Modular through-tubing casing gun

A novel and improved form of through-tubing perforating assembly conformable for use in various types of cased well bores having particular application in those in which a tubing string is positioned within the cased well bore and where extremely high pressures are encountered at the bottom of the well. A plurality of shaped charges are mounted in a modular carrier comprised of a plurality of generally tubular members interconnected in end-to-end relation to one another, each tubular member having an internal cavity defining a horizontally directed seating portion for supporting one of the shaped charges therein. An end cap is disposed at the lower end of the modular carrier, and a blasting cord extends continuously through the tubular members across one end of the shaped charges for detonating the charges when positioned opposite to that part of the formation to be perforated.

This invention relates to perforating devices adapted for use in oil and 
gas wells; and more particularly relates to a novel and improved modular 
through-tubing casing gun for use in perforating cased well bores beneath 
a tubing string. 
BACKGROUND AND FIELD OF THE INVENTION 
In oil and gas perforating operations, much greater penetration is achieved 
in casing gun assemblies than the through-tubing units. In particular, the 
through-tubing units presently in use may contain the same amount of 
charge as casing guns but have not been able to penetrate as deeply into 
the formation owing to their wider cone angle and limitations in overall 
size imposed by the inner concentric tubing strings through which they are 
deployed. The through-tubing devices are principally employed where high 
pressure and well conditions are such that perforating with casing gun 
assemblies is not practical. Typical of the casing gun types of 
perforating assemblies are those disclosed in prior U.S. Pat. No. 
4,253,523 and prior pending patent application, U.S. Ser. No. 299,479, 
filed Sept. 4, 1981, now U.S. Pat. No. 4,467,878 for SHAPED CHARGE AND 
CARRIER ASSEMBLY THEREFOR. 
It is now proposed to provide a through-tubing perforating assembly capable 
of achieving much greater penetration and specifically in such a way as to 
be able to employ standard casing gun charges possessing the desired 
penetrating configuration while withstanding high pressure conditions; yet 
can be passed through relatively small diameter tubing to the desired zone 
or formation to be perforated. 
Representative U.S. Letter Patents disclosing through-tubing perforating 
apparatus are U.S. Pat. Nos. 2,746,828 to H. H. Rachford, Jr.; 3,207,072 
to J. R. Holden; 3,234,875 to E. O. Tolson; 3,238,872 to L. Zernow et al; 
3,244,101 and 3,268,016 to W. T. Bell; 3,259,064 to N. G. Owens; 3,302,567 
to A. A. Venghiattis; 3,419,070 to E. A. Ernst; 3,517,745 to G. O. Suman, 
Jr.; and 3,627,045 to M. P. Lebourg. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide for a novel 
and improved perforating assembly adaptable for use in perforating 
subsurface oil and gas subsurface formations which is versatile and of 
simplified construction. 
It is another object to provide for a novel and improved form of 
perforating assembly which is capable of perforating either through casing 
or tubing and which is capable of using shaped charges normally employed 
in casing guns. 
Another object of the present invention is to provide for a through-tubing 
perforating assembly which employs casing gun charges to achieve narrow 
cone angles with much greater penetration than heretofore possible and 
permits disposition in phase or out of phase through an adjustable length 
carrier containing the desired number of charges. 
It is a still further object of the present invention to provide for a 
through-tubing perforating assembly which can be made up of the desired 
number of casing gun charges disposed either in centered or off-center 
relationship within a casing and capable of withstanding extremely high 
pressures at the bottom of a well. 
It is an additional object of the present invention to provide in a 
perforating assembly for novel and improved modular high-strength sections 
for mounting and support of a series of shaped charges either in phase or 
in out of phase relation to one another. 
