Electromagnetic telemetry apparatus and methods for minimizing cyclical or synchronous noise

A method for determining a signal component contained within a composite electromagnetic signal, the method comprising the steps of:

• (a) measuring said composite signal;
• (b) defining a plurality of strobe increments with a trigger sensitive to a stimulus and cooperating with a strobe;
• (c) measuring, during said plurality of strobe increments, increment composite noise signals;
• (d) summing algebraically said increment composite noise signals to define a cyclical noise component;
• and
• (e) combining said cyclical noise component with said composite signal to obtain said signal component.

An MWD logging system comprising:

• (a) a downhole electromagnetic transceiver for transmitting a signal component from a downhole sensor;
• (b) a surface electromagnetic transceiver for measuring a composite signal comprising said signal component;
• (c) a trigger responsive to an azimuth point on a rotating element of a drilling rig and cooperating with a strobe to define a plurality of strobe increments;
• and
• (d) a processor cooperating with said surface transceiver
• (i) to algebraically sum increment composite noise signals measured during said plurality of strobe increments to define a cyclical noise component, and
• (ii) to combine said cyclical noise component with said composite signal to obtain said signal component.

A method for determining a parameter of interest while drilling a borehole, the method comprising the steps of:

• (a) transmitting, with a downhole electromagnetic transceiver, a signal component from a downhole sensor;
• (b) receiving, with an electromagnetic surface transceiver, a composite signal comprising said signal component;
• (c) defining a plurality of strobe increments with a trigger responsive to an azimuth point on a rotating element of a drilling rig and cooperating with a strobe;
• and
• (d) algebraically summing increment composite noise signals measured during said plurality of strobe increments to define a cyclical noise component;
• (e) combining said cyclical noise component with said composite signal to obtain said signal component;
• and
• (f) converting said signal component into said parameter of interest using a predetermined relation.