Shaped charge and carrier assembly therefor

In a perforating apparatus, a series of explosive charges are mounted on a frangible strap which is pressfit within a frangible carrier which is suspended from a conventional form of wire line tool in such a way that when the charges are detonated the carrier assembly will be completely disintegrated and the wire line tool can be retrieved for subsequent reuse.

This invention relates to novel and improved perforating methods and 
apparatus and more particularly relates to a new and improved perforating 
apparatus employing shaped charges in a frangible carrier assembly 
suspended from a wire line tool. 
BACKGROUND AND FIELD OF THE INVENTION 
It is customary procedure to employ a plurality of shaped charges in 
perforating subsurface formations, such as, for example, in well bore 
completion operations. Typically, each charge is made up of a casing which 
contains explosive material of predetermined configuration and is recessed 
to receive a conical liner within the casing. When the explosive material 
is detonated, the liner is propelled with a high degree of force through 
the carrier wall, outer casing string and cement into the subsurface 
formation so as to open up the formation for flow of fluid upwardly 
through the casing string. In the past, the approach has been generally to 
fabricate the carrier assembly for the explosive material of a reusable 
material so that following detonation, the carrier can be retrieved. This 
has presented certain problems in that the construction of the carrier 
assembly must be such that it is capable of withstanding the explosive 
force of one or more charges which necessarily are directed through the 
wall of the carrier; also, expendable portions of the carrier through 
which the liner of a charge passes often tend to partially disengage from 
the carrier upon detonation and interfere with the retrieval of the 
carrier from the casing string. 
In copending application for patent, Ser. No. 23,657, filed Mar. 26, 1979 
entitled METHOD AND APATUS FOR WELL PERFORATION AND FRACTURING 
OPERATIONS, the foregoing and other problems are alluded to in the 
construction of a novel shaped charge device intended for perforating and 
stimulating wells. However, said application has to do more with the 
definite penetration of the charge into the formation surrounding the well 
bore as well as the construction and arrangement of various assemblies for 
use with the various explosive charges as disclosed therein. However, the 
present invention is concerned more with the construction of the carrier 
assembly for conventional shaped charges and specifically a way of 
permitting use of higher capacity charges for given size carriers while 
avoiding the problem of objectionable interference with the efficient 
retrieval of the carrier from the casing string. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide for a novel 
and improved perforating apparatus by which objectionable interference 
with efficient retrieval of the perforating apparatus from the well casing 
is avoided. 
Another object of the present invention is to provide in a well perforating 
apparatus for a novel and improved carrier assembly which is capable of 
undergoing complete disintegration so as not to interfere with the 
recovery of oil and gas through the well bore. 
A further object of the present invention is to provide for a novel and 
improved mounting and assembly of shaped charges in an expendible carrier 
and in predetermined orientation such that a blasting cord can be 
assembled with the charges to undergo detonation for optimum depth of 
penetration of the charges into a subsurface formation. 
It is an additional object of the present invention to provide for a well 
perforating apparatus in which the capacity of explosive charges employed 
can be substantially increased for a given size of well casing; and 
further wherein an expendable carrier is employed which is characterized 
by its simplicity and ruggedness of construction requiring a minimum 
number of parts which can be readily assembled to provide a highly 
efficient perforating apparatus. 
In accordance with the present invention, a preferred form of jet 
perforating apparatus incorporates a plurality of shaped charges, each 
contained within a flexible enclosure or casing, the casing being so 
configured as to facilitate ready insertion of the charges in 
predetermined spaced relation along the length of an elongated strap. A 
series of charges are assembled on the strap to extend in a direction 
transversely of the length of the strap, and a blasting cord is threaded 
through the ends of the casing for the charges so as to be in 
communication with the explosive material contained therein. The assembled 
charges and strap are inserted into a carrier, and the ends of the carrier 
are sealed off by end caps. The upper end cap has an aperture for upward 
extension of the blasting cord into a conventional form of wire line 
assembly, and the upper end cap is also fixed by means of a rod to the 
lower end of the wire line assembly. The carrier, end caps and strap are 
composed of thin-walled frangible materials such that they will completely 
disintegrate upon explosion. Further, the reduced wall thickness of the 
carrier will permit use of increased explosive capacity in each charge for 
a given internal diameter of the carrier. Here, the wall thickness of the 
carrier is uniformly reduced throughout by virtue of the absence of any 
special slots or grooves for mounting or retention either of the explosive 
charges or blasting cord.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring in detail to the drawings, there is illustrated in FIG. 1 the 
preferred embodiment of perforating apparatus 10 suspended in a casing 
string C at the lower end of a well bore. As shown in FIGS. 1 to 4, the 
apparatus 10 is broadly comprised of a carrier assembly 12 which is formed 
of a plurality of explosive charges 14 mounted on an elongated strap 16, 
and a blasting cord 18 extends downwardly through the carrier assembly 12 
for connection to an end of each charge 14. The upper end of the blasting 
cord 18 is connected to a blasting cap 20 at the lower end of a wire line 
tool T, the latter being connected to the upper end of the carrier 
assembly by a threaded rod 24. 
