U.S. patent application number 10/655859 was filed with the patent office on 2005-08-25 for high pressure exposed detonating cord detonator system.
Invention is credited to Barton, John A., Walker, Jerry L..
Application Number | 20050183610 10/655859 |
Document ID | / |
Family ID | 34860595 |
Filed Date | 2005-08-25 |
United States Patent
Application |
20050183610 |
Kind Code |
A1 |
Barton, John A. ; et
al. |
August 25, 2005 |
High pressure exposed detonating cord detonator system
Abstract
A detonator system for borehole systems which include detonating
cord exposed to borehole fluids, pressures and temperatures. A
firing head has a sealed chamber for an electrically fired
detonator and has a booster charge holder forming part of the seal.
The chamber is sealed by a wire line firing sub and by the booster
holder. The charge holder includes a bulkhead separating the
detonator chamber from a booster charge chamber and providing part
of the detonator chamber seal. The detonator explosive and the
booster charge are positioned on opposite sides of the bulkhead so
that upon detonation of the detonator, the bulkhead is ruptured and
the explosion transfers to the booster charge and from it to the
detonating cord. The firing head includes holes for attachment of
borehole tools such as perforating guns or back off tools to be
fired by the detonating cord.
Inventors: |
Barton, John A.; (Arlington,
TX) ; Walker, Jerry L.; (Ft. Worth, TX) |
Correspondence
Address: |
Albert C. Metrailer
Conley Rose
5700 Granite Parkway, Suite 330
Plano
TX
75024-6616
US
|
Family ID: |
34860595 |
Appl. No.: |
10/655859 |
Filed: |
September 5, 2003 |
Current U.S.
Class: |
102/275.11 |
Current CPC
Class: |
C06C 7/00 20130101; C06C
5/06 20130101; F42D 1/043 20130101 |
Class at
Publication: |
102/275.11 |
International
Class: |
C06C 005/06 |
Claims
1. A detonator system for detonating cord, comprising: a firing
head having a detonator chamber sized to receive at least a portion
of a detonator and having an upper sealing surface and a lower
sealing surface, the upper sealing surface adapted for forming a
fluid and pressure seal with a firing sub, and a booster charge
holder having an upper sealing surface and a bulkhead adapted for
forming a fluid and pressure seal with the firing head lower
sealing surface, the bulkhead and booster charge holder upper
sealing surface sized to position the bulkhead adjacent an
explosive component of a detonator carried in the detonator chamber
when the booster charge holder upper sealing surface is engaged
with the detonator chamber lower sealing surface and having a
booster charge chamber below the bulkhead adapted to receive a
booster charge adjacent the bulkhead.
2. A detonator system according to claim 1, wherein the detonator
chamber is sized to receive at least a portion of an electrically
fired detonator and the firing head upper sealing surface is
adapted for forming a fluid and pressure seal with a wireline
firing sub.
3. A detonator system according to claim 1, further comprising a
seal boot having a first end and a second end, the first end having
an outer surface sized to form a fluid tight seal with an inner
surface of the booster charge chamber and having inner surface
sized to form a fluid tight seal with a booster charge carried in
the booster charge chamber.
4. A detonator system according to claim 3, wherein the seal boot
second end has an inner surface sized to form a fluid tight seal
with a detonating cord.
5. A detonator system according to claim 4, wherein the seal boot
second end has an outer surface having a diameter smaller than a
diameter of the outer surface of the seal boot first end, thereby
forming a shoulder on the outer surface of the seal boot between
the seal boot first end and seal boot second end.
6. A detonator system according to claim 5, further comprising: a
thread on an outer surface of the booster charge chamber, a
retainer cap having an internal thread coupled to the booster
charge chamber thread and having an internal shoulder engaging the
shoulder on the outer surface of the seal boot and thereby
retaining a portion of the seal boot in the booster charge
chamber.
7. A detonator system according to claim 6, wherein the retainer
cap comprises a chamber for receiving the seal boot second end.
8. A detonator system according to claim 1, wherein the detonator
chamber is sized to receive only a portion of a detonator and to
position an explosive component of a detonator below the detonator
chamber lower sealing surface.
9. A detonator system according to claim 8 wherein the booster
charge holder comprises an upper chamber extending from the upper
sealing surface to the bulkhead, the chamber sized to receive a
portion of a detonator containing an explosive and to position the
explosive portion adjacent the bulkhead.
10. A detonator system according to claim 1, further comprising: an
electrically fired detonator carried in the detonator chamber, and
a wire line firing sub connected in sealing engagement with the
detonator chamber upper sealing surface, and electrically coupled
to the electrically fired detonator.
11. A detonator system according to claim 10, wherein the booster
charge holder upper sealing surface is connected in sealing
engagement with the detonator chamber lower sealing surface.
12. A detonator system according to claim 11, further comprising a
booster charge carried in the booster charge chamber adjacent the
bulkhead.
13. A detonator system according to claim 12, further comprising a
length of detonating cord having one end coupled to the booster
charge.
14. A detonator system according to claim 13, further comprising a
seal boot having a first end positioned in the booster charge
chamber between the booster charge and an inner surface of the
booster charge chamber, and forming a substantially fluid tight
seal the booster charge and the inner surface of the booster charge
chamber.
15. A detonator system according to claim 14, wherein the seal boot
comprises a second end extending along a portion of the detonating
cord and forming a substantially fluid tight seal with the
detonating cord.
16. A detonator system according to claim 15, wherein the seal boot
first end has an outer diameter greater than the outer diameter of
the seal boot second end, thereby forming a shoulder on the outer
surface of the seal boot between the seal boot first end and seal
boot second end.
17. A detonator system according to claim 16, further comprising: a
thread on an outer surface of the booster charge chamber, a
retainer cap having an internal thread coupled to the booster
charge chamber thread and having an internal shoulder engaging the
shoulder on the outer surface of the seal boot and thereby
retaining a portion of the seal boot in the booster charge
chamber.
18. A detonator system according to claim 17, wherein the retainer
cap comprises a chamber for receiving the seal boot second end.
19. A method for detonating detonating cord in a borehole,
comprising: placing a detonator in a firing head chamber, sealing a
first end of the firing head chamber with a firing sub, sealing a
second end of the firing head chamber with booster charge holder
having an internal bulkhead positioned below the detonator, and
positioning a booster charge below the bulkhead.
20. A method according to claim 19, wherein the detonator is an
electrically fired detonator and the firing sub is a wireline
firing sub.
21. A method according to claim 19, further comprising: providing a
booster charge chamber below the bulkhead, and positioning a fluid
seal between the booster charge and the booster charge chamber.
22. A method according to claim 21, further comprising coupling the
booster charge to one end of a section of detonating cord within
the booster charge chamber.
23. A method according to claim 22, further comprising positioning
a fluid seal between the detonating cord and the booster charge
chamber.
24. A method according to claim 23, further comprising firing the
detonator.
25. A method according to claim 22, further comprising mechanically
supporting a borehole explosive tool from the firing head.
26. A method according to claim 25, further comprising explosively
coupling the detonating cord to the explosive tool.
27. A method according to claim 26, further comprising positioning
the firing head and explosive tool in a borehole.
28. A method according to claim 27, further comprising firing the
detonator.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] None.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not applicable.
REFERENCE TO A MICROFICHE APPENDIX
[0003] Not applicable.
FIELD OF THE INVENTION
[0004] The invention relates to detonating systems, and more
particularly to detonators for explosive systems which include
detonating cord exposed to hostile environments including
high-pressure fluids.
BACKGROUND OF THE INVENTION
[0005] In oil well perforating operations, it is common practice to
use well perforating guns whose explosive components and shaped
charges are directly exposed to well bore fluids and pressures.
