It is frequently necessary or desirable in oil field operations to cut an object such as tubing in the bore of an oil or gas well. Because of the depth often involved, it is mandatory that the cut be successful on one attempt, otherwise unnecessary time and expense result in raising the first cutting device and lowering a second device.
Any downhole cutting device must employ means to anchor the device relative to the object to be cut, such that the chemical elements reacting with each other and exhausting onto the tubing be confined for a sufficient time to a precise area in order to insure a successful cut. Because high well head pressures are often encountered during downhole cutting operations, it is both necessary and desirable to generate within the cutting apparatus sufficient temperatures and pressures to overcome the wellhead pressure while at the same time developing a sufficient overpressure to attack and cut the tubing. Furthermore, it is highly desirable that the parts of the device directly involved with the reaction, such as the reaction chamber, be formed of a material which will not enter into the reaction and reduce the cutting effect. Considerations of both safety and efficiency make it desirable that no pressure be trapped in the device when the cutting operation has been completed.