As a setting for the present invention, reference is made to the preferred 
manner of suspension of the carrier assembly 12 from a conventional wire 
line tool T. Here, it is desirable that the carrier assembly be suspended 
from the tool T in such a manner that the tool can be retrieved and reused 
following detonation of the explosive charges 14 and destruction of the 
carrier assembly. Thus, the tool T establishes a means of suspension of 
the carrier assembly for extended distances downhole while providing the 
necessary means of energization of the primer cord or blasting cord 18 in 
the detonation of the charges 14. For this purpose, the tool T may be 
suitably comprised of a tapered cable end 26 to which is secured a sinker 
bar 27 and magnetic collar locator 28 which in turn is connected to a 
shooting head adaptor 30 at its lower end. The wire line tool is suspended 
from a cable 32 containing wire conductors 33 which pass downwardly 
through the interior of the tapered cable end 26 and through the entire 
length of the tool then project outwardly from the shooting head adaptor 
30. The wire conductors 33 are connected to the blasting cap 20, and the 
blasting cap 20 is connected as previously described to the upper end of 
the blasting cord 18. The carrier assembly 12 is suspended from the wire 
line tool by means of the threaded rod 24 which is releasably connected to 
the lower end of the adaptor 30, for example, by releasable fasteners in 
the form of a cotter pin 35. 
An important feature of the present invention resides in the construction 
and arrangement of the carrier assembly 12 and the manner of suspension 
and mounting of the explosive charges 14 within the carrier assembly. 
Preferably, the carrier assembly 12 is comprised of an elongated, hollow, 
generally cylindrical housing or tubular portion 40 which is of uniform 
wall thickness except at its ends which are counterbored or otherwise 
increased in diameter slightly to form enlarged inner wall surfaces 41 and 
42, each end terminating in a shoulder 43 and 44 at its intersection with 
the reduced diameter of the inner wall surface of the tubular portion 40. 
The opposite ends are adapted for insertion of the leading ends of upper 
and lower end caps 45 and 46, respectively. Each of the end caps 45 and 46 
is similarly of generally cup-shaped configuration having a rounded end or 
nose 47 and forwardly projecting, generally cylindrical wall 48 
terminating in a reduced leading end 49; i.e., the leading end 49 has a 
reduced external diameter corresponding to the internal diameter of the 
opposite ends 41 and 42 such that the external surfaces of the forwardly 
projecting walls 48 are flush with the external surface of the tubular 
portion 40. Annular grooves 50 are formed in the external surfaces of the 
leading ends 49 of the end caps for the purpose of receiving O-rings 52, 
there being preferably a pair of O-rings 52 mounted in axially spaced 
relation on the leading end of each cap 41 and 42 so as to establish a 
firm pressfit or interference fit between the end caps and opposite ends 
of the tubular portion. This may be aided by the application of a bonding 
agent, such as an epoxy, between the mating surfaces of the leading ends 
of the end caps and the opposite ends of the tubular portion. It will 
therefore be appreciated that the end caps are similarly constructed so as 
to effect a sealed connection at opposite ends of the tubular portion; 
however, the upper end cap 41 is provided with an aperture 54 passing 
through the nose 47 to permit insertion of the blasting cord 18. A 
Neoprene seal designated at 56 is interpositioned between the blasting 
cord and wall of the aperture 54 so as to effect a seal around the 
opening. The lower threaded end of the rod 24 is inserted into a threaded 
opening 57 in the upper end cap 41 and most desirably the threaded opening 
extends less than the full thickness of the nose 47. 
As a preliminary to the assembly of the end caps 41 and 42 at opposite ends 
of the tube 40, the explosive charges 14 are suspended in the carrier 
assembly 12 on the elongated strap 16. In the preferred form, the 
elongated strap 16 is of generally rectangular configuration and is given 
a length just less than that of the length of the tube 40. The strap most 
desirably corresponds to the length of the tube 40 between the shoulders 
43 and 44, and is of a width corresponding to the inner diameter of the 
tube 40 so that it can be inserted lengthwise in snug-fitting relation to 
the inner wall of the tube 40. The strap is provided with a series of 
charge-receiving openings 58 which correspond in configuration to the 
cross-sectional configuration of the charges 14. Thus, in the preferred 
form, the openings 58 are of generally circular configuration and are 
arranged at equally spaced intervals along the length of the strap 
intermediately between opposite side edges. Both the strap and the tubular 
portion 40 as well as the end caps 45 and 46 are composed of a frangible 
material which is capable of withstanding any high pressures encountered 
in downhole operations; yet, will completely disintegrate when the charges 
are detonated and exploded. For this purpose, the materials employed in 
the fabrication of the carrier assembly consisting of the strap, tubular 
portion and end caps are made up of on the order of 82 parts by weight of 
polystyrene and 18 parts by weight calcium carbonate, although these 
proportions may be suitably varied according to the size of the carrier 
assembly and desired wall thickness for a given charge or number of 
charges. 