Typically, these explosive components may be carried along a
flexible or semi-flexible strip of metallic carrying member and may
be locked to the carrying member and affixed through holes bored in
the strip, thus directly exposing the shaped charges to the well
bore environment.
[0006] Perforating guns of this type may be referred to as
expendable perforating guns in the sense that, when the explosive
charges are fired, the carrying member is destroyed or separated
into numerous small pieces by the explosion of the shaped charges
and may fall to the bottom of the well as small debris. Such
expendable carrier perforating guns have the advantage that the
maximum sized shaped charges for a given diameter of well can be
installed, as opposed to conventional hollow carrier shaped charge
perforating guns. Hollow carrier shaped charge guns carry a
plurality of shaped charges which must fit within a carrier tube
which protects them from the borehole environment.
[0007] The expendable perforating guns are typically run into a
well on an electrical wireline, which provides both mechanical
support and electrical connections for firing the perforating gun.
An electrically fired detonator is typically connected to the
wireline. A secondary explosive detonating cord is typically
ignited by the detonator and extends the length of the perforating
gun to sequentially fire each of the individual shaped charges
carried by the perforating gun.
[0008] The explosive components of a typical perforating gun
therefore comprise a detonator, a length of detonating cord, and a
plurality of shaped charges. The borehole environment affects these
components in various ways. Detonators are very sensitive to
borehole fluids and typically will not fire if the fluids enter or
contact the detonator. The shaped charges will not function
properly if they are filled with borehole fluids. Shaped charges
may be fitted with seals which exclude borehole fluids from the
explosive charges. Detonating cord functions properly when exposed
directly to the borehole pressure and fluids along most of its
length, as long as one end of the cord is protected from the fluids
where explosive transfer from the detonator is required.
[0009] Various other operations in oil and gas wells use exposed
detonating cord either as the primary explosive charge or for
explosive transfer from a detonator to other charges. Such
operations include exploration, production, stimulation and pipe
recovery operations. For example, a back off operation may use a
detonator and detonating cord without additional charges such as
shaped charges. The detonating cord itself provides the explosive
forces needed in the back off operation. The combination of a
detonator and exposed detonating cord may be used in all these
operations. In these operations, it is important to protect the
detonator and the explosive transfer connection to the detonating
cord from borehole fluids.
SUMMARY OF THE INVENTION
[0010] The present invention provides a detonator system for
detonating cord in well operations in which a detonator and its
coupling to the detonating cord is protected from the well
environment. The system includes a firing head having a sealed
detonator chamber for a detonator and a booster charge holder. The
charge holder includes a bulkhead separating the detonator chamber
from a booster charge. The firing head chamber is sealed at one end
by a firing sub and at the other end by the charge holder to form
an environmentally sealed chamber for a detonator. The charge
holder includes a booster charge chamber for receiving a booster
charge and one end of a detonating cord and positioning the booster
charge adjacent the bulkhead. A fluid tight seal is provided in the
booster charge chamber to restrict the flow of well fluids into the
booster charge chamber.
[0011] In one embodiment, the detonator is an electrically fired
detonator. The system is mechanically and electrically coupled to a
surface location by a wireline. A wireline firing sub provides
electrical connection from the wireline to the detonator and
provides a seal at one end of the firing head chamber. The firing
head chamber protects the electrical connection of the firing sub
to the detonator as well as protecting the electrically fired
detonator itself.
[0012] In one embodiment, the firing head is designed to be
reusable and the booster charge holder is designed to be
expendable. The booster charge holder includes a chamber for
receiving that portion of the detonator which contains the
detonator explosive and positioning it next to the bulkhead.
[0013] In one embodiment, the firing head includes means for
mechanically supporting borehole tools such as perforating guns,
back off tools, etc.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a cross sectional view of an assembled detonator
system according to an embodiment of the invention.
[0015] FIG. 2 is plan view of a booster charge holder according to
an embodiment of the invention.
