealed
with piston 120, ports 190 in piston 120 are closed preventing
free fluid flow between upper and lower chambers 100A and 100B.
At that time upper seal 182 disengages with bonnet 152 and
~ 23~
permits the fluid pressure of passageway 70 to pass into upper
chamber lOOA and be applied to the cross section of piston 120.
Fluid from passageway 70 flows through hole 168 between stem 174
and bonnet 152 and through bonnet ports 180 into blind bore 164
in bonnet 152. The fluid then passes from bore 164 into upper
chamber lOOA.
Upon the application of the fluid pressure from passageway
to piston 120, a pressure differential is created across
piston 120. The fluid pressure from passageway 70 is applied to
the upper face of piston 120 and atmospheric pressure is on the
lower face of piston 120 since lower chamber lOOB is at atmos-
.pheric~ This large pressure differentlal causes piston 120 to
snap downwardly. The lower reduced diameter portiQn around
piston 120 prevents any pressure lock as piston 120 moves down-
ward to cause firing pin 140 to impact initiator ~0.
The force of impact between pin 140 and initiator 90 ignites
prima cord 53 which in turn detonates the shaped charges 52 of
jet perforating gun 50. The formation 14 is perforated forming
perforations 44 and tunnels 46 to permit the hydrocarbons of
formation 14 to flow into annulus Z8.
Figures 5-8 illustrate another embodiment of the present
invention. Referring initially to Figures S and 6, the other
embodiment of the pressure actuated gun firing head 200, as
illustrated, is seen to include a main body composed of an upper
main body part 202 substantially the same as cylinder 64 of the
first embodiment including a cylindrical axial passageway 70
formed on the inside thereof, which enlarges in diameter into an
internally threaded surface 203, and terminates in a circumfer-
entially extending edge portion 204.
The main body includes a lower main body part 206 terminat-
ing in a female threaded interior surface 208, hereinafter also
called "a box or a box endn. The box end 210 has a circumferen-
tially extending lower terminal e~se portion 212.
~ ?~--\
1~34~
The box end 210 includes an axial bore 214 which is reduced
in diameter at 216. The outside diameter of the upper end of the
lower main body part 206 is reduced in diameter commencing at 204
to provide reduced diameter part 218. Outer surface 218 and
inner surface 220 are made in close fitting relationship relative
to one another so that one slidably receives the other in a tele-
scoping manner therewithin. The before mentioned coacting
threaded areas 203 releasably fasten the upper and lower main
body parts 202, 206 together.
An annular boss 224 projects inwardly from housing 200 and
is internally threaded at 226. The boss 224 increases in
diameter to provide a cylindrical portion 228, which again
increases in insi.de diameter at 230 to provide the illustrated
upper constant diameter inner surface which terminates at the
upper terminal end thereof in the ~orm of a shoulder 232.
The upper main body part 202 includes a shoulder 234 which
- is slightly spaced from the confronting shoulder 232. Axial
passageway 70 is in communication with the interior of the tubing
string 26. Trigger device 236 is positioned within the axial
passageway 70 and includes a shaft 238.
Shaft 238 is slidably received in close tolerance relation-
ship within a bore 240 in bushing 242. O-ring 244 seals the
interface between the bore 240 and the shaft 238. Shaft 238 is
screwed into the upper end of piston piug 250 which is of larger
diameter than shaft 238. O-ring 246 seals the interface between
the enlarged bore 248 and piston plug 250. The lower end of
pi.ston plug 250 is larger in diameter than the upper end provid-
ing a transition portion at 251. Circumferentially extending
grooves on piston plug 250 house an upper O-ring 252 and a lower
O-ring 2S4. O-ring 252 seals with further enlarged bore 256 of
bushing 242. Numeral 258 indicates the lower terminal end of
piston plug 250.
As best shown in Figure 5, bushing 242 is secured ~o lower
body part 206, and is provided with a contouxed entrance at 260.
Bushing 242 further includes an outer surface area defined by
outside diameter 262. The bushing is spaced from the wall of
axial bore 70, thereby forming an upwardly opening annulus 264.
The annulus 264 communicates with bore 256 by means of the illus-
trated radial passageway 270. The upper reduced diarneter end of
piston plug 250 includes at least one radial passageway 272 which
communicate with an axial passageway 274 which leads to a lower
radial passageway 276. Radial passageway 276 coTnmunicates, via
axial passageway 274, with the upper end of piston plug 250 which
is isolated from well fluids by means of the spaced O-rings 244
and 246.
