Patent Application
20070234921
The invention relates generally to a heat insulating container for a detonator.
Temperatures deep in wellbores typically can reach relatively high levels, sometimes reaching well over 500° F. To perform operations in a well, various types of tools are lowered into the well. These tools often include heat-sensitive components, such as electrical detonators. An electrical detonator is used for detonating explosives (such as shaped charges in perforating guns).
Many commercially available detonators are rated to operate at less than 500° F. for a relatively limited amount of time (such as one hour or so). With the oil and gas industry continuing to explore wells at ever deeper depths, the temperatures and pressures experienced by downhole tools can be quite high. The result is that many commercially available detonators will fail in high-temperature applications. Normally, a perforating job can take many hours to complete, in which the perforating tool, including an electrical detonator, remains downhole for such time. If the electrical detonator were to fail as a result of high temperature, then well operations may not be performed reliably, which can lead to increased well completion times (and thus increased costs), and reduced production of hydrocarbons.
In general, according to an embodiment, an apparatus for use in a wellbore comprises a heat insulating container containing a space and having a structure defining a vacuum. A reflective layer is arranged on a surface of the heat insulating container to reflect heat, and a signal-activated detonator is provided in the space of the heat insulating container.
Other or alternative features will become apparent from the following description, from the drawings, and from the claims.
In the following description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these details and that numerous variations or modifications from the described embodiments are possible.
As used here, the terms “up” and “down”; “upper” and “lower”; “upwardly” and “downwardly”; “upstream” and “downstream”; “above” and “below” and other like terms indicating relative positions above or below a given point or element are used in this description to more clearly described some embodiments of the invention. However, when applied to equipment and methods for use in wells that are deviated or horizontal, such terms may refer to a left to right, right to left, or other relationship as appropriate.
The firing head 104 includes a heat insulating container 112 according to an embodiment. The heat insulating container 112 contains a signal-activated detonator 114. A “signal-activated detonator” refers to any detonator that is activated in response to an electrical stimulus (electrical power or signaling), optical signaling, or pressure pulse signaling for exploding an explosive. Pressure pulse signaling refers to a sequence of pressure pulses having a predetermined pattern that is detectable as a signature by the detonator for activation of the detonator. A detonator that is activated by an electric stimulus is also referred to as an electrical detonator.
Although only one detonator 114 is shown as being contained in the heat insulating container 112, it is contemplated that in other embodiments, multiple detonators can be provided inside the heat insulating container 112. In yet further embodiments, multiple heat insulating containers 112 can be provided in the firing head 104 for containing respective detonators.
The detonator 114 is coupled to one or more electrical wires 110 that are electrically connected to a cable (e.g., electrical cable) in the carrier line 106. The detonator 114 is activated in response to electrical stimulus in the electrical wire(s) 110. Alternatively, a fiber optic cable can be carried by the carrier line 106, with a converter provided in the firing head 104 or elsewhere in the tool 102 to convert between optical signals and electrical signals. In yet another embodiment, the carrier line 106 does not need to include a cable if pressure pulse signals are used for activation of the detonator 114. In such an embodiment, the firing head 104 or other component would include a pressure transducer to detect a predefined sequence of pressure pulse signals.
In one embodiment, the one or more electrical wires 110 and carrier line cable communicate electrical power and signaling between the detonator 114 and a controller that can be located elsewhere in the wellbore 100 or at the earth surface from which the wellbore 100 extends. Power and signaling communicated down the cable in the carrier line 106 and through the one or more wires 110 to the detonator 114 causes activation of the detonator 114, which in turn causes initiation of a detonating cord 116 that is ballistically coupled to the detonator 114. The detonating cord 116 extends from the detonator 114 to shaped charges 118 (or other types of explosives) in the perforating gun 108. In other implementations, other types of components including explosives can be used with the detonator 114. Effectively, the detonating cord 116 ballistically connects the detonator 114 to the explosives.
In the embodiment of
The heat insulating container 112 provides heat insulation for reducing heat transfer by conduction, convection, and radiation between the wellbore environment and an inner space of the heat insulating container 112 that contains the detonator 114. Heat transfer by conduction is performed through solids; heat transfer by convection is performed through fluids, such as air or liquid; and heat transfer by radiation is transfer of heat by emission of electromagnetic waves.
To reduce heat conduction or convection, the heat insulating container 112 contains a structure that defines a vacuum between the wellbore environment around the perforating tool 102 and the inner space of the heat insulating container 112. The structure of the heat insulating container 112 that provides the vacuum can be a wall (or walls) of the heat insulating container 112 that define(s) a hollow area for storing or providing the vacuum. In some embodiments, the heat insulating container 112 is formed of glass, such as Pyrex® glass or silicate glass. Pyrex® glass refers to heat-resistant borosilicate rolled glass.
In accordance with some embodiments, heat transfer by radiation is reduced by providing one or more reflective layers (in the form of coatings on respective surfaces) in the heat insulating container 112 to reflect heat originated or produced in the wellbore environment away from the inner space of the container 112. Note that the tool 102 can be positioned downhole in a wellbore environment having elevated temperatures (such as in the range between 400-600° F.) for extended periods of time (such as greater than one hour). The heat insulating container 112 protects the detonator 114 from elevated wellbore temperatures that may cause damage to the detonator 114.
The heat insulating container 112 includes a thermal flask 200 (e.g., a Dewar flask) that has an inner space 202 in which the detonator 114 is provided. The thermal flask 200 has a wall 204 (e.g., a glass wall) or walls that define(s) a hollow area 206 containing a vacuum. The hollow area 206 is sealed by the wall(s) 204 of the thermal flask 200. The hollow region 206 provides a vacuum layer along the side of the thermal flask 200 and at a first end 208 of the thermal flask 200. This vacuum layer reduces heat conduction and convection.
