BACKGROUND

[0001] This section is intended to provide relevant background information to facilitate a better understanding of the various aspects of the described embodiments. Accordingly, it should be understood that these statements are to be read in this light and not as admissions of prior art.

[0002] The production of hydrocarbons may include stimulation of a subterranean formation by injecting fluids at a high pressure through a wellbore. However, before stimulation can occur, the casing of the wellbore must be perforated. This is typically done using a perforation gun, which includes shaped charges that are ignited via a detonator installed in the perforation gun.

[0003] Currently, detonators must either be installed at a wellsite or a ballistic interrupter must be installed prior to transit to prevent the inadvertent firing of the perforation gun during transit to the wellsite, such as in the event of an accident involving a fire. Both of these methods require the perforation gun to be disassembled at the wellsite, delaying stimulation of the formation and potentially introducing leak paths into the perforation gun. Accordingly, there exists a need for an improved detonator that can be installed in a perforation gun prior to transit to the wellsite and that does not require the removal of a ballistic interrupter at the wellsite.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] Embodiments of the self-disabling detonator are described with reference to the following figures. The same numbers are used throughout the figures to reference like features and components. The features depicted in the figures are not necessarily shown to scale. Certain features of the embodiments may be shown exaggerated in scale or in somewhat schematic form, and some details of elements may not be shown in the interest of clarity and conciseness.

[0005] Figure 1 is a schematic illustration of an offshore oil and gas platform, according to one or more embodiments; [0006] Figure 2 is a schematic illustration of a loaded perforation gun, according to one or more embodiments;

[0007] Figure 3 is a cross-sectional view of a self-disabling detonator, according to one or more embodiments;

[0008] Figure 4 is a cross-sectional view of a self-disabling detonator, according to one or more embodiments; and

DETAILED DESCRIPTION

[0009] The present disclosure provides a self-disabling detonator. The self- disabling detonator prevents the inadvertent firing of the perforation gun if the perforation gun is exposed to fire or heat, which may occur in an accident during transit to the wellsite.

[0010] As used herein, the term“thermally weak joint” refers to a joint that mechanically couples two connecting elements of the detonator. The thermally weak joint is a joint that maintains a proper function until it is exposed to temperatures or pressures that cause the joint to lose its mechanical functionality. Additionally, the term “initiation” refers to the action of beginning a detonation or deflagration of an energetic component as part of an explosive component and or explosive train such as a perforation gun.

[0011] Figure 1 is a schematic illustration of an offshore oil and gas platform 100, according to one or more embodiments. A semi-submersible platform 102 is centered over an oil and gas formation 104 located below the sea floor 106. A subsea conduit 108 extends from a deck 110 of the platform 102 to a wellhead installation 112 that includes blowout preventers 114. Platform 102 includes a hoisting apparatus 116 and a derrick 118 for raising and lowering pipe strings such as work string 120.

[0012] A wellbore 122 extends through the various earth strata including formation 104. A casing 124 is retained within the wellbore 122 using cement 126. The work string 120 includes various tools including a shaped charge perforation gun 128. When it is desired to perforate the formation 104, the work string 120 is lowered through the casing 124 until the shaped charge perforation gun 128 is positioned adjacent to the formation 104. Thereafter, the shaped charge perforation gun 128 is "fired" by detonating the shaped charges that are disposed within the exterior tubular 130 of the shaped charge perforation gun 128. If preferred, aligned recesses or scallops 132 are formed in the outer surface 134 of the exterior tubular 130. Upon detonation, the liners of the shaped charges form jets that pass through the exterior tubular 130 and form a spaced series of perforations extending outwardly through the casing 124 and the cement 126, and into the formation 104.

[0013] Even though FIG. 1 depicts a vertical well, it should be understood by those skilled in the art that the shaped charge perforation gun 128 is equally well-suited for use in wells having other configurations including deviated wells, inclined wells, horizontal wells, multilateral wells and the like. Accordingly, use of directional terms such as "above", "below", "upper", "lower" and the like are used for convenience in referring to the illustrations. Also, even though FIG. 1 depicts an offshore operation, it should be understood by those skilled in the art that the shaped charge perforation gun 128 of the present invention is equally well-suited for use in onshore operations.

