Device and method for measurement by guided waves on a metal string in a well

A method for detecting changes of resistivity or dielectric properties due to changes of fluid compositions in the near-well area around a well in a geological formation, comprising the steps:

• placing a tube string in the well;
• emitting from a transmitter antenna a first series of electromagnetic waves guided along the tubing string at a first time;
• receiving a first series of reflected electromagnetic waves in receiver antennas positioned near the tubing string;
• transforming the received first series of reflected electromagnetic waves into first registrations;
• emitting from the transmitter antenna a second series of electromagnetic waves along the tubing string at a second time;
• receiving the second series of reflected electromagnetic waves in the receiver antennas;
• transforming the received second series of reflected electromagnetic waves into second registrations;
• forming a difference by subtracting the first registrations from the second registrations;
• and
• interpreting the difference as a distance to a change of electromagnetic impedance caused by a liquid front.

A method for logging electrical properties in a geological formation during drilling of a well by a drillstring with an outer metallic surface, comprising the steps of:

• emitting from a transmitter antenna positioned outside the drillstring's outer metallic surface a first series of electromagnetic waves guided along the drillstring at a first time and a second series of electromagnetic waves guided along the drillstring at a second time;
• receiving a series of reflected electromagnetic waves in a receiver antenna positioned outside the drillstring's outer metallic surface, wherein the emitted first and second series of electromagnetic waves are canceled in the receiver antenna by a canceling device;
• transforming the received series of reflected electromagnetic waves into a registration;
• repeating the steps of emitting electromagnetic waves, receiving reflected electromagnetic waves and transforming received reflected electromagnetic waves into a registration multiple times as the drilling of the well progresses to form a log of registrations.

A device for detecting changes in resistivity or dielectrical properties in the near-well area around a well in a geological formation, comprising:

• a tubing string, the tubing string being electrically conductive and having a linear dimension with a first end and a second end;
• a means for providing electrical energy;
• a means for generating electrical signals coupled to the means for providing electrical energy;
• a means for emitting electromagnetic waves guided along the tubing string, the means for emitting electromagnetic waves being electronically coupled to the means for generating electrical signals;
• a means for receiving reflected electromagnetic waves along the tubing string;
• a means for canceling the emitted electromagnetic waves in the means for receiving reflected electromagnetic waves;
• a means for receiving signals induced in the means for receiving reflected electromagnetic waves, the means for receiving signals being electronically coupled to the means for receiving reflected electromagnetic waves;
• a means for processing the received signal induced in the means for receiving reflected electromagnetic waves, and for providing a processed signal output;
• and
• a means for transmitting signals representing the processed signal output and for receiving a control signal.