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(11) | EP 0 129 350 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Method and apparatus for detecting firing of perforating gun |
| (57) The present invention provides a method and apparatus for detecting complete firing
of a perforating gun (24), particularly a perforating gun suspended on a string of
tubing (14). The apparatus includes a time delay device (40) coupled to the lower
end of the perforating gun (24) and arranged for ignition by an ignition train within
the perforating gun. Completefiring of the perforating gun ignites the time delay
device, which produces a distinctive signal. The distinctive signal is detected at
the surface by at least one transducer (40), which is coupled to a recorder assembly
(48). The recorder assembly provides an indication as to whether the perforating gun
fired as intended. |
[0001] The present invention relates generally to the field of oil well completion and formation testing and, more particularly, to the art of perforating a geological formation for the purpose of producing hydrocarbon fluids therefrom. Still more particularly, the present invention includes a method and apparatus tor determining that the charges of a perforating gun have detonated, whereby one is assured that the perforating gun has operated .as intended.
[0002] There presently exists a variety of methods and apparatus for completing oil and/or gas wells. One common method involves the use of a perforating.gun or guns suspended within the borehole by means of a wireline. The wireline gun typically includes electrical apparatus for firing the gun, such apparatus including control means at the surface connected through an electrical cable to a firing means on the perforating gun. Once fired, the wireline gun may be retrieved relatively easily by winding the wireline out of the borehole. In the case of an expendable wireline gun, the gun self-destructs on firing rendering retrieval unnecessary.
[0003] A second completion method, now well known in the art, involves the use of a perforating gun or guns suspended at the lower end of a string of tubing. U.S. Patent No. 3,706,344 ;discloses the method of suspending a perforating gun on a tubing string within a cased borehole, setting a packer so as to sealingly enclose the lower end of the borehole between the tubing and the borehole casing above the hydrocarbon formation to be produced, actuating the perforating gun, and producing the well through the tubing string on perforation. The perforating gun may be actuated, for example, by dropping a bar through the tubing string to impact a firing head on the upper end of the perforating gun. It may be desirable, depending on the nature of the completion, to cascade a plurality of guns so as to achieve multiple perforations and/or completions.
[0004] Perforating guns are also used in connection with formation testing procedures, wherein the hydrocarbon formation is first perforated and then produced through testing apparatus to obtain the data necessary to evaluate the potential of the formation. Such data is also interpreted to determine other pertinent information, such as what techniques should be used to complete the well.
[0005] A typical perforating gun which may be used in the procedures described above includes a generally cylindrical housing having a plurality of outwardly radially oriented charges distributed about the periphery thereof. The typical gun may have as few as one charge per foot or as many as fifteen charges per foot. The charges may launch a projectile which perforates the cement casing and penetrates a short distance into the geological formation or may comprise shaped charges, the detonation of which produces a jet-like, high pressure stream of hot gases and small metallic particles which penetrate the casing and form tunnels within the formation. The charges typically are connected serially along a length of primacord. Where an impact-type firing head is used, the firing head may include a firing pin which initiates a percussion primer, which in turn ignites the primacord. As the primacord detonates, the individual charges are detonated and the casing and formation are perforated.
[0006] Successful firing of all charges within a perforating gun requires that the primacord along which the charges are positioned burn at a rate of 5000 to 7000 meters per second. Such high-speed burning is termed "detpnation" and is necessary so as to develop sufficient pressure to transfer detonation to the individual charges. Occasionally, the primacord will merely "deflagrate," or burn at a speed of 1000 to 2000 meters per second. A deflagrating cord will not develop enough pressure to successfully detonate the charges and, consequently, the perforating gun fails. Typically, once deflagration has begun, a primacord will not again detonate and thereafter all charges fail to detonate.
[0007] The failure of all charges within a perforating gun to detonate can sometimes be detected merely by listening, due to the absence of an explosion. When only a portion of the charges fail to detonate, however, it is difficult or impossible to detect the failure with the human ear. Because a detonating primacord burns at a very rapid rate, ignition of the individual charges serially connected along the primacord is perceived by the human ear as a single explosion. Thus, the failure of one or more charges may be imperceptible to the human ear.
[0008] Also, in some cases, the actual firing of the perforating gun may be obscured by or confused with other noises coincident with the gun firing sequence. For example, where an impact-type firing head is used, the bar dropped through the tubing string generates noises not unlike detonating charges as it strikes various objects on its way down the tubing string. Also, in offshore operations, the swaying motion of the rig generates noise which sometimes obscures the sound of detonating charges.
[0009] Consequently, it has become a standard practice in those cases where there is any doubt as to whether the perforating gun fired properly to pull the tubing string from the borehole and examine the gun. This visual inspection procedure has several disadvantages. First, a substantial amount of time and expense may be expended in pulling the tubing string. In deeper boreholes it may take as much as a day to remove the perforating gun for examination.
[0010] Second, movement of a potentially armed perforating gun must be done with great care, further lengthening the time required to remove the gun from 'the borehole. The visual inspection procedure exposes rig workers to the risk that the unexploded charges may be detonated accidently in their presence, causing the workers injury. Accidental detonation during removal of the gun also may damage the integrity of the borehole at some point above the production zone.
[0011] Finally, at least in some cases, it will be determined that the gun fired properly. In such a case substantial time and expense was expended despite the fact that all charges within the gun fired as intended. Clearly, the visual inspection procedure for verifying proper operation of a perforating gun includes many deficiencies.
[0012] Prior art techniques for detecting perforating gun firing generally include electronic apparatus downhole and for that reason are undesirable in the present application. Known prior art techniques include: (1) an inertial switch disposed within the perforating gun and arranged to interrupt the electrical gun firing circuit in response to gun recoil from firing; (2) an accelerometer disposed within the perforating gun and arranged to generate an electrical signal in response to recoil motion of the perforating gun (see D. S. Patent No. 4,208,966) and (3)'a downhole microphone (geophone) arranged to convey the sound of the perforating gun to a speaker at the surface. While the above list may not be exhaustive, it is believed to be at least representative of the type of detection techniques available in the
prior art.
[0013] The known prior art techniques are not applicable to perforating guns which function without the assistance of electrical apparatus for gun firing and detection thereof. Such nonelectric guns, including the impact-type gun previously described, are designed to operate independently of electrical apparatus so as to avoid the complexity and expense inherent in such apparatus. The use of additional surface electronics for monitoring the firing of an electrically operated perforating gun also increases the risk that the perforating gun will be inadvertently actuated by stray electrical signals. In addition, there are certain applications wherein the temperature conditions are too hostile for use of electronics downhole. Hence, it is apparent that known prior art techniques do not provide adequate means for detecting the complete firing of a nonelectric perforating gun.
[0014] Accordingly, there is provided herein a method and apparatus for determining whether a perforating gun has fired completely, including means affixed to the perforating gun for -generating a distinctive signal, sensing means for detecting the signal, and recording means for indicating to an operator whether the gun fired completely.
[0015] The distinctive signal includes a time delay of predetermined duration followed by ignition of a charge, the combination being detected by said sensing means as a unique signature. The distinctive signal is generated by a time delay device, which includes a booster assembly, a delay column, means for igniting the delay column, and a propellant charge for generating the signal.
[0016] : The booster assembly couples an ignition train of the perforating gun to an ignition train within.the time delay device. The delay column ignition means includes a percussion primer charge with a firing pin disposed thereabove, whereby the firing pin is forced against the primer charge, which is thereby ignited, if and only if the ignition train within the perforating gun is detonating when it reaches the booster assembly.
[0017] The primer charge ignites a transfer charge, which ignites the delay column. Because the delay column burns at a known rate, a time delay of predetermined duration may be included in the time delay device. The output end of the delay column ignites a second transfer charge which in turn ignites the propellant charge.
[0018] The propellant charge may comprise a mixture of tetramethylammonium perchlorate and potassium perchlorate, which is a fast-response gas-producing combination. The gas produced by ignition of the propellant charge pressurizes a cavity and launches a blow-out plug from a housing into a catcher assembly, thereby producing a unique signal and characteristic signature of complete perforating gun firing.
[0019] The sensing means includes at least one transducer and a molded silicon rubber fixture. The fixture is slotted and includes a pair of magnets so that it may be attached to the arcuate perimeter of a wellhead flange of variable dimensions. The transducer is supported within the fixture in intimate contact with the wellhead flange.
[0020] The transducer may be an acoustic emissions transducer, an accelerometer, or a pressure transducer. An acoustic emissions transducer produces an electrical signal in response to the detection of acoustic energy. within the borehole. An accelerometer produces such a signal in response to motion of the transducer and a pressure transducer responds similarly to changes in pressure. The electrical signal produced by one or more of the transducers is communicated via a cable to a recorder assembly, where the signal is interpreted and/or displayed for interpretation. In its simplest form, the recorder assembly may be a cassette tape recorder, whereby the gun firing sequence may be recorded and replayed to determine, based upon listening for the distinctive signal, whether the perforating gun fired completely.
[0021] The recorder assembly preferably includes an oscillograph strip chart recorder for plotting the electrical signals received from the transducers. Complete gun firing is assured from a recognition of -the signature associated with the distinctive signal. Finally, the recorder assembly may be a microprocessor-based apparatus which digitizes the electrical signals from the transducer, stores the digitized signals, compares the digitized signals with signal patterns representing complete firing of the perforating gun, and indicates whether the distinctive signal was recognized.
[0022] These and various other characteristics and advantages of the present invention will become readily apparent to those skilled in the art upon reading the following detailed description and claims and by referring to the accompanying drawings.
[0023] For a detailed description of the preferred embodiment of the invention, reference will now be made to the accompanying drawings, wherein:
Figure 1 shows a cross section of a borehole having disposed therein a perforating gun on a tubing string and apparatus structured according to the principles of the invention for detecting complete firing of the perforating gun;
Figure 2 shows a cut-away and cross-sectional elevation of a time delay device structured according to the principles of the invention; †
Figure 3 shows a cross section of a portion of the time delay device, the view in Figure 3 being taken along a line 3-3 shown in Figure 2;
Figure 4 shows a cut-away and cross-sectional elevation of an alternative embodiment of the time delay device;
Figure 5 shows a portion of the time delay device of Figure 4 in greater detail;
Figure 6 shows a perspective view of a transducer assembly for use in cooperation with the time delay devices of Figures 2 and 4;
Figure 7 shows a schematic diagram of a recorder apparatus for use in conjunction with the time delay device and the transducer assembly; and
Figure 8 shows a plot of the electrical output signal from an acoustic emissions transducer, indicating a complete firing of the perforating gun.
[0024] Testing and/or completion of an oil or gas well within a hydrocarbon formation typically includes perforating a cased borehole and the surrounding geological formation, whereby hydrocarbon fluids may flow through the perforations into the cased borehole. Perforation is accomplished by means of one or more perforating guns, each of which typically comprises a generally cylindrical housing, having disposed about the internal periphery thereof a plurality of charges oriented radially outwardly.
[0025] A typical completion involves the use of a plurality of perforating guns cascaded linearly and coupled by means of explosive charges. There may be from one to over one hundred guns cascaded for a single completion. Any one well also may have multiple completions, depending on the nature and number of the surrounding hydrocarbon formations.. For the purpose of simplifying the following discussion, perforating guns will hereafter be referred to in the singular and should be understood to include also arrangements of multiple cascaded perforating guns, which generally function as a single, long perforating gun.
[0026] Typically, a perforating gun includes a single length of primacord spiralling about the internal periphery of the cylindrical housing from the upper to the lower end of the housing. The lower end of the primacord extends below the cylindrical housing and terminates within a metal cup which is crimped on the end of the primacord. The metal cup prevents moisture from contaminating the inside of the primacord and houses a dense explosive charge ("booster charge") in intimate contact with the primacord. The metal cup with booster charge is referred to as a booster assembly.
[0027] The booster assembly provides.means for transferring detonation from gun to gun where a plurality of guns are used. Such guns are serially connected by attaching their respective housings end-to-end. Both the upper and lower end of the primacord within each gun includes a booster assembly. The booster assemblies of adjacent guns are held in intimate contact with one another by the attached housings, whereby transfer of detonation between guns is facilitated.
[0028] Within the cylindrical housing, charges are positioned about the internal periphery in intimate contact with the spiralling primacord. The density of charges within a gun may vary, for example, from one to fifteen charges per foot (300 nm) of gun. As the primacord detonates (burns at a rate of 5000-7000 metres per second), detonation is transferred serially to each of the shaped charges distributed along the primacord. Failure of a perforation gun to fire completely is referred to as "low ordering." A gun is said to have low ordered when the primacord changes from detonating to deflagrating (burning at a rate of 1000-2000 m/s). A deflagrating primacord does not develop sufficient pressure to transfer detonation to the charges. Hence charges encountered after deflagration begins do not fire. Once the primacord begins to deflagrate, it generally will not again detonate.
[0029] The perforating gun is lowered into the borehole to a point adjacent to the formation from which hydrocarbon fluids may be found and the gun is fired by any of several well known means. Each charge typically either launches a projectile which penetrates the casing and formation or produces a jet-like stream of hot gas and small metallic particles which penetrates the casing and forms tunnels into the formation.
[0030] Because the charges within a perforating gun occasionally fail in whole or in part to detonate, it becomes necessary to verify that the perforating gun has functioned properly. Such verification is complicated by the great distance between the surface and the perforating gun and by the confined conditions downhole. Accordingly, there is provided herein a method and apparatus for verifying the detonation of all charges within a multi-charge perforating gun, without need for pulling the perforating gun from the borehole to perform a visual inspection.