[0014] Figure 2 is a schematic illustration of a perforation gun 200, according to one or more embodiments. The perforation gun 200 may be used in place of or as the perforation gun 128 shown in FIG. 1. The perforation gun 200 includes a carrier gun body 202 made of a cylindrical sleeve and typically having a plurality of scallops or recesses 204. Radially aligned with each of the recesses 204 is a respective shaped charge 206 of a plurality of shaped charges 206. Each of the shaped charges 206 includes a charge case 208 and a liner 210. Disposed between each charge case 208 and liner 210 is a quantity of explosive.

[0015] The shaped charges 206 are retained within carrier gun body 202 by a charge holder 212, which includes an outer charge holder tube 214 and an inner charge holder tube 216. In this configuration, the outer charge holder tube 214 supports the discharge ends of shaped charges 206, while inner charge holder tube 216 supports the initiation ends of shaped charges 206. It is also known to use a single tube charge holder (not shown) to carry the shaped charges 206.

[0016] Disposed within inner tube 216 is a detonating cord 218, which is used to detonate the shaped charges 206. In the illustrated embodiment, the initiation ends of shaped charges 206 extend across the central longitudinal axis of perforation gun 200, allowing the detonating cord 218 to connect to the shaped charges 206 through an aperture defined at the apex of the charge case 208 of shaped charges 206. It is also known to use relatively larger sized shaped charges, some of which can extend across substantially the inner diameter of the carrier gun body 202.

[0017] Each of the shaped charges 206 is longitudinally and radially aligned with one of the recesses 204 in carrier gun body 202 when perforation gun 200 is fully assembled. In the illustrated embodiment, shaped charges 206 are arranged in a spiral pattern such that each shaped charge 206 is disposed on its own level or height and is to be individually detonated so that only one shaped charge 206 is fired at a time. It should be understood by those skilled in the art, however, that alternate arrangements of shaped charges 206 may be used, including cluster type designs (not shown) wherein more than one shaped charge 206 is at the same level and is detonated at the same time, without departing from the principles of the present invention.

[0018] A detonator sub 220 is be positioned at one end of the perforation gun 200, shown schematically in FIG. 2. The detonator sub 220 contains a detonator 222 that is used to ignite the detonating cord 218 and the shaped charges 206. In another embodiment, the detonator 222 may be positioned within the carrier gun body 202. One or more connectors 224 may be to connect the perforation gun 200 to a work string (not shown), a second perforation gun (not shown), a bull plug used to terminate the work string (as shown), a firing head (not shown), or any other type of device which may be attached to a carrier gun body 202 in a work string. Work string as used herein refers to tubing strings, wirelines, and similar, for lowering and supporting the perforation gun 200 in the wellbore.

[0019] Explosives typically used in detonators may be said to exhibit two modes of activity, a deflagration mode and a detonation mode. Deflagration may be referred to as a high reaction rate combustion, although the rate is subsonic compared to the speed of sound in the explosive. Detonation may be referred to as a very high reaction rate explosion. During detonation, the reaction propagates through the explosive material in excess of the speed of sound in the explosive. Primary explosives generally transition substantially immediately to detonation mode upon activation, that is, they have very short run-up distances to detonation. Secondary explosives first activate in a deflagration mode and later transition to a detonation mode. In secondary explosives, the run-up distance to detonation is generally longer than for primary explosives.

[0020] FIG. 3 is a cross-sectional view of a self-disabling detonator 300, according to one or more embodiments. The self-disabling detonator 300 may be used in place of the detonator 222 shown in FIG. 2. The self-disabling detonator 300 may include a deflagration-to-detonation transition tube 302, an ignitor 304 coupled to a first end portion of the transition tube 302, and a cap 306 coupled to a second end portion of the transition tube 302.

[0021] The transition tube 302 defines an internal cavity 308 extending through the axial length of the transition tube 302 that is filled with a low- density explosive material 310. The low-density explosive 310 material may be made up of one or more secondary explosive compositions known in the art. For example, the low-density explosive material 310 may be pentaerythritol tetranitrate (PETN), RDX, HMX, hexanitrostilbene (HNS), nonanitroterphenyl (NONA), BRX, PYX, CL-20, or any combination thereof. Further, the low- density explosive material 310 may have a density ranging from 0.1 g/cm ³ to 1.5 g/cm ³ . For example, the density of the low-density explosive material may be 0.1 g/cm ³ , 0.2 g/cm ³ , 0.3 g/cm ³ , 0.4 g/cm ³ , 0.5 g/cm ³ , 0.6 g/cm ³ , 0.7 g/cm ³ , 0.8 g/cm ³ , 0.9 g/cm ³ , 1.0 g/cm ³ , 1.1 g/cm ³ , 1.2 g/cm ³ , 1.3 g/cm ³ , 1.4 g/cm ³ , or 1.5 g/cm ³ .

