Method and apparatus for measuring resistivity of an earth formation

An apparatus for measuring a property of an earth formation surrounding a borehole and telemetering information through said earth formation, said apparatus comprising:

• a transmitter for emitting an electromagnetic induction signal into said earth formation at a first location in said borehole, a first characteristic of said signal being altered by passage through said earth formation, and wherein a second characteristic of said signal is modulated to carry encoded information;
• a receiver for receiving said signal at a second location in the borehole;
• means for demodulating said received signal to yield said encoded information;
• and
• means for determining said property of said earth formation from said first characteristic of said received signal.

An apparatus for measuring the resistivity of an earth formation surrounding a borehole and telemetering information while drilling said borehole, said apparatus comprising:

• a bottom hole assembly supported for rotation by a drill string, said bottom hole assembly including:
• a drilling motor having a bit shaft terminating in a bit box, said bit box having a drill bit attached thereto;
• instrument means for sensing one or more drilling and/or earth formation parameters and encoding said sensed parameters for transmission uphole;
• a transmitter for emitting an electromagnetic induction signal into said earth formation, said signal carrying said encoded sensed parameters, and wherein a characteristic of said signal is altered by passage through said earth formation;
• a receiver for receiving said signal;
• means for decoding said received signal to yield said drilling and/or earth formation parameters;
• and
• means for determining the resistivity of said earth formation from said characteristic of said received signal.

A method for controlled directional drilling of a borehole in an earth formation, said method comprising the steps of:

• transmitting an electromagnetic induction signal into said earth formation from a first location in said borehole, wherein a first characteristic of said signal is altered by passage through said earth formation, and a second characteristic of said signal is modulated to carry encoded information;
• receiving said signal at a second location in said borehole;
• demodulating said received signal to yield said encoded information;
• determining a property of said earth formation from said first characteristic of said received signal;
• and
• controlling the drilling of said borehole in response to said determined property of said earth formation.

An apparatus for controlled directional drilling of a borehole in an earth formation, said apparatus comprising:

• a bottom hole assembly supported for rotation by a drill string, said bottom hole assembly including:
• a drilling motor incorporating a bent housing therein and having a bit shaft terminating in a bit box, said bit box having a drill bit attached thereto;
• instrument means for sensing one or more drilling and/or earth formation parameters and encoding said sensed parameters for transmission uphole;
• A transmitter for emitting an electromagnetic induction signal into said earth formation, said signal carrying said encoded sensed parameters, and wherein a characteristic of said signal is altered by passage through said earth formation;
• a receiver for receiving said signal;
• means for decoding said received signal to yield said drilling and/or earth formation parameters;
• means for determining the resistivity of said earth formation from said characteristic of said received signal;
• and
• means for controlling the drilling of said borehole in response to the resistivity of said earth formation.