[0016] FIG. 3 is cross sectional view of the booster charge holder
of FIG. 2.
[0017] FIG. 4 is a perspective view of a rubber boot according to
an embodiment of the invention.
[0018] FIG. 5 is a cross sectional view of the rubber boot of FIG.
4.
[0019] FIG. 6 is a cross sectional view of a retainer cap according
to one embodiment of the invention.
[0020] FIG. 7 is a cross sectional view of an alternative retainer
cap according to another embodiment of the invention.
[0021] FIG. 8 is a perspective view of the retainer cap of FIG.
7.
DETAILED DESCRIPTION OF EMBODIMENTS
[0022] In the following description of embodiments, various terms
such as "above" and "below" and "up hole" and "down hole" are used
to indicate relative position of elements. These terms are used
with reference to the normal position of the apparatus when used in
a vertical borehole and are not intended to be limiting. In wells
which include slanted or horizontal portions, the term up hole or
above refers to the direction toward the surface location of the
well and down hole or below refers to the direction toward the end
of the well farthest from the surface location. It is to be
understood that the a system according to the present invention may
be inverted in some applications, for example bottom fired systems,
and the relative positions of the various elements may therefore be
reversed or inverted.
[0023] FIG. 1 provides a cross sectional view of an assembled
detonator system according to one embodiment. The primary
mechanical component of this embodiment is a firing head 10. Other
elements are attached to or contained within the firing head 10. An
upper portion 12 of firing head 10 is generally cylindrical and has
an interior chamber 14 sized to receive at least the upper portion
of a detonator 16. In this embodiment, the detonator 16 is an
electrically fired detonator. A firing sub 18 has a lower end
coupled to the upper end of chamber 14 by threads 20. In this
embodiment, the firing sub 18 is a conventional wireline firing
sub. One or more O-ring seals 22 are carried on the firing sub 18
above the threads 20 and provide a fluid tight pressure seal
protecting the chamber 14 from borehole fluids and pressure. As
well known in the art, the wireline firing sub 18 includes an
electrical conductor in its center which is insulated from the body
of the sub 18. The firing sub 18 is adapted for connection to the
lower end of a conventional wireline to provide an electrical
connection to firing systems at the surface location of a well.
[0024] A lower portion 24 of the firing head 10 is an extension of
the upper portion, but is not a complete cylinder. The lower
portion 24 has a thickness of about a quarter to three-quarters
that of the upper portion 12. It is effectively a half cylinder, or
U-shaped section, which provides good structural strength, but is
open on one side to allow easy assembly of other elements and allow
dissipation of explosive forces to minimize damage to the firing
head 10. One or more, in this embodiment three, holes 26 may be
provided in the lowermost portion of the firing head 10 for
attachment of tools, such as back off tools or perforating guns.
The lowermost section of the firing head 10 with the holes 26 may
taper to a point at the bottom and be machined to provide flat
surfaces for bolts to attach such tools.
[0025] A booster holder 28, shown in more detail in FIGS. 2 and 3,
has an upper end 30 positioned in the lower end of the detonator
chamber 14. One or more O-ring seals 32 are carried on the upper
end 30 to provide a fluid tight pressure seal protecting the
chamber 14 from borehole fluids and pressure. The booster holder 28
is generally cylindrical and includes an upper chamber 34 and a
lower chamber 36 separated by a bulkhead 38. The upper chamber 34
is sized and positioned to receive the lower end of detonator 16
which contains the actual explosive component of detonator 16. The
detonator 16 explosive component is positioned adjacent to and just
above the bulkhead 38.
[0026] The lower chamber 36 of booster holder 28 is sized to
receive a booster charge 40 coupled to the upper end of a length of
detonating cord 42. As illustrated, the booster charge 40 is
positioned adjacent to and just below the bulkhead 38. A rubber
boot 44, shown in more detail in FIGS. 4 and 5, provides a fluid
tight seal restricting the flow of well fluids into the booster
holder 28 lower chamber 36.