In accordance with the present invention, there has been devised a novel 
and improved form of through-tubing perforating assembly conformable for 
use in various types of cased well bores but having particular application 
in those in which a tubing string is positioned within the cased well bore 
and where extremely high pressures are encountered at the bottom of the 
well. In the preferred form of assembly, a plurality of shaped charges of 
the casing gun type are mounted in a modular carrier wherein the carrier 
comprises a plurality of generally tubular members interconnected in 
end-to-end relation to one another, each tubular member having an internal 
cavity defining a horizontally directed seating portion for supporting one 
of the shaped charges therein. An end cap is disposed at the lower end of 
the modular carrier, and a blasting cord extends continuously through the 
tubular members across one end of the shaped charges for detonating the 
charges when positioned opposite to that part of the formation to be 
perforated. Each of the tubular members is characterized in particular by 
the mounting and disposition of the shaped charges such that they can be 
cradled or supported within the tubular member and anchored in place by 
interconnection of each next tubular member in succession without the use 
of separate fastening elements. The desired number of charges and tubular 
members can be interconnected in end-to-end relation with the blasting 
cord extending through grooved portions passing across slotted ends of 
each of the shaped charges so that when the tubular members are made up 
together the shaped charge in each tubular member is caused to bear firmly 
against the blasting cord at its slotted end to assure detonation of the 
charge when the blasting cord is ignited. The tubular members are such 
that they can be aligned with their respective charges extending either in 
phase or in 180.degree. out of phase relation to one another and suspended 
downwardly through an inner tubing string to the desired depth. The 
charges may be placed either in centered relation to the cased wall bore 
or in off-center relation and may be suspended by various well-known 
means, such as, a wireline tool. 
Other objects, advantages and features of the present invention will become 
more readily appreciated and understood when taken together with the 
following detailed description in conjunction with the accompanying 
drawings, in which:

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
A preferred form of perforating assembly 10 is comprised of a plurality of 
tubular modules 12 interconnected in end-to-end relation to one another 
and terminating at their lower end in a nose cone 14 and at their upper 
end in a tubing support connector 16. The tubular modules 12 as well as 
nose cone 14 have upwardly directed socket ends, for example, as 
illustrated at 18 in FIG. 3 with diametrically opposed internal locking 
dogs or teeth 19 adapted to interengage with external locking dogs or 
teeth 20 at the lower end of each module 12 as well as the lower end of 
the upper support connector 16. Thus, each lower complementary end 22, as 
shown in FIGS. 3, 4 and 5, is of a reduced external diameter slightly less 
than the diameter of the internal wall surface of the upper socket ends 18 
and is provided with diametrically opposed dogs 20 which are advanced past 
the diametrically opposed internal locking dogs 19 then rotated into 
locking engagement behind the dogs as shown in FIG. 3. A circumferential 
groove 24 is spaced above the locking dogs 20 to accommodate an O-ring 
seal 25 which effects sealed engagement between the reduced lower end 22 
and upper socket end 18 of each of the modules when interconnected in 
end-to-end relation to one another. 
Each of the tubular modules 12 is provided intermediately of its upper and 
lower ends with an internal cavity defining a horizontally disposed cradle 
or support 26 for horizontal disposition of a shaped charge C, as 
illustrated in FIGS. 5 and 6. A Prima cord 30 is passed downwardly through 
the entire assembly of modules from the upper support connector 16 and 
through vertically extending slots 31 disposed at the ends of the supports 
26 in the modules so as to position the Prima cord at the nose end of the 
shaped charges C positioned therein. The lower extreme end of the Prima 
cord 30 is inserted into an arcuate groove 32 located internally of the 
lower extremity of the nose cone 14. As shown in FIG. 1, the upper end of 
the Prima cord 30 is secured to a blasting cap 34 in a conventional 
manner, the cap 34 having leads 35 passing upwardly through a central 
passage 36 in the upper support connector 16 for connection to a wireline 
tool in a manner hereinafter described. In this relation, the Prima cord 
30 is preferably of rectangular cross-section. 
Considering in more detail the construction of each modular tubing section 
12, each is correspondingly formed with a thin-walled socket end 18 having 
an inner wall surface 40 of a diameter to permit insertion of the external 
wall surface 42 of the male end of the next module. As described, the 
external diameter of the male end is reduced by an amount corresponding to 
the thickness of the socket end 18 and is relatively thick-walled with an 
inner wall surface 44 forming a central passage in communication with the 
socket end 18. The cradle support 26 is formed at the upper end of the 
passage 44 by arcuate recessed portions 46 in diametrically opposed sides 
of the inner wall surface and which together form a generally 
semi-cylindrical, horizontal support for the lower half of the shaped 
charge C. 
As seen from FIG. 6, an upper tubing adaptor module 12' is comprised of a 
hollow cylindrical body 52 having a lower end 20 corresponding to the male 
end 20 of modular sections 12 together with an oppositely directed male 
end 20' which corresponds to the male end 20 but is provided with one or 
more circumferential grooves 24' to facilitate interlocking sealed 
connection to lower socket end 54 on the tubing support connector 16. The 
support connector 16 also is of tubular construction having a lower socket 
end 18' provided with diametrically opposed internal locking dogs 19'. The 
support connector tapers rearwardly as at 58 into a threaded end portion 
59 to facilitate interconnection to a wireline tool, not shown, in a 
well-known manner. A central passage 62 extends through the support 
connector 16 into communication with the socket end 18' to permit 
extension of the connecting wires or leads from the wireline tool. 
