TECHNICAL FIELD

[0001] The present disclosure relates to devices and methods for detonating perforating guns.

BACKGROUND

[0002] One of the activities associated with the completion of an oil or gas well is the perforation of a well casing. During this procedure, perforations, such as passages or holes, are formed in the casing of the well to enable fluid communication between the well bore and the hydrocarbon producing formation that is intersected by the well. These perforations are usually made with a perforating gun loaded with shaped charges. The gun is lowered into the wellbore on electric wireline, slickline or coiled tubing, or other means until it is adjacent the hydrocarbon producing formation. Thereafter, a surface signal activates a detonator, which then initiates the detonation of the shaped charges. Projectiles or jets formed by the explosion of the shaped charges penetrate the casing to thereby allow formation fluids to flow from the formation through the perforations and into the production string for flowing to the surface.

[0003] Perforating guns are one non-limiting type of tool that can be detonated using a detonator. The present disclosure relates to methods and devices for more reliably and effectively detonating devices.

SUMMARY

[0004] In aspects, the present disclosure provides a detonator. The detonator includes a metal casing having a bore defined by an inner surface a electrical circuit. The electrical circuit may include an insulating body at least partially disposed in the bore, a first and a second lead wire at least partially enclosed by the insulating body, wherein the insulating body includes a gap forming an open space between the first and the second lead wire and the inner surface, and a heating element connecting the first lead wire to the second lead wire. The detonator may also include an energetic material positioned in the bore and next to the heating element.

[0005] It should be understood that certain features of the disclosure have been summarized rather broadly in order that the detailed description thereof that follows may be better understood, and in order that the contributions to the art may be appreciated. There are, of course, additional features of the disclosure that will be described hereinafter and which will in some cases form the subject of the claims appended thereto.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] For detailed understanding of the present disclosure, references should be made to the following detailed description taken in conjunction with the accompanying drawings, in which like elements have been given like numerals and wherein:

FIG. 1 schematically illustrates a side sectional view of a pre-activated switch according to one embodiment of the present disclosure;

FIG. 2 schematically illustrates a perforating gun assembly that incorporates switches according to the present disclosure; and

FIG. 3 schematically illustrates a side sectional view of a pre-activated switch according to one embodiment of the present disclosure that uses a bent lead section in the gap.

DETAILED DESCRIPTION

[0007] The present disclosure relates to devices and methods for detonating tools such as perforating guns. The present disclosure is susceptible to embodiments of different forms. There are shown in the drawings, and herein will be described in detail, specific embodiments of the present disclosure with the understanding that the present disclosure is to be considered an exemplification of the principles of the disclosure, and is not intended to limit the disclosure to that illustrated and described herein. For instance, while the present discussion is directed to a downhole tool (perforating gun), the teachings of the present disclosure can be advantageously applied to any tool, at the surface or downhole, that is activate by a detonation.

[0008] Referring to FIG. 1, there is schematically illustrated one embodiment of a detonator 100 made in accordance with the present disclosure. The detonator 100 includes a metal casing 110 that at least partially encloses a circuit assembly 120 and an energetic material 130. The circuit assembly 120 includes lead wires 122, an insulating body 124, and a heating element 126. The insulating body 124 is an electrically non-conductive body that electrically isolates the lead wires 122 from the metal casing 110. The material making up the insulating body 124 has electrical insulation properties at least sufficient to prevent current flow from the lead wires 122 to the metal casing 110 during the intended operating conditions of the detonator 100. The heating element 126 is positioned next to the energetic material 130. The heating element 126 is a resistor-type element that generates thermal energy when electricity flows through the lead wires 122. The generated heat detonates the energetic material 130. The energetic material 130 may be a pyrotechnic material including, but not limited to, BK 03 (Boron Potassium Nitrate), Black Powder, or Smokeless powder or other suitable pyrotechnic material.

[0009] If sparks occur in the near vicinity of the energetic material 130, then the energetic material 130 could be inadvertently detonated by the thermal energy released by the spark. Advantageously, detonators according to the present disclosure are constructed to minimize the risk of sparks occurring in the near vicinity of the energetic material 130.

[0010] In one embodiment, the detonator 100 includes a gap 140 between the lead wires 122 and the metal casing 110. The gap 140 may partially or completely separate the insulating body 124 into two sections. The gap 140 may have a predetermined width 142 and extend from a bare wire section 144 of the lead wires 122 to the inner wall of the metal casing 110. The bare wire sections 144 consists of sections of the lead wires 122 that have exposed metal surfaces. For example, the surrounding insulating layer or tube may have been stripped away. The gap 140 significantly increases the electrical conductivity between the lead wires 122 and the metal casing 110 as compared to the lead wires 122 enclosed by the insulating body 124. The gap 140 may be an open space that is filled with air or other substance that has an electrical conductivity similar to that of air. That is, the gap 140 does not include one or more substances that causes the electrical conductivity of the gap 140 to be the same as the electrical conductivity of the insulating body 124. In this arrangement, a section 146 of the insulating body 124 separates the gap 140 from the heating element 126. The axial length of the section 146 is selected to prevent a spark in the gap 140 from detonating the energetic material 130. For example, the axial length of the section 146 may be provide sufficient thermal isolation to prevent the thermal energy from the spark in the gap 140 from detonating the energetic material 130. The width of the section 146 may be at least two times, at least four times, or at least eight times the width of the gap 140.

[0011] The gap 140 may be advantageous if an electro-static discharge (ESD) or "sparking" event were to occur in the detonator 100. In an ESD event, a large positive and negative charge difference between the circuit assembly 120 and the metal casing 110 may create a charge differential in which a spark discharges from the circuit assembly 120 to the metal casing 110. Beneficially, such a spark would occur at the gap 140 because the electrical resistance is lower between the circuit assembly 120 and the metal casing 110 at the gap 140 than elsewhere in the metal casing 110. Therefore, there is little likelihood that the charge would travel from the circuit assembly 120, through the energetic material 130, and to the metal casing 110. If present, such a charge could detonate the energetic material 130. Thus, the strategic formation of the gap 140 at a location distal from the energetic material 130 protects the energetic material 130 from inadvertent detonations. [0012] Referring to Fig. 2, there is shown an illustrative use of a detonator 100 according to the present disclosure. In Fig. 2, there is shown a section of a perforating gun assembly 10. The perforating gun assembly 10 may include a plurality of shaped charges 12 that are ballistically connected to a detonator cord 14. The shaped charges 12 may be fixed in a suitable charge holder 16. The detonator 100 is configured to detonate the detonator cord 14 in response to an applied electrical signal. For instance, an electrical power source at the surface (not shown) may supply electrical current that acts as the electrical signal. During handling of the detonator 100 at the surface, assembly of the perforating gun 10, and subsequent deployment of the perforating gun 10, any condition that could result in an ESD would result in only the spark occurring safely away from the energetic material 130. Thus, such a spark does not inadvertently detonate the energetic material.

[0013] Referring to Fig. 3, there is shown another embodiment of a detonator 100 according to the present disclosure. In the Fig. 3 embodiment, the radial distance of the gap 140 has been reduced relative to the radial distance of the gap 140 in the insulating body 124 is shown in Fig. 1. The radial distance is the distance crossed by a spark from an outer surface of the lead wire 122 to an inner surface of the metal casing 110. Thus, a spark has a shorter distance to travel between an outer surface of the lead wires 122 and the metal casing 110. In one arrangement, the axial distance is reduced by bending a section 160 of the lead wires 122. The bend 162 forms a curvature such that at least a portion of the section 160 is positioned radially outward of at least some of the lead wire 122 in the metal casing 110. The bend may be a "U" shaped bend oriented such that an apex 164 of the bend 162 is further radially outward than the terminal ends 166 of the bend 162. The radial direction is relative to a center of the metal casing 110. The term bent means any shape that can shift the apex 164 radially outward relative to some or all of the remainder of the lead wire 122. Such bent shapes include "U," "V," squared shapes, etc.

[0014] In other embodiments, a conductive material (not shown) may be applied (e.g. , layered) on the wire such that the outer conductive surface of the lead wire 122 is shifted closer to the metal casing 110. Additionally or alternatively, the metal wire of the lead wire 122 at the section 160 may be diametrically enlarged as compared to the remainder of the metal wire of the lead wire 122. In arrangements, the gap 140 still has an electrical conductivity the same as air and a spark, if present, still travels between a material having an electrical conductivity the same as the lead wire 122, through the gap 140, and to the metal casing 110. Thus, a relatively high contrast in electrical conductivity is present in the gap 140. In other embodiments, the gap 140 may be partially or completely filled with a material that has an electrical conductivity that is greater than that of air.

[0015] It should be appreciated that the present teachings may be applied to any electrical arrangement in which a spark may undesirably affect another component. An undesirable effect is one that impairs the intended operation of such other component.

[0016] From the above, it should be appreciated that the present teachings include a detonator wherein a gap is formed in an insulating body of a circuit assembly. The gap may be physically located a safe distance away from a component that is sensitive to sparking. By "safe distance," it is meant a distance at which the spark cannot not interact with the spark-sensitive component in an undesirable manner such as cause an unintended detonation of that component.

[0017] The foregoing description is directed to particular embodiments of the present disclosure for the purpose of illustration and explanation. It will be apparent, however, to one skilled in the art that many modifications and changes to the embodiment set forth above are possible without departing from the scope of the disclosure. It is intended that the following claims be interpreted to embrace all such modifications and changes.