High temperature shaped charge perforating apparatus

A shaped charge perforating unit includes a housing having a cavity formed therein. An explosive charge of high explosive material is retained within the cavity by a liner of non-explosive material. The explosive charge consists of quantities of two explosive materials having different detonation sensitivities.

BACKGROUND OF THE INVENTION 
This invention relates in general to shaped charge perforators and more 
particularly, to a high temperature shaped charge perforating unit having 
two high explosive materials. 
Explosive shaped charge well perforating devices are often used in 
perforating well casing and the surrounding earth formations in the 
production of hydrocarbons. In a typical embodiment, a plurality of shaped 
charges are mounted in a fluid-tight, cylindrical, metal housing or on an 
elongated bar member which is adapted to traverse the borehole to be 
perforated. The shaped charges are mounted in the housing or on the bar 
member at longitudinally spaced intervals, with their axis of perforating 
directed generally laterally thereof. A more detailed description of a 
typical perforating apparatus is contained in U.S. Pat. No. 4,428,440, 
which is incorporated herein by reference. 
The shaped charge most common in well perforating is a conical shaped 
charge. A conical shaped charge consists of an explosive material having a 
substantially conical cavity formed in the front face. A metal liner 
material covers the face of the cavity. Upon detonation the shape of the 
explosive cavity focuses and propagates a progressive wave front against 
the outside surface of the metal line. At the pressures generated the 
metal acts as a fluid. Metal in fluid form is focused into a "jet" stream. 
The resultant focusing force moves particles to form a jet which lengthens 
as the wave front advances from apex to base of the conical cavity. The 
extreme high pressure, particle laden, jet stream breaks down and moves 
aside any material upon which it impinges. Penetration of such material is 
a result of the amount of pressure and the kinetic energy in the jet 
stream. One form of conical shaped charge used in well perforating is 
illustrated in U.S. Pat. No. 4,387,773, which is incorporated herein by 
reference. 
The present invention provides method and apparatus for perforating a well 
casing and the surrounding formations in a high temperature environment, 
above 500.degree. F., using a lined shaped charge employing an explosive 
material consisting of quantities of two explosive materials having 
different detonation sensitivities. 
SUMMARY OF THE INVENTION 
A shaped charge perforating unit comprises a charge case or housing with an 
internal cavity formed therein. An explosive charge of high explosive 
material conforms an exterior shape with the inside of the cavity and is 
retained in place by a liner of non-explosive material. The explosive 
material comprises quantities of two high temperature explosive materials, 
one having a relatively high detonation sensitivity and the other having a 
relatively low detonation sensitivity.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring now to the FIGURE, there is illustrated a lined shaped charge 
unit 10 adapted for use in a perforating gun for perforating oil well 
casing and the surrounding formations. The housing or shell 12 may be made 
of any suitable material, such as, for example steel. Housing or shell 12 
may have any one of numerous outside configurations as is common in the 
art, for example a generally uniform outside diameter or a frusto-conical 
appearance. 
The cavity formed in the interior of housing 12 may be conical, 
hemispherical or other suitable configuration. As illustrated in the 
FIGURE, the cavity has a generally cylindrical forward end portion 14, a 
tapered, intermediate portion 16 and an apex with a reduced rear end 
extension 18. Rear end extension 18 comprises an inwardly tapered first 
portion 34 and an outwardly tapered second portion 36. The explosive 
charge comprises a tubular or annulus shaped body of high explosive 
material 20, conforming in exterior shape with the shape of the inner 
surface of the cavity formed within housing 12. A liner 22 retains the 
explosive charge within housing 12. Liner 22 is illustrated as conical in 
shape, however, it should be recognized that it could be of other suitable 
shapes, for example hemispherical. Liner 22 is constructed of a suitable 
non-explosive material, preferably having a relatively high density, such 
as, for example copper. 
In the illustrated embodiment explosive material 20 consists of quantities 
of two high explosives having different detonation sensitivies. A quantity 
of a first high temperature, high explosive material 24 fills rear end 
portion 18 including inwardly tapered first portion 34 and outwardly 
tapered second portion 34. The remainder of the cavity, comprising forward 
end portion 14 and intermediate portion 16, contain a quantity of a second 
high temperature, high explosive material 26 having a detonation 
sensitivity differing from that of first explosive material 24. Explosive 
material 20 should consist of a relative distribution of one-third or less 
of first explosive material 24 with the remainder comprising second 
explosive material 26. 
In one embodiment of the present invention first explosive material 24 is 
an explosive having a relatively high detonation sensitivity. Such 
explosive will have an impact sensitivity in a range less than 30 cm. 
Examples of suitable explosive materials are hexanitrostilbene, commonly 
referred to as HNS. Other suitable first explosive materials are Picryl 
Sulfone and PYX. HNS, at a density of 1.70, has an impact sensitivity of 
28 cm. In this embodiment the second explosive material 26 is an explosive 
having a relatively low impact sensitivity. Such explosive will have an 
impact sensitivity in a range greater than 300 cm. Examples of suitable 
explosive materials are diamenotrinetrobenzene, commonly referred to as 
DATB, or Triaminotrinitro Benzene, commonly referred to as TATB. DATB, at 
a density of 1.6, has an impact sensitivity greater than 360 cm. 
Proximate the rear portion of the first explosive material 24 is located a 
high temperature detonating fuse 30. Detonating fuse 30 is a conventional 
detonator such a 80-100 grain high temperature detonating cord. A port 
plug or sealing member 32 is affixed to housing 12 to provide a fluid 
tight seal. Port plug 32 is formed with a relatively thin end wall 
positioned substantially in alignment with the axis of symmetry, the 
perforating axis, of the shaped charge unit. 
In the operation of the invention, detonator fuse 30 is detonated by an 
ignitor or blasting cap (not shown). Detonator fuse 30 will detonate 
explosive material 20. A detonation wave thus caused travels forwardly and 
strikes the apex of liner 22. The wavefront continues to travel forwardly 
through the main explosive material section, simultaneously collapsing 
liner 22 symmetrically inwardly about the axis of liner 22 causing the 
inner surface of liner 22 to flow and form part of a jet stream. The liner 
material upon arrival at the axis of symmetry separates into a fast moving 
jet carrying most of the particles. 
The detonation wavefront impacting liner 22 can be tailored by altering the 
design of the interface between first explosive material 24 and second 
explosive material 26. If the interface between first explosive material 
24 and second explosive material 26 is convex, the detonation waves can be 
made to arrive simultaneously at the apex of liner 22 providing a jet tip 
which is produced by implosion. Conventional initiation is produced by a 
flat interface between the two explosive materials, 24 and 26. 
Many modifications and variations besides those specifically mentioned may 
be made in the techniques and structures described herein and depicted in 
the accompanying drawing without departing substantially from the concept 
of the present invention. Accordingly, it should be clearly understood the 
form of the invention described and illustrated herein is exemplary only, 
and is not intended as a limitation on the scope of the present invention.