[0022] As shown, the ignitor 304 includes an ignitor body 312 that couples the ignitor 304 to the transition tube 302 through a threaded connection, a press fit, soldering, welding, brazing, adhesives, or similar means, a plurality of leg wires (two shown, 314), and a bridge 316 made of an electrically-conductive material. Although two leg wires 314 are shown, other embodiments may include additional leg wires 314. The leg wires 314 extend through the ignitor body 312 and are coupled to the bridge 316. The ignitor 304 also includes an ignition material 318 surrounding the bridge 316. The ignition material 318 made be made up of one or more chemicals, such as titanium hydride or a mixture of titanium sub-hydride and potassium perchlorate or another reactive salt, that will ignite when heated. The ignition material 318 may also be an explosive material, such as PETN, RDX, HMX, HNS, NONA, BRX, PYX, or CL-20, at a density that will readily ignite.

[0023] Igniting the ignition material 318 is accomplished by sending an electrical current through the leg wires 314 and into the bridge 316. As the electrical current passes through the bridge 316, the bridge 316 is heated, igniting the ignition material 318. Once ignited, the ignition material initiates a deflagration-to-detonation reaction within the self-disabling detonator 300. The deflagration-to-detonation reaction begins with the deflagration of the low- density explosive material 310 within the transition tube 302.

[0024] The ignitor 304 starts a deflagration reaction of the low-density explosive material at a combustion rate that is slower than the speed of sound within the self-disabling detonator 300. The combustion of the low-density explosive material 310 releases gasses and generates heat that cause pressure to build up within the transition tube 302. Once a sufficient pressure is reached, the combustion of the low-density explosive material 310 transitions from a deflagration reaction to a detonation reaction. The detonation pressure is typically reached in under a second from the initiation of the deflagration reaction via the ignitor 304. Once the detonation reaction occurs, the combustion rate of the low-density explosive material 310 increases to supersonic speeds. The detonation reaction of the low-density explosive material 310 then causes a detonation reaction in a high-density explosive material 320 contained within the cap 306. The detonation of the high-density explosive material 320 initiates detonation of a detonating cord (not shown), which, in turn, initiates detonation of shaped charges (not shown), as described above.

[0025] Similar to the low-density explosive material 310, the high-density explosive material 320 may be made up of one or more secondary explosive compositions known in the art. For example, the high-density explosive material 320 may be PETN, RDX, HMX, HNS, NONA, BRX, PYX, CL-20, or any combination thereof. However, the high-density explosive material 320 may have a density ranging from 1.0 g/cm ³ to 2.1 g/cm ³ . For example, the density of the low-density explosive material may be 1.0 g/cm ³ , 1.1 g/cm ³ , 1.2 g/cm ³ , 1.3 g/cm ³ , 1.4 g/cm ³ , 1.5 g/cm ³ , 1.6 g/cm ³ , 1.7 g/cm ³ , 1.8 g/cm ³ , 1.9 g/cm ³ , 2.0 g/cm ³ , or 2.1 g/cm ³ .

[0026] The self-disabling detonator 300 also includes a pressure relief mechanism 322, in this embodiment a vent 324, extending outwardly from the low-density explosive material 310, through the transition tube 302, and to an environment exterior to the transition tube 302. The pressure relief mechanism 322 may be located near the cap 306, as shown in FIG. 3. In other embodiments, the pressure relief mechanism 322 may be located near the ignitor 304, or at any point between the ignitor 304 and the cap 306. The self- disabling detonator 300 may also include multiple pressure relief mechanisms 322.

[0027] In some embodiments, the pressure relief mechanism 322 may be covered or plugged (not shown) to prevent moisture or debris from entering the self-disabling detonator 300. In such cases, the material used to cover or plug the pressure relief mechanism 322 may allow combustion or decomposition gasses to escape from the transition tube 302 or the material may be destroyed at a relatively low temperature. In other embodiments, a filler material (not shown) may be placed in the pressure relief vent. As with the previous case, the filler material either allows the combustion or decomposition gasses to escape from the transition tube 302 or is destroyed at a relatively low temperature.

[0028] As previously discussed, the deflagration reaction of the low-density explosive material 310 transitions to a detonation reaction once a sufficient pressure is reached within the transition tube 302. When initiated by the ignitor 304, the build-up to transition pressure happens in under a second. The pressure relief mechanism 322 is designed and configured, e.g., sized, such that this quick build-up of pressure cannot be dissipated in time to prevent the transition to a detonation reaction. However, if the self-disabling detonator 300 is exposed to heat, such as a fire of over 400°C resulting from an accident during transportation, decomposition gasses are released from the low-density explosive material at a lower rate, slowing the build-up of pressure within the transition tube 302. The pressure relief mechanism 322 allows the slowly released decomposition gasses to escape the transition tube 302, preventing pressure within the transition tube from building up to the pressure that is required for the transition from the deflagration reaction to a detonation reaction. Since detonation of the low-density explosive material 310 does not occur, the pressure relief mechanism 322 also prevents the detonation reaction of the high-explosive material 320 when the self-disabling detonator 300 is exposed to an external heat source.

[0029] FIG. 4 is a cross-sectional view of a self-disabling detonator 400, according to one or more embodiments. The self-disabling detonator 400 includes many elements that are similar to the elements described above in relation to the self-disabling detonator 300 shown in FIG. 3. Further, the functions of these elements are similar to those described above in relation to the self-disabling detonator 300 shown in FIG. 3. Accordingly, similar elements will not be described again in detail, except as where necessary for the understanding of the self-disabling detonator 400 shown in FIG. 4.

[0030] The self-disabling detonator 400 includes a deflagration-to-detonation transition tube 402 made up of a first portion 404 and a second portion 406. The first portion 404 and the second portion 406 of the transition tube 402 may be coupled together using pressure relief mechanism 322 comprising a thermally weak joint 408 extending from the low-density explosive material 310 to the external surface 410 of the transition tube 402. The thermally weak joint between the first portion 404 and the second portion 406 joins the first portion 404 and the second portion 406, but will separate once a specific pressure or temperature is reached. The thermally weak joint 408 may be formed using a soldering metal, an adhesive, an epoxy resin, or other similar materials known in the art to allow separation of a joint at a specific temperature or pressure.

[0031] Once the separation pressure or temperature is reached, the separation of the first portion 404 and the second portion 406 of the transition tube 402 vents any pressure that is built up within the transition tube 402 to the environment. Accordingly, the thermally weak joint 408 acts as the pressure relief mechanism 322 that may be used in place of or in addition to the pressure relief vent 324 shown in FIG. 3.

[0032] As previously discussed, an external heat source (not shown) causes a relatively slow increase in temperature and pressure within the transition tube 402, separating the first portion 404 and the second portion 406 of the transition tube 402 before the deflagration reaction of the low-density explosive material 310 can transition to a detonation reaction. However, the separation of the first portion 404 and the second portion 406 of the transition tube 402 happens too slowly to prevent the transition from deflagration-to-detonation when the ignitor 304 is used to initiate deflagration of the low-density explosive material 310. [0033] Similar pressure relief mechanisms 322 comprising thermally weak joints 412, 414 may be used to join the ignitor 304 and the transition tube 402 or to join the cap 306 and the transition tube 402. As with thermally weak joint 408, thermally weak joints 412 and 414 prevent the transition from deflagration to detonation of the low-density explosive material 310 when exposed to an external heat source, but allow detonation of the low-density material 310 when deflagration is initiated by the ignitor 304. Such thermally weak joints 412, 414 may be used in place of the thermally weak joint 408 in the transition tube 402. In another embodiment, the self-disabling detonator 400 may include multiple thermally weak joints 408, 412, 414. Other embodiments may include one or more pressure relief vents 324 and one or more thermally weak joints 408, 412, 414.

[0034] One or more specific embodiments of the self-disabling detonator have been described. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers’ specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

[0035] Certain terms are used throughout the description and claims to refer to particular features or components. As one skilled in the art will appreciate, different persons may refer to the same feature or component by different names. This document does not intend to distinguish between components or features that differ in name but not function.

[0036] Reference throughout this specification to“one embodiment,”“an embodiment,” “an embodiment,” “embodiments,” “some embodiments,” “certain embodiments,” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the present disclosure. Thus, these phrases or similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

[0037] The embodiments disclosed should not be interpreted, or otherwise used, as limiting the scope of the disclosure, including the claims. It is to be fully recognized that the different teachings of the embodiments discussed may be employed separately or in any suitable combination to produce desired results. In addition, one skilled in the art will understand that the description has broad application, and the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to suggest that the scope of the disclosure, including the claims, is limited to that embodiment.

