Patent Application
20130228066
The field of the invention is igniter systems for explosively operated subterranean tools and more particularly core guns.
As shown in
a shows the core barrel 16 tethered with a wire rope 18, a portion of which remains attached to the barrel 16 for retrieval after the barrel 16 is propelled into the formation 20. The gun body 22 may also contain additional barrels such as 24 that can be independently fired.
The ignition mix 12 has in the past caused small fires and presented a personnel safety hazard when assembled into a cartridge 26. Despite such risks core guns have been assembled with this dangerous ignition mix for many years.
Yet despite the existence of the chemical cutter of
The present invention removes the ignition mix and replaces the nichrome wire 10 with the ignition mix 12 combination with a precision resistor preferably under 50 ohms in the core gun to remove the stated disadvantages in the context of a core gun where the core is directly driven by the ignited propellant into the surrounding formation. Those skilled in the art will further appreciate these and other aspects of the invention from a review of the detailed description of the preferred embodiment and the associated drawing while appreciating that the full scope of the invention is to be found in the appended claims.
A core gun igniter assembly features a resistor under 50 ohms that is welded rather than soldered to a circuit. Upon energizing the circuit, the resistor creates the heat needed to directly set off the propellant to directly drive the core barrel into the surrounding formation to obtain the desired core sample. The use of a titanium powder ignition mix on a nichrome wire with its attendant safety risks is eliminated.
a and 1b represent a prior art core gun in the run in and shot positions respectively where the gun is set off with an ignition mix coated nichrome wire;
a and 3b are the core gun of the present invention shown in the run in and the fired conditions.
a shows a resistor 48 that when energized creates heat to burn the propellant 50 in the cartridge 52. The resistor is preferably under 50 ohms and is secured at opposed ends with welds 54 and 56. The barrel 58 is secured by the tether 60 that operates in the same manner as in
Those skilled in the art will appreciate that the elimination of the nichrome wire coated with the ignition mix that had been in persistent use in the past for years for core guns posed safety issues that caused fires and threatened personal injury for the assembly workers. The soldering process for attaching the wire also created reliability issues with the possibility that the barrel would not be propelled into the formation.
Now the core gun with a welded resistor of preferably under 50 ohms to set off the propellant to launch the barrel, the assembly safety issues are eliminated as are the reliability issues with the soldering using the welded connections. The preferred resistance is under 25 ohms. The design meets API safety standard API RP 67 IME SLP-20.
The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below:
