Boring or penetrating the earth – Boring with explosion in inaccessible hole – With bore condition firing control – or compensating means
Reexamination Certificate
2000-08-18
2001-10-09
Pezzuto, Robert E. (Department: 3671)
Boring or penetrating the earth
Boring with explosion in inaccessible hole
With bore condition firing control, or compensating means
C175S004600
Reexamination Certificate
active
06298924
ABSTRACT:
BACKGROUND
The invention relates to a safety method and apparatus for a perforating gun.
Referring to
FIG. 1
, a typical perforating gun string
10
may have several perforating guns
12
. Each perforating gun
12
may have phased shaped charges
14
that are used to penetrate a casing of a subterranean well and form fractures in surrounding formations to enhance the production of well fluids from these formations. Because the shaped charges
14
may potentially inflict harm if the charges
14
prematurely detonate, several safety mechanisms typically are used to prevent accidental detonation of the shaped charges
14
.
For example, the shaped charges
14
may be secondary explosives that, as compared to primary explosives, are very difficult to detonate. To detonate these secondary explosives, the perforating gun string
10
may have a firing head
11
that is associated with each perforating gun
12
. In this manner, the firing head
11
may include a detonator
15
that, when activated, detonates a primary explosive to initiate a shockwave on a detonating cord
17
that extends to the shaped charges
14
. The shockwave, in turn, propagates down the detonating cord
17
and detonates the shaped charges
14
. Because the primary explosive is capable of being detonated by naturally occurring phenomena, extreme care must be exercised to ensure that the primary explosive does not prematurely detonate.
The detonation of the perforating gun
12
may be remotely controlled from the surface of the well. To accomplish this, stimuli may be transmitted downhole to the firing head
11
to cause the detonator
15
to initiate the shockwave on the detonating cord
17
. As examples of techniques that are used to transmit the stimuli, an internal passageway of the string
10
, an annulus that surrounds the string
10
, a tubing of the string
10
, or a line (a slickline or a wireline, as examples) extending downhole may all be used. Other techniques may also be used to transmit command stimuli downhole.
Detonation of the primary explosive typically requires energy from an energy source, a source that may either be located at the surface of the well or downhole in the perforating gun string
10
. If the energy source is at the surface of the well, then an operator may disconnect the energy source until firing of the perforating guns
12
is desired. However, unfortunately for the other case, connection/disconnection of a downhole energy source may present difficulties, as circuitry (not shown) of the firing head
11
must connect/disconnect the energy source. For example, a battery
16
of the string
10
may provide the energy needed to cause the detonator
15
to initiate a shockwave on the detonating cord
17
. However, a problem with this arrangement is that the battery
16
is located downhole with the detonator
15
. Thus, if the circuitry that couples the battery
16
to the detonator
15
should fail, the shaped charges
14
may be inadvertently detonated.
Thus, there is a continuing need for a downhole safety system to reliably prevent accidental detonation of a perforating gun when an energy source to detonate the gun is located downhole with the gun.
SUMMARY
Generally, in one embodiment, an apparatus for use in a subterranean well includes a downhole energy source, a first switch, a second switch, a detonator, a first controller and a second controller. The first switch has a first predetermined state to transfer energy from the energy source, and the second switch has a second predetermined state to transfer the energy from the energy source. A detonator receives the energy from the energy source when the first switch and second switches are concurrently in the first and second predetermined states. A first controller independently detects a predetermined stimulus that is transmitted from the surface of the well and causes the first switch to enter to first predetermined state based on the detection by the first controller. A second controller independently detects the predetermined stimulus transmitted from the surface of the well and causes the second switch to enter the second predetermined state based on the detection by the second controller.
Generally, in another embodiment, a method for use in a subterranean well includes furnishing a predetermined stimulus downhole and using at least two controllers downhole to independently detect the predetermined stimulus. A downhole energy source is coupled to a detonator based on the detection of the stimulus by all of the at least two controllers.
Other embodiments will become apparent from the following description, from the drawing and from the claims.
REFERENCES:
patent: 4478294 (1984-10-01), Sumner
patent: 4660638 (1987-04-01), Yates, Jr.
patent: 4867266 (1989-09-01), Martin
patent: 4895218 (1990-01-01), Chen et al.
patent: 4928783 (1990-05-01), Crook
patent: 5278359 (1994-01-01), Miller et al.
Spring Christian C.
Vaynshteyn Vladimir
Pezzuto Robert E.
Schlumberger Technology Corporation
Trop Pruner & Hu P.C.
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