Should well fluids leak past seal 244 or 246 to act on the
upper end of piston plug 250, it will also be conducted by pas-
sages 272, 274, 276 to lower end 258 of piston plug 250 and exert
there a balancing force so that piston plug 250 will not be
moved. The upper end of piston plug 250 is releasably affixed to
bushing 242 by means of radially disposed shear pins 278. Shear
pins Z78 are selected to fail upon the application of a predeter-
mined force, as will be more fully discussed hereinafter.
In this embodiment of the present invention, shear pins 278
may be somewhat smaller. Because that portion of bore 248
between seals 244, 246 communicates with upper chamber 284, via
ports 272, 274, 276, there is atmospheric pressure on both sides
of the small diameter portion of plug 250 having little tendency
for moving plug 250. The only down force on plug 250 is the
difference in cross-sectional area between the larger lower
portion of piston 250 and the smaller upper portions of piston
250. Thus the smaller pins 278 can pin against a high hydro-
static.
Large piston 280 has an upwardly opening passageway 282
formed therewithin which is in communication with an upper
~34~
chamber 284 when the firing head is in the standby configuration
as shown in Figure 5. Lateral ports 286 place the lower chamber
288 in co~munication with piston passageway 282.
Initiator support 292 underlies the piston 280 and has an
outside diameter 294 fitting closely within the before mentioned
axial bore 214. The support 292 is provided with an axial bore
296 which sealingly receives the initiator 290 in sealed rela-
tionship therewithin, noting the plurality of spaced O-rings
located bet~een the initiator 290 and the bore 296. O-rings 298
lC seal the interface between outside diameter 294 and axial ~ore
214. Piston 280 is reduced in diameter at lower end 302 thereof.
The upper face 304 of piston 280 is disposed within the interior
of chamber 284. Lower face 308 of piston 280 is disposed within
lower chamber 288. The lower end of piston 280 is again reduced
at 310 to provide a ~iring pin 300 at the lower extremity
thereof.
Radial shear pins 312 are formed through the sidewall of the
lower main part 206 and extend into bores formed in a sidewall of
piston 280. Shear pins 312 are sized to insure that pins 312 do
not shear due to the weight of piston 280 or due to head 60 being
accidentally dropped. O-rings 314 seal against fluid ~low across'
the shear pins 312 and across the threads 203. O-rings 316
further seal against flow which may occur across shear pins 312
or from upper chamber 284 into lower chamber 288 under certain
conditions of operation, as will be further discussed later on in
this disclosure.
Locking screws 318 prevent inadvertent relative motion
between the upper and lower main body parts 202 and 206. Prima
cord 320 is routed through passageway 322 of sub 51 associated
with gun 50. The prima cord 320 is attached to the initiator
290, and to the shaped charges 52 so that when the firing pin 300
strikes face 324 of initiator 290, initiator 290 explodes, which
in turn explodes prima cord 320, and this action instantaneously
.~2~ Z
detonates all of the shaped charges 52 associated with the gun
50. In actual pxactice, the initiator explodes and thereafter
the prima cord 320 is progressively exploded, with each of the
shaped oharges 52 being se~uentially exploded; however, the time
frame within which this explosive train occurs is of such a short
duration that one could call this action "instantaneous",
although those skilled in the art of measuring phenomena that
occur within a millisecond would probably consider that the
explosion train requires a time duration.
Referring now to ~igure 7 showing partial actuation, shear
pin 278 is sheared by incre~sing the fluid pressure in passagewzy
? which, when appli~d to the cross-sectional area of shaft 238
projecting into passageway 70 and to the remaining cross-
sectional area of piston plug 250 in bore 256 ~ia ports 270, the
force will reach the predetermined amount which will shear pins
278. As piston plug 250 and shaft 238 move downwardly, the lower
end o~ piston plug 250 with O-ring seal 254 enters piston
passageway 282 where O-ring seal 254 sealingly engages piston
plug 250 and large piston 280 to close off lateral ports 286 in
large piston 280. Then, O-ring seals 244 on sha~t 238 and seal
ring 246 on the upper end of piston plug 250 mo~e into enlarged'
bushing bores 248, 256, respectively whereby seals 244, 246
disengage their sealing engagement with bushing 242. Further, as
piston plug 250 moves out o~ bore 256 of bushing 242, O-ring seal
252 also unseals with bushing 242. However, prior to the disen-
gagement of seals 244, 246 and 252, the lower seal 254 on piston
plug 250 sealingly engage the cylindrical wall of bore 282 in
piston 280 which in turn seals off piston ports 286. When plug
250 ~ottoms in cylinder 282 of piston 280, radial ports 272 are
in communication with ports 270.
