Borehole current correction methods and apparatus

An apparatus for use in a borehole traversing a formation, comprising:

• an elongated non-conductive support having a longitudinal axis and at least one conductive segment disposed thereon;
• at least one antenna disposed on the support such that the magnetic dipole moment of the antenna is tilted or perpendicular with respect to the longitudinal axis of the support;
• the at least one antenna being disposed along a conductive segment on the support;
• and
• each at least one antenna being adapted to transmit and/or receive electromagnetic energy.

An apparatus for use in a borehole traversing a formation, comprising:

• an elongated support having a longitudinal axis;
• at least one antenna disposed on the support such that the magnetic dipole moment of the antenna is tilted or perpendicular with respect to the longitudinal axis of the support, each at least one antenna being adapted to transmit and/or receive electromagnetic energy;
• a first pair of electrodes disposed on the support and adapted for joint electromagnetic interaction;
• the first pair of electrodes being disposed such that the at least one antenna is located between the electrodes;
• a second pair of electrodes disposed on the support and adapted for joint electromagnetic interaction;
• and
• the second pair of electrodes being disposed such that the first electrode pair is located between the second electrode pair.

An apparatus for induction logging within a borehole traversing a formation, comprising:

• an elongated conductive metal body having a longitudinal axis;
• and
• at least one antenna disposed on the body such that the magnetic dipole moment of the antenna is tilted or perpendicular with respect to the longitudinal axis of the body;
• wherein
• each at least one is antenna is adapted to transmit and/or receive electromagnetic energy for electromagnetic exploration of the formation.

A method for altering the flow of an axial electric current along a subsurface borehole in the vicinity of an antenna disposed within the borehole, the antenna being disposed such that the magnetic dipole moment of the antenna is tilted or perpendicular with respect to the borehole axis and being adapted to transmit and/or receive electromagnetic energy, comprising:

• a) providing first conductive means within the borehole;
• b) providing second conductive means within the borehole, the second conductive means positioned such that the antenna is located between the first and second conductive means;
• and
• c) coupling the first and second conductive means to provide a path through the antenna for the axial current to flow between the conductive means.

A method for altering the flow of an axial electric current along a subsurface borehole in the vicinity of an antenna disposed within the borehole, the antenna being disposed on a non-conductive support having a longitudinal axis and adapted for disposal within the borehole, the antenna being adapted to transmit and/or receive electromagnetic energy, comprising:

• a) mounting a conductive segment on the support such that the segment is exposed to the borehole when the support is disposed within the borehole;
• b) disposing the antenna along the conductive segment to provide a path through the antenna for the axial current flow when the support is disposed within the borehole;
• and
• c) disposing the antenna along the conductive segment such that the magnetic dipole moment of the antenna is tilted or perpendicular with respect to the longitudinal axis of the support.

A method for altering the flow of an axial electric current along a subsurface borehole in the vicinity of an antenna disposed within the borehole, the antenna being disposed such that the magnetic dipole moment of the antenna is tilted or perpendicular with respect to the borehole axis and being adapted to transmit and/or receive electromagnetic energy, comprising:

• (a) disposing a first pair of electrodes within the borehole such that the antenna is located between the electrodes, the first electrode pair being adapted for joint electromagnetic interaction;
• (b) disposing a second pair of electrodes within the borehole such that the first electrode pair is located between the second electrode pair, the second electrode pair being adapted for joint electromagnetic interaction;
• (c) measuring an electromagnetic property associated with the axial electric current at the first or second electrode pair;
• and
• (d) emitting a current within the borehole in response to the measured electromagnetic property of step (c), the current being emitted between:
• i) the first electrode pair if the second electrode pair was used in the measurement of step (c);
• or
• ii) the second electrode pair if the first electrode pair was used in the measurement of step (c).

A method for correcting for the effect of an axial electric current flow along a subsurface borehole in the vicinity of a receiver antenna disposed within the borehole, the receiver antenna being disposed such that the magnetic dipole moment of the antenna is tilted or perpendicular with respect to the borehole axis, the axial current being associated with electromagnetic energy transmitted from a transmitter antenna disposed within the borehole, comprising:

• (a) disposing a first pair of electrodes within the borehole such that the antenna is located between the electrodes, the first electrode pair being adapted for joint electromagnetic interaction;
• (b) disposing a second pair of electrodes within the borehole such that the first electrode pair is located between the second electrode pair, the second electrode pair being adapted for joint electromagnetic interaction.
• (c) measuring a voltage signal associated with the transmitted electromagnetic energy at the receiver antenna;
• (d) measuring a voltage difference between the first or second electrode pair, the voltage difference being associated with the transmitted electromagnetic energy;
• (e) shutting off transmission of the electromagnetic energy from the transmitter antenna;
• (f) emitting a current within the borehole, the current being emitted between:
• i) the first electrode pair if the second electrode pair was used in the measurement of step (d);
• or
• ii) the second electrode pair if the first electrode pair was used in the measurement of step (d);
• (g) measuring a voltage signal associated with the emitted current at the receiver antenna;
• (h) measuring a voltage difference between the electrode pair used in the measurement of step (d), the voltage difference being associated with the emitted current;
• and
• (i) calculating a voltage value based on the measured voltage signals and voltage differences.