A typical charge employed in jet perforating operations is illustrated in 
detail in FIGS. 3 and 4 and is seen to comprise a generally cylindrical 
steel jacket 60 having a closed end 61 provided with a bore 62 extending 
through the closed end 61. A generally conical shaped copper liner 64 is 
inserted into the open end of the jacket 60 with its apex 65 extending in 
a direction toward the bore 62 and an explosive material or combination of 
explosive materials is contained as at 68 between the conical liner 64 and 
jacket 60. The assembled charge is housed within a resilient casing which 
may actually be made in two halves consisting of a relatively thick-walled 
casing half 70 which houses the major portion of the jacket 60 and 
surrounds the closed end 61 of the jacket with an opening 71 extending 
through one end of the casing normal to and in communication with the bore 
62. This bore 71 is adapted for insertion of the blasting cord 
therethrough. A second casing half 72 is relatively thin-walled and again 
is composed of a resilient material which tapers away from surrounding 
relation to the open end of the jacket 60 and into a reduced end portion 
74. The thin-walled casing half 72 is joined to the thick-walled casing 
half 70 by any suitable bonding agent and, at the mating edges of the 
casing half, it will be seen that the thick-walled casing 70 forms 
somewhat of a lip 75 which is just greater than the size of the 
charge-receiving opening 58 in the strap 16. Thus, the thin-walled casing 
half 72 may be inserted through the opening until the lip 75 of the casing 
half 70 moves into abutting relation with the surrounding edge of each 
charge-receiving opening whereby to retain the casing and complete charge 
assembly in place with its length in perpendicular relation to the length 
of the strap 16. The overall length of the casing for the charge 
corresponds to the diameter of the inner wall of the tubular portion 40 so 
as to cooperate with the strap in maintaining a snug-fitting relationship 
between the charges and tubular portion 40 of the carrier assembly. The 
charges are, as stated earlier, preassembled on the strap such that each 
successive charge projects or extends in an opposite direction from the 
strap, and the blasting cord 18 is threaded downwardly through the opening 
71 in the charges as well as through limited openings 78 which are 
positioned at spaced intervals along the length of the strap 
intermediately between the charge-receiving openings 58. The lower 
extremity of the blasting cord as designated at 18' is merely suspended 
within the hollow interior of the lower end cap 46 when the end caps 45 
and 46 are assembled onto the ends of the tubular portion 40. 
By virtue of the pressfit relationship established between the casings, 
strap and inner wall of the tubular portion 40, it is possible to 
eliminate internal slots or positioning members for the charges. This 
relationship, coupled with the frangible composition of the carrier 
assembly and straps, has been found to permit utilization of higher 
capacity charges for a given sized carrier assembly, if desired. For 
instance, it has been found possible to employ a 4" carrier gun charge 
(22-22.7 grams) inside a 35/8" diameter carrier in place of the 
commercially available 31/8" or 37/8" 1/2" carriers which utilize 10 to 14 
gram charges. In actual practice, the threaded aluminum rod 24 is 
generally supplied or made up in sections and is of a length to isolate 
the wire line tool T from any possible damage when the charges are 
detonated and exploded. Generally, the explosion will cause the rod to be 
severed directly above its connection into the carrier assembly so that 
fragments of the rod may be left in the hole along with the disintegrated 
carrier assembly; however, the remainder of the rod and the entire wire 
line tool T may be completely retrieved following each operation. The 
aluminum rod section 24 may then be replaced and secured to another 
carrier assembly in preparation for the next perforating operation. 
It will recognized that other materials may be employed in fabrication of 
the carrier assembly which will lend the desired strength for suspension 
of a series of charges downhole yet will completely disintegrate upon 
detonation of the charges. In particular, the thermoplastics exhibit the 
requisite characteristics in combination with a minor proportion of a 
carrier, such as, calcium carbonate, to increase its specific gravity. 
When the blasting cap is set off, it will activate the blasting cord 18 to 
initiate a series of explosions proceeding in succession downwardly 
through the carrier assembly as each charge in succession is detonated by 
the blasting cord. As illustrated in FIGS. 5 to 8, the conical liner will 
undergo an inversion when the charge is set off so that the apex or 
pointed end 65 of the liner will be discharged through the wall of the 
carrier 40 and through the casing into the formation, as illustrated in 
FIGS. 5 and 6. As it proceeds outwardly into the formation as illustrated 
in successive stages in FIGS. 7 and 8, it will form a cavity or break in 
the formation so as to encourage the flow of fluid from the formation 
through the port formed in the casing and into the well bore. The 
composition of the carrier assembly and strap is such that it will 
completely disintegrate and collect in the well bore below the openings or 
ports formed in the casing so as not to interfere with or obstruct the 
flow of fluid into the interior of the casing from which it an be drawn 
upwardly for recovery. In this relation, the thin-walled construction of 
the carrier assembly and its frangible composition is such that it is not 
necessary to preform openings or sections of weakness in the wall for 
discharge of the liner upon detonation. 
It is therefore to be understood that various modifications and changes may 
be made in the construction and arrangement of parts as well as the 
composition of materials comprising the present invention without 
departing from the spirit and scope thereof as defined by the appended 
claims.