[0031] The present invention includes a signal means coupled to the perforating gun, a sensor means at the surface of the borehole, and a recording means coupled to the transducer means. Successful firing of all charges of the perforating gun is reported by the signal means in the form of a distinctive signal which may be distinguished from noises and other signals ordinarily generated in the course of firing a perforating gun. The distinctive signal generated by the signal means is detected by the sensor means and communicated to the recording means, which provides a readout indicative that all charges of the perforating gun detonated as intended.
[0032] As will become clear from the description which follows, the present invention was developed particularly for use in cooperation with a perforating gun suspended on a string of tubing ahd fired by nonelectric means. It should also be clear to one skilled in the art, however, that the method and apparatus disclosed herein have certain distinct advantages when applied also to other types of perforating guns, for example, an expendable wireline gun, and can be adapted to function with such other types of perforating guns by one skilled in the pertinent art.
[0033] Referring now to Figure 1, there is shown therein a string of casing 12 suspended and cemented within a borehole 10 and having suspended concentrically within the casing 12 a string of tubing 14. The tubing string 14, includes a packer 16, sealing the annular area between the tubing string 14 and the casing 12 so as to define an upper annulus 18 and a lower annulus 20, and a vent assembly 22, which includes a plurality of ports for communicating fluid from the lower annulus 20 into the tubing string 14.
[0034] The lower end of the tubing string 14 supports a perforating gun 24 having a plurality of charges 26 distributed about the periphery thereof and oriented radially outwardly. The charges 26 are preferably shaped charges which, when ignited, produce a jet of high-pressure gas containing fine metallic particles which penetrate the casing 12 and a surrounding hydrocarbon formation 28. The charges 26 are typically serially connected within the perforating gun 24 along a length of primacord. The perforating gun 24 includes an impact-type firing head (not shown), whereby a bar dropped through the tubing string 14 from the upper end thereof impacts the firing head causing a firing pin to detonate a percussion primer, which in turn ignites the primacord.
[0035] Referring still to Figure 1, in accordance with the principles of the invention, a time delay device 40 is connected to the lower end of the perforating gun 24. Successful firing of the perforating gun 24 causes the time device 40 to produce a distinctive signal. A transducer assembly 44 located at the surface of the borehole 10 detects the distinctive signal and communicates the signal via a shielded cable 46 to a recorder assembly 48, whereby one is informed as to whether, the perforating gun 24 fired as intended.
The Time Delay Device
[0036] Referring now to Figure 2, there is shown therein the time delay device 40 in cut-away and cross-sectional elevation. The time delay device 40 is supported at the lower end of the perforating gun and is coupled thereto by means of primacord 30 extending from the gun into the device 40. After successful firing of the perforating gun, detonation of the primacord is transferred to the time delay device 40, which provides a time delay of predetermined duration followed by production of a distinctive signal, which provides a unique signature indicating that the perforating gun fired as intended.
[0037] The time delay device 40 includes a tandem sub-assembly 200, a time delay cartridge 202, a catcher assembly 204, and a blowout plug 206. The tandem sub 200 comprises a generally cylindrical stainless steel housing having an axial bore 210 of varying diameter extending the length therethrough. The axial bore 210 within an upper end of the tandem sub 200 defines a passage 212 of relatively small diameter for receiving therewithin a length of primacord 30 and a booster assembly 214. The booster assembly 214 may alternatively be merely a metal cup crimped onto the end of the primacord 30 without explosives housed therein.
[0038] The axial bore 210 within the lower portion of the tandem sub 200 widens to define a cylindrical chamber 216 for receiving the time delay cartridge 202 and the blowout plug 206. The lower portion of the cylindrical chamber 216 may be of slightly greater diameter so as to readily define a position for the blowout plug 206. The outer dimensions of the time delay cartridge 202 and the blowout plug 206 are selected so as to achieve a close tolerance fit within the cylindrical chamber 216. Both the time delay cartridge 202 and the blowout plug 206 include upper and lower o-rings 218a,b, respectively, about their outer surfaces, supported within corresponding circumferential grooves. The o-rings prevent fluid flow along the inside wall of the cylinder chamber 216. The o-rings may, for example, be National C-67 o-rings, or, for high temperature applications, Viton V-23 o-rings.
[0039] Referring still to Figure 2, the upper exterior surface 224 of the tandem sub 200 is threaded for coupling to the lower end of a perforating gun (24 in Figure 1) or to an adapter (not shown) which facilitates attachment to a perforating gun. Also included within the exterior surface at the upper end of the tandem sub 200, immediately below the threaded surface 224, is a pair of o-rings 226a,b supported within corresponding circumferential grooves. The o-rings 226a,b prevent fluid flow into internal portions of the delay device 40 and may be, as noted above, o-rings such as those manufactured by National or Viton.
[0040] The lower exterior surface 228 of the tandem sub 200 also is threaded for engaging corresponding threads within the catcher assembly 204. The catcher assembly 204 comprises a generally cylindrical, hollow body having a lower end 230 sufficiently closed to prevent passage of the blowout plug 206 therethrough. The lower end 230 of the catcher assembly 204 may include a plurality of ports 232, each of lesser dimension than the blowout plug 206. The upper end of the catcher assembly is open for receiving the lower threaded surface 228 of the tandem sub 200 therewithin.
[0041] The blowout plug 206 is held within the tandem sub 200 by a plurality of carbon steel shear pins 234, which extend through bores within the tandem sub 200 to engage a circumferential groove within the lower end of the blowout plug 206. At a predetermined time after the perforating gun (24 in Figure 1) h'as successfully fired, the time delay cartridge 202 will generate sufficient pressure within the cylindrical chamber 210 to shear the pins 234 and launch the blowout plug into the base of the catcher assembly 204, thereby generating a signal which may be received by the transducer assembly (44 in Figure 1).
[0042] Referring now to Figure 3, there is shown an elevational view of the time delay cartridge 202 with portions thereof shown in cross-section according to the line 3-3 shown in Figure 2. The time delay cartridge 202 includes a housing 250, a primacord holder 252, a retainer sleeve 254, a firing pin 256, a primer cap 258, a primer anvil 260, a time delay column 262, and a power cartridge 263.
[0043] The cartridge housing 250 comprises a generally cylindrical element having an axial bore 266 of varying diameter extending the length therethrough. The upper end of the bore 266 is threaded for engaging corresponding threads on the generally cylindrical outer surfaces of the primacord holder 252 and the retainer sleeve 254. The booster assembly 214 is maintained in position within an axial bore within the primacord holder 252, in abutment with the upper surface of the firing pin 256. The exterior surface of the retainer sleeve includes an o-ring 272, such as a Viton V-23 o-ring, supported within a circumferential channel. The o-ring 272 prevents fluid contamination of pyrotechnic charges housed within the time delay cartridge 202.