Preferably, the support connector 16 is composed of a high strength metal 
which will not be damaged when the charges C are detonated so that the 
connector can be retrieved along with the wireline tool. However, the 
modules 12 are preferably composed of a ceramic material of sufficiently 
high strength to withstand substantial pressures downhole but which will 
be completely disintegrated by the detonation of the charges. 
In practice, the modules 12 are assembled first by positioning the lower 
end of the Prima cord 30 in the slot 32 formed in the interior of the end 
cap 14, followed by interconnection of the first module 12 to the end cap 
14. The Prima cord 30 is passed upwardly through the module 12 and 
inserted into the slot 31 prior to placement of a shaped charge C on the 
cradle 26 within the module. A slotted end C' of the charge C is aligned 
with the slot 31 so as to sandwich the Prima cord 30 therebetween. A 
second module 12 is then interlocked as described with the first module, 
the lower edge of the second module bearing lightly against the upper 
surface of the charge C so as to securely retain the charge in position 
within the first module. A series of modules 12 are successively assembled 
in the manner described with respect to the first and second modules in 
accordance with the number of charges C to be employed. For the purpose of 
illustration, the number of charges may vary over a wide range with each 
charge containing from 6 grams to 22 grams of explosive. The specific 
makeup of the charges, as such, forms no part of the present invention. 
However, of particular importance is the fact that the modular carrier is 
so constructed as to permit use of casing gun charges, such as, those of 
the type disclosed in my hereinbefore referred to U.S. Pat. No. 4,253,523 
and pending patent application. 
Alignment markings or arrows 50 on the external surfaces of the modules 12 
will assure exact alignment of the charges C within the modules so that 
the charges can be directed precisely in the same direction or with 
adjacent charge positioned at 180.degree. to one another throughout the 
assembly; i.e., the charges can be disposed either in phase or in out of 
phase relation to one another depending upon the specific application of 
the assembly. In FIG. 1, assembly 10 is shown suspended in off-center 
relation to a casing S which is cemented in a well bore. The tubing string 
T is sealed off at its lower end by a packer P above the section of the 
casing to be perforated, but imposes definite limitations on the size or 
diameter of the assembly 10, since it must be lowered through the tubing 
string. In the application shown in FIG. 6, where it is desired to 
maintain the assembly 10 in centered relation to a casing, suitable 
centralizers are employed between the assembly 10 and the wireline which 
will expand into engagement with the casing and maintain the assembly 10 
in the center of the casing. In such applications, it is desirable to 
position the charges C in out-of-phase relation to one another in order to 
penetrate through diametrically opposed sides of the casing and into the 
formation. 
From the foregoing, it will be readily appreciated by those skilled in the 
art that the through-tubing perforating assembly of the present invention 
offers the ability to enhance production capabilities on new and old 
wells. For instance, in deep wells where high pressure and temperature can 
complicate completion, the present invention offers the ability to 
maximize perforation performance for operations of up to 25,000 psi at 
650.degree. F.; or, where formation characteristics dictate multiple zone 
completion, it offers maximized perforation performance. Moreover, where 
perforation characteristics dictate massive interval completion, the 
present invention offers the ability to perforate at whatever shot density 
is desired and over the desired interval by making repeated runs. A 
modular perforating assembly of the type described further eliminates 
downhole obstruction below the tubing, which in some cases eliminates the 
possibility and avoids the necessity of workover procedures, such as, zone 
isolation. In large diameter holes completed through-tubing, the modular 
perforating assembly of the present invention offers the ability to use 
the same charges with the same perforation performance as normally would 
be expected using a hollow steel carrier gun in casing applications. 
Accordingly, the present invention offers a total expendible, 
acid-resistant ceramic carrier for use with powdered metal-shaped charges 
for debris-free completion. As a result, it is readily conformable for use 
with any superior shaped-charge technology with the added advantage of 
offering maximum perforation performance unaffected by high pressure and 
temperature conditions. 
Thus, while there has been described a preferred embodiment of the present 
invention, it is to be understood that various modifications and changes 
may be made as will be apparent to those skilled in the art without 
departing from the spirit and scope of the present invention as defined by 
the appended claims.