[0038] Certain embodiments of the disclosed invention may include a detonator. The detonator may include a deflagration-to-detonation transition tube, a cap, and an ignitor. The deflagration-to-detonation transition tube may include a pressure relief mechanism and a low-density explosive material. The cap may be coupled to a first end portion of the transition tube and include a high-density explosive material. The ignitor may be coupled to a second end portion of the transition tube and configured to ignite the low-density explosive material. The pressure relief mechanism may be configured to allow an increase in pressure that leads to a deflagration-to-detonation reaction upon ignition of the low-density explosive material via the ignitor and to prevent the increase in pressure when the detonator is exposed to heat.

[0039] In certain embodiments, the pressure relief mechanism may extend outwardly from the low-density explosive material through the deflagration-to- detonation transition tube.

[0040] In certain embodiments, the pressure relief mechanism may include a pressure relief vent. [0041] In certain embodiments, the pressure relief mechanism may include a thermally weak joint.

[0042] In certain embodiments, the thermally weak joint may be located between a first portion of the deflagration-to-detonation transition tube and a second portion of the deflagration-to-detonation transition tube.

[0043] In certain embodiments, the thermally weak joint may be located between the deflagration-to-detonation transition tube and the cap.

[0044] In certain embodiments, the thermally weak joint may be located between the deflagration-to-detonation transition tube and the ignitor.

[0045] In certain embodiments, the pressure relief mechanism may prevent the increase in pressure when the detonator is exposed to a temperature of at least 400°C.

[0046] Certain embodiments of the disclosed invention may include a perforation gun. The perforation gun may include a detonator, a detonating cord coupled to the detonator, and a plurality of shaped charges coupled to the detonating cord. The detonator may include a deflagration-to-detonation transition tube, a cap, and an ignitor. The deflagration-to-detonation transition tube may include a pressure relief mechanism and a low-density explosive material. The cap may be coupled to a first end portion of the transition tube and include a high-density explosive material. The ignitor may be coupled to a second end portion of the transition tube and configured to ignite the low- density explosive material. The pressure relief mechanism may be configured to allow an increase in pressure that leads to a deflagration-to-detonation reaction upon ignition of the low-density explosive material via the ignitor and to prevent the increase in pressure when the detonator is exposed to heat.

[0047] In certain embodiments, the pressure relief mechanism may extend outwardly from the low-density explosive material through the deflagration-to- detonation transition tube to an environment exterior to the deflagration-to- detonation transition tube. [0048] In certain embodiments, the pressure relief mechanism may include a pressure relief vent.

[0049] In certain embodiments, the pressure relief mechanism may include a thermally weak joint.

[0050] In certain embodiments, the thermally weak joint may be located between a first portion of the deflagration-to-detonation transition tube and a second portion of the deflagration-to-detonation transition tube.

[0051] In certain embodiments, the thermally weak joint may be located between the deflagration-to-detonation transition tube and the cap.

[0052] In certain embodiments, the thermally weak joint may be located between the deflagration-to-detonation transition tube and the ignitor.

[0053] In certain embodiments, the pressure relief mechanism may prevent the increase in pressure when the detonator is exposed to a temperature of at least 400°C.

[0054] Certain embodiments of the disclosed invention may include a method of preparing a perforation gun for transport. The method may include loading the perforation gun with shaped charges. The method may also include loading the perforation gun with a self-disabling detonator comprising a pressure relief mechanism. The pressure relief mechanism may be configured to allow an increase in pressure that leads to a deflagration-to-detonation reaction upon ignition of a low-density explosive material of the self-disabling detonator via an ignitor of the self-disabling detonator and to prevent the increase in pressure when the detonator is exposed to heat. The method may further include connecting shaped charges to the self-disabling detonator with a detonating cord.

[0055] In certain embodiments, the method may also include coupling a first portion of a deflagration-to-detonation transition tube of the self-disabling detonator to a second portion of the deflagration-to-detonation transition tube via a thermally weak joint to form the pressure relief mechanism of the self- disabling detonator.

[0056] In certain embodiments, the method may also include coupling a deflagration-to-detonation transition tube of the self-disabling detonator to either a cap of the self-disabling detonator or the ignitor via a thermally weak joint to form the pressure relief mechanism of the self-disabling detonator.

[0057] In certain embodiments, the pressure relief mechanism of the self- disabling detonator may include a pressure relief vent formed in a deflagration- to-detonation transition tube of the self-disabling detonator.