[0027] A retainer cap 46 is threaded onto the lower end of booster
holder 28 to hold the boot 44, booster charge 40 and detonating
cord 42 in position in the lower chamber 36. A retaining clip 48
engages the upper end of booster holder 28 to hold its upper end 30
in sealing contact with the lower end of firing head 10 chamber 14.
A screw 50 holds the retaining clip 48 in place.
[0028] In the illustrated embodiment, the detonator 16 is a Top
Fire RED-III detonator sold by Jet Research Center under part
number 101272595. However, the firing head 10 chamber 14 preferably
has interior dimensions selected to accept a variety of detonators.
No special detonator is required to withstand particular pressures
or types of fluids, since the chamber 14 is sealed against both
borehole pressure and fluids. In this embodiment, it is desirable
that the output energy of the detonator 16 be at least equivalent
to one-half gram of HMX explosive to provide sufficient energy to
rupture the bulkhead 38 and provide explosive transfer to the
booster charge 40. The bulkhead 38 should be of sufficient strength
to withstand expected borehole pressures, since it provides part of
the pressure seal protecting the detonator 16.
[0029] The detonating cord 42 may be conventional detonating cord
such as that sold under the trademark PRIMACORD. In this
embodiment, detonating cord 42 may contain an explosive charge of
eighty grains of HE explosive per foot.
[0030] The booster charge 40 is essentially a conventional
"blasting cap" type of device comprising a secondary explosive
contained in a metallic tube, for example aluminum. The tube is
closed on its upper end which contains the actual explosive
component. Its lower end is open and contains no booster charge
explosive. The upper end of detonating cord 42 is positioned in the
open lower end adjacent the actual explosive component comprising
booster charge 40. The open lower end is crimped onto the
detonating cord 42.
[0031] FIGS. 2 and 3 provide more details of the booster charge
holder 28 of FIG. 1. The parts which were identified in FIG. 1 and
are also shown in FIGS. 2 and 3 are identified by the same
reference numbers. The interior shapes of the upper chamber 34,
lower chamber 36, and the bulkhead 38 between chambers 34 and 36
are shown most clearly in FIG. 3. The upper chamber 34 may be
approximately cylindrical, but may have an enlarged portion 52 at
its upper end to conform to the electronics portion of the
detonator 16. The lower chamber 36 has a reduced diameter portion
54 at its upper end, sized to conform to the diameter of the
booster charge 40. A lower portion 56 of the chamber 36 is of
larger diameter, sized to receive the boot 44 with a fluid tight
fit.
[0032] Annular seal grooves 58 are provided on the outer surface of
the upper end 30 of booster charge holder 28 for carrying the
O-rings 22 shown in FIG. 1. An annular groove 60 is provided on the
outer surface between the upper end 30 and the main body of booster
holder 28 which is of somewhat smaller outer diameter than the
upper end 30. In this embodiment, the retainer clip 48, FIG. 1,
engages the groove 60 to retain the booster holder 28 in proper
position in the firing head 10. Threads 62 are provided on the
outer surface of the lower end of holder 28, to engage the retainer
cap 46, FIG. 1.
[0033] The booster charge holder 28 may be manufactured from easily
machined and inexpensive materials such as aluminum, copper or
brass. This reduces the cost of the charge holder 28, which in this
embodiment is destroyed when the detonator 16 is fired. The
particular selection of material depends on the pressure in the
well and types of fluids which will be encountered.