[0044] The firing pin 256 comprises a generally cylindrical body including an upper disk 268, an o-ring 274, and a hat section 276 at the lower end thereof. The firing pin 256 is slidably received within an axial bore through the retainer sleeve 254. The upper disk 268 includes an annular flange 269 supported on an annular ledge 270 about the upper, inside edge of the sleeve 254 and maintained on the ledge 270 by the lower surface of the primacord holder 252. The annular flange 269 fractures when exposed to more than 40,000 psi (280MN/m2) due to the detonation of the adjacent booster assembly 214.
[0045] The annular flange 269 of the upper disk 268 serves dual purposes. First, it ensures that the firing pin will not ignite the percussion primer charge (described below) unless primacord within the perforating gun (24 in Figure 1) is detonating when it reaches the time delay device (40 in Figure 1). If the primacord is detonating when it reaches the time delay device, all charges within the perforating gun, with rare exception, will have successfully detonated. The detonating primacord detonates the booster assembly 214, whereby the_upper end of the firing pin 256 is exposed to more than 40,000 psi (280 MN/m2) and, consequently, the pin 256 shears from the annular flange 269. However, if the primacord within the perforating gun is merely deflagrating, at least some of the lowermost charges within the perforating gun will not have detonated. Furthermore, deflagrating primacord will not detonate the booster assembly and there will be insufficient pressure to shear the firing pin 256 from the annular flange 269. Thus, ignition of the percussion primer indicates that all charges within the perforating gun were successfully detonated.
[0046] The second purpose of the annular flange 269 is to ensure that the firing pin 256 does not inadvertently contact the percussion primer, for example, in the event that the time delay device is accidently dropped. The substantial force required to shear the firing pin 256 from the annular flange 269 protects against accidental ignition of the device.
[0047] Referring still to Figure 3, the o-ring 274 circumscribing the firing pin 256, which may be, for example, a Viton V-23 o-ring, is supported within a circumferential groove about the exterior of firing pin 256, below the upper disk 268. The o-ring 274 seals the metal-to-metal, close tolerance junction between the firing pin 256 and the retainer sleeve 254. The hat section 276 comprises an downwardly axially oriented pin extension of the firing pin 256, arranged for contact with a primer 257 on detonation of the booster assembly 214.
[0048] The primer 257 is comprised of the primer cap 258, a primer anvil 260, and a primer charge .278 secured therebetween. The primer anvil 260 is a generally cylindrical body including means, such as boreholes 276, for communicating a spark from the primer charge 278 to the time delay column 262. The upper surface of the anvil 260 is covered by a thin metallic disk 280, which is clamped into position about its periphery between the anvil 260 and the primer cap 258.
[0049] The primer cap 258 comprises a generally cylindrical body having an axial bore open at the lower end to receive therein, and form a sleeve about, the anvil 260. The bore within the cap 258 is closed at the'upper end by a thin membrane 259 to form a small chamber into which the primer charge 278 is packed.
[0050] The primer charge 278 may comprise a percussive pyrotechnic charge which provides a deflagration output of low brisance, accompanied by the emission of hot particles. The hot particles penetrate the thin metallic disk 280, losing momentum in the process, and travel through the anvil bores 276 to reach and ignite the charges comprising the time delay column 262. The primer charge may be, for example, an M42C2-793 charge manufactured by Remington.
[0051] Referring still to Figure 3, a screen disk 282 separates the lower surface of the primer anvil 260 and the upper end of the time delay column 262. The screen disk 282 helps to reduce further the momentum of the hot particles from the primer charge 278 as they impact the column 262 and also helps to disperse the particles evenly about the column 262. Actual contact of the ignited primer charge 278 with the delay column 262 preferably should be limited to flame without any shock wave. The disk 282 is secured into position between a ledge 284 formed within the housing 250 and the lower surface of the primer cap 258.
[0052] The time delay column 262 comprises a relatively constricted portion of the axial bore 266 through the housing 250, which constricted portion is dense-packed with pyrotechnic charges for implementing a time delay.
[0053] The upper end of the delay column 262 is packed with a transfer charge 286. The transfer charge 286 (or "flash" charge) is a pyrotechnic charge which alters the cartridge ignition train from a fast burn to a slow burn and thereby provides a suitable interface between the primer 257 and a time delay charge 288, which is described below. The transfer charge 286 may be, for example, a flame-sensitive mixture of Si/CuO/Pb3O4, such as a charge known as Composition 430, which is manufactured by Unidynamics. The particular charge used is not critical so long as oxidation of the charge produces heat and is relatively gas free. The above-described mixture of Si/CuO/Pb3O4, produces a hot slag at the gas-free output rate of approximately 430 calories per gram (1.8 MJ/kg). It is also desirable that the transfer charge be relatively insensitive to physical shock.
[0054] The lower end of the transfer charge 286 abuts the upper end of the time delay charge 288 which is packed within the column 262. The time delay charge 288 comprises a pyrotechnic charge designed to burn at a predetermined slow rate which enables the incorporation of a known time delay into the ignition train. While the duration of the time delay is not particularly important so long as the length of the delay is known by the user of the apparatus, it has been determined that a delay of ten to fourteen seconds is desirable so as to permit noise generated by the gun firing sequence to dampen.
[0055] One such time delay charge 288 which may be used is a tungsten delay composition manufactured per Military Specification No. MIL-T-23132. The precise delay charge is not of great importance, however, other than,: perhaps, to maximize such safety constraints as are feasible and important to any particular user.
[0056] Referring still to Figure 3, the lower end of the time charge 288 terminates against a second transfer charge 290. The second transfer charge 290 (or "flash" charge) is a pyrotechnic charge which alters the ignition train from a slow burn to a fast burn and thereby provides a suitable interface between the delay charge 288 and the power cartridge 263, which is described further below. The second transfer charge 290 may be, for example, a mixture of titanium and potassium chlorate (Ti/KC104), which is a fast-response, high temperature pyrotechnic charge having an output of approximately 1750 calories per gram (7.1 MJ/kg). Again, the particular charge used is not critical so long as the characteristics of the charge are suitable to achieve the necessary transition.
[0057] The lower end of the second transfer charge 290 is packed against a thin metallic disk 292, which is resistance spot welded into a slight counterbore with the housing 250. Oxidation of the second transfer charge 290 burns through the disk 292 and ignites the propellant charge 264.
[0058] The power cartridge 263 comprises a relatively large diameter chamber 265 communicating with the axial bore 266 within the housing 250. The chamber 265 is densely packed with a propellant charge 264, comprising a pyrotechnic charge having several preferred characteristics. First, the propellant charge 264 must be a gas generator. Such is necessary so as to pressurize the internal cavity (chamber 210 of Figures 2) of the time delay device, so as to launch the blowout plug into the catcher assembly. Second, it is desirable that the propellant charge have a high autoignition temperature, whereby the risk of incidental ignition in a hostile environment is minimized. Third, it is desirable that the propellant charge have a rapid rate of reaction, so that the full potential of the gas generator is tapped before the blowout plug (206 in Figure 2) moves far enough to allow gas to vent from the device. Finally, it is desirable that the propellent charge be relatively insensitive to shock, so as to minimize the risk of ignition in the event that the device is, for example, dropped.
