Patent Application
20150345922
1. Field of Invention
The present disclosure relates in general to an igniter for igniting an explosive downhole, and which includes a propellant with a point of combustion adjacent the explosive.
2. Description of Prior Art
Explosives are sometimes used during downhole operations for the exploration and production of subterranean hydrocarbons. Perforating systems typically have shaped charges equipped with high explosive for generating a metal jet that pierces a wellbore wall to create perforations into the formation surrounding the wellbore. The shaped charges are disposed axially along the length of perforating guns that make up a perforating system. A detonation cord is usually placed adjacent each shaped charge, through which a detonation wave travels for initiating detonation of the high explosive.
Packers and plugs are typically elastomeric bladder like elements that expand radially outward from a mandrel or downhole tool and into sealing contact with an inner surface of a wellbore wall. The sealing contact creates a pressure/flow barrier in the annulus between the tool and wellbore wall for isolating a designated portion of the wellbore. Some downhole packers or plugs are set with explosives that are included with the downhole tool.
Igniters are usually included downhole for initiating combustion or detonation in a propellant, the detonating cord, or explosives. Typically, an igniter includes a cartridge, combustible material in the cartridge, and a resistive heating element inserted into combustible material. Electricity is supplied to the heating element via an electrode which ignites the combustible material. A flame exits the cartridge and is directed to an amount of combustible or explosive material adjacent the detonation cord or combustible material for ultimately detonating the shaped charges or setting the packer/plug.
Disclosed herein is an example of an igniter, and a method, for initiating combustion and/or detonation of an explosive downhole. One example of the igniter includes a housing having an opening proximate the explosive, a combustible material in the housing, an igniter assembly in the opening and that is in thermal contact with the combustible material, so that when the igniter element is heated to a temperature that initiates combustion of the combustible material, a flame is generated in the housing which is directed to the explosive and that ignites the explosive. The igniter element can be made of an elongated resistive element which is made from a conductive material that is heated when current flows through the resistive element. The resistive element can be mounted on a printed circuit board. An electrode can be included in the housing for electrically coupling the resistive element with an electrical source. The explosive can be part of a perforating system or can be used for setting a packer in a wellbore.
An alternative igniter for igniting an explosive downhole includes a housing having an opening, a propellant in the housing, an electrode inserted into the propellant and in electrical communication with a source of electricity, a resistive element in electrical communication with the electrode and in thermal contact with a surface of the propellant that is proximate the explosive, so that when electricity is supplied to the electrode from the source of electricity, current flows through the resistive element and heats the resistive element to a temperature that ignites the propellant, that in turn ignites the explosive. The resistive element may include an elongated electrically conductive member that is arranged in a helical configuration defined by a series of loops radially spaced away from one another. In this example, spacing between adjacent loops can be greater proximate an axis of the helical configuration. The resistive element may optionally be mounted on a printed circuit board that is set in the opening of the housing. The explosive can be used in a perforating system or for setting a packer.
A method of detonating an explosive downhole is disclosed that includes providing an amount of combustible material in a housing adjacent the explosive, initiating combustion of the combustible material on an end of the combustible material that is proximate the explosive so that a flame front is created in the combustible material that travels away from the explosive that in turn generates a flame that is directed from the housing to the explosive and which ignites the explosive. The method may further include flowing current through a resistive element that is in thermal contact with the end of the combustible material proximate the explosive, wherein the resistive element becomes heated and initiates combustion of the combustible material. The explosive can be used for initiating detonation of shaped charges that create subterranean perforations, or for setting a packer in a wellbore.
Some of the features and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which:
While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims.
The method and system of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. The method and system of the present disclosure may be in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey its scope to those skilled in the art. Like numbers refer to like elements throughout. In an embodiment, usage of the term about includes +/−5% of the cited magnitude.
It is to be further understood that the scope of the present disclosure is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation.
Shown in
Shown set in housing 12 and on an end of propellant 16 distal from body 14 is an igniter assembly 24 for initiating combustion of propellant 16. In the embodiment shown, igniter assembly 24 is disposed in an opening 25 of the housing 12 that is distal from body 12. Igniter assembly 24 includes a printed circuit board 26 and a resistive element 28 mounted on a surface of printed circuit board 26 facing propellant 16. Further in the example of
Referring now to
One example of operation of igniter 10 is shown in side sectional view in
Referring now to
Alternatively, igniter 10 is used in conjunction with a downhole tool 60 for setting a packer (or plug) 62 which projects radially outward from tool 60 and into sealing engagement with the walls of wellbore 45. Also in the example of
In an example, the explosive material making up the explosive 30 detonates after being initiated, wherein a definition of detonation describes a reaction that can propagate through the material being detonated at the sound speed of the material. In a further example, detonation describes a reaction or decomposition of an explosive that, typically in response to a shock wave or heat, forms a high pressure/temperature wave. Example velocities of the high pressure/temperature wave can range from 1000 m/s to in excess of 9000 m/s. In another example, the explosive 30 can deflagrate, wherein a definition of deflagration describes a rapid auto-combustion of a material, such as an explosive. Generally, explosives that detonate are referred to as high explosives and explosives that deflagrate are referred to as low explosives. Alternate embodiments exist wherein the explosive 30 includes a propellant that combusts (or is otherwise combustible), or is replaced with a propellant. In an example, combustion describes an exothermic reaction of a material that can produce an oxide.
The present invention described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment of the invention has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims.
