Abstract: A switching circuit for use in a subterranean probe for switching between to two modes of operation used to perform a survey of a well borehole. The switching circuit comprises a first voltage bias network which is biased to a predetermined overvoltage criterion; a second voltage bias network which is biased to a predetermined negative voltage criterion; a switch; and a negative voltage blocking diode for blocking the predetermined negative voltage criterion for allowing the first voltage bias network to fully realize the negative voltage criterion.

Abstract: A method of severing a downhole pipe for forming a region in the well borehole devoid of downhole pipe for enhancing the performance of a perforating gun comprising the steps of: severing, at an angle, by a first cutting tool the downhole pipe to form an upper downhole pipe portion and a lower downhole pipe portion to form a sloped cut line; releasing potential energy stored in the upper downhole pipe portion and the lower downhole pipe portion; inserting a plug to seal an up-hole portion of the upper downhole pipe portion; cutting the up-hole portion via a second cutting tool above the plug into an upper piece and a lower piece; and, jettisoning the lower piece downwardly wherein as the lower piece jettisons downwardly the region in the well borehole devoid of downhole pipe is formed. Such method eliminates the need for: removing a well head; a crane or rig for raising a cut up-hole pipe; and, a pump for controlling the pressure of the well.