[0059] Although it should be recognized that there are many charges which will function adequately to perform the task required of the propellant charge 264, it has been found that a mixture of potassium perchlorate . (KC104) and tetramethylammonium perchlorate (C4H12NH4C104 or "TMAP", for short) , in the proportions of 52% KCI04 and 48% TMAP, is particularly suitable. TMAP is a monopropellent having a very high reaction temperature, which provides the necessary gas output and prevents autoignition at temperatures below approximately 350° Centigrade. The addition of an oxidizer, such as KC104, increases the reaction speed of the TMAP to a speed near that of detonation. Hence, the mixture responds quickly and pressurizes the cylindrical chamber (210 in Figure 2) below the time delay cartridge 202, exerting a substantial, downwardly directed force on the blowout plug.
[0060] The power cartridge 263 may further include an enclosure disk 294 resistance spot welded to the 'lower end of the housing 250, so as to enclose the dense-packed propellant charge 264 within the housing 250. A protective barrier 296, such as a layer of silica (SiO2), may separate the propellant charge 264 from the closure disk 264, to prevent ignition of the propellent charge 264 during manufacture of the cartridge 202..-In summary of the operation of the time delay cartridge, the detonating primacord 30 detonates a booster charge within the booster assembly 214. Detonation of the booster charge generates a shock wave which forces the firing pin 256 downward, shearing the annular flange 269 on the upper disk 268 and igniting the percussion primer charge 278. The primer charge 278 generates a flame which is communicated through the primer anvil 260 and a screen disk 282 to the first transfer charge 286 in the time delay column 262.
[0061] The first transfer charge 286 produces a hot slag which ignites the time delay charge 288. The time delay charge 288 ' burns for a known duration. The lower.end of the time delay charge 288 ignites a second transfer charge 290, which changes the ignition train to a fast burn, burns through the metallic disk 292, and ignites the propellant charge 264.
[0062] The propellant charge 264 burns rapidly and produces a gas, which pops the closure disk 294 from the housing 250 and pressurizes the cylindrical chamber (210 in Figure 2), launching the blowout plug into the catcher assembly and generating a unique signal. Detection at the surface of the distinctive signature produced by the time delay followed by the signal generated by the launching of the blowout plug indicates that the perforating gun fired as desired.
An Alternative Time Delay Device .
[0063] Figures 4 and 5 depict an alternative embodiment of the time delay device 40 and the time delay cartridge, respectively. Unless otherwise noted in the following discussion, the features and operations of the device depicted in Figures 4 and 5 are identical to those set forth in the foregoing subsection entitled "The Time Delay Device," which is incorporated herein by reference.
[0064] Referring now to Figure 4, there is depicted therein a time delay device in cut-away and cross-sectional elevation. The time delay device 40 includes a time delay cartridge 50, a retainer housing 52, a tandem sub 56, and a blowout plug 58. The retainer housing 52 comprises a generally cylindrical stainless steel body having an axial bore 170 of varying diameter extending the length therethrough. The axial bore 170 within the upper end of the retainer housing 52 is of relatively large diameter, defining a comparatively thin side wall 172, for receiving therewithin a downward extension of the tandem sub 56, such downward extension being hereafter referred to as the retainer cap 54. The lower portion of the large-diameter bore is threaded for engaging corresponding threads on the outer surface of the retainer cap 54.
[0065] The axial bore 170 within the lower portion of the retainer housing 52 narrows to define a channel 171 for receiving the lower end of the time delay cartridge 50 and the blowout plug 58. The blowout plug 58, positioned within the channel 171, includes about its lower end a circumferential groove 174 for receiving a plurality of shear pins 176a,b through bores within the housing 52 for retaining the blowout plug.58 within the housing 52.
[0066] The retainer cap 54 comprises a generally cylindrical stainless steel element forming a part of the tandem sub 56 and threadedly engaged within the upper end of the retainer housing 52. The retainer cap 54 includes therethrough an axial bore 180 of varying diameter. The axial bore 180 includes a downwardly facing shoulder 182 and conforms substantially to the dimensions of the upper portion of the time delay cartridge 50 (described in greater detail below), whereby the time delay cartridge 50 is retained in essentially fixed position between an upwardly facing shoulder 184 of retainer housing 52 and the shoulder 182 on the retainer cap 54.
[0067] Referring still to Figure 4, the metal-to-metal junction between the time delay cartridge 50 and the retainer cap 54, within the axial bore 180 thereof, is sealed by means of a pair of o-rings 162a,b disposed within corresponding circumferential channels about the upper end of the delay housing 62. Similarly, the upper end of the retainer cap 54 includes a pair of circumferential channels supporting o-rings 166a,b for sealing the metal-to-metal junction of the retainer cap 54 and the retainer housing 52.
[0068] The tandem sub 56 further includes an upward extension 190, including o-rings 192a,b and a threaded portion 194, so that the upward extension 190 is substantially a mirror image of the retainer cap 54. The upward extension 190 is arranged for engagement with the lower end of the perforating gun (24 in Figure 1) Or an adapter therefor.
[0069] Referring now to Figure 5, the time delay cartridge 50 comprises a booster assembly coupling 60, a delay housing 62, a delay body 64, a firing pin 66, a delay cord 68, and a power cartridge assembly 70. The booster assembly coupling 60 facilitates a primacord coupling between the perforating gun (24 in Figure 1) and the time delay device (40 in Figure 4). The booster assembly coupling 60 is secured within the upper end of the delay housing 62 by means of a lead grommet 63 threadedly engaged at 61 within the housing 62. An axial bore 65 within the booster assembly coupling 60 receives therethrough a length of a primacord 72, which extends from. within the tandem sub (56 of Figure 2) to the firing pin 66. The axial bore 65 includes a flared portion 67 along the lower end thereof whereby a metallic ring 69 crimped around the primacord 72 is bound within the flared bore 67 to hold the primacord 72 in place.
[0070] A metal cup 74 is affixed to the upper end of the primacord 72 by means of crimping and includes therewithin an explosive charge. The upper end of the metal cup 74 abuts a similar, downwardly facing metal cup of a booster assembly (not shown) within the lower end of the perforating gun (24 in Figure 1), whereby the detonating primacord within the perforating gun transfers ignition through the opposed booster assemblies to the primacord 72 within the delay cartridge 50.
[0071] The firing pin 66 is slidably received within a firing pin sleeve 80, which is supported within a generally cylindrical sleeve bore 78 in the delay housing 62, below and axially aligned with the bore 65 within the booster assembly 60. The firing pin sleeve 80 includes within a medial circumferential groove an O-ring 82 for sealing the space between the sleeve bore 78 and the outer surface of the sleeve 80. The delay housing 62 further includes a primer bore 84 of lesser diameter than the sleeve bore 78. The primer bore 84 is axially aligned with and intersects the lower end of the sleeve bore 78, so as to define along the inside lower end of the sleeve 80 an annular ledge for supporting a high-temperature primer closure disk 86.