In some embodiments, the detonator 114 is a miniaturized detonator (as discussed further below) so that a large and bulky thermal flask does not have to be provided to receive the detonator 114. This allows the insulating container 112 according to some embodiments to be used with existing tools without having to redesign or significantly modify the designs of such tools.
The thermal flask 200 is positioned inside a protective outer shell 210 of the heat insulating container 112. The outer shell 210 can be formed of a metal (e.g., aluminum) or other material to protect the thermal flask 200 from damage during use. A filler layer 214 is provided between the thermal flask 200 and the outer shell 210. The filler layer 214 can be formed of a fiberglass or other heat-insulating material to provide relatively good insulation between the outer shell 210 and the thermal flask 200.
A filler mass 216 (which can also be formed of fiberglass or other heat insulating material) is provided in a portion of the inner space 202 of the thermal flask 200. The filler mass 216 generally surrounds the detonator 114 so the filler mass 216 separates the detonator 114 from the inner surface of the thermal flask 200. The filler mass 216 acts to prevent the detonator 114 from bouncing around or otherwise moving inside the inner space 202 of the thermal flask 200 during transportation or deployment into a well, which may cause damage to the detonator 114. Damage may occur if the detonator 114 were allowed to repeatedly and directly impact a hard object such as the thermal flask 200.
One or more surfaces of the thermal flask 200 can be coated with a reflective material (e.g., silver, gold, mercury, or even bright color paint such as white paint) to reflect radiated heat from the wellbore environment. The term “bright color paint” refers to any paint that is able to reflect a substantial amount of heat as opposed to absorbing the heat. Coating a surface with the reflective material causes a heat reflective layer to be adhered to the surface. In one embodiment, each of the outer surface 254 of the thermal flask 200 and the inner surface 256 of the thermal flask 200 can be coated with a respective layer of reflective material. Alternatively, surfaces of the outer shell 210 can also be coated with the reflective material layer.
By using the vacuum layer provided by the thermal flask 200 to reduce heat conduction and convection and the reflective layer(s) to reduce radiated heat, the rate at which temperature in the inner space 202 of the heat insulating container 112 increases due to elevated wellbore temperature is reduced.
Electrical wires 110 extend from the detonator 114 to a second end 220 of the thermal flask 200, where an opening 222 is defined through which the detonator 114 can be inserted into the inner space 202 of the thermal flask 200. Once the detonator 114 is inserted into the inner space 202 of the thermal flask 200, a plug 224 is sealably fitted into the opening 222 of the thermal flask 200 to seal the inner space 202 of the thermal flask 200 from the outside of the thermal flask 200. The plug 224 has an enlarged head portion 226 and a shaft 228 that extends from the enlarged head 226. The shaft 228 has an outer diameter that is generally the same as the inner diameter of the opening 222 at the top portion of the thermal flask 200 such that a snug fit can be provided between the plug 224 and the thermal flask 200. The plug 224 is formed of a glass, such as a Pyrex® glass or other type of silicate glass. The plug 224 includes a hollow region 230 (or plural hollow regions) that contain(s) a vacuum for improved heat insulation. Additionally, the plug 224 can also be coated with reflective layers to reflect heat away from the inner space of the thermal flask 200.
The plug 224 has a first through-bore 234 that allows a detonating cord 232 to pass from the detonator 114 to a location outside the thermal flask 200. One end of the detonating cord 232 is attached to a crimp shell 236 that is crimped (by radially inward compression) to the detonating cord 232. The crimp shell 236 can be attached to another detonating cord (such as detonating cord 116 of
The plug 224 also includes additional through-bores 238 through which the electrical wires 110 extend between the inside of the thermal flask 200 and the outside of the thermal flask 200. The wires 110 wrap around and extend in a space between thermal flask 200 and the outer shell 210.
The plug 224 is sealingly engaged with the thermal flask inner surface with high temperature insulation sealants. Also, the detonating cord 232 and wires 110 are sealing engaged in respective through-bores 234 and 236 with high temperature insulation sealants.
In operation, the tool 102 (
By using the heat insulating container according to some embodiments, the various heat sensitive components of the detonator 114 are protected from a potentially high heat wellbore environment. Such protection increases the reliability and life of the detonator 114 so that a wellbore operation can be successfully completed.
A multiplier 308 is also provided on the support substrate 320, where the multiplier 308 receives an input voltage from the electrical wires 110 and multiplies the input voltage by some amount to produce an output voltage that is greater than the input voltage. For example, the multiplier 308 can be a charge pump that takes the input voltage and steps the input voltage to a higher output voltage. The output voltage provided by the multiplier 308 is supplied to an energy source 310 (such as a capacitor) that is capable of storing the voltage provided by the multiplier 308. Also, the energy source 310 is coupled through a switch 312 to an initiator 314. The switch 312 is controlled by the microprocessor 306.
In response to an activation command, the microprocessor 306 closes the switch 312 to enable the charge in the energy source 310 to be provided to the initiator 314 to activate the initiator 314. Assuming that the initiator 314 is implemented as an EFI (exploding foil initiator), then closing of the switch 312 causes a rapid electrical discharge to be provided from the energy source 310 to the EFI 314, which causes a bridge structure 316 in the EFI 314 to rapidly change to a plasma and generate a high pressure gas, thereby causing a “flyer” to accelerate and impact a secondary explosive 318 to cause detonation of the explosive 318. Detonation of the explosive 318 causes initiation of the detonating cord 232 (or booster explosive).
The detonator 114 depicted in
While the invention has been disclosed with respect to a limited number of embodiments, those skilled in the art, having the benefit of this disclosure, will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover such modifications and variations as fall within the true spirit and scope of the invention.
