Apparatus and Method for At-Bit Resistivity Measurements By A Toroidal Transmitter

An apparatus for making formation resistivity measurements near a drill bit comprising:

• a tool body;
• a toroidal antenna deployed on the tool body near the drill bit;
• a coupler coupled to the toroidal antenna;
• a transmitter circuit coupled with the toroidal antenna via the coupler to provide voltage signals to energize the toroidal antenna;
• a receiver circuit coupled with the toroidal antenna via the coupler to couple electrical current signals flowing in the toroidal antenna to the receiver circuit;
• a controller and processor module coupled to the transmitter circuit and the receiver circuit to control the measurement operation and calculate formation resistivity;
• and
• wherein formation resistivity is computed based on the voltage signals to energize the toroidal antenna and the measured electrical current signals flowing in the toroidal antenna.

A method for making formation resistivity measurements near a drill bit comprising:

• deploying a tool body mounted with a toroidal antenna in a borehole;
• utilizing a transmitter to apply voltage signals to the toroidal antenna;
• utilizing a receiver to measure induced electrical current signals on the toroidal antenna;
• and
• computing corresponding formation resistivity based on the applied voltage signals and induced electrical current signals on the toroidal antenna.