Method and apparatus for eddy current suppression

A nuclear magnetic resonance well logging apparatus, comprising:

• a magnet for inducing a static magnetic field in earth formations penetrated by a wellbore;
• means for generating a radio frequency magnetic field in said earth formations;
• means for receiving nuclear magnetic resonance signals from said earth formations;
• and
• means for segmenting paths of eddy current flowing in an annular space between the exterior of said apparatus and the wall of said wellbore.

An electromagnetic induction well logging apparatus, comprising:

• a sonde adapted to traverse a wellbore penetrating earth formations;
• a source of alternating current;
• a transmitter antenna disposed on said sonde and connected to said source of alternating current;
• a receiver antenna disposed on said sonde axially spaced apart from said transmitter;
• a receiver circuit connected to said receiver antenna;
• and
• means for segmenting paths of eddy currents which would otherwise flow in an annular space between said sonde and said wellbore.

A method for electromagnetic logging earth formations penetrated by a wellbore having reduced effects of eddy current flowing in an annular space between a logging tool and said wellbore, comprising:

• inserting said logging tool into said wellbore;
• generating alternating electromagnetic fields in said earth formations by conducting alternating current through an antenna disposed in said logging tool;
• electrically segmenting said wellbore so as to interrupt paths of eddy currents which would otherwise flow in said annular space, said eddy currents resulting from said alternating electromagnetic fields;
• and
• detecting signals in said antenna corresponding to interaction of said alternating electromagnetic fields with said earth formations.

A method of nuclear magnetic resonance logging earth formations penetrated by a wellbore, comprising:

• inserting a nuclear magnetic resonance logging apparatus into said wellbore;
• inducing a static magnetic field in said earth formations;
• generating a radio frequency magnetic field in said earth formations so as to excite nuclei of said formations;
• electrically segmenting said an annular space between said logging apparatus and said wellbore so as to interrupt paths of eddy currents which would otherwise flow in said annular space;
• and
• detecting nuclear magnetic resonance signals induced by said excited nuclei in said earth formations.