[0034] FIGS. 4 and 5 provide perspective and cross sectional views
of the boot 44 of FIG. 1. The boot 44 is preferably made of an
elastomeric material, e.g. rubber. An upper end 64 of the boot 44
has a tapered shape and outer diameter selected to form a tight fit
within the booster holder 28 lower chamber 36 lower portion 56. A
lower end 66 has a smaller outer diameter, resulting in a shoulder
68 between the upper end 64 and the lower end 66. The shoulder 68
is engaged by the retainer cap 46, FIG. 1, to hold the boot 44 in
the booster holder 28 lower chamber 36. The boot 44 has an inner
diameter 70 at its upper end sized to form a tight fit over the
booster charge 40, FIG. 1. The boot 44 has an inner diameter 72 at
its lower end sized to form a tight fit over the detonating cord
42, FIG. 1. It is preferred to mold the boot 44 without a flashing
on its inner or outer surfaces in order to improve the fluid tight
seal between the booster charge 40, detonating cord 42, the boot 44
and the booster holder 28.
[0035] FIG. 6 provides a cross sectional view of the retainer cap
46 of FIG. 1. The cap 46 is a simple cylindrical cap having an
inner threaded surface 74 on its upper end sized to mate with the
threads 62 on the lower end of booster holder 28, FIGS. 2 and 3.
The lower end of cap 46 has an opening 76 sized to fit over the
lower end 66 of the boot 44. Between the threaded portion 74 and
the smaller diameter opening 76 is a shoulder 78 adapted to engage
the shoulder 68 on the boot 44, FIGS. 4 and 5. The outer surface of
cap 46 may be knurled, if desired, to facilitate manual tightening
of the cap 46 onto the booster holder 28.
[0036] FIGS. 7 and 8 provide cross sectional and perspective views
of an alternative retainer cap 80 which may be used in place of the
retainer cap 46 shown in FIGS. 1 and 6. The alternative cap 80
provides more protection for the boot 44 of FIGS. 4 and 5. An upper
end 82 of the retainer cap 80 is essentially identical to the
retainer cap 46. Retainer cap 80 has an inner threaded surface 84
on its upper end sized to mate with the threads 62 on the lower end
of booster holder 28, FIGS. 2 and 3. The lower end 86 of cap 80 is
basically a hollow cylinder sized to fit over and completely cover
the lower end 66 of the boot 44. Between the threaded portion 84
and the smaller diameter upper end 86 is a shoulder 88 adapted to
engage the shoulder 68 on the boot 44, FIGS. 4 and 5. An opening 90
on the lowermost end of the retainer cap 90 is sized to fit the
detonating cord 42 of FIG. 1. It can be seen that if the
alternative retainer cap 80 is substituted for the retainer cap 46
of FIG. 1, essentially the entire boot 44 is covered and protected
by the retainer cap 80. The retainer cap 80 is particularly useful
in wells in which the ambient conditions of pressure, temperature
and gases, such as methane, may cause the boot 44 to swell or lose
strength and possible allow borehole fluids to flow between the
detonating cord 42 and the boot 44. The retainer cap 80 maintains a
close fit of the boot 44 to the detonating cord 42. If any swelling
of boot 44 occurs, it will only increase the seal between the boot
44 and the cord 42, since the cap 80 is preferably made of metal
which will maintain its dimensions. The retainer cap 80 may have a
knurled outer surface to facilitate manual turning during the
assembly process described below.
[0037] With reference to the figures, assembly and operation of a
detonator system of the illustrated embodiment will be described.
Assembly begins with the main firing head 10 which is preferably
manufactured from high strength steel heavy wall tubing, or other
materials with sufficient strength for use in boreholes. The
chamber 14 may be machined to receive a particular electrically
fired detonator, but is preferably sized to receive a range of
commercially available electrically fired detonators. Typical
detonators, such as the above referenced RED-III detonator, are
adapted to be mechanically attached to the lower end of the firing
sub 18 by a rubber sleeve on the top portion of the detonator 16.