As illustrated in Figure 7, the fluid in passageway 70 is
now free to flow around bushing 242 in annulus 264 and through
bushing ports 270. Further, the fluid in passageway 70 can ~low
~ f'~
.1 ~ ;~ ~iL O ~
down bushing bore 240 between shaft 238 and bushing 242. Once
the fluid from passageway 70 reaches enlarged bushing bore 256
from either bore 242 or ports 270, the fluid can pass through
passageways 272, 274 and 276 in plug 250 into upper chamber 284
or through bushing bore 256 between piston plug 250 and ~ushing
242 into upper chamber ~84.
Referring now to Figure 8, pressure actuated firing head 200
is shown fully actuated. By unsealing ports 270 and unsealing
shaft 238 and piston plug 250 with bushing 242, the fluid pres-
sure from passageway 70 is applied in upper chamber 284.
~urther, because piston plug 250 has now sealed off piston ports
286, a fluid pressure differential is effected across large
piston 280. Upon the application of this increased fluid pres-
sure onto the upper face 304 of piston 280, and the impact of
piston plug 250 engaging the bottom of piston bore Z82, pins 312
are sheared and piston 380 moves downwardly in lower chamber 288
with firing pin 300 impacting initiator 290 and thereby detonate
charges 52 of perforating gun 50. Piston 280 snaps downwardly to
provide a substantial impact between firing pin 300 and initiator
290.
Should it be necessary to remove the tool string from the'
well for some reason such a~ the failure of the gun to discharge,
the packer may be unseated and the tool string raised. An
inadvertent activation of the firing head is not of concern. The
previously discussed safety features render the firing head safe.
The pressure effected on the firing head is reduced as the tubing
string is raised and the large piston remains pressure balanced.
The present invention may be used in a variety of applica-
tions. Figure 9 illustrates the use of the present invention in
a highly deviated well where a bar-actuated firing head cannot be
used because the bar will not travel down the tubing string with
enough speed to sufficiently impact a bar actuated firing head.
0'~
As shown in Figure 9, casing 16 extends downwardly in the verti-
cal direction and then is turned to a substantially horizontal
position. A tool stxing consisting of a packer 30, vent assem~ly
56, pressure ac~uated firing head 60, and jet perforating gun 50
suspended on a tubing string 26 is lowered into casing 16 until
gun 50 is adjacent formation 14. Tubing strin~ 26 is filled with
a fluid. Packer 30 is set and vent assembly 56 is opened. It
should be understood that a perforated nipple may be used rather
than a vent assembly. Pump pressure is applied down the ~low
bore 40 of tubing string 26 to actuate firing head 60 and fire
gun 50. The pump pressure is bled off to produce formation 14.
In this application, the perforating gun 50 is actuated without
the use of a bar.
Another application of the present invention is illustrated
in Figure 10. In this application the present invention is used
to test a plurality of payzones through a single tubing string.
Referring to Figure 10, there is shown a casing 350 extending
through a plurality of payzones such as upper payzone 352 and
lower payzone 354. The tool string includes an upper packer 356,
an upper vent 358, an u~per pressure actuated firing head 360, an
upper perforating gun 362, a lower packer 366, a lower vent 368,'
a lower pressure actuated firing head 370, a lower perforating
gun 372 and a bull plu~ 364, all suspended on tubing string 374.
Bull plug 370 closes the lower end of tubing string 374.
Although only two payzones and corresponding perforating guns are
shown, it should be understood that any number o payzones could
be tested by adjacent perforating guns mounted on tubing string
374. Upper and lower pressure actuated firing heads 360, 370 and
upper and lower perforating guns 362, 372 are mounted on the
exterior of tubing string 374. Each pressure actuated firing
head is in fluid communic~tion with the tubing flow bore of
tubing string 374 by means of a ported connector whereby pressure
,r~,
12~3'~f~
effected down the tubing flow bore of string 374 is applied to
the respective plugs 0c firing heads 360, 370. Vents 358, 368
may be sliding sleeves or one-way valves for the passage of
production fluids into the tubing 10w bore of string 374 after
perforation. It should be obvious that a bar cannot be used in
this situation since the perforating guns are disposed outside
the tubing string. The shear pins 188 in firing heads 360, 370
are se~ at 500 psi intervals whereby the lowest firing head 370
and ~un 372 will be actuated first. Thus lower pressure actuated
firing head 370 has shear pins 188 set to shear at a predeter-
mined pressure 500 psi lower than the predetermined pressure set
to shear the pins 188 in upp~r pressure actuated firing head 360.