[0072] Referring still to Figure 5, the upper end of the sleeve 80 is machined along the inside edge thereof to define a ledge for supporting an annular flange 88 formed about the upper end of the firing pin 66. The firing pin .66 also includes an o-ring 90 supported within a circumferential groove for sealing the inside of the sleeve 80 against the influx of contaminating fluids.
[0073] A primer anvil 85 is disposed within the primer bore 84 and includes a thin metallic membrane across the top thereof. The anvil 85 includes a plurality of bores 83 for communicating the ignition train through the anvil 85. The space between the closure disk 86 and the membrane on the anvil 85 is packed with a percussion primer pyrotechnic charge 87, which provides a deflagration output of low brisance, accompanied by the emission of hot particles. The percussion primer is ignited when the firing pin 66 contacts the primer closure disk 86.
[0074] The primer anvil bores 83 are connected through a short channel 92 to a large-diameter delay cord bore 94 which extends through the lower end of the delay housing 62. The generally cylindrical delay body 64 extends from a threaded engagement at 93 within the lower end of the delay housing 62 upwardly into the delay cord bore 94 and .includes in the upper end thereof a generally axial transfer charge bore 102 and an outer bore 106, which bores are aligned with and spaced from the channel 92 within the primer bore 84. A screen disk 104 covers the outer bore 102.
[0075] The transfer charge bore 102 is connected to a generally radial bore 108 which houses the upper end 101 of the delay cord 68. The delay cord 68 extends from the transfer charge bore 102 to the exterior of the delay body, where it is spooled circumferentially about the exterior of the delay body 64 in planes generally perpendicular to the common axis of rotation of the delay housing 62 and the delay body 64. The generally perpendicular orientation of the spooled delay cord 68 minimizes the effect of gun recoil momentum, directed along the axis of rotation of the delay body 64, on the cord 68.
[0076] The percussion primer charge 87 changes the ignition train from detonating to deflagrating. The ignited primer penetrates the membrane on- the anvil 85 and delivers a spark through the anvil bores 83 and the short channel 92 to the outer bore 106 and to the transfer charge bore 102. The transfer charge bore 102 is packed with an input transfer charge 103, for example, Composition 430 manufactured by. Unidynamics, which provides transition from a fast burn to a slow burn.
[0077] Hot slag from the input transfer charge reaction remains molten long enough to insure ignition of the delay cord 68. The delay cord 68 may comprise, for example, a fuse mixture of boron and barium chromate encased in a sheath of 0.999 percent lead. The cord 68 so formed may have an outer diameter of 0.068 to 0.072 inch (1.7 to 1.8 mm) and a core load of six to eight grain per foot (1.2 to 1.7 g/m). Finally, the lead sheath is coated with an insulation, such as No. 18 Varglass, manufactured by 3M Corporation, which prevents the burning cord from cross-propagating to adjacent spooled cord at the point of its winding about the delay body 64. The delay cord 68 may be designed to burn at a rate of approximately one inch of cord per second (25 mm/s), or any other suitable rate, thus enabling the incorporation of a time delay of predetermined duration within the device 40.
[0078] Referring still to Figure 5, the lower end 105 of the delay cord 68 extends through a generally radial bore 110 within the delay body 64 to a second transfer charge bore 112 at the axial center of the lower end of the delay body 64. The delay body 64 further includes an output charge bore 114 below, axially aligned with, of slightly larger diameter than, and intersecting the transfer charge bore 112. The lower end of the delay body 64 includes a threaded end bore 116, axially aligned with the output charge bore 114, for engaging the upper end of the power cartridge assembly 70.
[0079] The power cartridge assembly 70 comprises a cartridge housing 130 and a cartridge plug 132. The cartridge housing 130 includes a threaded neck 136 for. engagement within the threaded end bore 116 of the delay body 64. A central bore 138 along the axis of rotation of the cartridge housing 130 defines, through the cartridge housing neck 136, a path which connects the output charge bore 114 to an interior 140 of the cartridge housing 130. A closure disk 142 seals the central bore 138 from the output charge bore 114.
[0080] The cartridge plug 132 is slidably received within the cartridge housing 130 spaced from the downwardly facing interior surface 144 of the cartridge housing 130. A cartridge sealing disk 146, which is resistance spot welded onto an annular ledge 148 machined into the inner edge of the lower end face of the cartridge housing 130, retains the cartridge plug 132 within the housing 130.
[0081] The second transfer charge bore 112 is packed with a pyrotechnic transfer charge 113, such as Composition 430, which was described in greater detail above, in intimate contact with the lower end 105 of the delay cord 68. The second transfer charge 113 facilitates the transition from the slow burning delay cord 68 to a fast burn within the output charge bore 114.
[0082] The output charge bore 114 is packed with a pyrotechnic output charge 115, such as a fifty milligram mixture of titanium and potassium per chlorate (Ti/KCIO4) -sufficient to ignite the power cartridge 70. The Ti/KC104 charge is a fast-response, high temperature pyrotechnic with very high heat output, in the range of 1750 calories per gram. Once ignited by the transfer charge 113, the output charge 115 burns through the closure disk 142 to reach the charges within the power cartridge 70.
[0083] The power cartridge 70 includes within the central bore 138 of the neck 136 a preliminary ignition charge 135 and a propellant charge 137. The preliminary ignition charge 135, which comprises a mixture of titanium and potassium perchlorate (Ti/KC104), transfers ignition from the delay body 64 to the propellant charge 137, which preferably comprises a mixture of potassium perchlorate (RC104) and tetramethylammonium perchlorate ("TMAP").
[0084] The rapid increase in pressure within the cartridge housing 130 forces the cartridge plug 132 against the sealing disk 146, which is thereby popped off of the ledge. The increasing pressure continues to exert a downwardly directed force on the upper face of the cartridge plug 132, forcing the plug 132 against the blowout plug (58 in Figure 4), which is thereby launched from the lower end of the time delay device 40. As will be clear from the further description below, the launching of the blowout plug 58 is accompanied by a signal, which is detected at the surface of the borehole and interpreted as an indication that the perforating gun fired as intended.
[0085] 'Thus, in reference now to Figures 1 and 2, the time delay device 40 is coupled to the perforating gun 24 so as to produce a distinctive signal when ignited by a detonating primacord extending from the lower end of the perforating gun 24. The detonating primacord ignites the delay cord 68, invoking a time delay while the delay cord 68 slowly burns. At the end of the time delay, the delay cord 68 ignites the power cartridge assembly 70, which includes the propellant charge 137. The propellant charge 137 develops a pressure in excess of 40,000 psi (280 MN/m2) in less than one millisecond. The rapidly developed pressure shears the retainer pins 176a,b, forces the blowout plug 58 from the lower end of the retainer housing 52, and delivers a gas bubble from the open lower end of the retainer housing 62, generating acoustic, pressure, and motive signals distinct from the signals accompanying the firing of the perforating gun 24.
