Patent ID: 8810247

Claim:
Apparatus for target detection from a borehole being drilled, comprising: a drill string having multiple drill pipe sections connected end to end and carrying a drill bit; at least one of said drill pipe sections being electrically conductive to provide a drill pipe electrode section; at least one electrically insulating drill pipe sub electrically isolating said electrode section from adjacent drill pipe sections; a power supply in electrical communication with said at least one drill pipe electrode section and energizable to inject a time varying current into Earth formations surrounding said borehole to cause current flow in a target; an alternating electromagnetic dipole source in said drill string whose magnetic axis is substantially perpendicular to said drill string, for producing an auxiliary magnetic field; a sensor instrument at said drill bit for detecting magnetic fields produced by said current flow in a target and by said dipole source to determine a rotational orientation of the direction of drilling with respect to the direction to said target; and communication electronics located in said drill string for establishing communication between said sensor instrument and surface instrumentation for sending data to said surface instrumentation.