COMBINED ELECTRIC-FIELD TELEMETRY AND FORMATION EVALUATION APPARATUS

An apparatus for borehole electric field telemetry includes a source of modulated voltage or current, at least one axially extending collar connected between pipe sections in a pipe string, and a system of insulated wireline components providing electrical connections, insulated from drilling fluids, between the ends of the one or more aforementioned insulative collars in the pipe string, to transmit the voltage or current. The source of modulated voltage or current comprises an electrical pulse-producer for producing short duration pulse wave forms selected to obtain optimum transmission characteristics in the underground formation. The electrical connections are to the drillstring, and there are upper and lower instrument housings associated with the electrical connections, which are upper and lower connections. The housings are supported within the pipe string, the upper housing located above at least one of the insulative collars, and the lower housing projecting below the insulative collar. The pulse-producing means is located within at least one of such housings.