The Transducer Assembly
[0086] Referring again to Figure 1, the transducer assembly 44 is affixed to a wellhead 30 so as to detect the distinctive signal generated by the time delay device 40. The transducer assembly 44 may include an acoustic emissions transducer for detecting acoustic energy generated within the borehole 10, an accelerometer for detecting motion of the wellhead, or a pressure transducer for sensing tubing or annulus pressure. The assembly 44 may include all or any combination of the three types of trans- ducers. Referring now to Figure 6, the transducer assembly 44 is shown to comprise a transducer 300 and a fixture 302.
[0087] The transducer 300 may, for example, be an acoustic emission transducer, such as a Model No. 392A transducer, manufactured by PCB Piezotronics. The acoustic emissions transducer 300 is capable of detecting acoustic energy in the frequency range of 100 to 10,000 Hertz and generating an output signal of 100 millivolts to 2.0 volts. The transducer 300 could also be an acceler- ometer, such as a Model No. 303A accelerometer manufactured by PCB Piezotronics, or a standard pressure transducer, dynamic or static gauge-type, depending on the particular application. The acoustic transducer and the accelerometer could be affixed to the wellhead 30 by use of the fixture 302 for each. The pressure transducer must be connected to the tubing or annulus through a port and supported by commercially available apparatus.
[0088] The transducer 300 is held in position against the tubing string 14 by means of the fixture 302, which comprises a molded silicon rubber element including a central compartment for supporting the transducer 300, a pair of door lock-type magnets 304a,b, and a pair of slots 306a,b. The slots 306a,b enable the flexible fixture to assume a generally arcuate shape so as to conform substantially to the exterior surface of a flange, such as the flange supporting the tubing string. The magnets 304a,b permit easy attachment of the fixture 302 to the wellhead flange whereby the transducer 300 is retained in intimate contact with the wellhead (30 in Figure 1).
[0089] The fixture 302 further includes a pair of bores 308a,b, extending through the width thereof, for receiving a loop of the shielded cable 46, as shown in Figure 3. Such an arrangement relieves stress on the cable 46 at the point of its connection within the fixture 302 to the transducer 300 and dampens wire movement in response to external forces. Such movement might otherwise add extraneous signals to those received from within the borehole.
[0090] Thus, one or more transducers 300 are mounted on the wellhead (30 in Figure 1) whereby energy transmitted thereto by the tubing string (14 in Figure 1) or annulus is detected and com- municated to the recorder assembly 48 via the shielded cable 46.
The Recorder Assembly
[0091] Referring again briefly to Figure 1, the recorder assembly 48 includes the means by which the output signal of the trans- ducer assembly 44 is interpreted and indicated to an operator. There is shown in Figure 7 a particular recorder assembly 48, comprising an input amplifier 320, a cassette recorder 322, a high pass filter 324, and an oscillographic strip chart recorder 338.
[0092] Referring to Figures 6 and 7, the transducer 300 is con- nected to the input line 326 of the input amplifier 320 via the shielded cable 46. The input amplifier includes a current source 328 for supplying approximately 0.5 milliampere of current to'a source follower field effect transistor (FET) configuration (not shown) which provides the output signal within the acoustic emission transducer 300. The current source may be, for example, an LM334 device manufactured by National Semiconductor.
[0093] The input amplifier 320 further comprises a preamplifier composed of a pair of FET operational amplifiers 330, 332, such as are available on a TL082 device manufactured by Texas instruments, arranged to provide a voltage gain of approximately five so as to boost the transducer output signal to a point well within the input sensitivity of the cassette recorder 322. The input amplifier 320 includes an output line 334 which is connected to an input terminal of the cassette recorder 322. In a similar manner, an accelerator and/or a pressure transducer, if such are to be used, may be connected to input channels of the recorder 322.
[0094] The cassette recorder 322 may be any high quality cassette recorder, such as a Model No. PMD340 recorder manufactured by Marantz. If the recorder 322 is not capable of handling at least three input channels, then it may be necessary to use more than one recorder.
[0095] An output line 336 from the recorder 322 is connected'to a high pass filter 324 having a three decibel low frequency cutoff at 50 Hertz. The filter 324 attenuates..the low frequency components of the transducer output signal so as to improve the response of the strip chart recorder 338 to the distinctive signal generated by the time delay device. In the absence of such a filter the chart recorder 338 is generally unable to trace the higher frequency signals of interest herein. When more than one transducer 300 is in use, separate output channels 336, filters 324, and input channels to the strip chart recorder 338 will be required for each transducer.
[0096] The oscillographic strip chart recorder 338 is preferablyfa galvanometer-pinned type recorder rather than a servo driven recorder. The chart recorder 338 produces a real time, time- based, hard copy plot of the transducer output signal. Such recorders are commercially available from several manufacturers, including Soltec and Gould.
[0097] In operation, the transducer 300 is connected to the input amplifier 320. The cassette recorder is started after a gun- firing bar (not shown) has been dropped into the tubing string to fire the perforating gun (24 in Figure 1). When the bar strikes the firing head (not shown) at the upper end of the perforating gun, the gun fires and the time delay device (40 in Figure 1) is ignited (assuming, of course, that the primacord within the perforating gun detonates rather than deflagrates throughout the length of the perforating gun). All events within the borehole which generate energy are detected by the tranlducer(s) 300 and are communicated on the shielded cable (46 in Figure 1) to the cassette recorder 322 where they are recorded simultaneously on cassette tape and on the strip chart recorder 338.
[0098] Successful firing of the gun may be recognized readily by identifying the unique signature associated with the success of the event -- the presence of a gun firing signal, followed by a pause of predetermined duration, followed by the unique time delay cartridge signal. The output signals of the several types of transducers described above can be compared on the same time base to screen off noise from various sources arid to facilitate identification of the unique signature. The use of more than one transducer may be required, for example, in offshore operations.
[0099] Referring now to Figure 8, the unique features of the signal 350 generated by the time delay device (40 in Figure 1) vis-a-vis the signal 360 generated by the perforating gun may be observed, as reported by an acoustic: emissions transducer. First, the delay device signal 350 has a faster decay time than the gun signal 360. Second, the delay device signal 350 is of shorter duration than the gun signal 360. Thirdly, the delay device signal 350 reaches a peak amplitude quickly and dies off smoothly from there; whereas, the gun signal 360 has multiple peaks and does not die off smoothly. Finally, and most important, a predetermined period of time separates the delay device signal 350 from the gun firing signal 360 and other previous signals. Thus, the delay device signal 350 has certain unique characteristics by which it is readily recognized. It should be noted, however, that other unique signals could be used to accomplish substantially the same results.
