Importance

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Abstract

The present invention is an explosive device for use in a subterranean well, the downhole portion of the well being at a higher temperature than the surface, the explosive device comprising an explosive, an electrically conductive circuit capable of supplying electricity that can fire the explosive, and, a thermal switch electrically connected in the circuit, the thermal switch being switchable from open to close as the temperature of the thermal switch is changed from the temperature on the surface to the temperature in the downhole portion, the thermal switch being set such that the explosive cannot be electrically fired until the switch is at the downhole temperature. The thermal switch may operate in either of two ways. In one embodiment, the thermal switch is connected in series in the electrical circuit, and is open at the surface temperature, thereby acting as a break in the electrical continuity of the circuit and preventing electricity from reaching the explosive. In an alternate embodiment, the thermal switch is connected across the circuit and is closed at the surface temperature, thereby acting as a shunt and preventing electricity in the circuit from reaching the explosive. Once either type of switch is heated sufficiently (as when the tool is run into the hole, and is heated by the higher temperatures downhole), the switch changes position and the explosive device is rendered capable of firing. Either embodiment can be used with a variety of explosive devices and wiring configurations, utilizing a range of explosion initiation devices.

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First Claim