In operation, lower packer 366 is set to isolate payzone 354.
When the invention is used in a new well such that the annulus
below packers 356, 366 can be pressurized, lower vent 368 may be
a sliding sleeve which is opened using a wireline prior to per-
forating. Pressure is then effected down tubing string 374 until
shear pins 188 of lower firing head 370 are sheared and gun 372
is detonated. Prduction is then permitted into tubing string 374
via lower vent 368. After lower payzone 3S4 is tested, lower
vent 368 is closed and upper packer 356 is set if it has not'
already been set. Uppe~ vent 358 is then opened and pressure is
again applied through tubing string 374 until pin~ 188 in upper
firing head 360 are sheared and payzone 352 is perforated for
testing. Production is then permitted into tubing string 374 via
upper vent 358. Where the annulus below packers 356, 366 cannot
be pressurized, as for example where there are existing perfora-
tions already in payzones 352, 3~4, vents 358 r 368 may be one-way
valves which are opened to the flow of production fluids after
perforation either by bleeding the pressure off from tubing
strlng 374 or swabbing string 374 to open the one-way valve.
A still another appllcation of the present lnvention is with
a workover operation where the well ha~ previously been perfo-
~ ~ 3 L~ ~ L~
rated. As shown in Figure 1, a tool string with z packer 3G,vent assembly 56, releasable coupling 58, pressure actuated
firing head 60, and jet perforatiny gun 50 suspended on tubing
string 26 is run into the well with the vent assembly 56 closed.
Tubing strLng 26 is ~illed with fluid. Packer 30 i5 hydraulic-
ally set. Pump pressure is applied down the flow bore 40 of
tubing string 26 to ac~uate firing head 60 and f ire gun 50. Vent
assembly 56 is then opened, and the pump pressure is bled off or
the tubing string is swabbed to bring in the well. Vent assembly
56 could not have been opened prior to detonation due to the old
perforations in the payzone. Vent assembly 56 may be a sliding
sleeve or a check valve which opens when the
pressure in the tubing string is reduced. No underbalance, i.e.
downhole pressure less than formation pressure, is used. The
same procedure may be used in a new well where an overbalance is
desired, i.e. downhole pressure greater than formation pressure.
Gun S0 may b~ dropped by using releasable coupling 58.
In another application, the activation of head 60 is initi-
ated by dropping a bar. Where a bar may be dropped down tubing
string 26, a tool string with packer 30, vent assembly 56, Liring
head 60, and gun 50 suspended on tubing string 26 is run into the'
well with vent assembly 56 closed. Tubing string 26 is filled
with a light ~luid such as water creating a hydrostatic head
substantially less than the formation pressure so as to create an
underbalance. However, the shear pins 188 in the piston plug 160
require a force in excess of the hydrostatic head in the casing
annulus 28 plus a safety margin pressure. In order to maintain
the underbalance, it is necessary to actuate head 60 without
pressuring down the tubing flow bore 40 an amount necessary to
shear pins 188 since such a pressure would cause an overbalance
situation. Thus, a bar is dropped down the tublng string 26 to
open vent assembly 56 and impact head 178 on stem 174 OL plug 160
to shear pins 188 and open upper chamber lOOA to the hydrostatic
lz~3~a)~
head of the fluid in tubing flow bore 40. Although the hydro-
stztic head in tubing flow bore 40 i5 insufficient to shear pins
188, it is sufficient, when applied to the larger pressure area
of piston 120, to shear pins 150 and actuate head 60~ Thus, the
bar and hydrostatic head are used in combination to actuate head
60.
In this application, firing head 160 also acts as a fail
safe device. If, after dropping the bar, thP head does not
actuate because, for example, there is debris in the tubing
string preventing the bar from having sufficient impact on head
178 to shear plns 188, the operator has a second chance. Rather
than attempting to fish out the bar or unseat the packer and
remove the tubing string, pump pressure is added to the hydro-
static head in the tubing flow bore 40. Once the pressure in the
tubing flow bore 40 reaches the predetermined pressure, pins 188
are sheared and flring head 60 is actuated by pressure. Although
the underbalance is lost, the operator is still able to achieve a
well completion.