An electrical contact on top of detonator 16 makes contact with the
center conductor in the firing sub 18 to provide an electrical path
to a wireline. A second electrical contact, or ground connection,
is made between a conductor on the outer surface of detonator 16
and the inner wall of firing head 10. After the detonator 16 has
been attached to the lower end of the firing sub 18, the assembly
is lowered into the upper end 12 of firing head 10. The firing sub
is mechanically connected by threads 20 and forms a fluid tight
pressure seal in the top of chamber 14 by means of the O-ring seals
22. Note that in this embodiment, the lower portion of detonator
16, i.e. the portion containing an explosive material, extends
below the chamber 14 and into the lower portion 24 of the firing
head 10 which has one side open. The chamber 14 is therefore not
directly exposed to explosive forces produced by detonator 16, and
as a result the firing head 10 may be reused several times.
[0038] The next part of the process is assembly of the booster
charge holder 28, the booster charge 40, detonating cord 42, boot
44 and cap 46. The detonating cord 42 may be cut to the appropriate
length according to the desired operation and type of tool to be
bolted to the holes 26 in the lower end of firing head 10. A
retainer cap 46 or 80 may then be placed onto the detonating cord
42. Next, the detonating cord 42 is inserted through the boot 44.
The end 72 of boot 44 is sized to fit tightly onto the detonating
cord 42 and must be stretched to some extent when the cord 42 is
inserted. It is desirable to apply a lubricating and preferably
water sealing material, such as petroleum or silicone grease, to
the outer surface of the detonating cord 42 to facilitate insertion
of the cord 42 through the boot 44. It should be inserted until a
portion of the cord 42 protrudes from the large end 70 of the boot
44. The open end of the booster charge 40 is then slipped over the
end of the cord 42 and crimped onto the cord 42. The cord 42 and
booster 40 are then pushed back into the boot 44 until the lower
end of the booster 40 is seated in the large end 70 of the boot 44.
When seated, a portion of the closed end of booster 40 extends from
the boot 44, as shown in FIG. 1.
[0039] It is desirable to apply a lubricating and preferably water
sealing material, such as petroleum or silicone grease, to the
outer surface of the large tapered end 64 of the boot 44. The large
end 64 is then inserted into the lower chamber 36 of booster holder
28. Since the large end 64 of boot 44 is sized for a tight fit into
chamber 36, it must be forced in and the grease facilitates the
process. The process also applies compressional force on the boot
44 forming a fluid resistant seal between the detonating cord 42,
the boot 44 and the inner surface of chamber 36. When properly
inserted, the upper end of booster 40 is positioned adjacent or
preferably in contact with the lower surface of bulkhead 38. The
cap 46 or 80 is then slid up the cord 42, over the end 72 of boot
44 and threaded onto the threads 62 on the lower end of booster
holder 28. The cap 46 or 80 should be tightened to apply
compressional force to the shoulder 68 on boot 44 to restrict
movement of the boot 44 and booster charge 40 and to maintain the
fluid tight seal. If the cap 80 is used, it will also apply
compressional forces to the lower end 66 of the boot 44 to maintain
its fluid tight contact with the detonating cord 42.
[0040] Seals, e.g. O-ring seals, are then inserted into the grooves
58 on the upper end 30 of booster holder 28 and a lubricating and
preferably water sealing material, such as petroleum or silicone
grease, is preferably applied to the seals. The upper end 30 of
booster holder 28 is then slid over the exposed lower end of the
detonator 16 until the upper end 30 seats in the lower end of
chamber 14 in firing head 10. At this point, the lower end of the
detonator 16 should be adjacent the upper surface of the bulkhead
38. The retaining clip 40 is then inserted into the groove 60 in
booster holder 28 and attached to the firing head 10 with screw
50.
[0041] Various safety steps are usually added to the
above-described process. For example, the firing sub 18 may be
attached to a wireline before it is inserted into the firing head
10. Once connected to the wireline, a firing system should provide
a short circuit to keep the detonator 16 in safe condition. A tool,
such as a perforating gun may be attached to the holes 26 in the
lower end of firing sub 10 before the detonating cord 42 is cut to
length.
