Positive alignment insert (PAI) with imbedded explosive

Details Positive alignment insert (PAI) with imbedded explosive Positive alignment insert (PAI) with imbedded explosive

1999-05-20

2001-10-02

Johnson, Stephen M. (Department: 3641)

Ordnance

Well perforators

C102S275700, C102S275120

Reexamination Certificate

active

06295912

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates generally to perforating a well bore with a plurality of perforating guns. More specifically, the present invention relates to an improved apparatus for transferring the detonating reaction from one gun to the next gun without interruptions.
2. Description of the Related Art
Well bore or down hole perforating guns can be conveyed into a well bore in one of two methods—first by using a wireline for conveying the perforating gun, including slickline (conductorless wireline); and second, by using tubing for conveying the perforating gun. In the wireline conveyance method, a hollow carrier gun is attached to the wireline by means of a perforating head. A wireline is a cable which contains at least one electrical conductor. The gun is lowered into the well bore and aligned across the geologic zone of interest and electrically detonated from the surface. Wireline perforating is generally limited to combinations of guns totaling 30 or 40 feet in length due to the weight of the guns on the wireline.
The second conveyance method is by tubing conveying perforating (TCP) guns. Conveying perforating guns into a well bore using tubing generally requires a much longer time for descent to the geologic zone of interest. Once at the zone of interest, the guns are again aligned and detonated. Detonation is initiated either by percussion (i.e., by dropping a bar or weight through the tubing striking the detonation head of the perforating gun); pressure (i.e., by increasing the hydrostatic pressure within the tubing until it reaches a predetermined pressure on the perforation head, at which time a shear pin is broken and the perforating gun is detonated); or electrically (i.e., by lowering a wireline through the tubing which connects to the perforating head of the gun and detonating the perforating gun by passing an electrical current through the wireline to the perforating head).
There are two primary advantages of tubing conveying perforating guns over wireline conveying perforating guns. First, the length of the guns in the tubing conveying method can be much longer because tubing supports a much higher gun weight than wireline. Second, the well bore need not be vertical but might, instead, be highly deviated or even horizontal; and the tubing conveying perforating guns can still be deployed across the geologic zone of interest.
Wireline conveying perforating guns, on the other hand, have the advantage of reduced trip time in and out of the well bore. For instance, a thin geologic zone of interest which requires one run or trip in the well bore, where the well bore is substantially vertical, takes much less trip time than using tubing as a conveyance. A wireline conveying perforating gun can be lowered into the well bore, the casing perforated, and the spent perforating gun retrieved out of the well bore in less time than it would take to lower the tubing conveying perforating gun. As opposed to using wireline, it takes much longer to run lengths of tubing into the well bore by connecting one tubing stand or joint at a time and positioning detonating the tubing conveying perforating gun either hydraulically, mechanically or electrically.
However, because the maximum perforating gun weight for tubing is much higher than for wireline, one trip into the well bore using tubing might yield a perforated interval equivalent to many wireline trips into the well bore. Also, perforating horizontal and highly deviated wells may require tubing as a means to move the perforating gun because the perforating gun will no longer fall with gravity due to the amount of deviation in the well bore.
Generally, temperature increases with well depth, and well bore temperatures of 400° F. to 450° F. are not uncommon. The explosive components of a perforating gun are particularly susceptible to the effects of high temperatures in well bores. At temperatures above the rating of a particular explosive component, detonation results become unpredictable. A high order detonation (i.e., one in which the explosive reacts at an extremely rapid rate, generating a simultaneous pressure wave) is necessary for an explosive charge to perforate a well bore, and it is less likely in cases where the well bore temperature exceeds the temperature rating of the explosives. Another factor which reduces the likelihood of a high order detonation is the amount of time the explosive is exposed to certain temperatures. Explosives are rated by time limit and maximum temperature. Generally, the higher the temperature, the less time the explosive can tolerate that temperature and still predictably detonate at high order.
FIG. 1
illustrates a typical time/temperature chart for explosives used in perforating guns. 2,6-bis(Picrylamino)-3,5-dinitropyridine (PYX), hexanitrostilbene (HNS), cyclotetrimethylenetetrinitramine (HMX), and cyclotrimethylenetrinitramine (RDX) are common explosives used in the oil well perforating industry. Note from operating curve
10
, that PYX is rated at 450° F. for 1000 hours, but the time at 550° F. drops to 10 hours. The time/temperature operating curves for PYX
10
, HNS
20
, HMX
30
and RDX
40
are roughly parallel through different operational temperatures.
FIG. 2
illustrates the components in a typical perforating gun system. A conventional perforating gun consists of three explosive components. The first, used at the initiating stage, is the blasting cap or detonator (not shown). Detonators can be either electric or percussion. The blasting cap initiates the detonation that is transferred through detonating cord
102
(second component) to individual shape charges
104
(third component). The detonating cord may be run from one end of the gun to the other and provides an explosive shock wave of sufficient force to detonate each shape charge. Shape charges are usually oriented perpendicular from the axial line of the gun. The detonator cord runs behind each shape charge and triggers a small primer charge (not shown) in each individual shape charge
104
when detonated.
In instances where the interval to be perforated is longer than any one perforating gun length, perforating guns must be combined in order to obtain the proper length. In wireline operations, each gun can be configured with its own blasting cap and fired sequentially from the bottom up. However, there are instances in which two perforating guns are detonated simultaneously. Two guns, top or upper perforating gun
106
and bottom or lower perforating gun
108
can be joined with a gun head adapter or transfer sub which consists of two short, threaded stubs of steel crossover pin-and-box
110
and grooved tandem
120
. Detonating cord
102
fastens through crossover pin-and-box
110
and grooved tandem
120
, passing from the upper perforating gun
106
to the lower perforating gun
108
. Detonating cord
102
is usually separated at the makeup point between crossover pin-and-box
110
and grooved tandem
120
. Thus, the length of the gun can be divided into two smaller guns, upper perforating gun
106
and lower perforating gun
108
, and re-combined at the well site by inserting grooved tandem
120
into crossover pin-and-box
110
. The detonation, therefore, must propagate from detonating cord
102
in upper perforating gun
106
to detonating cord
102
in lower perforating gun
108
.
In order to facilitate the propagation of the detonation from upper perforating gun
106
to lower perforating gun
108
, or visa versa, each end of detonating cord
102
is usually terminated with a bi-directional booster at both crossover pin-and-box
110
and grooved tandem
120
. Upper bi-directional booster
116
is positioned by upper booster sleeve
126
in upper gun
106
and lower bi-directional booster
118
is positioned by lower booster sleeve
128
in lower gun
108
. A bi-directional booster provides an extra boost of explosive force, propelling the explosive shock wave from the first booster toward the second booster, which then reinitiates the detonating cord on the sec

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