In a variation to the above, the bar initiates activ tion of
the pressure actuated firing head but additional pressure must be
added to the tubing flow bore to complete actuation. The tool'
string is lowered into the well with a normally closed vent
assembly. In operation a bar is dropped downhole. The bar opens
vent assembly 56 and impacts against head 178, thereby driving
the plug 160 into the piston passageway 162 and forming a flow
path from the tubing string into the upper chamber 100A. The gun
firing head 160 now is the "armed" or "cocked" posit;ion and the
gun 50 is ready to fire upon the addition of sufficient pressure
being effected within the tubing string 26. The vent 56 can be
opened using wireline, bar, or packer actuated de~ices. Further
pressure is then applied. This preferably is accomplished using
N2, CO2, or flue gases, although a liquid could be employed
to elev~te the tubing hydrosta~ic head or fluid pressure t~ the
,~ ,r~,
iZ3 1L~
valve required to shear the piston pln 150. After the pressure
differential across the piston 120 has sheared the piston pins
150, the piston 120 strokes downhole, thus forcing firing p~n ~46
to strike the initiator 90, and explode the prima cord 53, which
detonates the individual shaped charges 52. After the casing 16
has been perforated, the tubing is swabbed until production is
achieved. In some instances it may be necessary for the well to
be put on a pumpjack unit because of the low `downhole formation
pressure. In the above example, it is, of course, necessary to
contain the downhole pressure by the provision of a hydrostatic
head achieved by the use of a suitable well fluid.
A still another application of the present invention is
shown in Figure 11 where a pressure actuated firing head is used
as an alternate firing head. Referring now to Figure 11, there
is shown a casing 380 extending though a formation 382. A tool
string with a packer 384, vent assembly 386, releasable coupling
388, bar actuated firing head 390, perforating gun 392, and
pressure actuated firing head 394 suspended on a drill string
396, is lowered in the borehole until the perforating gun 392 is
adjacent formation 382. The packer 384 is set to isolate forma-
tion 382 and a bar is dropped to actuate bar actuated firing head'
330. Vent assembly 386 is either packer actuated or bar actu-
ated. If, for some reason, bar-actuated firing head 390 does not
actuate, pressure actuated firing head 3g4 may be actuated by
pressuring down tubing string 396 and through open vent assembly
386 into lower annulus 398. Pressure actuated firing head 394 is
in fluid communication with the lower annulus 398, and therefore
pressure is effected on pressure actuated firing head 394 ~o
detonate gun 392. Thus, pressure actuated firing head 394 serves
as a back-up firing head.
Those skilled in the art, having digested the above descrip-
tion of this invention, will appreciate that the gun firing head
can be actuated b~- (1) elevated pressure of a predetermined
1~3~
magnitude; (2) bar and pressure combination; or (3) bar and
eleva~ed tubing pressure in two distinct steps.
One advantage of the present invention is to fire a perfo-
rating gun or guns under conditions which prevent firing with a
bar. One such condition would be to pressure the tubing or the
annulus to fire a lower gun prior to firins an upper gun wi~h the
upper gun and lower gun being attached to one another-. The upper
qun can thus be fired by dropping a bar. Therefore, the present
invention enables the charges of a casing gun to be detonated
l~ commencing at the bottom-most charge and proceeding uphole until
the uppermost charge has been fired. This may be accomplished by
inverting the gun and gun firing head, thereby locating the gun
firing head on the bottom ~f the gun "looking downhole". The
vent assembly by the lower gun must ~e opened in order to fire
the lower gun by elevating the bottom hole pressure as in (l)
above. A bar cannot be used as in (2) above in this instance.
An unusual feature of this invention lies in the plug,
piston and passageways being arranged whereby there is one large
apertured piston within which a plug must be sealingly received
in order for the head to be detonated. Thè plug and piston are
selectively moved by pressure, impact, or a combination thereof.'
Leakage of incompressible well fluids into the head is equalized
across the piston and thereafter there can be no pressure differ-
ential developed thereacross because of the presence of the
piston passageway. Leakage of well fluids into the sealed off
area is bled off to e~ualize the leakage pressure on the plug.
In the foregoing, the invention has been described primarily
with reference to shape and structure. It can be further
described from the standpoint of function.