[0100] Referring again to Figure 1, the recorder assembly 48 alternatively may include a microprocessor-based apparatus which monitors the output from the transducer (300 in Figure 6) and provides a signal upon recognition of the signal pattern characteristic of successful perforating gun firing. Such a microprocessor-based apparatus could be designed, constructed, and programmed by one skilled in the pertinent computer arts using as a guide the foregoing disclosure.
1. Apparatus for detecting complete firing of a perforating gun (24) positioned within
a borehole (10), comprising:
means (40) coupled to the perforating gun for generating a signal;
means (44) at the surface of the borehole (10) for sensing signals produced from within the borehole; and
means (48) in communication with said sensing means for identifying said signal produced by said generating means.
2. Apparatus according to Claim 1 wherein said signal includes a time delay of predetermined
duration following the firing of the perforating gun.
3. Apparatus according to Claim 1 or 2 wherein said signal includes ignition of a
charge (264) at the conclusion of said time delay.
4. Apparatus according to any of Claims 1 to 3 wherein said signal is generated if
and only if the perforating gun has fired completely.
5. Apparatus according to Claim 4 wherein said generating means comprises a time-delay
device (202), including:
means (252-260) for coupling said device to the perforating gun;
delay charge means (262) coupled to said coupling means for burning at a predetermined rate to effect said time delay; and
propellant charge means (264) coupled to said delay charge means for generating said signal.
6. In and about a cased borehole (10) having suspended therein from a wellhead a tubing
string (14) with a perforating gun (24) on the lower end thereof, apparatus for determining
whether the perforating gun fired completely, comprising:
cartridge means (263) affixed to the perforating gun, said cartridge means generating a signal after the perforating gun has fired;
sensor means (44) at the surface of the borehole for monitoring changes in energy within the borehole, said sensor means producing electrical signals in response thereto; and
recorder means (48) for recording said electrical signals from said sensor means and for reviewing said recorded electrical signals, whereby said signal from said cartridge means may be recognized as an indication that the perforating gun fired completely.
7. Apparatus according to Claim 6 wherein said signal includes a time delay of predetermined
duration followed by energy generated by ignition of a charge.
8. Apparatus according to Claim 7 wherein said cartridge means comprises:
booster means (60;214) for coupling said cartridge means to the perforating gun;
a delay cord (68;262) which burns at a predetermined rate;
means (66;256) responsive to said booster means for igniting said delay cord if the perforating gun fires completely; and
means (263;132) responsive to said delay cord for generating said signal.
9. Apparatus according to Claim 8 wherein said means for igniting said delay cord
comprises:
a percussion primer charge (87;278);
a firing pin (66;256) for igniting said percussion primer, said firing pin including an annular flange (269) capable of shearing from said firing pin upon application of a predetermined pressure to said firing pin; and
a sleeve (80;254) for slidably receiving therein said firing pin and supporting said annular flange, said sleeve retaining said firing pin spaced from said percussion primer, wherein complete firing of the perforating gun generates sufficient force to shear said firing pin from said annular flange and thereby ignite said percussion primer.
10. Apparatus according to Claim 9 wherein said delay cord (68) is arranged with the
lengthwise axis thereof substantially perpendicular to the lengthwise axis of said
cartridge means (70).
11. Apparatus according to Claim 9 wherein said delay cord (262) is arranged with
the lengthwise axis thereof substantially parallel to the lengthwise axis of said
cartridge means (263).
12. Apparatus according to any of Claims 8 to 11 wherein said means for generating
said signal comprises:
a housing (216) including an open end;
a blowout plug (206) slidably disposed within said open end of said housing; and
said charge being within said housing and being responsive to said delay cord, whereby ignition of said charge generates fluid pressure between said housing and said blowout plug, launching said blowout plug from said housing and releasing a fluid bubble.
13. Apparatus according to Claim 12 wherein said generating means further comprises
means 230 for catching said blowout plug after said plug is displaced from within
said housing.
14. Apparatus according to Claim 12 or 13 wherein said charge comprises a mixture
including tetramethylammonium perchlorate.
15. Apparatus according to Claim 14 wherein said mixture further includes potassium
perchlorate.
16. Apparatus according to any of Claims 6 to 15 wherein said sensor means comprises:
a transducer (300) for converting sensed energy to electric energy;
a cable (46) connecting said transducer to said recorder means; and
a flexible fixture (302) for removably securing said transducer to the wellhead at the surface of the borehole.
17. Apparatus according to any of Claims 6 to 16 wherein said sensor means monitors
acoustic energy generated within the borehole.
18. Apparatus according to any of Claims 6 to 17 wherein said sensor means monitors
motion of apparatus which extends within the borehole.
19. Apparatus according to any of Claims 6 to 18 wherein said sensor means monitors
a pressure within the borehole.
20. Apparatus according to any of Claims 16 to 19 wherein said flexible fixture (302)
comprises a molded rubber element including:
a compartment for supporting said transducer (300) with a portion of said transducer in intimate contact with the wellhead;
at least one slot (306a, b) for enabling said element to assume a generally arcuate configuration; and
at least one magnet (304a, b) for removably securing said element to the wellhead.
21. Apparatus according to any of Claims 6 to 20 wherein said recorder means comprises
a charge recorded (338) for plotting said signal.
22. Apparatus according to Claim 21 wherein said recorder means further comprises
a tape recorder for simultaneously recording said signal on magnetic tape (324).
23. Apparatus according to any of Claims 6 to 22 wherein said recorder means comprises
a microprocessor-based apparatus, including:
means for receiving said electrical signals from said sensor means;
means for digitizing said electrical signals;
means for storing digitized electrical signals from said digitizing means;
means for comparing said digitized electrical signals with signal patterns representing complete firing of the perforating gun; and
means for indicating the output of said comparing means.
24. A method for determining whether a perforating gun (24) suspended within a borehole
(10) fired completely, comprising the steps of:
firing the perforating gun;
generating a distinctive signal if the perforating gun fires completely;
detecting at the surface energy generated from within the borehole from a point in time prior to said gun firing; and
interpreting said detected energy to determine whether said distinctive signal was generated.
25. A method according to Claim 24 wherein said generating step comprises the steps
of:
triggering a time delay if and only if the perforating gun fires completely; and
igniting a charge on expiration of said time delay.
26. A method according to claim 25 wherein said detecting step comprises the steps
of:
sensing the presence of energy; and
providing an electrical signal indicative of said energy.
27. A method according to claim 26 wherein said interpreting step comprises the steps
of:
receiving said electrical signal indicative of said energy;
recording said electrical signal on tape; and
reviewing said recording to determine whether said time delay and said charge are present.
28. A method according to claim 26 wherein said interpreting step comprises the steps
of:
receiving said electrical signal indicative of said energy;
digitizing said electrical signal;
storing said digitized electrical signal;
comparing said digitized electrical signal with signal patterns representing complete firing of the perforating gun; and
indicating whether said distinctive signal is present.