Systems and Methods for Downhole Electromagnetic Field Measurement

A downhole electromagnetic field measurement system that comprises:

• a first downhole micro-opto-electro-mechanical system (MOEMS) electromagnetic field sensor that includes:
• a first surface that is at least partially reflective;
• a second surface that is at least partially reflective, said second surface suspended by one or more flexible members to define an optical cavity having a variable distance between the first and second surfaces;
• a first conductive layer attached to the first surface;
• and
• a second conductive layer attached to the second surface, the first and second conductive layers having an electrical potential proportional to an electromagnetic field within a formation surrounding the first sensor, the electrical potential producing an electric field that displaces the second surface to alter the variable distance and cause a spectrum variation in light exiting the first sensor;
• a transmitter that induces said electromagnetic field;
• and
• a computer that processes optical signals received from the first sensor to measure said electromagnetic field and to derive a formation property based at least in part on said electromagnetic field.

A method for measuring an electromagnetic field using one or more downhole micro-opto-electro-mechanical system (MOEMS) electromagnetic field sensor, the method including:

• inducing an electromagnetic field into a formation surrounding a borehole;
• applying an electrical potential produced by the electromagnetic field across two conductive layers, each conductive layer attached to one of two surfaces that are at least partially reflective and that define an optical cavity within a first sensor having a variable distance between the two surfaces;
• directing to the borehole surface light exiting the first sensor;
• detecting a spectrum variation in the light exiting the first sensor, the applied electrical potential causing a displacement of one of the two surfaces to alter the variable distance and cause the spectrum variation;
• and
• processing a first signal representing the detected spectrum variation to measure said electromagnetic field and to derive a formation property based at least in part on said electromagnetic field.