It is desired to detonate the gun hydraulically tor con-
ceivably by any fluid pressure, including gas). To that end a so
called hydraulic cylinder, i.e. a cylinder in which moves a
piston, is employed~ Since circular cross-section is merely
usual but not essential, the cylinder may be referred to as an
expansible chamber having a movable wall (the piston).
It is desired to admit pressure fluid to the interior of the
expansible chamber to move its movable wall to detonate the gun
by means of a firing pin carried by the wall. So an inlet fluid
passage is provided through a fixed wall of the expansible cham-
ber and a valve is placed in the inlet. In the present case the
small plug 160 and bushing 152 provide such a valve. Radial
ports 180 are this valve inlet. The cylindrical surface of
piston bore 166 is the valve seat. Large piston 120 is the valve
closure. The valve outlet is the lower end of cylinder 164,
which discharges into upper chamber lOOA when the valve is open,
as shown in Figures 3, 4 and 7. In Figures 2 and 5 this valve is
shown in closed position.
Should this primary valve leak and fluid enter the expans-
ible chamber, the movable wall would move the firing pin to
detonate this gun. This is the pro~lem faced and solved by this
invention.
An equalizing passage i~ provided through the movable wall
communicating the interior of the expansible chamber with the
outside of the movable wall. As long as this equalizing passage~
is open, no differential pressure can build up on opposite sides
of the movable wall and the gun will not fire since the movable
wall is held fixed by shear pins.
To arm the firing head, the equalizing fluid passage must be
closed. This is achieved by means of an auxiliary valve which,
in the present case, includes a valve closure provided by ~he
lower end of the small plug 160, such valve closure cooperating
with ~ valve seat provided by the inner periphery of cylinder 162
in the large piston 120.
It will be seen that the ~.wo valves are connected togeth~r
or interlocked so that when the primary or supply valve is
closed, the auxiliary or equiiizer valve is opèn, as shown in
1~3~0'~
Figures 2 and 5; when the primary or supply valve is open, the
auxiliary or equilizer valve is closed, as shown in Figures 3, 4
and 7. Furthermoxe, the seal spacing, referring to seals 182 and
184, is such that the auxiliary valve (seal 134) closes before
the primary valve (seals 182) opens, so that opening of the
primary or supply valve will not admit fluid to the outside of
the expansible chamber (below the.big piston~ and hydraulically
lock the firing head.
Recapitulating, according to the invention a perforating gun
firing head comprises a pipe nipple to be connected at its lower
end to a gun and and at its upper end to a pipe string. The
nipple has a transverse wall at its upper end and a detonator
mounted in its lower end. ~ A piston is secured in the nipple
between its ends by lower shear pins. The piston carries a
firing pin on it~ lower side and has a pressure equalizing fluid
passage from its upper side to its lower side. The transvexse
. wall has a fluid supply passage from its upper side to its lower
side to admit pressure fluid ~rom the pipe string to the upper
side of the piston. A valve in the fluid supply passage includes
a plunger normally closing the supply passage and held in closed
position by upper shear pins, the lower end of the plunger moving'
to close the pressure equalizing passage when the upper shear
pins are sheared and the plunger moves to open the fluid supply
passage to admit pressure fluid to the upper side of the piston.
The plunger is moved down a.nd the upper shear pins sheared either
by pressure on an area of the plunger or by a h~mmer blow on an
anvil connected by a stem to the upper end of the plunger.
Another area around the plungex below ~he stem is sealed off ~rom
pressure fluid and passages in the plunger equalize pressure
between the sealed area and the lower end of the piston.
It is to be understood that although it is preferred that
the upper shear pins break at a higher pressure than the lower
shear pins, as that operation without the use of a b~r, i.e. all
. --
~Z~ 4~ .
pressure operation, will cause a snap action of the firing head,
it would also be possible to provide a firing head in which the
upper shear pins sheared at a lower tubing pressure than the
lower shear pins, whereby a two stage all pressure operation
could be achieved, the head first being armed by raising the
tubing pressure to a certain value to shear the upper chear pins
and thereafter at any time the pressure could be raised to.a
higher pressure sufficient to shear the lower shear pins and move
the lower.piston to detonate the gun.
It would also be possible to provide that the upper and
lower shear pins both shear at the same pressure.
While a preferred e~bodiment of the invention has been shown
and described, modifications thereof can be made by one skilled
in the art without departing from the spirit of the invention.