[0042] Once assembled with a desired tool, the complete assembly
may be inserted into and lowered down a borehole by use of a
wireline. As the assembly travels down hole it will be immersed in
borehole fluids including oil, salt water and various gases. The
pressure will increase with depth and can easily reach thousands of
pounds per square inch. The chamber 14 is sealed from exposure to
the high pressure fluids at its top by firing sub 18 and seals 22
and at its bottom by the booster holder 28, including seals 32 and
the bulkhead 38. The upper chamber 34 of booster holder 28 is
effectively an extension of chamber 14 and is also protected from
borehole fluids and pressure.
[0043] The lower chamber 36 of booster holder 28 is protected from
borehole fluids by the seals formed between boot 44, the detonator
cord 42 and the inner surface of lower chamber 36 in booster holder
28. External pressure from borehole fluids urges the detonator cord
42 and boot 44 into the chamber 36, improving the fluid tight seal.
The forces do not degrade the performance of the booster 40 and
detonating cord 42. The seal however, substantially prevents any
borehole fluids from entering the lower chamber 36 or the booster
charge 40 where they might otherwise interfere with explosive
transfer from the booster charge 40 to the detonating cord 42.
[0044] Once the assembly has reached the selected depth, the
detonator may be fired by application of an appropriate signal from
a firing system at the surface location of the well through the
wireline. The explosion from the detonator ruptures the bulkhead 38
and transfers the explosion to the booster charge 40 which
detonates. The detonation of the booster charge 40 initiates
detonation of the detonating cord which may transfer the explosion
to other explosive components down hole. In the illustrated
embodiment, the explosive forces will destroy the booster holder.
However, firing head 10 is not directly exposed to the explosive
forces in that none of the explosive material is fired within a
closed chamber 14 in the firing head 10. As a result, the firing
head 10 in this embodiment may normally be reused several
times.
[0045] If reuse of firing head 10 is not desired, the chamber 14
could be extended on its lower end so that the entire detonator 16
is contained within chamber 14. The booster holder 28 could be
shortened so that the bulkhead 38 is located at the upper end of
charge holder 28. This would place the bulkhead adjacent the lower
end of the detonator 16 and the booster charge just below the
bulkhead. The chamber 14 would still be sealed from environmental
pressure and fluids to protect the detonator. However, the forces
generated by detonation of the detonator in chamber 14 may damage
the firing head 10 sufficiently to prevent its reuse. For example,
even a small expansion of the lower end of chamber 14 may prevent
forming a fluid and pressure tight seal with a new booster charge
holder 28.
[0046] The embodiment described above includes an electrically
fired detonator and is conveyed into a borehole and fired by a
wireline and wireline firing sub. It is apparent that other types
of detonators and other types of conveyance and firing means may be
substituted within the scope of the present invention. For example
the system may be conveyed into a borehole on coiled tubing. A
firing sub connected to coiled tubing may include an electrical
power source to fire an electrically fired detonator and may be
initiated by hydraulic pressure, a coded acoustic signal, a timer,
by a mechanical device dropped or otherwise conveyed down the
tubing, etc. A mechanically fired detonator may be coupled to a
firing sub on coiled tubing and fired by a pressure pulse or by a
mechanical device dropped or otherwise conveyed down the tubing.
Such devices may be conveyed downhole on a work string in place of
a coiled tubing or wireline. In any of these cases, the firing sub
may still provide a fluid and pressure seal for the firing head
detonator chamber protecting the detonator from borehole
fluids.
[0047] As described above, most of the parts of the described
embodiments have approximately cylindrical outer surfaces and inner
chambers. Cylindrical shapes are generally preferred in borehole
applications and for making threaded couplings or fluid and
pressure seals using O-rings. However, the cylindrical shapes are
not essential for practicing the present invention. Sealing and
coupling arrangements are available for other cross sectional
shapes such as square or hexagonal in which the components of the
present invention could be made.
[0048] While the present invention has been illustrated and
described with reference to particular embodiments and methods of
use, it is apparent that various changes and substitutions of parts
may be made within the scope of the invention as defined by the
appended claims.
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