Ammunition and explosives – Blasting – Patterned blasting
Reexamination Certificate
2000-02-03
2002-10-08
Nelson, Peter A. (Department: 3641)
Ammunition and explosives
Blasting
Patterned blasting
C102S313000, C102S331000
Reexamination Certificate
active
06460463
ABSTRACT:
BACKGROUND
The invention is generally related to recesses in explosive carrier housings (such as perforating gun carrier housings) that provide for improved explosive performance (such as improved performance perforating shaped charges).
After a well has been drilled and casing has been cemented in the well, perforations are created to allow communication of fluids between reservoirs in the formation and the wellbore. Shaped charge perforating is commonly used, in which shaped charges are mounted in perforating guns that are conveyed into the well on a slickline, wireline, tubing, or another type of carrier. The perforating guns are then fired to create openings in the casing and to extend perforations into the formation.
Various types of perforating guns exist. A first type is a strip gun that includes a strip carrier on which capsule shaped charges may be mounted. The capsule shaped charges are contained in sealed capsules to protect the shaped charges from the well environment. Another type of gun is a sealed hollow carrier gun, which includes a hollow carrier in which non-capsule shaped charges may be mounted. The shaped charges may be mounted on a loading tube or a strip inside the hollow carrier. Thinned areas (referred to as recesses) may be formed in the wall of the hollow carrier housing to allow easier penetration by perforating jets from fired shaped charges. Another type of gun is a sealed hollow carrier shot-by-shot gun, which includes a plurality of hollow carrier gun segments in each of which one non-capsule shaped charge may be mounted.
Another type of gun is a puncher gun, designed to perforate the interior tubing, casing, drillpipe or similar wellbore lining while leaving the exterior tubing, casing, drillpipe, drill collar or similar wellbore lining intact. Another type of gun is a cutter designed to perforate the tubing, casing, drillpipe, drill collar or similar wellbore lining in a pattern which will allow removal of same without damage to the formation or other wellbore structures.
Referring to
FIGS. 1A-1C
, an example of a conventional perforating gun
10
including a hollow carrier
12
is illustrated. The hollow carrier
12
contains plural shaped charges
20
that are attached to a strip
22
. Alternatively, the shaped charges
20
may be attached to a loading tube inside the hollow carrier
12
. In the illustrated arrangement, the shaped charges
20
are arranged in a phased pattern. Non-phased arrangements may also be provided.
The hollow carrier
12
has a housing that includes recesses
14
that have generally circular recesses, as illustrated in FIG.
1
A. The recesses
14
are designed to line up with corresponding shaped charges
20
so that the perforating jet exits through the recess to provide a low resistance path for the perforating jet. This enhances performance of the jet to create openings in the surrounding casing as well as to extend perforations into the formation behind the casing.
As shown in the cross-sectional view of FIG.
1
B and the longitudinal sectional view of
FIG. 1C
, each recess
14
includes a bottom surface
18
and a side surface
16
. A web
19
(which is a thinned region of the carrier housing
12
) is formed below the recess
14
. The side surface
16
and the bottom surface
18
are generally perpendicular to each other. The bottom surface
18
and side surface
16
define a generally cylindrical geometry in the recess
14
. As will be described below, the generally perpendicular side surface
16
of a typical recess
14
causes reflection of compression waves that interfere with the perforating jet (from a fired shaped charge) as it extends through the recess
14
. For big hole charges, this reduces the opening in the casing created by the perforating jet. For deep penetrating charges, the depth of penetration may be reduced.
Referring to
FIGS. 2A-2B
, a generally conical shaped charge
20
includes an outer case
32
that acts as a containment vessel designed to hold the detonation force of the detonating explosive long enough for a perforating jet to form. The generally conical shaped charge
20
is a deep penetrator charge that provides relatively deep penetration. Another type of shaped charge includes substantially non-conical shaped charges (such as pseudo-hemispherical, parabolic, or tulip-shaped charges). The substantially non-conical shaped charges are big hole charges that are designed to create large entrance holes in casing. Another type of shaped charge is a puncher charge which is a specialized version of a big hole charge designed to create large hole with a specific, short range of penetration.
The conical shaped charge
20
illustrated in
FIG. 2A
includes a main explosive
36
that is contained inside the outer case
32
and is sandwiched between the inner wall of the outer case
32
and the outer surface of a liner
40
that has generally a conical shape. A primer
34
provides the detonating link between a detonating cord (not shown) and the main explosive
36
. The primer
34
is initiated by the detonating cord, which in turn initiates detonation of the main explosive
36
to create a detonation wave that sweeps through the shaped charge
20
. As shown in
FIG. 2B
, upon detonation, the liner
40
(original liner
40
represented with dashed lines) collapses under the detonation force of the main explosive
36
. Material from the collapsed liner
40
flows along streams (such as those indicated as
49
) to form a perforating jet
46
along a J axis.
The tip of the perforating jet travels at speeds of approximately 25,000 feet per second and produces impact pressures in the millions of pounds per square inch. The tip portion is the first to penetrate the web
19
below the recess
14
in the housing
12
of the gun carrier. The perforating jet tip then penetrates the wellbore fluid immediately in front of the web and inside the geometry of the recess
14
. At the velocity and impact pressures generated by the jet tip, the wellbore fluid is compressed out and away from the tip of the jet. However, due to confinement of the wellbore fluid by the substantially perpendicular side surface
16
of the recess
14
, the expansion, compression, and movement of the wellbore fluid is limited and the wellbore fluid may quickly be reflected back upon the jet at a later portion of the jet (behind the tip).
As the perforating jet passes through the recess
14
(FIGS.
1
B and
1
C), a compression wave front is created by the perforating jet in the fluid that is located in the recess. When the compression wave impacts the side surface
16
, a large portion of the compression wave is reflected back towards the perforating jet, which carries the wellbore fluid back to the jet. The reflected wellbore fluid interferes with the perforating jet. The effect is more pronounced in a relatively deep recess with a perpendicular side surface (such as side surface
16
), or if the clearance between the gun carrier and the casing is limited (that is, the gun carrier is close to the casing). When the clearance between the gun carrier and the casing is limited, interactions between the reflected compression wave off the inside surface of the wellbore casing and the reflected compression wave off the side surface
16
of the recess
14
also combine to impede the free passage of the shaped charge jet through the wellbore fluid. The resultant interference with the perforating jet may reduce the depth of penetration (for deep penetrating charges) or the size of the casing entrance hole (for big hole charges).
In addition to the desire to improve performance of the perforating jet, the recess formed in a gun carrier housing should also account for other factors. As shown in
FIGS. 1B and 1C
, the recess
14
is formed below the outer surface of the carrier housing
12
. As the shaped charge perforating jet passes through the web
19
of the carrier housing
12
, an exit burr may be created that protrudes towards the outside of the carrier housing. However, by having recesses (and webs below the recesses) for the jets to p
Denney Janet S.
Fayard Alfredo
Lands Jack F.
Parrott Robert A.
Griffin Jeffrey E.
Jeffery Brigitte
Nelson Peter A.
Schlumberger Technology Corporation
Trop Pruner & Hu P.C.
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